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9 Cards in this Set
- Front
- Back
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coronary circulation is unique because |
never gets to rest to repay metabolic debt so must supply O2 as rapidly as it is consumed
vessels surrounded by contracting muscle, so flow peaks around ventricle during diastole
extraction ratio for O2 is very high so can't just start taking out more |
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in persons with healthy coronary circulation blood flow adjusts to match ...
it can match because of..
they include? |
metabolic demand so MVo2
metabolic factors which change proportional to metabolic demand
PO2, [H] [K] adenosine but only in hypoxia |
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what is the throttle effect |
the flow in coronary arteries goes down to almost zero during systole because the contraction shuts the opening
it's another manifestation of transmural pressure: if the external pressure exeeds internal pressure the diameter becomes zero |
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what accentuates throttle effect?
so what does this translate to? |
tachycardia: diastole shorter % of cardiac cycle increase in BP: transmural pressure positive inotropism: metabolic demand is higher
people with CAD are more likely to have ischemia during those times |
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which region of the heart wall is most susceptible to ischemia? why? |
sub-endocardium
systolic compression effect increases as vessel descends deeper into myocardium |
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coronary flow CBF does not change ___ with arterial perfusion pressure- explain
what other vasc beds do this? |
linearly
even if pressure drops low or goes high, the CBF doesn't change markedly-
flow auto-regulation: myogenic - stretch causes contraction
cerebral and renal |
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increased cardiac sympathetic has what effect on the coronary vessels |
it can vasoconstrict but in healthy ppl metabolic vasodilation overrides this influence
in CAD pt that don't have metabolic reserve, can really limit CBF |
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can people be scared to death?
why? |
yes transient peak in coronary vascular resistance from alpha1 mediated input
one dog froze and had high CVR the entire time because HR plummeted |
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what is the metabolic reserve concept? |
the CBF in atherosclerotic pt is same as healthy because the distal aa have dilated.
when they need increased flow, though, they can't dilate out much more than that, so that sympathetic vasoconstriction on the already narrowed sections is a real danger |
