MEASUREMENT OF THE LATERAL THORACIC REFLEX LATENCY IN PONIES

Lateral thoracic nerve reflex latencies values were measured in ponies using a simple, non-invasive technique. The reflex was elicited using an external triggering hammer attached to an electrodiagnostic unit. The resulting evoked, compound muscle action potentials were recorded with electrodes, which were placed over the 6th ribs or 11th rib level with the axilla, Two superimposed repeats of 4 signal-averaged sweeps of 50 or 100 milliseconds were recorded and the estimated reflex path way was measured for each subject in order to calculate the reflex lat encies and latency velocities. Mean left and right Gth rib peak latenc ies were not significantly different from each other (P = .609), but l eft 6th rib latencies were shorter than those recorded from the 11th r ib (P < .0001), substantiating the existence of an indirect (central) pathway to the reflex. The calculated left and right 6th rib latency v elocities were not significantly different from each other (P = .58) b ut left 6th rib latency velocities were different from left 11th rib ( P = .009). The calculated latency velocities were within the broad ran ge for corticospinal tract motor conduction velocities and comparable to magnetic motor evoked latency velocities. The use of lateral thorac ic reflex latency measurements to objectively identify the site of spi nal cord lesions is discussed.