Effect of transmural pressure on the estimation of arterial stiffness index from the photoplethysmographic waveform.

The aim of this study was to find the effect of transmural pressure on the determination of the photoplethysmographic (PPG) waveform arterial stiffness index (PPGAI). The study was conducted on 51 subjects without diagnosis of cardiovascular disease, aged between 24 and 74 years. The relation between the transmural pressure, which is the difference between the arterial blood pressure and the PPG sensor contact pressure, and the PPGAI was determined. PPG, beat-to-beat blood pressure, and sensor contact pressure signals were recorded from the index, middle, and ring finger. The PPG sensor contact pressure of the index finger was increased from 20 to 120 mmHg. The aortic augmentation index (AIx@75) was estimated with a SphygmoCor device as a reference. High correlation coefficients r = 0.79 and r = 0.83 between PPGAI and AIx@75, and low PPGAI standard deviations were observed at the transmural pressures of 10 and 20 mmHg, respectively. Transmural pressure of 20 mmHg can be considered suitable for the PPG signal registration and PPGAI calculation for the assessment of arterial stiffness. In summary, the contact pressure of the sensor should be selected according to theblood pressure of the subject finger in order to achieve the transmural pressure suitable for the assessment of PPGAI and arterial stiffness.