³¹P-NMR Study of Skeletal Muscle Metabolism in Patients with Chronic Respiratory Impairment

Abstract

To evaluate the energy metabolism of peripheral skeletal muscle during exercise in patients with chronic respiratory impairment, the 31P-nuclear magnetic resonance (NMR) spectra of forearm muscle were investigated in nine patients and nine age-matched control subjects. We calculated the phosphocreatine (PCr) to PCr + inorganic phosphate (PI) ratio, the time constant of PCr recovery and the intracellular pH. The exercise consisted of repetitive hand grips against a 2-kg load every 3 s for 6 min (0.33 W). The patients showed a marked decrease in the PCr/(PCr + PI) ratio and pH in the muscle during exercise in contrast to the control subjects whose PCr/(PCr + PI) showed a minor decrease without any change in pH. The relationship between PCr utilization and pH demonstrated that anaerobic glycolysis switched on earlier in patients with chronic respiratory impairment. A split PI peak was observed in five of nine patients during exercise. The PCr/(PCr + PI) ratio during the last minute of exercise correlated significantly with the vital capacity (% predicted), with the FEV1/FVC, with the body weight, with the maximum strength of hand grip, and with the muscle mass. The results indicate impaired oxidative phosphorylation and the early activation of anaerobic glycolysis in the muscles of patients with chronic respiratory impairment. Several factors related to chronic respiratory impairment, such as disuse, malnutrition and dysoxia, would contribute to the metabolic changes observed in the muscles examined.

Deoxygenated Hemoglobin/Myoglobin Kinetics of Forearm Muscles from Rest to Exercise in Patients with Chronic Obstructive Pulmonary Disease

“…Here, we adjusted the lifted weight to 7% of the maximal grip power, and the exercise intensity did not differ between patients and healthy individuals. Since our previous study showed that arterial oxygen saturation was constant during this exercise protocol in patients with COPD (Kutsuzawa et al 1992), a smaller increase in blood flow compared with that of O 2 utilization during the on-transition might cause the shorter TD in PtA. Vascular control during exercise might relate to a smaller increase in blood flow during the on-transition.…”

“…Metabolic and morphological changes in the skeletal muscles of patients with COPD have been demonstrated, such as decreased oxidative enzyme activity (Jakobsson et al 1995;Maltais et al 1996) and an increased proportion of type II fibers in the lower limbs (Jobin et al 1998). We also found changes in the skeletal muscle metabolism of patients with chronic respiratory impairment using 31-phosphorus nuclear magnetic resonance spectroscopy ( 31 P-MRS) (Kutsuzawa et al 1992(Kutsuzawa et al , 1995. Skeletal muscle intracellular pH (pHi) and high-energy phosphate compounds can be dynamically measured using noninvasive 31 P-MRS (Taylor et al 1983).…”

“…The spectrometer was operated at 85 MHz for 1 H and at 34.5 MHz for 31 P. A surface coil (4 cm) was placed on the proximal third of the non-dominant forearm. The 31 P-MR spectra were obtained using a single 90° pulse (50 μ sec) (Kutsuzawa et al 1992) with a repetition time of 3 s and accumulated for 15 s.…”

“…The signal intensity was determined as the area under the spectral line for inorganic phosphates (Pi) and PCr, which was determined by means of Gaussian curve fitting (Kutsuzawa et al 1992) from each spectrum. Relative concentrations of PCr and Pi were evaluated using normalized units of the PCr index (PCr/[PCr + Pi]).…”

“…A decrease in pHi during exercise suggests lactic acid accumulation in exercising muscle (Taylor et al 1983). Patients with chronic respiratory impairment have significant decreases in phosphocreatine (PCr) and pHi during mild exercise, suggesting reduced oxidative capacity and the early accumulation of lactate in their muscles (Kutsuzawa et al 1992). Thus, muscle oxygenation states during exercise might differ between patients with COPD and healthy individuals.…”