Study objectives: To characterize acute changes in the dynamic, passive mechanical properties of the lungs and chest wall, elastance (E) and resistance (R), caused by lung volume reduction surgery (LVRS).
Design: Prospective data collection.
Patients: Nine anesthetized/paralyzed patients with severe emphysema.
Interventions: Bilateral LVRS.
Measurements and results: From measurements of airway and esophageal pressures and flow during mechanical ventilation throughout the physiologic range of breathing frequency (f) and tidal volume (VT), E and R of the total respiratory system (Ers and Rrs), lungs (EL and RL), and chest wall (Ecw and Rcw) immediately before and after LVRS were calculated. After surgery, Ers, EL, Rrs, and RL were all greatly increased at each combination of f and VT (p<0.05). Ecw and Rcw showed no consistent changes (p>0.05). The increases in EL were greatest in those patients with the lowest residual volumes, highest FEV1 values, and highest maximum voluntary ventilations measured 3 months preoperatively (p<0.05); the increases in RL were greatest in those patients with the lowest preoperative residual volumes (p<0.05). The largest increases in RL were in those patients with the largest decreases in residual volume and total lung capacity, measured 3 months postoperatively, caused by LVRS (p<0.05).
Conclusion: Acute effects of LVRS are large increases in lung elastic tension and resistance; these increases need to be considered in immediate postoperative care, and can be predicted roughly from results of preoperative pulmonary function tests.