Correlation of Laryngeal Chemoreflex Severity With Laryngeal Muscle Response

Abstract

Objectives: To examine the relationship between the severity of the laryngeal chemoreflex (LCR) and the pattern of laryngeal muscle activity during an LCR‐induced apnea. Methods: The laryngeal mucosa of 20 piglets aged 17 to 20 days was stimulated under both hypoxic and normoxic conditions. Respiration, blood pressure, and activity of the thyroarytenoid (TA) and posterior cricoarytenoid (PCA) muscles were monitored during the LCR‐induced apnea. Results: Hypoxemia resulted in a shorter average apnea duration but a greater degree of hypotension. All piglets recovered spontaneously following normoxic LCR stimulation. Hypoxic stimulation resulted in two divergent apneic responses: transient with a spontaneous recovery (17 piglets) or profound requiring resuscitation (three piglets). An increase in TA muscle activity and a decrease in PCA muscle activity was the most common response to LCR stimulation. The response of the TA and PCA muscles was maintained in piglets destined for spontaneous recovery. Decreasing TA activity and increasing PCA activity correlated with the development of a profound response. Conclusions: The piglet demonstrates two distinct responses to hypoxic laryngeal chemostimulation that correlate with the activity of the intrinsic laryngeal muscles. Failure to maintain the activity of the TA and PCA muscles during a profound response is associated with the development of severe cardiovascular instability. This study suggests that the critical event involving the LCR is the development of complications secondary to hypoxia.

Effects of Intralaryngeal Carbon Dioxide and Acetazolamide on the Laryngeal Chemoreflex

“…However, profound or fatal apneas are more common under hypoxic conditions. 18 The results of the present study show that laryngeal stimulation during hypoxia (Pa02 of 50 to 65 mm Hg) results in a decrease in mean apnea duration and that a higher level of oxygénation before laryngeal stimulation results in a higher Pa02 level at the end of the apneic response. Despite this effect on apnea duration and recovery Pa02 level, hypoxia as defined in this study (mean prestimulation Pa02 level of 58.5 versus 82.5 mm Hg) did not affect the ability to recover from the apneic response without assistance.…”

Differential development of 5‐HT receptor and the serotonin transporter binding in the human infant medulla

“…In experimental animals this nucleus receives significant innervation from the 5-HT neurons of the caudal raphé, i.e., RPa, ROb, and to a lesser extent, RMg (Bago et al, 2002;Li et al, 1993;Manaker and Tischler, 1993), but does not contain any 5-HT neuronal cell bodies. Furthermore, HG motoneurons are stimulated by firing of the raphé 5-HT neurons (Fornal et al, 1996;Jacobs and Azmitia, 1992;Jacobs and Fornal, 1993;Veasey et al, 1995), and by 5-HT both in vitro (Arita and Ochiishi, 1991;Berger et al, 1992;Kubin et al, 1992) and in vivo, enhancing upper airway flow (Goding, 1998). The HG nucleus displays a progressive increase in volume, but not cell number, with increasing postnatal age in both humans (Nara et al, 1989) and experimental animals (Berger et al, 1992;O'Kusky, 1998).…”

Determinants of Fatal Apnea Responses to Acid Stimulation of the Larynx in Piglets

“…[1][2][3][4] In some animals, the response can last longer, resulting in severe hypoxia and potentially death. [14][15][16][17][18] The physiological determinants of response severity are still unknown. Specifically, it has been observed that two young animals that undergo laryngeal chemostimulation under seemingly similar physiologic conditions can have marked differences in response severity.…”

“…Specifically, it has been observed that two young animals that undergo laryngeal chemostimulation under seemingly similar physiologic conditions can have marked differences in response severity. 10,[14][15][16][17] Some animals may recover uneventfully, and others may have profound or fatal responses. When laryngeal stimulation is performed under hypoxic conditions, one of two responses has been observed: a shorter, more transient response or a more profound, fatal response.l'' It has been shown that when laryngeal stimulation is performed under normoxic conditions, resumption of respiration occurs when the PaC02 reaches a certain threshold.l'' In that study, severity of response, as defined by apnea duration, was associated with the Pa02 at the time respiration was resumed.…”