Postnatal development of heart rate (HR), mean aortic pressure and arterial flow responses to carotid baroreceptor stimulation (CS) or inhibition (BCCO), and to sciatic nerve stimulation (SNS), was studied in 60 newborn piglets under halothane-N2O anesthesia. There was no HR change in most piglets during CS or BCCO, but tachycardia was observed during high frequency or intensity SNS and after bilateral vagotomy. In younger animals, smaller pressor effects were observed during high frequency or intensity SNS than in older ones. There were also age-dependent changes in femoral and renal flows and resistances to CS, BCCO, SNS or bilateral vagotomy. The results indicate postnatal maturation of regulatory mechanisms for HR and peripheral flow.
Regional blood flow changes in response to hypercapnia, hemorrhage, and sciatic nerve stimulation were studied in 22 newborn piglets. Femoral, renal and/or carotid arterial flows were recorded simultaneously with aortic pressure and heart rate in piglets lightly anesthetized with halothane. Observations were made while ventilation was regulated to maintain arterial pH and pCO2 within the normal range, and when ventilation was adjusted to produce increased pCO2 and decreased pH uncomplicated by hypoxia. The ability of the neonate to respond to low or high frequency and intensity sciatic nerve stimulation was studied during control, hypercapnia, and hypercapnia complicated by hemorrhage. The results indicate immaturity of the mechanisms normally utilized to compensate for these stresses.
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