Pulse transit time-estimated blood pressure: a comparison of beat-to-beat and intermittent measurement

Pulse transit time (PTT), which refers to the travel time between two arterial sites within the same cardiac cycle, has been developed as a novel cuffless form of continuous blood pressure (BP) monitoring. The aim of this study was to investigate differences in BP parameters, including BP variability, between those assessed by beat-to-beat PTT-estimated BP (eBP(BTB)) and those assessed by intermittent PTT-estimated BP at fixed time intervals (eBP(INT)) in patients suspected of having sleep disordered breathing (SDB). In 330 patients with SDB (average age, 66.8 +/- 11.9 years; 3% oxygen desaturation index [ODI], 21.0 +/- 15.0/h) from 8 institutes, PTT-estimated BP was continuously recorded during the nighttime. The average systolic eBP(BTB), maximum systolic and diastolic eBP(BTB), standard deviation (SD) of systolic and diastolic eBP(BTB), and coefficient variation (CV) of systolic and diastolic eBP(BTB) were higher than the respective values of eBP(INT) (all P < 0.05). Bland-Altman analysis showed a close agreement between eBP(BTB) and eBP(INT) in average systolic BP and SD and CV of systolic BP, while there were disagreements in both minimum and maximum values of eBP(BTB) and eBP(INT) in patients with high systolic BP (P < 0.05). Although systolic BP variability incrementally increased according to the tertiles of 3%ODI in both eBP(BTB) and eBP(INT) (all P < 0.05), there was no difference in this tendency between eBP(BTB) and eBP(INT). In patients with suspected SDB, the difference between e eBP(BTB) and eBP(INT) was minimal, and there were disagreements regarding both the minimum and maximum BP. However, there were agreements in regard to the index of BP variability between eBP(BTB) and eBP(INT).