What is Cerebral Ischemia (Stroke)?
The human brain, despite making up just 2.5% of a person’s body weight, uses up about 25% of the body’s energy. This high energy usage makes the brain extremely sensitive to any changes in blood flow. There are intricate systems in the body that work to keep the flow of blood to the brain steady, providing about 50 milliliters of blood for every 100 grams of brain tissue each minute. This is a process called cerebrovascular autoregulation.
If the blood flow to the brain is disrupted or reduced, it can result in a condition called cerebral ischemia, a common cause of brain damage and dysfunction. This basically means that part of the brain is not getting enough blood. The amount of damage to the brain cells depends on how severe the reduced blood flow is and how long it lasts. It’s important to keep the blood flowing to our brains properly in order to stay healthy.
What Causes Cerebral Ischemia (Stroke)?
Cerebral ischemia, or a lack of blood flow to the brain, can take two forms: global or focal. Global cerebral ischemia mostly happens due to overall body issues, often shock, and is frequently caused by low blood pressure. There may be a temporary decrease in blood flow to the brain when the automatic systems controlling your blood pressure and heart rate are disrupted, which can happen in situations like fainting or rapid heart rate conditions. Problems with the heart, particularly irregular heartbeats, are the second most common cause. If brief, this condition often leads to presyncope (a state of lightheadedness, muscular weakness, and feeling faint) or syncope (fainting). Prolonged global ischemia can unfortunately lead to permanent neurological damage.
On the other hand, focal brain ischemia is typically caused by blockage of blood flow to specific parts of the brain. This usually occurs due to clot formation or blockages that have traveled elsewhere in the body (embolism). If the blockage persists for a long time, it can cause irreversible brain cell loss, leading to a stroke. Existing narrow or blocked arteries can suddenly clot, or an embolism can happen when a clot forms in the heart or a large artery, which is the most common cause, accounting for 60% to 70% percent of brief or full strokes. Other materials can also cause blockages, like fat or air, though these are less common.
There are also other rare causes of ischemia. Sometimes, a tear in the neck blood vessels can cause brain ischemia and could be a reason for stroke in younger patients. In some cases, the brain’s blood vessels can contract – a condition called vasospasm. Infections can also, rarely, lead to strokes. It’s worth mentioning that the frequency of strokes has increased with COVID-19.
The causes of brain ischemia and stroke are commonly classified using the TOAST criteria. This classification divides ischemic stroke causes into large artery disease (usually due to narrow or blocked arteries), cardioembolic (heart-related causes like abnormal heart rhythms, valve problems, or issues in heart wall movement), small vessel occlusive disease (affects small arteries, often due to high blood pressure), stroke of other origin (known causes for the stroke such as inflammation of blood vessels or drug use), or a stroke of unknown cause (no reason found despite medical testing).
Risk Factors and Frequency for Cerebral Ischemia (Stroke)
Stroke is a common vascular disease across the globe and is the 5th leading cause of death in the United States. It is estimated that 20 million Americans over 20 years old have had a stroke. Additionally, around 795,000 individuals experience a stroke annually. Most strokes, about 75%, affect those over the age of 65. African Americans and Hispanic people have a higher prevalence of strokes compared to Caucasians. The occurrence of strokes in females and males is nearly equal, although there has been a slight decrease in male cases over the last 15 years.
A stroke refers to a neurological injury caused by different vascular conditions. The most prevalent type of stroke is called an ischemic stroke, accounting for 87% of all stroke cases. This type of stroke is caused by acute ischemia, a condition where a particular area of the brain does not get sufficient blood supply, resulting in damage to that area. Notably, ischemic strokes are a major cause of disability and death in the US and globally. Syncope, a temporary complete lack of blood supply to the brain, is one of the most common symptoms across all populations. Hence, brain ischemia is among the most frequent causes of disability worldwide.
Signs and Symptoms of Cerebral Ischemia (Stroke)
The evaluation process for a patient with symptoms relating to the nervous system mainly depends on the detailed history of patient’s symptoms. Cerebral ischemia, a condition where there is inadequate blood flow to the brain, usually results in symptoms related to the affected brain tissue’s loss of function. Symptoms can vary depending on whether the entire brain is affected (global cerebral ischemia) or only certain areas (focal cerebral ischemia).
Global cerebral ischemia typically affects a patient’s consciousness. Momentary changes in consciousness, such as fainting or feeling lightheaded, can be triggered by actions like standing up that cause a drop in blood pressure to the brain. This condition usually improves when the patient lowers their head. In case of severe or persistent global cerebral ischemia, it may lead to a coma.
On the other hand, focal cerebral ischemia’s symptoms can vary depending on the specific part of the brain that is not receiving enough blood. The time when symptoms start and how they progress over time is essential in deciding the treatment course. In cases where the exact time the symptoms began is unknown, the last known time the patient was normal is used to make treatment decisions.
Trained medical experts are able to recognize certain stroke syndromes, which are patterns of symptoms related to blockages in specific blood vessels in the brain. For example, lesions in the cerebral hemisphere (left or right side of the brain) may cause weakness or sensory loss on the opposite side of the body. Signs of dysfunction in the cerebral cortex (the brain’s outer layer) may indicate a blockage in a major artery, such as the middle cerebral artery. This could result in speech difficulties, neglect of one side of the body, and other symptoms. Recognizing these signs quickly is crucial because early treatment can greatly improve the outcome for stroke patients.
As the most effective treatments for stroke are time-dependent, it’s vital for the public to recognize the signs and symptoms of a stroke. A popular acronym to remember these is ‘BE FAST’: Balance, Eyes, Face, Arms, Speech, and Time. Each letter represents a symptom of stroke.
- Balance – Loss of balance
- Eyes – Change in vision
- Face – Facial droop
- Arms – Asymmetry in the strength of the upper extremities
- Speech – Difficulty speaking or slurred speech
- Time – Urges the public to seek medical care promptly
Besides considering the time of symptom onset, a detailed medical history should be taken. It’s important to note any history of risk factors like hypertension, diabetes, abnormal heart rhythm, high cholesterol, and smoking, as this could indicate possible causes of the stroke. The patient’s current medication list is also essential because certain medicines might be contraindicated (advised against) in patients taking blood thinners.
Finally, the physical examination focuses on identifying signs of brain dysfunction to locate the brain lesion. One common tool used to assess strokes is the NIH Stroke Scale. This examination quickly evaluates the patient’s consciousness level, eye movement, visual fields, motor function, sensation, cerebellar function, language, and attention or neglect. The findings of the exam are given a score between 0 and 40, which helps healthcare providers communicate and track the patient’s progress over time.
Testing for Cerebral Ischemia (Stroke)
If you’re experiencing symptoms that suggest you could have a blockage in the blood supply to your brain – a condition referred to as cerebral ischemia – there are certain tests your doctor will likely order. These tests may include basic lab tests, like a blood glucose test, a complete blood count, a chemistry panel, coagulation factors for blood clotting, an EKG to check your heart’s electrical activity, and cardiac enzyme tests that can indicate damage to the heart muscle.
One of the first procedures they may perform is a non-contrast head CT scan. This is done urgently to rule out any bleeding in the brain or the presence of a brain tumor. They may follow this with vascular imaging, such as a CT-angiogram or an MR-angiogram. Vascular imaging is extremely helpful as it can assist in identifying the cause of the stroke, especially in situations where there is a build-up of fats and cholesterol in the arteries (atherosclerosis). This type of imaging can reveal if there is a large blood vessel obstruction, and if so, pinpoint its location.
If you’ve had a sudden stroke and a non-contrast head CT shows no abnormalities, especially if you’re still in the early stages of the condition, your doctor may suggest an MRI or a CT perfusion. These are used to determine if the brain tissue affected by the reduced blood supply is still living. The damaged part of the brain from the stroke is known as the core infarct, and it is usually surrounded by an area of brain tissue that remains viable – this is known as the penumbra.
The type of imaging used will depend on the patient’s individual situation, but it’s crucial to know that people thought to have significant blood vessel blockages may require advanced imaging to see if they would benefit from interventions to remove the blockage. If a patient shows signs of a large blood vessel block being the cause of the stroke, it’s worth considering immediately moving them to a center that specializes in comprehensive stroke care or a center capable of performing a thrombectomy (clot extraction).
Treatment Options for Cerebral Ischemia (Stroke)
The treatment of global brain ischemia, a condition where the brain is not getting enough blood, mainly focuses on fixing the cause. Doctors will aim to improve blood flow to the brain as one of their first steps which can be helped by positioning the patient in a certain way while giving other treatments.
In the case of an acute ischemic stroke, where blood flow to part of the brain is blocked, the first priority is to decide if the patient is suitable for a treatment designed to restore blood flow. For over 25 years, a type of drug called thrombolytics has been used to treat acute ischemic strokes. One of these is called tissue plasminogen activator (TPA), and it’s the only one currently approved by the Food and Drug Administration to treat acute ischemic strokes. There are ongoing investigations into other thrombolytics, like tenecteplase. TPA is usually given within 3 hours of the onset of the stroke, but research suggests it can be effective up to 4.5 hours after the stroke begins.
Some patients who’ve had an acute ischemic stroke caused by a big blood vessel being blocked might need a procedure called a mechanical thrombectomy. Whether a patient can have this procedure depends on when their symptoms started, how severe their symptoms are, where the blocked blood vessel is and whether the tissue affected by the blockage is still alive. Patients thought to have a large vessel blockage should be transferred to a specialist centre as quickly as possible. However, transporting the patient should not delay or stop treatment with TPA if they also qualify for it.
After the initial stages of an ischemic stroke, treatment focuses on preventing another stroke from happening and supporting recovery. The doctor will look at the patient’s medical history to identify risk factors that might lead to another stroke, like diabetes, high blood pressure, tobacco use, high levels of fat in the blood, and a heart condition called atrial fibrillation. Treatments that can help protect against another stroke include antiplatelet drugs like aspirin or clopidogrel, and statins. In strokes caused by atrial fibrillation, anticoagulant medication is recommended. Patients who have a narrowing of the carotid artery, which was the cause of their stroke or a smaller stroke-like episode, will be assessed to see if they need a procedure to widen the artery.
Stopping smoking, maintaining a healthy weight, and getting regular exercise are recommended for all patients who’ve had a stroke. There’s evidence that these lifestyle changes can offer more protection against another stroke happening than medication. As part of their recovery, patients who’ve had a stroke should have care from a team of different health care professionals such as occupational and physical therapists and speech-language pathologists.
What else can Cerebral Ischemia (Stroke) be?
When someone shows symptoms similar to an ischemic stroke, several different conditions could be the actual cause. These include:
- Low blood sugar (hypoglycemia)
- Imbalance of body salts, like low sodium (hyponatremia)
- Drug use
- Infections such as meningitis
- Fainting due to heart issues (cardiogenic syncope)
- Mini stroke (TIA)
- Swelling in blood vessels (vasculitis)
- Migraines
- Tumors
- Bleeding in the brain (cerebral hemorrhage)
- Seizures
What to expect with Cerebral Ischemia (Stroke)
The impacts of a lack of blood flow to the brain can vary depending on how long it lasts. It can lead to temporary brain dysfunction, long-lasting dysfunction with permanent brain damage, with or without lasting symptoms and disability.
The after-effects of this blood flow deficiency in the brain, otherwise known as cerebral ischemia, can differ greatly. Some people might not experience any permanent effects, while others may end up with lasting disabilities or even death. The severity of these effects is usually dependent on the person’s health condition before they had the blood flow problem.
For instance, patients who already had mild mental difficulties or dementia saw greater relative mental struggles after a stroke triggered by ischemia. This suggests that their brain cells have a lower tolerance for lack of blood flow. Age can also play a significant factor in this.
Possible Complications When Diagnosed with Cerebral Ischemia (Stroke)
While it’s crucial to quickly restore blood flow after a stroke to save the brain function, doing so can sometimes cause cell damage and tissue dysfunction. This is called cerebral ischemia-reperfusion injury. It commonly happens following treatments like dissolving blood clots or physically removing them from the brain. These treatments can restore blood flow and save damaged tissues. However, if the stroke happened a while ago, the return of blood flow can sometimes make the injury larger than the initial one. This process can lead to problems like white blood cells invading the damaged area, blood platelet activation, activation of defensive proteins in the body, and breakdown of the blood-brain barrier causing fluid leak into the brain.
Converting to hemorrhagic stroke after using clot-busting drugs is another complication. This condition should be seriously considered if the patient’s condition worsens after receiving these drugs. Signs might include changes in awareness, worsening neurological assessments, increasing weakness, new or worsening headaches, or changes in blood pressure or heart rate. If this happens, an immediate head CT scan and lab tests should be performed, and a neurosurgeon should be consulted.
People with acute ischemic stroke also have the risk of complications due to not being mobile, including infections and blood clots. As there’s a risk of choking, patients should undergo a swallow test before being given food or drink. Healthcare providers should aim to reduce infection by taking precautions against aspiration or drawing fluids into the respiratory tract and reducing the use of invasive tools like urinary catheters. Mechanical procedures to prevent the formation of deep vein blood clots should be applied where possible. Using drugs for the same purpose should be considered, but is not recommended within 24 hours of using clot-busting drugs or for patients who have converted to hemorrhagic stroke.
Common Conditions:
- Cerebral ischemia-reperfusion injury
- Conversion to hemorrhagic stroke
- Immobilization complications
- Infections
- Formation of blood clots
- Risk of choking
- Increased risk of urinary infection
Preventing Cerebral Ischemia (Stroke)
Cerebral ischemia, which is a condition where there is not enough blood flow to the brain, can be influenced by various factors. Some of the factors include heart diseases like atrial fibrillation, diabetes, obesity, high blood pressure, and conditions that lead to the buildup of fats in your arteries (atherosclerosis) or high levels of fat in your blood (hyperlipidemia). Additionally, a history of strokes can also increase the risk. People’s behaviors can also contribute to the risk. These include not getting enough physical activity, having poor sleep habits, being obese, drinking too much alcohol, and smoking.
People with sickle cell disease or other disorders that affect their blood, particularly if their blood clots more than it should (hypercoagulable conditions), are also at a higher risk of experiencing a type of stroke caused by a lack of blood flow to the brain, known as ischemic stroke.
The risk of stroke can be lessened by managing and treating these conditions. This could be done through maintaining a healthy diet, regular exercise, and adhering to prescribed medications. Certain medications, like statins (which help to lower cholesterol levels) and blood thinners, have been found to help reduce the risk of an ischemic stroke.
