Effect of a second laryngeal stimulation during recovery from the laryngeal chemoreflex

The laryngeal chemoreflex is a potential mechanism for sudden infant death. In experimental protocols in which a full recovery is allowed between stimuli, no laryngeal chemoreflex responses result in a fatal outcome. In the clinical situation there are no controls to prevent repeated laryngeal stimulation before a full recovery. The effect of a laryngeal stimulus applied during or soon after a laryngeal chemoreflex-induced apnea was investigated. Eighteen piglets were divided into groups aged 10 to 12 days, 17 to 21 days, and 32 to 36 days. Laryngeal stimulation was performed under normoxic conditions with water applied to the mucosa. Baseline respiratory and cardiovascular response data were measured. After recovery an initial stimulation was applied, followed by a second stimulation during the apnea or 5, 30, 60, or 120 seconds after restoration of breathing. No profound apneas occurred with baseline laryngeal stimulation. In piglets aged 32 to 36 and 17 to 21 days, a second laryngeal stimulus resulted in a shortened apnea duration. The response varied in piglets aged 10 to 12 days with profound apneas observed in 2 of 6 subjects and 4 of 30 trials. Piglets aged 17 to 36 days are less susceptible to the laryngeal chemoreflex during the immediate recovery period. In piglets aged 10 to 12 days, the laryngeal chemoreflex response may be more severe after a second stimulus.