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Dyspnea on Exertion in Obese Women

Association with an Increased Oxygen Cost of Breathing

¹ Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, and the University of Texas Southwestern Medical Center, Dallas, Texas

Correspondence and requests for reprints should be addressed to T. G. Babb, Ph.D., Institute for Exercise and Environmental Medicine, 7232 Greenville Avenue, Ste 435, Dallas, TX 75231. E-mail: tonybabb{at}texashealth.org

Rationale: Although exertional dyspnea in obesity is an important and prolific clinical concern, the underlying mechanism remains unclear.

Objectives: To investigate whether dyspnea on exertion in otherwise healthy obese women was associated with an increase in the oxygen cost of breathing or cardiovascular deconditioning.

Methods: Obese women with and without dyspnea on exertion participated in two independent experiments (n = 16 and n = 14). All participants underwent pulmonary function testing, hydrostatic weighing, ratings of perceived breathlessness during cycling at 60 W, and determination of the oxygen cost of breathing during eucapnic voluntary hyperpnea at 40 and 60 L/min. Cardiovascular exercise capacity, fat distribution, and respiratory mechanics were determined in 14 women in experiment 2. Data were analyzed between groups by independent t test, and the relationship between the variables was determined by regression analysis.

Measurements and Main Results: In both experiments, breathlessness during 60 W cycling was markedly increased in over 37% of the obese women (P < 0.01). Age, height, weight, lung function, and %body fat were not different between the groups in either experiment. In contrast, the oxygen cost of breathing was significantly (P < 0.01) and markedly (38–70%) greater in the obese women with dyspnea on exertion. The oxygen cost of breathing was significantly (P < 0.001) correlated with the rating of perceived breathlessness obtained during the 60 W exercise in experiment 1 (r² = 0.57) and experiment 2 (r² = 0.72). Peak cardiovascular exercise capacity, fat distribution, and respiratory mechanics were not different between groups in experiment 2.

Conclusions: Dyspnea on exertion is prevalent in otherwise healthy obese women, which seems to be strongly associated with an increased oxygen cost of breathing. Exercise capacity is not reduced in obese women with dyspnea on exertion.

Key Words: obesity • shortness of breath during exercise • breathlessness during exertion • work of breathing • exercise

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Most obese patients with dyspnea on exertion are generally considered to be deconditioned. However, there are preliminary data that challenge this premise. What This Study Adds to the Field The results of this study demonstrate that breathlessness during exercise in obese women seems to be strongly associated with an increased oxygen cost of breathing and that peak cardiovascular exercise capacity is not decreased.

 

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