Effect of acute compartmental pressure change on response to vibratory stimuli in primates.

This study investigated the possibility that a vibratory stimulus could discriminate the effect of relatively low pressures on nerve function in an acute compartmental syndrome in a primate model. The first phase of the study utilized somatosensory-evoked potentials to determine the outcome of varying pressures in an acute carpal tunnel syndrome in the anesthetized monkey. For increasing carpal tunnel pressures above 30 mmHg, the amplitude of the compound action potential of the A beta wave (touch fiber) generated in the median nerve by an electric stimulus to the index finger progressively decreased to a complete conduction block. It took progressively less time to achieve the conduction block at higher compartmental pressures. When compartmental pressure was released, the time required for the conduction block to return to normal was in direct relationship to the time required to complete the block. For carpal tunnel pressure between 15 and 30 mmHg, an increase in the height of this compound action potential was observed. The second phase of the study utilized the perceptual judgments of an awake monkey trained to discriminate differences in amplitude of a 10-Hz vibratory stimulus to the hairs of the dorsum of the foot. An anterior compartment pressure of 37 mmHg for 1 1/2 hours significantly decreased the monkey's ability to discriminate between the two amplitudes. At 50 mmHg in the anterior compartment, ability to discriminate between vibratory stimuli was further impaired. This study supports the use of noninvasive vibratory stimuli, such as a tuning fork, to evaluate acute compartmental syndromes.