Prostaglandin-Angiotensin Interactions for Blood Pressure Regulation

Abstract

Blood pressure (BP) measured on the first day of life varies directly with the gestational age of the infant (1). Arterial BP is the product of blood flow through a vessel, which varies directly with cardiac output, and the resistance to flow, which varies inversely with the crosssectional diameter⁴ of the vessel. Cardiac output can be altered by changes in blood volume (BV), heart rate or stroke volume, but BP in the neonate is predominantly low when BV, cardiac output, heart rate and stroke volume are high relative to the adult (Table). Mean arterial BP divided by cardiac output is the calculated arbitrary value which reflects total peripheral resistance (TPR). In the newborn, TPR is lower than in the adult. In order for the newborn to maintain BP at 40 mmHg if cardiac output were reduced to that of the adult (100 ml/min/kg), TPR must increase from 0.3 to 0.4 units. On the other hand, if BP in the newborn were reduced to 20 mmHg but cardiac output remained unchanged (300ml/min/kg), TPR must decrease to 0.07 units.