Ballistocardiogram as Proximal Timing Reference for Pulse Transit Time Measurement: Potential for Cuffless Blood Pressure Monitoring

Abstract

Goal We tested the hypothesis that the ballistocardiogram (BCG) waveform could yield a viable proximal timing reference for measuring pulse transit time (PTT). Methods From fifteen healthy volunteers, we measured PTT as the time interval between BCG and a non-invasively measured finger blood pressure (BP) waveform. To evaluate the efficacy of the BCG-based PTT in estimating BP, we likewise measured pulse arrival time (PAT) using the electrocardiogram (ECG) as proximal timing reference and compared their correlations to BP. Results BCG-based PTT was correlated with BP reasonably well: the mean correlation coefficient (r) was 0.62 for diastolic (DP), 0.65 for mean (MP) and 0.66 for systolic (SP) pressures when the intersecting tangent method was used as distal timing reference. Comparing four distal timing references (intersecting tangent, maximum second derivative, diastolic minimum and systolic maximum), PTT exhibited the best correlation with BP when the systolic maximum method was used (mean r value was 0.66 for DP, 0.67 for MP and 0.70 for SP). PTT was more strongly correlated with DP than PAT regardless of the distal timing reference: mean r value was 0.62 versus 0.51 (p=0.07) for intersecting tangent, 0.54 versus 0.49 (p=0.17) for maximum second derivative, 0.58 versus 0.52 (p=0.37) for diastolic minimum, and 0.66 versus 0.60 (p=0.10) for systolic maximum methods. The difference between PTT and PAT in estimating DP was significant (p=0.01) when the r values associated with all the distal timing references were compared altogether. However, PAT appeared to outperform PTT in estimating SP (p=0.31 when the r values associated with all the distal timing references were compared altogether). Conclusion We conclude that BCG is an adequate proximal timing reference in deriving PTT, and that BCG-based PTT may be superior to ECG-based PAT in estimating DP. Significance PTT with BCG as proximal timing reference has potential to enable convenient and ubiquitous cuffless BP monitoring.

Weighing Scale-Based Pulse Transit Time is a Superior Marker of Blood Pressure than Conventional Pulse Arrival Time

“…However, the use of animals remained a shortcoming. We also showed that PTT via BCG and finger cuff BP waveforms correlated better with diastolic BP than PAT via ECG and finger cuff BP waveforms in healthy humans during interventions that changed BP but also induced confounding motion artifact19. While the use of human subjects was relevant, the distal waveform represented a limitation in that it was not realistic of a cuff-less BP monitoring application and did not permit PTT measurement through larger, more elastic arteries.…”

“…We further smoothed the BCG waveform segments using an exponential filter to suppress motion artifact19. We then detected the fiducial points of interest for each beat as follows.…”

“…We then identified the I wave as the local minimum between the ECG R wave and J wave nearest to the J wave. We detected the PPG troughs by applying the intersecting tangent method between successive ECG R waves181920 and the ICG B point as the maximum of the first derivative between consecutive R waves (which turned out to be the best amongst various possible fiducial points). We next took the differences between the times of appropriate pairs of fiducial points to determine the time delays for each beat.…”

Cuffless Blood Pressure Estimation Algorithms for Continuous Health-Care Monitoring

“…In other words, PAT consists of the PTT in addition to the time interval between the electrical activation and the mechanical movement of the heart. Although, it is shown that using PAT instead of PTT can reduce the DBP estimation accuracy [19], in literature, it is widely used as a proximal reference due to its convenience of measurement [7]. In order to measure the PTT (or PAT) value between proximal and distal in a non-invasive manner, various vital signals such as photoplethysmograph (PPG), electrocardiogram (ECG), as well as other signals such as ballistocardiogram (BCG) and seismocardiogram (SCG) can be used [7].…”

Direct Pulse Transit Time Measurement from an Electronic Weighing Scale

“…This has been suggested, for example, for the H wave [11], even though it precedes cardiac ejection and some authors have attributed it to ventricular movements due to its absence in recordings without ventricular contraction [13]. The I wave has also shown better results than the H and J waves when used as a surrogate of the pressure pulse at proximal sites [14] but a detailed analysis has not yet been reported. The different dynamics of the I and J waves with respect to the R peak of the ECG during paced respiration reported in [15] suggest that the interval between the I and J waves, named IJ interval, is sensitive to parameters other than the PEP, perhaps because of the dependence of the J wave on events posterior to cardiac ejection.…”