Photoplethysmographic augmentation index using the signal fourth derivative

This work aimed to provide, that using the derivatives of photoplethysmographic signal enhance the location of inflection points. Furthermore, using the signal fourth derivative, it is possible to locate inflections points as photoplethysmographic augmentation index (PAI). A computing photoplethysmographic analyzer was developed. The first, second, third and fourth derivatives were obtained by the mean square error interpolation method. The PAI was quantified by fourth derivative. PAI was calculated similar to augmentation index for pressure (AIx). The AIx is obtained as the difference between late and early systolic inflections expressed as a percentage of the pulse pressure. A study with 36 people, 18 healthy volunteers and 18 subjects with previously diagnosed cardiovascular disease was carried out. A t-tested distribution between healthy volunteers and patients showed a significant differences in calculated PAI (0.0231 vs 0.4678, p <; 0.0001). In conclusion, PAI has shown to be a noninvasive indicator for vascular assessments. Using the fourth derivative, inflection point identification on the photoplethysmographic signal is more accurate mainly in subjects with previously diagnosed cardiovascular disease.