Nerve-roots of the cauda equina. The effect of hypotension and acute graded compression on function.

The influence of hypotension on the function of nerve-roots of the cauda equina under acute graded compression was studied with use of an established porcine model. In twenty adult miniature pigs, the nerve-roots of the cauda equina were compressed at pressures of zero (sham), fifty, 100, or 200 millimeters of mercury, and hypotension was induced with sodium nitroprusside. Compression was maintained for two hours, and a ninety-minute period of recovery followed. The nerve-roots were monitored electrophysiologically throughout the experiment. To assess the effect of compression and hypotension on the function of the nerve-roots, values of afferent and efferent amplitude and nerve-conduction velocity were compared with values in twenty adult miniature pigs that had similar graded compression without hypotension. Hypotension significantly affected efferent and afferent amplitudes at the end of the compression period; the effect remained significant at the end of the recovery period. The most profound effect of hypotension occurred during compression at fifty millimeters of mercury--a pressure that had no effect on the function of the nerves in normotensive animals.