Within‐session repeatability of Doppler ultrasound leg blood flow assessments during exercise in patients with chronic obstructive pulmonary disease

Doppler ultrasound can be used to evaluate leg blood flow (Q̇_leg), especially of interest when investigating peripheral vascular limitations in patients with chronic obstructive pulmonary disease (COPD). However, the within-session repeatability, a subdomain of test-retest reliability, of this method remains unknown. This study aimed to provide within-session repeatability estimates of Doppler ultrasound-based Q̇_leg at rest and during single-leg knee-extensor exercise (KEE) in patients with COPD, and to compare these estimates to matched healthy controls. In this case-controlled study, 16 participants with COPD were matched based on sex and age with 16 healthy controls. All participants underwent measurement of Q̇_leg using Doppler ultrasound in a KEE setup at various intensities with the same measurement being performed again separated by 10 s. Smallest real difference (SRD) was lowest at rest in both groups and increased during exercise, reaching values ranging from 164 to 231 mL in COPD and 122-180 mL in the control group. The coefficient of variance (CV) was highest at rest and decreased during exercise to values ranging from 4.0% to 5.0% in COPD and 2.6%-3.2% in the control group. The CV was significantly lower in the control group during 0 watt and exercise at 20% of max watt, but apart from that, no reliability estimates were different between groups. To conclude, Doppler ultrasound showed nearly equal within-session repeatability when evaluating Q̇_leg in COPD patients and healthy individuals with a CV not exceeding 5% during exercise for both groups.