WO2003022143A2

WO2003022143A2 - Detecting vital signs from impedance cardiograph and electrocardiogram signals

Info

Publication number: WO2003022143A2
Application number: PCT/US2002/028376
Authority: WO
Inventors: Han Chool Ryoo; Hun H. Sun
Original assignee: Drexel University
Priority date: 2001-09-06
Filing date: 2002-09-06
Publication date: 2003-03-20
Also published as: WO2003022143A3; AU2002341609A1

Abstract

The present invention involves a method and apparatus to reliably determine physiological points such as 'B', 'C', 'X' and 'O' on impedance cardiograph (ICG) signal. Simple but very accurate algorithm has been invented for processing ICG signals considering the relationship between distances of physiologic points (R-B,R-C,R-X,R-O) and R-R intervals. It is aimed to pick localized physiologic points by controlling window size and location around those points adapted to R-R intervals measured from ECG signals. It is found that the time intervals between R-B and R-C are not correlated to R-R intervals; that is, they almost remain constant regardless of R-R intervals. However the intervals of R-X and R-O showed linear relationship with regard to R-R intervals. By using such new findings, the location and the varying window size around these physiologic points were deterined and the slope changes inside the window were monitored. This simple method avoided sophisticated signal processing techniques but it showed high efficiency and promising results by precisely locating PPs for more than 99 % of the time.

Description

APPARATUS AND METHOD FOR DETECTING PHYSIOLOGICAL POINTS

INCLUDING "O" WAVE CHANGES FROM IMPEDANCE CARDIOGRAPH

ADAPTED TO ELECTROCARDIOGRAM USING R-R INTERVALS

Field of the Invention.

The invention relates to physiological vital sign monitoring by using impedance cardiograph (ICG) and electrocardiogram (ECG) signals. More specifically, the field of the invention is that of detecting "B", "C", "X" and especially "O" wave changes of ICG signals with the aid of ECG signals.

Description of the Related Art.

What is ICG: ICG is a noninvasive technique to measure hemodynamics and thoracic fluid status. ICG monitoring can be quickly implemented by clinicians in virtually any clinical setting. It allows clinicians to improve patient outcome through early intervention by early recognition of hemodynamic abnormalities and perfusion problems.

Unlike conventional hemodynamic monitoring technique, namely, the invasive thermodilution pulmonary artery ("PA") catheter that requires a physician for its insertion in a surgical setting, ICG monitoring can be accomplished by clinicians at a non-surgical bedside, using only ICG and ECG electrodes that can be placed within minutes. ICG provides useful information regarding overall fluid in the chest and information about left ventricular ("LV") function, preload, afterload, contractility and even mitral regurgitation, to name just a few.

What Does ICG Measure: ICG measures the total impedance (or resistance in most part, because the imaginary section of the impedance is less 3% of the total impedance value) to the flow of electricity, in the chest. Impedance is represented by the symbol Z and is measured in ohms. Similar to conventional hemodynamic monitoring, ICG measures stroke volume ("SV") that is calculated on a beat-to-beat basis by using certain physiological equation, such as the Kubicek or modified Kubicek equation, and is derived from the impedance dZ/dt waveform. ICG measures left ventricular ("LV") function through the cardiac output ("CO") and the cardiac index ("CI"). To estimate CO, patient's stroke volume ("SV") is multiplied by patient's heart rate ("HR"). The CI is calculated in the usual way, namely, by dividing CO by body surface area ("BSA").

Similar to conventional hemodynamic monitoring, ICG looks at factors that affect tissue and organ perfusion: for instance, blood volume, vascular tone and cardiac action. Clinical studies have shown excellent correlation between ICG and thermodilution estimates of CO in multiple patient populations. Impedance cardiography aids in the assessment and management of thoracic fluid status, cardiac performance, oxygen debt, hypoperfusion and preload. The ability to objectively and continuously quantify, trend and manipulate the determinants of CO (preload, afterload, contractility and heart rate) and the fluid status of the chest provides physicians with a continuous, innovative and essential pathway to patient management.

The base impedance ("Z₀") is also known to reflect the total fluid status of the chest. Clinical studies have demonstrated a strong correlation between Z₀ and chest X-ray findings. The more fluid a chest has, the lower the Z₀ becomes, simply due to the fact that electrical current travels more easily through a wet chest in which plasma and fluid have accumulated due to pulmonary edema, effusions, or infiltrates. On the contrary, a high Z₀ value reflects low fluid level in the chest.

The ability to continuously monitor the fluid status of the chest may allow early detection and decrease or negate some complications observed in the critical care area. Pulmonary congestion and edema are frequent problems in the critical care unit. Aggressive fluid resuscitation, unavoidable in some situations, frequently contributes to increasing pulmonary fluid and additional complications. A slow decrease in Z₀ may indicate increasing pulmonary edema and alert clinicians to alter fluid management. A decrease in Z₀ may also be associated with development of pleural effusions or infiltrates. A rapid downward trend in Z₀ may be observed in patients who develop mechanical bleeding after cardiothoracic surgery. These capabilities make ICG a unique clinical tool that may be fit into any clinical settings. ICG Waveform: As shown in Figure 1, the impedance waveform is known as the dZ/dt waveform, where dZ/dt representing impedance change in time, which is derived by taking the first derivative of impedance signal Z. Therefore, dZ/dt provides data regarding blood flow changes: the change in impedance is produced by variations in blood flow and volume in the ascending aorta during one cardiac cycle because changes in the volume of blood and the alignment of the erythrocytes cause a relative impedance change during systole and diastole thus contributing to the change of dZ/dt signal.

During systole, the increased blood volume and velocity in the aorta cause the erythrocytes to align, lowering impedance. During diastole, less blood volume and velocity in the aorta cause a more random alignment of erythrocytes, thus contributing to higher impedance. The dZ/dt waveform therefore represents the change of mechanical activity of the left ventricle. Therefore, as shown in Figure 2, ECG signal represents electrical activity of the heart whereas ICG signal represents mechanical activity.

ICG Waveform Morphology: Like many other physiologic waveforms, the dZ/dt waveform provides a significant amount of diagnostic information. Figure 1 shows the "B" and "X" points, which denote aortic valve opening and closure, respectively. The time interval between the "B" and "X" points reflects ventricular ejection time ("VET"). The "C" point (dZ/dt_max) corresponds to the peak flow of blood from the LV into the aorta, or the maximum impedance change, which is influenced by the SV.

The morphology of the systolic portion of the dZ/dt waveform includes the opening ("B") and closing ("X") of the aortic valve, the peak flow of blood ("C"), and the maximum impedance change dZ/dt_max. An "A" wave precedes the opening of the aortic valve and corresponds to atrial filling (atrial diastole). The ventricular diastolic portion of the waveform includes an "O" wave, which has a temporal relationship with mitral valve closure. An "O" wave exaggerated in amplitude, also known as an early diastolic wave, is associated with the rapid ventricular filling phase (early ventricular diastole).

The presence of a large early diastolic "O" wave identified patients at higher risk for various forms of cardiomyopathies and may be used as a predictor of outcomes, both in terms of functional disability and death. Patients with mitral regurgitation were found to have a modified dZ/dt waveform, including a pronounced "O" wave. These changes correlated with the severity of mitral regurgitation as measured by cardiac catheterization, and the "O" wave returned to normal in all patients who underwent a mitral valve replacement.

Investigators have noted that the dZ/dt waveform may prove to be a sensitive noninvasive measure of the severity of aortic regurgitation. Heart failure patients were found to have abnormal dZ/dt waveforms. The systolic portion of the waveform was low and widened, with a notched or W pattern observed in some patients, and an exaggerated "O" wave was present in the diastolic portion of the waveform.

ICG monitoring may improve patient management through use of nearly or real time and continuous data and is not associated with the risks of invasive monitoring. Early detection of hemodynamic abnormalities in the critically ill may lead to early intervention and improved patient outcomes. ICG is easy to apply, requires less nursing time, and can be used in any health care setting.

At the present time, much work has been successfully done by both clinicians and medical device manufacturers in the filed of ICG signal detection, including detection of "B", "C" and "X" points, for the purpose of calculating SV and CO. Although "O" wave presents significant clinical value, little success, however, has been obtained for the detection of "O" wave, due to the difficulty of reliably capturing "O" wave which often times disappears into signal noise or other artifacts. For example, extremely large amount of thoracic fluid, usually caused by severe pulmonary edema, or patient body movement or other environmental interferences, may damp or interfere with the impedance dZ/dt signal, making signal detection unattainable or unreliable. Although some investigators have attempted to examine the morphology of the dZ/dt waveform for the detection of "O" wave, much work is yet to be done, providing multiple opportunities for clinical research in the area of waveform analysis.

As stated above that associated with ECG signal, ICG signals have been used for noninvasive cardiac monitoring system, for example, the IQ system by Wantagh, Inc. For better diagnosis, a monitoring system must have ability to localize physiologically significant points ("PP"), for instance, for ICG signals in particular, the "B" point which relates to aortic valve opening, the "C" point for maximal blood flow during systole, the "X" point which relates to closing of aortic valve, and finally, the "O" point relating to early diastolic stage. The detection of these points needs to be gated by R-R intervals, which are durations in time between R peaks of ECG signals.

SUMMARY OF THE INVENTION The present invention presents a new, simple and efficient algorithm with higher accuracy for processing ICG signals (dZ/dt) by considering the relationship between distances of physiologic points (R-B, R-C, R-X, R-O) and R-R intervals. It is aimed to pick localized physiologic points by adaptively adjusting window locations around those points adapted to R-R intervals measured from ECG signals.

Interestingly this invention discloses that the time intervals between R-B and R-C are not correlated to R-R intervals; that is, they almost remain constant regardless of R-R intervals. However the intervals of R-X and R-O showed linear relationships with regard to R-R intervals. By using such new findings, the location and the varying window size around physiologic points are determined and the slope changes inside the window are monitored. This simple technique avoided time-consuming ensemble averaging process and sophisticated signal processing techniques. Real-time processed experimental results with normal subject data showed high efficiency that precisely located all PPs for more than 99% of the time. Different from conventional signal processing techniques, this invention has the ability to detect "O" waves that provide important diagnostic information for sick patients.

The present invention, in one form, relates to a method or an algorithm, and an apparatus of locating multiple gating windows within each R-R interval, where the multiple gating windows each relates to a physiological point to be detected. First, physiological distances from "R" wave to "B", "C", "X" and "O" are determined from normal test subjects. Second, their linear relationships with regard to R-R intervals are determined. Third, multiple gating windows are calculated based upon such linear relationships. And finally, physiological points are located within each of these window durations.

BRIEF DESCRIPTION OF THE DRAWINGS The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: Figure 1 shows a typical ICG signal marked with physiological points. Figure 2 shows a typical ICG signal aligned in time with its corresponding ECG signal.

Figure 3 is the hardware implementation schematics. Figure 4 is an implementation flow chart using the present invention.

Figure 5 shows the relationship of R-R intervals and physiological distances (R-B, R-C, R-X and R-O).

Figure 6 shows R-peaks and impedance (dZ/dt) signals with windows superimposed. Figure 7 shows detection of physiological points ("B", "C", "X" and "O") by the present invention.

Corresponding reference characters indicate corresponding parts throughout the several views. Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present invention. The exemplification set out herein illustrates an embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DESCRIPTION OF THE PRESENT INVENTION The embodiment disclosed below is not intended to be exhaustive or limit the invention to the precise form disclosed in the following detailed description. Rather, the embodiment is chosen and described so that others skilled in the art may utilize its teachings.

The detailed descriptions which follow are presented in part in terms of algorithms and symbolic representations of operations on signals within a computer memory representing alphanumeric characters or other information. These descriptions and representations are the means used by those skilled in the art of data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. These steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It proves convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, symbols, characters, display data, terms, numbers, or the like. It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely used here as convenient labels applied to these quantities.

Some algorithms may use data structures for both inputting information and producing the desired result. Data structures greatly facilitate data management by data processing systems, and are not accessible except through sophisticated software systems. Data structures are not the information content of a memory, rather they represent specific electronic structural elements which impart a physical organization on the information stored in memory. More than mere abstraction, the data structures are specific electrical or magnetic structural elements in memory which simultaneously represent complex data accurately and provide increased efficiency in computer operation.

Further, the manipulations performed are often referred to in terms, such as comparing or adding, commonly associated with mental operations performed by a human operator. No such capability of a human operator is necessary, or desirable in most cases, in any of the operations described herein which form part of the present invention; the operations are machine operations. Useful machines for performing the operations of the present invention include general purpose digital computers or other similar devices. In all cases the distinction between the method operations in operating a computer and the method of computation itself should be recognized. The present invention relates to a method and apparatus for operating a computer in processing electrical or other (e.g., mechanical, chemical) physical signals to generate other desired physical signals and results.

The present invention also relates to an apparatus for performing these operations. This apparatus may be specifically constructed for the required purposes or it may comprise a general purpose computer as selectively activated or reconfigured by a computer program stored in the computer. The algorithm presented herein is not inherently related to any particular computer or other apparatus. In particular, various general purpose machines may be used with programs written in accordance with the teachings herein, or it may prove more convenient to construct more specialized apparatus to perform the required method steps. The required structure for a variety of these machines will appear from the description below.

In particular, the present invention involves providing a method and apparatus to detect physiological points on ICG signals with the aid of R-R intervals on corresponding ECG signals. In order to locate physiologic points (PP), the window of certain width has to slide down along the signal sequence to pinpoint PP inside the window. But blind translation of the window can cause erroneous results. Therefore, the relationship between PP and R-R intervals needs to be studied. For this purpose, 12 data sets acquired from four (4) normal subjects (who have not been identified with cardiac disease) under standing posture were arbitrarily chosen and the relationship was studied.

Physiologic distances from "R" wave to "B", "C", "X", and "O" waves are illustrated in Figure 5. As can be seen, the distances of R-B and R-C are seemingly not related to R-R intervals because regardless of R-R intervals, those distances are almost constantly maintained. However, the distances from "R" to "X" and "O" waves have linearly increasing tendency as R-R intervals increase.

With this relationship introduced above, the window widths for "B" and "C" waves are fixed after "R" peaks, whereas the window widths for "X" and "O" are linearly proportional to R-R intervals as shown below: Window duration for "B" wave: 0.05 ~ 0.1 seconds

Window duration for "C" wave: 0.1 - 0.17 seconds Window duration for "X" wave: T = 0.1695 x RR + 0.16 ~ T = 0.1695 x RR + 0.23 Window duration for "O" wave: T = 0.1695 x RR + 0.26 ~ T = 0.1695 x RR + 0.36

The window widths for "X" and "O" points are determined as a linear function of R-R intervals with same slope (=0.1695) as can be seen in Figure 5 but with different y-intercepts, namely, adaptive window widths to R-R intervals in time. One example of these windows superimposed on dZ/dt signals is shown in Figure 6. Therefore, an algorithm is developed based on the relationship disclosed above. In the interior of the window, the slope changes were observed to locate "B", "C", "X" and "O" points. For "B" points, we can see one feature that is consistently present in all related windows, provided that the C-wave is salient on the dZ/dt waveform. This feature is a concave point on the ascending limb toward the maximum of dZ/dt. Similar characteristic can be found at "X" points. This concept is utilized to monitor the slope changes, namely, at the falling and rising edge of dZ/dt signal. Conversely, maxima on the dZ/dt waveforms inside the corresponding windows are found to locate "C" and "O" points. As shown in Figure 7, all physiological points are detected accurately by this algorithm and they are indicated by dotted lines and marked by corresponding letters.

Even though the above window widths for "B" and "C" points were found to be about the ranges of 0.05 ~ 0.1 seconds and 0.1 - 0.17 seconds, respectively, it is likely that other slightly different widths or boundaries may be usable as well. It is the spirit of the invention that these window widths or boundaries are not related to the R-R intervals and, therefore, any modifications and departures from these widths or boundaries are within the spirit of the invention.

For the window widths of "X" and "O" points, even though our present invention reveals a linear relationship with R-R intervals, it is likely and obvious that higher orders of relationships may also be usable, and better correlations by such higher orders of relationship may be found in our later development. The spirit of the invention is that such window widths and boundaries may be found independent of any complicated filtering or timing process, they can be found simply by the information of R-R alone.

Figure 3 shows the hardware schematics of the invention. The ICG and ECG signals of a patient 200 are picked up and sent to an amplifier (AMP) 202 for amplification. The amplified ICG and ECG signals are then sent to an analog-to- digital (A/D) converter 204 to be converted into digital signals. The converted digital ICG and ECG signals are then sent to a digital signal processing (DSP) unit 206 for signal processing and calculations. A display unit (DISPLAY) 208 displays the final results. All devices are controlled by a central processing unit (CPU) 210.

Figure 4 shows the implementation flow chart using the present invention. First, at step 102, the invention determines all R-R intervals and store them into a memory space. At step 104, the invention calculates constant window durations for "B" and "C" points (W_B,W ). At step 106, the invention determines linear relationships among R-X and R-O for one R-R interval in sequential order of R-R interval group. At step 108, window durations for X and O are calculated (W and Wo). At step 110, a concave, maximum, concave and maximum point of dZ/dt signal within windows W_B,W_c,Wχ and Wo are located (B_con, C_max, X_mj_n and O_max) respectively, and finally at step 112, B_COn, C_max, X_m;_n and O_ma are converted into actual corresponding time markers "B", "C", "X" and "O". At step 114, the system checks if it is at the end of the R-R interval group, if not, it goes to step 106 to repeat the process, if yes, it goes to step 116 to finish.

The present invention can be implemented by either high level programming languages such as C or C++, or by "object-oriented" software, and particularly with an "object-oriented" operating system. The "object-oriented" software is organized into "objects", each comprising a block of computer instructions describing various procedures ("methods") to be performed in response to "messages" sent to the object or "events" which occur with the object. Such operations include, for example, the manipulation of variables, the activation of an object by an external event, and the transmission of one or more messages to other objects.

Messages are sent and received between objects having certain functions and knowledge to carry out processes. Messages are generated in response to user instructions, for example, by a user activating an icon with a "mouse" pointer generating an event. Also, messages may be generated by an object in response to the receipt of a message. When one of the objects receives a message, the object carries out an operation (a message procedure) corresponding to the message and, if necessary, returns a result of the operation. Each object has a region where internal states (instance variables) of the object itself are stored and where the other objects are not allowed to access. One feature of the object-oriented system is inheritance. For example, an object for drawing a "circle" on a display may inherit functions and knowledge from another object for drawing a "shape" on a display.

A programmer "programs" in an object-oriented programming language by writing individual blocks of code each of which creates an object by defining its methods. A collection of such objects adapted to communicate with one another by means of messages comprises an object-oriented program. Object-oriented computer programming facilitates the modeling of interactive systems in that each component of the system can be modeled with an object, the behavior of each component being simulated by the methods of its corresponding object, and the interactions between components being simulated by messages transmitted between objects.

An operator may stimulate a collection of interrelated objects comprising an object-oriented program by sending a message to one of the objects. The receipt of the message may cause the object to respond by carrying out predetermined functions which may include sending additional messages to one or more other objects. The other objects may in turn carry out additional functions in response to the messages they receive, including sending still more messages. In this manner, sequences of message and response may continue indefinitely or may come to an end when all messages have been responded to and no new messages are being sent. When modeling systems utilizing an object-oriented language, a programmer need only think in terms of how each component of a modeled system responds to a stimulus and not in terms of the sequence of operations to be performed in response to some stimulus. Such sequence of operations naturally flows out of the interactions between the objects in response to the stimulus and need not be preordained by the programmer.

Although object-oriented programming makes simulation of systems of interrelated components more intuitive, the operation of an object-oriented program is often difficult to understand because the sequence of operations carried out by an object-oriented program is usually not immediately apparent from a software listing as in the case for sequentially organized programs. Nor is it easy to determine how an object-oriented program works through observation of the readily apparent manifestations of its operation. Most of the operations carried out by a computer in response to a program are "invisible" to an observer since only a relatively few steps in a program typically produce an observable computer output.

In conclusion, the present invention provides a method and apparatus that can reliably calculate important physiological points on ICG signals without the help of complex and sophisticated signal processing techniques. Further, no averaging process of several heartbeats is required and the calculation results are fast but reliable and efficient, thus making online real-time processing possible.

While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. For instance, although not desired for real-time purpose, such inventive concept may be utilized to calculate window durations for said physiological points from an ensembled ICG signal group by using an averaged R-R interval from a group of corresponding R-R intervals. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.

Claims

WHAT IS CLAIMED IS:

1. A method of detecting patient vital signs in real time, by detecting significant multiple physiological points on the patient's impedance cardiograph (ICG) signal with the aid of electrocardiogram (ECG) signal obtained synchronously from the patient comprising the steps of: (a) locating an R-R interval from said ECG signal; characterized by (b) providing a first plurality of constant window durations for a first plurality of physiological points independent of said R-R interval; (c) calculating a second plurality of window durations for a second plurality of physiological points using a plurality of coupled equations based on said R-R interval; (d) finding a first and second plurality of physiological points on said ICG signal in said first and second plurality of window durations, respectively, referencing in time with a first R location in said R-R interval; and (e) converting said first and second plurality of physiological points into time markers referencing in time with a first R location in said R-R interval.

2. The method of Claim 1 characterized by the steps of: (a) locating a plurality of R-R intervals from said ECG signal; (b) storing said R-R intervals as a group sequentially into a memory space; (c) providing a first plurality of constant window durations for a first plurality of physiological points independent of said R-R intervals; (d) calculating a second plurality of window durations for a second plurality of physiological points using a plurality of coupled equations based on one of said R- R intervals; (e) finding a first and second plurality of physiological points on said ICG signal in said first and second plurality of window durations, respectively, referencing in time with a first R location in said R-R interval; (f) converting said first and second plurality of physiological points into time markers referencing in time with a first R location in said R-R interval; and (g) repeating steps (d) through (f) until all R-R intervals run out.

3. The method of Claim 1 characterized in that said first and second plurality of physiological points further comprises "B", "C" and "X" and "O" respectively on said ICG signal.

4. The method of Claim 1 characterized in that said first plurality of constant window durations further comprises a first duration of about 0.05 to 0.1 seconds.

5. The method of Claim 1 characterized in that said first plurality constant window durations further comprises a second duration of about 0.1 to 0.17 seconds.

6. The method of Claim 4 characterized in that said first constant window duration of about 0.05 to 0.1 seconds relates to said physiological point "B".

7. The method of Claim 5 characterized in that said second constant window duration of about 0.1 to 0.17 seconds relates to said physiological point "C".

8. The method of Claim 1 characterized in that said calculating a second plurality of window durations for a second plurality of physiological points further comprising a first coupled linear equations for the calculation of a third window duration.

9. The method of Claim 8 characterized in that said first coupled linear equations further comprising a proportional relationship to said R-R interval and said first coupled linear equations relating to said physiological point "X".

10. The method of Claim 9 characterized in that said first coupled linear equations are to generate boundaries about 0.1695 x R-R interval + 0.16 to 0.1695 x R-R interval + 0.23 for the calculation of said third window duration.

11. The method of Claim 1 characterized in that said calculating a second plurality of window durations for a second plurality of physiological points further comprising a second coupled linear equations for the calculation of a fourth window duration.

12. The method of Claim 11 characterized in that said second coupled linear equations further comprising a proportional relationship to said R-R interval and said second coupled linear equations relating to said physiological point "O".

13. The method of Claim 12 characterized in that said second coupled linear equations are to generate boundaries about 0.1695 x R-R interval + 0.26 to

0.1695 x R-R interval + 0.3623 for the calculation of said fourth window duration.

14. The method of Claim 1 characterized in that said finding a first plurality of physiological points on said ICG signal in said first plurality of window durations further comprising finding a concave point on the ascending limb of said ICG signal during said first constant window duration.

15. The method of Claim 14 characterized in that said concave point on said ICG signal relates to said "B" point.

16. The method of Claim 1 characterized in that said finding a first plurality of physiological points on said ICG signal in said first plurality of window durations further comprising finding a maximum point on said ICG signal during said second constant window duration.

17. The method of Claim 16 characterized in that said maximum point on said ICG signal relates to said "C" point.

18. The method of Claim 1 characterized in that said finding a second plurality of physiological points on said ICG signal in said second plurality of window durations respectively, further comprising finding a concave point on said ICG signal during said third window duration.

19. The method of Claim 18 characterized in that said concave point on said ICG signal relates to said "X" point.

20. The method of Claim 1 characterized in that said finding a second plurality of physiological points on said ICG signal in said second plurality of window durations respectively, further comprising finding a maximum point on said ICG signal during said fourth window duration.

21. The method of Claim 20 characterized in that said maximum point on said ICG signal relates to said "O" point

22. The method of Claim 1 characterized in that said converting said first and second plurality of physiological points into time markers further comprising finding corresponding time locations on said ICG signal for said first, second, third and fourth physiological points, "B", "C", "X" and "O", respectively, referencing in time with said first R location in said R-R interval.

23. A machine-readable program storage device for storing encoded instructions for a method of detecting patient vital signs in real time, by detecting significant multiple physiological points on the patient's impedance cardiograph (ICG) signal with the aid of electrocardiogram (ECG) signal obtained synchronously from the patient, said method comprising the steps of: (a) locating an R-R interval from said ECG signal; characterized by (b) providing a first plurality of constant window durations for a first plurality of physiological points independent of said R-R interval; (c) calculating a second plurality of window durations for a second plurality of physiological points using a plurality of coupled equations based on said R-R interval; (d) finding a first and second plurality of physiological points on said ICG signal in said first and second plurality of window durations, respectively, referencing in time with a first R location in said R-R interval; and (e) converting said first and second plurality of physiological points into time markers referencing in time with a first R location in said R-R interval.

24. The machine-readable program storage device of Claim 23 with said method characterized by the steps of: (a) locating a plurality of R-R intervals from said ECG signal; (b) storing said R-R intervals as a group sequentially into a memory space; (c) providing a first plurality of constant window durations for a first plurality of physiological points regardless of said R-R intervals; (d) calculating a second plurality of window durations for a second plurality of physiological points using a plurality of coupled equations based on one of said R-R intervals; (e) finding a first and second plurality of physiological points on said ICG signal in said first and second plurality of window durations, respectively, referencing in time with a first R location in said R-R interval; (f) converting said first and second plurality of physiological points into time markers referencing in time with a first R location in said R-R interval; and (g) repeating steps (d) through (f) until all R-R intervals run out.

25. The machine-readable program storage device of Claim 23 characterized in that said physiological points further comprises "B", "C", "X" and "O" on said ICG signal.

26. The machine-readable program storage device of Claim 23 characterized in that said first plurality of constant window durations further comprises a first duration of about 0.05 to 0.1 seconds.

27. The machine-readable program storage device of Claim 23 characterized in that said first plurality of constant window durations further comprises a second duration of about 0.1 to 0.17 seconds.

28. The machine-readable program storage device of Claim 26 characterized in that said first constant window duration of about 0.05 to 0.1 seconds relates to said physiological point "B".

29. The machine-readable program storage device of Claim 27 characterized in that said second constant window duration of about 0.1 to 0.17 seconds relates to said physiological point "C".

30. The machine-readable program storage device of Claim 23 characterized in that said calculating a second plurality of window durations for a second plurality of physiological points further comprises a first coupled linear equations for the calculation of a third window duration.

31. The machine-readable program storage device of Claim 30 characterized in that said first coupled linear equations further comprises a proportional relationship to said R-R interval and said first coupled linear equations relating to said physiological point "X".

32. The machine-readable program storage device of Claim 31 characterized in that said first coupled linear equations are to generate boundaries about 0.1695 x R-R interval + 0.16 to 0.1695 x R-R interval + 0.23 for the calculation of said third window duration.

33. The machine-readable program storage device of Claim 23 characterized in that said calculating a second plurality of window durations for a second plurality of physiological points further comprises a second coupled linear equations for the calculation of a fourth window duration.

34. The machine-readable program storage device of Claim 33 characterized in that said second coupled linear equations further comprises a proportional relationship to said R-R interval and said second coupled linear equations relating to said physiological point "O".

35. The machine-readable program storage device of Claim 34 characterized in that said second coupled linear equations are to generate boundaries about 0.1695 x R-R interval + 0.26 to 0.1695 x R-R interval + 0.3623 for the calculation of said fourth window duration.

36. The machine-readable program storage device of Claim 23 characterized in that said finding a first plurality of physiological points on said ICG signal in said first plurality of window durations further comprises finding a concave point on the ascending limb of said ICG signal during said first constant window duration.

37. The machine-readable program storage device of Claim 36 characterized in that said concave point on said ICG signal relates to said "B" point.

38. The machine-readable program storage device of Claim 23 characterized in that said finding a first plurality of physiological points on said ICG signal in said first plurality of window durations further comprises finding a maximum point on said ICG signal during said second constant window duration.

39. The machine-readable program storage device of Claim 38 characterized in that said maximum point on said ICG signal relates to said "C" point.

40. The machine-readable program storage device of Claim 23 characterized in that said finding a second plurality of physiological points on said ICG signal in said second plurality of window durations further comprises finding a concave point on said ICG signal during said third window duration.

41. The machine-readable program storage device of Claim 40 characterized in that said concave point on said ICG signal relates to said "X" point.

42. The machine-readable program storage device of Claim 23 characterized in that said finding a second plurality of physiological points on said ICG signal in said second plurality of window durations further comprises finding a maximum point on said ICG signal during said fourth window duration.

43. The machine-readable program storage device of Claim 42 characterized in that said maximum point on said ICG signal relates to said "O" point.

44. The machine-readable program storage device of Claim 23 characterized in that said converting said first and second plurality of physiological points into time markers further comprises finding corresponding time locations on said ICG signal for said first, second, third and fourth physiological points, "B", "C", "X" and "O", respectively, referencing in time with said first R location in said R-R interval.

45. An apparatus for detecting patient vital signs in real time, by detecting significant multiple physiological points on the patient's impedance cardiograph (ICG) signal with the aid of electrocardiogram (ECG) signal obtained synchronously from the patient, said apparatus comprising: (a) an amplifying device (AMP) for amplifying said ICG and ECG signals obtained synchronously from the patient; (b) an analog-to-digital (A/D) converter for converting said amplified ICG and ECG analog signals into digital signals; characterized by (c) a digital signal processing processor (DSP) capable of processing said digital ICG and ECG signals for detecting significant multiple physiological points on the patient's said ICG signal with the aid of said ECG signal obtained synchronously from the patient; (d) a display device (DISPLAY) for displaying calculated results by said DSP device; and (e) a central processing unit (CPU) controlling said AMP, A/D, DSP and DISPLAY devices.

46. The apparatus of Claim 45 wherein said DSP device is characterized by certain programmed software pre-installed which uses a certain method for the calculation of said multiple physiological points on the patient' s said ICG signal with the aid of said ECG signal obtained synchronously from the patient, said method comprising the steps of: (a) locating an R-R interval from said ECG signal; (b) providing a first plurality of constant window durations for a first plurality of physiological points regardless of said R-R interval; (c) calculating a second plurality of window durations for a second plurality of physiological points using a plurality of coupled equations based on said R-R interval; (d) finding a first and second plurality of physiological points on said ICG signal in said first and second plurality of window durations, respectively, referencing in time with a first R location in said R-R interval; and (e) converting said first and second plurality of physiological points into time markers referencing in time with a first R location in said R-R interval.

47. The apparatus of Claim 46 wherein said method is further characterized by the steps of: (a) locating a plurality of R-R intervals from said ECG signals; (b) storing said R-R intervals as a group sequentially into a memory space; (c) providing a first plurality of constant window durations for a first plurality of physiological points regardless of said R-R intervals; (d) calculating a second plurality of window durations for a second plurality of physiological points using a plurality of coupled equations based on one of said R-R intervals; (e) finding a first and second plurality of physiological points on said ICG signal in said first and second plurality of window durations, respectively, referencing in time with a first R location in said R-R interval; (f) converting said first and second plurality of physiological points into time markers referencing in time with a first R location in said R-R interval; and (g) repeating steps (d) through (f) until all R-R intervals run out.

48. The apparatus of Claim 46 characterized in that said physiological points further comprising "B", "C", "X" and "O" on said ICG signal.

49. The apparatus of Claim 46 characterized in that said first plurality of constant window durations further comprising a first duration of about 0.05 to 0.1 seconds.

50. The apparatus of Claim 46 characterized in that said first plurality of constant window durations further comprises a second duration of about 0.1 to 0.17 seconds.

51. The apparatus of Claim 49 characterized in that said first constant window duration of about 0.05 to 0.1 seconds relates to said physiological point "B".

52. The apparatus of Claim 50 characterized in that said second constant window duration of about 0.1 to 0.17 seconds relates to said physiological point "C".

53. The apparatus of Claim 46 characterized in that said calculating a second plurality of window durations for a second plurality of physiological points further comprises a first coupled linear equations for the calculation of a third window duration.

54. The apparatus of Claim 53 characterized in that said first coupled linear equations further comprises a proportional relationship to said R-R interval and said first coupled linear equations relating to said physiological point "X".

55. The apparatus of Claim 54 characterized in that said first coupled linear equations are to generate boundaries about 0.1695 x R-R interval + 0.16 to

0.1695 x R-R interval + 0.23 for the calculation of said third window duration.

56. The apparatus of Claim 46 characterized in that said calculating a second plurality of window durations for a second plurality of physiological points further comprises a second coupled linear equations for the calculation of a fourth window duration.

57. The apparatus of Claim 56 characterized in that said second coupled linear equations further comprises a proportional relationship to said R-R interval and said second coupled linear equations relating to said physiological point "O".

58. The apparatus of Claim 57 characterized in that said second coupled linear equations are to generate boundaries about 0.1695 x R-R interval + 0.26 to

59. The apparatus of Claim 46 characterized in that said finding a first plurality of physiological points on said ICG signal in said first plurality of window durations further comprises finding a concave point on the ascending limb of said ICG signal during said first constant window duration.

60. The apparatus of Claim 59 characterized in that said concave point on said ICG signal relates to said "B" point.

61. The apparatus of Claim 46 characterized in that said finding a first plurality of physiological points on said ICG signal in said first plurality of window durations further comprises finding a maximum point on said ICG signal during said second constant window duration.

62. The apparatus of Claim 61 characterized in that said maximum point on said ICG signal relates to said "C" point.

63. The apparatus of Claim 46 characterized in that said finding a second plurality of physiological points on said ICG signal in said second plurality of window durations further comprises finding a concave point on said ICG signal during said third window duration.

64. The apparatus of Claim 63 characterized in that said concave point on said ICG signal relates to said "X" point.

65. The apparatus of Claim 46 characterized in that said finding a second plurality of physiological points on said ICG signal in said second plurality of window durations further comprises finding a maximum point on said ICG signal during said fourth window duration.

66. The apparatus of Claim 65 characterized in that said maximum point on said ICG signal relates to said "O" point.

67. The apparatus of Claim 46 characterized in that said converting said first and second plurality of physiological points into time markers further comprises finding corresponding time locations on said ICG signal for said first, second, third and fourth physiological points, "B", "C", "X" and "O", respectively, referencing in time with said first R location in said R-R interval.