physilogy sleep
TRANSCRIPT
![Page 1: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/1.jpg)
![Page 2: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/2.jpg)
Cerebral Blood Flow regulation
![Page 3: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/3.jpg)
Learning Objectives
By the end of this lectures all students should be able to:
• Describe the cerebral blood flow auto regulation that protect the brain from changes in arterial pressure.
• Describe the effect of carbondioxide, hydrogen ions and oxygen on cerebral blood flow.
![Page 4: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/4.jpg)
Cerebral Blood Flow
• Normal blood flow through
the brain of the adult
person averages 50 to 65
milliliters per 100 grams of
brain tissue per minute.
• 15 % of the resting cardiac
output.
![Page 5: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/5.jpg)
![Page 6: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/6.jpg)
Regulation of Cerebral Blood Flow
Three metabolic factors have potent effects in
controlling cerebral blood flow :
1. Carbon dioxide concentration
2. Hydrogen ion con centration
3. Oxygen concentration
![Page 7: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/7.jpg)
Cerebral Blood Flow
![Page 8: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/8.jpg)
Excess Carbon Dioxide & Hydrogen Ions:
• Increase Carbon dioxide concentration in arterial blood, perfusing the brain greatly increases cerebral blood flow. 70 per cent increase in arterial PCO2 approximately doubles
cerebral blood flow.
![Page 9: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/9.jpg)
• Carbon dioxide combines first with Water in the body fluids
to form Carbonic acid
• Subsequent dissociation of this carbonic acid gives rise to
Hydrogen ions.
• The Hydrogen ions then cause vasodilatation of the cerebral
vessels. THUS INCREASING THE CBF.
![Page 10: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/10.jpg)
Substances Increasing H-ion Conc.
• Lactic acid.
• Pyruvic acid.
• Acidic material formed during the course of
tissue metabolism.
![Page 11: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/11.jpg)
Importance of Cerebral Blood Flow Control by Carbon Dioxide
and Hydrogen Ions.
![Page 12: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/12.jpg)
• H- ion concentration greatly depresses neuronal
activity. But, it also increase the blood flow which
inturn carry the following away from the brain:
• Hydrogen ions.
• Carbon dioxide.
• Acid forming substances.
![Page 13: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/13.jpg)
Loss Of Carbon Dioxide
• Loss of carbon dioxide removes carbonic acid and other acids from the tissues.
• H-ion conc. comes back to normal.
• This inturn , maintain the normal neuronal activity.
![Page 14: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/14.jpg)
Increased CO2 and H+ ion concentration and oxygen defeciency cause vasodilationdepressed neuronal activity
![Page 15: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/15.jpg)
CBF and CO2
• Carbon dioxide causes cerebral vasodilation. As the arterial tension of CO2 rises, CBV and CBF increases and when it is reduced vasoconstriction is induced.
![Page 16: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/16.jpg)
Oxygen Deficiency as a Regulator of Cerebral Blood Flow
• Rate of utilization of oxygen by the brain tissue under normal conditions is almost exactly 3.5 (± 0.2) milliliters of oxygen per 100 grams of brain tissue per minute except, for intense period of brain activity.
![Page 17: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/17.jpg)
• Decrease/ insufficient blood flow & Oxygen to brain
• Stimulates Oxygen Deficiency mechanism
• Vasodilation , restoring the blood flow & oxygen supply to brain.
![Page 18: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/18.jpg)
Importance
• Value of P02 is 35 to 40 mm of Hg for normal brain
activity.
• Value below 30 mm Hg immediately begins to increase
cerebral blood flow by causing vasodilation.
• P02 levels below 20 mm Hg. lead to diminished cerebral
neuronal activity and derangement of mental capability.
![Page 19: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/19.jpg)
Increasing CBF-Hyperemia
• Low arterial oxygen tension has profound effects on cerebral blood flow. When it falls below 50 mmHg (6.7 kPa), there is a rapid increase in CBF and arterial blood volume
![Page 20: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/20.jpg)
Measurement of Cerebral Blood Flow, and Effect of Brain Activity
on the Flow
![Page 21: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/21.jpg)
• A method has been developed to record blood flow in as many as 256 isolated segments of the human cerebral cortex simultaneously.
• A radioactive substance, such as radioactive xenon, is injected into the carotid artery
• Then the radioactivity of each segment of the cortex is recorded as the radioactive substance passes through the brain tissue.
![Page 22: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/22.jpg)
• For this purpose, 256 small radioactive scintillation detectors are pressed against the surface of the cortex.
• The rapidity of rise and decay of radioactivity in each tissue segment is a direct measure of the rate of blood flow through that segment.
![Page 23: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/23.jpg)
Events leading To Alteration In Cerebral Blood Flow:
• Making a fist of the hand.
• Reading a book.
• Epileptic attacks.
• Directing intense light into the eyes for sometime.
![Page 24: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/24.jpg)
Autoregulation of Cerebral Blood Flow With Arterial Pressure Changes
![Page 25: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/25.jpg)
Autoregulation
• CBF is maintained at a constant level in normal brain in the face of the usual fluctuations in blood pressure by the process of autoregulation.
• Normally autoregulation maintains a constant blood flow between CPP 50 mmHg and 150 mmHg.
![Page 26: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/26.jpg)
• Cerebral blood flow is "autoregulated" extremely well between arterial pressure limits of 60 and 140 mm Hg.
• Below 60 mm of Hg of arterial pressure the cerebral pressure become severely decreased.
![Page 27: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/27.jpg)
Metabolic Autoregulation
• Arterioles dilate in response to potent chemicals that are by-products of metabolism such as lactic acid, carbon dioxide and pyruvic acid.
• CO2 is a potent vasodilator • Increased CO2/decreased BP --> vasodilation • Decreased CO2/increased BP -->vasoconstriction
![Page 28: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/28.jpg)
Neurogenic Autoregulation• Autonomic system and neurochemical
control of CBF in general is a minor control.•Metabolic autoregulation is most
important being majorly in control of CBF.
![Page 29: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/29.jpg)
Pressure autoregulation
• Changes in cerebral perfusion pressure will be followed by changes in cerebral blood flow unless diameter regulation takes place.
• This type of autoregulation is termed pressure autoregulation and is the type of autoregulation referred to as autoregulation after head injury.
![Page 30: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/30.jpg)
• The limits of pressure autoregulation range from 40 to 150 mm of mercury of perfusion pressure.
• Beyond these limits, vessel caliber follows flow passively leading to collapse of vessels at low pressure and forced dilatation or pressure breakthrough at high pressures.
![Page 31: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/31.jpg)
Role of the Sympathetic Nervous System In Controlling Cerebral Blood Flow
![Page 32: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/32.jpg)
• Sympathetic innervation of cerebral circulatory system passes upward from the superior cervical sympathetic ganglia in the neck and then into the brain along with the cerebral arteries.
![Page 33: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/33.jpg)
![Page 34: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/34.jpg)
Sympathatic innervation supply to the following:• Large brain arteries.• Arteries which penetrate the substance of the
brain.• Autoregulation mechanism is not effected by
the nervous supply so, transection or stimulation of it does not much effect the cerebral blood flow. Autoregulation is effected only slightly by the neural system.
![Page 35: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/35.jpg)
Clinical Importance Of Sympathatic Supply:
• In response to increased mean arterial pressure due to excerise or other states of excessive circulatory activity.
Sympathatic innervation causes vasoconstriction
![Page 36: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/36.jpg)
Cerebral Microcirculation
• The number of blood
capillaries in the brain is
greatest because of its
increase metabolic needs. • The overall metabolic rate
of the brain gray matter where the neuronal cell bodies lie is about four times as great as that of white matter
![Page 37: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/37.jpg)
Characteristics Of Brain Capillaries
![Page 38: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/38.jpg)
• Gray matter in the brain is the portion
containing the neuronal cells it has the
following features:
• Metabolic rate is high.
• Increase number of capilllaries.
• Rate of blood flow is also high.
• Capillaries are less leaky.
![Page 39: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/39.jpg)
Clinical Importance
![Page 40: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/40.jpg)
Walls Of The Small Arterioles:
• Arterioles leading to the brain capillaries
become greatly thickened in high blood
pressure, and these arterioles remain
significantly constricted all the time to prevent
transmission of the high pressure to the
capillaries.
![Page 41: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/41.jpg)
• Capillaries are supported on all sides by "glial
feet," which are small projections from these
surrounding glial cells.
• These projections protect and provide physical
support to prevent overstretching of the
capillaries in case of high capillary blood
pressure.
![Page 42: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/42.jpg)
Cerebral Stroke
• It is a condition in which there is blockage of
arteries of the brain that cause serious
disturbance of brain function it is called
"stroke."
![Page 43: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/43.jpg)
Types Of Stroke
Ischemic Stroke Hemorrhagic Stroke
Ischemic Stroke:
It occurs due to interruption of blood flow to a part of brain by thrombus or artherosclerotic embolus.
![Page 44: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/44.jpg)
Hemorrhagic Stroke
• It develops by the rupture of a blood vessel in the brain and spilling of blood into the surrounding area. This spillage causes pressure effects in the surrounding structures and thus depressing their respective functions.
![Page 45: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/45.jpg)
Clinical Features Of Stroke
• Hemorrhage occurs , compressing the local brain tissue and further compressing its functions.
• The neurological effects of stroke are determined by the area of the brain affected.
![Page 46: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/46.jpg)
Risk Factors for Stroke
• Heart Disease
• Hypertension
• High Cholesterol
• Diabetes
• Excessive smoking
• Heavy Consumption of Alcohol.
![Page 47: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/47.jpg)
Most Common Arteries Effected In Stroke:
• Middle Cerebral Artery.
• Posterior Cerebral Artery.
![Page 48: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/48.jpg)
![Page 49: Physilogy sleep](https://reader036.vdocuments.site/reader036/viewer/2022081605/587acfa71a28ab760f8b6753/html5/thumbnails/49.jpg)