Basal and exercise tests on morbidly obese patients before and after gastric bypass.

The psysiologic responses of 13 morbidly obese patients (nine women and four men) were studied during basal and exercise conditions before and after gastric bypass. The mean age of the group was 33 +/- 2.3 years, the weight was 157 +/- 11.3 kg, and the body mass index (BMI = weight [kg]/height [m]2) was 54. Initial mean oxygen consumption (VO2) values were extraordinarily elevated, being 453 ml/min at rest and 2084 ml/min during level walking on a treadmill at 2 mph. The mean weight loss 6.9 months after operation was 41.6 +/- 4 kg (0.2 kg/day). Retesting revealed striking improvement in all measured parameters, with some values approaching the values of the matched control group of lean subjects. Spirometric results were normal for the nonsmokers (n = 8), although insignificant improvement occurred after weight loss. The basic requirement to be accepted for operation was that the patient must be able to exercise for 6 minutes on the treadmill at 2 mph, zero elevation, without developing metabolic acidosis and a respiratory quotient above 1.0. Three superobese men (BMI = 69) with hypercarbia failed to meet the exercise requirement. Their poor performance resulted in hospital treatment until they were in suitable condition upon retesting to undergo operation. Their elevated Paco2 values did not correct to normal until several months after operation. In this study, the basal and exercise VO2 values proved to be sensitive indicators for the amount of weight loss after gastric bypass (P = 0.01 and 0.001, respectively).