Work of Breathing in Obese Men with and without Dyspnea on Exertion

Abstract

INTRODUCTIONBreathlessness during exercise, or dyspnea on exertion (DOE), is a common complaint in otherwise healthy obese adults. It is possible that the higher perception of breathlessness is due to a higher work of breathing. Thus, we investigated whether obese men with high DOE (+DOE) have a higher work of breathing (i.e., oxygen cost) than obese men with a low DOE (−DOE).METHODS27 obese men underwent underwater weighing and a 6‐min constant load submaximal cycling exercise at 105 W. They also performed eucapnic voluntary hyperpnea (EVH) to determine the oxygen cost of breathing. Participants were classified as +DOE, if their Rating of Perceived Breathlessness (RPB, Borg 0–10 scale) was ≥ 4 (n = 16) and as −DOE if RPB was ≤ 2 (n = 11) during minute 6 of the exercise test. The oxygen cost of breathing was obtained by calculating the slope of the oxygen uptake (ml/min) vs. ventilation (L/min) relationship at rest and during EVH at 60 and 90 L/min. RPB was also collected during the last minute of each EVH trial. Following the 90 L/min EVH trial, participants were asked to choose the “top 3 descriptors that best describe[d] the respiratory sensations [they] felt during the test” from a list of 15 descriptors. Data were analyzed between groups by independent t‐test.RESULTSThere were no significant differences between +DOE and −DOE groups in age, BMI, or body fat percentage, respectively (+DOE: 35 ± 6 yr, 36 ± 5 kg/m2, 39 ± 5%; −DOE: 32 ± 6 yr, 35 ± 3 kg/m2, 37 ± 6%; mean ± SD, p > 0.05). Breathlessness ratings during each level of EVH was significantly greater in the +DOE than the −DOE group (p < 0.01). However, there was no significant difference in the oxygen cost of breathing between +DOE (2.05 ± 0.63 ml/L) and −DOE (1.99 ± 0.78 ml/L, p > 0.05). Eleven of the 16 men +DOE felt that their breathing required effort or work (only 3 of the 11 men −DOE).CONCLUSIONSThe otherwise healthy obese men who rated higher breathlessness during exercise also perceived higher breathlessness during the EVH trials. The increase in the intensity of breathlessness was not due to an increased oxygen cost of breathing. Even though the measured work of breathing was not different, the +DOE group more frequently described their breathing to require more work/effort; this perception of effort may be due to changes in neural transmission in the brain, such as a reduced gating of respiratory sensations related to the work of breathing.Support or Funding InformationSupported by NIH Grant R01 HL096782 and King Charitable Foundation Trust.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.