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 (O(2)) of respiratory muscles to total O(2) (%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). %O(2)resp was 23.1% at rest and 55.5% at maximal ventilation. LVRS reduced %O(2)resp at maximal ventilation to 49.0% (p < 0.05), but %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.