Kp 1.3.2.6 Prinsip Hemodinamik 1 (2 Jam)

7/24/2019 Kp 1.3.2.6 Prinsip Hemodinamik 1 (2 Jam)

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PRINSIP HEMODINAMIK

Rahmatina B. Herman

Bagian FisiologiFakultas Kedokteran - Unand


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Cardiovascular System

Closed circulatory system:

Arterial system

Heart

Capillary system

Venous system

VentricleAtrium


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SIRKULASI

(CIRCULATION)


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Introduction

In general, the function of cardiovascular systemis to maintain appropriate environment in alltissue fluids optimal survival and function of thecells homeostasis

The function of the circulation is to service theneeds of body tissues as a transport system of:

- Essential materials to tissues: nutrients and O2

- Waste products away to excretory system- Humoral communication throughout the body

(including hormones and electrolytes)

- Body temperature


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Introduction..

The rate of blood flow through tissues is controlled inresponse to tissue need for nutrients and O2

The heart and circulation in turn are controlled to

provide necessary cardiac output (COP) and arterial

pressure to cause the needed tissue blood flow

COP is the quantity of blood pumped into the aorta

each minute by heart the quantity of blood that

flows through circulation

COP = stroke volume (SV) X heart rate (HR)


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Physical Characteristics of Circulation

The Circulation is divided into:- Systemic circulation

- Pulmonary circulation

Because systemic circulation supplies blood flow to alltissues of the body , it is also called:

- Greater circulation or

- Peripheral circulation


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Systemic Circulation

Left ventricleLeft atrium Left A-V valve

Aorta

Left semilunar valve

Throughout bodyVena Cava

Right atrium

Capillary


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Pulmonary Circulation

Right ventricleRight atrium Right A-V valve

Pulmonary

trunkLungPulmonary

vein

Atrium kiri Right semilunar valve

Capillary


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Distribution of blood in different parts of circulatory system


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The Function of Parts of Circulation

Arteries:To transport blood under high pressure to the tissues

Have strong vascular walls

Blood flows at a high velocity

Arterioles:

The last small branches of arterial system

Acts as control blood released into capillaries

Have strong muscular wall that can close(constriction) the arteriole completely and also can

dilate (relaxation) several folds in response to the

need of tissue


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The Function of Parts of Circulation..

Capillaries:To exchangefluid and substances between the blood

and the interstitial fluid:

Transfer tissue needs to interstitial fluids

Uptake tissue waste products from interstitial fluids

The capillary walls:

are very thin (only a single layer of endothelial) have numerous minute capillary pores permeable to

water and other small molecular substances


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The Function of Parts of Circulation..

Venules:To collect blood from capillaries and gradually coalesce

into progressively larger veins

Veins: Blood transport from venules back to the heart

the pressure is very low (lower than in capillary) the walls are thin even so muscular enough to contract or expand

Acts as controllable reservoir for the extra blood

depending on the needs of circulation

Serve as major reservoir of extra blood


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Cross-Sectional Areas of Vessels


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Cross-Sectional Areas of Vessels..

Note particularly: the much larger cross-sectional areasof veins than of arteries, averaging 4 times large

storage of blood in venous system

The same volume of blood must flow through each

segment per minute blood flow velocity is inversely

proportional to vascular cross-sectional area

Under resting conditions, the average velocity in:

Aorta: 33 m/sec Capillaries: 0.3 m/sec (1/1000 as in aorta)

The capillary length: 0.3-1 mm blood remains in

capillary for only 1-3 sec rapidly exchanging process


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Pressure in Portions of Circulation

Systemic CirculationAorta: Heart pumping is pulsatile pressure alternates

between 120 mmHg (systolic) & 80 mmHg (diastolic)

Capillaries:In systemic capillaries varies: 35 mmHg near arteriolar ends 17 mmHg in most vascular beds 10 mmHg near venous endsVenous: Mean pressure falls progressively to 0 mmHg when

blood empty into right atrium


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Pressure in Portions of Circulation..

Pulmonary CirculationPulmonary artery:

Heart pumping is also pulsatile pressure alternates

between 25 mmHg (systolic) & 8 mmHg (diastolic)Capillaries:

Average 7 mmHg

Venous:

Total blood flow through the lung each minutes =

through systemic, in accord with the lung needs all

that is required to expose the blood in pulmonary

capillaries to O2 and other gases in alveoli


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Pressure in Portions of Circulation..


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Diagram of the changes in pressure and velocity as blood flows

through systemic circulation


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Basic Theory of Circulatory Function

3 basic principles that underlie all functions of system:1. Rate of blood flow to each tissue is almost always

precisely controlled in relation to the tissue need

When tissues are active the need increased

occasionally 20-30 x resting level

Heart only can increase COP 4-7 x resting level

Microvessels dilating or constricting to controllocal blood flow precisely to the level required

Central nervous system provides additional help

in controlling tissue blood flow


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Basic Theory of Circulatory Function..

2. COPis controlled mainly by the sum of all local tissueflows.

When blood flows from tissues immediately

returns to the heart (venous return) the heart

responds automatically (acts as automation:

Frank-Starling mechanism) pumping force

increased SV increased COP increased

Central nervous system provides additional helpto make it pump the required amounts of blood

flow


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Basic Theory of Circulatory Function..

3. Arterial pressure is controlled independently of eitherlocal blood flow control or COP control.

When pressure falls < normal within secondsnervous reflexes elicits a series of circulatory

changes to raise pressure back toward normal:a. Increase the force of heart pumpingb. Contraction of large venous more blood to the heartc. Generalized constriction of most arterioles throughout

body more blood accumulates in large arteries to

increase arterial pressure Over more prolonged periods (hoursdays), kidney

play additional major role:a. Secreting pressure- controlling hormones

b. Regulating blood volume


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Biophysical of Circulatory Physiology..

Interrelationship among pressure, flow, andresistance

Blood flow through a blood vessel is determined by

two factors:

1. Pressure difference of the blood between the two

ends of the vessel, sometimes called pressure

gradient

2. The impediment to blood flow through the vessel,called vascular resistance


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Ohms law:

Q =

P

R

Q = flow

P = pressure differenceR = resistance


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Blood flow- Blood flow means the quantity of blood that

passes a given point in the circulation in a given

period of time- The overall blood flow in total circulation of an

adult person at rest is 5000 ml/min.

It is the amount of blood pumped into aorta by

heart each minute or cardiac output


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Methods for Measuring Blood Flow

Using flowmeter Electromagnetic flowmeter:


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Methods for Measuring Blood Flow

Using flowmeter Ultrasonic Doppler flowmeter:


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Blood Flow in Vessels

Laminar flowWhen blood flows at a steady state rate in smooth

blood vessel flows streamline or laminar flow:

- each layer of blood remaining the same distance

from the vessel wall- the central most portion of the blood stays in the

center of blood vessel

Turbulent flow

- the opposite of streamline flow

- blood flowing in all direction in the vessel and

continually mixing within the vessel


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Blood Flow in Vessels..

Parabolic velocity profile during laminar flow,due to:

- The fluid molecules touching the wall barely move

because of adherence to the wall vessel wall.

- The next layer of molecules slips over these

- The third layer over the second, the fourth layer

over the third, and so forth

Thus, each layer toward the center flows progressively

more rapidly than the outer layers


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Diagram of velocities of concentric laminas of a viscous fluid

flowing in a tube, illustrating parabolicdistribution of velocities

(Laminar flow)


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Turbulent flow means:- The blood flows crosswise in the vessel as well as

along the vessel

- Usually forming whorls in the blood, called eddy

currents, similar to the whirlpools that frequently

see in a rapidly flowing river at a point of obstruction

Turbulent flow under conditions:

- when rate of flow becomes too great and> passes by an obstruction makes a sharp turn

> or passes over a rough surface


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Effect of constriction on velocities profile


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Probability of turbulence:

Re : Reynolds numberv : velocityd : diameter

p : density of fluid: viscosity of fluid

When Re rises above 200-400, turbulent will occur at

some branches of vessels but will die out along thesmooth portions of vessels

Flow is usually not turbulent if Re is less than 2000

Flow is almost always present if Re is more than 3000


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Conditions that appropriate for turbulence:1. high velocity

2. pulsatile nature of flow

3. sudden change in vessel diameter4. large vessel diameter

In small vessels, Re is almost never enough to

cause turbulence


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Average Velocity

Velocity (V) is proportional to flow (Q) divided by area

of the conduit (A):

If flow constant, velocity increase in direct proportion

to any decrease in A

The average velocity of fluid movement is inversely tothe total cross sectional area the average velocity of

blood is high in aorta, declines steadily in smaller

vessels, and lowest in capillaries, then increase again

as the blood enters the vein


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Resistance to Blood Flow

Resistance is the impediment to blood flow in a vesselResistance must be calculated from measurements of

blood flow and pressure difference between two

points in the vessel.

The unit used to express resistance is peripheral

resistance unit (PRU)

The rate of blood flow through entire circulatory

systemis equal to COP = 100 ml/secThe pressure difference from systemic arteries to

systemic veins is 100 mmHg

So, the total peripheral resistance is 100/100 = 1 PRU


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Viscosity and Resistance

The resistance of blood flow is determined by:- radius of blood vessels

- viscosity of blood

Plasma is 1.8 times as viscous as water and whole

blood is 3-4 times as viscous as water viscositydepends on hematocrit

In large vessels, hematocrit viscosity ,

but in vessel < 100 m in diameter (arterioles,

capillaries, venules) viscosity change per unit change in

hematocrit is much less than it is in large vessels

hematocrit changes have relatively little effect on

peripheral resistance, except the changes are large


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Viscosity and Resistance..

In severe polycythemia, resistance thework of heart

In marked anemia, peripheral resistance is

decreased, because of decline in viscosity blood flow

The decrease in Hb decreased the O2-

carrying ability, but the increased blood flowpartially compensates for this


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Effect of changes in hematocrit on relative viscosity of blood

measured in a glass viscometer and in hind leg of a dog


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Critical Closing Pressure

In rigid tubes, the relationship between pressure and flow

of homogenous fluid is linear

But in vivo, in thin-walled blood vessels: when pressure

a point is reached at which no blood flows, even though

the pressure is not zero, because vessels are surrounded bytissues that exert small but definite pressure on them

intraluminal pressure below the tissue pressure the

vessels collapse

In inactive tissues, the pressure in many capillaries is low,because precapillary sphincters and metarterioles are

constricted many of the capillaries are collapsed

The pressure at which flow ceases is called the critical

closing pressure


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Conductance

Conductance is a measure of blood flowthrough a vessel for a given pressure difference

Conductance =

Very slight changes in diameter of a vessel can

change its conductance tremendously

1

Resistance


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Law of Laplace

This law states that tension in the wall of cylinder (T) isequal to the product of the transmural pressure (P)

and the radius (r) divided by the wall thickness (w)

T= Pr/w

The transmural pressure = pressure inside cylinder pressure outside cylinder

But tissue pressure in body is low, it can be generally

ignored and P = pressure inside the viscusIn a thin-walled viscus, w is very small and can be

ignored, but it becomes significant factor in arteries


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Relationship between distending pressures (P) and wall tension (T)


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Law of Laplace..

So, in thin-walled viscus: P=T divided by the twoprincipal radii of curvature of the viscus

In a cylinder such as blood vessel, one radius is infinite,so

Consequently, the smaller the radius of blood vessel,

the lower the tension in the wall necessary to balancethe distending pressure

In aorta the tension at normal pressure is 170,000

dynes/cm, in vena cava 21,000, in capillaries 16


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Law of Laplace..

The law of Laplace makes clear a disadvantage facedby dilated hearts

When radius of heart chamber is increased a greater

tension must be developed in myocardium to produce

any given pressure a dilated heart must do morework than a non-dilated heart

In the lungs, the radii of curvature of alveoli become

smaller during expiration tend to collapse becauseof the pull of surface tension if the tension were not

reduced by the surface-tension-lowering agent,

surfactant

d l


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Resistance and Capacitance Vessels

The vena is called capacitance vessels, becausea large amount of blood can be added to the

venous system before the veins become

distended to the point where further

increments in volume produce a large rise in

venous pressure

The small arteries and arterioles are referred to

as resistance vessels, because they are the

principal site of peripheral resistance


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Resistance and Capacitance Vessels

At rest, at least 50% of circulating blood volume is insystemic veins, 12% in heart cavities, 18% in

pulmonary circulation; only 2% in aorta, 8% in arteries,

1% in arterioles, and 5% in capillaries

When extra blood is administered by transfusion,

- < 1% of it is distributed in the arterial system (the

high-pressure system), and

- all rest is found in systemic veins, pulmonarycirculation, and heart chambers other than the left

ventricle (the low-pressure system)


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Kp 1.3.2.6 Prinsip Hemodinamik 1 (2 Jam)

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