3 hemodynamics 2ndyears

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Hemodynamics Physics of Blood flow in the circulation

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Page 1: 3 Hemodynamics 2ndyears

Hemodynamics

Physics of Blood flow in the circulation

Page 2: 3 Hemodynamics 2ndyears

Circulatory System

• Heart:

Has 2 collecting chambers - (Left, Right

Atria)

Has 2 Pumping chambers - (Left, Right

Ventricles)

Page 3: 3 Hemodynamics 2ndyears
Page 4: 3 Hemodynamics 2ndyears

Circulation Schematic

Lungs Tissues

Left Side of Heart

Right Side of Heart

A V

V A

Pulmonary Vein

Pulmonary Artery

Aorta

Sup. & Inf. Vena Cava

Mitral Valve

Pulmonary Valve

Aortic Valve

Tricuspid Valve

Page 5: 3 Hemodynamics 2ndyears

Heart Valves

• Atrioventricular (A-V) valves - separate Atria from Ventricles

• Bicuspid (Mitral) - Left Side

• Tricuspid - Right Side

• Semi-Lunar Valves - separate ventricles from Arteries

Page 6: 3 Hemodynamics 2ndyears

Opening, Closing of Valves - Depends on Pressuredifferences between bloodin adjacent areas

Page 7: 3 Hemodynamics 2ndyears

Heart Sounds

• ‘Lubb’ (1st sound) - Closure of A-V valves• ‘Dupp’ (2nd sound) - Closure of S-L valves

Caused by Turbulence on closing.

Anything extra ’Murmur’ (swishing of blood)

Could be due to:• Stenosis of Valves (calcification)• Valves not closing properly

(Incompetence, Insufficiency)

Increases Pressure on heart

Page 8: 3 Hemodynamics 2ndyears

Blood Vessels

• Arteries• Capillaries• Veins

Systemic Pathway:Left Ventricle Aorta Arteries Arterioles

of Heart Capillaries

Venules Veins Right Atrium of Heart

Page 9: 3 Hemodynamics 2ndyears

Blood

• Composition:– Approx 45% by Vol. Solid Components

» Red Blood Cells (12m x 2 m)

» White Cells

» Platelets

– Approx 55% Liquid (plasma)» 91.5% of which is water

» 7% plasma proteins

» 1.5% other solutes

Page 10: 3 Hemodynamics 2ndyears

Blood Functions

• Transportation

of blood gases, nutrients, wastes

• Homeostasis (regulation)

of Ph, Body Temp, water content

• Protection

Page 11: 3 Hemodynamics 2ndyears

As a Result …….

• Blood behaves as a simple Newtonian Fluid when flowing in blood vessels

i.e. Viscous stresses Viscosity, strain rate

dy

du y u(y)

No slip at wall

Page 12: 3 Hemodynamics 2ndyears

• Viscosity of Blood = 3 3.5 times of water

• Blood acts as a non-newtonian fluid in smaller vessels (including capillaries)

Page 13: 3 Hemodynamics 2ndyears

Cardiac Output• Flow of blood is usually measured in l/min• Total amount of blood flowing through the

circulation = Cardiac Output (CO)

Cardiac Ouput = Stroke Vol. x Heart Rate

= 5 l/min

Influenced by Blood Pressure & Resistance

Force of bloodagainst vessel wall

•Blood viscosity•Vessel Length•Vessel Elasticity•Vasconstriction / Vasodilation

with water retention with dehydration, hemorrage

Page 14: 3 Hemodynamics 2ndyears

Overall

• Greater Pressure Greater Blood

Differences Flow

• Greater Resistance Lesser Blood Flow

Page 15: 3 Hemodynamics 2ndyears

Driving force for blood flow is pressure created by ventricular contraction

Elastic arterial walls expand and recoil

continuous blood flow

Blood PressureBlood Pressure

Page 16: 3 Hemodynamics 2ndyears

Blood pressure is highest in the arteries (Aorta!) and falls continuously . . .

Systolic pressure in Aorta: 120 mm Hg

Diastolic pressure in Aorta: 80 mm Hg

Diastolic pressure in ventricle: ?? mm Hg

Page 17: 3 Hemodynamics 2ndyears

Ventricular pressure difficult to measure

arterial blood pressure assumed to indicate driving pressure for blood flow

Arterial pressure is pulsatile

useful to have single value for driving pressure: Mean Arterial Pressure

MAP = diastolic P + 1/3 pulse pressure

Page 18: 3 Hemodynamics 2ndyears

Pulse Pressure = systolic pressure - ??

= measure of amplitude of blood pressure wave

Page 19: 3 Hemodynamics 2ndyears

MAP influenced by

• Cardiac output

• Peripheral resistance

MAP CO x Rarterioles

• Blood volume– fairly constant due to homeostatic mechanisms

(kidneys!!)

Page 20: 3 Hemodynamics 2ndyears

BP too low:BP too low:

• Driving force for blood flow unable to overcome gravity

O2 supply to brain

Symptoms?

Page 21: 3 Hemodynamics 2ndyears

BP too high:BP too high:

• Weakening of arterial walls - AneurysmWeakening of arterial walls - Aneurysm

Risk of rupture & hemorrhageRisk of rupture & hemorrhage

Cerebral hemorrhage: ?Cerebral hemorrhage: ?

Rupture of major artery: Rupture of major artery:

Page 22: 3 Hemodynamics 2ndyears

Auscultation of brachial artery with stethoscope

Laminar flow vs. turbulent flow

BP estimated by SphygmomanometryBP estimated by Sphygmomanometry

Page 23: 3 Hemodynamics 2ndyears

Principles ofPrinciples of SphygmomanometrySphygmomanometry

Cuff inflated until brachial artery compressed and blood flow stopped what kind of sound?what kind of sound?

Page 24: 3 Hemodynamics 2ndyears

turbulent flow

Slowly release pressure in cuff:

Page 25: 3 Hemodynamics 2ndyears

Pressure at which . . .

. . . sound (= blood flow) first heard:

. . . sound disappeared:

Page 26: 3 Hemodynamics 2ndyears

• Pressure can be stated in terms of column of fluid.

Pressure Units

mm Hg cm H2O PSI ATM

50 68 0.9 0.065

100 136 1.9 0.13

200 272 3.8 0.26

300 408 5.7 0.39

400 544 7.6 0.52

Page 27: 3 Hemodynamics 2ndyears

Pressure = Height x Density

or P = gh

If Right Atrial pressure = 1 cm H2O in an open column of

blood

Pressure in feet = 140 cm H2O

Rupture

Venous Valves

Density of blood= 1.035 that of water

Incompetent venous valves Varicosities

Actual Pressure in foot= 4-5 cm H2O

Page 28: 3 Hemodynamics 2ndyears

Pressures in the circulation

• Pressures in the arteries, veins and heart chambers are the result of the pumping action of the heart

• The right and left ventricles have similar waveforms but different pressures

• The right and left atria also have similar waveforms with pressures that are similar but not identical

Page 29: 3 Hemodynamics 2ndyears

1. The LV pressure begins to rise after the QRS wave of the ECG

2. Pressure rises until the LV pressure exceeds the aortic pressure

The blood begins to move from the ventricle to the aorta

3. As blood enters the aorta, the aortic pressure begins to rise to form the systolic pulse

4. As the LV pressure falls in late systole the aortic pressure falls until the LV pressure is below the aortic diastolic press.

5. Then the aortic valve closes and LV pressure falls to LA pressure

Page 30: 3 Hemodynamics 2ndyears

•The first wave of atrial pressure (the A wave) is due to atrial contraction•The second wave of atrial pressure (the V wave) is due to ventricular contraction

Page 31: 3 Hemodynamics 2ndyears

Normal Pressures

• RV and pulmonary systolic pressure are 12-15 mm Hg

• Pulmonary diastolic pressure is 6-10 mm Hg• LA pressure is difficult to measure because access

to the LA is not direct

Page 32: 3 Hemodynamics 2ndyears

• The severity of AS is determined by the pressure drop across the aortic valve or by the aortic valve area

• The high velocity of blood flow through the narrowed valve causes turbulence and a characteristic murmur AS can be diagnosed with a stethoscope

AS produces a pressure gradient between the aorta and LV

i.e. For blood to move rapidly through a narrowed aortic valve orifice, the pressure must be higher in the ventricle

Page 33: 3 Hemodynamics 2ndyears

Pressure Measurement

• Accurate pressure measurements are essential to understanding the status of the circulation

• In 1733 Steven Hales connected a long glass tube directly to the left femoral artery of a horse and measured the height of a column of blood (8 feet, 3 inches) to determine mean BP

• Direct pressure measurements are made frequently in the cardiac catheterization laboratory, the ICU and the OR

Page 34: 3 Hemodynamics 2ndyears

• A tube is inserted into an artery and connected to an electrical strain gauge that converts pressure into force that is sensed electrically

• The output of the transducer is an electrical signal that is amplified and recorded on a strip chart

• For correct pressure measurements the cannula and transducer must be free of air, the cannula should be stiff and short

Page 35: 3 Hemodynamics 2ndyears

Cardiac Output (CO)Measurement

• The measurement of blood flow through the circulation is usually done clinically using either the Fick method

• The Fick method states that the cardiac output is equal to the oxygen consumption divided by the arterial-venous oxygen difference

CO = Oxygen consumption / A-V O2

Page 36: 3 Hemodynamics 2ndyears

• The measurement is done by determining the oxygen consumption using respiratory gas measurements and the O2 content of arterial and mixed venous blood

• The mixed venous blood sample is obtained from a PA with a catheter

• The arterial sample can be drawn from any artery