Individuals with morbid obesity breathe at low lung volumes. This study determined whether flow limitation was present at these low lung volumes and, if so, whether it contributed to exercise limitation and dyspnea.
We studied 21 morbidly obese individuals without clinical lung disease, airflow limitation, or hypoxemia at rest. Following recording of maximal expiratory and inspiratory flow volume loops at rest, incremental cardiopulmonary exercise testing on a cycle ergometer was performed. Unloaded pedaling for three minutes was followed by 20 watt increments every minute to symptom limitation. Flow-volume loops and inspiratory capacity measurements were recorded every minute, and dyspnea/fatigue were measured every three minutes using a Borg scale. Flow limitation during peak exercise was defined as a greater than or equal to 50% overlap of the exercise flow volume loop with the maximal flow volume loop.
Three males and 18 females were studied (age 34 ± 8 years, BMI 49 ± 6 kg/m2). Peak oxygen consumption (VO2) was 1.71 ± 0.45 L/min, or 85 ± 11 percent of predicted based on ideal body weight. When related to actual body weight, peak VO2 was 12.5 ± 2.2 mL/kg/min, or 36 ± 4 percent of predicted. Seven patients (33%) had flow limitation at peak exercise; these patients had lower end-expiratory lung volumes (EELV) than those without flow limitation at rest (0.42 vs 0.84 L, respectively, p. = 0.01) and at peak exercise (0.71 vs. 1.18 L, respectively p. = 0.015). Both groups had significant, similar increases in EELV at peak exercise (0.29 and 0.34 L, respectively, both, p. < 0.03). Flow limitation was not related to peak work rate or dyspnea/leg fatigue.
Flow limitation during exercise is present in a minority of morbidly obese individuals without apparent lung disease, although a dynamic increase in end expiratory lung volumes is common.
Only a minority of morbidly obese subjects have flow limitation during exercise. Flow limitation did not appear to be related to exercise capacity or exercise-limiting symptoms.
P. Grover, None.