Model based analysis of the variation in Korotkoff sound onset timeduring exercise

Abstract

In this study, a minimal mathematical model of the cardiovascular system isused to study the effects of changes in arterial compliance and cardiaccontractility on the onset time of Korotkoff sounds during an auscultatoryprocedure. The model provides blood pressure waveforms in the ventricle, theaorta and the brachial artery. From these waveforms, pre-ejection time, pulsepropagation time and rise time of the blood pressure at the brachial arterycan be computed. The time delay between onset time of ECG Q wave and onsettime of Korotkoff sound is the sum of these three times. Rise time is zero andthe time delay is minimal when the cuff pressure is slightly above thediastolic pressure. This minimum time delay is represented by QKD. Simulationresults suggest that during the Bruce exercise protocol QKD decreases toone-third of its pre-exercise value if the cardiac contractility increasesthreefold. The effect of arterial compliance is not as significant as that ofthe cardiac contractility. From data recorded during an exercise test, it isobserved that QKD decreases considerably as the test load is increased. Weshow in this study that the amount of decrease in QKD can be used as an indexof the amount of increase in cardiac contractility during an exercise ECGtest. Use of signal averaging for reducing the effect of motion artifactsduring an exercise test is also shown to be very instrumental for makingaccurate QKD measurements.