Muscle conduction velocity and morphology after prolonged hypoxemia and diabetes in rats

One of the electrophysiological abnormalities in the experimental rat model of chronic hypoxia (10% O2) and in the experimental rat model of diabetes is an increase in jitter in the stimulated single fibre EMG, which is thought to result from a primary disorder of the axon with its terminal branches. But muscle fibre alterations that influence the propagation of muscle action potentials can also increase jitter. The contribution of possible changes in muscle conduction velocity and muscle morphology to jitter were investigated in the present study. Muscle conduction velocities were determined and compared with the morphological properties of muscle fibers in muscles of control, chronic hypoxic and terminal-stage diabetic rats. The mean muscle conduction velocities were in the same range in the three groups. The muscle fibre type composition and the mean muscle fibre diameters were about the same in the hypoxic and the control rats, whereas the muscles of the diabetic rats showed a higher percentage of intermediate type muscle fibres, which is suggestive of muscle degeneration, and a smaller mean muscle fibre diameter in comparison with muscles of the hypoxic and the control rats. It is concluded that the similarities between the electrophysiological properties of the muscles despite differences in their morphology, indicate that there is primary axonal degeneration in diabetic hypoxic rats.