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 (O 2 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 O 2 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 O 2 cost were measured perioperatively by utilizing a method of continuous dead space. In addition, we calculated the proportion of oxygen consumption (V̇ o 2 ) of respiratory muscles to total V̇ o 2 (%V̇ o 2 resp) from the measured energy expenditure and the predicted values. Results: FEV 1 and arterial oxygen pressure increased after surgery while lung volume and dyspnea decreased (p < 0.01), and O 2 cost was also reduced from 0.044 to 0.026 log(mL/min)/(L/min) [p < 0.001]. Moreover, the change in O 2 cost had a strong negative correlation with that of FEV 1 ( 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). %V̇ o 2 resp was 23.1% at rest and 55.5% at maximal ventilation. LVRS reduced %V̇ o 2 resp at maximal ventilation to 49.0% (p < 0.05), but %V̇ o 2 resp 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.