| IntroductionPreterm infants are particularly vulnerable to hypoxic - ischemic brain injury, alternations of cerebral blood flow(CBF) are considered to be an important pathogenetic mechanism. CBF of a preterm infant is influenced by rapid changes in mean arterial blood pressure (MABP) , arterial carbon dioxide tension (PaCO2) and arterial oxygen tension (PaO2) , and also by variables such as hematocrit( HCT) and hypoglycemia. CBF maintains constant over a given range of MABP , which is called autoregulation of CBF. In healthy preterm infants , there is an intact autoregulation CBF, but no a definite range of MABP at present. Autoregulation of CBF can be impaired in preterm infants after asphyxia, exposing their brains to the effects of hyper -and hypoperfusion, resulting in intracranial hemorrhage ( ICH) and perivetricular leukomalacia ( PVL) respectively. Another important factor mediating CBF is PaC02. CBF increases with the rise of PaCO2, decreases with the reduction of PaCO2. Brain reacts to PaO2 changes by inverse CBF changes, the direct effect of Pa02 is 10 times less than the effect of PaCO2.Although there are many methods for our studying CBF, ultrasound Doppler still has many advantages over other methods. For example, it has no radiation, no invasion, real time monitoring, simpleoperating and so on. It is one of the best ways for studying CBF of newborns.The purpose of this study was to evaluate influence of gestational age(GA) , birth weight (BW) , MABP, PaCO2, PaO2 on CBF variables in preterm infants, and the changes of CBF in asphyxiated pre-term infants, to give help for prevention and treatment of HIBI.Patients and methodsA total of 42 inpatient preterm infants were assessed during Jun to Dec 2001. All the infants were appropriate for GA, who were divided into two groups by the standard of asphyxia. 17 asphyxiated infants with GA 32.9 2. 3W, BW 1960 389g, 25 healthy infants with GA 33. 1 2.0W,BW 1920 405g, who had no neurological, respiratory, circulatory system diseases.The infants with normal body temperature, who were fed at least 30 minutes before the study. The infants kept quite, were placed su-prinely with head in a middle position when we were studying.The velocities of CBF of anterior cerebral artery ( ACA ) and internal carotid artery (IC A) were measured by a Doppler with a 5 MHz probe (Aloka SSD -650 Made in Japan). After we froze the spectrum on the screen, we measured the peak systolic velocity, the end dias-tolic velocity and average velocity, then calculated resistance index ( RI) , pulsitive index ( PI).Every infant was measured for 7 days consecutively from birth. MABP was taken by the cuff pressure oscillation amplitude (Dinamap TM 847) and blood gas was measured by Compact 2 blood gas machine in the first day.Linear regression analysis, t test, student - Newman - Keuls multiple range test were used as appropriated.ResultsIn healthy infants, there was a linear increase of all velocities of ICA and AC A with increasing GA and BW, no correlation between all velocities and MABP, PaC02, Pa02 each other, and there was an obvious increase in Vs and mV of the two arteries over the second day of life, and much higher than that of the first day, Vd of the two arteries also increased with the number of day, but there was no significant difference in 7 days. In contrast to all velocities, neither PI nor RI had no relation to GA, BW, MABP, PaC02, Pa02 respectly. The CBF velocities in the ICA were higher than that in ACA, there were no significant changes in RI and PI of the two arteries.In asphyxiated infants, there was a linear increase of all velocities with MABP, no correlations with the other parameters. In first two days after birth, Vs, Vd, mV reduced, more significant difference compared with those of the normal group. After the third day, Vs, Vd, mV gradually increased, by the normal level on the seventh day.DiscussionThe pathogenesis of HIBI is related to three major interacting factors , which are pressure - passive cerebr...
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