Continuous blood pressure measurement by using the pulse transit time: comparison to a cuff-based method

Abstract

Pulse transit time (PTT) and pulse wave velocity (PWV), respectively, were shown to have a correlation with systolic blood pressure (SBP) and have been reported to be suitable for indirect BP measurements. The aim of this study was to create a function between SBP and PWV, and to test its reliability for the determination of absolute SBP using a non-linear algorithm and a one-point calibration. 63 volunteers performed exercise to induce rises in BP. Arterial PTT was measured between the R-spike of the ECG and the plethysmographic curve of finger pulse-oximetry. The reference BP was measured using a cuff-based sphygmomanometric aneroid device. Data from 13 of the 63 volunteers served for the detection of the PWV–BP relationship. The created non-linear function was used to calculate BP values after individual correction for the BP offset in a group of 50 volunteers. Individual correlation coefficients for SBP measured by PTT (SBP_PTT) and by cuff (SBP_CUFF) varied between r = 0.69 and r = 0.99. Taking all data together, we found r = 0.83 (276 measurements in 50 volunteers). In the Bland–Altman plot, the limits of agreement were ${\text{mean}}_{{{\text{SBP}}_{\text{PTT}} , {\text{SBP}}_{\text{CUFF}} }}$± 19.8 mmHg. In conclusion, comparing SBP values using the PTT-based method and those measured by cuff resulted in a significant correlation. However, the Bland–Altman plot shows relevant differences between both methods, which are partly due to greater variability of the SBP_PTT measurement during intensified exercise. Results suggest that PTT can be used for measuring absolute SBP when performing an individual correction for the offset of the BP–PWV relation.