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Basic Anatomy & Pathophysiology of ischemic stroke
- 1. Ischemic Stroke: Basic Anatomy and Pathophysiology Dr. Ajay Kumar Agarwalla Phase- A Resident (Neurology) Blue Unit, Neurology dept. , BSMMU
- 2. Road Map • Artery supply of the brain • Findings associated with occlusion • Key features of cerebral blood flow • Auto regulation of cerebral blood flow • Pathophysiology of infarction in brain • Factors influence ischemic stroke
- 3. Arterial supply of the Brain
- 4. Anterior Cerebral Artery Occlusion Contralateral hemiparesis and hemisensory loss involving mainly the leg and foot (paracentral lobule of cortex) Inability to identify objects correctly, apathy, and personality changes (frontal and parietal lobes)
- 5. Contralateral hemiparesis and hemisensory loss involving mainly the face and arm (precentral and postcentral gyri) Aphasia if the left hemisphere is affected (rarely if the right hemisphere is affected) Contralateral homonymous hemianopia (damage to the optic radiation) Middle Cerebral Artery Occlusion
- 6. Contralateral homonymous hemianopia with some degree of macular sparing (damage to the calcarine cortex) Visual agnosia (ischemia of the left occipital lobe) Impairment of memory (damage of medial aspect of the temporal lobe) Posterior Cerebral Artery Occlusion
- 7. Key features of blood flow in BRAIN • In an adult, CBF is typically 750 ml/min or 45-50ml/100g/min or 15 % of the cardiac output (CO) In normal individuals, CBF remains constant when the mean arterial pressure varies between “60 and 160 mmHg”
- 8. Ideal Cerebral Auto regulationIdeal Cerebral Auto regulation Lassen NA. Physiol Rev. 1959;39:183-238 Strandgaard S, Paulson OB. Stroke.1984;15:413-416
- 9. Matter of Concern Cerebral Blood Flow (CBF) : • Less than 23ml/100g/min, physiological electrical function of the cell begins to fail- “ischemic penumbra”. • Below 10 ml/100g/min, ionic membrane transport failure, Irreversible cell death- which leads to- “infarction”.
- 11. Factors Influence Ischemic Stroke • Rate and onset of duration • Collateral circulation • Systemic circulation • Hypercoagulable states • Increased temperature • Hyper/hypo glycemia
- 12. Reference Snells Clinical Neuroanatomy, 7th edition Davidson’s Principles and Practice of Medicine, 22nd edition Harrison’s Principles of Internal Medicine, 19th edition http://what-when-how.com/neuroscience/blood-supply-of-the- http://en.wikipedia.org/wiki/Cerebral_blood_flow Stroke Pathophysiology Sid Shah, MD
Notas del editor
- It is a characteristic of the brain to adjust its own blood supply. The brain accounts for only 2-3% of total body weight and does not do any mechanical work, yet it receives 20% of all cardiac output.
- Ideally, when aterial blood pressure increase or decrease between 70-150 mmhg , the cerebral autoregulation can make the blood flow velocity constant , beyond the range, the blood flow velocity will increase or decrease dramaticaly with the blood pressure
- A thrombus or an embolus can occlude a cerebral artery and cause ischemia in the affected vascular territory. It is often not possible to distinguish between a lesion caused by a thrombus and one caused by an embolus. Thrombosis of a vessel can result in artery-to-artery embolism. Mechanisms of neuronal injuy at the cellular level are governed by hypoxia or anoxia from any cause that is reviewed below. At a gross tissue level, the vascular compromise leading to acute stroke is a dynamic process that evolves over time. The progression and the extent of ischemic injury is influenced by many factors. 2-5 Rate of onset and duration: the brain better tolerates an ischemic event of short duration or one with slow onset. Collateral circulation: the impact of ischemic injury is greatly influenced by the state of collateral circulation in the affected area of the brain. A good collateral circulation is associated with a better outcome. Health of systemic circulation: Constant cerebral perfusion pressure depends on adequate systemic blood pressure. Systemic hypotension from any reason can result in global cerebral ischemia. Hematological factors: a hypercoagulable state increases the progression and extent of microscopic thrombi, exacerbating vascular occlusion. Temperature: elevated body temperature is associated with greater cerebral ischemic injury. Glucose metabolism: hyper- hypoglycemia can adversely influence the size of an infarct.