Cerebral vascular resistance in premature infants.

The cerebral vascular bed is a low-resistance system in which continuous forward or advancing diastolic blood flow can be demonstrated. This advancing flow increases progressively with vasodilation and decreases or is absent when vessels are constricted. By using the Doppler technique, an indirect assessment of vascular resistance can be made by comparing systolic and diastolic flow amplitudes. We examined nine premature infants and found that respiratory acidosis alone, or hypoxia and acidosis in combination, resulted in significant vasodilation. This effect was reversible when arterial blood gas tensions returned to normal. The results indicate that within a physiologic range of BPs, premature infants with acute respiratory distress can alter their cerebral vascular resistance in response to spontaneous changes in blood gas tensions.