Objective: To investigate dyspnea in individuals with Class II or III obesity and look for correlations among the respiratory data related to such individuals. Methods: This study involved 49 subjects with a body mass index >35 kg/m2, divided into two groups (those with dyspnea and those without). The baseline dyspnea index was evaluated, as were spirometry findings, maximal respiratory pressures and arterial blood gas analysis. Results: Of the 49 subjects evaluated, 37 reported dyspnea and 12 reported no dyspnea. The baseline dyspnea index differed between the two groups. The mean values were within the range of normality for all subjects and all parameters, except for the following: ratio of residual volume to total lung capacity; expiratory reserve volume; and the alveolar-arterial oxygen gradient. The subjects with dyspnea presented significantly lower values for expiratory reserve volume, maximal expiratory pressure and arterial pH. In all subjects, body mass index correlated significantly with the following: baseline dyspnea index; the residual volume/total lung capacity ratio; the forced expiratory volume in one second/forced vital capacity ratio; forced expiratory flow between 25% and 75% of forced vital capacity; arterial oxygen tension; the alveolar-arterial oxygen gradient; and arterial carbon dioxide tension. The baseline dyspnea index was found to correlate significantly with the following parameters: residual volume/total lung capacity ratio; expiratory reserve volume; arterial oxygen tension; the alveolar-arterial oxygen gradient; and arterial carbon dioxide tension. Conclusion:  Dyspnea is a common complaint in individuals with class II or III obesity. Such individuals present a pronounced reduction in expiratory reserve volume and an increase in the alveolar-arterial oxygen gradient. The correlations found suggest that obese individuals present dysfunction of the lower airways, and that obesity itself plays a role in the genesis of dyspnea.

Keywords: Obesity/complications; Dyspnea/epidemiology; Dyspnea/physiopathology; Respiratory function tests