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

Intrapleural pressure during a forced vital capacity (VC) maneuver 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 maneuvers at varying efforts while airflow, volume, and esophageal pressure (P_OES ) were measured. Quasistatic expiratory deflation curves were used to obtain lung recoil (P_LUNG ) and alveolar pressures (i.e., P_ALV  = P_OES -P_LUNG ). The raw maximal expiratory flow-volume (MEFV_raw ) curve was obtained from the "maximum effort" VC maneuver. The TGC-corrected curve was obtained by constructing a "maximal perimeter" curve from all VC efforts (MEFV_corr ). TGC was examined via differences between curves in FEFs (∆FEF), area under the expiratory curves (∆A_EX ), and estimated compressed gas volume (∆VGC) across the VC range. Men displayed greater total ∆A_EX (5.4 ± 2.0 vs. 2.0 ± 1.5 L² ·s^-1 ; p < .001). ∆FEF was greater in men at 25% of exhaled volume only (p < .05), whereas ∆VGC was systematically greater in men across the entire VC (main effect; p < .05). P_ALV was also greater in men throughout forced expiration (p < .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 maneuver.