Background and objectives: Lung volume reduction surgery (LVRS) improves ventilatory function in selected patients with severe COPD. The reasons for the observed benefits include the following: increased elastic recoil, improved airflow, and lesser dynamic hyperinflation and decreased lung volumes. We reasoned that these changes could also alter respiratory drive.
Methods: Respiratory central drive was prospectively assessed using the mouth occlusion pressure (P0.1), and the P0.1 response to increasing CO2 (P0.1/PETCO2 [end-tidal CO2 pressure]), in eight sequential patients before and 3 to 5 months after LVRS. Results were compared with those from 13 control subjects.
Results: LVRS decreased total lung capacity from 7.44±1.8 L to 5.92±1.3 L (p<0.05) and residual volume from 4.97±1.5 L to 3.56±1.1 L (p<0.05). It also significantly improved FEV1 from 0.85±0.26 L to 0.99±0.26 L (p<0.05). Baseline P0.1 (3.4±1.8 vs 1.4±0.4 cm H2O, p<0.01) and P0.1/PETCO2 (0.24±0.07 vs 0.11±0.04 cm H2O/mm Hg, p<0.05) were higher in patients than in control subjects. After LVRS, P0.1 decreased from 3.4±1.8 to 1.3±0.75 cm H2O (p<0.01) and P0.1/PETCO2 from 0.24±0.07 to 0.16±0.06 cm H2O/mm Hg (p<0.05). These postoperative values were similar to those of control subjects. There were no correlations between changes in the factors known to influence central drive (PaO2, PaCO2, age, weight, height, FVC, and FEV1) and changes in P0.1.
Conclusions: We conclude that decreased ventilatory drive should be added to the list of benefits of LVRS, and may help explain the symptomatic improvement reported by many patients after this surgery.