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 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.