Oxygen uptake kinetics during exercise reveal central and peripheral limitation in patients with iliofemoral venous...

Pulmonary oxygen uptake (V˙O₂) kinetics measured during the initiation of exercise mirror energetic transition during daily activity. The aim of this study was to elucidate the pathophysiological mechanisms of exercise limitation of patients with chronic iliofemoral vein obstruction after deep vein thrombosis by measuring V˙O₂ kinetics compared with patients with peripheral arterial disease (PAD) and healthy individuals.

Eleven patients with iliofemoral vein obstruction (7 men; age, 20-65 years), seven patients with PAD (all men; age 44-60 years) and eight healthy participants (5 men; age 28-58 years) were studied. Participants performed upper and lower limb symptom-limited cardiopulmonary exercise tests on cycle ergometers; and four repeat lower limb tests at a constant work rate corresponding with 90% of the gas exchange threshold for determining V˙O₂ kinetics.

Phase I V˙O₂ amplitude in the constant work rate tests (percent increase over resting V˙O₂), representing the initial surge in cardiac output caused by the emptying of leg veins, was 59 ± 19% in the iliofemoral vein obstruction group, 73 ± 22% in PAD, and 85 ± 26% in healthy participants (P = .055 for iliofemoral vein obstruction vs healthy). Phase II V˙O₂ kinetics, which largely reflect the kinetics of O₂ consumption in the exercising muscles, were slower in iliofemoral vein obstruction (tau = 42 ± 6 seconds), and PAD (tau = 49 ± 19 seconds), compared with healthy participants (23 ± 4 seconds; P < .01).

Slow phase II V˙O₂ kinetics reflect a slow onset of muscular aerobic metabolism in both iliofemoral vein obstruction and PAD. The low amplitude phase I of V˙O₂ kinetics observed in iliofemoral vein obstruction suggests a damped cardiodynamic phase, consistent with decreased venous return from the obstructed veins. These abnormalities of V˙O₂ kinetics may contribute to exercise intolerance in iliofemoral vein obstruction and PAD.