Coronary Blood Flow and Ischemic heart Disease

Question 1

determinants of metabolic needs

Answer 1

wall stress

heart rate

contractility

Question 2

double product index of oxygen demand

Answer 2

HR x peak systolic BP = MV_O2

MV_O2 = CBF x (A-V)_O2

Question 3

physiological factors governing coronary blood flow

Answer 3

flow = driving pressure/resistance

coronary flow = P_Ao/R_coronary

Question 4

components of coronary resistance

Answer 4

conduit artery resistance (usually small)

microvascular resistance (autoregulatory resistance)

compressive resistance

Question 5

conduit artery resistance

Answer 5

normally very small

can be affected by endothelial and autonomic factors

increased when coronary artherosclerosis narrows the arterial lumen

Question 6

microcirculatory resistance

Answer 6

primary mechanism by which flow adjusts to demand, and by which flow can be maintained constant when arterial pressure changes

relates to caliber of arterial microvessels and changes modestly in response to stimuli

normally high under basal conditions, there is a large reserve capacity for vasodilation

adjusted on a local basis

Question 7

What governs R2?

Answer 7

metabolic factors such as adenosine and P_O2

endothelial factors - EDRF (NO), endothelial-derived hyperpolarizing factor (EDHF), prostacyclins, endothelins

neurohormonal factors - autonomic nervous system and circulating vasoactive agents, alpha-adrenergic vasoconstriction and beta-adrenergic vasodilation

Question 8

Endothelial-derive drelaxing factor (EDRF or NO)

Answer 8

synthesized continuously by coronary vascular endothelium, particularly microvessels > 100 um

rate of production varies (directly) with flow (local shear stress)

exerts a tonic vasodilating influence on R₂

has similar but smaller effects on conduit vessels

Question 9

compressive resistance

Answer 9

results from compression of coronary blood vessels during systole

causes flow during systole to be only a small fraction of that during diastole

greatest

Question 10

autoregulation of coronary blood flow

Answer 10

coronary microvascular resistance (R₂) adjusts to keep flow at the level appropriate to myocrdial O₂ demand

Question 11

reactive hyperemia

Answer 11

the increase in coronary flow which follows a brief period of coronary artery occlusion

Question 12

coronary flow reserve

Answer 12

the ratio of flow during maximum coronary vasodilation to flow under resting conditions

Question 13

negative atherosclarotic narrowing

Answer 13

luminal narrowing

Question 14

positive atherosclerotic narrowing

Answer 14

increased wall thickness - occurs before negative narrowing

Question 15

dynamic factors affecting pressure and narrowing across a stenosis

Answer 15

endothelial products

ANS vasoconstriction

vasoactive agents

sudden increases: plaque fissuring, thrombus formation

Question 16

coronary collateral circulation

Answer 16

develops frequently as the degree of stenosis becomes critical

provides modest degree of perfusion to areas in jeopardy

Question 17

principles of coronary stenosis treatment

Answer 17

limit increases in myocardial O₂ demand - minimize increases in systolic BP, heart rate

augment flow to ischemic areas - counter dynamic incresaes in stenosis severity, counter endothelial dysfunction, counter abnormal vasoconstriction, increase collateral flow, intervention