Spontaneous mechanical activities of dog trachealis muscle in vivo

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Abstract
Isometric strain gauge arches attached transversely and longitudinally to cervical trachealis muscle (CTM) recorded spontaneous mechanical activities (SMA), passive constriction and longitudinal tension in 64 dogs anesthetized with pentobarbital. Inspiratory tracheal elongation increased longitudinal tension and passively constricted CTM. Occasional overlapping of tracheal cartilages observed on initial exposure of cervical trachea appeared to be due to unprovoked persistent increases in SMA. Three major types of rhythmic SMA oscillations occurred in 42 lightly anesthetized dogs: slow oscillations 50-200 s/cycle (19 dogs); sine-like waves 20-30 s/cycle (12 dogs); and sine-like waves superimposed on slow oscillations (11 dogs). These rhythms were dampened by pharmacologically induced increases or decreases in SMA. They disappeared following deeper anesthesia, atropinization or bilateral vagotomy. I.v. acetylcholine increased while isoproterenol decreased SMA before and after bilateral vagotomy in spontaneously breathing dogs and in artificially ventilated, curarized dogs whose tracheas were isolated in situ. Atropine blocked acetylcholine actions and propranolol blocked those of isoproterenol. Changes in SMA induced pharmacologically did not correlate with simultaneous alterations in systemic arterial pressure or ventilatory patterns.