Compensatory Exercise Hyperventilation is Restored in the Morbidly Obese After Bariatric Surgery

Background Morbidly obese individuals may have poor compensatory hyperventilation during exercise. The objective was to examine pulmonary gas exchange and the compensatory hyperventilatory response during exercise pre- and post-weight reduction surgery in obese subjects. Methods Fifteen patients (age = 39 ± 8 years, body mass index = 47 ± 6 kg/m 2 ), with an excess weight of 69 ± 17 kg, were recruited. Pulmonary function at rest was assessed and arterial-blood gases were sampled at rest and all levels of exercise pre- and 10 ± 3 weeks postsurgery. Results There was a loss of excess weight 21 ± 6 kg ( p < 0.01). Waist and hip circumference decreased by 13 ± 9 and 8 ± 7 cm, respectively ( p < 0.01). Prior to surgery, there was no compensatory hyperventilation between rest and peak exercise as arterial PCO 2 (PaCO 2 ) remained unchanged (37± 3 mm Hg). However, postsurgery, there was compensatory hyperventilation as PaCO 2 decreased to 33 ± 2 mm Hg at peak exercise ( p < 0.01), with no change in peak oxygen consumption (VO 2peak in L/min). Multiple linear regression revealed that the restored ventilatory response to exercise was most strongly associated with the reduction in overall fat mass (adjusted r 2 = 0.25; p = 0.03). Total weight loss of 21 kg induces adequate compensatory hyperventilation that begins to show at about 50% of VO 2peak , resulting in improved gas exchange at moderate to peak exercise intensities. Conclusion Improvement in compensatory hyperventilation is most closely related to loss in overall fat mass.