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 +/- 89.42 cm(3)) (p < 0.001) than in the IC/TLC > 25% group (575.20 +/- 11.76 cm3). 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. (C) 2016 Sociedade Portuguesa de Pneumologia. Published by Elsevier Espana, S.L.U. This is an open access article under the CC BY-NC-ND license.