Integrated cardiovascular responses to combined somatic afferent stimulation in newborn piglets

Heart rate, mean aortic pressure and arterial flow responses to interactions of afferent stimulation of the sciatic (SNS) and median nerve of the brachial plexus (BNS) were studied in 30 newborn piglets under halothane-N2O anesthesia. High frequency or intensity SNS or BNS stimulation resulted in pressor responses accompanied by significant increases in the femoral flow and carotid and renal resistance. Combined stimulation produced responses smaller than the estimated sum of the responses. Low frequency or intensity SNS or BNS resulted in depressor responses accompanied by significant decreases in mean femoral flow without change in heart rate; combined stimulation produced responses smaller than the estimated sum. When pressor and depressor patterns of stimulation were combined, pressor responses always dominated. The absence of facilitation to any combination of interactions implies that the cardiovascular regulatory system is not fully developed at birth and undergoes, therefore, postnatal maturation.