CA1205526A

CA1205526A - Method and apparatus for monitoring vascular flow

Info

Publication number: CA1205526A
Application number: CA000401110A
Authority: CA
Inventors: James W. May, Jr.; Frederick N. Lukash; Kenneth H. Cohn
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-04-17
Filing date: 1982-04-16
Publication date: 1986-06-03
Also published as: EP0063900A3; US4419999A; EP0063900A2; EP0063900B1; AU550070B2; AU8251182A; DE3274792D1

Abstract

METHOD AND APPARATUS FOR MONITORING VASCULAR FLOW

ABSTRACT
A method and device for measuring blood Plow through a blood vessel within human or animal bodies. It utilizes the principle of energy conversion to heat by myocardial activity, organ metabolism, and laminar frictional flow in blood vessels and measures the heat dissipation through the vessel wall with obstruction to flow. When the device of the invention is placed next to the vessel wall, the output signal correlates blood flow with temperature. With an obstruction to flow, the temperature drops. The device is placed in series proximal and distal to the repaired vessel to be studied. The leads are brought through the skin and attached to a temperature monitor.

Description

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6 BACKGRoUNn o~ y~
7 This inven~ion relates in general to a method and 8 apparatus for ~ea~urement of blood flow and more particularly to g the measurement of blood flow with an implantable device, especially 6uitable for use in conjunction with both micro- nnd 11 macrosurgical procedures.

12 The principle of reconstructive vascular aurgery is to 13 provide and maintain blood flow to tissues and organs. With 14 circulatory interruption distal tissues become ischemic. Over time this ischemia progresse~ ~rom a reversible form (one in 16 which restoration of blood flow re-establishe6 ti~sue viability) 17 to an irreversible form ~one in which there is cell death and 18 irrevocable tissue damage).

19 Of prime importance is the monitoring of the patients, specifically the area which has been vascularized, 80 that if 21 there i5 circulatory embarrafisment it is diEcovered during the 22 period of reversible ischemia. With early intervention and 23 correction, tissue viability i8 restored and pres0rved.

2~ Various techniques have been employed in the past for measuring blood flow in large and small blood vessels. The~e 26 have included direct observ~tion (blanche and refill techni~ue) 27 in tis~ues with a cutaneous component; Doppler and ultra sound - , . .

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monitors; transcutanecus oxygen probes; laser optic monitors;
tracer scans; arteriography; and electromagnetic flow meters.
All of these methods are limited in that they are either episodic in their monitoring, risky in their application, or not entirely reliable in their interpretation.
What is needed is a monitor that can be placed under direct vision next to a vessel and which would give continuous, reliable information regarding blood flow through that vessel;
and one which would warn of any flow abnormalities. When no longer needed, the monitor should have the ability to be removed atraumatically and transcutaneously. Its use should be valid in all types of vascular surgery (microsurgical, macrosurgical) in all types of repairs (arteries, veins, vein grafts, prosthetic grafts). Uses may also include moni-toring organ function, for example for diagnosis.

SUMMARY OF THE INVENTION
The present invention relates to the measurement of blood flow at a selected site in tissue of an animal body by monitoring temperature with sensor means and comprises a surgically-implantable temperature sensing element having electrical signal conductors, the temperature sensing element providing on the conductors an electrical output signal indicative of its temperature, and a surgically-implantable housing element of biologically inert suturable material, the housing element having a semi-lunar portion with a tubular con-figuration conforming to a blood vessel and having the sensing element fixed at a tubular inner surface thereof for disposi-tion contiguous with tissue in which the housing element is implanted, the housing element with the sensing element fixed thereto having an elongated configuration adapted for atraumatic and transcutaneous removal from surgical implantation upon

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?552~i the application of tension to the signal conductors.

DESCRIPTION OF THE DRAWING
_ In the drawing:

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1 Fig. 1 iB an illustration in perspective view Or 2 blood flow senQor constructed in accordance with principles oi 3 -this invention;

4 Fig. 2 i~ a cross-sectional view of the sen~or of

5 Fig. l;

6 Pig. 3 is an illustration of sensors constructed in

7 accordance with principles of this invention attached at proximal

8 and distal locations on a blood ve~sel for practicing the method

9 of the invention;

10 Fig. 4 is an illustration in perspective view of a

11 different embodiment of a sensor con6tructed in accordance with

12 principles of this invention; and

13 Figs. 5a, b, c and d are illu~tration~ in generally

14 schematic form of an example of the practice of the method of

15 this invention.

16 DESCRIPTION OF PREFERRED EMBODIME~TS

17 Referring to Figs. 1 and 2, there is illustrated one

18 embodiment of the devlce of the invention. A silicon elastomer

19 tubing 10, which typically would be formed of a tubing having

20 1.1 mm internal diameter and 1.7 mm external diameter, has one

21 end cut away leaving a semilunar cap ~ection 14, in which i8

22 embedded a thermal sen~or in the form o~ a thermocouple 16.

23 Electrical leads 15 from the thermocouple 16 are brought out

24 through the full tubing section 12 of the elastomer tube. The

25 semi-lunar cap, or sheath, is placed in close juxtapositio~

26 around blood ve~sel 6, with the thermocouple element 16 0

27 immediately adjacent to the adventitia of the vessel. The .

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thermocouple 16 may be any suitable thermocoupLe such as those manufactured as type T by Omega Electronic Hartford, Connecticut. A suitable thermocouple was made bv stripping Teflon insulation from the ends of matc~d, 3 mil constantan and chromel alloys. Teflon i5 a tr~de mark for tetrafluoroethylene fluorocarbon polymers; the name also applies to fluorinated ethylene - propylene resins. After twisting the ends together on one side and soldering them, the thermocouple junction w~s insulated by dipping in a dilute solution of lacquer and glyptol.
Glyptol is a trade mark for a group of alXyd-type polymers and plasticizers. While a thermocouple is illustrated in Fig. 1, the temperature sensor could be formed o~ a thermistor or any other suita~ly sized, suitably sensitive, tem~erature detector.

The polymer housed thermocouple unit w~ich FIGURES 1 and 2 illustrate is specifically designed sush that the thermocouple and its insulation are enclosed within the polymer cylinderO The polymer cylinaer is flattened and semilunar at one end and is structurec i~
such a way to allow the thermocouple junction to ~e~ai~
only a fraction of a millimeter from the surface tem~e~ature ~o be measured. The polymer housing is constructed in such a way as to allow laxity of thermocouple wiring within the polymer housing such that any longitudinaL
traction on the housing will not disrupt ~nd damage the thermocouple. Further, the polymer housing of a silicone or other typical innert flesible, stretchable and malleable material is made in such a way as to allow a suture needle to be driven easily through the housing with which a~tach-ment of the housing to an appropriate tissue location can be utilized. The various sizes of the polymer housing are made to appropriatel~y ~it the tissue mounting pu_pose which is required in the specific clinical use. Furth~r, the housing is constructed in such a way with a smootn external surface such that adherence to surrounding .
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1 tissue~ is minimized and, thus, the entire unit can be extraoted 2 transcutaneously from the indwelling wound in a trauma-~ree way.
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3 With reference to Fig. 3, the blood flow detector o~
4 the invention is shown implanted within the h~nan leg. In th$~
embodiment, a control sensor 20 i8 sutured to the periva~cular 6 tissue around artery 30 at a location above the point of 7 anastomisis to the artery of the vascularized tis~ue trans~er 8 (flap) 34. A 3econd probe 22, identical to the fis6t, i~
9 sutured, again through sutures 24 to the perivascular tissue around the artery 30 at a point proximal to the vascularized 11 tissue flap 34. The leads 25 and 27, respectively, from the 12 control probe and the flap probe, are brought out through the 13 skin to connect to a temperature monitor 30. The monitor as is 14 illustrated schematically can present separate readings for temperature of the control probe and the flap probe, or could be 16 arranged to provide only a differential temperature output.
17 Additionally, the monitor 30 is shown as pro~iding an alar~, 18 which will provide a visual or audio output when the dif~erential 19 between the temperature at the control probe and the flap probe exceeds a predetermined amount. A suitable monitor is that sold 21 under the type designation TH-6, by Bailey Instrument Inc. of 22 Saddle Brook, New J~rsey.

23 Procedurally, the probes illustrated in Figs. 1, 2 and 24 3, are attached with sutures to the tissue around the artery after completion of the surgical anastomisis, and the leads ar~
26 taken out through the skin in a manner similar to drains. ~he 27 wound i6 then clo~ed and the temperature monitored on a continual

28 basis. It has been found, in ~nimal t~sts, that occlusion of th~

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1 artery will result in a temperature drop of approximately 1- _ 2 Centigrade. This i8 in contrast to a significantly lesaer drop 3 in tempera~ure a measured by the two probes when the artery ~8 4 patent. When the monitor is no longer needed, approximately 72 hours after completion of the surgery, the 6utures 24 have 6 absorbed and the leads may be atraumatically and transcutaneously 7 removed.

8 In Fig. 4 there is illustrated a second embodiment of a 9 sensor configuration suitable for use in the invention. In the probe of Fig, 4, the silicon~elastomer tubing 40 has had a 11 section at the end cut as shown to produce a series of tabs ~2.
12 A heat sensor 46, which would typically be a thermistor or 13 thermocouple, i8 again embedded in the upper wall of the sheath 14 in a manner similar to that described for the embodiment of Fig.
2. In applicatlon, the probe of Fig. 4 is slipped over the 16 artery and is held in place by virtue of the gripping action o~
17 the tabs 42. In this embodiment, then, no sutures would be 18 utllized.

19 A sensor or probe for practice of the invention thus has a support element that carries a thermal sensor element. The 21 support element i8 of readily sterlized, surgical grade, 22 electrically insulating material which is chemically inert to the 23 body in which it i6 implanted. Further, to facilitate removal of 24 the probe, the material is of a character to which body ti~sue does not adhere or cling and into which tissue does not grow.
26 The 6upport element i~ configured to di6po~e the thermal element 27 in the desired heat transfer relation with the tis~ue being 28 monitored. The illustrated ~upport element ~tructures have at ',,'~ .

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~2~? 5 S ~6 1 least a partial tubular configuration to dispo~e the thermal 2 element clo6e to, if not contiguous with, a va~cular body member, 3 e.g. a vessel. In one illustrated instance, i.e. FIGURE 1, the 4 support element is ~utured in place, and in another in~tance, i.e. FIG~RE 4, the support element is configured for resiliently 6 and releasably attaching to the vascular member.

7 The support element preferably i6 arranged, moreover, 8 for atraumatic and transcutaneous removal from the implantation 9 site being monitored simply upon pulling on the electrical leads from the thermal element. This feature of a support element 11 according to the invention calls for the probe to be elongated 12 longitudinal with the extension of the leads from the ~ensor 13 element and to have ~ufficient pliability and streamlined 14 configuration (e.g. be free o~ rigid lateral protruberances) for safe extraction in thiG manner from the body in which it is 16 implanted.

17 As further described, the thermal sensor element of the 18 probe i~ affixed to the support element, typically on or recessed 19 in an inner tubular surface thereo~.

In Fig. 5 there is illustrated a series of experiments 21 demonstrating ~he method of this invention, utilizing the 22 principles of heat generation through frictional flow.
23 Thermistor monitors were used to correlate temperature drops with 24 occlusions in one-to~two mm blood vessels in experimental animals. In Sprague-Dawley rats, New Zealand white rabbit~, and 26 Ilongrel dogs, three flow-occlu~ion models were teated with 27 implantable thermistor monitors to directly measure Yessel 28 temperature. In Fig. 5a there i~ ~llustrated a single sensor ..... . .. . _ .

1 monitoring of a femoral artery with repeated occlusions ~nd 2 releases. Thi~ experiment was carried out with 6ix 300 mg 3 Sprague-Dawley rats. In Fig. 5b, there ifi illustrated 4 schematically the simultaneous monitoring of a femoral artery 5 with monitors proximal and distal to a situs of occlusion. Thi~
6 experiment was carried out with three 300 mg Sprague-Dawley rat~, 7 two 3 kg New Zealand white rabbits and two 30 kg mongrel dogs.In r 8 Fig. 5c there i8 illustrated the simultaneously monitoring of the 9 arterial inflow into an isolated epigastric flap, based on the 10 inferior epigastric ve~sels, with and without occlusion. This 11 experiment was carried out on five 3 kg New Zealand white rabbit.

12 In all of the experiments illustrated schematically ~n 13 Fig. 5 the blood vessels were exposed and the sensors secured 14 with the thermistors flush to the adventitia of the particular 15 vessels. ~he signal lines from the sensor~ were brought out 16 through separate sites. A standard vessel occlusion loop was 17 placed around the femoral artery and also brought out with a 18 9mall catheter through a separate opening. The wounds were then 19 clo8ed. Free flowing base line data was established and 20 thereafter the vessels were occluded. After data related to the 21 occlusion was recorded, the occlusion loop was reopened and flow 22 data again recorded. At the conclusion of each of the 23 experiments the sensors were removed transcutaneously and the 24 wound was then opened and the vessels examined for injury~

25 The results of the above described experiments were as 26 fOllows 27 a) the occlusion of the vessels in the rat~ resulted 28 in a 1- Centrigrade drop in temperature at the point distal to

29 the point of occlusion, , .

l;~'Q5526 1 b) occluding the blood vessels in rabbits and dog- -2 resulted in a 0.5 Centigrade drop in temperature at a point 3 distal to the point of occlusion, 4 c) in all of the experiments reestabli~hment of tho flow following the removal of ~he occlusion resulted in a all of 6 the temperature readings returning to the previous base line, 7 d) the transcutaneous removal of the sensor resulted 8 in no trauma to the blood vessels.

9 In the preferred method described the blood flow through the vessels results in maintenance of temperature at the 11 sensors, while occlusion results in decreased temperature.
12 However, there may be situations, for exa~ple in locations deep 13 within a body, where the ambient temperature is sufficiently high 14 so that even when the vessel is occluded the temperature will not drop appreciably. One method which may be used under such 16 circumstances is to provide heat to the sen ors, for example 17 electrical current to the thermocouples. 8100d flow through the J' 18 vessel will then cool the thermocouples at an essentially equal 19 rate. If, however, there i6 an occlu~ion, the lack of flow within the vessel at the sensor distal to the occlusion will 21 result in a slower rate of cooling at that sensor. ~his 22 differential may be monitored by conventional techniques, thu~
23 providing an indication of occlusion~

24 It i6 believed that the utility of the heat sensing probe techniques and devices o this invention in diagnosing 26 vAscular disturbance within a free tissue transfer can include 27 topical application of the probe on the surface of the free . I

S5~6 l tissue transrer or within the ~ubstance of the transfer itnel~.
2 Although the temperature differential between a proximal ve~el 3 and a distal vessel supplying the transfer, a~ exemplified in the 4 foregoing illustrated embodiments, may be among~t the most sensitive methods of tissue transfer monitoring, it is considered 6 that other sources of heat production may be used as the controi 7 source within the body, ~uch as an adjacent Vi8CUS or muscle 8 which i6 deep within the body or extremity, and utilize the g parenchyma o the transferred tissue as the monitoring surface analogous to the distal artery. This technique may be ll particularly useful where the medical risk of placing the probe 12 in contact with the vessel is extensive and there is acceptable 13 reliability in placing the thermocouple in contact with the 14 tissue to be transferred or a proximal heat source.

Having described the invention, various modifications 16 and additions will occur to those skilled in the art, and the 17 invention should be construed as limited only by the spirit and 18 6cope of the appended claims.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for the measurement of blood flow in tissue of an animal body by monitoring tissue temperature, a surgically-implantable temperature-sensing device com-prising:
A. a surgically-implantable temperature sensing element having electrical signal conductors, said temperature sensing element providing on said conductors an electrical output signal indicative of its temperature, and B. a surgically-implantable housing element of biologically inert suturable material, said housing element having a semi-lunar portion with a tubular configuration con-forming to a blood vessel and having said sensing element fixed at a tubular inner surface thereof for disposition con-tiguous with tissue in which said housing element is implanted, said housing element with said sensing element fixed thereto having an elongated configuration adapted for atraumatic and transcutaneous removal from surgical implantation upon the application of tension to said signal conductors.

2. An apparatus according to claim 2, the improve-ment wherein said sensing element includes a thermocouple sensor.