Lecture 12: Cerebral autoregulation Flashcards
Why is cerebral blood flow highly important?
The brain is highly metabolically active:
- Consumes 20% O2, glucose
- Has little metabolic reserve therefore depends on blood flow supply of O2 and glucose
Whats the challenge of cerebral blood flow?
Upright posture
- Brain is the highest point (hydrostatic barrier)
- Challenge for perfusion
Describe pressure around the body
Diastolic/systolic pressure is different around the body depending on the region
What implication does the cranium have on intracerebral pressure?
The rigid cranium prevents expansion therefore can lead to interregional shunting of blood to more active areas (because brain perfusion cant increase in a highly active brain)
Describe a normal response to standing upright for a long period of time:
VR = Decrease SV = Decrease Pulse Pressure = Decrease Symp tone = Increase (baroreflex) Vagal tone = Decrease HR = increase Systolic pressure = Stable Diastolic Pressure = Increase
Describe syncope in response to standing for a long period of time (fainting);
VR = Decrease SV = Decrease Pulse Pressure = Decrease Symp tone = no change Vagal tone = Increase HR = Decrease Systolic pressure = Drops dramatically Diastolic Pressure = Decrease
No baroreflex, b/c disease or the bodies way of increasing brain perfusion by lying the body down
How does the body cope with the hydrstatic challenge of being erect?
Muscle pumps in the legs
- Bicuspid valves
What is orthostatic/postural hypotension?
A 20mmHg drop in systolic pressure and/or a 10mmHg decline in diastolic BP when changing form supine to erect position.
What are the risk factors for postural hypotension?
7 factors
Age Disease (hypertension, HF, Spinal cord injury (interupts efferent symp) Medications Heat Exposure Bed rest Pregnancy Alcohol
How does Bp affect ppstural hypotension?
The higher your blood pressure the greater it falls when you stand
What reduces the effects of postrual hypotension?
Postural hypotension effets are reduced by chronic anti-hypertensive treatments
What else can contribute to postural hypotension?
Post medications can increase blood flow and also increases postural hypotension
- Younger people less prone to this, severely impacts hypertensive patients
What pathologies increase the risk of syncope?
5 pathologies
Diabetes Congestive heart failure Anemia COPD Pneumonia
What is cerebral autoregulation?
The physical mechanism to maintain blood flow at an appropriate level during changes in blood pressure
look at notes regarding the graph of cerebral autoregulation
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