Key result
Local cold exposure had little effect on PTT terminating at the foot of the PPG pulse, but affected PTT terminating at the peak, suggesting foot-based measurements are more reliable.
Why the study?
Does finger cold exposure affect pulse transit time measurements in healthy normotensive subjects?
Does finger cold exposure affect pulse transit time measurements in healthy normotensive subjects?
PTT measurements terminating at the foot of the PPG pulse are reliable under local cold exposure, whereas those terminating at the peak are affected, which may impact the accuracy of PTT-based blood pressure monitoring.
Pulse transit time (PTT) has attracted great interest for developing continuous and noninvasive blood pressure (BP) monitoring devices. This study investigated the effect of finger cold exposure on PTT. 13 healthy and normotensive subjects, including 6 males and 7 females took part in the experiment. Cold exposure was performed by asking subjects to immerse one finger into cold water (9±2°C) for 2 minutes. The photoplethysmographic (PPG) signals were recorded from the cooled and adjacent non-cooled finger simultaneously. PTT was measured between the R-wave of the electrocardiogram (ECG) and a fiducial point in finger PPG pulse for each heartbeat. Three definitions of PTT were investigated and the difference of PTT between two fingers was calculated for each subject. By comparing the difference before and after cold exposure, it was found that local cold exposure had little effect on PTT1, which terminates at the foot of the PPG pulse; however, it affected the PTT3, which terminates at the peak of the PPG pulse. The results suggest that the measurement of PTT which terminates at the foot of the PPG pulse is reliable, while those measurements which terminate at the peak of the PPG pulse or other fiducial points nearby are subject to the effect of local cold exposure and can possibly affect the accuracy of PTT-based applications.
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Zhang et al. (2005) studied Healthy and normotensive (n=13). Finger cold exposure vs. Adjacent non-cooled finger / baseline was evaluated on Difference in pulse transit time (PTT) between cooled and non-cooled fingers. Local cold exposure had little effect on PTT terminating at the foot of the PPG pulse, but affected PTT terminating at the peak, suggesting foot-based measurements are more reliable.
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