What happens inside the brain during a stroke?

A stroke is an urgent situation where either the flow of blood to the brain is cut off, or there is a rupture of the blood vessels in the brain. Oxygen and glucose are the two elements essential for brain activity. Interruption of their supply results in impairment of brain activity and eventual damage of brain tissues -- and this damage occurs in minutes. The first few hours of a stroke, therefore, determine how damaged the brain can become.Types of strokesStrokes can be categorised into ischemic strokes and haemorrhagic strokes. In ischemic strokes, the stroke occurs due to the blocking of an artery by a blood clot. In haemorrhagic strokes, there is a rupture of the blood vessel, which leads to blood in the brain tissue. Regardless of the type of stroke, the result is damage to the brain tissue, which can result in vital body functions including speaking, movement, vision, memory and coordination becoming impaired.An ischemic stroke is accompanied by oxygen starvation of the affected brain tissue. Due to insufficient energy resources, brain cells cannot function normally. The chemical composition of the brain cells, therefore, changes, which results in the accumulation of toxic substances that harm brain cells and other structures. With continued oxygen starvation, cells continue to deteriorate. The damage, however, does not occur uniformly. In the central area of the brain (core) where oxygen starvation is critical, damage can occur rapidly and irreversibly. Around this area, there is a zone called the ischemic penumbra. Here, even if blood flow is low, brain cells can survive for a certain period of time. They can be saved if blood flow is restored promptly. The effect of bleeding in a haemorrhagic stroke is brought about by the leaking of blood into the brain when there is a rupture of a blood vessel. This may lead to injury of brain cells, and also interfere with proper blood and cerebral spinal fluid flow in the brain.The first few hoursThere are only so many minutes that the brain can withstand interrupted blood flow. Brain cells (neurons) begins to undergo irreversible damage within 3 to 5 minutes of interrupted blood flow. With each minute that goes by, 1.9 million neurons, i.e. 32 neurons per second, die due to lack of oxygenation, which is why we emphasise that ‘time is brain’. The first few hours are critical since at this point, one needs to assess what kind of stroke it is and start appropriate treatment.In some cases of ischemic stroke, intravenous thrombolysis, the administration of drugs that dissolve the clot within the blood vessels, might be given in the first 4.5 hours after symptoms develop. In some patients with large vessel blockage, there might be indications for mechanical thrombectomy. In simple terms, a mechanical thrombectomy involves the removal of the clot using special equipment, and it might be done up to 24 hours after the patient was last seen without symptoms. In cases of haemorrhagic strokes, others strategies must be employed: this includes blood pressure control, correction of the consequences of taking blood thinners, management of intracranial pressure, and surgical procedures, where necessary.Not all patients automatically qualify for all interventions. There are other issues that have to be taken into account, including the patient’s medical status, imaging studies, timing of stroke symptoms, and dangers involved in the therapy. Even some of those who come after these time windows, can still be eligible for certain treatment procedures after imaging is done. How brain function is affectedThe effects of a stroke vary, depending on the site and degree of damage within the brain. Movement centres can be damaged leading to weakness or paralysis that usually affects one side of the body. Speech centres could be damaged causing speech problems and comprehension difficulties or trouble reading and writing. A stroke involving the visual pathways leads to a sudden loss of vision or partial visual fields. If the cerebellum or the brainstem is involved, there could be a problem with dizziness, poor coordination, problems swallowing, double vision or loss of balance. There could also be memory, attention and decision-making problems and problems with emotional regulation.It is important to know and understand these symptoms since sometimes a stroke occurs without the characteristic facial drooping or arm weakness of the disease.Recognising warning signsThe BE FAST method is an effective means of identifying the symptoms of a stroke: B – Balance: Sudden loss of balance, dizziness or difficulty walking E – Eyes: Sudden blurred vision, double vision or loss of vision F – Face: One side of the face is drooping or numb A – Arms: One arm is weak or dropping down S – Speech: Slurred speech T – Time: Call for help immediately Sudden changes in vision, lack of balance, confusion or even a severe headache without apparent reason might be symptoms of a stroke as well. Disappearing symptoms within a minute or two shouldn’t be considered harmless and require immediate medical examination. After the golden hourThe ‘golden hour’ is significant to preserve as much of brain function as possible and to ensure best possible outcomes, but this does not mean medical professionals cease working after this window is over. Medical teams will continue monitoring the condition of the patient, controlling blood pressure and preventing additional harm to him or her. In case the condition of the patient becomes satisfactory, it is likely that he or she will be offered physiotherapy, speech and language therapy, occupational therapy and cognitive therapy.It is worth noting that every stroke patient has his or her own path to recovery, which depends greatly on the level of injuries, the affected area of the brain, timely assistance and the patient’s health in general. For all individuals, however, it is important to understand how the brain functions, remember the signs of a stroke and seek timely help for oneself or a loved one.(Dr. B. K. Madhusudhan is lead consultant – neurology, Aster RV Hospital, Bengaluru. madhusudhan.bk@asterhospital.in)