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

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.

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.

Prospective cohort study. Setting, patients, and interventions: Twenty-three patients who underwent LVRS in Tohoku University Hospital.

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.

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.

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.