Sex differences in the evolution of net respiratory muscle pressures during incremental exercise
Authors: Cross Troy James , Coriell Catherine L. , Gideon Elizabeth A. , Betts Aaron W. , Duke Joseph W. 
Published: April 2020

The respiratory muscle pressure (Pmus) waveform lends insight into the patterns of net inspiratory v expiratory muscle recruitment under a wide variety of conditions, including mechanical ventilation, spontaneous breathing, and during exercise. On this last point, inspection of the Pmus waveform during incremental and constant work rate cycling reveals that inspiratory and expiratory muscle recruitment systematically increase with rising minute ventilations, and that the duration of post‐inspiratory inspiratory activity (PIIA) gradually disappears from low to high levels of respiratory motor output. In recent years, it has become increasingly evident that the work of breathing is systematically higher for women compared with men at a given minute ventilation during exercise. Yet, no study has examined the potential sex differences in the evolution of Pmus (and its components; e.g., PIIA) during exercise. Thus, a comprehensive assessment of the Pmus waveform during exercise between sexes is warranted.PurposeTo compare the evolution of inspiratory and expiratory Pmus between men and women during incremental cycling.MethodsThirteen men (21 ± yrs; 181 ± 5 cm; 82 ± 11 kg) and 10 women (21 ± 1 yrs; 165 ± 6 cm; 62 ± 6 kg) visited the laboratory on two separate occasions. The first occasion was used to obtain informed consent and to screen participants for normal pulmonary function (>85% age‐predicted). On the second visit, participants were instrumented with an esophageal balloon catheter to estimate variations in pleural pressure (Ppl). Quasi‐static relaxation curves were obtained to measure chest wall recoil pressure (Pcw). Participants then completed an incremental cycling protocol until volitional exhaustion. Pmus was calculated at given minute ventilations during the exercise protocol as follows: Pmus = Pcw – Ppl.ResultsThe peak inspiratory Pmus were significantly greater in females compared with men at a given minute ventilation during incremental cycling (P < 0.05), yet peak expiratory Pmus was similar between sexes. The average rates of change (slope) in Pmus during inspiration & expiration were significantly faster in females than males at a given minute ventilation (P < 0.05). Finally, the duration of PIIA (expressed as a fraction of expiratory time) gradually decreased with increasing minute ventilation during exercise (P < 0.05). This reduction in PIIA was however similar between men and women.ConclusionThe primary finding of this study was that the pattern of respiratory muscle recruitment was different between sexes during incremental cycling, insofar as women displayed systematically larger inspiratory Pmus, and faster rates of net inspiratory & expiratory pressure‐development compared with men at matched ventilations. However, no differences in PIIA between sexes were observed.Support or Funding InformationThis research was funded by preliminary data funds provided by Northern Arizona University (JWD). TJC was supported by the Irene Diamond Fund/American Federation for Aging Research Postdoctoral Transition Award during the time of this study.