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Physiology of the heart I.

Features of the cardiac muscle

The cardiac cycle

The heart as a pump

Cardiac sounds

(Learning objectives 35-36)

prof. Gyula Sáry

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Cardiovascular physiology

•Cardiac function, pumping activity of the heart

•Cardiac cycle

•Characteristics of the cardiac muscle

•Electrophysiology of the heart

•The normal electrocardiogram (ECG)

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Things to consider:

• blood flows „downhill”, follows a pressure gradient

• pressure gradient is generated by the heart

• the heart can not store blood –

what comes in, must get out

• the circulation is a closed loop

• valves in the heart only play a passive role

• the heart must cope with different needs

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Cardiac, skeletal and smooth muscles

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Characteristics of skeletal, cardiac and smooth muscle

cross striated muscles

Characteristics skeletal muscles cardiac muscles smooth muscles

Thickness 40-100 µm 10-20 µm 5-10 µm

Lengthup to 20 cm

(M. sartorius)100-150 µm 30-200 µm

Nucleusmany, on the

peripheryone central nucleus one central nucleus

Organization of the

contractile fibresparallel, in sarcomers parallel, in sarcomers

no sarcomers, net-like

meshwork

Neuronal supply somatic nerves autonomic nerves autonomic nerves

Communication

between cellsno

fast, through gap

junctionsthrough gap junctions

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Physiologic anatomy 1.

• sarcomers (~ 2 μm)

• 30-60 sarcomers covered with sarcolemma

= cardiac muscle fibre

• T- and axial tubular system, sarcoplasmic reticulum

• mitochondria (sarcosomes, 30% of the myocardial cells)

• capillaries (up to 4000/mm2)

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Physiologic anatomy 2.

• gap junctions

(connexon, 6 subunits, 2 nm space to pass ions)

• longitudinal conduction is very fast

gap junctions at end-to-end

no transversal gap junctions

• functional syncytium

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Action potential lengths in the excitable tissues

Refractory periods

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Tetanic contraction in skeletal muscle NO tetanic contraction in cardiac muscle

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plateau phase

repolarization fastdepolarization

time (ms)

pote

ntial (m

V)

membrane

intracell.

extrtracell.

time (ms)

perm

eabili

ty

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1111

Electromechanical coupling in the myocardiac cell

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2 8

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Ca2+

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6

1212

Ca++ and cardiac muscle contraction;

extracellular Ca++ acts as a trigger

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1313

Ca2+ channel open muscarinergic receptor

inhib. G protein stimulating G protein

beta receptor

cell membrane

cardiac muscle cell

Stimulation and inhibition of Ca++ channels

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• no external neural impulse, automatic

• gap junction---very fast conduction

• all the fibres contract - unlike in skeletal muscles

• AP and contraction lasts for hundreds of ms

• Ca++ also from extracellular space (trigger)

• removal: Ca++ pumps and Ca++ antiporter

• contraction force depends on Ca++

symp. stimulation

extracellular Ca++ increase

cardiac glycosides

Contraction of the myocardium

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The cardiac cycle

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left ventricular pressure

time [s]

bal kamrai nyomás

bal kamrai térfogat

Pressure changes during the cardiac cycle

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right

atrium

right

ventricle

left

atrium

left ventricle

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left ventricular

pressure (mmHg)

left ventricular

volume (ml)

isovolumetric

contraction

ejection

isovolumetric

relaxation

filling

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The cardiac cycle (0.8 sec)

Systole 0.27 sec

isovolumetric contraction

maximal (rapid) ejection

decreased ejection

Diastole 0.53 sec

isovolumetric relaxation

rapid filling

slow filling

atrial contraction

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Blood volumes during the cardiac cycle

• end-diastolic volume (EDV) : 110-160 ml

• stroke volume (SV) : 70 - 80 ml

• end-systolic volume (ESV) : 40 - 80 ml

• ejection fraction: SV / EDV ~ 50 - 70%

increasing stroke volume:

increasing the EDV and/or decreasing the ESV

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valve plane in systole

shifts down

the valve plane in diastole

moves back ejection of blood

ventricular filling

The valve-plane mechanism

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The atria contribute to the diastolic filling of the

ventricles

• 75-80 % of the blood volume flows directly through the atria into the

ventricles

• atrial contraction („atrial systole”) can contribute 20-25%

(increases effectiveness and speed of filling)

• under normal conditions „atrial systole” has only minimal

importance

• heart rate & exercise

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Function of the valves

• A-V valves prevent backflow during systole

• semilunar valves prevent backflow during diastole

• the valves act passively !

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The jugular pulse

• Fluctuations in the right atrial pressure cause

pressure oscillations in the jugular vein.

• Physiologically only visible during increased venous

pressure (weight lifting, Valsalva manouvre).

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carotid pulse

jugular pulse

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Normal jugular venous pulse:

A, a positive wave due to contraction of the right atrium;

C, a positive deflection due to bulging of the tricuspid valve toward the atria at the onset

of ventricular contraction;

X, a negative deflection due to atrial relaxation during the ventricular systole;

V, a positive deflection due to filling of the right atrium against the closed tricuspid valve

during ventricular contraction;

Y, a negative deflection due to emptying of the right atrium upon ventricular relaxation.

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The heart as a pump

• stroke volume x heart rate = cardiac output

• cardiac output = blood volume leaving the ventricle in 1 minute

~ 5.5 l/min

• cardiac index = cardiac output/body surface

~ 3.1 l/m2/min

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• Since the time of

Hippocrates (5th Century

BC) doctors usually placed

their ears on a patient's

chest to listen to the

heartbeat and lung sounds.

• Faced with a breasty

woman, Dr Rene Laennec

modestly insisted on using a

rolled-up sheet of paper as

shown on picture. Thus, in

1816, the first stethoscope

was conceived.

Aorta valve: 2R2

Pulmonary valve: 2L2

Tricuspidal valve: 4-5R1

Mitral valve: 5L6-8

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Cardiac sounds

auscultation on the chest

1. (systolic) sound: contraction, valves, ejection of blood

2. (diastolic) sound: valves, can be split

3. (diastolic) sound: cuspidal valves during rapid filling

4. (late diastolic) sound: atrial contraction

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