Advanced Mechanical Ventilatory Constraints During Incremental Exercise in Class III Obese Male Subjects

Abstract

Background: We investigated the role of mechanical ventilatory constraints in obese class III subjects during incremental exercise.

Methods: We examined 14 control subjects (body mass index [BMI], 23.6 ± 3.2 kg/m(2)), 15 obese class II subjects (BMI, 37.2 ± 4.5 kg/m(2)), and 17 obese class III subjects (BMI, 53.4 ± 6.8 kg/m(2)). All subjects performed pulmonary function tests and maximal inspiratory pressure at rest, ventilatory parameters, flow-volume loops, and rated perceived exertion and breathlessness during exercise.

Results: All subjects had normal pulmonary function. Obesity resulted in increased minute ventilation for a given submaximal work rate, although minute ventilation during peak exercise was lowest in the obese class III subjects. End-expiratory lung volume was significantly lower in the obese subjects at rest and during exercise at the ventilatory threshold but not during peak exercise. During heavy-to-peak exercise, the obese subjects increased their end-expiratory lung volume, whereas the control group continued to decrease this parameter. Compared with controls, end-inspiratory lung volume was significantly lower in obese class II subjects and obese class III subjects at rest and at the ventilatory threshold but not during peak exercise. At maximal exercise, obese class III subjects had a greater end-inspiratory lung volume than obese class II subjects and controls. Obese class III subjects displayed a greater expiratory air flow limitation at rest, at the ventilatory threshold, and during peak exercise than both controls and obese class II subjects.

Conclusions: Mechanical ventilatory constraints increase progressively with degrees of obesity, contributing to exercise limitation in obese subjects.

Keywords: breathing strategy; dyspnea; end-expiratory lung volumes; end-inspiratory lung volume; expiratory air flow limitation; work of breathing.