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In summary, the determinants of oxygen supply are:
carrying capacity of blood
blood flow, which is dependent on pressure and resistance
The determinants of oxygen demand are:
General Causes of Ischemia
Decreased aortic perfusion pressure (hypotension, aortic regurg)
Decreased blood oxygen carrying capacity (anemia, blood loss)
Increasing O2 demand: aortic stenosis (increased wall stress)
I did not find the epidemiology of ischemic heart disease. Maybe we will hear about it in class?
Pathophysiology of Ischemia
(not in objectives, but it’s gotta be important. Some overlaps with objective from Day 1, which merit review anyway)
reduction in blood flow resulting from combination of fixed vessel narrowing and
abnormal tone (endothelial cell dysfunction).
Fixed Vessel Narrowing
the hemodynamic significance of stenotic lesion depends on its LENGTH but more importantly by the DEGREE OF VESSEL NARROWING (L/r^4)
coronary vessels consist of proximal epicardial segement and distal resistance vessels
plaque formation happens in the proximal segments
resistance vessels try to compensate for any narrowing in the proximal vessel
less than 60% occlusion is not significant…ie, max blood flow can still occur, even though the vessel is narrowed by 60%
when the vessel diameter is narrowed by more than 70%, max blood flow is reduced, even with full dilation of the resistance vessels
this results in coronary blood that is inadequate when oxygen demand increases (physical exertion).
Here, there is a mismatch between oxygen supply and demandÆANGINA
If the vessel is occluded by more than 90%, you can have angina at REST