Why is exercise capacity reduced in subjects with pectus excavatum?

Background: Exercise capacity is often limited in subjects with pectus excavatum (PE), but the mechanism is unknown. Objectives: We attempted to quantify exercise capacity and to investigate whether limitation of venous return to the heart contributes to exercise intolerance in PE. Methods: A total of 13 patients with PE (mean age, 19 ± 6 years) and 20 control subjects (mean age, 25 ± 11 years) underwent sitting and supine incremental cycling and exercise Doppler stroke volume (SV) measurements. Results: Supine peak oxygen uptake (V'O₂ max) for the patients (1351 ± 345 mL/min) and control subjects (1505 ± 330 mL/min) was not different. In contrast, sitting V'O₂ max was lower in the patients than in the control subjects, 1480 ± 462 and 1994 ± 581 mL/min, respectively (P = .02). Supine exercise SV was not different between groups. Moreover, only in the patients with PE was supine exercise SV, 70 ± 18 mL, higher than sitting exercise SV, 55 ± 14 mL (P = .015). The corresponding values for the control subjects were 70 ± 18 mL and 65 ± 19 mL (P = NS). Conclusions: Patients with PE exercising in the sitting position have reduced V'O₂ max and SV, whereas during supine exercise they approached the control values. The supine advantage in PE suggests that upright exercise capacity in this disease is affected by reduced filling of the heart in the non-supine position.