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. 2016 Dec 15:6:39273.
doi: 10.1038/srep39273.

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

Stephanie L-O Martin  1 , Andrew M Carek  2 , Chang-Sei Kim  1 , Hazar Ashouri  2 , Omer T Inan  2 , Jin-Oh Hahn  1 , Ramakrishna Mukkamala  3
Affiliations

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

Stephanie L-O Martin et al. Sci Rep. .

Erratum in

Abstract

Pulse transit time (PTT) is being widely pursued for cuff-less blood pressure (BP) monitoring. Most efforts have employed the time delay between ECG and finger photoplethysmography (PPG) waveforms as a convenient surrogate of PTT. However, these conventional pulse arrival time (PAT) measurements include the pre-ejection period (PEP) and the time delay through small, muscular arteries and may thus be an unreliable marker of BP. We assessed a bathroom weighing scale-like system for convenient measurement of ballistocardiography and foot PPG waveforms - and thus PTT through larger, more elastic arteries - in terms of its ability to improve tracking of BP in individual subjects. We measured "scale PTT", conventional PAT, and cuff BP in humans during interventions that increased BP but changed PEP and smooth muscle contraction differently. Scale PTT tracked the diastolic BP changes well, with correlation coefficient of -0.80 ± 0.02 (mean ± SE) and root-mean-squared-error of 7.6 ± 0.5 mmHg after a best-case calibration. Conventional PAT was significantly inferior in tracking these changes, with correlation coefficient of -0.60 ± 0.04 and root-mean-squared-error of 14.6 ± 1.5 mmHg (p < 0.05). Scale PTT also tracked the systolic BP changes better than conventional PAT but not to an acceptable level. With further development, scale PTT may permit reliable, convenient measurement of BP.

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Conflict of interest statement

OTI is a Scientific Advisor for, and has patents licensed to, Physiowave, Inc., a company that is commercializing BCG-based devices. All other authors declare no conflicts of interest.

Figures

Figure 1
Figure 1. Data collection for comparing weighing scale-based pulse transit time (PTT) to conventional pulse arrival time (PAT) as markers of blood pressure (BP) in humans.
(A) Ballistocardiography (BCG) and foot photoplethysmography (PPG) waveforms were measured with a custom system similar to a weighing scale; ECG, finger PPG, and impedance cardiography (ICG) waveforms were measured with standard sensors; and a reference finger cuff BP waveform was measured with a volume-clamp device. (B) The waveforms were recorded during three baseline periods (R1, R2, R3) and three interventions (mental arithmetic (MA), cold pressor (CP), post-exercise (PE)) to increase BP but change the pre-ejection period (PEP) differently.
Figure 2
Figure 2. Data analysis for comparing scale PTT to conventional PAT as markers of BP in humans.
(A) Scale PTT, conventional PAT, PEP, and other time delays were detected from the waveforms. (B) The time delays were assessed and compared in terms of their ability to track the intervention-induced BP changes via the correlation coefficient (r) and root-mean-squared-error (RMSE) after a best-case calibration.
Figure 3
Figure 3
Group average (mean ± SE for N = 22) of (A) diastolic and systolic BP, (B) scale PTT and conventional PAT, (C) PEP, and (D) arm PTT for each baseline period and intervention. In contrast to conventional PAT, scale PTT was able to correctly track the BP changes on average mainly due to the elimination of PEP but perhaps also due to mitigation of the impact of smooth muscle contraction following the CP intervention.
Figure 4
Figure 4. Group average correlation coefficients between scale PTT and each BP level and conventional PAT and each BP level.
Scale PTT correlated with both diastolic and systolic BP significantly better than conventional PAT.
Figure 5
Figure 5. Representative correlation plots of diastolic BP versus scale PTT and versus conventional PAT in three subjects.
The improved BP correlation offered by scale PTT varied from subject to subject mainly due to the variable performance of conventional PAT and its PEP and arm PTT components.
Figure 6
Figure 6. Correlation plots of predicted BP via scale PTT and via conventional PAT after best-case calibration for each time delay versus cuff BP and Bland-Altman plots of the errors between the predicted and measured BP versus cuff BP pooled over all the subjects, along with the group average RMSEs.
The different symbols correspond to each of the subjects. Scale PTT yielded a good diastolic BP RMSE, whereas conventional PAT produced unacceptable diastolic and systolic BP RMSEs.
See this image and copyright information in PMC

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