Cardiac Physiology (III) A. Rüçhan Akar Ankara University School of Medicine December- 2003 A. Rüçhan Akar Ankara University School of Medicine December-

Cardiac Physiology(III)

Cardiac Physiology(III)

A. Rüçhan Akar

Ankara University

School of Medicine

December- 2003

A. Rüçhan Akar

Ankara University

School of Medicine

December- 2003

Coronary CirculationCoronary Circulation

Coronary Blood Flow 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 < 150 mmHg

• oxygenated by superb membrane oxygenator-”the lungs”

Cerebral Blood FlowCerebral Blood Flow

• Cerebral blood flow: 750 ml/min

• 15% of resting cardiac output

• 50-55 ml blood/100g tissue/min

• Cerebral blood flow: 750 ml/min

• 15% of resting cardiac output

• 50-55 ml blood/100g tissue/min

Right coronary blood flow

Left coronary blood flow

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

*

Cessation of Myocardial Blood Flow Cessation of Myocardial Blood Flow

mitochondria

cellular pO2 < 5mmHg within seconds

oxidative phosporilation stops

cytosol

anaerobic glycolysis

glycogen

glucose-6-phosphate

pyruvate

lactate

cellular acidosis

depletion of ATP

Depletion of ATP < 50% of Normal Level-Depletion of ATP < 50% of Normal Level-

irreversible lethal cell injury

• glycolysis is blocked

• increasing cellular acidity

• protein denaturation

• structural, enzymatic, nuclear changes

Blood VesselBlood Vessel

Measurement of Cardiac OutputMeasurement of Cardiac Output

Fick PrincipleFick Principle

The Fick Principle

Q = VO2

CaO2 – CvO2

.

–

Q: cardiac outputVO2: O2 consumption

CaO2:arterial O2 content

CvO2: mixed venous O2 content

Blood VesselBlood Vessel

• Intima primarily the endothelial lining

• Mediavascular smooth muscle, collagen, elastin

• Adventitiaconnective tissue

• Intima primarily the endothelial lining

• Mediavascular smooth muscle, collagen, elastin

• Adventitiaconnective tissue

Vascular EndotheliumVascular Endothelium

Vasodilators VasoconstrictorsVasodilators Vasoconstrictors

Nitric OxideProstacyclinEndothelium-derived hyperpolarizing factorBradykinin

Endothelin-1 Angiotensin II

Wilson SH, Lerman A.Heart Physiology and Pathophysiology, Academic Press(edited by Sperelakis N.) 473-480

L-Arginine is converted to NO by the enzyme nitric oxide synthase (NOS)

Nitric Oxide (NO)Function

Nitric Oxide (NO)Function

• Vasodilator

• Inhibitor of vascular smooth muscle cell proliferation

• Inhibitor of platelet adherence/aggregation

• Inhibitor of leukocyte/endothelial interactions

• Vasodilator

• Inhibitor of vascular smooth muscle cell proliferation

• Inhibitor of platelet adherence/aggregation

• Inhibitor of leukocyte/endothelial interactions

Endothelin-1(ET-1)

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”

• 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”

Endothelial DysfunctionEndothelial Dysfunction

• Imbalance of endothelium-derived relaxing and contracting factors• Imbalance of endothelium-derived

relaxing and contracting factors

Atherosclerotic risk factors

Decreased NO bioavailabilityIncreased levels of ET-1

Functional Classification of Vessel WallFunctional Classification of Vessel Wall

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

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

JR Levick, 1995An Introduction to Cardiovascular PhysiologyButterworth-Heinemann

Elastic ArteriesElastic Arteries

• aorta, pulmonary artery and major branches

• diameter = 1-2 cm

• tunica media is rich in elastin (extensible)

• collagen (prevents overdistension)

• aorta, pulmonary artery and major branches

• diameter = 1-2 cm

• tunica media is rich in elastin (extensible)

• collagen (prevents overdistension)

intima

media

Elastic fibers

Smooth muscle

adventitia

AORTA

Bergman RA, Afifi AK, Heidger PMAtlas of Microscopic Anatomy, 1989W.B. Saunders Company

Conduit (Muscular) ArteriesConduit (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)

• diameter = 1mm-1cm

• popliteal, radial, cerebral, coronary arteries

• tunica media is thicker, contains more smooth muscle

• rich autonomic nerve supply (contraction and relaxation)

Resistance VesselsResistance Vessels

• main resistance to blood flow resides in the;

– smallest, terminal arteries (diameter = 100-500m)

– arterioles (< 100m) “single layer of muscle in the media”

• richly innervated by vasoconstrictor nerve fibres

• actively regulate local blood flow to match local demand

• main resistance to blood flow resides in the;

– smallest, terminal arteries (diameter = 100-500m)

– arterioles (< 100m) “single layer of muscle in the media”

• richly innervated by vasoconstrictor nerve fibres

• actively regulate local blood flow to match local demand

Capillaries (Exchange vessels)Capillaries (Exchange vessels)

• diameter: 4-7m

• wall: single layer of endothelial cells

• wall thickness = 0.5m

• large cross-sectional area

• slow blood velocity

• red cell transit time = 1-2 sec

• diameter: 4-7m

• wall: single layer of endothelial cells

• wall thickness = 0.5m

• large cross-sectional area

• slow blood velocity

• red cell transit time = 1-2 sec

Arteriovenous AnastomosisArteriovenous Anastomosis

• shunt vessels ( diameter = 20-135m)

• connect arterioles to venules, bypassing the capillaries

• skin, nasal mucosa

• temperature regulation

• shunt vessels ( diameter = 20-135m)

• connect arterioles to venules, bypassing the capillaries

• skin, nasal mucosa

• temperature regulation

The Veins“Capacitance Vessels”

The Veins“Capacitance Vessels”

• diameter 50-200m

• 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

• diameter 50-200m

• 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

Distribution of blood volume in a resting man ( 5.5 litres)

Folkow B, Neil E. 1971, Oxford University Press, London