Determinants of fatal apnea responses to acid stimulation of the larynx in piglets

Objectives: This study explores the physiological determinants of laryngeal chemoreflex (LCR) response severity under hypoxic conditions. Methods: Thirty-four piglets underwent hypoxic laryngeal stimulation. Physiologic data were collected, and responses were graded as mild, moderate, or profound. Results: Prestimulation hypoxia caused respiratory depression and carbon dioxide retention in profound responders and respiratory stimulation in mild and moderate responders (p < .05). Resumption of respiration occurred in all animals when the PaCO2 rose by a mean ± SD of 15.1 ± 6.5 mm Hg (p > .05). There was a significant difference between mild, moderate, and severe responders in change in arterial PaO2 and hydrogenated hemoglobin saturation during the LCR-induced response (p < .001 for both). Conclusions: Resumption of respiration is associated with accumulation of arterial PaCO2. The respiratory response to hypoxia predicts the severity of the LCR response. The severity of the LCR-induced response is associated with changes in arterial PaO2 and hydrogenated hemoglobin saturation during the LCR-induced apnea.