Comparative impact of morbid obesity vs heart failure on cardiorespiratory fitness.

BACKGROUND: We are in the midst of an obesity pandemic. Morbid obesity is associated with dyspnea on exertion and higher overall mortality rates. The relations between measures of cardiorespiratory fitness in morbidly obese persons compared to those with heart failure are unknown.

METHODS: We compared cardiorespiratory fitness in patients with morbid obesity (n = 43) and established systolic dysfunction heart failure (n = 235), and in age-matched medical control subjects (n = 222) who had been referred for diagnostic exercise testing with simultaneous metabolic measurements. Only patients who completed an adequate test for maximum exertion manifested by a respiratory exchange ratio of > or = 1.10 were included in the study.

RESULTS: The mean (+/- SD) body mass index (BMI) values for the three groups were 47.8 +/- 5.1, 30.1 +/- 5.7, and 33.8 +/- 9.0, respectively (p < 0.0001 for comparisons between morbidly obese patients and each comparator). The mean left ventricular ejection fraction for the heart failure group was 21.5 +/- 8.4%. Despite achieving higher peak heart rate and BP values, the morbidly obese patients had a mean maximum oxygen uptake (V(O2)max) that was similar to that of those with heart failure (17.8 +/- 3.6 vs 16.5 +/- 5.6 mL/kg/min, respectively; p = 0.14) and was considerably lower than that of the control group (17.8 +/- 3.6 vs 21.3 +/- 8.2 mL/kg/min, respectively; p = 0.007). In addition, among subjects in the control group, there was a graded inverse relation between BMI and V(O2)max.

CONCLUSIONS: Morbidly obese individuals have severely reduced cardiorespiratory fitness that is similar to those with established systolic dysfunction heart failure. In addition, in those persons who are referred for stress testing for medical reasons, there is an inverse graded relationship between BMI and cardiorespiratory fitness. These data suggest that the impairment in V(O2)max in morbidly obese persons is related to BMI and possibly to other factors that impair peak cardiac performance. These findings are consistent with overall higher expected mortality in morbidly obese persons.