Definition and comparison of a new vascular index between young healthy and aged subjects

In an effort to identify a useful noninvasive screening tool for cardiovascular diseases (CVD) screening, photoplethysmograph (PPG) signals were acquired and analyzed. These PPG signals were recorded during reactive hyperemia experiments consisting of a 4-minute blood flow blockage of the right arm (RA) brachial artery (BA) using a blood pressure cuff inflator. This procedure is usually done for the assessment of endothelial dysfunction which is a risk factor for developing CVD. In this study, signals of the infrared (IR) and red (R) LED's of the PPG sensor were analyzed. These signals were preprocessed, normalized and slow varying component of the signal (DC values) and the pulsatile component (AC values) were extracted and evaluated for peak response during the reactive hyperemia after the release of blood flow blockage. PPG data of five healthy young female individuals (mean age 32.0 ± 1.6 years) were compared to that of five aged female individuals (mean age 64.0 ± 2.9 years). Results show that the IR PPG signals behave similarly to that of the R PPG signals (AC and DC) for both study groups. The young healthy subjects peak AC-IR and peak AC-R are significantly smaller than that of the aged subjects, (4.0 ± 2.4 versus 9.3 ± 5.0, p-value 0.06) and (2.0 ± 1.3 versus 5.4 ± 2.5, p-value 0.03), respectively. Nevertheless, the peak DC-R for the young subjects is significantly higher than that of the aged subjects (23.4 ± 8.3 versus 11.8 ± 6.3, p-value 0.04). The time to reach the peak points is not significantly different between the groups, which confirms our previous study. Since this optical technique is non-invasive and low-cost, it could be ultimately performed in routine clinical setting for the screening of endothelial dysfunction disorders.