Experimental Study of Laryngeal Chemoreflex in Puppies

Park, Han Q; Kim, Kwang Moon; Hong, Won Pyo; Kim, Young Ho; Kim, Myung Sang; Kim, Dong Young

Abstract

BACKGROUND AND OBJECTIVES: Mechanical or chemical stimulation of the supraglottic mucosa may result in either or both of two responses: the laryngeal adductor reflex response (LAR), which causes glottic closure, and the laryngeal chemoreflex (LCR), which results in centrally mediated apnea, hemodynamic instability and swallowing. Exaggeration of this normally protective reflexes is thought to be responsible for several disorders, including the sudden infant death syndrome (SIDS).
MATERIALS AND METHODS
The supraglottic laryngeal mucosa which was topically stimulated by saline, distilled water, cow's milk and acid at pH 1.0 was introduced in 14 anesthetized puppies of three different age groups. In group I, four puppies were 2-weeks-of-age, and in group II and III, five puppies were 4 and 6-weeks-of-age, respectively. RESULT: 1) Strong acid (pH 1.0) induced the LCR response.20) After stimulating, respiration was depressed initially, followed by later hyperventilation. We found strong contraction or laryngospasm of thyroarytenoid (TA) muscle after a short period of latency. 3) Respiration was not, or minimally depressed in group I. Moderate depression or apnea was elicited in group II and III. 4) After stimulating, the heart rate was reduced, but it had no statistical meaning. 5) We found 3 types of TA muscle contraction pattern. Type I showed no laryngospasm, but large contraction wave was noted by EMG. Type II showed no laryngospasm, but strong contraction was noted initially and followed by some large waves by EMG. Type III showed laryngospasm that was visible to the naked eye and by EMG. 6) Peak to peak amplitude differences of TA muscle were significantly increased statistically in all age groups.
CONCLUSION
We suggest that the LCR is an age-dependent response which is absent in very young puppies before 2 weeks and appears after that age. Thus, it has important implications that postnatal neural maturation may influence laryngeal reflex to some extent.