Conventional pulse transit times as markers of blood pressure changes in humans

Abstract

Pulse transit time (PTT) represents a potential approach for cuff-less blood pressure (BP) monitoring. Conventionally, PTT is determined by (1) measuring (a) ECG and ear, finger, or toe PPG waveforms or (b) two of these PPG waveforms and (2) detecting the time delay between the waveforms. The conventional PTTs (cPTTs) were compared in terms of correlation with BP in humans. Thirty-two volunteers [50% female; 52 (17) (mean (SD)) years; 25% hypertensive] were studied. The four waveforms and manual cuff BP were recorded before and after slow breathing, mental arithmetic, cold pressor, and sublingual nitroglycerin. Six cPTTs were detected as the time delays between the ECG R-wave and ear PPG foot, R-wave and finger PPG foot [finger pulse arrival time (PAT)], R-wave and toe PPG foot (toe PAT), ear and finger PPG feet, ear and toe PPG feet, and finger and toe PPG feet. These time delays were also detected via PPG peaks. The best correlation by a substantial extent was between toe PAT via the PPG foot and systolic BP [- 0.63 ± 0.05 (mean ± SE); p < 0.001 via one-way ANOVA]. Toe PAT is superior to other cPTTs including the popular finger PAT as a marker of changes in BP and systolic BP in particular.

Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1

Data collection for comparing conventional pulse transit times (cPTTs) as markers of blood pressure (BP) changes in humans. The (A) sensors and (B) BP-varying interventions were employed in the reclining volunteer.

Figure 2

Data exclusion criteria with number of included and excluded subjects and measurement sets. A measurement set comprises the ECG waveform, ear, finger, and toe photo-plethysmography (PPG) waveforms, and manual cuff BP for a subject and condition (see Fig. 1B). The criteria were strict to ensure a valid comparison of cPTTs as markers of BP changes.

Figure 3

Data analysis for comparing cPTTs as markers of BP changes in humans. The six detected time delays include three pulse arrival times (PATs) and three differences between two PTTs (dPTTs). The time delays were averaged over multiple beats and compared in terms of tracking the intervention-induced BP changes via the intra-subject correlation coefficient.

Figure 4

Mean (with SE) over the subjects (N = 32) of systolic and diastolic BP and the cPTTs for the baseline period, each intervention, and each recovery period (see Figs. 1 and 3 for definitions of interventions and cPTTs). The toe PAT trend appeared most inversely related to the systolic BP trend, whereas the toe PAT and finger PAT trends appeared most inversely related to the diastolic BP trend.

Figure 5

Mean (with SE) of the correlation coefficients between each cPTT and each BP over the subjects (see Figs. 1 and 3 for cPTT definitions). The correlation coefficients differed significantly for both systolic and diastolic BP according to one-way ANOVA. *Indicates significant pairwise differences based on a Tukey test. The best correlation by a substantial extent was between toe PAT and systolic BP.

Figure 6

Mean (with SE) of the correlation coefficients between toe PAT detected via the PPG foot (see Fig. 3) and peak and systolic BP over the subjects. *Indicates significant difference based on a paired t-test. Toe PAT detected via the PPG foot afforded much better correlation.

Figure 7

Subject-by-subject plots of systolic BP versus toe PAT detected via the PPG foot (see Fig. 3). Dashed lines are lines of best fit. The correlation coefficient (CC) varied per subject.