Measurement of endothelial function using photoplethysmography with continuous correction approach: a pilot study

Background: Photoplethysmography flow-mediated dilatation (PPG-FMD) is an endothelial function measurement tool, and its use is increasing as it is easy to apply and relatively inexpensive. The analysis protocol of PPG-FMD has not yet been standardized. This study aimed to define the continuous correction method in PPG-FMD analysis and interpret the results obtained from a healthy population. Methods: The study population consisted of 30 healthy persons. Endothelial function measurement was done with the PPG-FMD method. In the correction process of the PPG signal, a continuous (element-wise) correction approach was defined and applied. PPG-dilation indexes (PPG-DI) were calculated for each subject, and its correlation with demographic and anthropometric data were analyzed. Finally, the study group was divided into subgroups, and endothelial function results were compared. Results: The median PPG-DI (IQR) value of the whole study group was 112% (60). The Pearson correlation coefficients (r) obtained in the analysis were as follows; r=-0.6278 for age, r=-0.4635 for BMI, r=-0.4628 for waist circumference, r=-0.4207 for systolic blood pressure, r=-0.2804 for diastolic blood pressure. In the subgroup analysis, groups with older age, high BMI, male sex, smoker, and high waist circumference had lower PPG-DI results. Conclusions: PPG-FMD could be a good alternative in the endothelial function measurement, with its operator-independent and easily applicable nature. Although the measurement protocol is similar to USG-FMD, PPG-FMD contains much more technical details during the analysis process. We introduced a novel signal correction method, and we believe that this will be a basis for future studies on this subject.