Contribution of lung and chest wall mechanics following emphysema resection

To determine the contributions of (1) chest wall (Pcw) and (2) lung elastic recoil pressure (PL) to (3) total elastic recoil pressure exerted by the respiratory system (Prs) in 18 patients (12 men) aged 66 +/- 6 years (mean +/- 1 SD) with severe emphysema who underwent video-assisted thoracoscopic bilateral lung volume reduction surgery under paralyzed (vecuronium) general anesthesia (isoflurane).

We measured preoperative and 6-week postoperative lung function studies, and intraoperative inspiratory lung conductance (GL), PL, Pcw, and Prs (cm H2O) at end-expiratory lung volume (EELV), EELV plus 0.60 +/- 0.0 L, and EELV plus 1.15 +/- 0.0 L. All values are mean +/- SEM.

Preoperative vs postoperative FVC was 1.9 +/- 0.1 L vs 2.3 +/- 0.1 L (p = 0.03); FEV1 was 0.6 +/- 0.1 L vs 0.9 +/- 0.1 L (p < 0.02); total lung capacity was 7.4 +/- 0.4 L vs 5.9 +/- 0.3 L (p < 0.001); functional residual capacity was 5.7 +/- 0.4 L vs 4.4 +/- 0.2 L (p = 0.001). At EELV preoperative vs postoperative, PL was 0.0 +/- 0.3 vs 1.1 +/- 0.05 (p = 0.04), Pcw was 5.0 +/- 0.7 vs 2.4 +/- 0.9 (p = 0.02), and Prs was 5.0 +/- 0.8 vs 3.5 +/- 0.7 (p = 0.08). AT EELV plus 0.60 L, PL was 3.2 +/- 0.6 vs 6.1 +/- 0.9 (p < 0.001), Pcw was 8.8 +/- 0.8 vs 7.0 +/- 0.9 (p = 0.12), and Prs was 12.0 +/- 0.8 vs 13.1 +/- 0.7 (p = 0.80). At EELV plus 1.15 L, PL was 6.8 +/- 0.9 vs 10.3 +/- 1.1 (p < 0.001), Pcw was 13.5 +/- 1.0 vs 11.2 +/- 1.2 (p = 0.12), and Prs was 20 +/- 1.2 vs 21.5 +/- 1.0 p = 0.93). AT EELV plus 0.06 L, GL was 0.09 +/- 0.00 L/S/cm H2O vs 0.16 +/- 0.01 (p < 0.01). At EELV plus 1.15 L, GL was 0.12 +/- 0.01 vs 0.21 +/- 0.03 (p < 0.05) with similar preoperative vs postoperative GL/PL slopes.

The increase in PL and decrease in Pcw following LVRS for emphysema may be responsible for the increase in spirometry and airway conductance.