Are Korotkoff sounds reliable markers for accurate estimation of systolic and diastolic pressure using brachial cuff sphygmomanometry.

The accurate measurement of non-invasive blood pressure (NIBP) is a fundamental public health requirement, yet we are aware that NIBP measurements significantly underestimate true systolic blood pressure (SBP) and overestimate diastolic blood pressure (DBP). The aetiology for these errors has not yet been fully established. This study aimed to investigate the accuracy of Korotkoff sounds for accurate detection of SBP and DBP as used in brachial cuff sphygmomanometry. Brachial cuff pressure (CP) and Korotkoff sounds were obtained in 11 patients (6 males: 69.0 6.2 years, 5 females: 71.8 5.5 years) undergoing diagnostic coronary angiography. Fiducial K2 Korotkoff sounds were obtained by high-pass filtering (>20 Hz) the microphone-recorded signal to eliminate low frequency components related to the haemodynamic impact of the arterial pulse on the cuff during occlusion. Noninvasive SBP and DBP based on the recording of K2 Korotkoff sounds, were simultaneously compared with intraarterial pressure. Analysis of simultaneous timing events of K2 Korotkoff sounds, cuff pressure and intra-arterial pressure shows that the onset of K2 Korotkoff sounds reliably detect the start of blood flow under the brachial cuff and their termination marks the cuff pressure closely coincident with DBP. We have made the critical observation that blood flow under the cuff does not begin when cuff pressure falls just below SBP as is conventionally assumed, and that a delay in the opening of the artery following occlusion, and the consequent delay in the generation of Korotkoff sounds, may lead to significant errors in the determination of SBP of up to 24 mmHg. The mechanism for the delay is not well understood but linear modelling demonstrates that Gender, DBP, heart rate (HR) and waveform features related to arterial properties, such as early pressure rise (dP/dtmax) and augmentation index (AI) are all significant contributors to the error in the conventional auscultatory determination of SBP using Korotkoff sounds. These data suggest a potential role of arterial stiffness as a major component of the errors recorded, with underestimation of SBP much more significant for subjects with stiff arteries than for subjects with more compliant arteries. These preliminary data suggest the need to completely review the mandating of brachial cuff sphygmomanometry as the standard for calibration of NIBP monitors.