MUSCLE FIBRE DIAMETER AND SENSITIVITY TO NEUROMUSCULAR BLOCKING DRUGS

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Abstract
In order to in vestigate the relationship between muscle fibre composition or size and muscle sensitivity to neuromuscular blocking drugs, data on the fibre composition and size of the ulnaris laterails, thyroarytenoideus, cricoarytenoideus dorsails and diaphragm muscles of the goat were related to the rate of reco very of these muscles from suxamethonium or vecuronium block. Muscle sen sitivity (time to spontaneous 25% recovery of evoked EMG response after 100% block) correlated well with fibre size, the association being significant for the diameter of type I (r≥0.94; P≤0.016) and types I and II fibres taken together (r≥0.95; P≤0.0 13), but not for type II fibre diameter (r≤0.83; P≥0.084), for both suxamethonium and vecuronium. There was no association between the composition of types I or II fibres in these muscles and sensitivity (r≤0.37; P≥0.546). This suggests that muscle sensitivity to both depolarizing and non-depolarizing drugs increases with fibre size, and may account partly for the unequal sensitivities of different muscles. (Br. J. Anaesth. 1993; 71: 732–733)

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