Continuous non-invasive determination of nocturnal blood pressure variation using photoplethysmographic pulse wave signals: comparison of pulse propagation time, pulse transit time and RR-interval

Abstract

Objective: Cardiovascular diseases are the leading cause of death, whereas nocturnal ambulatory blood pressure (BP) is the most potent predictor for cardiovascular risk. The volume clamp and pulse transit time (PTT) are common methods for continuous non-invasive BP measurement, but have drawbacks during unsupervised ambulatory use and undisturbed sleep. The pulse propagation time (PPT), defined as the time between pulse wave systolic peak and diastolic peak, provides valid information about the pressure pulse waveform. However, the use of PPT for nocturnal BP variation determination and whether such variation is affected by BP or heart rate (i.e. RR-interval or RRI) has not been investigated.

Approach: To assess whether the PPT method is suitable for ubiquitous nocturnal BP monitoring, we compared systolic blood pressure (SBP) estimates derived from PPT, PTT, and RRI signals with parallel recorded BP measurements. The RRI-derived SBP signals were used as a baseline for testing a potential heart rate dependency. This work provides an overview of BP measurements, presents the developed real-time signal analysis, and describes the performance assessment. The signal analysis was validated with data records from 42 subjects acquired from an ergometry and sleep laboratory in equal parts.

Main results: The algorithms applied to the ergometry laboratory database achieved a correlation coefficient between reference SBP and estimated SBP_PPT of 0.89 (p < 0.001) with bias 0.1 mmHg and limits of agreement (LoA) -29.8 to 30.0 mmHg, SBP_PTT of 0.97 (p < 0.001) with bias 0.0 mmHg and LoA -15.2 to 15.3 mmHg, and SBP_RRI of 0.96 (p < 0.001) with bias 0.0 mmHg and LoA -19.5 to 19.5 mmHg. For the sleep laboratory database, the correlation coefficient was 0.95 (p < 0.001) with bias 0.2 mmHg and LoA -18.3 to 18.8 mmHg for SBP_PPT, 0.88 (p < 0.001) with bias 0.0 mmHg and LoA -25.0 to 24.9 mmHg for SBP_PTT, and 0.88 (p < 0.001) with bias of 0.1 mmHg and LoA -23.6 to 23.7 mmHg for SBP_RRI. A heart rate dependency of PPT or PTT could not be found. The analysis of variance shows no significant differences between the reference SBP values and the estimated values for either the ergometry (F(3, 627) = 2.27, p = 0.08) or the sleep laboratory (F(3, 327) = 2.28, p = 0.08).

Significance: In conclusion, the PPT method seems to be an interesting alternative for continuous determination of SBP during simplified cardiovascular monitoring and sleep screening compared to more expensive devices based on volume clamp or PTT methods.