Regional Blood Flow Flashcards
What is responsible for phasic fluctuations in blood flow
Rhythmic pulsations in aortic pressure
Changing intramural myocardial pressure
What is happening during systole regarding
- Intramural myocardial P
- Blood flow in LV
- IM P in RV
- RCA blood flow
- coronary sinus
- IM myocardial pressure increases, compressing coronary BVs (mainly in SUB-ENDOCARDIUM)
- Complete interruption of blood flow in LV during early systole due to high P development - thus its mainly in DIASTOLE
- IM P is low in RV
- RCA blood flow can occur during systole - follows fluctuations in aortic P
- Surge of venous blood flow out of coronary sinus due to compression of muscular wall of heart
What are sub-endocardial regions of LV vulnerable to
Decreased blood flow
What is delivery of blood to endocardial regions influenced by
Intramyocardial pressure
How much of CO does cerebral circulation receive
13%
held constant at 50 ml/min/100g
CNS has no capacity for anaerobic metabolism
mean arterial pressure range of cerebral blood flow
50-150 mmHg
Mechanism of autoregulation of blood flow to the brain
Myogenic
increase in perfusion pressure => vasoconstriction of cerebral arterioles and vice versa
What is local blood flow in cerebral tissue regulated by
Vasodilator metabolites
What is the regulation of CBF more sensitive to
CO2 than O2
What does an increase in PaCO2 cause
An increase in blood flow
What is the dizziness felt after excessive hyperventilation a result of
decreased CBF induced by a fall in PaCO2
When is there an effect of a decrease in PO2 on CBF
When Pressure drops from 100 mmHg -> 50 mmHg
CBF x 2 if PaO2 is further decreased to 25 mmHg
What happens if PaO2 decreases sufficiently or MAP falls below autoregulation range
CBF falls, O2 delivery to brain is impaired and a period of unconsciousness can follow
syncope, faint, coma
What is the drainage function of the brain
Cerebrospinal fluid
Consequences of an increase in pressure exerted by CSF
Increase in cranial pressure
Compresses cerebral BVs
Decrease in CBF
2 ways we overcome a decrease in CBF
LOCAL VASODILATORS
- PCO2
- PO2
STIMULATION OF CV CENTRES
- Activates vasomotor sympathetic activity to the heart and systemic BVs
- Resultant increase in MAP will increase CBF
CBF and age
Cerebral blood flow decreases with age