Altered hemodynamics and regional cerebral blood flow in patients with hemodynamically significant stenoses.
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BACKGROUND AND PURPOSE: Blood oxygen level-dependent (BOLD) contrast largely depends on changes in cerebral blood flow (CBF). Because cerebrovascular disease may result in altered CBF, we assessed the temporal dynamics and magnitude of the BOLD response in patients with major arterial stenoses. METHODS: Seven patients with hemodynamically significant stenoses affecting the anterior circulation (primarily left internal carotid and middle cerebral arteries) were compared with 7 neurologically healthy subjects. Continuous arterial spin-labeled perfusion MRI was used to measure resting CBF globally and within various vascular distributions. The BOLD response was acquired during a visually guided bilateral handball squeeze task while motor performance was recorded by a pressure transducer. RESULTS: Baseline CBF was reduced in bilateral middle cerebral artery and left anterior cerebral artery territories in patients. A prolonged BOLD hemodynamic response was observed in patients in bilateral primary motor cortices but not visual cortex. Patients also exhibited a larger early negative BOLD response, or "initial dip," in left primary motor cortex. There were no differences in motor performance between groups, suggesting behavioral differences were not primarily responsible for the characteristics of the BOLD response. CONCLUSIONS: An initial deoxygenation followed by a delayed hyperemic BOLD response was observed in patients, although resting flow values were not within an ischemic range. A simple visuomotor BOLD activation paradigm can reflect alterations in the hemodynamic response in patients with hemodynamically significant stenoses. (+info)
Influence of partial volume on venous output and arterial input function.
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BACKGROUND: CT perfusion (CTP) is an important diagnostic tool for the imaging of cerebral hemodynamics. To obtain quantitative values of cerebral blood volume (CBV), blood flow (CBF), and mean transit time (MTT), measurement of the arterial input function (AIF) is required. To correct for partial volume effects (PVEs), it is common to normalize the AIF with respect to the venous output function (VOF). This correction assumes that measurement of the VOF is unhampered by PVEs. The purpose of this study was to evaluate the effect of PVE on the measurement of the AIF and VOF and, consequently, on the absolute perfusion parameters. METHODS: In 10 patients the mean area under the curve (AUC) of the AIF and VOF were quantified for 3-, 6-, and 12-mm-thick sections. Differences in the mean (1) AUC of the VOF, (2) AUC of the AIF, and (3) width of the AIF were compared for the 3 section thicknesses, and the influence on the absolute values of CBV, CBF, and MTT were studied. RESULTS: With thinner sections, the AUC of the VOF and the AIF increased significantly and the width of the AIF decreased slightly. Differences in AUC between the 3 section thicknesses were larger for the AIF than for the VOF. CONCLUSION: PVEs affect not only the AIF, but also the VOF. This results in an overestimation of CBV and CBF when a thicker section is used. To avoid PVE, VOF measurements should be performed at lower section thicknesses. (+info)
Partitioning locomotor energy use among and within muscles. Muscle blood flow as a measure of muscle oxygen consumption.
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Linking the mechanics and energetics of locomotion in vertebrates has been hampered by a lack of information regarding the energy use of individual skeletal muscles in vivo. Here, we present a review of the available data concerning the relationship between the rates of skeletal muscle blood flow and oxygen consumption (V(O2)). In active muscle, during aerobically supported exercise, there is a linear relationship between these variables, irrespective of the muscle fiber type and intensity of exercise through most of the aerobic exercise range. We conclude that the rate of blood flow is the best available indicator of aerobic metabolic rate in multiple individual muscles or regions of muscles during locomotion. The practical considerations of using the injectable microsphere technique to measure muscle blood flow in this context are discussed. (+info)
The cost of running uphill: linking organismal and muscle energy use in guinea fowl (Numida meleagris).
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Uphill running requires more energy than level running at the same speed, largely due to the additional mechanical work of elevating the body weight. We explored the distribution of energy use among the leg muscles of guinea fowl running on the level and uphill using both organismal energy expenditure (oxygen consumption) and muscle blood flow measurements. We tested each bird under four conditions: (1) rest, (2) a moderate-speed level run at 1.5 m s(-1), (3) an incline run at 1.5 m s(-1) with a 15% gradient and (4) a fast level run at a speed eliciting the same metabolic rate as did running at a 15% gradient at 1.5 m s(-1) (2.28-2.39 m s(-1)). The organismal energy expenditure increased by 30% between the moderate-speed level run and both the fast level run and the incline run, and was matched by a proportional increase in total blood flow to the leg muscles. We found that blood flow increased significantly to nearly all the leg muscles between the moderate-speed level run and the incline run. However, the increase in flow was distributed unevenly across the leg muscles, with just three muscles being responsible for over 50% of the total increase in blood flow during uphill running. Three muscles showed significant increases in blood flow with increased incline but not with an increase in speed. Increasing the volume of active muscle may explain why in a previous study a higher maximal rate of oxygen consumption was measured during uphill running. The majority of the increase in energy expenditure between level and incline running was used in stance-phase muscles. Proximal stance-phase extensor muscles with parallel fibers and short tendons, which have been considered particularly well suited for doing positive work on the center of mass, increased their mass-specific energy use during uphill running significantly more than pinnate stance-phase muscles. This finding provides some evidence for a division of labor among muscles used for mechanical work production based on their muscle-tendon architecture. Nevertheless, 33% of the total increase in energy use (40% of the increase in stance-phase energy use) during uphill running was provided by pinnate stance-phase muscles. Swing-phase muscles also increase their energy expenditure during uphill running, although to a lesser extent than that required by running faster on the level. These results suggest that neither muscle-tendon nor musculoskeletal architecture appear to greatly restrict the ability of muscles to do work during locomotor tasks such as uphill running, and that the added energy cost of running uphill is not solely due to lifting the body center of mass. (+info)
Scale-space analysis of time series in circulatory research.
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Statistical analysis of time series is still inadequate within circulation research. With the advent of increasing computational power and real-time recordings from hemodynamic studies, one is increasingly dealing with vast amounts of data in time series. This paper aims to illustrate how statistical analysis using the significant nonstationarities (SiNoS) method may complement traditional repeated-measures ANOVA and linear mixed models. We applied these methods on a dataset of local hepatic and systemic circulatory changes induced by aortoportal shunting and graded liver resection. We found SiNoS analysis more comprehensive when compared with traditional statistical analysis in the following four ways: 1) the method allows better signal-to-noise detection; 2) including all data points from real time recordings in a statistical analysis permits better detection of significant features in the data; 3) analysis with multiple scales of resolution facilitates a more differentiated observation of the material; and 4) the method affords excellent visual presentation by combining group differences, time trends, and multiscale statistical analysis allowing the observer to quickly view and evaluate the material. It is our opinion that SiNoS analysis of time series is a very powerful statistical tool that may be used to complement conventional statistical methods. (+info)
Cerebral blood flow in immediate and sustained anxiety.
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The goal of this study was to compare cerebral blood flow (CBF) changes associated with phasic cued fear versus those associated with sustained contextual anxiety. Positron emission tomography images of CBF were acquired using [O-15]H2O in 17 healthy human subjects as they anticipated unpleasant electric shocks that were administered predictably (signaled by a visual cue) or unpredictably (threatened by the context). Presentation of the cue in either threat condition was associated with increased CBF in the left amygdala. A cue that specifically predicted the shock was associated with CBF increases in the ventral prefrontal cortex (PFC), hypothalamus, anterior cingulate cortex, left insula, and bilateral putamen. The sustained threat context increased CBF in the right hippocampus, mid-cingulate gyrus, subgenual PFC, midbrain periaqueductal gray, thalamus, bilateral ventral striatum, and parieto-occipital cortex. This study showed distinct neuronal networks involved in cued fear and contextual anxiety underlying the importance of this distinction for studies on the pathophysiology of anxiety disorders. (+info)
The relationship between blood flow and neuronal activity in the rodent olfactory bulb.
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In the brain, neuronal activation triggers an increase in cerebral blood flow (CBF). Here, we use two animal models and several techniques (two-photon imaging of CBF and neuronal calcium dynamics, intracellular and extracellular recordings, local pharmacology) to analyze the relationship between neuronal activity and local CBF during odor stimulation in the rodent olfactory bulb. Application of glutamate receptor antagonists or tetrodotoxin directly into single rat olfactory glomeruli blocked postsynaptic responses but did not affect the local odor-evoked CBF increases. This suggests that in our experimental conditions, odor always activates more than one glomerulus and that silencing one of a few clustered glomeruli does not affect the vascular response. To block synaptic transmission more widely, we then superfused glutamate antagonists over the surface of the olfactory bulb in transgenic G-CaMP2 mice. This was for two reasons: (1) mice have a thin olfactory nerve layer compared to rats and this will favor drug access to the glomerular layer, and (2) transgenic G-CaMP2 mice express the fluorescent calcium sensor protein G-CaMP2 in mitral cells. In G-CaMP2 mice, odor-evoked, odor-specific, and concentration-dependent calcium increases in glomeruli. Superfusion of glutamate receptor antagonists blocked odor-evoked postsynaptic calcium signals and CBF responses. We conclude that activation of postsynaptic glutamate receptors and rises in dendritic calcium are major steps for neurovascular coupling in olfactory bulb glomeruli. (+info)
Altered resting cerebral blood flow in adolescents with in utero cocaine exposure revealed by perfusion functional MRI.
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OBJECTIVES: Animal studies have clearly demonstrated the effects of in utero cocaine exposure on neural ontogeny, especially in dopamine-rich areas of cerebral cortex; however, less is known about how in utero cocaine exposure affects longitudinal neurocognitive development of the human brain. We used continuous arterial spin-labeling perfusion functional MRI to measure the effect of in utero cocaine exposure on resting brain function by comparing resting cerebral blood flow of cocaine-exposed adolescents with non-cocaine-exposed control subjects. PATIENTS AND METHODS: Twenty-four cocaine-exposed adolescents and 25 matched non-cocaine-exposed control subjects underwent structural and perfusion functional MRI during resting states. Direct subtraction, voxel-wise general linear modeling, and region-of-interest analyses were performed on the cerebral blood flow images to compare the resting cerebral blood flow between the 2 groups. RESULTS: Compared with control subjects, cocaine-exposed adolescents showed significantly reduced global cerebral blood flow. The decrease of cerebral blood flow in cocaine-exposed adolescents was observed mainly in posterior and inferior brain regions, including the occipital cortex and thalamus. After adjusting for global cerebral blood flow, however, a significant increase in relative cerebral blood flow in cocaine-exposed adolescents was found in anterior and superior brain regions, including the prefrontal, cingulate, insular, amygdala, and superior parietal cortex. Furthermore, the functional modulations by in utero cocaine exposure on all of these regions except amygdala cannot be accounted for by the variation in brain anatomy. CONCLUSIONS: In utero cocaine exposure may reduce global cerebral blood flow, and this reduction may persist into adolescence. The relative increase of cerebral blood flow in anterior and superior brain regions in cocaine-exposed adolescent participants suggests that compensatory mechanisms for reduced global cerebral blood flow may develop during neural ontogeny. Arterial spin-labeling perfusion MRI may be a valuable tool for investigating the long-term effects of in utero drug exposure. (+info)