PURPOSE: To compare exercise capacity in obese vs. non-obese patients with regard to maximal O2 consumption (VO2max), exercise time and mechanics of breathing in patients with unilateral diaphragm paralysis.
METHODS: Cardiopulmonary exercise testing (CPET) was done using a graded treadmill protocol in 16 patients with diaphragm paralysis (DP) and 33 others without diaphragm paralysis (controls). We determined DP by paradoxical diaphragmatic motion on sniff-testing. In each group, we compared obese (BMI>30) to non-obese patients with regard to VO2max (expressed as percent predicted for body weight) and total exercise time. We also collected data on breathing reserve at peak exercise (MVV-peak ventilation, L/min) and forced vital capacity as percent predicted (FVC%). Results (mean +/- SD) were compared by two-tailed unpaired t tests.
RESULTS: DP and control patients were similar in age, BMI, and cardiopulmonary co-morbidities. Compared to controls, DP patients had lower FVC% (61 +/- 14 vs. 94 +/- 17) and lower breathing reserve (1 +/- 14 vs. 17 +/- 18). Among DP patients, VO2max was lower in obese compared to non-obese patients (53 +/- 21 % predicted vs. 80 +/- 25 % predicted, P=0.04); total exercise time was insignificantly shorter (5+/-3 vs. 7+/-4, P=0.15). Among controls, the VO2max was similar in obese compared to non-obese patients (85 +/- 22 % predicted vs. 93 +/- 23 % predicted, P=0.35); exercise time was identical (8+/-2 min vs. 8+/-3 min, P=0.98). In both groups, FVC% and breathing reserve were similar between obese and non-obese patients.
CONCLUSIONS: Obesity is associated with lower exercise capacity in patients with DP, but not in patients with functional diaphragms. This effect is not related to a mechanical limitation to breathing.
CLINICAL IMPLICATIONS: Patients with diaphragm paralysis who become obese have reduced exercise capacity, but factor(s) other than mechanical restriction may be the cause. This suggests weight loss to BMI<30 may be effective in improving exercise capacity in these patients.
DISCLOSURE: The following authors have nothing to disclose: Pomin Yeung, Paul Richman, Gerald Smaldone
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