Effects of lung volume reduction surgery for emphysema on oxygen cost of breathing

Background: Patients with severe pulmonary emphysema have a greatly increased oxygen cost of breathing (O₂ cost), and this is the cause of serious malnutrition, or respiratory cachexia, in such patients. Study objectives: To clarify the effect of lung volume reduction surgery (LVRS) on respiratory function and the nutritional state of these patients through a reduction in the O₂ cost of the respiratory, muscles. Design: Prospective cohort study. Setting, patients, and interventions: Twenty-three patients who underwent LVRS in Tohoku University Hospital. Measurements: Pulmonary function and O₂ cost were measured perioperatively by utilizing a method of continuous dead space. In addition, we calculated the proportion of oxygen consumption (V̇O₂) of respiratory muscles to total V̇O₂ (%V̇O₂resp) from the measured energy expenditure and the predicted values. Results: FEV₁ and arterial oxygen pressure increased after surgery while lung volume and dyspnea decreased (p < 0.01), and O₂ cost was also reduced from 0.044 to 0.026 log(mL/min)/(L/min) [p < 0.001]. Moreover, the change in O₂ cost had a strong negative correlation with that of FEW₁ (r = -0.70, p < 0.001), and a moderate positive correlation with that of the ratio of residual volume to total lung capacity (r = 0.54, p < 0.01). %V̇O₂resp was 23.1% at rest and 55.5% at maximal ventilation. LVRS reduced %V̇O₂resp at maximal ventilation to 49.0% (p < 0.05), but %V̇O₂resp at rest did not decrease after surgery. Conclusions: LVRS reduces energy expenditure of respiratory muscles especially during exercise by decreasing small airway obstruction and hyperinflated lung volume. This may reverse the malnourished state in end-stage emphysema.