Test–retest reliability of Doppler ultrasound‐based leg blood flow assessments during exercise in patients with chronic obstructive pulmonary disease

Doppler ultrasound may be used to assess leg blood flow ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>Q</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>leg</mml:mi></mml:msub> <mml:annotation>${{\dot{Q}}_{{\mathrm{leg}}}}$</mml:annotation></mml:semantics> </mml:math> ), but the reliability of this method remains unexplored in patients with chronic obstructive pulmonary disease (COPD), where between-subject variability may be larger than healthy due to peripheral vascular changes. This study aimed to investigate the reliability of Doppler ultrasound in quantifying <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>Q</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>leg</mml:mi></mml:msub> <mml:annotation>${{\dot{Q}}_{{\mathrm{leg}}}}$</mml:annotation></mml:semantics> </mml:math> during single-leg knee-extensor exercise (KEE) in COPD patients compared with those obtained from healthy matched controls. In this case-control study, 16 participants with COPD were matched based on sex and age with 16 healthy controls. All participants underwent measurement of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>Q</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>leg</mml:mi></mml:msub> <mml:annotation>${{\dot{Q}}_{{\mathrm{leg}}}}$</mml:annotation></mml:semantics> </mml:math> using Doppler ultrasound in a KEE set-up at various intensities on two separate visits. Confounding factors on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>Q</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>leg</mml:mi></mml:msub> <mml:annotation>${{\dot{Q}}_{{\mathrm{leg}}}}$</mml:annotation></mml:semantics> </mml:math> were controlled for, and the ultrasound scans were consistently performed by the same sonographer. During exercise, smallest real difference (SRD) ranged from 367 mL to 583 mL in COPD and 438 mL to 667 mL in the control group. The coefficient of variation (CV) ranged from 7.9% to 14.3% in COPD and 9.4% to 10.4% in the control group. The intraclass correlation coefficient ranged from 0.75 to 0.92 in COPD and 0.67 to 0.84 in the control group. CV was lower in the control group during exercise at 0 W, but apart from that, reliability was not different between groups during exercise. Doppler ultrasound showed nearly equal reliability when evaluating <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>Q</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mi>leg</mml:mi></mml:msub> <mml:annotation>${{\dot{Q}}_{{\mathrm{leg}}}}$</mml:annotation></mml:semantics> </mml:math> in COPD patients and healthy individuals with a CV below 15% during exercise for both groups. HIGHLIGHTS: What is the central question of this study? What is the between-day reliability of Doppler ultrasound when quantifying leg blood flow during single-leg knee-extensor exercise in COPD patients compared to healthy matched controls? What is the main finding and its importance? This study demonstrates a coefficient of variation ranging from 7.9 to 14.3% during single-leg knee-extensor exercise for between-day reliability when applying Doppler ultrasound to assess leg blood flow in patients with COPD. Furthermore, it offers insights into the peripheral circulatory constraints in COPD, as evidenced by diminished leg blood flow. This study is the first of its kind to evaluate the reliability of Doppler ultrasound in the assessment of the peripheral circulation during exercise in COPD.