Background: The value of photoplethysmography (PPG) has been questioned because of a lack of reproducibility. We performed this study to determine whether new digital technology has improved the reproducibility of PPG in the noninvasive assessment of lower limb venous function in patients with isolated superficial venous reflux.
Methods: This was a prospective study of 140 legs in 110 patients (65% female; median age [interquartile range], 45 years [36-59.25 years]; CEAP clinical grade C2/3, n = 114; C4-6, n = 26) who underwent repeated digital PPG measurements of refilling time (RT) in both the sitting and standing position after standard exercise regimens by a single observer. RT was measured in all patients 2 to 5 minutes apart and in a randomly selected subgroup of 30 patients (38 limbs) 1 to 2 weeks apart. RT variability was assessed by using Bland and Altman's coefficient of repeatability (CR-RT), where the CR-RT was 1.96 times the standard deviation of the mean difference in RT between two tests. Venous duplex scanning of both the deep and superficial veins was also performed, and a reverse flow of greater than 0.5 seconds was considered abnormal. Only patients with isolated superficial venous reflux were included in the study.
Results: The CR-RT of the tests on 140 limbs performed 2 to 5 minutes apart was 10 seconds overall, 3 seconds for RT up to 10 seconds, and 16 seconds for RT between 20 and 40 seconds. The CR-RT of the 38 tests performed 1 to 2 weeks apart was also 10 seconds. No systematic variation due to a nonrandom error was found between the measurements performed either 2 to 5 minutes or 1 to 2 weeks apart.
Conclusions: Digital PPG performed in the seated position in patients with isolated superficial venous reflux provides a reproducible method for the noninvasive assessment of lower limb venous function for both clinical and research purposes. However, the variation in precision of RT with the magnitude of the measurement must be taken into account when results are interpreted in individual patients.