Motor paralysis during asphyxial block of the ulnar nerve

During blocks of the ulnar nerve induced by inflating a sphygmomanometer cuff round the arm, the strengths of the movements of ulnar deviation of the individual fingers and adduction of the thumb were measured by means of a pressure transducer. No statistically significant differences were found between the times at which failure of these movements occurred, and there was no evidence of the occurrence of a centripetal motor paralysis within the territory of the ulnar nerve in the hand. However, the flexor carpi ulnaris did not become paralysed until significantly later than the small muscles of the hand. The results do not support the idea that long motor fibres are more susceptible to asphyxia than short ones, at least when the difference in length is 4 cm or less. Such a theory could certainly explain the relative immunity of the flexor carpi ulnaris, but other explanations for this finding may be available.