Thoracic gas compression during forced expiration is greater in men than women

  • Elizabeth A. Gideon (Contributor)
  • Troy J. Cross (Contributor)
  • Brooke E. Cayo (Contributor)
  • Aaron W. Betts (Contributor)
  • Dallin S. Merrell (Contributor)
  • Catherine L. Coriell (Contributor)
  • Lauren E. Hays (Contributor)
  • Jj Duke (Contributor)



Intrapleural pressure during a forced vital capacity (VC) manoeuvre is often in excess of that required to generate maximal expiratory airflow. This excess pressure compresses alveolar gas (i.e., thoracic gas compression; TGC), resulting in underestimated forced expiratory flows (FEFs) at a given lung volume. It is unknown if TGC is influenced by sex; however, because men have larger lungs and stronger respiratory muscles, we hypothesized that men would have greater TGC. We examined TGC across the "effort-dependent" region of VC in healthy young men (n=11) and women (n=12). Subjects performed VC manoeuvres at varying efforts while airflow, volume, and oesophageal pressure (P<sub>OES</sub>) were measured. Quasi-static expiratory deflation curves were used to obtain lung recoil (P<sub>LUNG</sub>) and alveolar pressures (i.e., P<sub>ALV</sub>=P<sub>OES</sub>–P<sub>LUNG</sub>). The raw maximal expiratory flow-volume (MEFV<sub>raw</sub>) curve was obtained from the "maximum effort" VC manoeuvre. The TGC-corrected curve was obtained by constructing a "maximal perimeter" curve from all VC efforts (MEFV<sub>corr</sub>). TGC was examined via differences between curves in FEFs (∆FEF), area under the expiratory curves (∆A<sub>EX</sub>), and estimated compressed gas volume (∆VGC) across the VC range. Men displayed greater total ∆A<sub>EX</sub> (5.4±2.0 vs. 2.0±1.5 L<sup>2</sup>∙s<sup>-1</sup>; <i>p</i>&lt;0.001). ∆FEF was greater in men at 25% of exhaled volume only (<i>p</i>&lt;0.05), whereas ∆VGC was systematically greater in men across the entire VC (main effect; <i>p</i>&lt;0.05). P<sub>ALV</sub> was also greater in men throughout forced expiration (<i>p</i>&lt;0.01). Taken together, these findings demonstrate that men display more TGC, occurring early in forced expiration, likely due to greater expiratory pressures throughout the forced VC manoeuvre. 
Date made available2020

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