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CardioRenal II > Phys- Coronary Flow > Flashcards

Phys- Coronary Flow Flashcards

1
Q

Oxygen delivery equation

A

Oxygen Deliivery = Blood Flow x Oxygen Content

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2
Q

Flick Equation

A

VO2= Blood Flow x (CaO2 - CvO2)

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3
Q

Extraction equation

A

Difference between what goes in and what comes out CaO2-CvO2

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4
Q

If coronary O2 extraction is nearly maximal at rest how does the heart match O2 delivery with increases in myocardial VO2?

A

increased blood flow

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5
Q

Control of coronary blood flow

A

Primarily under local metabolic control

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6
Q

Intramural arteries

A

penetrate the myocardium and are subject to high transmural pressure during systole (surround pressure)

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7
Q

capillary to fiber ratio in cardiac muscle

A

(number or capillaries per muscle fiber) 1 capillary/fiber

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8
Q

Cardiac Capillary density

A

VERY high (~3500 capollaries/mm^2 ) to support the metabolism of the heart

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9
Q

describe cardiac capillary perfusion at rest

A

heterogeneous- not all are well perfused at rest

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10
Q

Capillary recruitment

A

increased myocardial work increases blood flow and more uniform perfusion of capillaries

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11
Q

How do we get more uniform perfusion of capillaries during capillary recruitment

A

Increased myocardial work causes 1.) Increased “Functional” capillary density 2.) Decreased diffusion distances 3.)Enhanced capillary exchange

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12
Q

Coronary Collateral Vessels

A

Arterial-to arterial anastamoses: Coronary arteries form collateral channels to ensure myocardial perfusion and help protect the mycoardium against ischemia

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13
Q

Native coronary collateral vessels

A

exist in all hearts - relatively small and few in number

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14
Q

Mature (or stimulated) coronary collaterals

A

Myocardial ischemia stimulates collarteral growth. The lumen of collateral vesslesl enlarges followed by significant wall thickening.

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15
Q

Myocardial Oxygen Consumption depends on what variables

A

Blood flow (Q) and coronary oxygen extraction (CaO2-CvO2) where MVO2 = Q x (CaO2-CvO2)

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16
Q

In the heart, when is oxygen extraction nearly maximal

A

under resting conditions

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17
Q

what is the only way to increase MVO2

A

by increasing blood flow (remember: oxygen extraction is at near max under resting conditions)

18
Q

MVO2 increases in proportion to what

A

Myocardial work- Maximal MVO2 can increase 5-6 fold from resting MVO2

19
Q

Determinants of MVO2 “The Big 3”

A

1.) Contractility 2.) Heart Rate 3.) Wall Tension

20
Q

Theory behind how increases in ionotropy increases MVO2

A

thought to be related to the metabolic cost of Ca release and uptake

21
Q

Discuss the increase in MVO2 as a result of wall tension

A

MVO2 increases linearly with peak systolic pressure (or peak systolic wall tension) developed by the left ventricle (Law of LaPlace Wall tension = (pressure x radius)/2thickness)

22
Q

Discuss tratments if there is a mismatch between MVO2 and the ability to deliver O2 to the tissue

A

1.) B-Blockers (decreases HR and Contractility= decrease Myocardial work by decreasing MVO2) 2.) Ca channel blockers (decrease contractility = decrease MVO2) 3.) Nitrates (decrease afterload by causing peripheral vasodilation and decrease preload through venodilation)

23
Q

Determinants of MVO2 “The Little 3”

A

1.) Basal requirements (cellular metabolism) 2.) Activation Energy (cost of electrical activation) 3.) Ejection of Blood (Cost of shortening muscle)

24
Q

Myocardial Metabolic Substrate Utilization

A

1.) ATP (used for contraction ) is in dynamic equilibrium with a pool of creatine phosphate 2.) Oxidative Metabolism (fatty acids) - 60% of substrate utilization- balance is glucose and lactate 3.) Glycolysis - 40% of substrate metabolism

25
Q

Discuss situations where Glycolysis predominates in myocardial substrate utilization

A

During ischemia and hypoxemia - glycolysis predominates and the heart switched from net lactate uptake to net lactate production. NOTE: more predominant but less efficient

26
Q

How does the heart meat increased O2 demands (increased MVO2)

A

almost entirely though increasing blood flow

27
Q

Does the percentage of cardiac output used changed when MVO2 is increased?

A

NO. Flow increases up to 5 fold as MVO2 increased but cadiac output remains ~5% (as it is in resting conditions)

28
Q

What is the drivig pressure for coronary flow

A

Aortic diastolic pressure

29
Q

Describe the coronary flow in ventricular systole

A

Coronary flow decreased due to “systolic squeeze” (Psurround > Pdiastolic in coronaries) Flow begins to increase again in diastole

30
Q

When does coronary perfusion occur

A

Diastole

31
Q

Describe the phasic nature of coronary flow

A

Flow increases during early diastole and follows aortic pressure

32
Q

Where does “systolic Squeeze” have the greatest effect

A

the left ventricle (occurs to a lesser extent in the low pressure right ventricle)

33
Q

Is phasic flow more pronounced in subendocardium or subepicardium?

A

Subendoardium due to systolic squeeze (still occurs in the subepicardium but to a lesser extent)

34
Q

Effect of Aortic Stenosis and coronary perfusion

A

Increases left ventricular work but will NOT increase coronary perfusion pressure or flow - creates and unfavoralble supply/demand ratio

35
Q

What is the most important determinant of Coronary Blood Flow

A

Myocardial oxygen consumption

36
Q

Autonomic control of coronary flow

A

1.) Direct effects - innervated by both sympathetic (vasoconstriction) and parasympathetic (modest vasodilatio) 2.) Indirect effects- MORE IMPORTANT- Metabolic vasoregulation

37
Q

Coronary Vasoregulation

A

Changes in metabolic demand due to changes in HR, contractility, or blood pressure are far more important in determining vascular caliber and myocardial blood flow

38
Q

Adenosine Hypotheis

A

Adenosine causes vasodilation in hypoxia

39
Q

what substrates can induce vasodilation in coronary arteries

A

Adenosine, hyperkalemia (K) , hypercapnia (high CO2), acidosis (H) , lactate, and prostaglandins

40
Q

Vascular Reserve (Coronary Autoregulation)

A

How much we can increase flow at a given pressure (difference between the autoregulating curve and the maximally vasodilated curve)

41
Q

Conditions of reduced coronary reserve

A

1.) Lower perfusion pressures (low diastolic pressure) 2.) Chronically higher MVO2 (increased flow) 3.) Increased fixed resistance (eg: atherosclerosis)

42
Q

Which has less fow reserve, subendo or subepi? What is the risk of this?

A

Subendo has less flow reserve - greater risk of ischemia, injury, and infarction

CardioRenal II (12 decks)

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