Coronary Circulation Flashcards
How many people does coronary artery disease kill annually in the UK?
66,000 people
Special requirements of coronary circulation?
- High basal supply of O2 – 20x resting skeletal muscle
- Increase O2 supply in proportion to increased cardiac work
Special structural features of coronary circulation?
- High capillary density
- Large SA for O2 transfer
How to reduce diffusion distance to myocyte?
- High capillary density
- Large SA for O2 transfer
Why reduce diffusion distance to myocyte?
t ∝ X² – so transport O2 is fast
Fibre diameter in skeletal vs cardiac muscle?
50μm vs 18μm
Special functional features of coronary circulation during rest?
- High blood flow - 10x the flow per weight of rest of body
- Sparse sympathetic-mediated vasoconstriction
- High NO released : vasodilatation
- High O2 extraction (75%) - body is 25%
Special functional features of coronary circulation during exercise?
-Coronary blood flow increases in proportion to demands
-Production of vasodilators : adenosine, K+, acidosis
‘out-compete’ sympathetic vasoconstriction during exercise
-Circulating A dilates coronary vessels due to β2-adrenoceptors
Why has only 25% O2 been extracted from tissues in circulation?
- arterial blood has an O2 content of 200
- mixed venous blood has O2 content of 150
- so 25% of O2 extracted from tissues in the circulation
Why has 75% O2 been extracted from arterial blood in coronary circulation?
- arterial blood has an O2 content of 200
- coronary sinus flow has O2 content of 50
- so 75% of O2 removed from arterial blood entering coronary circulation
Why should you increase blood flow with increased demand?
- extraction is near max during normal activity
- so need more O2
- so increase BF
What’s metabolic hyperaemia?
increased BF by myocardium metabolism generating metabolites –> vasodilatation
How’s adenosine produced + released?
by ATP metabolism + released from cardiac myocytes
eg of metabolites produced for vasodilation?
adenosine, PCO2, H+, K+ levels
Special problems of coronary circulation?
- Systole obstructs coronary blood flow
- Ischemic heart disease
When does coronary blood flow occur?
during diastole
What’s sudden obstruction?
acute thrombosis, Acute Coronary Syndrome (ACS), COMPLETE BLOCK, no O2 delivery –> MI
What’s slow obstruction?
atheroma (sub-endothelium lipid plaques) –> chronic narrowing of lumen, less O2 delivery –> angina
Why’s there no coronary perfusion during systole?
Pressure in ventricles is = or > aorta
Mechanical factors reducing coronary flow?
Shortening diastole, e.g. high heart rate
Increased ventricular end-diastolic pressure, e.g. volume-overload heart failure
Reduced diastolic arterial pressure, e.g. hypotension, aortic regurgitation
Mechanical factors reducing coronary flow?
- Shortening diastole : high HR
- Increased ventricular end-diastolic pressure : volume-overload HF
- Reduced diastolic arterial pressure : hypotension, aortic regurgitation