The head-down tilt(HDT) position infuses changes in cerebral blood flow, intracranial pressure, hemodynamic and respiratory system. This study was performed to evaluate the changes in cerebral blood flow and the onset of autoregulation according to the different degree of HDT.

The subjects were 12 healthy adult female volunteers. They were divided two groups : 10° HDT(group 1) and 15° HDT(group 2). The systolic, diastolic and mean blood pressure, heart rate, end-tidal CO₂ concentration and cerebral blood flow velocity on middle cerebral artery by transcranial Doppler were measured before positioning and 1,2,3,5,7,9,11 minute after positioning.

There was no significant changes in cerebral blood flow velocities statistically according to the HDT under 15 degrees. In group 1, vean arterial blood pressure were increased at 5 minutes and returned to control value at 7 minutes after HDT with statistical significances. Diastolic blood pressure in group 1 were increased at 1 and 2 minutes after HDT with statistical significances. In froup 2, systolic blood pressure were increased at 5,7,9,11 minutes after HDT statistically significantly.

There were no significant changes of cerebral blood flow under less than 15° HDT. But systolic blood pressure were increased with 15° HDT in the healthy adults statistically significantly(p<0.05) not but clinically. So, we suggested that if HDT is required, we should take care of the partients more than 10 minutes after HDT.

To access the changes of cerebral blood flow velocity according to the time after surfactant administration, we prospectively studied in the Hyaline Membrane Disease using Doppler ultrasonography.

The patients were 26 infants. The mean gestational age was 3l⁴wks (range, 18⁴ to 38wk). The ratio of male : female was 16 : 10, mean weight was 1.76±0.88Kg, Apgar score at 5min was 6.9, and type of delivery was C-section : vaginal delivery 19 : 4. Before and after, 10, 30min, 1, 6, l2hr, 1, 3, 5, 7days after surfactant administration, peak systolic and end-diastolic flow velocity(PSFV, EDFV) were estimated by Doppler method measuring MCA flow velocity. The Resistive index was calculated according to the mathematics. For the evaluation of the clinical status, systolic and diastolic systemic BP, PaO₂, PaCO₂, FiO₂, pH, and respiratory rate(RR) were checked.

The cerebral blood flow velocity showed initial increase of PSFV just after synthetic surfactant administration, and the increased PSFV continued until the 30 minites and then decreased. PSFV returns to initial level at 6hr, and then increased again. The changes of EDFV was not significant. The changes of RI & PI were no significant changes. The effects of surfactant to the systemic BP had no significance. The changes of PaCO₂ and PaO₂ were not significant. FiO₂ showed steady improvement. Initial tachypnea and acidosis progressively improved without clinical significance.

The administration of Surfactant in the HMD patients results in transient increase of cerebral blood flow velocity.