Continuous wave Doppler ultrasound in evaluation of cerebral blood flow in neonates

Augmented Velocity Index: A New Doppler Index Associated with Arterial Stiffness

Augmented Velocity Index (Avi) is a new Doppler index developed to quantify velocity changes at the late systolic peak. We examined its reliability, association with arterial stiffness and cardiovascular risk factors. The Avi is calculated as (late systolic peak velocity - early systolic peak velocity)/(highest peak systolic velocity - end-diastolic velocity). Fifty volunteers (mean age ± standard deviation: 43.5 ± 14.2 y, men: 52%) without known medical illnesses or drug use were recruited. Carotid Doppler waveforms with measurements of Avi were recorded. Carotid pressure waveforms were obtained by applanation tonometry for measurement of the Augmentation Index (AI). Clinical measurements including body mass index (BMI) and blood pressure (BP) were assessed, and fasting blood was taken for measurement of glycemia and lipid profile. Another 15 volunteers (age range: 22-60 y, men: 33.3%) were recruited to study the reliability of Avi measurement. The results revealed that carotid Avi closely correlated with the index of arterial stiffness, AI (r = 0.76, p < 0.001) on Pearson correlation. On multiple linear regression analysis, Avi remained a significant independent determinant of AI after adjustments for clinical variables. The Avi had significant associations with cardiovascular risk factors (age, BMI, total cholesterol, low-density lipoprotein cholesterol, systolic and diastolic BP). The intra-class correlation coefficients for inter-observer and intra-observer reliability of Avi measurements were 0.93 (95% confidence interval [CI]: 0.8-0.98) and 0.97 (95% CI: 0.92-0.99) respectively. In conclusion, the Avi is a reproducible new Doppler index, independently associated with arterial stiffness in terms of the AI, which initially correlated with cardiovascular risk factors.

Resistive indices of cerebral arteries in very preterm infants: values throughout stay in the neonatal intensive care unit and impact of patent ductus arteriosus

BACKGROUND

Little is known about cerebral artery resistive index values in infants born extremely preterm.

OBJECTIVE

To report resistive index values in various cerebral arteries in a prospective cohort of preterm infants born at <29 weeks' gestation, and to compare resistive index in these arteries and assess the relationship between resistive index and hemodynamically significant patent ductus arteriosus.

MATERIALS AND METHODS

Using Doppler imaging, we obtained resistive index values of internal carotid arteries, basilar artery, anterior cerebral artery, and pial and striatal arteries in the first 3 days of age and weekly thereafter until discharge or death. We analyzed paired observations using the Wilcoxon signed-rank test, between-group comparisons with the Mann-Whitney test.

RESULTS

We performed 771 examinations in 235 infants. Resistive indices differed among arteries: vessels with larger diameters showed significantly higher resistive indices. Resistive index in infants without patent ductus arteriosus was lower than that in infants with hemodynamically significant patent ductus arteriosus (median in anterior cerebral artery: 0.75 and 0.82, respectively; P<0.001), though this was not statistically significant in all arteries. There was no difference in pre- and post-ligation resistive indices in infants who underwent patent ductus arteriosus ligation.

CONCLUSION

For accurate follow-up and comparison of cerebral artery resistive index, the same artery should be examined on each occasion.

State of the art cranial ultrasound imaging in neonates

Cranial ultrasound (CUS) is a reputable tool for brain imaging in critically ill neonates. It is safe, relatively cheap and easy to use, even when a patient is unstable. In addition it is radiation-free and allows serial imaging. CUS possibilities have steadily expanded. However, in many neonatal intensive care units, these possibilities are not optimally used. We present a comprehensive approach for neonatal CUS, focusing on optimal settings, different probes, multiple acoustic windows and Doppler techniques. This approach is suited for both routine clinical practice and research purposes. In a live demonstration, we show how this technique is performed in the neonatal intensive care unit. Using optimal settings and probes allows for better imaging quality and improves the diagnostic value of CUS in experienced hands. Traditionally, images are obtained through the anterior fontanel. Use of supplemental acoustic windows (lambdoid, mastoid, and lateral fontanels) improves detection of brain injury. Adding Doppler studies allows screening of patency of large intracranial arteries and veins. Flow velocities and indices can be obtained. Doppler CUS offers the possibility of detecting cerebral sinovenous thrombosis at an early stage, creating a window for therapeutic intervention prior to thrombosis-induced tissue damage. Equipment, data storage and safety aspects are also addressed.

Effect of head position to the cerebral arterial flow in neonates

The objective of this study is to determine the difference of the flow velocities of left and right cerebral arteries. We also studied the effect of head position to the cerebral arterial flow velocities. Eligible for inclusion in this study were 60 neonatal infants whose gestational age was 33.1+/-3.5 weeks and whose birth weight was 1793+/-613 g. The ultrasonographic examinations were performed in the first and second weeks after birth. In an axial scan through a temporal window, the Doppler sample volume was positioned at the center of the M1 portion of the middle cerebral artery and the flow velocity curve was detected. No statistical difference was seen in the flow velocities between the left and right middle cerebral arteries. However, the flow velocities in the upper side were significantly higher than those in the lower side. RI in the upper side was significantly smaller than that in the lower one. This change of flow velocities stabilized in 5 min after the head was turned upside down. The effect of head positioning to the intracranial blood flow must be considered when cerebral ultrasonography of neonates is performed.

Haemodynamic responses and population pharmacokinetics of midazolam following administration to ventilated, preterm neonates

OBJECTIVE

To evaluate the effects of intravenous midazolam on haemodynamic variables and cerebral blood flow velocity (CBFV) and to determine the pharmacokinetics using a population approach in very low birthweight (VLBW) ventilated infants.

METHODOLOGY

Physiological variables were measured at predetermined times in 10 infants with birthweight < or = 1500 g following a bolus dose of intravenous midazolam (0.1 mg/kg). Heart rate, mean arterial blood pressure (MAP) and transcutaneous CO2 (TcPCO2) were recorded and CBFV was assessed by Doppler ultrasound. Midazolam concentrations were also measured and pharmacokinetic parameters determined using a population modelling package.

RESULTS

No change in heart rate occurred during the study period, while the MAP decreased by 3 mmHg 5 min after midazolam administration compared to baseline values. A non-significant fall in TcPCO2 was seen at 20 min. Mean CBFV decreased from the baseline by 12% at 5 min, then returning to predose values. Midazolam concentrations were in the range shown to be effective in sedation of paediatric intensive care infants with the elimination being delayed in comparison to older children.

CONCLUSIONS

As only minor cerebral and haemodynamic effects were found with the use of midazolam in stable ventilated preterm infants, it appears to be a safe, short-term sedative agent.

Normal developmental changes in carotid arterial blood flow measured by Doppler flowmetry in children

We examined the developmental changes in carotid arterial blood flow in a group of neonates, infants, and children using a Doppler flowmeter. The mean, maximum and minimum carotid arterial blood flow (CABF) were measured serially in 35 healthy newborns during the first 5 days of life (total 175 records), and in 62 healthy children aged 1 month to 13 years. In newborns, the mean CABF increased significantly on the second day of life, while the maximum and minimum CABFs increased significantly every day during the first 3 days of life. The mean, maximum, and minimum CABFs increased steadily and significantly in those older than 1 month but reached a plateau after 2 to 4 years of age. Our results indicate that CABF changes with age in early life, reflecting a change in cardiac contraction and carotid-cerebral circulatory system. The measurement of CABF by Doppler flowmetry may be useful for examining cardiac and carotid-cerebral circulatory disorder.

Developmental change in carotid artery blood flow waveform by component analysis in children

The carotid artery blood flow waveform (CABFW) is regarded as a summation of cardiac impulse responses. These impulse responses are divided into several components through a two-dimensional autoregressive modelling approach. Using this approach, we determined the developmental change in CABFW in 94 normal subjects from the neonatal period to adolescence. Our analysis demonstrated that: (i) the total power of impulse response increased significantly with increasing age. The component of impulse response was divided into six groups according to the damping frequency: group I (0 Hz), group II (1-5 Hz), group III (5-8 Hz), group IV (8-13 Hz), group V (13-17 Hz) and group VI (> 17 Hz); (ii) the power-density and the damping time of group I and II impulse response increased significantly with increasing age; (iii) the power-density and percent power of group III impulse response and power-density of group IV impulse response increased significantly with increasing age. Our results indicated that CABFW contained some regular impulses and that group I, II, III and IV, which were influenced by several factors, including cardiac contraction and the compliance and frictional forces of the carotid artery, appeared to be important to the developmental change of CABFW in children.

Effect of fetal brainsparing on the early neonatal cerebral circulation

The effect of antenatal brainsparing on subsequent neonatal cerebral blood flow velocity (CBFV) was studied in very preterm infants. CBFV was determined, using a pulsed Doppler technique, both in the fetal and neonatal period. Neonatally, blood pressure and transcutaneous carbon dioxide tension (TcPCO2) was monitored simultaneously; daily cranial ultrasound examinations were performed. In infants with evidence of brainsparing a higher mean value of CBFV and a different pattern of changes of CBFV during the first week of life was demonstrated compared with infants with normal fetal cerebral haemodynamics. No differences were found in blood pressure and TcPCO2. The incidence of intracranial haemorrhages and of ischaemic echo-dense lesions was also the same for both groups. In a multivariate statistical model gestational age, antepartum brainsparing, and TcPCO2 all contributed significantly in explanation of variation in CBFV. It is speculated that a different setting of cerebral autoregulation related to differences in gestational age or to brainsparing might explain the difference in changes found in neonatal CBFV.

Early postnatal cerebral Doppler changes in relation to birth weight

Serial Doppler studies of the anterior cerebral artery were performed on 50 healthy term infants in the first 5 days of life. This study aims to establish a normative database for cerebral Doppler measurements in infants born appropriate for gestational age (AGA) and to compare them with those born small for gestational age (SGA). The difference between SGA and AGA infants was documented. In AGA infants, the Pourcelot's resistance index (PI) decreased over the first 5 days, while both the peak systolic flow velocity and end diastolic flow velocity increased. In SGA infants, the PI was significantly lower in the first 24 h of life. This was accounted for by an increase in the end diastolic flow velocity which may be a continuation of the intrauterine situation. The significance of the difference is discussed.

Neonatal cerebral Doppler flow velocity waveforms in the uncomplicated pre-term infant: reference values

In a longitudinal study of 217 infants delivering at < 37 completed weeks gestation, Doppler flow velocity waveforms were obtained and resistance index (RI) values calculated from the middle (MCA) and anterior (ACA) cerebral arteries during the first 10 days of life. One hundred thirty-seven of these infants were non-acidotic at delivery and during the early neonatal period, and had normal cerebral ultrasound scans throughout the study period. These infants formed the reference group. In three gestational subgroups considered (< or = 32 weeks, 33-34 weeks, > or = 35 weeks) from the reference group, the median RI for both the ACA and MCA was noted to fall significantly during the first 12 h of life (P < 0.01 for all groups). For infants delivering at > or = 33 weeks gestation, both MCA and ACA RI values reached a steady state with no significant change in the median value for the remainder of the study period. For infants delivering at < or = 32 weeks, there was a further significant fall in both the MCA and ACA RI between 12 and 24 h of life (P < 0.05), after which a steady state value was reached. During the first 12 h of life the RI for both vessels was significantly higher in infants delivering at < or = 32 weeks compared to the more mature infants (P < 0.01), but for the remainder of the study period, there were no significant differences in RI values between the gestational subgroups.(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler velocimetry in cerebral vessels of small for gestational age infants

Using the duplex Doppler system, blood velocity was measured serially at two sites of the anterior cerebral artery (ACA) and in the middle cerebral artery (MCA) during the first 3 days of life, in eight term, small for gestational age (SGA) infants (birthweight, 2179 +/- 230 g; mean +/- S.D.), and 13 term, appropriate for gestational age (AGA) infants (3376 +/- 441 g). All infants in both groups had normal Apgar scores and none manifested signs of respiratory distress. At 1 h post partum, the average MCA mean velocity in the SGA group (25.8 +/- 6.9 cm/s) was higher than that in the AGA group (19.6 +/- 5.7 cm/s), whereas the average values of the two ACA sites did not differ between the groups. A significantly increased value of the average mean velocity as compared to the value at 4 h post partum was reached earlier in the AGA group at all three vessel sites. The pulsatility index (as defined by Gosling) was lower at all vessel sites up to 72 h in the SGA group. Pulse pressure was significantly lower in the SGA group due to increased diastolic blood pressure. We suggest the results imply a state of cerebral vasodilation in the SGA infants and a poor ability to respond with an increased perfusion in the frontal regions supplied by the ACA. Changes in blood pressure and cerebral haemodynamics appear to exist in SGA infants in the absence of postnatal hypoxia which might explain the vulnerability of the growth-retarded infant to perinatal hypoxia.

Cerebrovascular stability during isoflurane anaesthesia in children

The aims of this study were firstly, to determine the effect of various concentrations of isoflurane on cerebrovascular circulation and secondly, to examine the time-response characteristics of the drug on cerebral blood flow velocity in anaesthetized children. Thirty-two ASA physical status I or II patients aged one to eight years and scheduled for urological surgery were studied. Anaesthesia was induced with thiopentone 5 mg.kg-1 and fentanyl 2 micrograms.kg-1. Muscle relaxation was provided with vercuronium 0.1 mg.kg-1. Tracheal intubation was performed in all cases. Anaesthesia was maintained with isoflurane in a mixture of air and oxygen to produce an inspired oxygen fraction (FIO2) of 0.3. Ventilation was adjusted to maintain normocapnia. A caudal or lumbar epidural catheter was inserted before skin incision and a continuous bupivacaine, without epinephrine, infusion established. During the first part of this study, the initial isoflurane concentration for 24 patients was randomized and age-adjusted to 0.5 MAC, 1.0 MAC, or 1.5 MAC. After steady-state was reached, the subsequent isoflurane MAC concentration was randomized by either raising or lowering it from the initial concentration. In the second part of this study, the time-response effect of isoflurane was examined. Eight patients received 1.0 MAC isoflurane over 90 to 150 min. Temperature, heart rate, and systolic blood pressure were unchanged throughout the study. Cerebral blood flow velocity (CBFV) and resistance index (RI+), a measure of cerebrovascular resistance, were measured in the M1 segment of the middle cerebral artery (MCA) with a 2 MHz transcranial Doppler monitor.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral blood flow velocity in term infants treated with phototherapy

The relationship between phototherapy and changes in the cerebral circulation was studied in 50 jaundiced newborn infants. The aim of the study was to determine whether important alterations in cerebral hemodynamic occur under blue light therapy. Blood flow velocity, i.e., the pulsatility index (PI) and the area under the velocity curve (AUVC), was measured in the anterior cerebral arteries (ACA) using a Duplex scan technique. No prominent changes compromise flow in the ACA. PI and AUVC values were similar during and after phototherapy (p greater than 0.5) suggesting effective cerebral autoregulation in term infants undergoing light treatment for hyperbilirubinemia.

Cerebrovascular responses to carbon dioxide in children anaesthetized with halothane and isoflurane

To determine the effects of isoflurane and halothane on cerebrovascular reactivity to CO2, 30 children aged one to six years were anaesthetized with isoflurane or halothane in an air and oxygen mixture with an FIO2 of 0.3. The end-tidal concentrations (0.5 minimum alveolar concentration (MAC) or 1.0 MAC) of isoflurane or halothane were age-adjusted. After achieving a steady-state at both 0.5 MAC and 1.0 MAC isoflurane and halothane, the end-tidal carbon dioxide tension (PETCO2) was randomly adjusted to 20, 40, or 60 mmHg. Cerebral blood flow velocity (CBFV) and the cerebrovascular resistance index (RI+) in the middle cerebral artery (MCA) were measured by a transcranial Doppler monitor. Three measurements of CBFV and RI+ were obtained at each PETCO2 and isoflurane or halothane concentration. Any rise in the PETCO2 caused an increase in CBFV during both 0.5 MAC (r2 = 0.99 and 0.99) and 1.0 MAC (r2 = 0.96 and 0.95) isoflurane and halothane anaesthesia, respectively (P less than 0.05). The CBFV for isoflurane increased as PETCO2 increased from 20 to 60 mmHg for both 0.5 MAC and 1.0 MAC (P less than 0.05). The CBFV for halothane increased as PETCO2 increased from 20 to 40 mmHg for both 0.5 MAC and 1.0 MAC halothane (P less than 0.05), but did not change as PETCO2 increased from 40 to 60 mmHg for both 0.5 MAC and 1.0 MAC halothane. The RI+ showed an inverse relationship with CBFV at each PETCO2 for 0.5 MAC (r2 = 0.98 and 0.99) and 1.0 MAC (r2 = 0.76 and 0.53) isoflurane and halothane, respectively (P less than 0.05). The CBFV did not differ significantly between 0.5 and 1.0 MAC isoflurane and halothane at corresponding PETCO2 values. The cerebrovascular response to CO2 at 20 mmHg between 0.5 MAC and 1.0 MAC halothane was not significantly different. These data strongly suggest that isoflurane and halothane in doses up to 1.0 MAC do not affect the cerebrovascular reactivity of the MCA to CO2 in anaesthetized, healthy children.

Cerebral blood flow velocities in the anterior cerebral arteries and basilar artery in hydrocephalus before and after treatment

We studied Pourcelot's index (PI), which shows cerebral vascular resistance, in the anterior cerebral arteries and basilar artery, and the PI ratio (Pourcelot's index in the anterior cerebral artery/Pourcelot's index in the basilar artery) in 11 measurements of hydrocephalus. The mean values of PI in the anterior cerebral artery, basilar artery, and the PI ratio before treatment were significantly higher than those after treatment and those in normal infants. Before treatment, the mean PI in the anterior cerebral arteries was significantly higher than the mean PI in the basilar artery. All PI ratios increased to 1.00 or more. After treatment and in normal infants, the mean PI in the anterior cerebral arteries was significantly lower than the mean PI in the basilar artery. All PI ratios decreased to less than 1.00. We believe that the PI ratio is useful to evaluate the need or effect of treatment in hydrocephalus.

Cerebral and abdominal arterial hemodynamics in preterm infants with patent ductus arteriosus

Using Doppler echocardiography we evaluated the effect of ductal shunt flow on the cerebral and abdominal arterial blood flow in 25 preterm infants. Eligible for inclusion in this study were healthy preterm newborn infants. They were divided into two groups based on their gestational age: group A, 33-36 weeks (15 infants) and group B, 28-32 weeks (10 infants). Two-dimensional Doppler echocardiograms were obtained in each infant during the first 8 hours of life and repeated every 6-12 hours until no ductal shunt flow could be detected. Flow in the ductus arteriosus, the basilar artery and the coeliac artery were examined. Closure of the ductus arteriosus occurred significantly later (p less than 0.05) in group B than in group A. Pulsatility indices of flow in the basilar and coeliac arteries were high when the ductus was patent, decreasing to a fixed level with closure. This study suggests that a shunt of the patent ductus arteriosus (PDA) adversely influences the cerebral and abdominal blood flow in preterm infants.

The influence of behavioural states on cerebral blood flow velocity patterns in stable preterm infants

Previous Doppler ultrasound studies assessing cerebral blood flow velocities in the anterior cerebral artery (ACA) among healthy term and preterm infants, showed a widespread range for the calculated flow indices. However, only one of these studies accounted for the infant's behavioural state. In the present study a stable pattern of the cerebral blood flow velocity tracings and of the Pulsatility Index (PI) was observed during state 1, whereas marked fluctuations in cerebral blood flow velocity and PI were found during state 4 or active wakefulness. During state 2, minor variations of cerebral blood flow velocity and PI occurred though tended to be less pronounced than during active wakefulness. Thus at the time of Doppler assessment the cerebral blood flow velocity pattern and its variability will be better understood by taking into account the behavioural state of the infant.

Effects of partial plasma exchange transfusion on cerebral blood flow velocity in polycythaemic preterm, term and small for date newborn infants

Isovolemic haemodilution with plasma was performed in 36 newborn infants with polycythaemia 3h after birth. Continuous wave Doppler ultrasonography was used to study the short and longer term influence of partial plasma exchange transfusion on cerebral blood flow velocity in both the anterior cerebral and mid cerebral arterial system up to 24h after haemodilution. The study group consisted of 11 preterm infants, 12 term infants, and 13 small for date infants. After exchange transfusion peripheral venous haemotocrit decreased from 72.5% to 59.4%. In all experimental groups cerebral blood flow velocity (CBFV) before exchange transfusion was significantly lower (18%-44%) than matched controls, and increased to control levels after exchange transfusion. CBFV improved most in preterm infants. After the transfusion the values were no different from the age-, weight-, sex- and parity-matched control groups, and they remained at this level during the next 24 h. No differences could be found between the anterior and mid-cerebral arterial system. When clinical symptoms were present, they subsided in all infants. In conclusion, partial plasma exchange transfusion has a favourable effect for at least 24 h on cerebral blood flow velocity in newborn infants with polycythaemia.

Intracranial vessels with color Doppler echoencephalography in infants

A technique for imaging of the intracranial vessels in infants was described, which used high resolution, commercially available, color Doppler ultrasonography (real-time two-dimensional Doppler). On 12 normal infants, serial scans were obtained in sagittal, coronal, and axial plains. A large number of intracranial arteries and veins could be clearly demonstrated in real-time, including anterior cerebral artery, pericallosal artery, middle cerebral artery, posterior cerebral artery, basilar artery, communicating artery, internal cerebral vein, inferior and superior sagittal sinuses, great cerebral vein, straight sinus, occipital sinus and transverse sinus. In conclusion, color Doppler examination is useful in the detection of vessels in infants and in the measurement of intracranial blood flow velocity.

Serial measurements of cerebral blood flow velocity in preterm infants during the first 72 hours of life

Serial measurements of cerebral blood flow velocity (CBFV) were made in 29 preterm infants, using continuous wave Doppler ultrasound. CBFV was measured in both anterior cerebral arteries and quantitative measurements of CBFV were determined using the area under the velocity curve. In all ventilated infants, CBFV increased significantly during the first 6 hours of life and continued to increase until 16 hours of age. Thereafter, CBFV remained relatively constant. This increase in CBFV was primarily the result of increased diastolic flow. Three infants who had evidence of intraventricular haemorrhage on cranial ultrasound, had similar CBFV compared with the infants with no evidence of haemorrhage. Two infants died and both demonstrated areas of periventricular leukomalacia at autopsy. These infants had a prolonged period of low CBFV. These measurements provide normal data for ventilated, preterm infants. As previously suggested in term infants, the initial rise in CBFV may be secondary to closure of the ductus although a generalized decrease in peripheral vascular resistance could also be a contributing factor. Fluctuations in CBFV rather than individual readings are probably more important in the genesis of IVH. An episode of significantly reduced CBFV is a poor prognostic sign.

Age dependence of flow velocities in basal cerebral arteries

Flow velocities in the basal cerebral arteries were studied by transcranial Doppler sonography. A longitudinal study was undertaken on 25 healthy newborn babies during the first 20 days of life, and a cross sectional study was performed on 112 healthy children between 1 day and 18 years of age. A rapid linear increase of flow velocities was found within the first 20 days with higher velocities in neonates of higher birth weight and gestational age. Maximal values were recorded at the age of 5 to 6 years. After that the velocities decreased linearly to 70% of their maximum at the age of 18 years. Reference values were derived from the data considering age and birth weight. The increasing flow velocities probably reflect the increasing cerebral blood flow during the first years of life. Our results also support the hypothesis of a decrease in cerebrovascular resistance during infancy. With the technique of transcranial Doppler sonography and the introduced reference values normal and abnormal intracranial flow velocities can now be assessed by non-invasive methods in all paediatric age groups.

Cerebral blood flow velocity in term newborn infants: changes associated with ductal flow

The effects of ductal closure on range-gated pulsed Doppler cerebral blood flow velocity (CBFV) patterns in the internal carotid, anterior cerebral, and middle cerebral arteries were studied in 10 normal term infants (mean birth weight 3302 +/- 294 g (SD) and mean gestational age 39.6 +/- 1.3 weeks). Pulsatility was calculated from flow velocities and used as an estimate of cerebral blood flow (CBF). Ductal closure was associated with a rise in mean blood pressure from 45.0 +/- 4.2 to 51.3 +/- 6.5 mm Hg (P less than 0.05) and a significant decrease in pulsatility in all three vessels (mean = 0.77 +/- 0.07 vs 0.70 +/- 0.05 (P less than 0.02]. Changes in pulsatility were correlated with changes in mean blood pressure (P less than 0.02), providing evidence that systemic blood pressure may influence postnatal cerebral arterial pulsatility indices. We also noted significant differences in the velocity and pulsatility of individual vessels that were independent of blood pressure, suggesting that Doppler flow studies may be useful in describing regional CBF patterns. The temporal association between ductal closure and decreased pulsatility suggests that CBFV patterns reflect ductal shunting in normal term newborn infants. Diastolic runoff and reduced systemic blood pressure in the presence of ductal shunting appear to reduce diastolic flow velocity and increase CBFV pulsatility in normal term infants during the first days of life. Normal mechanisms of cerebral autoregulation compensate for decreased flow with vasodilation; therefore the increased pulsatility associated with ductal shunting may be due to diastolic runoff rather than increased cerebrovascular resistance.

Alterations of intracranial pressure and cerebral blood flow velocity in healthy neonates and their implication in the origin of perinatal brain damage

Intracranial pressure and cerebral blood flow velocity were recorded in term healthy neonates during the first 3 days of life using non-invasive methods (LADD-fontanometry and cw-Doppler sonography). Intracranial pressure increased from 4.0 +/- 2.7 cm H2O to 5.8 +/- 2.7 cm H2O and maximal cerebral blood flow velocity in the anterior cerebral artery (ACA) increased from 33 cm/s to 58 cm/s as calculated from a Doppler shift of 0.63 to 1.10 kHz and vascular resistance decreased between the 1st and 3rd day of life. These alterations could not be demonstrated in the femoral artery. This is in accordance with other registrations obtained by different methods and under various conditions. They allow an explanation of some well known physiological phenomena like alterations of cranial volume and the structure of the bony skull in the first days of life. Furthermore, these physiological variations may have implications for the origin of cerebral damage during the perinatal period, especially of hypoxic-ischaemic encephalopathies.

Aetiological rôle of cerebral blood-flow alterations in development and extension of peri-intraventricular haemorrhage

The aetiology and extension of peri-intraventricular haemorrhage (PIVH) are thought to be related to cerebral blood-flow alterations, and especially to increased cerebral blood-flow and fluctuating velocity of blood-flow. Using transcutaneous Doppler technique, the authors investigated cerebral blood-flow in 60 infants with gestations of less than 34 weeks. Pulsatility index (PI) and area under the velocity curve (AUVC) of the anterior cerebral arteries (ACA) were used as qualitative measures of cerebral blood-flow, and the coefficient of variation of PI and AUVC as indicators of fluctuations in blood-flow velocity. A reasonable correlation was found between PI and AUVC and their coefficients of variation in the ACA. First onset of PIVH was related to fluctuating blood-flow velocity, and extension of PIVH with both increased velocity (indicating increased blood-flow) and fluctuating velocity. Increased cerebral blood-flow and its fluctuating pattern were positively correlated with arterial carbon dioxide tension.

Cerebral blood flow velocity pattern in healthy and asphyxiated newborns: a controlled study

In a controlled study serial determinations of cerebral blood flow velocity using Doppler ultrasound and repeated real-time ultrasonographic- or computerized axial tomographic studies of the brain were performed in 17 (nearly) full-term newborns who experienced perinatal asphyxia and in 17 healthy matched controls during the first week of life. A higher cerebral blood flow velocity was found during the first 4 days of life, indicating a lower cerebrovascular resistance in the asphyxiated infants compared to the control infants. These haemodynamic changes coincided with cerebral oedema and neurological abnormalities. It is speculated that the changes in the cerebral circulation in asphyxiated infants are at least partly caused by cerebral oedema-induced increase of intracranial pressure due to severe perinatal asphyxia. Serial Doppler ultrasound investigations of the brain may be a useful non-invasive method for early detection and follow-up of the consequences of severe perinatal asphyxia.

Neurodevelopmental outcome and school performance of very-low-birth-weight infants at 8 years of age

The neurodevelopmental outcome and school performance of 50 appropriate for gestational age (AGA) and 33 small for gestational age (SGA) very-low-birth-weight (VLBW) infants, compared to a control group (41 Term infants) were assessed at 8 years of age. The incidence of major handicaps among AGA and SGA/VLBW infants respectively, was 16% and 6%. No major handicap was found in the control group. The incidence of neurodevelopmental abnormalities (NDA) among AGA's (40%) and SGA's (57.6%) compared with the control group (31.7%) was found to be significantly higher. School failure occurred more frequently among VLBW infants (22.9%) and was related in children with NDA--and more particularly among AGA's--to the presence of language disorders or associated NDA. Evaluation of the consequences of NDA and school problems for later academic and professional achievement now requires further follow-up studies.

Decreased cerebrovascular resistance in small for gestational age infants

Using a transcutaneous Doppler technique we found a significantly lower cerebrovascular resistance and higher cerebral blood flow velocity indicating vasodilatation and increase of cerebral blood flow in small for gestational age infants compared with appropriate for gestational age infants during the first days of life. We speculate that these findings are due to a continuation of the fetal situation in which chronic hypoxia, mostly caused by pregnancy-induced hypertension, possibly causes a prostacyclin-induced vasodilatation.

Reproducibility of intracranial Doppler flow velocimetry

Doppler velocimetry for assessment of flow in deep cerebral arteries was investigated in 9 term and 11 preterm healthy infants. A combined range gated and continuous wave Doppler instrument was used. A satisfactory reproducibility was found with a variation coefficient of 8-10% between repeated measurements. No systematic difference between examiners or head positions was recorded. The term infants had significantly higher mean flow velocities, 21.1 (3.1) cm/s (mean and 1 SD), compared to the preterm infants', 15.1 (3.6) cm/s (p less than 0.01). Both systolic and diastolic flow velocities were higher in the term infants, whereas the pulsatility index was higher in the preterm infants. Recordings from the intracranial part of the internal carotid arteries were found to be easy to obtain with a satisfactory reproducibility.

Doppler ultrasound examination of the anterior cerebral arteries of normal newborn infants: the effect of postnatal age

Twenty-four normal term infants were examined by Doppler ultrasonography of the anterior cerebral arteries at least twice in the first 5 days of life. It was found by comparison with a duplex Doppler unit that the anterior cerebral arteries could be reliably insonated using a continuous wave Doppler ultrasound probe without the concomitant use of real time ultrasound sector scanning. It was shown that the pulsatility of the velocity waveform decreased and that diastolic frequency increased over the 5 days. The significance of, and possible mechanism for, this change is discussed.