Prolonged dynamic changes in autonomic heart rate modulation induced by acid laryngeal stimulation in non-sedated lambs.
BACKGROUND
Exaggerated laryngeal chemoreflexes (LCR) have been implicated in the occurrence and prolongation of apnea in premature and term neonates.


OBJECTIVE
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.


CONCLUSIONS
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.
Beuchée
Alain
A
Neonatal Intensive Care Unit, CHU Pontchaillou, Rennes, France. alain.beuchee@chu-rennes.fr
Nsegbe
Elise
E
St Hilaire
Marie
M
Carrault
Guy
G
Branger
Bernard
B
Pladys
Patrick
P
Praud
Jean-Paul
JP
D000818:Animals; D000831:Animals, Newborn; D001049:Apnea / Q000139:chemically induced / Q000503:physiopathology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000502:physiology*; D019343:Citric Acid / Q000008:administration & dosage; D004195:Disease Models, Animal; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D007823:Laryngeal Nerves / Q000187:drug effects / Q000502:physiology*; D007830:Larynx / Q000187:drug effects* / Q000502:physiology; D012018:Reflex / Q000187:drug effects / Q000502:physiology*; D012756:Sheep
D019343:Citric Acid