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Effects of Lung Volume Reduction Surgery for Emphysema on Oxygen Cost of Breathing^*

^* From the Division of Advanced Surgical Science and Technology (Drs. Takayama, Kurokawa, and Satomi), Medical Technology (Dr. Shindoh), Informatics on Pathophysiology (Dr. Hida), Internal Medicine and Rehabilitation Science (Dr. Kurosawa), and Infection and Respiratory Disease (Dr. Ogawa), Tohoku University, Sendai, Japan.

Correspondence to: Tetsuro Takayama, MD, Division of Advanced Surgical Science and Technology, Graduate School of Medicine, Tohoku University, 1-1 Seiryo-machi, Aoba-ku, Sendai 980-8574, Japan; e-mail: takayama{at}gonryo.med.tohoku.ac.jp

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 (O₂) of respiratory muscles to total O₂ (%O₂resp) 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). %O₂resp was 23.1% at rest and 55.5% at maximal ventilation. LVRS reduced %O₂resp at maximal ventilation to 49.0% (p < 0.05), but %O₂resp 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.

Key Words: lung volume reduction surgery • oxygen cost of breathing • pulmonary emphysema • respiratory muscles

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