Background: Oxygen consumption volume (VO2) and resting energy expenditure are increased in emphysema because of impaired respiratory function and mechanics, with greater oxygen cost of breathing and altered metabolism. We hypothesized that lung volume reduction surgery may improve energy expenditure and metabolism.
Methods: In this 1-year prospective study, 30 patients with moderate-to-severe emphysema underwent bilateral lung volume reduction surgery; 28 similar patients, who refused operation, followed a standard respiratory rehabilitation program. Oxygen consumption volume and resting energy expenditure, both corrected for fat-free mass, VO2 proportion of respiratory muscles (%VO2Resp), respiratory quotient, and energy substrate oxidation were determined by using a calorimetric chamber with indirect methods.
Results: Only after surgery significant improvements resulted in 1-second forced expiratory volume (+20.4%, p = 0.009), residual volume (-24.8%, p = 0.001), diffusion-lung carbon-monoxide (+18.4%, p = 0.008), body mass index (+5.5%, p = 0.01), resting energy expenditure (-8.2%, p = 0.006), and %VO2Resp (-44.1%, p = 0.0008) with increase in respiratory quotient (0.79 versus 0.84, p = 0.03) and conversion from prevalent lipid (44.6% versus 34.3%, p = 0.0007) to prevalent carbohydrate (25.2% versus 42.2%, p = 0.0006) metabolism. Thirteen operated on patients discontinued oral steroids, showing the most significant improvements. The remaining 17 experienced significant changes compared with the rehabilitation group despite oral steroids (resting energy expenditure -7.0% versus +4.1%, and %VO2Resp -34.0% versus +0.7%, p = 0.001). Decrease of resting energy expenditure and %VO2Resp correlated with reduction of residual volume (p = 0.02 and p = 0.001) and increment of body mass index (p = 0.03 and p = 0.004).
Conclusions: Lung volume reduction surgery significantly decreased %VO2Resp and resting energy expenditure over respiratory rehabilitation and despite oral steroid therapy. Substrate oxidation changed from prevalent lipid to prevalent carbohydrate. Correlations with residual volume and nutritional status suggest that restoration of respiratory mechanics reduces energy expenditure and approximates metabolism to normal.