Inspiratory fraction as a marker of skeletal muscle dysfunction in patients with COPD.

Background: An inspiratory capacity to total lung capacity (IC/TLC) ratio of ≤25% has emerged as a better marker of mortality in chronic obstructive pulmonary disease (COPD) patients. The relationship among the IC/TLC ratio to lower extremity skeletal muscle function remains unknown.

Methods: Thirty-five men with moderate to severe COPD were divided into those with IC/TLC≤25% (n=16) and >25% (n=19). The subjects were tested for thigh muscle mass volume (MMT), maximal strength, power output of the lower extremities, and physical activity.

Results: Total MMT in the IC/TLC<25% group was significantly lower (413.91±89.42cm) (p<0.001) than in the IC/TLC>25% group (575.20±11.76cm). In the IC/TLC≤25% group, maximal strength of the lower extremities and muscle peak power output of the lower extremities were 36-56% lower (p<0.01) than among the patients in the IC/TLC>25% group.

Conclusion: IC/TLC≤25% is associated with reduced maximal strength and peak power output of the lower extremities. IC/TLC≤25% may have an important clinical relevance as an index to determine peripheral muscle dysfunction.