Method and apparatus for the measurement of cardiac output

Details Method and apparatus for the measurement of cardiac output Method and apparatus for the measurement of cardiac output

1999-04-15

2000-06-06

Kamm, William E.

Surgery

Diagnostic testing

Cardiovascular

A61B 5029

Patent

active

060712449

DESCRIPTION:

BRIEF SUMMARY
The present application is the U.S. national phase of international application number PCT/GB97/00017.
The present invention relates to an improved method and apparatus for the measurement of cardiac output and in particular to an improved method and apparatus which has a rapid rate of response.
It has been suggested since at least 1904 (Erlanger and Hooker, Bull. John Hopkins Hosp. 15:179) that the arterial pulse pressure could be regarded as a rough index to the stroke volume of the heart and, in combination with the heart rate, could provide the cardiac output. This approach was found to be simplistic, particularly at high arterial pressures where the relationship breaks down.
Accordingly, various correction factors were introduced such as age, weight, height and aortic compliance/distensibility. Whilst these correction factors improved the results there was still a disturbing number of conditions in patients where disappointing results were obtained, e.g. patients with low cardiac outputs and high arterial pulse pressures, or vice versa.
Various approaches to the derivation of cardiac output from pressure waveform analysis have also been attempted: e.g. from the pulse wave velocity and by integration of the pulse contour. As stand alone methods these have proved equally disappointing with a major difficulty in measuring the major morphological features of the waveform in pathologic situations, e.g. peaks, systolic areas, dicrotic notch etc. During major surgery, or in an intensive care situation, the pressure waveform may not exhibit a dicrotic notch at all.
In addition to using correction factors Hamilton (The physiology of cardiac output. Circulation 8: 527, 1953) suggested that cardiac output could be derived from a patient's blood pressure pulse height following calibration by another cardiac output method, such as dye dilution. Furthermore, more recently Jansen et al (Continuous cardiac output monitoring by pulse contour during cardiac surgery, Eur. Heart Journal 1990, 11:26-32) discuss a `corrected pulse contour` method where the pulse contour is calibrated used a thermodilution technique.
U.S. Pat. No. 5,400,793 describes a method for determining blood stroke volume from a pulsatile aorta blood-flow pressure signal in a subject. The method uses a simulation model of the aorta as a transmission line supplemented with a Windkessel compliance including a pressure volume relationship for the aorta that is known in the art.
In essence, the pressure waves recorded from the aorta are used to calculate the characteristic impedance of the transmission line, and the parameters of the Windkessel are adapted until the pressure in the model is consistent with that recorded in the aorta. The flow indicated by the model is then integrated over the period of systole. Ideally, this method requires a high fidelity pressure recording system in the aorta. Although a method of correcting a pressure measurement in a peripheral artery is mentioned, this method cannot be used with the poor frequency response given by most pressure transducers that are now routinely in clinical use: in the presence of noise an "anti-resonance filter" cannot recover the information that is lost by the poor quality of these transducers.
U.S. Pat. No. 5,390,679 discloses a method of determining cardiac output from a cardiac pressure waveform in which the pressure waveform is continuously sensed and converted into a digital data stream. When a complete beat frame of data is sensed, the processor extracts a plurality of features from the sensed waveform which characterises the waveform. This data is compared with stored representative pressure waveforms (RPW's) which have a known cardiac output obtained by applying a pattern recognition technology thereto. It is necessary, however, to store thousands of RPW's in order to build up a data base against which the cardiac pressure waveform can be compared.
Finally, Irlbeck et al (Continuous measurement of cardiac output with pulse contour analysis, Anaesthetist 1995, 44:493-500) propose that the

REFERENCES:
Erlanger, et al., An Experimental Study of Blood-Pressure and of Pulse-Pressure in Man, Johns Hopkins Hospital Reports 12: 145-378 (1904).
Jansen et al., Continuous Cardiac Output Monitoring by Pulse Contour During Cardiac Surgery, European Heart Journal, 11: (1990) 27-33 (1990).
Irlbeck, et al., Die kontinuierliche Messung des Herzzeitvolumens mit der Pulskonturanalyse, Anaesthesist 44: 493-500 (1995) (English abstract on p. 494).
W. F. Hamilton, Ph.D., The Lewis A. Connor Memorial Lecture--The Physiology of the Cardiac Output, Hamilton, Circulation, VII: 527-543 (1953).

Affiliated with

Also associated with

Rating

Method and apparatus for the measurement of cardiac output does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method and apparatus for the measurement of cardiac output, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for the measurement of cardiac output will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2209965