Dyspnea on exertion in obese women: association with an increased oxygen cost of breathing.
BACKGROUND
Although exertional dyspnea in obesity is an important and prolific clinical concern, the underlying mechanism remains unclear.


OBJECTIVE
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.


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 (r(2) = 0.57) and experiment 2 (r(2) = 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.
Babb
Tony G
TG
Institute for Exercise and Environmental Medicine, 7232 Greenville Avenue, Dallas, TX 75231, USA. tonybabb@texashealth.org
Ranasinghe
Kamalini G
KG
Comeau
Laurie A
LA
Semon
Trisha L
TL
Schwartz
Belinda
B
D000328:Adult; D050218:Body Fat Distribution; D018493:Cardiovascular Deconditioning; D004417:Dyspnea / Q000453:epidemiology / Q000209:etiology*; D015444:Exercise; D005080:Exercise Test; D017079:Exercise Tolerance; D005260:Female; D006801:Humans; D009765:Obesity / Q000150:complications*; D010100:Oxygen / Q000378:metabolism*; D005082:Physical Exertion; D015995:Prevalence; D011659:Pulmonary Gas Exchange; D012123:Pulmonary Ventilation; D012044:Regression Analysis; D015656:Respiratory Mechanics; D014481:United States / Q000453:epidemiology; D014939:Work of Breathing
D010100:Oxygen