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.

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NMR lineshapes were calculated for a model of lung, and NMR proton spectra were measured for individual voxels in an excised inflated rat lung. NMR lines for parenchymal lung regions containing alveoli, alveolar ducts, and capillaries were calculated using a computer simulation of the NMR signal from a three-dimensional honeycomb-like structure, a collection of modified Wigner-Seitz cells. These cells were modified by rounding the corners and increasing the thickness of the boundaries to model various degrees of lung inflation and lung water. NMR lineshapes were also calculated for the central or nonparenchymal lung regions containing bronchi and large blood vessels. A comparison of theoretical lineshapes with those measured in individual voxels both in the parenchymal and in the central (largely nonparenchymal) regions in excised rat lungs at an inflation pressure of 30 cm of water shows excellent agreement. These results indicate that the NMR lineshape reflects the underlying lung geometry. This research constitutes the first calculations and measurements of NMR lineshapes in lung. The appendix describes a new method for calculating the magnetic field inside a weakly diamagnetic material of arbitrary shape placed in an otherwise uniform external magnetic field. This new method does not require either solution of simultaneous equations or evaluation of integral expressions.

We investigated the relationship between nutritional status and muscle energy metabolism during exercise in 18 male patients with chronic obstructive pulmonary disease (COPD) and 15 male control subjects using 31P nuclear magnetic resonance spectroscopy (31P-MRS). The patients and control subjects were further categorized as in either a well-nourished (% ideal body weight, % IBW > or = 90) or malnourished (% IBW < 90) state. Muscle energy metabolism was evaluated by determining the ratios PCr/(PCr + Pi) (PCr, phosphocreatine; Pi, inorganic phosphate), and ATP/(PCr + Pi + ATP). The exercise consisted of repetitive hand grips performed against a load. The work rate was normalized for the individual's lean muscle mass by dividing work performed by the forearm fat-free cross-sectional area, which was calculated using 1H-MRS. The PCr/(PCr + Pi) values during exercise did not correlate with the % IBW in any of the groups of control subjects or COPD patients. Furthermore, the PCr/(PCr + Pi) did not correlate with the normalized work rate in either the well-nourished or malnourished subject groups. However, there were correlations within the groups of control subjects and COPD patients. The PCr/(PCr + Pi) values for the normalized work rate were consistently lower in the COPD patients than in the control subjects. These findings suggest that the altered muscle metabolism in COPD patients is not affected by their nutritional status.

NMR relaxation times (T1 and T2) and the water content (WC) of in vitro rat lungs were measured during the course of endotoxin lung injury in rats. Measurements of normal lungs, untreated endotoxin-injured lungs, and endotoxin-injured lungs treated with methylprednisolone (MPSL) were compared. The untreated endotoxin lungs showed prolongation of the fast and slow T2 components (T2f and T2s), but no significant changes in T1 or water content. Also, there was no correlation between 1/WC and relaxation rates or between T1 and T2. MPSL treatment prevented T2f and T2s prolongation; however, the duration of MPSL effectiveness was limited. Animals which were treated with MPSL more than 7 h prior to measurements showed T2 prolongation. This study indicates that NMR relaxation times, particularly T2, can be useful in evaluating lung injuries and their treatments.