Cerebral arterial asymmetries in the neonate
AuthorJansen van Vuuren, Anica
AffiliationMelbourne School of Psychological Sciences
Document TypePhD thesis
Access StatusOpen Access
© 2018 Dr. Anica Jansen van Vuuren
In spite of the symmetric embryological origins of many paired anatomical structures, the human body is inherently asymmetric. Adult studies reveal leftward asymmetries in the structure and haemodynamics of supra-aortic extracranial and intracranial vessels. At the level of the carotid arteries, these asymmetries are meaningfully related to hand preference. The existence of an arterial correlate of handedness in adults poses a key question. Do lateral biases in blood supply to the brain arise as a consequence of language acquisition and the emergence of manual dexterity, or do they predate these lateralised functions? In essence, is the ground plan of adult arterial asymmetries discernible in neonates? To our knowledge, this is the first time that neonatal cerebrovasculature has been imaged non-invasively at a sufficient level of resolution to accurately measure vessel diameter and corresponding blood flow. A new transcranial Doppler ultrasonography dual-view scanning protocol, with concurrent B-flow and Pulsed-wave imaging, was used to acquire multivariate data on neonatal middle cerebral arterial structure and function. Detailed diametric measurements were taken of the trunk origin and terminus using RadiAnt DICOM Viewer (64-bit) imaging software. Haemodynamic parameters of the Doppler waveform were recorded, including peak systolic and end-diastolic velocity, resistive index, pulsatility index, and blood flow volume. This dissertation documents significant asymmetries in the middle cerebral artery origin and distal trunk of healthy term neonates (n = 97). A systematic leftward arterial dominance was found in vessel calibre and cortically directed blood flow. The arterial asymmetry was also meaningfully related to the supine head orientation bias, an endogenously driven behaviour that reliably predicts future hand preference. By and large the arterio-postural relationship is characterised by larger arterial diameters and higher blood flow volumes in the left hemisphere of right-postured neonates. Deviations from this typical arterio-postural association begin to unfold increasing lateral heterogeneity in head turning behaviour. In left turning newborns, the coherence of the arterio-postural relationship is dependent on the magnitude of arterial asymmetry across the midline of the brain, and maintenance of these larger arterial diameters from the proximal to distal regions of the right trunk. Commensurately asymmetric haemodynamic vulnerabilities were identified. Endothelial wall shear stress was asymmetric across the midline and varied according to geometric and behavioural lateralisation. Shearing asymmetries systematically disadvantaged left hemispheric endothelium with lower left-than-right peak systolic and end-diastolic endothelial shearing forces in neonates with larger left-sided arteries and with right-sided head postures. Unfavourable shearing forces, which are a by-product of the arterial asymmetries described here, might contribute to a greater risk of cerebrovascular pathology in the left hemisphere in neonates and adults. We conclude that arterial structure and blood supply in the brain are laterally asymmetric in newborns, predating the advent of neurobehavioral expressions of cerebral lateralisation, such as language and manual dexterity. The empirical support for an arterial correlate for lateralised cerebral function has key implications for the understanding of the origins of human cerebral organisation from evolutionary and ontogenetic perspectives.
Keywordsmiddle cerebral artery; arterial diameter; blood flow volume; asymmetry; neonatal; shear stress; healthy term neonates; transcranial Doppler ultrasonography; head posture
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