CORRELATION OF LARYNGEAL CHEMOREFLEX SEVERITY WITH LARYNGEAL MUSCLE RESPONSE

Objectives: To examine the relationship between the severity of the la ryngeal chemoreflex (LCR) and the pattern of laryngeal muscle activity during an LCR-induced apnea, Methods: The laryngeal mucosa of 20 pigl ets aged 17 to 20 days was stimulated under both hypoxic and normoxic conditions. Respiration, blood pressure, and activity of the thyroaryt enoid (TA) and posterior cricoarytenoid (PCA) muscles were monitored d uring the LCR-induced apnea. Results: Hypoxemia resulted in a shorter average apnea duration but a greater degree of hypotension. All piglet s recovered spontaneously following normoxic LCR stimulation, Hypoxic stimulation resulted in two divergent apneic responses: transient with a spontaneous recovery (17 piglets) or profound requiring resuscitati on (three piglets), An increase in TA muscle activity and a decrease i n PCA muscle activity was the most common response to LCR stimulation. The response of the TA and PCA muscles was maintained in piglets dest ined for spontaneous recovery Decreasing TA activity and increasing PC A activity correlated with the development of a profound response. Con clusions: The piglet demonstrates two distinct responses to hypoxic la ryngeal chemostimulation that correlate with the activity of the intri nsic laryngeal muscles. Failure to maintain the activity of the TA and PCA muscles during a profound response is associated with the develop ment of severe cardiovascular instability. This study suggests that th e critical event involving the LCR is the development of complications secondary to hypoxia.