Stimulation of respiratory changes in alae nasi length by chemoreceptor activation

Respiratory-related changes in length of the nasal dilator muscle, the alae nasi muscle, were measured using sonomicrometry in ten anesthetized (pentobarbital), tracheostomized, spontaneously breathing dogs. Piezoelectric crystals were inserted 7-25 mm apart along the direction of the alae nasi muscle fibers, and the effects of progressive hyperoxic hypercapnia and a peripheral and central chemoreceptor stimulant, nicotine (10-500 micrograms intravenously), were ascertained. The alae nasi shortened during inspiration in all animals, started to lengthen again towards the end of inspiration, returned to resting length during the first portion of expiration (Te-1), and remained at resting length for the remainder of expiration (Te-2). The amount of alae nasi inspiratory shortening was increased by occluding the airway for a single breath. Progressive hypercapnia caused progressive increases in the amount and velocity of nasal muscle inspiratory shortening during both unoccluded and occluded breaths; similar stimulatory effects on inspiratory shortening were seen following nicotine administration. Furthermore, both chemoreceptor stimulants caused a delay in the return of the muscle to its resting length during expiration, resulting in a significant increase in Te-1 relative to Te (Te-1/Te), and a greater amount of nasal muscle shortening to be present during Te-1. In some animals these agents also caused tonic shortening of the alae nasi, so that the muscle never returned to its resting length. These results suggest that inspiratory shortening of the alae nasi is inhibited by vagal inputs, but that chemoreceptor activation increases the amount of muscle shortening during both inspiration and early expiration.