Why is exercise capacity reduced in subjects with pectus excavatum?

Background: Exercise capacity is often limited in subjects with pectus exca vatum (PE), but the mechanism is unknown. Objectives: We attempted to quantify exercise capacity and to investigate w hether limitation of venous return to the heart contributes to exercise:int olerance in PE. Methods: A total of 13 patients with PE (mean age, 19 +/- 6 years) and 20 c ontrol subjects (mean age, 25 +/- 11 years) underwent sitting and supine:in cremental cycling and exercise Doppler stroke volume (SV) measurements. Results: Supine peak oxygen uptake (V'O(2)max) for the patients (1351 +/- 3 45 mL/min) and control subjects (1505 +/- 330 mL/min) was not different. In contrast, sitting V'O(2)max was lower in the patients than in the;control subjects, 1480 +/- 462 and 1994 +/- 581 mL/min, respectively (P = .02). Sup ine exercise SV was not different between groups, Moreover, only in the pat ients with pi was supine exercise SV, 70 +/- 18 mt, higher than sitting exe rcise 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-reduc ed: V'O(2)max and SV, whereas during supine exercise they approached the-co ntrol values. The supine advantage in PE suggests that-upright exercise cap acity in this disease is affected by reduced filling of the heart in the no n-supine position.