6) Haemodynamics Flashcards
Heart
Sustains blood circulation
Can be modelled as a twin suction pump
Cardiac cycle has 3 main phases
- diastole (relaxation)
- systole (contraction)
- pause
Blood vessels - aorta
Walls of blood vessels are elastic
Blood enters through the aorta by portions - pulsation flow
Blood velocity in aorta is 0.5
Blood flow in aorta is turbulent
Blood vessels - artery
Blood velocity in arteries is lower than in aorta bc of larger cross section of arteries
Blood flow is laminar
- larger total cross section results in lower velocity
- stretching of walls is used to smooth down pulsation
Blood vessels
Capillaries and veins
Blood velocity in capillaries is reduced to about 0.5mm/s
In veins it increases to about 0.35m/s as total cross section is smaller
I’m capillaries and veins blood flow is laminar
Hydrodynamic novel of the cardiovascular system
DRAWING
Heart is the mechanical pump
The vessel with elastic walls is the aorta and the artery
The tube with the ridged walls is the capillary
Electrical model of the cardiovascular system
DRAWING
Heart -alternating voltage source
Diode- heart valve
Capacitor- vessel with elastic walls
Resistor- capillaries
Pulse wave
At systole the walls of the aorta and arteries are stretched and a mechanical stress wave propagates along the vessel = pulse wave
Velocity is usually 6-8 m/s
Blood pressure
The difference between the pressure of blood in the cardiovascular system and the atmospheric pressure
Depends on:
Function of heart
Where reading was taken
Atmospheric pressure
Blood pressure in blood vessels
DRAWJNG
Blood pressure in aorta and arteries
Pressure of blood is pulsating
Maximum pressure at systole is 16kpa
The minimum at diastole is 11Kpa
Blood pressure in vessels
P1-P2 = nv_0 X
n is heart rate
V_0 is stroke volume of the heart
X is the total hydraulic resistance of the circulatory system
Input pressure - output pressure
Blood pressure measurement
Blood pressure differs along the circulatory system
For comparability measure on the upper left arm brachial artery
It’s measured using:
Direct invasive methods
Indirect compensatory methods
Direct blood pressure measurement
A cannula is introduced into blood vessels
The cannula is connected to manometer
Not normally used on humans
Indirect blood pressure measurement
Pressure of blood in the artery he balanced by compensating pressure
External compensation pressure is measured by manometer
Work of the heart
Most of the work is done by contraction of the ventricles
Contracting left ventricle performs work for :
Overcoming the pressure of the blood
Overcoming hydraulic resistance
