Electronic Mail: Messages between computer users via COMPUTER COMMUNICATION NETWORKS. This feature duplicates most of the features of paper mail, such as forwarding, multiple copies, and attachments of images and other file types, but with a speed advantage. The term also refers to an individual message sent in this way.Blood Flow Velocity: A value equal to the total volume flow divided by the cross-sectional area of the vascular bed.Cerebrovascular Circulation: The circulation of blood through the BLOOD VESSELS of the BRAIN.Phenobarbital: A barbituric acid derivative that acts as a nonselective central nervous system depressant. It potentiates GAMMA-AMINOBUTYRIC ACID action on GABA-A RECEPTORS, and modulates chloride currents through receptor channels. It also inhibits glutamate induced depolarizations.Ultrasonography, Doppler, Transcranial: A non-invasive technique using ultrasound for the measurement of cerebrovascular hemodynamics, particularly cerebral blood flow velocity and cerebral collateral flow. With a high-intensity, low-frequency pulse probe, the intracranial arteries may be studied transtemporally, transorbitally, or from below the foramen magnum.Pediatrics: A medical specialty concerned with maintaining health and providing medical care to children from birth to adolescence.Middle Cerebral Artery: The largest of the cerebral arteries. It trifurcates into temporal, frontal, and parietal branches supplying blood to most of the parenchyma of these lobes in the CEREBRAL CORTEX. These are the areas involved in motor, sensory, and speech activities.Cerebral Arteries: The arterial blood vessels supplying the CEREBRUM.Regional Blood Flow: The flow of BLOOD through or around an organ or region of the body.Hypocapnia: Clinical manifestation consisting of a deficiency of carbon dioxide in arterial blood.Brain: The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM.Nerve Fibers, Myelinated: A class of nerve fibers as defined by their structure, specifically the nerve sheath arrangement. The AXONS of the myelinated nerve fibers are completely encased in a MYELIN SHEATH. They are fibers of relatively large and varied diameters. Their NEURAL CONDUCTION rates are faster than those of the unmyelinated nerve fibers (NERVE FIBERS, UNMYELINATED). Myelinated nerve fibers are present in somatic and autonomic nerves.Magnetic Resonance Imaging: Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques.Atrophy: Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes.Diabetes Mellitus: A heterogeneous group of disorders characterized by HYPERGLYCEMIA and GLUCOSE INTOLERANCE.Hypercapnia: A clinical manifestation of abnormal increase in the amount of carbon dioxide in arterial blood.Mucormycosis: Infection in humans and animals caused by any fungus in the order Mucorales (e.g., Absidia, Mucor, Rhizopus etc.) There are many clinical types associated with infection of the central nervous system, lung, gastrointestinal tract, skin, orbit and paranasal sinuses. In humans, it usually occurs as an opportunistic infection in patients with a chronic debilitating disease, particularly uncontrolled diabetes, or who are receiving immunosuppressive agents. (From Dorland, 28th ed)Multiple Sclerosis: An autoimmune disorder mainly affecting young adults and characterized by destruction of myelin in the central nervous system. Pathologic findings include multiple sharply demarcated areas of demyelination throughout the white matter of the central nervous system. Clinical manifestations include visual loss, extra-ocular movement disorders, paresthesias, loss of sensation, weakness, dysarthria, spasticity, ataxia, and bladder dysfunction. The usual pattern is one of recurrent attacks followed by partial recovery (see MULTIPLE SCLEROSIS, RELAPSING-REMITTING), but acute fulminating and chronic progressive forms (see MULTIPLE SCLEROSIS, CHRONIC PROGRESSIVE) also occur. (Adams et al., Principles of Neurology, 6th ed, p903)Tomography, Optical: Projection of near-IR light (INFRARED RAYS), in the 700-1000 nm region, across an object in parallel beams to an array of sensitive photodetectors. This is repeated at various angles and a mathematical reconstruction provides three dimensional MEDICAL IMAGING of tissues. Based on the relative transparency of tissues to this spectra, it has been used to monitor local oxygenation, brain and joints.Magnetic Resonance Angiography: Non-invasive method of vascular imaging and determination of internal anatomy without injection of contrast media or radiation exposure. The technique is used especially in CEREBRAL ANGIOGRAPHY as well as for studies of other vascular structures.Transducers: Any device or element which converts an input signal into an output signal of a different form. Examples include the microphone, phonographic pickup, loudspeaker, barometer, photoelectric cell, automobile horn, doorbell, and underwater sound transducer. (McGraw Hill Dictionary of Scientific and Technical Terms, 4th ed)Angiography: Radiography of blood vessels after injection of a contrast medium.Genetic Vectors: DNA molecules capable of autonomous replication within a host cell and into which other DNA sequences can be inserted and thus amplified. Many are derived from PLASMIDS; BACTERIOPHAGES; or VIRUSES. They are used for transporting foreign genes into recipient cells. Genetic vectors possess a functional replicator site and contain GENETIC MARKERS to facilitate their selective recognition.Computer Simulation: Computer-based representation of physical systems and phenomena such as chemical processes.Ultrasonography: The visualization of deep structures of the body by recording the reflections or echoes of ultrasonic pulses directed into the tissues. Use of ultrasound for imaging or diagnostic purposes employs frequencies ranging from 1.6 to 10 megahertz.Hyperemia: The presence of an increased amount of blood in a body part or an organ leading to congestion or engorgement of blood vessels. Hyperemia can be due to increase of blood flow into the area (active or arterial), or due to obstruction of outflow of blood from the area (passive or venous).Brachial Artery: The continuation of the axillary artery; it branches into the radial and ulnar arteries.Diaphragmatic Eventration: A congenital abnormality characterized by the elevation of the DIAPHRAGM dome. It is the result of a thinned diaphragmatic muscle and injured PHRENIC NERVE, allowing the intra-abdominal viscera to push the diaphragm upward against the LUNG.Coronary Circulation: The circulation of blood through the CORONARY VESSELS of the HEART.Carotid Artery Diseases: Pathological conditions involving the CAROTID ARTERIES, including the common, internal, and external carotid arteries. ATHEROSCLEROSIS and TRAUMA are relatively frequent causes of carotid artery pathology.Posture: The position or attitude of the body.Intracranial Pressure: Pressure within the cranial cavity. It is influenced by brain mass, the circulatory system, CSF dynamics, and skull rigidity.ArchivesNeurosurgery: A surgical specialty concerned with the treatment of diseases and disorders of the brain, spinal cord, and peripheral and sympathetic nervous system.Constriction: The act of constricting.Echoencephalography: Use of reflected ultrasound in the diagnosis of intracranial pathologic processes.Nails: The thin, horny plates that cover the dorsal surfaces of the distal phalanges of the fingers and toes of primates.Microscopic Angioscopy: The noninvasive microscopic examination of the microcirculation, commonly done in the nailbed or conjunctiva. In addition to the capillaries themselves, observations can be made of passing blood cells or intravenously injected substances. This is not the same as endoscopic examination of blood vessels (ANGIOSCOPY).Ophthalmic Artery: Artery originating from the internal carotid artery and distributing to the eye, orbit and adjacent facial structures.Raynaud Disease: An idiopathic vascular disorder characterized by bilateral Raynaud phenomenon, the abrupt onset of digital paleness or CYANOSIS in response to cold exposure or stress.Capillaries: The minute vessels that connect the arterioles and venules.Visual Fields: The total area or space visible in a person's peripheral vision with the eye looking straightforward.Glaucoma, Open-Angle: Glaucoma in which the angle of the anterior chamber is open and the trabecular meshwork does not encroach on the base of the iris.Fingers: Four or five slender jointed digits in humans and primates, attached to each HAND.Scleroderma, Systemic: A chronic multi-system disorder of CONNECTIVE TISSUE. It is characterized by SCLEROSIS in the SKIN, the LUNGS, the HEART, the GASTROINTESTINAL TRACT, the KIDNEYS, and the MUSCULOSKELETAL SYSTEM. Other important features include diseased small BLOOD VESSELS and AUTOANTIBODIES. The disorder is named for its most prominent feature (hard skin), and classified into subsets by the extent of skin thickening: LIMITED SCLERODERMA and DIFFUSE SCLERODERMA.Motion Pictures as Topic: The art, technique, or business of producing motion pictures for entertainment, propaganda, or instruction.Microcirculation: The circulation of the BLOOD through the MICROVASCULAR NETWORK.Arterioles: The smallest divisions of the arteries located between the muscular arteries and the capillaries.Venules: The minute vessels that collect blood from the capillary plexuses and join together to form veins.Dogs: The domestic dog, Canis familiaris, comprising about 400 breeds, of the carnivore family CANIDAE. They are worldwide in distribution and live in association with people. (Walker's Mammals of the World, 5th ed, p1065)Diastole: Post-systolic relaxation of the HEART, especially the HEART VENTRICLES.Echocardiography, Doppler: Measurement of intracardiac blood flow using an M-mode and/or two-dimensional (2-D) echocardiogram while simultaneously recording the spectrum of the audible Doppler signal (e.g., velocity, direction, amplitude, intensity, timing) reflected from the moving column of red blood cells.Heart Ventricles: The lower right and left chambers of the heart. The right ventricle pumps venous BLOOD into the LUNGS and the left ventricle pumps oxygenated blood into the systemic arterial circulation.Hydrocephalus: Excessive accumulation of cerebrospinal fluid within the cranium which may be associated with dilation of cerebral ventricles, INTRACRANIAL HYPERTENSION; HEADACHE; lethargy; URINARY INCONTINENCE; and ATAXIA.Cerebrospinal Fluid Shunts: Tubes inserted to create communication between a cerebral ventricle and the internal jugular vein. Their emplacement permits draining of cerebrospinal fluid for relief of hydrocephalus or other condition leading to fluid accumulation in the ventricles.Drainage: The removal of fluids or discharges from the body, such as from a wound, sore, or cavity.Anterior Cerebral Artery: Artery formed by the bifurcation of the internal carotid artery (CAROTID ARTERY, INTERNAL). Branches of the anterior cerebral artery supply the CAUDATE NUCLEUS; INTERNAL CAPSULE; PUTAMEN; SEPTAL NUCLEI; GYRUS CINGULI; and surfaces of the FRONTAL LOBE and PARIETAL LOBE.Intracranial Aneurysm: Abnormal outpouching in the wall of intracranial blood vessels. Most common are the saccular (berry) aneurysms located at branch points in CIRCLE OF WILLIS at the base of the brain. Vessel rupture results in SUBARACHNOID HEMORRHAGE or INTRACRANIAL HEMORRHAGES. Giant aneurysms (>2.5 cm in diameter) may compress adjacent structures, including the OCULOMOTOR NERVE. (From Adams et al., Principles of Neurology, 6th ed, p841)Aneurysm: Pathological outpouching or sac-like dilatation in the wall of any blood vessel (ARTERIES or VEINS) or the heart (HEART ANEURYSM). It indicates a thin and weakened area in the wall which may later rupture. Aneurysms are classified by location, etiology, or other characteristics.Cerebral Angiography: Radiography of the vascular system of the brain after injection of a contrast medium.Carotid Artery, Internal: Branch of the common carotid artery which supplies the anterior part of the brain, the eye and its appendages, the forehead and nose.Urinary Diversion: Temporary or permanent diversion of the flow of urine through the ureter away from the URINARY BLADDER in the presence of a bladder disease or after cystectomy. There is a variety of techniques: direct anastomosis of ureter and bowel, cutaneous ureterostomy, ileal, jejunal or colon conduit, ureterosigmoidostomy, etc. (From Campbell's Urology, 6th ed, p2654)Stents: Devices that provide support for tubular structures that are being anastomosed or for body cavities during skin grafting.Blood Vessel Prosthesis: Device constructed of either synthetic or biological material that is used for the repair of injured or diseased blood vessels.Hydrodynamics: The motion of fluids, especially noncompressible liquids, under the influence of internal and external forces.Aneurysm, Infected: Aneurysm due to growth of microorganisms in the arterial wall, or infection arising within preexisting arteriosclerotic aneurysms.Altitude Sickness: Multiple symptoms associated with reduced oxygen at high ALTITUDE.Mountaineering: A sport involving mountain climbing techniques.Altitude: A vertical distance measured from a known level on the surface of a planet or other celestial body.Magnesium: A metallic element that has the atomic symbol Mg, atomic number 12, and atomic weight 24.31. It is important for the activity of many enzymes, especially those involved in OXIDATIVE PHOSPHORYLATION.Expeditions: Usually refers to planned scientific data-gathering excursions.Magnesium Deficiency: A nutritional condition produced by a deficiency of magnesium in the diet, characterized by anorexia, nausea, vomiting, lethargy, and weakness. Symptoms are paresthesias, muscle cramps, irritability, decreased attention span, and mental confusion, possibly requiring months to appear. Deficiency of body magnesium can exist even when serum values are normal. In addition, magnesium deficiency may be organ-selective, since certain tissues become deficient before others. (Harrison's Principles of Internal Medicine, 12th ed, p1936)Klippel-Feil Syndrome: A syndrome characterised by a low hairline and a shortened neck resulting from a reduced number of vertebrae or the fusion of multiple hemivertebrae into one osseous mass.Manipulation, Spinal: Adjustment and manipulation of the vertebral column.Vertebral Artery: The first branch of the SUBCLAVIAN ARTERY with distribution to muscles of the NECK; VERTEBRAE; SPINAL CORD; CEREBELLUM; and interior of the CEREBRUM.Forensic Ballistics: The science of studying projectiles in motion, ballistics, being applied to law. Ballistics on firearm projectiles, such as bullets, include the study of what happens inside the weapon, during the flight of the projectile, and when the projectile strikes the target, such as body tissue.Cervical Vertebrae: The first seven VERTEBRAE of the SPINAL COLUMN, which correspond to the VERTEBRAE of the NECK.Vertebral Artery Dissection: Splitting of the vessel wall in the VERTEBRAL ARTERY. Interstitial hemorrhage into the media of the vessel wall can lead to occlusion of the vertebral artery, aneurysm formation, or THROMBOEMBOLISM. Vertebral artery dissection is often associated with TRAUMA and injuries to the head-neck region but can occur spontaneously.Athletic Injuries: Injuries incurred during participation in competitive or non-competitive sports.Neck Injuries: General or unspecified injuries to the neck. It includes injuries to the skin, muscles, and other soft tissues of the neck.Vertebrobasilar Insufficiency: Localized or diffuse reduction in blood flow through the vertebrobasilar arterial system, which supplies the BRAIN STEM; CEREBELLUM; OCCIPITAL LOBE; medial TEMPORAL LOBE; and THALAMUS. Characteristic clinical features include SYNCOPE; lightheadedness; visual disturbances; and VERTIGO. BRAIN STEM INFARCTIONS or other BRAIN INFARCTION may be associated.Coronary Vessel Anomalies: Malformations of CORONARY VESSELS, either arteries or veins. Included are anomalous origins of coronary arteries; ARTERIOVENOUS FISTULA; CORONARY ANEURYSM; MYOCARDIAL BRIDGING; and others.