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Neurology Seminar

Neurology Seminar. Cerebral Blood Flow Cerebral Perfusion Cerebral Metabolism. Outline. Anatomy of the vascular system Arterial Venous Physiology of the vascular system Cerebral blood flow Cerebral perfusion Cerebral metabolism. Anatomy of the vascular system Overview.

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Neurology Seminar

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  1. Neurology Seminar Cerebral Blood FlowCerebral PerfusionCerebral Metabolism

  2. Outline • Anatomy of the vascular system • Arterial • Venous • Physiology of the vascular system • Cerebral blood flow • Cerebral perfusion • Cerebral metabolism

  3. Anatomy of the vascular systemOverview • Brain has two major arterial systems • Carotid = cerebral hemispheres • Vertebrobasilar = post fossa, occipital lobe, part of the temporal lobe • Interconnections • Circle of Willis • Surface of the neuraxsis= large circumferential arteries Deep structures = smaller penetrating arteries and arterioles

  4. Anatomy of the vascular system

  5. Anatomy of the vascular system • Internal carotids in the cranium • Carotid siphon • Lies within the cavernous sinus • Subarachnoid space->ophthalmic a. • Ant. and middle cerebral a.

  6. Anatomy of the vascular system • Vertebral a. branch of subclavian a. • Trans. cervical foramen • Foramen magnum • Frequent anatomic variation • Lt. vertebral a. directly from aorta • Unequal caliber b/n the 2 vertebral a. • Ventrolateral surface of medulla • Unite at pons->basilar a. • Rt and Lt post cerebral a. at midbrain

  7. Anatomy of the vascular system

  8. Anatomy of the vascular systemCircle of Willis • At the base of the brain • Surrounds the optic chiasm and pit. stalk • Frequent anatomic variations 50%

  9. Anatomy of the vascular system

  10. Anatomy of the vascular systemBlood supply of cerebral hemispheres • Anterior cerebral a. • Medial surface of cerebrum • Superior border of frontal and parietal lobe • Middle cerebral a. • Most of the lateral surface of cerebral h. • Lateral frontal lobe • Sup and lat temporal lobe • Deep structures of frontal and parietal lobe • Posterior cerebral a. • Occipital lobe • Inferior and medial temporal lobe • Penetrating branches of big a supply deeper struct. • Lenticulostriate a. of MCA for BG and Int. cap • Perforating br of PCA for thalamus

  11. Anatomy of the vascular systemAnastomoses and collateral circulation • Circle of Willis • Corticomeningeal anastomoses • The 3 major a. on the surface of hemis. • b/n extra and intracranial a. • Ophthalmic a. of internal carotid with superficial temporal and facial branch of ext. carotid at face region. • Ext carotid and vertebral a. at the neck

  12. Anatomy of the vascular systemBlood supply of posterior fossa

  13. Carotid system Hemiparesis (contralateral body and face) Hemisensory loss (contralateral body and face) Homonymous hemianopia Monocular visual loss Aphasia Vertebrobasilar Hemiparesis (contralateral body, ipsilateral face) Hemisensory loss (contralateral body, ipsilateral face) Diplopia Dysphagia Dysarthria Dysequilibrium Neurologic signs

  14. Anatomy of the vascular systemVenous system • Superficial and deep system • SSS • Superficial v. of sup half of brain • Lateral Sinus • Inferior half • Deep system (great v. of Galen and inferior sagittal and strait sinus) • Deep white matter & deep brain nuclei • Cavernous sinus • Inferior cerebral surface • Carotid a., cranial n.,

  15. Anatomy of the vascular systemVenous system

  16. Anatomy of the vascular systemVenous system

  17. Physiology of the vascular system • Cerebral Blood Flow (CBF) • Amount of blood that enters the brain. • Brain is 2% of body weight • About 10% of the intra cranial space • About 15% of Cardiac output • 50 ml Bl. per 100 gm of brain tissue/min • 750 ml/ min • About 20% of Ox used at basal state • Total Ox used 50ml/min, 3.7ml/100gm • There is an oxygen metabolic reserve of only 8-10 seconds

  18. Physiology of the vascular system • Cortical gray matter has 6X bl. flow than the white matter due to metab.demand • CBF is tightly regulated and maintained within narrow limits • too little blood causes ischemia, • results if blood flow to the brain is below 18 to 20 ml per 100 g per minute, • tissue death occurs if flow dips below 8 to 10 ml per 100 g per minute • Too much blood can raise ICP • CBF > 55 to 60 ml per 100 g per minute

  19. Physiology of the vascular system • Cerebral Perfusion Pressure (CPP) • net pressure of blood flow to the brain • CPP = MAP − ICP • NL b/n 70-90 mmHg in an adult human, • Below 70 mmHg for a sustained period causes ischemic brain damage • Children have pressure of at least 60 mmHg

  20. Physiology of the vascular system • Autoregulation • Physiologic response where by CBF remains constant and brain maintains proper CPP over a wide range of Blood pressures variations. • to lower pressure, arterioles dilate, and to raise pressure they constrict. • At their most constricted, pressure of 150 mmHg, • At their most dilated the pressure is 60 mmHg.

  21. Physiology of the vascular system • Autoregulation • When pressures are outside 50 to 150 mmHg, the blood vessels' ability to autoregulate pressure through dilation and constriction is lost, and cerebral perfusion is determined by blood pressure alone, • pressure-passive flow

  22. Physiology of the vascular system • Factors affecting CBF (the ff equation)= Mean arterial pressure - central venous pressure Cerebro-vascular resistance • Extra cerebral • Systemic BP • CV function • Blood Viscosity • Intra cerebral • Cerebral vasculature • CSF pressure • Auto regulatory mechanisms

  23. Physiology of the vascular system

  24. Physiology of the vascular system • Regulation of CBF • Metabolic regulation • Auto regulation • Chemical factors • Neurogenic factors

  25. Physiology of the vascular system • Metabolic regulation • CBF is coupled directly to neuronal metabolic activity • Occurs with short latency of 1-2 sec. • Strictly regional effect • Little effect on the total blood flow • E.g.. Sleep, coma, seizure • Vasodilator substances • Adenosine, K+, H+, prostaglandin, free radicals, NO

  26. Physiology of the vascular system

  27. Physiology of the vascular system • Auto regulation • The ability of brain to maintain its blood flow constant for all but the widest extremes in perfusion pressure • MAP 60-150 mmHg • Primarily pressure controlled myogenic mechanism that operates independently but synergistically with other neurogenic and chemical metabolic mechanism. • Both small and large arterioles • Major homeostatic and protective mechanism.

  28. Physiology of the vascular system

  29. Physiology of the vascular system

  30. Physiology of the vascular system Regional increase in metabolism   CO2  Local vasodilatation Increased blood flow  Accommodate metabolic demand

  31. Physiology of the vascular system Regional ischemia (occlusive disease)   Intra Luminal pressure  oxygen  CO2  lactate Acidotic tissue  Vasodilatation of nearby vessels  Increase blood flow to the area of ischemia Reduce size of infarct  Reduced cerebro-vascular resistance (infarct zone)

  32. Physiology of the vascular system Reduced cerebro-vascular resistance  Little change in CVP  Major determinant of BF to the region of ischemia will be MAP  Proper maintenance of SBP in Mx of ischemic stroke

  33. Physiology of the vascular system • Chemical factors • Strong influence on CBF • Mech= sm ms, NT, pH • CO2 readily crosses BBB end product of cerebral metabolism •  PaCO2=Vasodilatation & CBF •  PaO2= Vasodilatation & CBF •  pH= Vasodilatation & CBF • Lactic acid is a potent vasodilator

  34. Physiology of the vascular system

  35. Physiology of the vascular system • Neurogenic control • Not as strong as the chem. And metab. • Composed of • Extrinsic control • Intrinsic control • Local components

  36. Physiology of the vascular system

  37. Cerebral Metabolism • High metabolic activity & high O2 consumption • Energy dependant processes • Membrane potential • Maintainace of trans-membrane ion gradient • Membrane transport • Synthesis of cellular constituents • Prot, Nucleic acid, Lipids, NT • Energy supplied by high energy phosphate bond (ATP), synthesized in brain. • Glycolytic pathway • Krebs cycle 38 moles of ATP/ mole of glucose • Respiratory chain (aerobic) • Anaerobic 2 ATP • Creatine Phosphate from ADP glycogen

  38. Cerebral Metabolism

  39. Cerebral Metabolism, ischemic cascade •  in CBF ->  in glucose and Ox. • Less impaired function at the periphery • Local auto regulatory mech, response to chemical & metab changes is lost • Anaerobic glycolysis • Fall in glycogen and pH • Rise in lactate • Zone of increased perfusion in the periphery of ischemic zone

  40. Cerebral Metabolism, ischemic cascade • Substrate depletion->mitoch. failure • Leakage of K from cells •  IC Na, Cl, Ca, free fatty acids • Neuronal depolarization Loss of trans membrane potential increase in tissue water Impaired ATP dependent NT uptake

  41. Cerebral Metabolism, ischemic cascade •  release of excitatory NT glutamate which activates NMDA and AMPA receptors • permeability to Na ions • Cellular swelling and lysis • Massive entry of Ca into post synaptic neurons ->more release of excitatory NT

  42. Cerebral Metabolism, ischemic cascade •  IC Ca-> activates • Phospholipases • Protease membrane • Endonuclease mitoch. DNA cell • Ox free radical microtubular damage death • Nitric oxide

  43. Ischemic Penumbra

  44. Ischemic Neuronal Injury (cascade)

  45. Ischemic Neuronal Injury (cascade)

  46. Incomplete Ischemia Complete Ischemia Hypoxia Lactic acid accumulation Cell swelling Enough glucose Enough glucose Local accumulation of Adenosine Potassium Hydrogen Ion Infarction Lesser degree of anoxic change Affection of BBB Vasodilatation Hypoglycemia Water content of Brain tissue Increases BRAIN EDEMA Restoration of blood supply Adequate Ox Scavenger cells Energy maintained By creatinine Phos. Cystic cavity

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