Noninvasive tracking of systolic arterial blood pressure using pulse transit time measured with ECG and carotid doppler signals with intermittent calibration

Summary : We have developed a non-invasive blood pressure measurement system using pulse transit time (PTT) from the heart to the common carotid artery, measured by using an electrocardiogram (ECG) R-wave and carotid arterial Doppler signals at the anterior neck. In this study, we examined the validity of our system by comparing PTT derived systolic blood pressure (Dopp_SBP) with invasive radial systolic arterial pressure (Inv_SBP) with calibration every 15 min in the ICU setting. M ethods: 17 patients under invasive mechanical ventilation in the ICU were studied. Carotid arterial flow via an 8-MHz Doppler flow probe, ECG, and radial arterial pressure signals were transferred to a personal computer at a rate of 1 kHz and processed to calculate Dopp_SBP from PTT using our own calibration formula. Results: We recorded 3,770 pairs of Inv_SBP and Dopp_SBP in 17 patients. Inv_SBP ranged from 213 to 82 mmH g, and Dopp_SBP from 185 to 71 mmHg. The Bland-Altman plot of the comparison between Inv_SBP and Dopp_SBP revealed limits of agreement of –20.1 to 17.7 mmHg (mean difference, –1.2 mmHg). There was a statistically significant close linear correlation between Inv_SBP and Dopp_SBP (y = 0.9494x + 7.5171, R 2 = 0.8471, p < 0.0001). Conclusions: The results of the present study show that our system using Doppler ultrasound flow and ECG signals, is feasible for systolic blood pressure tracking over a longer interval if it is combined with intermittent calibration.