Cardiac Physiology III

1
Cardiac Physiology(III)

• A. Rüçhan Akar
• Ankara University
• School of Medicine
• December- 2003

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Coronary Circulation
3
Coronary Blood Flow

• coronary blood flow 250 ml/min
• 5 of resting cardiac output
• 60-80 ml blood/100g tissue/min
• entirely during diastole
• aortic diastolic pressure minus LVDP
• duration of diastole
• pressure lt 150 mmHg
• oxygenated by superb membrane oxygenator-the
  lungs

4
Cerebral Blood Flow

• Cerebral blood flow 750 ml/min
• 15 of resting cardiac output
• 50-55 ml blood/100g tissue/min

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The peak left coronary flow occurs at the end
of isovolumetric relaxation

Left coronary blood flow
Right coronary blood flow
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Cessation of Myocardial Blood Flow

• mitochondria
• cellular pO2 lt 5mmHg within seconds
• oxidative phosporilation stops

• cytosol
• anaerobic glycolysis
• glycogen
• glucose-6-phosphate
• pyruvate
• lactate
• cellular acidosis
• depletion of ATP

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Depletion of ATP lt 50 of Normal Level-

• irreversible lethal cell injury
• glycolysis is blocked
• increasing cellular acidity
• protein denaturation
• structural, enzymatic, nuclear changes

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Blood Vessel
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Measurement of Cardiac Output

• Fick Principle

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The Fick Principle
.
VO2 CaO2
CvO2
Q

Q cardiac output VO2 O2 consumption CaO2arteria
l O2 content CvO2 mixed venous O2 content
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Blood Vessel

• Intima
• primarily the endothelial lining
• Media
• vascular smooth muscle, collagen, elastin
• Adventitia
• connective tissue

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Vascular Endothelium

• Vasodilators Vasoconstrictors

Nitric Oxide Prostacyclin Endothelium-derived
hyperpolarizing factor Bradykinin
Endothelin-1 Angiotensin II
Wilson SH, Lerman A. Heart Physiology and
Pathophysiology, Academic Press (edited by
Sperelakis N.) 473-480
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L-Arginine is converted to NO by the enzyme
nitric oxide synthase (NOS)
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Nitric Oxide (NO)Function

• Vasodilator
• Inhibitor of vascular smooth muscle cell
  proliferation
• Inhibitor of platelet adherence/aggregation
• Inhibitor of leukocyte/endothelial interactions

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Endothelin-1(ET-1)

• Peptide first sequenced in 1988
• Most potent vasoconstrictor in humans
• Maintenance of basal arterial vasomotor tone
• Strong chemoattractant for circulating monocytes
  and macrophage activation proatherogenic

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Endothelial Dysfunction

• Imbalance of endothelium-derived relaxing and
  contracting factors

Atherosclerotic risk factors
Decreased NO bioavailability Increased levels of
ET-1
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Functional Classification of Vessel Wall

• elastic arteries
• muscular arteries
• resistance vessels
• capillaries (exchange vessels)
• venules (capacitance vessels)

JR Levick, 1995 An Introduction to Cardiovascular
Physiology Butterworth-Heinemann
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Elastic Arteries

• aorta, pulmonary artery and major branches
• diameter 1-2 cm
• tunica media is rich in elastin (extensible)
• collagen (prevents overdistension)

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intima
AORTA
Elastic fibers
Smooth muscle
media
adventitia
Bergman RA, Afifi AK, Heidger PM Atlas of
Microscopic Anatomy, 1989 W.B. Saunders Company
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Conduit (Muscular) Arteries

• diameter 1mm-1cm
• popliteal, radial, cerebral, coronary arteries
• tunica media is thicker, contains more smooth
  muscle
• rich autonomic nerve supply (contraction and
  relaxation)

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Resistance Vessels

• main resistance to blood flow resides in the
• smallest, terminal arteries (diameter
  100-500mm)
• arterioles (lt 100mm) single layer of muscle in
  the media
• richly innervated by vasoconstrictor nerve fibres
• actively regulate local blood flow to match local
  demand

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Capillaries (Exchange vessels)

• diameter 4-7mm
• wall single layer of endothelial cells
• wall thickness 0.5mm
• large cross-sectional area
• slow blood velocity
• red cell transit time 1-2 sec

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Arteriovenous Anastomosis

• shunt vessels ( diameter 20-135mm)
• connect arterioles to venules, bypassing the
  capillaries
• skin, nasal mucosa
• temperature regulation

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The VeinsCapacitance Vessels

• diameter 50-200mm
• thin wall
• in limb veins, intima possesses pairs of valves
• low resistance to flow
• storing large volumes of blood under low pressure
• 60-70 of the circulating blood volume

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Distribution of blood volume in a resting man (
5.5 litres)
Folkow B, Neil E. 1971, Oxford University Press,
London