Evaluation of Cardiorespiratory Fitness in Morbidly Obese Adults

Abstract

1000 BACKGROUND: The emergence of bariatric surgery as a viable option for the treatment of extreme obesity has created the need to evaluate the cardiovascular status of this escalating patient population as part of a pre-surgical screening protocol. Maximal exercise testing in this cohort is often limited by confounding variables such as early onset of fatigue, physical discomfort, poor motivation, equipment limitations, or combinations thereof. These factors, singly and collectively, often preclude the completion of a valid and reliable test. PURPOSE: To minimize the body habitus limitations presented by conventional motorized treadmills or cycle ergometers, we used the NuStep TRS 4000 recumbent cross trainer (NuStep, Inc. Ann Arbor, MI) to evaluate the cardiorespiratory fitness of this unique population. METHODS: Maximal exercise testing was performed in conjunction with the direct measurement of somatic oxygen consumption on 12 (5 men, 7 women; mean ± SD age = 51 years) morbidly obese individuals (mean ± SD BMI 62 ± 13 kg/m2) using the NuStep recumbent cross trainer. These patients were referred to our laboratory as a component of their pre-bariatric surgical screening. Primary indications for the use of this protocol were a body weight greater than 400 lbs. (182 kg), physical limitations preventing the use of a treadmill or cycle ergometer, or both. Exercise testing was initiated at a workload approximating 450 kpm/min and increased ∼120 kpm/min every two minutes to volitional fatigue, or when the designated pedaling rate (100 steps per minute) could no longer be maintained. RESULTS: Patients achieved a VO2 peak of 12.5 ± 3.4 ml/kg/min at an average respiratory exchange ratio of 1.0 ± 0.10. Rating of perceived exertion at peak exercise averaged “17” (very hard) on the Borg (6–20) category scale. Anaerobic threshold was determined in 8 of the 12 subjects, with a mean value occurring at 7.4 ± 2.4 ml/kg/min, equal to 63 ± 16% VO2 peak. Peak heart rate averaged 135 ± 19 bpm, corresponding to 80% of age predicted maximal values. Only two of the 12 patients were on beta-blocker therapy. Moreover, all tests were competed safely, with no cardiovascular or musculoskeletal complications, and without ischemic ST segment changes, anginal chest pain, or malignant ventricular arrhythmias. CONCLUSION: Peak or symptom-limited exercise testing of morbidly obese patients can be completed safely and effectively utilizing the NuStep recumbent cross trainer. The information obtained can reliably be used to assess the patient's electrocardiographic response, hemodynamics, and cardiorespiratory fitness prior to bariatric surgery.