Reliability of Finger Photoplethysmogram Assessment: Effect of Mental Stress and Day-to-Day Variability

Abstract

Frequent assessment of vascular health (e.g., arterial stiffness) may predict the incidence of cardiovascular disease. The Second Derivative of the finger Photoplethysmogram Aging Index (SDPTGAI) may be used as an index of vascular aging and a screening tool for arteriosclerotic disease. To test its reliability as a measurement of arterial stiffness, we compared SDPTGAI with aortic Augmentation Index (AIx) at rest and during short-term mental stress (study 1). In addition, the day-to-day variability of SDPTGAI was evaluated (study 2). In study 1, a total of 31 apparently healthy adults were measured with the photoplethysmogram on the right index finger in the sitting resting condition. Simultaneously, the applanation tonometry was used to record blood pressure waveforms from the left radial artery (for aortic pressure waveform estimation via a general transfer function). Subsequently, 22 subjects underwent a 30-s arithmetic test (double-digit subtraction). In study 2, 10 young adults were measured with SDPTGAI for five consecutive days. In study 1, we found that SDPTGAI was significantly correlated with AIx (r = 0.682, p < 0.001). During the arithmetic task, heart rate and SDPTGAI were significantly increased from the baseline values (p < 0.05 for both) whereas AIx remained to be unchanged. In study 2, SDPTGAI showed 12.0 ± 9.9% of Coefficient of Variation (CV) across all subjects, which is comparable to CV of heart rate (12.5 ± 5.4%). These findings suggest that SDPTGAI has the potential for evaluating arterial stiffness and wave reflection at the resting condition, but it needs to be measured under well-rested relaxed condition because the finger photoplethysmogram may easily be affected by mental stressor.