Background: Long-term effects of lung volume reduction surgery (LVRS) on respiratory muscle strength and effects of age, sex, and emphysema pattern on these changes are unknown. Therefore, we aimed to determine the long-term effect of LVRS on respiratory muscle strength changes in severe emphysema. Methods: The National Emphysema Treatment Trial was a prospective controlled multicentered trial, comparing LVRS to optimal medical treatment on survival and maximal exercise capacity. We examined percentage change in maximum inspiratory pressure (MIP) from baseline to 36 months follow-up to determine impact of LVRS as well as age, sex, emphysema pattern and exercise capacity on changes in MIP compared to medical treatment. Results: LVRS individuals had significantly greater increases in MIP from baseline compared to medical individuals at all follow-ups (LVRS 19.8 ± 42.3%, medical 3.2 ± 29.3%, p<0.0001, 12 months). The LVRS group had significant decreases in total lung capacity (TLC), residual volume (RV), functional residual capacity (FRC) and RV/TLC compared to the medical arm at all follow-up periods. Males and individuals 65-70 years of age had significantly greater increases in MIP following LVRS compared to the medical arm at all follow-ups; this same relationship was seen at up to 24 months for low exercise capacity, upper lobe predominant emphysema. Conclusions: LVRS significantly increases inspiratory muscle strength up to 3 years post-operatively, with male sex, age 65-70 years and low exercise capacity, upper lobe predominant emphysema especially associated with increased MIP. Inspiratory muscle strength increases were associated with decreases in non-invasive markers of dynamic hyperinflation, suggesting that LVRS allows inspiratory muscles to return to their optimal length-tension relationship.
Keywords: age; dynamic hyperinflation; emphysema; exercise capacity; lung volume reduction surgery; mean inspiratory pressure; respiratory muscle strength; sex.