Pulse Transit Time Based Continuous Cuffless Blood Pressure Estimation: A New Extension and A Comprehensive Evaluation

Abstract

Cuffless technique enables continuous blood pressure (BP) measurement in an unobtrusive manner, and thus has the potential to revolutionize the conventional cuff-based approaches. This study extends the pulse transit time (PTT) based cuffless BP measurement method by introducing a new indicator – the photoplethysmogram (PPG) intensity ratio (PIR). The performance of the models with PTT and PIR was comprehensively evaluated in comparison with six models that are based on sole PTT. The validation conducted on 33 subjects with and without hypertension, at rest and under various maneuvers with induced BP changes, and over an extended calibration interval, respectively. The results showed that, comparing to the PTT models, the proposed methods achieved better accuracy on each subject group at rest state and over 24 hours calibration interval. Although the BP estimation errors under dynamic maneuvers and over extended calibration interval were significantly increased for all methods, the proposed methods still outperformed the compared methods in the latter situation. These findings suggest that additional BP-related indicator other than PTT has added value for improving the accuracy of cuffless BP measurement. This study also offers insights into future research in cuffless BP measurement for tracking dynamic BP changes and over extended periods of time.

Multimodal Photoplethysmography-Based Approaches for Improved Detection of Hypertension

“…For example, Wang et al [38] showed a significant correlation between HR and BP and demonstrated that the addition of both HR and previous BP measurements to the PTT-BP estimation significantly improved the error (p < 0.05). Other measurements such as PIR have been incorporated into the PTT-BP estimation [16,51,67,69,71,78,82] as it reflects the low-frequency component of arterial diameter changes, which are not normally picked up by conventional PTT measurements. Here, PIR is measured as the ratio of minimum to maximum amplitudes of a PPG waveform in one cardiac cycle.…”

“…Here, PIR is measured as the ratio of minimum to maximum amplitudes of a PPG waveform in one cardiac cycle. Ding et al [69] proved that the addition of PIR improved BP estimation, decreased error, and maintained accuracy over extended (24 h) calibration periods; however, other studies incorporating PIR struggled to obtain acceptable SD values. Recently, the heart-rate power spectrum ratio (HPSR), a new parameter, has been added to PTT-PIR estimation to more accurately identify the increase in sympathetic activity in hypertensive patients [82].…”

“…Of the 73 included studies, 22 reported the correlation (r) between estimated and reference BP for both SBP and DBP [15,17,20,21,23,25,27,29,31,40,43,44,51,52,55,[59][60][61]65,67,81,82]. Further, 15 studies reported the measurement variance in estimated versus reference BP for both SBP and DBP through mean error and standard deviation [21,22,33,34,38,51,59,60,64,67,69,72,78,82,83]. Various different biosignal combinations of ECG, BCG, SCG, ICG, IPG, and SBS were combined with PPG for BP estimation.…”

Multimodal Monitoring of Cardiovascular Responses to Postural Changes

“…PPG may enable monitoring BP in superficial arteries, e.g., the radial artery (wrist) or digital artery (finger). PPG amplitude was reported to correlate with BP (Hennig and Patzak, 2013;Lim et al, 2015;Gao et al, 2016;Sun et al, 2016;Ding et al, 2017;Wang et al, 2018). When combined with ECG, PPG can be used to compute pulse wave velocity (PWV), a parameter reflecting both BP, arterial stiffness and arterial vasoconstriction (Salvi, 2017).…”

Alignment‐Free Liquid‐Capsule Pressure Sensor for Cardiovascular Monitoring

“…Mechanical sensors may also be used in tonometry, while PPG sensors are usually used together with the electrocardiogram (ECG) to predict BP through an indirect algorithm, i.e., the pulse transmit time (PTT) method. [7a,12] Accordingly, mechanical methods may provide a more precise, compact, and energy‐efficient solution for long‐term BP monitoring.…”