Repeated experiences of air hunger and ventilatory behavior in response to hypercapnia in the standardized rebreathing test: Effects of anxiety

In this study, we assessed air hunger (AH) and ventilatory responses to repeated CO2 exposures in healthy women (N = 31), scoring high or low for trait anxiety. A standardized rebreathing test, implying a gradually increasing CO2 stimulus, was administered three times with 15-min intervals. Respiratory behavior and the intensity of AH perception were measured continuously. Across repeated exposures, maximal tolerance for AH habituated and the slope of AH (increase in AH per unit increase in CO2) diminished. Also the dynamics of the breathing response changed across trials. The thresholds for AH and tidal volume (VT) moved closer to each other, whereas the threshold for the respiratory rate (RR) was generally postponed. In addition, the association between AH and VT was stronger than between AH and RR, and the latter association became weaker over trials, particularly in high anxious persons. This suggests that AH perception became increasingly influenced by psychological factors, especially in high anxious persons. The results suggest that habituation of perceived air hunger is depending on a complex interplay between both changes in respiratory behavior and in perceptual-cognitive processes related to trait anxiety.