Noninvasive measurement of beat-to-beat arterial blood pressure by the Korotkoff sound delay time

OBJECTIVE: To propose a novel noninvasive beat-to-beat arterial blood pressure measurement method based on the Korotkoff sound delay time (KDT) and evaluate its accuracy in preliminary experiments. METHODS: KDT decreases as the cuff pressure P deflates, which can be described by a function KDT=f (P). Actually, KDT is a function of arterial transmural pressure. Therefore, the variation in blood pressure can be obtained by the transmural pressure, which is estimated by the KDT. Holding the cuff pressure at an approximate constant pressure between systolic pressure and diastolic pressure, the variation in blood pressure ΔEBP between successive heartbeats can be estimated according to KDT and f'(p), which represents the variation of KDT corresponding to unit pressure. Then the blood pressure for each heartbeat can be obtained by accumulating the ΔEBP. Invasive and noninvasive blood pressure values of six participants were measured simultaneously to evaluate the method. RESULTS: The average of the correlation coefficients between the invasive mean arterial pressure (MAP) and the KDT for six participants was -0.91. The average of the correlation coefficients between the invasive MAP and the estimated mean blood pressure (EBP) was 0.92. The mean difference between EBP and MAP was 0.51 mmHg, and the SD was 2.65 mmHg. The mean blood pressure estimated by the KDT is consistent with the invasive MAP. CONCLUSION: The beat-to-beat blood pressure estimated by KDT provides an accurate estimate of MAP in the preliminary experiments and represents a potential acceptable alternative to invasive blood pressure monitoring during laboratory studies.