Recently, we reported that dyspnea on exertion is strongly associated with an increased oxygen cost of breathing in otherwise healthy obese women; the mechanism of dyspnea on exertion in obese men is unknown. Obese men underwent measurements of body composition, fat distribution, pulmonary function, steady state and maximal graded cycle ergometry, and oxygen cost of breathing. Nine men (34±8yr, 35±4 BMI) with ratings of perceived breathlessness of ≤ 2 during cycling, and ten men (36±9yr, 38±5 BMI) with ratings of perceived breathlessness ≥ 4 were studied (ratings of perceived breathlessness: 1.8±0.4 vs. 4.7±0.8, respectively; p<0.0001). Groups had only minor differences in fat distribution, pulmonary function, and steady state exercise. There was no association between ratings of perceived breathlessness and oxygen cost of breathing; but ratings of perceived breathlessness was strongly correlated with ratings of perceived exertion (RPE, rho=0.87, p<0.0001). The differences in exercise intensity, ventilatory demand, cardiovascular conditioning and/or the quality of respiratory sensation did not appear to play a role in the development of dyspnea on exertion. The mechanism of dyspnea on exertion in obese men seems unrelated to the oxygen cost of breathing.

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During constant load exercise, some otherwise healthy obese women experience dyspnea on exertion (+DOE), while others do not (−DOE). We investigated how the subjective quality of respiratory sensations differed between these groups. 80 women were categorized based on their Ratings of Perceived Breathlessness (RPB, Borg 0–10 scale) after 6 minutes of 60 W cycling. 34 women rated RPB ≥ 4 (+DOE) (34 ± 7 yr, 36 ± 5 BMI) and 24 women rated RPB ≤ 2 (−DOE) (33 ± 8 yr, 37 ± 4 BMI). 22 women with RPB = 3 were excluded to better delineate the groups. After exercise, subjects were asked to pick three of fifteen statements that best described their respiratory sensations. Descriptor data were analyzed as frequency statistics and compared using Fisher's exact test. The top descriptors chosen by +DOE women were “Breathing is heavy” (53%, p < 0.05), ”Breathing requires work” (50%), and “Breathing requires effort” (38%); −DOE women selected “I am breathing more” (82%, p < 0.05), “Breathing is rapid” (38%), and “Breathing is shallow” (38%, p < 0.05) most often (p values depict those descriptors that were different between groups). Not only is the intensity of breathlessness significantly different between these groups, but also the qualitative aspects of their breathlessness. +DOE women may have an increased sensation of the work of breathing than − DOE women, which may be related to the elevated RPB.NIH HL096782, King Charitable Foundation Trust.