CA1243361A - Stroke volume controlled pacer - Google Patents
Stroke volume controlled pacerInfo
- Publication number
- CA1243361A CA1243361A CA000457692A CA457692A CA1243361A CA 1243361 A CA1243361 A CA 1243361A CA 000457692 A CA000457692 A CA 000457692A CA 457692 A CA457692 A CA 457692A CA 1243361 A CA1243361 A CA 1243361A
- Authority
- CA
- Canada
- Prior art keywords
- value
- stroke volume
- heart
- heart rate
- rate value
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/18—Applying electric currents by contact electrodes
- A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
- A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
- A61N1/362—Heart stimulators
- A61N1/365—Heart stimulators controlled by a physiological parameter, e.g. heart potential
- A61N1/36514—Heart stimulators controlled by a physiological parameter, e.g. heart potential controlled by a physiological quantity other than heart potential, e.g. blood pressure
- A61N1/36521—Heart stimulators controlled by a physiological parameter, e.g. heart potential controlled by a physiological quantity other than heart potential, e.g. blood pressure the parameter being derived from measurement of an electrical impedance
Abstract
ABSTRACT
A rate responsive pacer which paces the heart at a rate dependent on detected variations in the stroke volume of the heart. A measuring device periodically infers the stroke volume of the heart and produces a sequence of stroke volume measurements and a pulse generator provides stimulation pulses to the heart at a frequency proportional to a heart rate value. A device coupled to the measuring device and the pulse generator determines a heart rate value in response to stroke volume measurement.
A rate responsive pacer which paces the heart at a rate dependent on detected variations in the stroke volume of the heart. A measuring device periodically infers the stroke volume of the heart and produces a sequence of stroke volume measurements and a pulse generator provides stimulation pulses to the heart at a frequency proportional to a heart rate value. A device coupled to the measuring device and the pulse generator determines a heart rate value in response to stroke volume measurement.
Description
STROI;E VOLllMr CONTROLLEn PACER
BACKGROIIND ~F TIIE INVENT1ON
~ . . . .
This invention relates generally to the -field of carcliac pacemakers and more particularly to a pacemaker 5 having an escape intfrval which is set in response to a medsured physioloyic variahle of -the patient.
When the body undergces exercise a variety of changes take place. These include an increase in respiration diversion of hlood flow to the active 10 skeletal muscles and arI increase in cardiac output.
These changes cooperate to deliver an incredsed arnount of oxygen and nutrients to the active muscles.
-The mass flow rate o-f oxygenated blood from the heart is referred to as the cardiac output of the heart and it 15 is equal to the product of the heart rate in beats per minute dnd the heart s stroke volume in litres.
The increase in cardiac output is achieved by an increase In the stroke volume o~ the heart; up to two fo)d~
as well as an increase in the heart rate; up to three 20 fold.
The changes in stroke volume are mediated by venous return contractility and afterload while thr changes in the heart s rate are mediated through -the autonomic nervous system which operates on a structure called the ~5 S-A Node.
The S-A Node is located on the atria of the heart.
An electrical signal generated by this natural pacernaker causes the at ia or upper chambers of the heart to contract. This forces blond into the lower chambers or 30 ventricles of the heart. The signal from the S~A Node is propagated to the lower ch~dmI)ers of Lhe heart through a structure called the Atrio-VentricuIar or A-V Node after a brief delay. The signal -frôm the A-V Node cdusras the ventricles to contract forcing the blood throughout the 35 body.
.- ~
33~i~
BACKGROIIND ~F TIIE INVENT1ON
~ . . . .
This invention relates generally to the -field of carcliac pacemakers and more particularly to a pacemaker 5 having an escape intfrval which is set in response to a medsured physioloyic variahle of -the patient.
When the body undergces exercise a variety of changes take place. These include an increase in respiration diversion of hlood flow to the active 10 skeletal muscles and arI increase in cardiac output.
These changes cooperate to deliver an incredsed arnount of oxygen and nutrients to the active muscles.
-The mass flow rate o-f oxygenated blood from the heart is referred to as the cardiac output of the heart and it 15 is equal to the product of the heart rate in beats per minute dnd the heart s stroke volume in litres.
The increase in cardiac output is achieved by an increase In the stroke volume o~ the heart; up to two fo)d~
as well as an increase in the heart rate; up to three 20 fold.
The changes in stroke volume are mediated by venous return contractility and afterload while thr changes in the heart s rate are mediated through -the autonomic nervous system which operates on a structure called the ~5 S-A Node.
The S-A Node is located on the atria of the heart.
An electrical signal generated by this natural pacernaker causes the at ia or upper chambers of the heart to contract. This forces blond into the lower chambers or 30 ventricles of the heart. The signal from the S~A Node is propagated to the lower ch~dmI)ers of Lhe heart through a structure called the Atrio-VentricuIar or A-V Node after a brief delay. The signal -frôm the A-V Node cdusras the ventricles to contract forcing the blood throughout the 35 body.
.- ~
33~i~
-2-Many forms of hedrt disease imnaiI the function of the S-A and A-~ No~es, and their associated conductive tissues. Patient's exhit~5ting these in(licdtions mdy be candidates -for artificial pacemaker therapy.
S Initially, pacelnakers wele implanted in patients who exrlibited complete A-V block. This conduction disturbance is manifested by the inability of the signal from the S-A
Node to reach the lower challlbers of tlle heart to in-itiate a ventricular contractiorl.
The earliest form uf implantable pacernaker for the long-term stim~lldtion of the heart is known from lJ.S.
Patent No. 3,057,356 issued to W. Greatbatch~ This asynchronous pdcemaker, in essence, replaced the heart's natural conduction system and periodically provided an 15 electrical stinlulus to the ventricle to cause contractions.
In some patients, the A-V block condition is intermittant and occasionally the artificial pacemaker and the natural S-A Node of the heart compete for control of 20 the velltricular action of the heart. This competition is undesirable. The demand pacelnaker avoids this competitive pacing. An example of an implantable version of the demand pacemaker is known From U.S. Patent No. 3,47~,74r5, to W. Greatbatch.
In operation, the demand mode pacemaker senses the ventricular contraction of the heart, and provides stimulation to the ventricles only in the absence of naturally occurring contractions of the heart. Such demand pacemakers synchronize their timing witll the heart 30 and provide stimulated bedts if the natural cardiac rhyth drops below a preset rate. Both the asynchronous and demand type of pacemaker thus provided for a fixed lower rate for the patient's healt rate.
When a patient has no intrinsic rhythrn and is being 35 paced at a fixed rate, any increment in demand for cardiac output must come solely from naturally induced changes in stroke volume. For these patients, strenuous work is impossible since stroke volume chan~es alone are insl~fficient to raise the cardiac output enough to supply the skeletal muscles dur-ing heavy exercise.
~y way of contrasl, the P-syncllronous mocle of 5 pacemaker, as exemplified by U.S. Patent No. 3,253,596 to J. W. Keller, monitored electrical activity in the atrium~ and triggered a ventricular action after a short tirne period. This form of pacemaker permits the patient's naturally occurring atrial rate to control the rate o-f 10 ventricular stimulation.
Other pacernakers which exhibit -the atrial tracking feature include the atr-ial-synchronized, ventricularly inhibited pacemaker known -frorn U.S. Patent No. 396~,707 to W. Greatbatch, as well as the dual-sense, dual-pace 15 pacemaker known fronl U.S. Patent No. 4,3129355 to H.
Funke~ The advantage of atrial synchronized pacing is that it permits the pacernaker's rate -to be determined by the S-A Node which in turn intreprets the body's demand for cardiac ou-tput.
Another forrn of rate adaptive pacer is known from ~S. Patent No. 4~29~007 to ~right et al. This device monitors the atrial ra-te and alters the ventricular escape interval in response to the atrial rate.
For these patients, the pacemaker mimics the natural 25 conductive system of the heart and increased demand for cardiac output comes froM both an increase in heart rate controlled by the S-A Node as well as concomitan-t increase in stroke volume.
I-lowever, in many patienks, the S-A Node is not a 30 reliable source of information concerning the body's demand for cardiac outpu-t. Incorporatin~ an S-A Node replacement to provide rate adaptive pacin~ would be desirable.
One form of rate responsive pacemaker which relies on 35 the detection of blood saturation of oxygen is known from U.S. Patent No. ~,202,339 to Wirtzfield. This device u-tilizes an optical measurill~J probe which is inserted into ~33~
the heart -to monitor the oxygen saturation of the blood. This measurement is then used to alter the stimulating -frequency of an associated pacemaker.
Another form of rate responsive pacemaker is known from United States Patent No.4,009,721 to Alcidi. This device utilizes a pll measurement probe which alters the pacemaker's rate in response to the measurement of blood pH.
Another form of rate adaptive pacemaker is known from United Sta-tes Patent No.~,140,132 to Dahl, which utilizes an accelerometer to monitor the physical activi*y of the patient, and which alters the pacemaker's escape interval.
Another form of rate adaptive pacer is known from United States Patent No.4,228,803 to Rickards. This patent discloses a pacer which monitors the Q-T interval of the cardiac cycle and increases the pacer rate in response to shortening of the Q-T interval.
Each of the preceding pacemakers has taken advantage of a physiologic parameter which varies with the body's demand for cardiac output.
DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a block diagram of a pacemaker incorpora-ting the invention.
FIGURE 2 is a flow chart and a functional block representation of the algorithm of the present invention.
FIGURE 3 is sequence of graphs which illustrate the relationship between the stroke volume and rate of the heart.
Re-turning to cardiac physiology, and in reference to FIGURE 3A it :is important to note that the cardiac output of-the heart, measured :in litres oE
blood per minute, is -the product o:E the patient's heart ra-te times the stroke volume of the heart. The figure shows a family of constant cardiac output
S Initially, pacelnakers wele implanted in patients who exrlibited complete A-V block. This conduction disturbance is manifested by the inability of the signal from the S-A
Node to reach the lower challlbers of tlle heart to in-itiate a ventricular contractiorl.
The earliest form uf implantable pacernaker for the long-term stim~lldtion of the heart is known from lJ.S.
Patent No. 3,057,356 issued to W. Greatbatch~ This asynchronous pdcemaker, in essence, replaced the heart's natural conduction system and periodically provided an 15 electrical stinlulus to the ventricle to cause contractions.
In some patients, the A-V block condition is intermittant and occasionally the artificial pacemaker and the natural S-A Node of the heart compete for control of 20 the velltricular action of the heart. This competition is undesirable. The demand pacelnaker avoids this competitive pacing. An example of an implantable version of the demand pacemaker is known From U.S. Patent No. 3,47~,74r5, to W. Greatbatch.
In operation, the demand mode pacemaker senses the ventricular contraction of the heart, and provides stimulation to the ventricles only in the absence of naturally occurring contractions of the heart. Such demand pacemakers synchronize their timing witll the heart 30 and provide stimulated bedts if the natural cardiac rhyth drops below a preset rate. Both the asynchronous and demand type of pacemaker thus provided for a fixed lower rate for the patient's healt rate.
When a patient has no intrinsic rhythrn and is being 35 paced at a fixed rate, any increment in demand for cardiac output must come solely from naturally induced changes in stroke volume. For these patients, strenuous work is impossible since stroke volume chan~es alone are insl~fficient to raise the cardiac output enough to supply the skeletal muscles dur-ing heavy exercise.
~y way of contrasl, the P-syncllronous mocle of 5 pacemaker, as exemplified by U.S. Patent No. 3,253,596 to J. W. Keller, monitored electrical activity in the atrium~ and triggered a ventricular action after a short tirne period. This form of pacemaker permits the patient's naturally occurring atrial rate to control the rate o-f 10 ventricular stimulation.
Other pacernakers which exhibit -the atrial tracking feature include the atr-ial-synchronized, ventricularly inhibited pacemaker known -frorn U.S. Patent No. 396~,707 to W. Greatbatch, as well as the dual-sense, dual-pace 15 pacemaker known fronl U.S. Patent No. 4,3129355 to H.
Funke~ The advantage of atrial synchronized pacing is that it permits the pacernaker's rate -to be determined by the S-A Node which in turn intreprets the body's demand for cardiac ou-tput.
Another forrn of rate adaptive pacer is known from ~S. Patent No. 4~29~007 to ~right et al. This device monitors the atrial ra-te and alters the ventricular escape interval in response to the atrial rate.
For these patients, the pacemaker mimics the natural 25 conductive system of the heart and increased demand for cardiac output comes froM both an increase in heart rate controlled by the S-A Node as well as concomitan-t increase in stroke volume.
I-lowever, in many patienks, the S-A Node is not a 30 reliable source of information concerning the body's demand for cardiac outpu-t. Incorporatin~ an S-A Node replacement to provide rate adaptive pacin~ would be desirable.
One form of rate responsive pacemaker which relies on 35 the detection of blood saturation of oxygen is known from U.S. Patent No. ~,202,339 to Wirtzfield. This device u-tilizes an optical measurill~J probe which is inserted into ~33~
the heart -to monitor the oxygen saturation of the blood. This measurement is then used to alter the stimulating -frequency of an associated pacemaker.
Another form of rate responsive pacemaker is known from United States Patent No.4,009,721 to Alcidi. This device utilizes a pll measurement probe which alters the pacemaker's rate in response to the measurement of blood pH.
Another form of rate adaptive pacemaker is known from United Sta-tes Patent No.~,140,132 to Dahl, which utilizes an accelerometer to monitor the physical activi*y of the patient, and which alters the pacemaker's escape interval.
Another form of rate adaptive pacer is known from United States Patent No.4,228,803 to Rickards. This patent discloses a pacer which monitors the Q-T interval of the cardiac cycle and increases the pacer rate in response to shortening of the Q-T interval.
Each of the preceding pacemakers has taken advantage of a physiologic parameter which varies with the body's demand for cardiac output.
DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a block diagram of a pacemaker incorpora-ting the invention.
FIGURE 2 is a flow chart and a functional block representation of the algorithm of the present invention.
FIGURE 3 is sequence of graphs which illustrate the relationship between the stroke volume and rate of the heart.
Re-turning to cardiac physiology, and in reference to FIGURE 3A it :is important to note that the cardiac output of-the heart, measured :in litres oE
blood per minute, is -the product o:E the patient's heart ra-te times the stroke volume of the heart. The figure shows a family of constant cardiac output
3~
curves callecl isopleths corresponding to cardiac outputs of 1 to 6 L/M.
As previously indicated, increased physical activity in normal individuals, results in an increased cardiac output. In the normal heart, both the heart rate and the stroke volume increase to satis~y the body's need for oxygenated blood. Studies by Versteeg (1981) show that for exercise this cardiac transfer function is a first order linear function with a 10-12 second time constant. This normal cardiac response to increasing work loads is shown by the cardiac load line 300 on l:IGURE 3A. In the figure, a work load corresponding to cardiac output of 2L/M is met by a heart rate of 75 bpm at a stroke volume of 26 ml. An increase in work load calling for a cardiac output of 5L/M is met wi~h a rate increase of 1~0 bpm and a stroke volume increase to 36 ml.
In -those patients who have complete heart block and a fixed-rate pacemaker, it has been noted that increased demand for cardiac output due -to physical exertion results in an increase in the measured stroke volume of a patientls heart. This is depicted in FIGURE 3B, where the load line 310 corresponds to pacing at a fixed rate, as in asynchronous (V00), demand pacing (VVI) or A-V sequential (DVI) pacing. This figure indicates that those paced patients who have S-A Node dysfunction can only change s-troke volume in response to exercise. Ior example, at 2 L/M of cardiac output th:is patient exhibits a stroke volume of 20 ml at a rate of 100 bpm. An increase to 5 L/M
calls for a stroke volume increase to 5() ml which may well be beyond the patien-t's capabi:Lity.
Thus, the prior art discloses rate adaptive pacers which monitor a physiologic parameter.
Additionally, the response of the hear-t's s-troke volume to physical exertion is well-known in -the art.
67~2-250 BRIEF SUMMARY OF THE INVENTION
_.
In contrast to these preceding forms of rate variable pacemakers, the pacemaker of the present invention moni.tors the s-troke volume of the patient and al-ters the pacing rate in accordance wi-th an algorithm. The sys-tem controls the patien-t's heart rate and also permits the s-troke volume of the patient's heart to vary over a controlled range.
In accordance with a broad aspect of -the invention there is provided a cardiac pacer for the therapeutic stimula-tion of a heart comprising:
lead system means for coupling said pacer to the patient's heart;
measuring means coupled to said lead for inferring the stroke volume of said heart from the measurement of a physiologic parame-ter and fcr producing a measurement indicative of stroke volume;
computation and control means coupled to said measuring means for determining a heart rate value in response to said stroke volume measurements wherein said heart rate is defined as the V- V
interval;
means for comparing the value of said s-troke volume measurement with the value of a s-troke volume set point for producing a stroke volume difference value;
means for determining a heart ra-te difference value, wherein said heart rate value is defined as -the V_ V interval, from said stroke volume difference value;
means for adding said hear-t rate difference value to -the previous heart rate value yielding a current, heart rate value; and pulse generator means coupled to said lead system and said computational and control means for providing stimulation pulses to said heart at a frequency which is a function of said heart rate value.
In accordance wi-th another broad aspect of the invention there is provided a cardiac pacer for the therapeutic stimulation of a hear-t comprising:
measuring means for periodically inferring the stroke volume of said heart and for producing a sequence of stroke volume measurements;
pulse generator means for providing stimulation pulses to said heart at a frequency proportional to a hear-t rate value wherein said hear-t rate value is defined as the V - V interval;
means coupled to said measuring means and coupled to said pulse generator means for determining said heart rate value in response to stroke volume measurement;
means for comparing -the value of said stroke volume measurement with -the value of a stroke volume set point for producing a stroke volume difference value;
means for determining a hear-t rate di:Eference value, wherein said hear-t ra-te value is defined as -the V- V interval, from said stroke volume difference value; and means for adding said heart rate difference value to the previous heart rate value yielding a current, heart rate value.
In accordance with another broad aspect of -the invention, there is provided a cardiac pacer for the therapeutic stimulation -6a-of a heart comprising:
measuring means for measuring the ven-tricular volume of said heart a-t end dias-tole and a-t end systole and for inferring a stroke volume measurement from said end sys-tolic and end diastolic measurements;
pulse yenerator means Eor providing stimulation pulses to said heart at a frequency propor-tional to a heart rate value where in said hear-t ra-te value is defined as the V--~V interval;
computa-tional control means coupled to said measuring means and coupled to said pulse generator means for determining said heart rate value in response to the stroke volume measurement, means for comparing the value of said stroke volume measurement with the value of a stroke volume set point for pro-ducing a stroke volume difference value;
means for determining a heart rate difference value,wherein said heart rate value i5 defined as the V - V interval, from said stroke volume difference value; and means for adding said heart rate difference value to -the previous heart rate value yielding a current, heart rate value.
DESCRIPTION OF THE PREFERRED EMBODIMENT
__ __ _ __ _ The present invention combines three pacer subsys-tems with the hear-t to form a closed loop pacer for pacing the heart.
I:n FIGURE 1, -the heart 10 is coupled -to a stroke volume measurement appaxatus 20 through a lead system 12. The stroke volume measurement system 20 delivers in:Eormation regarding the stroke volume of the heart -to computa-tion and control locJic 22.
-6b-~%~33~
6~2-25~
This apparatus utilizes information related to stroke vol:ume to determine a desired pacing rate for the heart. Rate control information is provided to a pulse generator 2~ which may provide stimulation -to the heart 10 through lead system 12. The pulse generator 24 may operate in any of the known stimulation modes.
However, the algorithm is described in the con-text of a rate variable asynchronous or VOO mode pacer. A system suitable for incorporating the output data oE -the algorithm into a demand mode pacer may be found in Canadian Patent Application Serial No.
416,050 filed 22 November, 1982 and assigned -to the Assignee of the present invention.
STROKE VOLUME MEASUREMENT SYSTEM
In response to an increase in demand for cardiac output the normal heart increases both its rate and stroke volume. The present invention utilizes the body's demand for cardiac output to control the rate of pacing. This technique requires a reliable measurement of a physiologic variable which is related to cardiac stroke volume.
-6c-Stroke volurme may be inferred by a variety o-f rneasurements taken in the right or le-ft heart including pressure-time histories of arterial blood Flow as ~ell as direct flow measurements in the ma~jor blood vessels of the 5 heart.
Another method of deterrnining the s-troke volume of the heart is through the tecllnique of impedance plethysrnography. This technique has been widely studied (Rushmer 1953 Geddes 19~6 Baan 19~1). In this technique lO an electrode system is inserted into the rigilt or left heart. As shown in FIG. 1 current is passed frorn an anode 13 to a cathode 1~ and the voltage between the electrode pair is measured. I'he accuracy of this method may be increased by utilizing a rnultiplicity of electrode pairs.
15 (Baan 19~1). The magnitude of the voltage measurements from the sensing electrode pairs is a function of the impedance of the heart cavity (Zm) This impedance is in turn, a function of the volume of the chamber. In general volume res-istivity of the l)lood remains constdllt 20 and the magnitude of the voltage sensed depends solely upon the volume of the chdnlber during the measllrelnent.
One may measure chamber volume sequentially (~l~
Z2~ . . . Zn~) over the en-tire cardiac cycle and can be used to ascertain the maxima and minima of cardiac chalnber 25 volume. However in general~ the maximum cardiac volume is achieved at end diastole just prior to -the contrdction of the ventricle. Likewise t~e minimum volume of the ventricle occurs at thr end of the contractiorl of the ventricular muscles called end systole. By rneasuring the 30 heart volume at end systole and end diastole the stroke volurne measurement apparatus may determine the stroke volurne for tilat cardiac contraction or cycle. The computation and control circuitry which receives the stroke volume measurement information may average the 35 stroke volume measurements over a nurnber of cardiac cycles or may operate on a beat-to-beat basis. Further detai'ls regardirlg the measllrenlent of stroke vo'lume through - ~ -the use of an intrdcard ac cathetel may be found in Cardiovascular Research 1981 15 328-334 COMPUTATION AND CONTROI APPARATUS
The structural and -functional aspects of computation 5 and control system 22 are shown in FIG. 2.
The computation and control system 22 receives stroke volume informatiorl labeled SVm on a beat-to-beat basis from the stroke volume measurement system 20 which in turn, is coupled to heart 10. The computa-tion and control 10 system 22 operates on this information and generdtes a heart rate value la~el~d HRN. This rate infolmatioll is used to control the escape interval of the pulse generator 2~ portion of the pacer.
The series of sequential stroke volume measurements 15 denoted [SVm SVm~1 SVm+2...] are delivered to a computational block 100 which calcula-tes an average stroke volume value~ denoted SVM by adding together the values of M measurements and then dividing by M. This process may be expressed:
M
1 SVM=1/M ~ SVm m=1 Experiments have been performed on do~s where the value of M has been varied from 1 to 12. The control 25 algorithm appears to be rela~ively insensitive to this interval and a value of M=1 may be taken dS a representative value.
The measured value of average stroke volume SVM is compared with d reference value for stroke volume denoted 30 SVR. The value for SVR -is calculated by functional block 112 which will be described shortly.
The cornparison betweell SVM and the stroke volume set point SVR is accompl-ished by functional node 10~
which calculates the difFerence between the two values 35 yielding a difference value denoted ~SVM.
~3~
g The value of~ SVM is used to calculate a value of the change in heart rate value denoted~HRn in -the figure. This computdtion -is performed in functional block 106. Experimental work has been performed with a linear 5 relationship hetween ~SVM and the computed value of HRn expressed:
2 ~HRn--K3~SvM
~ lowever other relationships sdtisfying the general expression~ HRn=f(~SVM) may prove workable.
The proportionality constant K3 has units of beats per minute/liter. The value of K3 affects the response tirne of the system -to changes in the measured stroke vol~me. It appears from animal experimentation that the value of K3 is not critical ~or the s-tabi~iity of the 15 system. A typical value for K3 may be taken as 600 bpm/L .
The vallle of HR~I computed as a function of SVM is used to update the exis-ting value for heart rate denoted HRn 1 This calculation is performed at node 108 20 where the value of change in heart rate (~HRn) is added to the preceding value of heart rate (HR" 1). It is important that this operation preserves the sign o-f the change of heart rate, so tha-t the updated value of heart rate can increase or decrease in comparison with the 25 preceding value.
The updated value for heart rate (HRn) is permitted to range between a minimuln heart rate value (HRnlin) and a maxinlunl heart rate value (HRInax). The rate limit check is per-formed by functional block 110. The value of the hear-t 30 rate delivered to the pulse generator 24 is denoted HRN
where HRN=f~HRn). Ihe computed value for HRN replaces the prexisting value for HRrl-1 stored at lll for use at node 108. This value is used to calculate a new value for the stroke volume re-ference value SVR at functional 35 block 112 as follows.
The stroke volume reference value SVR is set to an initial value SVo during systeln initiali2at-ion (norlnal resting value)O Subsequent values are computed as a func-tion of the heart rate value SVR=SVo~K2HRn_1 where the reference value is a linear func~ion of the existing value of heart rate.
5 However other relationships satisfying the general expression: SVR~f(HRN-I) rnay prove workable.
The value of SVO sets the operating point of the control systern as will be discussed with reference to FlGs. 3c and 3d. The value of the proportionality 10 constant K2 controls the slope of the cardiac load line discussed in connection with FlGs. 3c and 3d.
The values for the 2veraging interval M the initial stroke volume set point SVO and K2 and K3 are likely to be patient specific parameters and it may prove 15 desirable to permit alteration of these values by the physician to adapt the pacer to the patient. Likewise the values of HRmax and HRmin may be physician alterable to adapt the stimulation rate to the needs of the patient.
Pulse Generator System 24 The HRN signal is accepted by the pulse generator system 24 and interpreted as an escape interval for the pacemaker function of the device. In operationS -the pacemaker escape interval will vary with the measured 25 stroke volume of the heart. As previously indicated during exercise the escape interval o-f the pacemaker will shorten. If the heart fails to beat within the designated escape interval, then a pacing stimulus will be provided, from pulse amplifier 27 to the heart through sensing 30 stirnulating electrode 11 as shown in FIG. 1. If a natural heal~tbeat is detected prior to the expiration of the escape interval through sensing stimulating electrode 11, a sense amplifier 26 will inhibit the delivery of the pacing s-timulus. Either or both chambers of the heart rnay 35 be stimulated by the pulse generator and the device may operate in an inhibited mode.
3~
It should be recognize~, however, that the stroke volume controlled system can be incoporated into an atrial tracking pacemaker moddlity wherein the ultimate escape interval of the pacemaker may be influenced by the 5 detected atridl rdte o~ the hedrt as well as by variations in the patient's cardi dC stroke volume.
The objective of this stroke volume controlled pacer is to achieve a pacernaker escape interval which reflects 10 the patient's physiologic demand for cardiac output.
The illpUt signal to this control system is the stroke volume of the patient's heart and the output variable of this system is the pacemaker's escape interval.
Experimental data has been taken with a blood flow 15 meter attached to the aorta of the heart, thus providing a direct measure of the stroke volume of the heart, on a beat by beat basis. It is expectedl however, that for a fully implantable system it will be preferable to use the impedance plethysmography approach previously described.
20 The integral of the mass ~low rate signal from the transducer provides a sequence of stroke volume measurements S~lm. These values may be averaged over a multiple number of cardiac cycles to provide a measure of the average stroke volume of the heart. If a very small 25 number of cycles is used, it is possible that the beat-to-beat v~riation in the patient's stroke volume may cause the control sys-tem to generate a sequence of escape intervals which dither about a physiologicdlly optimunl escape rate. On the other hand, if the number of beats 30 taken to form the averaye is large, the response time of the control system may be insufficient to provide the requisite cardiac output for the instantaneous work level of the patient. Experimental work indicates that a value of M = l is suitable for a canine with induced heart 35 block.
The average stroke volume value SVM is comparecl with a stroke volume reference value which may be selected :; ~
~33~
by tile physician and which is constrained within limits.
If this stroke volume reference value is fixed at a specific stroke volume value, then the cardiac load line 320 as shown in FIG. 3C~ will have an infinite slope.
5 Under this regime, small increments in stroke volume due to increments in the exercise level o~ the object result in relatively large increments in hear-t rate, thus forcing the stroke volume of the heart back toward the se-t point reference SVR. In this operating mode the patient is 10 paced at a rate which results in a fixed stroke volume for the heart. Experimental research with canine reveals a poten-tial defect of fixed stroke volume pacing. As indicated in FIG. 3c, an escape interval dictatPd by fixed stroke volulne may call for heart rates subslantially above 15 those which are safe for the subject.
By permitting the stroke volume re-ference point value to vary within constrained limits, one can con-trol the slope of the cardiac load line. Permitting the stroke volume reference point value to vary over a range of 20 approximately 30 ml results in a control system response depicted by FIG. 3d.
In this system the instantaneous value of the stroke volume re~erence poin-t SVR is a function of the instantaneous value of the heart rate. The linear 25 relationship depicted by functional block 112 of FIG. 2 results in a cardiac load line 330 as shown in FIG. 3D.
While a larger value of the portionality constant K2 as shown by curve 112b in FIG. 2 results in a cardiac load line similar to cardiac load line 3~0 in FIG. 3D. Thus, 30 the proportionality constant K2 controls the slope of the cardiac load line and may vary -the cardiac response from that observed in fixed rate pacing as depicted in FIG. 3B
to that which results from pacing to a fixed stroke volume depicted in FIG. 3C. An appropriate value for K2 must be 35 selected by the physician based upon informàtion 67~2-250 concerning the subject patient's heart contractility and stroke volume variations.
The initial value of the stroke volume set point is taken as SV0 which may also be a physician programmable variable in the pacemaking sys-tem. This value controls the initial opera-ting point Eor the system at resting values of cardiac output.
The variation in stroke volume rneasuremen-t compu-ted at nocle 104 is utilized to calculate the change in hear-t rate of the pace-maker in functional bnock 106. Once again a linear rela-tionship between -the change in heart rate and the change in s-troke volume is illustrated in functional block 106. It is qui-te likely that other functions may be suitable for these relationships.
The value of the proportionality constant K3 which control the slope of the function controls the response time of the pacing system -to changes in stroke volume of the patient.
Since it is desirable to have a fast ac~ing sys-tem and it is desirable to have a large value of K3. In canine work values for -the proportionality constan-t have varied from 156 bpm/L to 1250 bpm/L with a value of 600 bpm/L proving suitable for canines with induced hear-t block.
The calcula-tecl value of the chancJe in the desirecl heart rate computed in func-tional block 106 is added to -the existing value of the heart ra-te and if this new value falls within the limits prescribed by functional block 1]0 it is delivered to the pulse generator -to con-trol the pacing of the patients' heart.
It is desirable -to have the maximum and minimum heart ra-tes for the system physician prescribecl.
curves callecl isopleths corresponding to cardiac outputs of 1 to 6 L/M.
As previously indicated, increased physical activity in normal individuals, results in an increased cardiac output. In the normal heart, both the heart rate and the stroke volume increase to satis~y the body's need for oxygenated blood. Studies by Versteeg (1981) show that for exercise this cardiac transfer function is a first order linear function with a 10-12 second time constant. This normal cardiac response to increasing work loads is shown by the cardiac load line 300 on l:IGURE 3A. In the figure, a work load corresponding to cardiac output of 2L/M is met by a heart rate of 75 bpm at a stroke volume of 26 ml. An increase in work load calling for a cardiac output of 5L/M is met wi~h a rate increase of 1~0 bpm and a stroke volume increase to 36 ml.
In -those patients who have complete heart block and a fixed-rate pacemaker, it has been noted that increased demand for cardiac output due -to physical exertion results in an increase in the measured stroke volume of a patientls heart. This is depicted in FIGURE 3B, where the load line 310 corresponds to pacing at a fixed rate, as in asynchronous (V00), demand pacing (VVI) or A-V sequential (DVI) pacing. This figure indicates that those paced patients who have S-A Node dysfunction can only change s-troke volume in response to exercise. Ior example, at 2 L/M of cardiac output th:is patient exhibits a stroke volume of 20 ml at a rate of 100 bpm. An increase to 5 L/M
calls for a stroke volume increase to 5() ml which may well be beyond the patien-t's capabi:Lity.
Thus, the prior art discloses rate adaptive pacers which monitor a physiologic parameter.
Additionally, the response of the hear-t's s-troke volume to physical exertion is well-known in -the art.
67~2-250 BRIEF SUMMARY OF THE INVENTION
_.
In contrast to these preceding forms of rate variable pacemakers, the pacemaker of the present invention moni.tors the s-troke volume of the patient and al-ters the pacing rate in accordance wi-th an algorithm. The sys-tem controls the patien-t's heart rate and also permits the s-troke volume of the patient's heart to vary over a controlled range.
In accordance with a broad aspect of -the invention there is provided a cardiac pacer for the therapeutic stimula-tion of a heart comprising:
lead system means for coupling said pacer to the patient's heart;
measuring means coupled to said lead for inferring the stroke volume of said heart from the measurement of a physiologic parame-ter and fcr producing a measurement indicative of stroke volume;
computation and control means coupled to said measuring means for determining a heart rate value in response to said stroke volume measurements wherein said heart rate is defined as the V- V
interval;
means for comparing the value of said s-troke volume measurement with the value of a s-troke volume set point for producing a stroke volume difference value;
means for determining a heart ra-te difference value, wherein said heart rate value is defined as -the V_ V interval, from said stroke volume difference value;
means for adding said hear-t rate difference value to -the previous heart rate value yielding a current, heart rate value; and pulse generator means coupled to said lead system and said computational and control means for providing stimulation pulses to said heart at a frequency which is a function of said heart rate value.
In accordance wi-th another broad aspect of the invention there is provided a cardiac pacer for the therapeutic stimulation of a hear-t comprising:
measuring means for periodically inferring the stroke volume of said heart and for producing a sequence of stroke volume measurements;
pulse generator means for providing stimulation pulses to said heart at a frequency proportional to a hear-t rate value wherein said hear-t rate value is defined as the V - V interval;
means coupled to said measuring means and coupled to said pulse generator means for determining said heart rate value in response to stroke volume measurement;
means for comparing -the value of said stroke volume measurement with -the value of a stroke volume set point for producing a stroke volume difference value;
means for determining a hear-t rate di:Eference value, wherein said hear-t ra-te value is defined as -the V- V interval, from said stroke volume difference value; and means for adding said heart rate difference value to the previous heart rate value yielding a current, heart rate value.
In accordance with another broad aspect of -the invention, there is provided a cardiac pacer for the therapeutic stimulation -6a-of a heart comprising:
measuring means for measuring the ven-tricular volume of said heart a-t end dias-tole and a-t end systole and for inferring a stroke volume measurement from said end sys-tolic and end diastolic measurements;
pulse yenerator means Eor providing stimulation pulses to said heart at a frequency propor-tional to a heart rate value where in said hear-t ra-te value is defined as the V--~V interval;
computa-tional control means coupled to said measuring means and coupled to said pulse generator means for determining said heart rate value in response to the stroke volume measurement, means for comparing the value of said stroke volume measurement with the value of a stroke volume set point for pro-ducing a stroke volume difference value;
means for determining a heart rate difference value,wherein said heart rate value i5 defined as the V - V interval, from said stroke volume difference value; and means for adding said heart rate difference value to -the previous heart rate value yielding a current, heart rate value.
DESCRIPTION OF THE PREFERRED EMBODIMENT
__ __ _ __ _ The present invention combines three pacer subsys-tems with the hear-t to form a closed loop pacer for pacing the heart.
I:n FIGURE 1, -the heart 10 is coupled -to a stroke volume measurement appaxatus 20 through a lead system 12. The stroke volume measurement system 20 delivers in:Eormation regarding the stroke volume of the heart -to computa-tion and control locJic 22.
-6b-~%~33~
6~2-25~
This apparatus utilizes information related to stroke vol:ume to determine a desired pacing rate for the heart. Rate control information is provided to a pulse generator 2~ which may provide stimulation -to the heart 10 through lead system 12. The pulse generator 24 may operate in any of the known stimulation modes.
However, the algorithm is described in the con-text of a rate variable asynchronous or VOO mode pacer. A system suitable for incorporating the output data oE -the algorithm into a demand mode pacer may be found in Canadian Patent Application Serial No.
416,050 filed 22 November, 1982 and assigned -to the Assignee of the present invention.
STROKE VOLUME MEASUREMENT SYSTEM
In response to an increase in demand for cardiac output the normal heart increases both its rate and stroke volume. The present invention utilizes the body's demand for cardiac output to control the rate of pacing. This technique requires a reliable measurement of a physiologic variable which is related to cardiac stroke volume.
-6c-Stroke volurme may be inferred by a variety o-f rneasurements taken in the right or le-ft heart including pressure-time histories of arterial blood Flow as ~ell as direct flow measurements in the ma~jor blood vessels of the 5 heart.
Another method of deterrnining the s-troke volume of the heart is through the tecllnique of impedance plethysrnography. This technique has been widely studied (Rushmer 1953 Geddes 19~6 Baan 19~1). In this technique lO an electrode system is inserted into the rigilt or left heart. As shown in FIG. 1 current is passed frorn an anode 13 to a cathode 1~ and the voltage between the electrode pair is measured. I'he accuracy of this method may be increased by utilizing a rnultiplicity of electrode pairs.
15 (Baan 19~1). The magnitude of the voltage measurements from the sensing electrode pairs is a function of the impedance of the heart cavity (Zm) This impedance is in turn, a function of the volume of the chamber. In general volume res-istivity of the l)lood remains constdllt 20 and the magnitude of the voltage sensed depends solely upon the volume of the chdnlber during the measllrelnent.
One may measure chamber volume sequentially (~l~
Z2~ . . . Zn~) over the en-tire cardiac cycle and can be used to ascertain the maxima and minima of cardiac chalnber 25 volume. However in general~ the maximum cardiac volume is achieved at end diastole just prior to -the contrdction of the ventricle. Likewise t~e minimum volume of the ventricle occurs at thr end of the contractiorl of the ventricular muscles called end systole. By rneasuring the 30 heart volume at end systole and end diastole the stroke volurne measurement apparatus may determine the stroke volurne for tilat cardiac contraction or cycle. The computation and control circuitry which receives the stroke volume measurement information may average the 35 stroke volume measurements over a nurnber of cardiac cycles or may operate on a beat-to-beat basis. Further detai'ls regardirlg the measllrenlent of stroke vo'lume through - ~ -the use of an intrdcard ac cathetel may be found in Cardiovascular Research 1981 15 328-334 COMPUTATION AND CONTROI APPARATUS
The structural and -functional aspects of computation 5 and control system 22 are shown in FIG. 2.
The computation and control system 22 receives stroke volume informatiorl labeled SVm on a beat-to-beat basis from the stroke volume measurement system 20 which in turn, is coupled to heart 10. The computa-tion and control 10 system 22 operates on this information and generdtes a heart rate value la~el~d HRN. This rate infolmatioll is used to control the escape interval of the pulse generator 2~ portion of the pacer.
The series of sequential stroke volume measurements 15 denoted [SVm SVm~1 SVm+2...] are delivered to a computational block 100 which calcula-tes an average stroke volume value~ denoted SVM by adding together the values of M measurements and then dividing by M. This process may be expressed:
M
1 SVM=1/M ~ SVm m=1 Experiments have been performed on do~s where the value of M has been varied from 1 to 12. The control 25 algorithm appears to be rela~ively insensitive to this interval and a value of M=1 may be taken dS a representative value.
The measured value of average stroke volume SVM is compared with d reference value for stroke volume denoted 30 SVR. The value for SVR -is calculated by functional block 112 which will be described shortly.
The cornparison betweell SVM and the stroke volume set point SVR is accompl-ished by functional node 10~
which calculates the difFerence between the two values 35 yielding a difference value denoted ~SVM.
~3~
g The value of~ SVM is used to calculate a value of the change in heart rate value denoted~HRn in -the figure. This computdtion -is performed in functional block 106. Experimental work has been performed with a linear 5 relationship hetween ~SVM and the computed value of HRn expressed:
2 ~HRn--K3~SvM
~ lowever other relationships sdtisfying the general expression~ HRn=f(~SVM) may prove workable.
The proportionality constant K3 has units of beats per minute/liter. The value of K3 affects the response tirne of the system -to changes in the measured stroke vol~me. It appears from animal experimentation that the value of K3 is not critical ~or the s-tabi~iity of the 15 system. A typical value for K3 may be taken as 600 bpm/L .
The vallle of HR~I computed as a function of SVM is used to update the exis-ting value for heart rate denoted HRn 1 This calculation is performed at node 108 20 where the value of change in heart rate (~HRn) is added to the preceding value of heart rate (HR" 1). It is important that this operation preserves the sign o-f the change of heart rate, so tha-t the updated value of heart rate can increase or decrease in comparison with the 25 preceding value.
The updated value for heart rate (HRn) is permitted to range between a minimuln heart rate value (HRnlin) and a maxinlunl heart rate value (HRInax). The rate limit check is per-formed by functional block 110. The value of the hear-t 30 rate delivered to the pulse generator 24 is denoted HRN
where HRN=f~HRn). Ihe computed value for HRN replaces the prexisting value for HRrl-1 stored at lll for use at node 108. This value is used to calculate a new value for the stroke volume re-ference value SVR at functional 35 block 112 as follows.
The stroke volume reference value SVR is set to an initial value SVo during systeln initiali2at-ion (norlnal resting value)O Subsequent values are computed as a func-tion of the heart rate value SVR=SVo~K2HRn_1 where the reference value is a linear func~ion of the existing value of heart rate.
5 However other relationships satisfying the general expression: SVR~f(HRN-I) rnay prove workable.
The value of SVO sets the operating point of the control systern as will be discussed with reference to FlGs. 3c and 3d. The value of the proportionality 10 constant K2 controls the slope of the cardiac load line discussed in connection with FlGs. 3c and 3d.
The values for the 2veraging interval M the initial stroke volume set point SVO and K2 and K3 are likely to be patient specific parameters and it may prove 15 desirable to permit alteration of these values by the physician to adapt the pacer to the patient. Likewise the values of HRmax and HRmin may be physician alterable to adapt the stimulation rate to the needs of the patient.
Pulse Generator System 24 The HRN signal is accepted by the pulse generator system 24 and interpreted as an escape interval for the pacemaker function of the device. In operationS -the pacemaker escape interval will vary with the measured 25 stroke volume of the heart. As previously indicated during exercise the escape interval o-f the pacemaker will shorten. If the heart fails to beat within the designated escape interval, then a pacing stimulus will be provided, from pulse amplifier 27 to the heart through sensing 30 stirnulating electrode 11 as shown in FIG. 1. If a natural heal~tbeat is detected prior to the expiration of the escape interval through sensing stimulating electrode 11, a sense amplifier 26 will inhibit the delivery of the pacing s-timulus. Either or both chambers of the heart rnay 35 be stimulated by the pulse generator and the device may operate in an inhibited mode.
3~
It should be recognize~, however, that the stroke volume controlled system can be incoporated into an atrial tracking pacemaker moddlity wherein the ultimate escape interval of the pacemaker may be influenced by the 5 detected atridl rdte o~ the hedrt as well as by variations in the patient's cardi dC stroke volume.
The objective of this stroke volume controlled pacer is to achieve a pacernaker escape interval which reflects 10 the patient's physiologic demand for cardiac output.
The illpUt signal to this control system is the stroke volume of the patient's heart and the output variable of this system is the pacemaker's escape interval.
Experimental data has been taken with a blood flow 15 meter attached to the aorta of the heart, thus providing a direct measure of the stroke volume of the heart, on a beat by beat basis. It is expectedl however, that for a fully implantable system it will be preferable to use the impedance plethysmography approach previously described.
20 The integral of the mass ~low rate signal from the transducer provides a sequence of stroke volume measurements S~lm. These values may be averaged over a multiple number of cardiac cycles to provide a measure of the average stroke volume of the heart. If a very small 25 number of cycles is used, it is possible that the beat-to-beat v~riation in the patient's stroke volume may cause the control sys-tem to generate a sequence of escape intervals which dither about a physiologicdlly optimunl escape rate. On the other hand, if the number of beats 30 taken to form the averaye is large, the response time of the control system may be insufficient to provide the requisite cardiac output for the instantaneous work level of the patient. Experimental work indicates that a value of M = l is suitable for a canine with induced heart 35 block.
The average stroke volume value SVM is comparecl with a stroke volume reference value which may be selected :; ~
~33~
by tile physician and which is constrained within limits.
If this stroke volume reference value is fixed at a specific stroke volume value, then the cardiac load line 320 as shown in FIG. 3C~ will have an infinite slope.
5 Under this regime, small increments in stroke volume due to increments in the exercise level o~ the object result in relatively large increments in hear-t rate, thus forcing the stroke volume of the heart back toward the se-t point reference SVR. In this operating mode the patient is 10 paced at a rate which results in a fixed stroke volume for the heart. Experimental research with canine reveals a poten-tial defect of fixed stroke volume pacing. As indicated in FIG. 3c, an escape interval dictatPd by fixed stroke volulne may call for heart rates subslantially above 15 those which are safe for the subject.
By permitting the stroke volume re-ference point value to vary within constrained limits, one can con-trol the slope of the cardiac load line. Permitting the stroke volume reference point value to vary over a range of 20 approximately 30 ml results in a control system response depicted by FIG. 3d.
In this system the instantaneous value of the stroke volume re~erence poin-t SVR is a function of the instantaneous value of the heart rate. The linear 25 relationship depicted by functional block 112 of FIG. 2 results in a cardiac load line 330 as shown in FIG. 3D.
While a larger value of the portionality constant K2 as shown by curve 112b in FIG. 2 results in a cardiac load line similar to cardiac load line 3~0 in FIG. 3D. Thus, 30 the proportionality constant K2 controls the slope of the cardiac load line and may vary -the cardiac response from that observed in fixed rate pacing as depicted in FIG. 3B
to that which results from pacing to a fixed stroke volume depicted in FIG. 3C. An appropriate value for K2 must be 35 selected by the physician based upon informàtion 67~2-250 concerning the subject patient's heart contractility and stroke volume variations.
The initial value of the stroke volume set point is taken as SV0 which may also be a physician programmable variable in the pacemaking sys-tem. This value controls the initial opera-ting point Eor the system at resting values of cardiac output.
The variation in stroke volume rneasuremen-t compu-ted at nocle 104 is utilized to calculate the change in hear-t rate of the pace-maker in functional bnock 106. Once again a linear rela-tionship between -the change in heart rate and the change in s-troke volume is illustrated in functional block 106. It is qui-te likely that other functions may be suitable for these relationships.
The value of the proportionality constant K3 which control the slope of the function controls the response time of the pacing system -to changes in stroke volume of the patient.
Since it is desirable to have a fast ac~ing sys-tem and it is desirable to have a large value of K3. In canine work values for -the proportionality constan-t have varied from 156 bpm/L to 1250 bpm/L with a value of 600 bpm/L proving suitable for canines with induced hear-t block.
The calcula-tecl value of the chancJe in the desirecl heart rate computed in func-tional block 106 is added to -the existing value of the heart ra-te and if this new value falls within the limits prescribed by functional block 1]0 it is delivered to the pulse generator -to con-trol the pacing of the patients' heart.
It is desirable -to have the maximum and minimum heart ra-tes for the system physician prescribecl.
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A cardiac pacer for the therapeutic stimulation of a heart comprising:
lead system means for coupling said pacer to the patient's heart;
measuring means coupled to said lead for inferring the stroke volume of said heart from the measurement of a physiologic para-meter and for producing a measurement indicative of stroke volume;
computation and control means coupled to said measuring means for determining a heart rate value in response to said stroke volume measurements wherein said heart rate is defined as the V-V interval;
means for comparing the value of said stroke volume measure-ment with the value of a stroke volume set point for producing a stroke volume difference value;
means for determining a heart rate difference value, wherein said heart rate value is defined as the V-V interval, from said stroke volume difference value;
means for adding said heart rate difference value to the previous heart rate value yielding a current, heart rate value;
and pulse generator means coupled to said lead system and said computational and control means for providing stimulation pulses to said heart at a frequency which is a function of said heart rate value.
lead system means for coupling said pacer to the patient's heart;
measuring means coupled to said lead for inferring the stroke volume of said heart from the measurement of a physiologic para-meter and for producing a measurement indicative of stroke volume;
computation and control means coupled to said measuring means for determining a heart rate value in response to said stroke volume measurements wherein said heart rate is defined as the V-V interval;
means for comparing the value of said stroke volume measure-ment with the value of a stroke volume set point for producing a stroke volume difference value;
means for determining a heart rate difference value, wherein said heart rate value is defined as the V-V interval, from said stroke volume difference value;
means for adding said heart rate difference value to the previous heart rate value yielding a current, heart rate value;
and pulse generator means coupled to said lead system and said computational and control means for providing stimulation pulses to said heart at a frequency which is a function of said heart rate value.
2. A cardiac pacer for the therapeutic stimulation of a heart comprising:
measuring means for periodically inferring the stroke volume of said heart and for producing a sequence of stroke volume measurements;
pulse generator means for providing stimulation pulses to said heart at a frequency proportional to a heart rate value wherein said heart rate value is defined as the V-V interval;
means coupled to said measuring means and coupled to said pulse generator means for determining said heart rate value in response to stroke volume measurement;
means for comparing the value of said stroke volume measurement with the value of a stroke volume set point for producing a stroke volume difference value;
means for determining a heart rate difference value, wherein said heart rate value is defined as the V-V interval, from said stroke volume difference value; and means for adding said heart rate difference value to the previous heart rate value yielding a current, heart rate value.
measuring means for periodically inferring the stroke volume of said heart and for producing a sequence of stroke volume measurements;
pulse generator means for providing stimulation pulses to said heart at a frequency proportional to a heart rate value wherein said heart rate value is defined as the V-V interval;
means coupled to said measuring means and coupled to said pulse generator means for determining said heart rate value in response to stroke volume measurement;
means for comparing the value of said stroke volume measurement with the value of a stroke volume set point for producing a stroke volume difference value;
means for determining a heart rate difference value, wherein said heart rate value is defined as the V-V interval, from said stroke volume difference value; and means for adding said heart rate difference value to the previous heart rate value yielding a current, heart rate value.
3. A cardiac pacer for the therapeutic stimulation of a heart comprising:
measuring means for measuring the ventricular volume of said heart at end diastole and at end systole and for inferring a stroke volume measurement from said end systolic and end diastolic measurements;
pulse generator means for providing stimulation pulses to said heart at a frequency proportional to a heart rate value wherein said heart rate value is defined as the V-V interval;
computational control means coupled to said measureing means and coupled to said pulse generator means for determining said heart rate value in response to the stroke volume measurement;
means for comparing the value of said stroke volume measure-ment with the value of a stroke volume set point for producing a stroke volume difference value;
means for determining a heart rate difference value, wherein said heart rate value is defined as the V-V interval, from said stroke volume difference value; and means for adding said heart rate difference value to the previous heart rate value yielding a current, heart rate value.
measuring means for measuring the ventricular volume of said heart at end diastole and at end systole and for inferring a stroke volume measurement from said end systolic and end diastolic measurements;
pulse generator means for providing stimulation pulses to said heart at a frequency proportional to a heart rate value wherein said heart rate value is defined as the V-V interval;
computational control means coupled to said measureing means and coupled to said pulse generator means for determining said heart rate value in response to the stroke volume measurement;
means for comparing the value of said stroke volume measure-ment with the value of a stroke volume set point for producing a stroke volume difference value;
means for determining a heart rate difference value, wherein said heart rate value is defined as the V-V interval, from said stroke volume difference value; and means for adding said heart rate difference value to the previous heart rate value yielding a current, heart rate value.
4. The cardiac pacer of claim 1 or claim 2 or claim 3 wherein said computation and control means further includes:
means for determining said stroke volume set point value from said heart rate value.
means for determining said stroke volume set point value from said heart rate value.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US509,573 | 1983-06-30 | ||
US06/509,573 US4535774A (en) | 1983-06-30 | 1983-06-30 | Stroke volume controlled pacer |
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CA1243361A true CA1243361A (en) | 1988-10-18 |
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Family Applications (1)
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CA000457692A Expired CA1243361A (en) | 1983-06-30 | 1984-06-28 | Stroke volume controlled pacer |
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US (1) | US4535774A (en) |
EP (1) | EP0140472B1 (en) |
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-
1983
- 1983-06-30 US US06/509,573 patent/US4535774A/en not_active Expired - Lifetime
-
1984
- 1984-06-27 JP JP59132804A patent/JPS6034462A/en active Granted
- 1984-06-28 CA CA000457692A patent/CA1243361A/en not_active Expired
- 1984-06-29 DE DE8484304486T patent/DE3479709D1/en not_active Expired
- 1984-06-29 EP EP84304486A patent/EP0140472B1/en not_active Expired
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EP0140472A1 (en) | 1985-05-08 |
DE3479709D1 (en) | 1989-10-19 |
US4535774A (en) | 1985-08-20 |
EP0140472B1 (en) | 1989-09-13 |
JPS6034462A (en) | 1985-02-22 |
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