Neonatal cerebral Doppler: arterial and venous flow velocity measurements using color and pulsed Doppler system

Low frequency cerebral arterial and venous flow oscillations in healthy neonates measured by NeoDoppler

BACKGROUND

A cerebroprotective effect of low frequency oscillations (LFO) in cerebral blood flow (CBF) has been suggested in adults, but its significance in neonates is not known. This observational study evaluates normal arterial and venous cerebral blood flow in healthy neonates using NeoDoppler, a novel Doppler ultrasound system which can measure cerebral hemodynamics continuously.

METHOD

Ultrasound Doppler data was collected for 2 h on the first and second day of life in 36 healthy term born neonates. LFO (0.04-0.15 Hz) were extracted from the velocity curve by a bandpass filter. An angle independent LFO index was calculated as the coefficient of variation of the filtered curve. Separate analyses were done for arterial and venous signals, and results were related to postnatal age and behavioral state (asleep or awake).

RESULTS

The paper describes normal physiologic variations of arterial and venous cerebral hemodynamics. Mean (SD) arterial and venous LFO indices (%) were 6.52 (2.55) and 3.91 (2.54) on day one, and 5.60 (1.86) and 3.32 (2.03) on day two. After adjusting for possible confounding factors, the arterial LFO index was estimated to decrease by 0.92 percent points per postnatal day (p < 0.001). The venous LFO index did not change significantly with postnatal age (p = 0.539). Arterial and venous LFO were not notably influenced by behavioral state.

CONCLUSION

The results indicate that arterial LFO decrease during the first 2 days of life in healthy neonates. This decrease most likely represents normal physiological changes related to the transitional period. A similar decrease for venous LFO was not found.

[Normal values of cerebral blood flow velocities in neonates]

INTRODUCTION

There was used color Doppler ultrasonography (cD-USI), allowing simultaneous examination of parenchymal and vascular cerebral structures. The evaluation of blood flow velocities in cerebral arteries is important in the assessment of cerebral circulation in hypoxic-ischaemic and haemorrhagic brain damage in neonates.

OBJECTIVE

The aim of this study was to estimate normal values of cerebral blood flow velocities (CBFV) and Doppler indices--pulsatility index (PI) and resistance index (RI)--in the anterior cerebral artery (ACA) during the first days of life in infants.

METHODS

CBFV, PI and RI were obtained during the first week of life with cD-US in 70 infants divided in four groups of gestational age (GA): < or =28 gestational weeks (GW); 29-32 GW; 33-36 GW; and > or =37 GW. Infants with congenital malformations, severe perinatal asphyxia, cerebral haemorrhagic lesion, DAP or severe hypotension were excluded.

RESULTS

The mean GA of infants was 34.5 +/- 5.5 GW (range 26-40 GW) and the mean birth weight (BW) was 2540 +/- 950 g (range 750-4000 g). In the 1st group of 10 infants, < or =28 GW, the mean BW was 950 +/- 110 g and values of RI were 0.59 +/- 0.10 and PI 1.06 +/- 0.080. In the 2nd group of 20 infants, 29-32 GW, the mean BW was 1350 +/- 290 g and values of RI were 0.60 +/- 0.10 and PI 1.10 +/- 0.15. In the 3rd group of 20 infants, 33-36 GW, the mean BW was 1950 +/- 750 g and values of RI were 0.63 +/- 0.08 and PI 1.15 +/- 0.30. In the 4th group of 20 infants, > or =37 GW, the mean BW was 3540 +/- 950 g and values of RI were 0.65 +/- 0.05 and PI 1.18 +/- 0.35.

CONCLUSION

Values of CBFV progressively increase with GA and BW due to progressive increase of cardiac output, blood pressure and closing of ductus arteriosus. Values of RI and PI gradually increase with GA and BW as a result of progressive maturation and opening of vascular cerebral bed with a reduction of the cerebrovascular resistance.

The effect of preterm birth on neonatal cerebral vasculature studied with magnetic resonance angiography at 3 Tesla

Preterm birth is associated with a high incidence of neurodevelopmental deficits. Magnetic resonance imaging (MRI) has proved to be a valuable tool for monitoring development in the preterm brain. We used a dedicated time-of-flight (TOF) magnetic resonance angiography (MRA) protocol at 3 Tesla (3T) optimized to assess morphological characteristics of the neonatal cerebral vessels associated with preterm birth in a sample of 37 infants. We found statistically significant decreased tortuosity in all proximal segments of the cerebral vasculature (anterior, middle and posterior cerebral arteries) in the preterm infants imaged at term equivalent age compared to the term born infants, with no differences in vessel diameter between the two groups. This distinct phenotype of decreased tortuosity was shown to persist until 18 months of age in longitudinal MRA studies in infants born preterm, suggesting that this is not a delay in maturation. Biparietal head diameter measurements were significantly smaller in the preterm at term infants and were inversely correlated with middle cerebral artery tortuosity measurements in both the term born and the preterm at term infants. To our knowledge, this is the first systematic MRA study on the effect of preterm delivery on neonatal cerebral vasculature. Our intention is to build on the findings of this study by combining the data with other measurements of brain growth and vascular haemodynamics to understand more about the interdependence of vessel and brain development and their relationship to prematurity.