Skeletal muscle oxidative capacity in patients with cystic fibrosis

Abstract

What is the central question of this study? Do patients with cystic fibrosis have reduced skeletal muscle oxidative capacity, measured with near-infrared spectroscopy, compared with demographically matched control subjects? What is the main finding and is its importance? Patients with cystic fibrosis have impairments in skeletal muscle oxidative capacity. This reduced skeletal muscle oxidative capacity not only appears to be accelerated by age, but it may also contribute to exercise intolerance in patients with cystic fibrosis. Exercise intolerance predicts mortality in patients with cystic fibrosis (CF); however, the mechanisms have yet to be elucidated fully. Using near-infrared spectroscopy, in this study we compared skeletal muscle oxidative capacity in patients with CF versus healthy control subjects. Thirteen patients and 16 demographically matched control subjects participated in this study. Near-infrared spectroscopy was used to measure the recovery rate of oxygen consumption ( mus V̇O2max) of the vastus lateralis muscle after 15 s of electrical stimulation (4 Hz) and subsequent repeated transient arterial occlusions. The mus V̇O2max was reduced in patients with CF (1.82 ± 0.4 min(-1) ) compared with control subjects (2.13 ± 0.5 min(-1) , P = 0.04). A significant inverse relationship between age and mus V̇O2max was observed in patients with CF (r = -0.676, P = 0.011) but not in control subjects (r = -0.291, P = 0.274). Patients with CF exhibit a reduction in skeletal muscle oxidative capacity compared with control subjects. It appears that the reduced skeletal muscle oxidative capacity is accelerated by age and could probably contribute to exercise intolerance in patients with CF.

Conflict of interest statement

Conflict of Interest: The authors have not conflicts of interest to report.

© 2015 The Authors. Experimental Physiology © 2015 The Physiological Society.

Figures

Figure 1

Representative raw NIRS data during a single recovery kinetics test. Electrical stimulation (15 sec, 4 Hz) was used to increase muscle metabolic rate which was followed by a series of repeated arterial occlusion cuffs. The red signalrepresents oxyhemoglobin (O2HB), the blue signal represents deoxyhemoglobin (HHb), and the green signal represents total hemogloblin (tHB). Slopes of the NIRS signal during the repeated arterial occlusions were measured and fit to an exponential curve. Rate constants were calculated to represent skeletal muscle oxidative capacity.

Figure 2

Individual data and mean difference in musVO2max between patients with CF (CF) and healthy controls (HC). *Significant difference between groups.

Figure 3

Association between musVO2max and age in patients with CF (Panel A) and healthy controls (Panel B).