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 FEV1 (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.