Improved gas exchange during exercise after weight loss in morbid obesity

The aim of this study was to determine the effect of weight loss induced by 6 weeks very-low-calorie-diet (VLCD) and behavioural intervention on pulmonary gas exchange during exercise in non-smoking morbid obese (BMI>40 kg/m2) otherwise healthy patients. Seven obese patients underwent a maximal bicycle ergometer test with continuous analysis of expired air and arterial blood sampling before and after a mean weight loss of 18% (25.7 kg, range: 10-50 kg). Body mass index (BMI) decreased with weight loss from 46.6 (6.3) kg/m2 to 38.0 (4.7) kg/m2 (P<0.01). Oxygen consumption (VO2) at low and submaximal exercise levels decreased after weight reduction, but the change was not statistically significant. The peak oxygen consumption related to body weight (VO2/kg) increased 22% from the initial 16.2 (3.6) ml/min/kg to 19.8 (3.1) ml/min/kg (P<0.05). Decrease in VCO2 was significant at submaximal exercise level. Ventilatory equivalent for CO2 increased significantly after weight reduction (P<0.05). Standing up and light exercise resulted in a significant increase in the mean arterial oxygen tension (PaO2) (P<0.05) and a significant decrease in the mean alveolar-arterial difference P(A-a)O2 (P<0.05) when compared to supine values. The mean increase in PaO2 with weight loss was not significant. The peak P(A-a)O2 decreased significantly after weight reduction. In conclusion, weight reduction induced by VLCD and behavioural intervention without exercise therapy can improve gas exchange during exercise in morbid obesity. Increased wasted ventilation, and a tendency to alveolar hyperventilation, after weight loss may reflect a delay in the adaptation of regulation of breathing to rapid weight loss.