About: Blood flow is a(n) research topic. Over the lifetime, 27604 publication(s) have been published within this topic receiving 735527 citation(s).
Abstract: Paramagnetic deoxyhemoglobin in venous blood is a naturally occurring contrast agent for magnetic resonance imaging (MRI). By accentuating the effects of this agent through the use of gradient-echo techniques in high fields, we demonstrate in vivo images of brain microvasculature with image contrast reflecting the blood oxygen level. This blood oxygenation level-dependent (BOLD) contrast follows blood oxygen changes induced by anesthetics, by insulin-induced hypoglycemia, and by inhaled gas mixtures that alter metabolic demand or blood flow. The results suggest that BOLD contrast can be used to provide in vivo real-time maps of blood oxygenation in the brain under normal physiological conditions. BOLD contrast adds an additional feature to magnetic resonance imaging and complements other techniques that are attempting to provide positron emission tomography-like measurements related to regional neural activity.
Abstract: Neuronal activity causes local changes in cerebral blood flow, blood volume, and blood oxygenation. Magnetic resonance imaging (MRI) techniques sensitive to changes in cerebral blood flow and blood oxygenation were developed by high-speed echo planar imaging. These techniques were used to obtain completely noninvasive tomographic maps of human brain activity, by using visual and motor stimulus paradigms. Changes in blood oxygenation were detected by using a gradient echo (GE) imaging sequence sensitive to the paramagnetic state of deoxygenated hemoglobin. Blood flow changes were evaluated by a spin-echo inversion recovery (IR), tissue relaxation parameter T1-sensitive pulse sequence. A series of images were acquired continuously with the same imaging pulse sequence (either GE or IR) during task activation. Cine display of subtraction images (activated minus baseline) directly demonstrates activity-induced changes in brain MR signal observed at a temporal resolution of seconds. During 8-Hz patterned-flash photic stimulation, a significant increase in signal intensity (paired t test; P less than 0.001) of 1.8% +/- 0.8% (GE) and 1.8% +/- 0.9% (IR) was observed in the primary visual cortex (V1) of seven normal volunteers. The mean rise-time constant of the signal change was 4.4 +/- 2.2 s for the GE images and 8.9 +/- 2.8 s for the IR images. The stimulation frequency dependence of visual activation agrees with previous positron emission tomography observations, with the largest MR signal response occurring at 8 Hz. Similar signal changes were observed within the human primary motor cortex (M1) during a hand squeezing task and in animal models of increased blood flow by hypercapnia. By using intrinsic blood-tissue contrast, functional MRI opens a spatial-temporal window onto individual brain physiology.
01 Sep 1975-JAMA Neurology
TL;DR: Cerebral blood flow per 100 gm brain per minute was normal in the primary degenerative group but low in the multi-infarct group, suggesting the blood flow is adequate for metabolic needs of the brain in patients withPrimary degenerative dementia but inadequate for those with multi- infarct dementia.
Abstract: • Twenty-four patients of comparable age, blood pressure, and degree of dementia were classified by an "Ischemic Score" based on clinical features into "multi-infarct" and "primary degenerative" dementia. Regional cerebral blood flow (CBF) was measured by the intracarotid xenon 133 method. Both groups showed a decreased proportion of rapidly clearing brain tissue (largely gray matter). Cerebral blood flow per 100 gm brain per minute was normal in the primary degenerative group but low in the multi-infarct group. This suggests the blood flow is adequate for metabolic needs of the brain in patients with primary degenerative dementia but inadequate for those with multi-infarct dementia. There was no correlation between degree of dementia and CBF in the primary degenerative group but an inverse relationship existed in the multi-infarct group. Reactivity of blood vessels to reduction of arterial carbon dioxide pressure was normal in both groups.
28 Apr 2005-
TL;DR: The nature and flow of a fluid properties of the normanl arterial wall changes to properties of that wall pulsatile pressure flow relationships measuring principles of arterial waves ultrasonic techniques and measurements contour of pressure and flow waves in arteries wave reflection are studied.
Abstract: Foreword Michael Taylor Foreword David A. Kass and Myron L. Weisfeldt Preface List of Abbreviations Introduction The nature of flow of a liquid Properties of the arterial wall: theory Properties of the arterial wall: practice Endothelial function General principles for measuring arterial waves Pulsatile pressure-flow relations Ultrasound Wave reflections Contours of pressure and flow waves in arteries Principles of recording and analysis of arterial waveforms Vascular impedance Aortic input impedance as ventricular load Coupling of the left ventricle with the systemic circulation: implications to cardiac failure Cardiac failure: clinical implications The pulmonary circulation The coronary circulation Special circulations Aging Hypertension Interpretation of blood pressure in epidemiological studies and clinical trials Arterial biomarkers Atherosclerosis Specific arterial disease Generalized and metabolic disease Therapeutic strategies Exercise Central arterial pressure Lifestyle and environment Pressure pulse waveform analysis Bibliography
11 Nov 2010-Nature
TL;DR: It is now recognized that neurotransmitter-mediated signalling has a key role in regulating cerebral blood flow, that much of this control is mediated by astrocytes, that oxygen modulates blood flow regulation, and that blood flow may be controlled by capillaries as well as by arterioles.
Abstract: Blood flow in the brain is regulated by neurons and astrocytes. Knowledge of how these cells control blood flow is crucial for understanding how neural computation is powered, for interpreting functional imaging scans of brains, and for developing treatments for neurological disorders. It is now recognized that neurotransmitter-mediated signalling has a key role in regulating cerebral blood flow, that much of this control is mediated by astrocytes, that oxygen modulates blood flow regulation, and that blood flow may be controlled by capillaries as well as by arterioles. These conceptual shifts in our understanding of cerebral blood flow control have important implications for the development of new therapeutic approaches.