Fatigue resistance of canine vocal fold muscle

The objective of the experiment was to provide data from dogs, the best nonprimate model for the contractile properties of laryngeal muscles, on the fatigue characteristics of vocal fold muscle. Isometric muscle force was recorded from a transducer attached to the section of the thyroid cartilage on which the muscle inserted. Twitch contractions were recorded during supramaximal indirect electrical stimulation by DC pulses for at least 30 minutes. At 5 pulses per second (p/s), potentiation was observed in all records, peaking at an average of 7.5 minutes after stimulation onset. At 10 p/s, the peak of the potentiated average trace was earlier. One third of these records did not show potentiation. Where moderate or large potentiation was observed, the peak twitch tension declined and reached an asymptote above the initial tension, while when potentiation was small or absent, the final force was smaller than initially. Canine vocal fold muscle was observed to be fatigue-resistant, but in phonation other factors may produce fatigue.