conary blood flow

1. Coronary blood flow

2. Oxygen consumption
• Highest per tissue mass of all human organs
• 250ml per min
• 0.8 ml per min per gram of heart muscle
• 5% of cardiac output
• Oxygen extraction is 70-80% (25%)

3. Coronary blood flow
• Increased oxygen consumption must be met
by increasing the blood flow
• May increase five fold during exercise
• Supply usually matches the demand
• Gregg effect: an increase in coronary blood
flow can increase myocardial oxygen
consumption

4. ANATOMY
• Two main coronary arteris
• Left and Right
• Epicardial arteries
• Intramuscular arteries penetrate the
myocardium to form subendocardial arterial
plexuses
• Coronary sinus
• Anterior coronary vein, Thebesian veins

5. Determinants of coronary blood flow
• Coronary perfusion pressure
• Perfusion time
• Vessel wall diameter

6. • Coronary perfusion pressure:
• Systole: blood flow to LV is lowest
• Diastole: flow resumes
• Aortic diastolic pressure-LVEDP=CPP
• Phasic changes in blood flow are less in
rt.ventricle

7. • Perfusion time:
Any increase in heart rate
impinges on diastolic time more than systolic
time and reduces the perfusion time.

8. • Vessel Wall Diameter:
• Vasomotor tone
• Deposits
• Mechanism/regulation

9. Factors-Vasomotor Tone
• Myocardial oxygen demand
• Hypoxia: adenosine, ATPase K+
• Autoregulation
– Intraluminal pressure changes
– Metabolic regulation
– Myocardial o2 tension, vasoconstrictors, vasodilators

10. • Nervous control: weak
• Epicardial vessels alpha receptors
• Anti-steal effect
• Intramuscular, subendocardial blood vessels beta-
2 receptors
• Sympathetic stimulation: 02 demand, beta
activation – increased flow
• Parasympathetic : vasodilatory, intact
endothelium, acetyl choline

11. • Humoral Control:
• Intact endothelium, peptide harmones
• ADH causes vasoconstriction in stress
• Others vasodialtion – ANP, VIP, calcitonin gene
related peptide
• AT-2 causes vasoconstriction
• ACE inhibits bradykinin - vasodilator

12. • Vascular Endothelium:
• Final common pathway in regulation blood flow
• Modulates the contractile activity of the
underlying smooth muscle
• vasorelaxants: EDRF, NO, prostacyclin, bradykinin
• Vasoconstrictos: endothelin, ThromboxaneA2
• Balance between these determines the flow

13. Myocardial oxygen balance
• Oxygen delivery is the product of arterial oxygen
carrying capacity and myocardial blood flow.
• diastolic pressure time index (DPTI):
• Useful measure of coronary blood flow
• Product of coronary perfusion pressure and
diastolic time
• Tension time index (TTI):
• Oxygen demand
• Product of systolic pressure and systolic time

14. • EVR (endocardial viability ratio):
• DPTI/TTI Ratio
• Myocardial oxygen supply-demand balance
• Normal is 1 or more
• ratio <0.7 is associated with subendocardial
ischemia

15. diseases
• CAD (coronary artery disease):
• Change in artery diameter
• Coronary steal
• Hypertension: LVH
• Heart Failure: impaired ejection, LDV, LVEDP,
lowered coronary perfusion pressure
• Vasoconstriction: increases o2 demand, work
load, improves perfusion

16. DRUGS
• Antiplatelet drugs, anticoagulants and lipid
lowering drugs
• Nitrates
• Calcium channel blockers
• Drugs acting on angiotensin
• Potassium channel openers
• B-blockers
• Vasopressors and inotropes

17. Anesthesia and myocardial oxygen balance
• Halogenated inhalational agents
• Isoflurane
• Sevoflurane
• Halothane
• Desflurane???
• Central neuraxial block
• Sympathetic stmulation

18. • Key points:
• Blood flow to the heart occurs mainly during
diastole.
• Coronary blood flow is mainly determined by
local oxygen demand.
• The vascular endothelium is the final common
pathway controlling vasomotor tone.
• When anaesthetising patients with coronary
artery disease, maintain coronary perfusion
pressure and avoid tachycardia.