Critical appraisal of cerebral blood flow measured from brain stem and cerebellar regions after 133 Xe inhalation in humans

Cerebrospinal fluid dynamics coupled to the global circulation in holistic setting: Mathematical models, numerical methods and applications

This paper presents a mathematical model of the global, arterio-venous circulation in the entire human body, coupled to a refined description of the cerebrospinal fluid (CSF) dynamics in the craniospinal cavity. The present model represents a substantially revised version of the original Müller-Toro mathematical model. It includes one-dimensional (1D), non-linear systems of partial differential equations for 323 major blood vessels and 85 zero-dimensional, differential-algebraic systems for the remaining components. Highlights include the myogenic mechanism of cerebral blood regulation; refined vasculature for the inner ear, the brainstem and the cerebellum; and viscoelastic, rather than purely elastic, models for all blood vessels, arterial and venous. The derived 1D parabolic systems of partial differential equations for all major vessels are approximated by hyperbolic systems with stiff source terms following a relaxation approach. A major novelty of this paper is the coupling of the circulation, as described, to a refined description of the CSF dynamics in the craniospinal cavity, following Linninger et al. The numerical solution methodology employed to approximate the hyperbolic non-linear systems of partial differential equations with stiff source terms is based on the Arbitrary DERivative Riemann problem finite volume framework, supplemented with a well-balanced formulation, and a local time stepping procedure. The full model is validated through comparison of computational results against published data and bespoke MRI measurements. Then we present two medical applications: (i) transverse sinus stenoses and their relation to Idiopathic Intracranial Hypertension; and (ii) extra-cranial venous strictures and their impact in the inner ear circulation, and its implications for Ménière's disease.

Hyperfrontality of regional cerebral blood flow distribution in normals during resting wakefulness: fact or artifact?

Earlier studies with two-dimensional measurement techniques consistently found higher frontal flow in normal subjects during resting wakefulness. However, this finding could not be confirmed by several laboratories with the more modern and technologically more sophisticated three-dimensional measurement techniques. This discrepancy can have strong implications for psychiatric research in which both types of techniques are frequently used. This article reviews the existing literature, discusses possible reasons for the discrepancy, and evaluates evidence from other sources on the activity of the frontal lobe during wakefulness.

Regional cerebral blood flow characteristics and variations with age in resting normal subjects

Regional cerebral blood flow (rCBF) was measured during resting in 97 normal subjects, 19-68 years old. The results showed that the mean CBF level decreased progressively with age. The decrease was more prominent in frontotemporal and inferior Rolandic areas bilaterally. Frontal areas showed the highest values in all age groups. This hyperfrontality weakened somewhat with age. Mean CBF in the right hemisphere was significantly higher than in the left, as was flow in superior frontal, inferior frontal, and parietal areas. These asymmetries were age invariant. The age-related decrease of rCBF is interpreted as reflecting aging of the brain per se, although the influence of asymptomatic brain disease can not be ruled out. The flow asymmetries are interpreted as being related to functional lateralization of some aspects of attentional activation.

Cerebral blood flow in normal and abnormal sleep and dreaming

Measurements of regional or local cerebral blood flow (CBF) by the xenon-133 inhalation method and stable xenon computerized tomography CBF (CTCBF) method were made during relaxed wakefulness and different stages of REM and non-REM sleep in normal age-matched volunteers, narcoleptics, and sleep apneics. In the awake state, CBF values were reduced in both narcoleptics and sleep apneics in the brainstem and cerebellar regions. During sleep onset, whether REM or stage I-II, CBF values were paradoxically increased in narcoleptics but decreased severely in sleep apneics, while in normal volunteers they became diffusely but more moderately decreased. In REM sleep and dreaming CBF values greatly increased, particularly in right temporo-parietal regions in subjects experiencing both visual and auditory dreaming.

Noninvasive method of estimating human newborn regional cerebral blood flow

A noninvasive method of estimating regional cerebral blood flow (rCBF) in premature and full-term babies has been developed. Based on a modification of the xenon-133 inhalation rCBF technique, this method uses eight extracranial NaI scintillation detectors and an i.v. bolus injection of xenon-133 (approximately 0.5 mCi/kg). Arterial xenon concentration was estimated with an external chest detector. Cerebral blood flow was measured in 15 healthy, neurologically normal premature infants. Using Obrist's method of two-compartment analysis, normal values were calculated for flow in both compartments, relative weight and fractional flow in the first compartment (gray matter), initial slope of gray matter blood flow, mean cerebral blood flow, and initial slope index of mean cerebral blood flow. The application of this technique to newborns, its relative advantages, and its potential uses are discussed.

Sleep apnea, narcolepsy, and dreaming: regional cerebral hemodynamics

Regional cerebral flow after inhalation of xenon 133 as well as polysomnography were recorded during daytime sleep and the awake state in patients with narcolepsy and sleep apnea. Brainstem-cerebellar (BSC) gray matter blood flow (Fg) values in the awake state were reduced below normal (p less than 0.05) in both narcolepsy and sleep apnea; in sleep apnea, bihemispheric Fg values were also reduced in the awake state. After sleep onset, Fg paradoxically increased in narcolepsy but decreased further in sleep apnea. Maximal regional Fg changes occurred in BSC regions in both groups of patients. Oral administration of methylphenidate hydrochloride (Ritalin) increased resting Fg values in awake narcoleptics, particularly in BSC regions, but attentuated Fg increases during sleep onset. Regional Fg values during visual dreaming or hypnagogic hallucinations in narcoleptics were maximally increased in right parietooccipital regions. In narcoleptics, impaired control of sleep-wake and REM mechanisms is attentuated by methylphenidate. In patients with sleep apnea, brainstem functional activity is low in the awake state but becomes critically reduced during sleep, culminating in apnea-stimulated arousal followed by repetitive cycles as sleep recurs.

Normal human sleep: regional cerebral hemodynamics

Measurements of regional cerebral blood flow (rCBF) by the xenon 133 inhalation method along with polygraph recordings were made serially during relaxed wakefulness and different stages of nocturnal sleep in 18 right-handed normal volunteers. During stage I-II sleep the fast flow (Fg) values declined significantly, more in the brainstem-cerebellar (BSC) regions than in hemispheric regions. During stage III-IV sleep, Fg further declined diffusely in both hemispheric (-28%) and BSC (-29%) regions. During awakening from stage IV sleep to alpha-frequency wakefulness, BSC flow values increased more than hemispheric flow values. During REM sleep, regional Fg values increased diffusely in both hemispheric (+41%) and BSC (+47%) regions compared with wakefulness. There was a significant inverse correlation between the increase in end-tidal partial pressure for carbon dioxide and the reduction in bihemispheric Fg during sleep. Cerebral vasomotor responsiveness to carbon dioxide is decreased during both REM and non-REM sleep.