Prolonged dynamic changes in autonomic heart rate modulation induced by acid laryngeal stimulation in non-sedated lambs.

Abstract

BACKGROUND: Exaggerated laryngeal chemoreflexes (LCR) have been implicated in the occurrence and prolongation of apnea in premature and term neonates. OBJECTIVES: To test the hypothesis that the cardiovascular component of the LCR can occur and be prolonged in the absence of apnea. METHODS: Bolus injections of 0.5 ml of citric acid (CitAc) and serum saline were administered onto the larynx in seven non-sedated lambs, aged 4-5 days, during quiet sleep. Blood pressure (BP) and heart rate (HR) variability measurements were taken and compared with results obtained prior to stimulation and with saline. RESULTS: Apneas were rare and occurred consistently in the 32-beat period (10 s) following stimulation. The increase in BP and decrease in HR were consistent after CitAc and saline. All the studied components of HR variability significantly increased after CitAc, but not after saline. The low frequency estimates were significantly increased during a 480-beat period (133 +/- 6.6 s) following CitAc stimulation. Analysis of gains and respiration showed that bradycardia and HR variability changes were neither related to an apnea nor a vagal arterial baroreflex. CONCLUSION: This long-lasting increase in HR variability indicates a prolonged disturbance of the cardiovascular regulatory systems, consisting in increased sympathetic and parasympathetic tones following CitAc stimulation.