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Drew Elliott1, Gracie Whitley1, Gabriel Zieff1, Keeron Stone2, Craig Paterson2, Simon Fryer2, Jake Diana1, Jade Blackwell3, Lee Stoner, FACSM1. 1University of North Carolina at Chapel Hill, Chapel Hill, NC. 2University of Gloucestershire, Cheltenham. 3University of Arizona, Tucson, NC.

BACKGROUND: The purpose of this study was to determine the reliability of photoplethysmography (PPG) derived heart-temple pulse-wave velocity (htPWV) in a supine position. Pulse-wave velocity (PWV) is a common measure of arterial stiffness but traditional methods (tonometric and oscillometric) are limited to capturing non-continuous measurements. However, electrocardiogram (ECG) and PPG can be used in conjunction to continuously measure PWV at multiple arterial segments simultaneously. Measuring PWV continuously would enable a better understanding of novel arterial stiffness measures such as htPWV. Further, if shown to be reliable, htPWV may have implications for cerebrovascular health. METHODS: htPWV was assessed in healthy young adults (n = 30, 24.6 ± 4.8 y, 25.2 kg/m2,18 F) using a PPG-ECG approach. A PPG sensor was placed on the temple and electrodes for a three-lead ECG were placed on the chest. PWV was calculated as distance (m) divided by transit-time (s). Distance was measured as the sum of the distance between the suprasternal notch and the location of the carotid pulse, and the distance between the location of the carotid pulse and the temple cuff. Transit time was calculated as the time between the peak of the QRS complex on the ECG and the peak of the second derivative of the PPG waveform. The second derivative peak was used as the ending point as it corresponded closely with the upstroke of the raw waveform. Two supine measurements were obtained five minutes apart and were used to calculate measurement reliability via intraclass correlation coefficient (ICC). RESULTS: htPWV had excellent (ICC>0.75) reliability (ICC=0.95, 95%CI: 0.93 - 0.99). The mean htPWV for the first measurement was 1.50 ± 0.23 m/s and the mean htPWV for the second measurement was 1.48 ± 0.21 m/s. CONCLUSIONS: PPG-ECG is a reliable, continuous method for measuring htPWV. This may be a useful strategy for assessing changes in arterial stiffness in a novel, and potentially clinically important arterial segment.

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