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Lettris is a curious tetris-clone game where all the bricks have the same square shape but different content. Each square carries a letter. To make squares disappear and save space for other squares you have to assemble English words (left, right, up, down) from the falling squares.
Boggle gives you 3 minutes to find as many words (3 letters or more) as you can in a grid of 16 letters. You can also try the grid of 16 letters. Letters must be adjacent and longer words score better. See if you can get into the grid Hall of Fame !
Change the target language to find translations.
Tips: browse the semantic fields (see From ideas to words) in two languages to learn more.
1.a method of moving the arms and legs to push against the water and propel the swimmer forward
2.a light touch with the hands
3.a single complete movement
4.(sports) the act of swinging or striking at a ball with a club or racket or bat or cue or hand"it took two strokes to get out of the bunker" "a good shot requires good balance and tempo" "he left me an almost impossible shot"
5.any one of the repeated movements of the limbs and body used for locomotion in swimming or rowing
6.a mark made on a surface by a pen, pencil, or paintbrush"she applied the paint in careful strokes"
7.a punctuation mark (/) used to separate related items of information
8.the maximum movement available to a pivoted or reciprocating piece by a cam
9.a light touch
10.the oarsman nearest the stern of the shell who sets the pace for the rest of the crew
11.a sudden loss of consciousness resulting when the rupture or occlusion of a blood vessel leads to oxygen lack in the brain
12.anything that happens suddenly or by chance without an apparent cause"winning the lottery was a happy accident" "the pregnancy was a stroke of bad luck" "it was due to an accident or fortuity"
13.(golf) the unit of scoring in golf is the act of hitting the ball with a club"Nicklaus won by three strokes"
14.a powerful stroke with the fist or a weapon"a blow on the head"
15.(ellipsis)a discharge of lightning accompanied by thunder
1.treat gingerly or carefully"You have to stroke the boss"
2.strike a ball with a smooth blow
3.row at a particular rate
4.touch lightly and repeatedly, as with brushing motions"He stroked his long beard"
1.(MeSH)A group of pathological conditions characterized by sudden, non-convulsive loss of neurological function due to BRAIN ISCHEMIA or INTRACRANIAL HEMORRHAGES. Stroke is classified by the type of tissue NECROSIS, such as the anatomic location, vasculature involved, etiology, age of the affected individual, and hemorrhagic vs. non-hemorrhagic nature. (From Adams et al., Principles of Neurology, 6th ed, pp777-810)
StrokeStroke (?), obs. imp. of Strike. Struck.
StrokeStroke, n. [OE. strok, strook, strak, fr. striken. See Strike, v. t.]
1. The act of striking; a blow; a hit; a knock; esp., a violent or hostile attack made with the arm or hand, or with an instrument or weapon.
His hand fetcheth a stroke with the ax to cut down the tree. Deut. xix. 5.
A fool's lips enter into contention and his mouth calleth for strokes. Prov. xviii. 6.
He entered and won the whole kingdom of Naples without striking a stroke. Bacon.
2. The result of effect of a striking; injury or affliction; soreness.
In the day that Lord bindeth up the breach of his people, and healeth the stroke of their wound. Isa. xxx. 26.
3. The striking of the clock to tell the hour.
Well, but what's o'clock?
- Upon the stroke of ten. -- Well, let is strike. Shak.
4. A gentle, caressing touch or movement upon something; a stroking. Dryden.
5. A mark or dash in writing or printing; a line; the touch of a pen or pencil; as, an up stroke; a firm stroke.
O, lasting as those colors may they shine,
Free as thy stroke, yet faultless as thy line. Pope.
6. Hence, by extension, an addition or amandment to a written composition; a touch; as, to give some finishing strokes to an essay. Addison.
7. A sudden attack of disease; especially, a fatal attack; a severe disaster; any affliction or calamity, especially a sudden one; as, a stroke of apoplexy; the stroke of death.
At this one stroke the man looked dead in law. Harte.
8. A throb or beat, as of the heart. Tennyson.
9. One of a series of beats or movements against a resisting medium, by means of which movement through or upon it is accomplished; as, the stroke of a bird's wing in flying, or an oar in rowing, of a skater, swimmer, etc.; also: (Rowing) (a) The rate of succession of stroke; as, a quick stroke. (b) The oar nearest the stern of a boat, by which the other oars are guided; -- called also stroke oar. (c) The rower who pulls the stroke oar; the strokesman.
10. A powerful or sudden effort by which something is done, produced, or accomplished; also, something done or accomplished by such an effort; as, a stroke of genius; a stroke of business; a master stroke of policy.
11. (Mach.) The movement, in either direction, of the piston plunger, piston rod, crosshead, etc., as of a steam engine or a pump, in which these parts have a reciprocating motion; as, the forward stroke of a piston; also, the entire distance passed through, as by a piston, in such a movement; as, the piston is at half stroke.
☞ The respective strokes are distinguished as up and down strokes, outward and inward strokes, forward and back strokes, the forward stroke in stationary steam engines being toward the crosshead, but in locomotives toward the front of the vehicle.
12. Power; influence. [Obs.] “Where money beareth [hath] all the stroke.” Robynson (More's Utopia).
He has a great stroke with the reader. Dryden.
13. Appetite. [Obs.] Swift.
To keep stroke, to make strokes in unison.
The oars where silver,
Which to the tune of flutes kept stroke. Shak.
StrokeStroke (?), v. t. [imp. & p. p. Strokeed (?); p. pr. & vb. n. Strokeing.] [OE. stroken, straken, AS. strācian, fr. strīcan to go over, pass. See Strike, v. t., and cf. Straggle.]
1. To strike. [Obs.]
Ye mote with the plat sword again
Stroken him in the wound, and it will close. Chaucer.
2. To rib gently in one direction; especially, to pass the hand gently over by way of expressing kindness or tenderness; to caress; to soothe.
He dried the falling drops, and, yet more kind,
He stroked her cheeks. Dryden.
3. To make smooth by rubbing. Longfellow.
4. (Masonry) To give a finely fluted surface to.
5. To row the stroke oar of; as, to stroke a boat.
Apoplexy (MeSH), Cerebral Stroke (MeSH), Cerebrovascular Accident (MeSH), Cerebrovascular Accident, Acute (MeSH), Cerebrovascular Apoplexy (MeSH), Cerebrovascular Stroke (MeSH), CVA (Cerebrovascular Accident) (MeSH), Stroke, Acute (MeSH), Vascular Accident, Brain (MeSH)
accident, apoplexy, bang, biff, blow, bop, bow, brushstroke, buffet, cam stroke, caress, cerebral haemorrhage, cerebrovascular accident, chance event, clip, cuff, CVA, dash, diagonal, fit, fortuity, hit, jerk, line, movement, percussion, rap, seizure, separatrix, shot, slap, slash, smack, solidus, stroking, swimming, swimming stroke, swing, throw, thrust, thump, virgule, wallop, whack, wrench
Brain stem stroke syndrome • Brainstem Stroke • Cerebellar stroke syndrome • Cerebral Stroke • Cerebrovascular Stroke • Family history of stroke • Heat Stroke • Key-stroke • Lightning Stroke • Middle Cerebral Artery Stroke • Sequelae of stroke, not specified as haemorrhage or infarction • Stroke Volume • Stroke, Acute • Stroke, Anterior Cerebral Artery • Stroke, Middle Cerebral Artery • Stroke, Posterior Cerebral Artery • Stroke, not specified as haemorrhage or infarction • Sun Stroke • Two-stroke • amnestic stroke • at a stroke • at one stroke • backhand stroke • butterfly stroke • cam stroke • finishing stroke • forehand stroke • four-stroke engine • four-stroke internal-combustion engine • golf stroke • ground stroke • haemorrhagic stroke • hair stroke • hemorrhagic stroke • ischaemic stroke • ischemic stroke • key stroke • master stroke • off one's stroke • return stroke • sequelae of stroke • single-stroke bell • stroke of lightning • stroke of luck • stroke play • swimming stroke • tennis stroke • thin stroke • thromboembolic stroke • two-stroke • two-stroke engine • up stroke • up-stroke • up-stroke of piston • upward stroke
2-stroke power valve system • 4 Stroke Internal Combustion Engine • 4-stroke power valve system • A Bold Stroke for a Wife • A Stroke of Good Fortune • A Stroke of Midnight • Action stroke dance notation • All In (Stroke 9 album) • Anatomy of a rowing stroke • Animal models of ischemic stroke • Animal models of stroke • B with stroke • Ballistic stroke • Boy Meets Girl (Stroke 9 album) • Brain stem stroke syndrome • Breast stroke • Butt stroke • Butterfly stroke • C with stroke • Canadian Stroke Network • Cerebellar stroke syndrome • Che with vertical stroke • Cincinnati Prehospital Stroke Scale • Claude von Stroke • Crower six stroke • D with stroke • D with stroke (disambiguation) • Delayed stroke • Dolorous Stroke • Downward stroke • E with stroke • Equitable Stroke Control • Ford Power Stroke engine • Four-stroke • Four-stroke engine • Four-stroke-engine • Ghe with stroke and hook • Golf stroke mechanics • H with stroke • Heart and Stroke Foundation • Heart and Stroke Foundation of Canada • Hidden Treasures (Stroke 9 album) • J with stroke • K with stroke • Ka with stroke • Ka with vertical stroke • L with stroke • Lacunar stroke • Latin letter O with stroke • List of kanji by stroke count • Man Stroke Woman • Master Stroke • Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes • NIH stroke scale • National Institute of Neurological Disorders and Stroke • National Institutes of Health Stroke Scale • P with stroke • Penalty stroke • Post stroke depression • Power Stroke Diesel • Power Stroke V8 Turbodiesel • Power stroke • Q with stroke • R with stroke • Registry of the Canadian Stroke Network • Return stroke • Saab two-stroke • Sheffer stroke • Single stroke • Single stroke air gun • Single stroke air guns • Single stroke air pistol • Single stroke air pistols • Single stroke air rifle • Single stroke air rifles • Single stroke gun • Single stroke guns • Single stroke pistol • Single stroke pistols • Single stroke pneumatic gun • Single stroke pneumatic guns • Single stroke pneumatic pistol • Single stroke pneumatic pistols • Single stroke pneumatic rifle • Single stroke pneumatic rifles • Single stroke rifle • Single stroke rifles • Single-stroke • Single-stroke air gun • Single-stroke air guns • Single-stroke air pistol • Single-stroke air pistols • Single-stroke air rifle • Single-stroke air rifles • Single-stroke gun • Single-stroke guns • Single-stroke pistol • Single-stroke pistols • Single-stroke pneumatic gun • Single-stroke pneumatic guns • Single-stroke pneumatic pistol • Single-stroke pneumatic pistols • Single-stroke pneumatic rifle • Single-stroke pneumatic rifles • Single-stroke rifle • Single-stroke rifles • Six-stroke engine • Split stroke • Stroke (CJK character) • Stroke (disambiguation) • Stroke (engine) • Stroke (rowing) • Stroke 9 • Stroke Alliance for Europe • Stroke Belt • Stroke Heroes Act FAST • Stroke Network, Inc. • Stroke count method • Stroke in China • Stroke of Fate • Stroke of state • Stroke order • Stroke play • Stroke ratio • Stroke recovery • Stroke speed • Stroke unit • Stroke volume • Stroke-ornamented ware culture • Surname stroke order • Swim stroke • Swimming stroke • Swimmming stroke • Tennis stroke • The Fairy Feller's Master-Stroke • The Finishing Stroke • The Stroke • The Stroke Association • Train to End Stroke • Two and four stroke engines • Two stroke diesel • Two-stroke engine • Two-stroke oil • Up for the Down Stroke • Up for the Down Stroke (song) • Watershed stroke • Whip stroke • Whip-stroke • Y with stroke • Zero stroke
Brain Diseases, Brain Disorders, Brain Pathology, Central Nervous System Disorders, Intracranial, Central Nervous System Intracranial Disorders, CNS Disorders, Intracranial, Encephalon Diseases, Intracranial Central Nervous System Disorders, Intracranial CNS Disorders, Pathology, Brain - Vascular Diseases[Hyper.]
Stroke (n.) [MeSH]
technique spécifique (fr)[Classe...]
stroke; swimming stroke[ClasseHyper.]
phénomène atmosphérique de temps d'orage (fr)[ClasseParExt.]
éclat lumineux (fr)[ClasseParExt...]
phénomène électrique (fr)[Classe]
phénomène électrique (fr)[Classe...]
stroke (n.) [ellipsis]
geste affectueux (fr)[Classe]
aimer les personnes (fr)[Thème]
geste de la main (fr)[Classe]
témoignage d'affection (fr)[Classe]
motion; movement; move; action[ClasseHyper.]
play - play - channelise, channelize, direct, guide, head, maneuver, manoeuver, manoeuvre, point, steer - shot, stroke - cavort, disport, frisk, frolic, gambol, lark, lark about, rollick, romp, run around, skylark, sport - acrobatic, athletic, gymnastic[Dérivé]
action, motion, move, movement[Hyper.]
punctuation; punctuation mark[ClasseHyper.]
R2 : Signes de ponctuation (fr)[Classe...]
(punctuation; punctuation mark)[termes liés]
punctuation, punctuation mark[Hyper.]
contact, impinging, striking[Hyper.]
personne qui rame (fr)[Classe]
boater, boatman, waterman[Hyper.]
pull, row, scull[PersonneQui~]
maladie : système nerveux (fr)[Classe]
qualificatif d'une maladie (fr)[DomaineDescription]
maladie du cerveau (fr)[Classe]
event, happening, occurrence[Hyper.]
sport de balle (fr)[Classe]
(turf; lawn)[termes liés]
combat : fait de se battre (fr)[Classe]
stroke (v. tr.)
stroke (v. tr.)
row; pull; scull[ClasseHyper.]
stroke (v. tr.)
touch; dab; dab at[Classe]
geste de la main (fr)[Classe]
témoignage d'affection (fr)[Classe]
stroke (v. tr.)
|Classification and external resources|
CT scan slice of the brain showing a right-hemispheric ischemic stroke (left side of image).
|eMedicine||neuro/9 emerg/558 emerg/557 pmr/187|
A stroke, or cerebrovascular accident (CVA), is the rapid loss of brain function(s) due to disturbance in the blood supply to the brain. This can be due to ischemia (lack of blood flow) caused by blockage (thrombosis, arterial embolism), or a hemorrhage (leakage of blood). As a result, the affected area of the brain cannot function, which might result in an inability to move one or more limbs on one side of the body, inability to understand or formulate speech, or an inability to see one side of the visual field.
A stroke is a medical emergency and can cause permanent neurological damage, complications, and death. It is the leading cause of adult disability in the United States and Europe and the second leading cause of death worldwide. Risk factors for stroke include old age, hypertension (high blood pressure), previous stroke or transient ischemic attack (TIA), diabetes, high cholesterol, cigarette smoking and atrial fibrillation. High blood pressure is the most important modifiable risk factor of stroke.
An ischemic stroke is occasionally treated in a hospital with thrombolysis (also known as a "clot buster"), and some hemorrhagic strokes benefit from neurosurgery. Treatment to recover any lost function is termed stroke rehabilitation, ideally in a stroke unit and involving health professions such as speech and language therapy, physical therapy and occupational therapy. Prevention of recurrence may involve the administration of antiplatelet drugs such as aspirin and dipyridamole, control and reduction of hypertension, and the use of statins. Selected patients may benefit from carotid endarterectomy and the use of anticoagulants.
Strokes can be classified into two major categories: ischemic and hemorrhagic. Ischemic strokes are those that are caused by interruption of the blood supply, while hemorrhagic strokes are the ones which result from rupture of a blood vessel or an abnormal vascular structure. About 87% of strokes are caused by ischemia, and the remainder by hemorrhage. Some hemorrhages develop inside areas of ischemia ("hemorrhagic transformation"). It is unknown how many hemorrhages actually start as ischemic stroke.
In an ischemic stroke, blood supply to part of the brain is decreased, leading to dysfunction of the brain tissue in that area. There are four reasons why this might happen:
There are various classification systems for acute ischemic stroke. The Oxford Community Stroke Project classification (OCSP, also known as the Bamford or Oxford classification) relies primarily on the initial symptoms; based on the extent of the symptoms, the stroke episode is classified as total anterior circulation infarct (TACI), partial anterior circulation infarct (PACI), lacunar infarct (LACI) or posterior circulation infarct (POCI). These four entities predict the extent of the stroke, the area of the brain affected, the underlying cause, and the prognosis. The TOAST (Trial of Org 10172 in Acute Stroke Treatment) classification is based on clinical symptoms as well as results of further investigations; on this basis, a stroke is classified as being due to (1) thrombosis or embolism due to atherosclerosis of a large artery, (2) embolism of cardiac origin, (3) occlusion of a small blood vessel, (4) other determined cause, (5) undetermined cause (two possible causes, no cause identified, or incomplete investigation).
Intracranial hemorrhage is the accumulation of blood anywhere within the skull vault. A distinction is made between intra-axial hemorrhage (blood inside the brain) and extra-axial hemorrhage (blood inside the skull but outside the brain). Intra-axial hemorrhage is due to intraparenchymal hemorrhage or intraventricular hemorrhage (blood in the ventricular system). The main types of extra-axial hemorrhage are epidural hematoma (bleeding between the dura mater and the skull), subdural hematoma (in the subdural space) and subarachnoid hemorrhage (between the arachnoid mater and pia mater). Most of the hemorrhagic stroke syndromes have specific symptoms (e.g., headache, previous head injury).
Stroke symptoms typically start suddenly, over seconds to minutes, and in most cases do not progress further. The symptoms depend on the area of the brain affected. The more extensive the area of brain affected, the more functions that are likely to be lost. Some forms of stroke can cause additional symptoms. For example, in intracranial hemorrhage, the affected area may compress other structures. Most forms of stroke are not associated with headache, apart from subarachnoid hemorrhage and cerebral venous thrombosis and occasionally intracerebral hemorrhage.
Various systems have been proposed to increase recognition of stroke by patients, relatives and emergency first responders. A systematic review, updating a previous systematic review from 1994, looked at a number of trials to evaluate how well different physical examination findings are able to predict the presence or absence of stroke. It was found that sudden-onset face weakness, arm drift (i.e., if a person, when asked to raise both arms, involuntarily lets one arm drift downward) and abnormal speech are the findings most likely to lead to the correct identification of a case of stroke (+ likelihood ratio of 5.5 when at least one of these is present). Similarly, when all three of these are absent, the likelihood of stroke is significantly decreased (– likelihood ratio of 0.39). While these findings are not perfect for diagnosing stroke, the fact that they can be evaluated relatively rapidly and easily make them very valuable in the acute setting.
Proposed systems include FAST (stroke) (face, arm, speech, and time), as advocated by the Department of Health (United Kingdom) and The Stroke Association, the American Stroke Association (www.strokeassociation.org), National Stroke Association (US www.stroke.org), the Los Angeles Prehospital Stroke Screen (LAPSS) and the Cincinnati Prehospital Stroke Scale (CPSS). Use of these scales is recommended by professional guidelines.
For people referred to the emergency room, early recognition of stroke is deemed important as this can expedite diagnostic tests and treatments. A scoring system called ROSIER (recognition of stroke in the emergency room) is recommended for this purpose; it is based on features from the medical history and physical examination.
If the area of the brain affected contains one of the three prominent central nervous system pathways—the spinothalamic tract, corticospinal tract, and dorsal column (medial lemniscus), symptoms may include:
In most cases, the symptoms affect only one side of the body (unilateral). Depending on the part of the brain affected, the defect in the brain is usually on the opposite side of the body. However, since these pathways also travel in the spinal cord and any lesion there can also produce these symptoms, the presence of any one of these symptoms does not necessarily indicate a stroke.
In addition to the above CNS pathways, the brainstem gives rise to most of the twelve cranial nerves. A stroke affecting the brain stem and brain therefore can produce symptoms relating to deficits in these cranial nerves:
If the cerebral cortex is involved, the CNS pathways can again be affected, but also can produce the following symptoms:
If the cerebellum is involved, the patient may have the following:
Loss of consciousness, headache, and vomiting usually occurs more often in hemorrhagic stroke than in thrombosis because of the increased intracranial pressure from the leaking blood compressing the brain.
If symptoms are maximal at onset, the cause is more likely to be a subarachnoid hemorrhage or an embolic stroke.
|This section needs additional citations for verification. (September 2008)|
In thrombotic stroke a thrombus (blood clot) usually forms around atherosclerotic plaques. Since blockage of the artery is gradual, onset of symptomatic thrombotic strokes is slower. A thrombus itself (even if non-occluding) can lead to an embolic stroke (see below) if the thrombus breaks off, at which point it is called an "embolus." Two types of thrombosis can cause stroke:
Sickle-cell anemia, which can cause blood cells to clump up and block blood vessels, can also lead to stroke. A stroke is the second leading killer of people under 20 who suffer from sickle-cell anemia.
An embolic stroke refers to the blockage of an artery by an arterial embolus, a travelling particle or debris in the arterial bloodstream originating from elsewhere. An embolus is most frequently a thrombus, but it can also be a number of other substances including fat (e.g., from bone marrow in a broken bone), air, cancer cells or clumps of bacteria (usually from infectious endocarditis).
Because an embolus arises from elsewhere, local therapy solves the problem only temporarily. Thus, the source of the embolus must be identified. Because the embolic blockage is sudden in onset, symptoms usually are maximal at start. Also, symptoms may be transient as the embolus is partially resorbed and moves to a different location or dissipates altogether.
Emboli most commonly arise from the heart (especially in atrial fibrillation) but may originate from elsewhere in the arterial tree. In paradoxical embolism, a deep vein thrombosis embolises through an atrial or ventricular septal defect in the heart into the brain.
Cardiac causes can be distinguished between high and low-risk:
Systemic hypoperfusion is the reduction of blood flow to all parts of the body. It is most commonly due to cardiac pump failure from cardiac arrest or arrhythmias, or from reduced cardiac output as a result of myocardial infarction, pulmonary embolism, pericardial effusion, or bleeding. Hypoxemia (low blood oxygen content) may precipitate the hypoperfusion. Because the reduction in blood flow is global, all parts of the brain may be affected, especially "watershed" areas - border zone regions supplied by the major cerebral arteries. A watershed stroke refers to the condition when blood supply to these areas is compromised. Blood flow to these areas does not necessarily stop, but instead it may lessen to the point where brain damage can occur. This phenomenon is also referred to as "last meadow" to point to the fact that in irrigation the last meadow receives the least amount of water.
Cerebral venous sinus thrombosis leads to stroke due to locally increased venous pressure, which exceeds the pressure generated by the arteries. Infarcts are more likely to undergo hemorrhagic transformation (leaking of blood into the damaged area) than other types of ischemic stroke.
It generally occurs in small arteries or arterioles and is commonly due to hypertension, intracranial vascular malformations (including cavernous angiomas or arteriovenous malformations), cerebral amyloid angiopathy, or infarcts into which secondary haemorrhage has occurred. Other potential causes are trauma, bleeding disorders, amyloid angiopathy, illicit drug use (e.g., amphetamines or cocaine). The hematoma enlarges until pressure from surrounding tissue limits its growth, or until it decompresses by emptying into the ventricular system, CSF or the pial surface. A third of intracerebral bleed is into the brain's ventricles. ICH has a mortality rate of 44 percent after 30 days, higher than ischemic stroke or subarachnoid hemorrhage (which technically may also be classified as a type of stroke).
A silent stroke is a stroke that does not have any outward symptoms, and the patients are typically unaware they have suffered a stroke. Despite not causing identifiable symptoms, a silent stroke still causes damage to the brain, and places the patient at increased risk for both transient ischemic attack and major stroke in the future. Conversely, those who have suffered a major stroke are at risk of having silent strokes. In a broad study in 1998, more than 11 million people were estimated to have experienced a stroke in the United States. Approximately 770,000 of these strokes were symptomatic and 11 million were first-ever silent MRI infarcts or hemorrhages. Silent strokes typically cause lesions which are detected via the use of neuroimaging such as MRI. Silent strokes are estimated to occur at five times the rate of symptomatic strokes. The risk of silent stroke increases with age, but may also affect younger adults and children, especially those with acute anemia.
|This section needs additional citations for verification. (September 2008)|
Ischemic stroke occurs because of a loss of blood supply to part of the brain, initiating the ischemic cascade. Brain tissue ceases to function if deprived of oxygen for more than 60 to 90 seconds and after approximately three hours, will suffer irreversible injury possibly leading to death of the tissue, i.e., infarction. (This is why fibrinolytics such as alteplase are given only until three hours since the onset of the stroke.) Atherosclerosis may disrupt the blood supply by narrowing the lumen of blood vessels leading to a reduction of blood flow, by causing the formation of blood clots within the vessel, or by releasing showers of small emboli through the disintegration of atherosclerotic plaques. Embolic infarction occurs when emboli formed elsewhere in the circulatory system, typically in the heart as a consequence of atrial fibrillation, or in the carotid arteries, break off, enter the cerebral circulation, then lodge in and occlude brain blood vessels. Since blood vessels in the brain are now occluded, the brain becomes low in energy, and thus it resorts into using anaerobic metabolism within the region of brain tissue affected by ischemia. Unfortunately, this kind of metabolism produces less adenosine triphosphate (ATP) but releases a by-product called lactic acid. Lactic acid is an irritant which could potentially destroy cells since it is an acid and disrupts the normal acid-base balance in the brain. The ischemia area is referred to as the "ischemic penumbra".
Then, as oxygen or glucose becomes depleted in ischemic brain tissue, the production of high energy phosphate compounds such as adenosine triphosphate (ATP) fails, leading to failure of energy-dependent processes (such as ion pumping) necessary for tissue cell survival. This sets off a series of interrelated events that result in cellular injury and death. A major cause of neuronal injury is release of the excitatory neurotransmitter glutamate. The concentration of glutamate outside the cells of the nervous system is normally kept low by so-called uptake carriers, which are powered by the concentration gradients of ions (mainly Na+) across the cell membrane. However, stroke cuts off the supply of oxygen and glucose which powers the ion pumps maintaining these gradients. As a result the transmembrane ion gradients run down, and glutamate transporters reverse their direction, releasing glutamate into the extracellular space. Glutamate acts on receptors in nerve cells (especially NMDA receptors), producing an influx of calcium which activates enzymes that digest the cells' proteins, lipids and nuclear material. Calcium influx can also lead to the failure of mitochondria, which can lead further toward energy depletion and may trigger cell death due to apoptosis.
Ischemia also induces production of oxygen free radicals and other reactive oxygen species. These react with and damage a number of cellular and extracellular elements. Damage to the blood vessel lining or endothelium is particularly important. In fact, many antioxidant neuroprotectants such as uric acid and NXY-059 work at the level of the endothelium and not in the brain per se. Free radicals also directly initiate elements of the apoptosis cascade by means of redox signaling.
These processes are the same for any type of ischemic tissue and are referred to collectively as the ischemic cascade. However, brain tissue is especially vulnerable to ischemia since it has little respiratory reserve and is completely dependent on aerobic metabolism, unlike most other organs.
Brain tissue survival can be improved to some extent if one or more of these processes is inhibited. Drugs that scavenge reactive oxygen species, inhibit apoptosis, or inhibit excitatory neurotransmitters, for example, have been shown experimentally to reduce tissue injury caused by ischemia. Agents that work in this way are referred to as being neuroprotective. Until recently, human clinical trials with neuroprotective agents have failed, with the probable exception of deep barbiturate coma. However, more recently NXY-059, the disulfonyl derivative of the radical-scavenging spintrap phenylbutylnitrone, is reported to be neuroprotective in stroke. This agent appears to work at the level of the blood vessel lining or endothelium. Unfortunately, after producing favorable results in one large-scale clinical trial, a second trial failed to show favorable results.
In addition to injurious effects on brain cells, ischemia and infarction can result in loss of structural integrity of brain tissue and blood vessels, partly through the release of matrix metalloproteases, which are zinc- and calcium-dependent enzymes that break down collagen, hyaluronic acid, and other elements of connective tissue. Other proteases also contribute to this process. The loss of vascular structural integrity results in a breakdown of the protective blood brain barrier that contributes to cerebral edema, which can cause secondary progression of the brain injury.
As is the case with any type of brain injury, the immune system is activated by cerebral infarction and may under some circumstances exacerbate the injury caused by the infarction. Inhibition of the inflammatory response has been shown experimentally to reduce tissue injury due to cerebral infarction, but this has not proved out in clinical studies.
Hemorrhagic strokes result in tissue injury by causing compression of tissue from an expanding hematoma or hematomas. This can distort and injure tissue. In addition, the pressure may lead to a loss of blood supply to affected tissue with resulting infarction, and the blood released by brain hemorrhage appears to have direct toxic effects on brain tissue and vasculature. Inflammation contributes to the secondary brain injury after hemorrhage.
Stroke is diagnosed through several techniques: a neurological examination (such as the Nihss), CT scans (most often without contrast enhancements) or MRI scans, Doppler ultrasound, and arteriography. The diagnosis of stroke itself is clinical, with assistance from the imaging techniques. Imaging techniques also assist in determining the subtypes and cause of stroke. There is yet no commonly used blood test for the stroke diagnosis itself, though blood tests may be of help in finding out the likely cause of stroke.
The traditional definition of stroke, devised by the World Health Organization in the 1970s, is a "neurological deficit of cerebrovascular cause that persists beyond 24 hours or is interrupted by death within 24 hours". This definition was supposed to reflect the reversibility of tissue damage and was devised for the purpose, with the time frame of 24 hours being chosen arbitrarily. The 24-hour limit divides stroke from transient ischemic attack, which is a related syndrome of stroke symptoms that resolve completely within 24 hours. With the availability of treatments that, when given early, can reduce stroke severity, many now prefer alternative concepts, such as brain attack and acute ischemic cerebrovascular syndrome (modeled after heart attack and acute coronary syndrome, respectively), that reflect the urgency of stroke symptoms and the need to act swiftly.
A physical examination, including taking a medical history of the symptoms and a neurological status, helps giving an evaluation of the location and severity of a stroke. It can give a standard score on e.g., the NIH stroke scale.
For diagnosing ischemic stroke in the emergency setting:
For diagnosing hemorrhagic stroke in the emergency setting:
For detecting chronic hemorrhages, MRI scan is more sensitive.
For the assessment of stable stroke, nuclear medicine scans SPECT and PET/CT may be helpful. SPECT documents cerebral blood flow and PET with FDG isotope the metabolic activity of the neurons.
When a stroke has been diagnosed, various other studies may be performed to determine the underlying cause. With the current treatment and diagnosis options available, it is of particular importance to determine whether there is a peripheral source of emboli. Test selection may vary, since the cause of stroke varies with age, comorbidity and the clinical presentation. Commonly used techniques include:
Given the disease burden of strokes, prevention is an important public health concern. Primary prevention is less effective than secondary prevention (as judged by the number needed to treat to prevent one stroke per year). Recent guidelines detail the evidence for primary prevention in stroke. Because stroke may indicate underlying atherosclerosis, it is important to determine the patient's risk for other cardiovascular diseases such as coronary heart disease. Conversely, aspirin confers some protection against first stroke in patients who have suffered a myocardial infarction or patients with a high cardiovascular risk.
The most important modifiable risk factors for stroke are high blood pressure and atrial fibrillation (although magnitude of this effect is small: the evidence from the Medical Research Council trials is that 833 patients have to be treated for 1 year to prevent one stroke). Other modifiable risk factors include high blood cholesterol levels, diabetes, cigarette smoking (active and passive), heavy alcohol consumption and drug use, lack of physical activity, obesity, processed red meat consumption and unhealthy diet. Alcohol use could predispose to ischemic stroke, and intracerebral and subarachnoid hemorrhage via multiple mechanisms (for example via hypertension, atrial fibrillation, rebound thrombocytosis and platelet aggregation and clotting disturbances). The drugs most commonly associated with stroke are cocaine, amphetamines causing hemorrhagic stroke, but also over-the-counter cough and cold drugs containing sympathomimetics.
No high quality studies have shown the effectiveness of interventions aimed at weight reduction, promotion of regular exercise, reducing alcohol consumption or smoking cessation. Nonetheless, given the large body of circumstantial evidence, best medical management for stroke includes advice on diet, exercise, smoking and alcohol use. Medication or drug therapy is the most common method of stroke prevention; carotid endarterectomy can be a useful surgical method of preventing stroke.
Hypertension accounts for 35-50% of stroke risk. Epidemiological studies suggest that even a small blood pressure reduction (5 to 6 mmHg systolic, 2 to 3 mmHg diastolic) would result in 40% fewer strokes. Lowering blood pressure has been conclusively shown to prevent both ischemic and hemorrhagic strokes. It is equally important in secondary prevention. Even patients older than 80 years and those with isolated systolic hypertension benefit from antihypertensive therapy. Studies show that intensive antihypertensive therapy results in a greater risk reduction. The available evidence does not show large differences in stroke prevention between antihypertensive drugs —therefore, other factors such as protection against other forms of cardiovascular disease should be considered and cost.
Patients with atrial fibrillation have a risk of 5% each year to develop stroke, and this risk is even higher in those with valvular atrial fibrillation. Depending on the stroke risk, anticoagulation with medications such as coumarins or aspirin is warranted for stroke prevention.
High cholesterol levels have been inconsistently associated with (ischemic) stroke. Statins have been shown to reduce the risk of stroke by about 15%. Since earlier meta-analyses of other lipid-lowering drugs did not show a decreased risk, statins might exert their effect through mechanisms other than their lipid-lowering effects.
Patients with diabetes mellitus are 2 to 3 times more likely to develop stroke, and they commonly have hypertension and hyperlipidemia. Intensive disease control has been shown to reduce microvascular complications such as nephropathy and retinopathy but not macrovascular complications such as stroke.
Oral anticoagulants such as warfarin have been the mainstay of stroke prevention for over 50 years. However, several studies have shown that aspirin and antiplatelet drugs are highly effective in secondary prevention after a stroke or transient ischemic attack. Low doses of aspirin (for example 75–150 mg) are as effective as high doses but have fewer side effects; the lowest effective dose remains unknown. Thienopyridines (clopidogrel, ticlopidine) "might be slightly more effective" than aspirin and have a decreased risk of gastrointestinal bleeding, but they are more expensive. Their exact role remains controversial. Ticlopidine has more skin rash, diarrhea, neutropenia and thrombotic thrombocytopenic purpura. Dipyridamole can be added to aspirin therapy to provide a small additional benefit, even though headache is a common side effect. Low-dose aspirin is also effective for stroke prevention after sustaining a myocardial infarction. Except for in atrial fibrillation, oral anticoagulants are not advised for stroke prevention —any benefit is offset by bleeding risk.
In primary prevention however, antiplatelet drugs did not reduce the risk of ischemic stroke while increasing the risk of major bleeding. Further studies are needed to investigate a possible protective effect of aspirin against ischemic stroke in women.
Surgical procedures such as carotid endarterectomy or carotid angioplasty can be used to remove significant atherosclerotic narrowing (stenosis) of the carotid artery, which supplies blood to the brain. There is a large body of evidence supporting this procedure in selected cases. Endarterectomy for a significant stenosis has been shown to be useful in the secondary prevention after a previous symptomatic stroke. Carotid artery stenting has not been shown to be equally useful. Patients are selected for surgery based on age, gender, degree of stenosis, time since symptoms and patients' preferences. Surgery is most efficient when not delayed too long —the risk of recurrent stroke in a patient who has a 50% or greater stenosis is up to 20% after 5 years, but endarterectomy reduces this risk to around 5%. The number of procedures needed to cure one patient was 5 for early surgery (within two weeks after the initial stroke), but 125 if delayed longer than 12 weeks.
Screening for carotid artery narrowing has not been shown to be a useful screening test in the general population. Studies of surgical intervention for carotid artery stenosis without symptoms have shown only a small decrease in the risk of stroke. To be beneficial, the complication rate of the surgery should be kept below 4%. Even then, for 100 surgeries, 5 patients will benefit by avoiding stroke, 3 will develop stroke despite surgery, 3 will develop stroke or die due to the surgery itself, and 89 will remain stroke-free but would also have done so without intervention.
With regard to lowering homocysteine, a meta-analysis of previous trials has concluded that lowering homocysteine with folic acid and other supplements may reduce stroke risk. However, the two largest randomized controlled trials included in the meta-analysis had conflicting results. One reported positive results; whereas the other was negative.
The European Society of Cardiology and the European Association for Cardiovascular Prevention and Rehabilitation have developed an interactive tool for prediction and managing the risk of heart attack and stroke in Europe. HeartScore is aimed at supporting clinicians in optimising individual cardiovascular risk reduction. The Heartscore Programme is available in 12 languages and offers web based or PC version.
Ideally, people who have had a stroke are admitted to a "stroke unit", a ward or dedicated area in hospital staffed by nurses and therapists with experience in stroke treatment. It has been shown that people admitted to a stroke unit have a higher chance of surviving than those admitted elsewhere in hospital, even if they are being cared for by doctors without experience in stroke.
When an acute stroke is suspected by history and physical examination, the goal of early assessment is to determine the cause. Treatment varies according to the underlying cause of the stroke, thromboembolic (ischemic) or hemorrhagic. A non-contrast head CT scan can rapidly identify a hemorrhagic stroke by imaging bleeding in or around the brain. If no bleeding is seen, a presumptive diagnosis of ischemic stroke is made.
An ischemic stroke is caused by a thrombus (blood clot) occluding blood flow to an artery supplying the brain. Definitive therapy is aimed at removing the blockage by breaking the clot down (thrombolysis), or by removing it mechanically (thrombectomy). The more rapidly blood flow is restored to the brain, the fewer brain cells die.
Other medical therapies are aimed at minimizing clot enlargement or preventing new clots from forming. To this end, treatment with medications such as aspirin, clopidogrel and dipyridamole may be given to prevent platelets from aggregating.
Tight control of blood sugars in the first few hours does not improve outcomes and may cause harm. High blood pressure is also not typically lowered as this has not been found to be helpful.
Thrombolysis with recombinant tissue plasminogen activator (rtPA) in acute ischemic stroke, when given before three to six hours of symptom onset increases the risk of death in the short term but in the long term improves the rate of independence and late mortality; there is no net change in mortality. It use is endorsed by the American Heart Association and the American Academy of Neurology as the recommended treatment for acute stroke within three hours of onset of symptoms as long as there are not other contraindications (such as abnormal lab values, high blood pressure, or recent surgery). This position for tPA is based upon the findings of two studies by one group of investigators which showed that tPA improves the chances for a good neurological outcome. When administered within the first three hours thrombolysis improves functional outcome without affecting mortality. Alteplase for thrombolysis in ischemic stroke may be of benefit with administration 3 to 4.5 hours after stroke onset. 6.4% of people with large strokes developed substantial brain hemorrhage as a complication from being given tPA thus part of the reason for increased short term mortality. Additionally, it is the position of the American Academy of Emergency Medicine that objective evidence regarding the efficacy, safety, and applicability of tPA for acute ischemic stroke is insufficient to warrant its classification as standard of care. Intra-arterial fibrinolysis, where a catheter is passed up an artery into the brain and the medication is injected at the site of thrombosis, has been found to improve outcomes in people with acute ischemic stroke.
Another intervention for acute ischemic stroke is removal of the offending thrombus directly. This is accomplished by inserting a catheter into the femoral artery, directing it into the cerebral circulation, and deploying a corkscrew-like device to ensnare the clot, which is then withdrawn from the body. Mechanical embolectomy devices have been demonstrated effective at restoring blood flow in patients who were unable to receive thrombolytic drugs or for whom the drugs were ineffective, though no differences have been found between newer and older versions of the devices. The devices have only been tested on patients treated with mechanical clot embolectomy within eight hours of the onset of symptoms.
Angioplasty and stenting have begun to be looked at as possible viable options in treatment of acute ischemic stroke. In a systematic review of six uncontrolled, single-center trials, involving a total of 300 patients, of intra-cranial stenting in symptomatic intracranial arterial stenosis, the rate of technical success (reduction to stenosis of <50%) ranged from 90-98%, and the rate of major peri-procedural complications ranged from 4-10%. The rates of restenosis and/or stroke following the treatment were also favorable. This data suggests that a large, randomized controlled trial is needed to more completely evaluate the possible therapeutic advantage of this treatment.
Large territory strokes can cause significant edema of the brain with secondary brain injury in surrounding tissue. This phenomenon is mainly encountered in strokes of the middle cerebral artery territory, and is also called "malignant cerebral infaction" because it carries a dismal prognosis. Relief of the pressure may be attempted with medication, but some require hemicraniectomy, the temporary surgical removal of the skull on one side of the head. This confers a marked improvement in the risk of death, although some more people survive with disability who would otherwise have died.
Anticoagulation can prevent recurrent stroke. Among patients with nonvalvular atrial fibrillation, anticoagulation can reduce stroke by 60% while antiplatelet agents can reduce stroke by 20%. However, a recent meta-analysis suggests harm from anti-coagulation started early after an embolic stroke. Stroke prevention treatment for atrial fibrillation is determined according to the CHADS/CHADS2 system. The most widely used anticoagulant to prevent thromboembolic stroke in patients with nonvalvular atrial fibrillation is the oral agent Warfarin while dabigatran is a new alternative which does not require prothrombin time monitoring.
If studies show carotid stenosis, and the patient has residual function in the affected side, carotid endarterectomy (surgical removal of the stenosis) may decrease the risk of recurrence if performed rapidly after stroke.
People with intracerebral hemorrhage require neurosurgical evaluation to detect and treat the cause of the bleeding, although many may not need surgery. Anticoagulants and antithrombotics, key in treating ischemic stroke, can make bleeding worse and cannot be used in intracerebral hemorrhage. Patients are monitored for changes in the level of consciousness, and their blood pressure, blood sugar, and oxygenation are kept at optimum levels.
Stroke rehabilitation is the process by which patients with disabling strokes undergo treatment to help them return to normal life as much as possible by regaining and relearning the skills of everyday living. It also aims to help the survivor understand and adapt to difficulties, prevent secondary complications and educate family members to play a supporting role.
A rehabilitation team is usually multidisciplinary as it involves staff with different skills working together to help the patient. These include nursing staff, physiotherapy, occupational therapy, speech and language therapy, and usually a physician trained in rehabilitation medicine. Some teams may also include psychologists, social workers, and pharmacists since at least one third of the patients manifest post stroke depression. Validated instruments such as the Barthel scale may be used to assess the likelihood of a stroke patient being able to manage at home with or without support subsequent to discharge from hospital.
Good nursing care is fundamental in maintaining skin care, feeding, hydration, positioning, and monitoring vital signs such as temperature, pulse, and blood pressure. Stroke rehabilitation begins almost immediately.
For most stroke patients, physical therapy (PT), occupational therapy (OT) and speech-language pathology (SLP) are the cornerstones of the rehabilitation process. Often, assistive technology such as a wheelchair, walkers, canes, and orthosis may be beneficial. PT and OT have overlapping areas of expertise, however PT focuses on joint range of motion and strength by performing exercises and re-learning functional tasks such as bed mobility, transferring, walking and other gross motor functions. Physiotherapists can also work with patients to improve awareness and use of the hemiplegic side. Rehabilitation involves working on the ability to produce strong movements or the ability to perform tasks using normal patterns. Emphasis is often concentrated on functional tasks and patient’s goals. One example physiotherapists employ to promote motor learning involves constraint-induced movement therapy. Through continuous practice the patient relearns to use and adapt the hemiplegic limb during functional activities to create lasting permanent changes. OT is involved in training to help relearn everyday activities known as the Activities of daily living (ADLs) such as eating, drinking, dressing, bathing, cooking, reading and writing, and toileting. Speech and language therapy is appropriate for patients with the speech production disorders: dysarthria and apraxia of speech, aphasia, cognitive-communication impairments and/or dysphagia (problems with swallowing).
Patients may have particular problems, such as dysphagia, which can cause swallowed material to pass into the lungs and cause aspiration pneumonia. The condition may improve with time, but in the interim, a nasogastric tube may be inserted, enabling liquid food to be given directly into the stomach. If swallowing is still deemed unsafe, then a percutaneous endoscopic gastrostomy (PEG) tube is passed and this can remain indefinitely.
Treatment of spasticity related to stroke often involves early mobilisations, commonly performed by a physiotherapist, combined with elongation of spastic muscles and sustained stretching through various positioning. Gaining initial improvements in range of motion is often achieved through rhythmic rotational patterns associated with the affected limb. After full range has been achieved by the therapist, the limb should be positioned in the lengthened positions to prevent against further contractures, skin breakdown, and disuse of the limb with the use of splints or other tools to stabilize the joint. Cold in the form of ice wraps or ice packs have been proven to briefly reduce spasticity by temporarily dampening neural firing rates. Electrical stimulation to the antagonist muscles or vibrations has also been used with some success.
Stroke rehabilitation should be started as quickly as possible and can last anywhere from a few days to over a year. Most return of function is seen in the first few months, and then improvement falls off with the "window" considered officially by U.S. state rehabilitation units and others to be closed after six months, with little chance of further improvement. However, patients have been known to continue to improve for years, regaining and strengthening abilities like writing, walking, running, and talking. Daily rehabilitation exercises should continue to be part of the stroke patient's routine. Complete recovery is unusual but not impossible and most patients will improve to some extent: proper diet and exercise are known to help the brain to recover.
Some current and future therapy methods include the use of virtual reality and video games for rehabilitation. These forms of rehabilitation offer potential for motivating patients to perform specific therapy tasks that many other forms do not. Many clinics and hospitals are adopting the use of these off-the-shelf devices for exercise, social interaction and rehabilitation because they are affordable, accessible and can be used within the clinic and home..
Other novel non-invasive rehabilitation methods are currently being developed to augment physical therapy to improve motor function of stroke patients, such as transcranial magnetic stimulation (TMS) and transcranial direct-current stimulation (tDCS) and robotic therapies.
Disability affects 75% of stroke survivors enough to decrease their employability. Stroke can affect patients physically, mentally, emotionally, or a combination of the three. The results of stroke vary widely depending on size and location of the lesion. Dysfunctions correspond to areas in the brain that have been damaged.
Some of the physical disabilities that can result from stroke include muscle weakness, numbness, pressure sores, pneumonia, incontinence, apraxia (inability to perform learned movements), difficulties carrying out daily activities, appetite loss, speech loss, vision loss, and pain. If the stroke is severe enough, or in a certain location such as parts of the brainstem, coma or death can result.
Emotional problems resulting from stroke can result from direct damage to emotional centers in the brain or from frustration and difficulty adapting to new limitations. Post-stroke emotional difficulties include anxiety, panic attacks, flat affect (failure to express emotions), mania, apathy, and psychosis.
30 to 50% of stroke survivors suffer post stroke depression, which is characterized by lethargy, irritability, sleep disturbances, lowered self esteem, and withdrawal. Depression can reduce motivation and worsen outcome, but can be treated with antidepressants.
Emotional lability, another consequence of stroke, causes the patient to switch quickly between emotional highs and lows and to express emotions inappropriately, for instance with an excess of laughing or crying with little or no provocation. While these expressions of emotion usually correspond to the patient's actual emotions, a more severe form of emotional lability causes patients to laugh and cry pathologically, without regard to context or emotion. Some patients show the opposite of what they feel, for example crying when they are happy. Emotional lability occurs in about 20% of stroke patients.
Cognitive deficits resulting from stroke include perceptual disorders, Aphasia, dementia, and problems with attention and memory. A stroke sufferer may be unaware of his or her own disabilities, a condition called anosognosia. In a condition called hemispatial neglect, a patient is unable to attend to anything on the side of space opposite to the damaged hemisphere.
Stroke could soon be the most common cause of death worldwide. Stroke is currently the second leading cause of death in the Western world, ranking after heart disease and before cancer, and causes 10% of deaths worldwide. Geographic disparities in stroke incidence have been observed, including the existence of a "stroke belt" in the southeastern United States, but causes of these disparities have not been explained.
The incidence of stroke increases exponentially from 30 years of age, and etiology varies by age. Advanced age is one of the most significant stroke risk factors. 95% of strokes occur in people age 45 and older, and two-thirds of strokes occur in those over the age of 65. A person's risk of dying if he or she does have a stroke also increases with age. However, stroke can occur at any age, including in childhood.
Family members may have a genetic tendency for stroke or share a lifestyle that contributes to stroke. Higher levels of Von Willebrand factor are more common amongst people who have had ischemic stroke for the first time. The results of this study found that the only significant genetic factor was the person's blood type. Having had a stroke in the past greatly increases one's risk of future strokes.
Men are 25% more likely to suffer strokes than women, yet 60% of deaths from stroke occur in women. Since women live longer, they are older on average when they have their strokes and thus more often killed (NIMH 2002). Some risk factors for stroke apply only to women. Primary among these are pregnancy, childbirth, menopause and the treatment thereof (HRT).
Episodes of stroke and familial stroke have been reported from the 2nd millennium BC onward in ancient Mesopotamia and Persia. Hippocrates (460 to 370 BC) was first to describe the phenomenon of sudden paralysis that is often associated with ischemia. Apoplexy, from the Greek word meaning "struck down with violence," first appeared in Hippocratic writings to describe this phenomenon.
In 1658, in his Apoplexia, Johann Jacob Wepfer (1620–1695) identified the cause of hemorrhagic stroke when he suggested that people who had died of apoplexy had bleeding in their brains. Wepfer also identified the main arteries supplying the brain, the vertebral and carotid arteries, and identified the cause of ischemic stroke [also known as cerebral infarction] when he suggested that apoplexy might be caused by a blockage to those vessels.