Biomedical subjects
B M Ances
Publications and source records attributed to B M Ances.
Caudate blood flow and volume are reduced in HIV+ neurocognitively impaired patients.
OBJECTIVE: To evaluate the effects of HIV-associated neurocognitive impairment on caudate blood flow and volume. METHODS: The authors performed continuous arterial spin labeled MRI on 42 HIV+ patients (23 subsyndromic and 19 HIV neurosymptomatic) on highly active antiretroviral therapy and 17 seronegative controls. They compared caudate blood flow and volume among groups. RESULTS: A stepwise decrease in both caudate blood flow and volume was observed with increasing HIV-associated neurocognitive impairment. Compared with seronegative controls, baseline caudate blood flow was reduced in HIV+ neurosymptomatic patients (p = 0.001) with a similar decreasing trend for subsyndromic HIV+ patients (p = 0.070). Differences in caudate volume were observed only for neurosymptomatic HIV+ patients compared with controls (p = 0.010). A Jonckheere-Terpstra test for trends was significant for both caudate blood flow and volume for each of the three subgroups. Pearson product moment correlation coefficients were not significant between caudate blood flow and volume for each group. CONCLUSIONS: Decreasing trends in caudate blood flow and volume were associated with significantly increasing HIV-associated neurocognitive impairment (HNCI), with the greatest decreases observed for more severely impaired patients. However, reductions in caudate blood flow and volume were poorly correlated. Changes in residual caudate blood flow may act as a surrogate biomarker for classifying the degree of HNCI.
Intracranial fat embolization due to baclofen pump.
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Balint syndrome due to Creutzfeldt-Jakob disease.
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FDG-PET of poststroke oculomotor repair.
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Perfusion changes with photic stimulation during two phases of the menstrual cycle: a pilot study comparing controls and true menstrual migraine patients.
This pilot study investigated the effect of menstrual cycle phase (late luteal and mid-follicular) on cerebral perfusion changes during photic stimulation in both controls (n = 5) and true menstrual migraine patients (n = 5). No significant differences in resting baseline perfusion were observed between the two groups during either phase of the menstrual cycle. During the late luteal phase, changes in perfusion within the occipital lobe due to photic stimulation were similar for both groups. However, during the mid-follicular phase, occipital perfusion during visual stimulation decreased for controls but significantly increased for true menstrual migraine patients (P < 0.05). A two way repeated measures anova also demonstrated a significant difference between menstrual migraine patients and controls for photic activation (P < 0.05).
The effects of graded hypercapnia on the activation flow coupling response due to forepaw stimulation in alpha-chloralose anesthetized rats.
Activation flow coupling (AFC), changes in cerebral blood flow (CBF) due to changes in neural activity with functional stimulation, provides the physiological basis of many neuroimaging techniques. Hypercapnia leads to an increase in CBF while neural activity remains unaffected. Laser Doppler (LD) flowmetry was used to measure CBF changes (LD(CBF)) in the somatosensory cortex due to periodic electrical forepaw stimulation (4 s in duration) before and during graded hypercapnia (3% CO(2), 5% CO(2) and 10% CO(2)). With increasing CO(2) concentrations, the baseline LD(CBF) progressively increased. The peak height (PH) of the LD(CBF) response, expressed as a percent change from the observed baseline for each hypercapnic state, significantly decreased (P<0.05) with increasing CO(2) concentrations. However, the absolute magnitude of the LD(CBF) change was independent of CO(2) concentration. The temporal dynamics of the LD(CBF) response during hypercapnia were significantly prolonged compared to baseline conditions (P<0.05).
Temporal dynamics of the partial pressure of brain tissue oxygen during functional forepaw stimulation in rats.
The partial pressure of tissue oxygen (pO2) was measured in rat somatosensory cortex during periodic electrical forepaw stimulation of either 1 min or 4 s in duration, and correlated with simultaneous laser Doppler flowmetry. For both stimulus durations, a transient decrease in tissue pO2 preceded blood flow changes, followed by a peak in blood flow and an overshoot in tissue pO2. With protracted stimulation, tissue pO2 remained only slightly above pre-stimulus baseline, while blood flow was maintained at a reduced plateau phase. A sustained post-stimulus undershoot in tissue pO2 was observed only for the 1 min stimulus. These findings suggest a complex dynamic relationship between oxygen utilization and blood flow.
Sex differences in the cerebral blood flow response after brief hypercapnia in the rat.
Hypercapnia primarily affects cerebral blood flow (CBF) and not cerebral metabolism. We compared the CBF responses due to electrical forepaw stimulation before and after brief hypercapnia in male, non-ovarectomized female, and ovarectomized female rats. Prior to hypercapnia the CBF responses were similar for all three groups. Seven minutes after brief hypercapnic exposure the CBF responses to forepaw stimulation were augmented in all groups. However, both 30 and 60 min after hypercapnia, the magnitude of the CBF responses to forepaw stimulation remained elevated for males and ovarectomized females, but not for non-ovarectomized females. These results suggest that estrogen may modulate the upregulation of the CBF response observed after transient hypercapnia.
Dynamic changes in cerebral blood flow, O2 tension, and calculated cerebral metabolic rate of O2 during functional activation using oxygen phosphorescence quenching.
Changes in cerebral blood flow (CBF) using laser-Doppler and microvascular O2 oxygen tension using oxygen-dependent phosphorescence quenching in the rat somatosensory cortex were obtained during electrical forepaw stimulation. The signal-averaged CBF response resulting from electrical forepaw stimulation consisted of an initial peak (t = 3.1 +/- 0.8 seconds after onset of stimulation), followed by a plateau phase that was maintained throughout the length of the stimulus. In contrast, microvascular O2 tension changes were delayed, reached a plateau level (t = 23.5 +/- 1.7 seconds after the onset of stimulation) that remained for the length of the stimulus and for several seconds after stimulus termination, and then returned to baseline. Using Fick's equation and these dynamic measurements, changes in the calculated cerebral metabolic rate of oxygen (CMRO2) during functional stimulation were determined. The calculated CMRO2 response initially was comparable with the CBF, but with protracted stimulation, CMRO2 changes were approximately one-third that of CBF changes. These results suggest that a complex relation exists, with comparable changes in CBF and CMRO2 initially occurring after stimulation but excessive changes in CBF compared with CMRO2 arising with protracted stimulation.
Laser Doppler imaging of changes in cerebral blood flow during acute carotid occlusion.
OBJECTIVE: To determine by laser Doppler imaging (LDI) the spatial and temporal characteristics of the changes in cerebral blood flow (CBF) in response to electrical forepaw stimulation in rats before and during acute unilateral carotid occlusion. BACKGROUND DATA: Single laser Doppler (LD) probes provide a minimally invasive approach for measuring CBF changes due to functional stimulation. Using an electrical forepaw stimulation model in rats, we have previously demonstrated a prolongation in the temporal dynamics of the CBF response during acute mechanical carotid occlusion. However, the spatial resolution of this model system was limited by the diameter of the single LD probe. Recently, we have successfully used LDI, which uses an optically driven low power laser beam to measure CBF changes in two dimensions, to investigate the spatial and temporal changes in CBF due to forepaw stimulation. METHODS: LDI was used to measure the spatial and temporal characteristics of the changes in CBF response in a-chloralose anesthetized rats (n = 5) both before and during acute unilateral occlusion of the common carotid contralateral to the forepaw stimulated. RESULTS: Acute mechanical occlusion of the common carotid contralateral to the forepaw stimulated did not affect the area of activation due to functional stimulation. However, the amplitude of the CBF response was significantly reduced compared to prior to occlusion. Further, acute occlusion led to a significant prolongation of temporal dynamics of the CBF response. These observations are in agreement with previous results we have obtained using a single LD probe. CONCLUSIONS: Our results suggest a promising role for the application of LDI to study the spatial and temporal characteristics of CBF changes in animal models and may allow a diagnostic technique for testing patients with carotid occlusion.
Effects of variations in interstimulus interval on activation-flow coupling response and somatosensory evoked potentials with forepaw stimulation in the rat.
In functional neuroimaging studies, the hemodynamic response to functional activation is used as a surrogate marker for neuronal activity, typically in response to task paradigms that use periodic stimuli. With use of a model system of electrical forepaw stimulation in rats (n = 14) with laser-Doppler (LD) monitoring of cerebral blood flow (CBF) changes in the somatosensory cortex, the effects of variations in the interstimulus interval (ISI) on the hemodynamic response to periodic stimuli were examined. A characteristic peak flow response was seen for 4-second stimuli and a peak and plateau response were seen for all 8-second stimuli regardless of ISI. However, both the amplitude of the LD(CBF) response and the integrated response were significantly reduced for shorter ISIs, whereas the baseline flow was not altered. Somatosensory evoked potential responses were also recorded in some rats (n = 8) and remained unchanged for the various ISIs for a particular stimulus duration. These results suggest that the decrease in the LD(CBF) responses observed with shorter ISIs likely represents a refractoriness of the hemodynamic response and not neuronal function. These results may have important implications for the optimization and interpretation of functional activation paradigms that use periodic stimuli.
Coupling of neural activation to blood flow in the somatosensory cortex of rats is time-intensity separable, but not linear.
Changes in cerebral blood flow (CBF) because of functional activation are used as a surrogate for neural activity in many functional neuroimaging studies. In these studies, it is often assumed that the CBF response is a linear-time invariant (LTI) transform of the underlying neural activity. By using a previously developed animal model system of electrical forepaw stimulation in rats (n = 11), laser Doppler measurements of CBF, and somatosensory evoked potentials, measurements of neural activity were obtained when the stimulus duration and intensity were separately varied. These two sets of time series data were used to assess the LTI assumption. The CBF data were modeled as a transform of neural activity (N1-P2 amplitude of the somatosensory evoked potential) by using first-order (linear) and second-order (nonlinear) components. Although a pure LTI model explained a large amount of the variance in the data for changes in stimulus duration, our results demonstrated that the second-order kernel (i.e., a nonlinear component) contributed an explanatory component that is both statistically significant and appreciable in magnitude. For variations in stimulus intensity, a pure LTI model explained almost all of the variance in the CBF data. In particular, the shape of the CBF response did not depend on intensity of neural activity when duration was held constant (time-intensity separability). These results have important implications for the analysis and interpretation of neuroimaging data.
Acute carotid occlusion alters the activation flow coupling response to forepaw stimulation in a rat model.
BACKGROUND AND PURPOSE: To determine whether the hemodynamic response to functional stimulation is sensitive to proximal arterial occlusion, we measured the activation flow coupling response in a rat model of acute reversible vascular occlusion. METHODS: In alpha-chloralose-anesthetized rats (n=18), laser Doppler measurements were made through a thinned skull over the somatosensory cortex in response to electrical forepaw stimulation. Signal-averaged responses to 4 and 8 seconds of electrical forepaw stimulation were obtained before, during, and shortly after acute unilateral or bilateral carotid occlusion produced with the use of a surgically placed snare. RESULTS: Baseline cerebral blood flow was significantly decreased over the forepaw region of the somatosensory cortex after both occlusion of the carotid contralateral to the stimulated forepaw and bilateral occlusion compared with preocclusion (P<0.05). Postocclusion and ipsilateral occlusion led to a nonsignificant increase in baseline cerebral blood flow compared with preocclusion. Contralateral carotid occlusion and bilateral occlusion significantly prolonged the temporal characteristics of the flow response, especially the delay to peak (P<0.05), compared with preocclusion, whereas ipsilateral carotid occlusion significantly shortened the delay to peak (P<0.05). Only contralateral carotid occlusion produced a significant reduction in the peak amplitude of the flow response compared with preocclusion (P<0.05). CONCLUSIONS: These findings suggest that temporal characteristics of functional activation responses are sensitive to alterations in the proximal arterial supply and, conversely, that functional activation studies must be interpreted with consideration of proximal arterial disease.
Neuroimaging of recovery of function after stroke: implications for rehabilitation.
Stroke is a leading cause of morbidity and mortality in individuals. Many patients have good functional recovery after stroke. The mechanisms of recovery remain largely unknown. Neuroimaging of patients recovering from stroke may provide important insight into the mechanisms of recovery as well as assist in the development of new rehabilitation techniques. The first part of this article reviews previous neuroimaging studies that have monitored the reorganization within the motor and language areas after stroke. In the second section, a unifying theory based on John Hughlings Jackson's "Principles of Compensation" is presented as a possible theory for recovery of function. In the final portion of the article, possible implications and future applications of neuroimaging studies for rehabilitation are presented.
Marchiafava-Bignami disease: literature review and case report.
OBJECTIVE: We postulated that disruption of callosal pathways as occurs in Marchiafava-Bignami disease (MBD) is associated with marked impairment in brain functioning as measured by cognitive assessment and neuroimaging. BACKGROUND: MBD is considered to be a rare and severe complication of chronic alcoholism. It is characterized by necrosis and subsequent atrophy of the corpus callosum, which is the major brain structure connecting corresponding areas of both hemispheres. METHODS: We review the existing literature on MBD with respect to conceptualization, theories of pathogenesis, forms of the disease, and neuroimaging and neuropsychological findings. We then present the case of a middle-aged man with MBD who underwent extensive clinical, neuropsychological, and neuroimaging studies. RESULTS: Neuropsychological evaluation revealed a pattern of severe global dementia. Magnetic resonance imaging showed moderate atrophy of anterior callosal regions and severe atrophy of posterior callosal regions in the setting of cortical and subcortical atrophy. Resting metabolism positron emission tomography revealed decreased glucose metabolism most pronounced in subcortical and mesial frontal regions. The differential diagnosis, function of the corpus callosum, and potential limitations of our case study are discussed. CONCLUSIONS: On account of the history, clinical presentation, and results of magnetic resonance imaging of the brain, we diagnosed our patient with chronic MBD.
Laser doppler imaging of activation-flow coupling in the rat somatosensory cortex.
Activation-flow coupling (AFC) provides a physiological basis for mapping cerebral activation using cerebral blood flow (CBF) as a surrogate marker for neuronal function. Laser Doppler offers a minimally invasive approach for measuring changes in cerebral blood flow but the spatial resolution of this technique is limited by the number of individual probes that can be used. Recently, laser Doppler imaging (LDI) scanners, which use computer-driven optics to scan and measure LD changes in two dimensions, have successfully measured flow changes in the exposed cortex of animals. Here we demonstrate the use of an LDI device through a thinned skull to determine the spatiotemporal characteristics of AFC in alpha-chloralose anesthetized rats in response to electrical forepaw stimulation. The spatial and temporal characteristics of the AFC response measured by LDI are in agreement with prior results obtained using a single LD probe. These results suggest a promising role for LDI in the characterization of the spatiotemporal characteristics of AFC in animal models and possibly for intraoperative monitoring in the human brain.
Activation-flow coupling with forepaw stimulation in female and male rats.
Activation-flow coupling (AFC), the coupling of changes in cerebral blood flow (CBF) with neuronal function, is the basis for many functional neuroimaging techniques. Prior studies have shown that females have higher cerebral blood flow levels than males and that estrogen may affect the mediators involved in AFC. No studies have compared AFC responses between males and females. We assessed the AFC responses to forepaw stimulation using signal-averaged laser Doppler (LD) measurements of CBF in alpha-chloralose anesthetized female and male rats. Results for various stimulus parameters were similar for both sexes except at 2 Hz where females had a higher blood flow response. These results suggest that the AFC responses in males and females are similar, but require further validation in humans.