Beyond blood pressure measurements: monitoring of the appearance time of Korotkoff sounds

Abstract

We have recently proposed a new method to evaluate the physical properties of arteries based on measurement of the QKD interval together with blood pressure and heart rate with an ambulatory blood pressure monitoring device. This interval is the time between the onset of the depolarization (QRS) on the electrocardiogram (Q) and detection of the last Korotkoff (K) sound at the level of brachial artery during cuff deflation, corresponding to diastolic blood pressure (D). The QKD interval is the sum of the pre-ejection period and of the pulse transmission time from the aortic valves and the microphone. Thus, it is linked to the pulse wave velocity on an arterial segment which includes the ascending aorta and a portion of the subclavian and brachial arteries. From each 24 h monitoring, the average 24 h QKD, the slope of variation of QKD against blood pressure and a normalized QKD (QKD100-60) for systolic blood pressure of 100 mmHg and heart rate of 60 beats/min are calculated. Stiffer arteries as observed with ageing or hypertension are characterized by the reduction of these three parameters. The reproducibility of this method is good. In a pilot study of elderly hypertensive patients we have shown that QKD 100-60 has a strong and independent predictive value for future cardiovascular events. Therefore, this method may add significant information to ambulatory blood pressure monitoring.