Postnatal maturation of baroreflex heart rate control in neonatal swine.
OBJECTIVE
Despite extensive knowledge about basic baroreceptor function, there continues to be controversy as to whether there is postnatal maturation of the cardiovascular baroreflex. DESIGN/ANIMALS: Acutely studied postnatal developmental changes in baroreflex sensitivity with a neonatal porcine model in 28 chloralose-anesthetized piglets from birth to six weeks of age.


METHODS
Steady-state heart rate versus blood pressure response curves were generated by altering blood pressure with increasing doses of phenylephrine or nitroprusside. Data were fitted to the Hill equation for sigmoidal curves, and the maximum heart rate, maximum slope (sensitivity) and blood pressure at 50% maximal heart rate (P50) were calculated.


RESULTS
Baroreflex sensitivity was found to increase from birth to six weeks of age (P < 0.0001), with the most rapid changes occurring after two weeks of age. Increasing age was accompanied by shift of the baroresponse curve to an increased range of heart rate changes at higher blood pressures. Maximal heart rates did not differ with advancing postnatal age.


CONCLUSIONS
Swine baroreflex sensitivity increases from birth to six weeks of age, with higher blood pressures causing greater bradycardia in older piglets. These findings are consistent with postnatal maturation of the cardiovascular autonomic nervous system.
Patton
D J
DJ
Department of Pediatric Cardiology, Izaak Walton Killam Children's Hospital, Halifax, Nova Scotia.
Hanna
B D
BD
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001341:Autonomic Nervous System / Q000187:drug effects / Q000254:growth & development; D017704:Baroreflex / Q000187:drug effects / Q000502:physiology*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D001919:Bradycardia / Q000209:etiology / Q000503:physiopathology; D002319:Cardiovascular System / Q000187:drug effects / Q000254:growth & development*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D016014:Linear Models; D016015:Logistic Models; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D013552:Swine
D009599:Nitroprusside; D010656:Phenylephrine