CAN RECORDING KOROTKOFF SOUNDS DURING BRACHIAL CUFF INFLATION PROVIDE MORE ACCURATE NON-INVASIVE ESTIMATES OF INTRA-ARTERIAL BLOOD PRESSURE?

Abstract

Objective: We have previously demonstrated that recording onset and termination of Korotkoff sounds as markers of systolic (SBP) and diastolic (DBP) during brachial cuff deflation results in underestimation of true SBP. In this study we explore whether recording Korotkoff sounds during cuff inflation provides more accurate non-invasive estimates of intra-arterial blood pressure (IABP). Design and method: Experiments were carried out on 15 participants, (14 males, 64.3 ± 10.4 years; one female, 86 yo), undergoing coronary angiography. A conventional (oscillometric) BP cuff, with a microphone for Korotkoff sounds, was placed on the upper arm. The cuff was inflated at rate of approximately 2.5mm Hg/sec and deflated at the same rate. Inflation and deflation cycles were randomised and separated by 2 - 3 minutes. IABP was measured below the cuff with a fluid-filled catheter inserted via the radial artery and an external transducer. Korotkoff sounds were processed electronically, and custom algorithms identified the cuff pressure (CP) at which the first and last Korotkoff sounds were heard. Results: Systolic (SBP), and diastolic (DBP) pressure were 147.7.6 ± 12.7 and 70.7 ± 9.7mmHg. The CP at which the brachial artery closes during rapid (∼20mmHg/sec) cuff inflation (132.0 ± 17.1) was similar to that of slow (2.5mmHg/sec) inflation (132.0 ± 16.3 mmHg). However, peak Korotkoff sound energy was significantly reduced (P = 0.003) from 0.19 ± 0.1 to 0.15 ± 0.09 RMS volts and the Korotkoff sounds were often observed to disappear prematurely before brachial artery closure. Difference between intra-arterial SBP and CP at the last recorded Korotkoff sound (27.5 ± 9.3 mmHg) during cuff inflation was significantly higher (P = 0.0025) than during slow cuff deflation (18.9 ± 8.3 mmHg). In contrast, DBP recorded at first onset of the Korotkoff sounds (70.5 ± 11.1 mmHg) was consistently similar to intra-arterial DBP (70.7 ± 9.7 mmHg). Conclusions: SBP estimates derived from the last Korotkoff sound recorded as the cuff inflates generates greater errors than when Korotkoff sounds are first recorded as the cuff deflates. In contrast, the estimate of DBP derived from the first onset of the Korotkoff sound as the cuff inflates, appears to reflect accurately the true intra-arterial DBP.