Haemodynamics Flashcards
What is haemodynamics?
The physical factors that control blood flow
What dictates the delivery of blood to different organs?
The metabolic demands of the organs
What determines the way that blood moves?
The pressure gradient
(High pressure to low pressure)
Flows as a fluid from a high pressure to a low pressure
What is the composition of blood?
Red blood cells
White blood cells
Plasma
What is serum?
Plasma with no clotting factors (no platelets …)
What is the affect of heparin on the blood?
Makes it unable to clot
How can the whole blood viscosity change?
How does this affect the blood?
Changes in number of blood cells:
Polycythaemia (more RBCs/higher Haematocrit)
Thrombocythaemia (more platelets)
Leukaemia (more WBCs)
Thicker sludge blood - gangrene in peripheries
How can plasma viscosity change?
Plasma protein composition can change
-fibrinogen
-c reactive proteins
What is C-reactive protein used to measure?
Inflammation
High usually indicates bacterial infection
What is the FLOW of blood?
Volume of blood transferred per unit time
Ml/min or L/min
What is pressure and what is blood pressure measured in?
Force per unit area exerted by the blood
(mmHg) mm of mercury
What is cardiac output? (Equation)
CO = stroke volume x heart rate
What is stroke volume?
Volume of blood squeezed out of the left ventricle every cardiac cycle
What factors influence FLOW of blood?
Conductance (ease of flow/resistance)
Pressure gradient/difference
What equation can relate flow to conductance and pressure difference?
Flow = conductance x pressure difference
What is vascular resistance?
Resistance to blood flow in blood vessels
How are resistance and flow related?
Inversely proportional
As resistance increases flow decreases
What factor is normally changed if flow needs to be increased to an area?
Resistance decreased
What are the 2 types of blood flow?
Laminar flow (smooth/silent and maintains energy, travels in stream lines)
Turbulent flow (disorganised, noisy energy lost)
What is a stenosis?
Abnormal discrete narrowing of an artery or open area of a heart valve
What point does laminar flow become turbulent?
When flow can not increase proportionally to match the increased pressure in the blood vessel
What is the point called which pressure increases beyond which flow can match it linearly so flow becomes turbulent?
Critical Reynolds number
What is the main factor which affects resistance to blood flow?
Blood vessel diameter
(Vessel length doesn’t usually change and viscosity is very tightly regulated)
What does a drop in pressure indicate in terms of resistance to flow?
Changed
Why does the aorta have a low resistance?
Large diameter
Short
Which blood vessel type has the biggest affect of total peripheral resistance?
Arterioles
What is velocity?
Distance fluid (blood moves in a given time
The capillaries have a very large cross sectional area, this slows blood flow down, why is this useful?
Allows time for nutrients and waste to be exchanged between blood and tissues
Does increasing vessel diameter increase or decrease blood velocity?
Why does this happen?
Increases
Inc vessel diameter = less resistance (less blood touching vessel wall/less friction) = more blood flow at higher speed
What is diastole?
When heart is relaxed and filling up with blood
What is systole?
When heart contracts squeezing out blood
What is pulse pressure?
Difference between peak systolic pressure and end diastolic pressure
What is considered a normal blood pressure?
120/80 mmHg or below
(90/60 - 120/80 mmHg)
What is the Dicrotic notch on a blood pressure time graph?
The point which pressure starts to increase when the atrioventricular valves close
What are the 2 equations for Mean Arterial pressure?
MAP = Diastolic blood pressure + 1/3(Pulse pressure)
MAP = Diastolic blood pressure + 1/3(Systolic pressure - Diastolic pressure)
OR
MAP = Cardiac output x total peripheral resistance
What determines pulse pressure?
Volume of blood ejected (SV)
Compliance of the blood vessels
How does haemorrhaging affect pulse pressure?
Decreases it
Less blood volume ejected
How can age affect pulse pressure, what condition of the vessels usually occurs with age?
How does this affect pulse pressure?
Atherosclerosis reduces vessel compliance
Increased pulse pressure as vessel compliance reduces
What is the pulse?
The shock wave that arrives before the blood
What does a strong and weak pulse indicate (in terms of stroke volume)?
Strong = high stroke volume
Weak = low stroke volume
What happens to the velocity of blood in a stenosis?
Initially it decreases since the resistance of the vessel increases since its become narrower
So the heart pumps harder increasing stroke volume to increase the velocity to maintain the cardiac output
What can be heard from a stenosed vessel?
Bruit
What can be felt from a stenosed vessel?
A thrill
Why can a thrill be felt and a bruit be heard from a stenosed vessel?
Laminar flow changed to turbulent flow by narrowing of the blood vessel
How is blood pressure measured?
Using a pressure cuff
What artery is targeted and squeezed by the pressure cuff?
Brachial artery
Describe how a pressure cuff is used to measure blood pressure:
Pressure of cuff increased restricting blood flow through the brachial artery occluding it
Pressure is then slowly reduced
blood flow is changed from laminar to turbulent flow causing sounds to be heard called Korotokoff sounds
First point at which Korotokoff sounds can be heard is the systolic blood pressure
Once the blood flow goes from turbulent to laminar/silent this is the diastolic blood pressure
What are Korotokoff sounds?
The tapping noises created by converting laminar flow into turbulent flow
How is systolic pressure determined using a pressure cuff?
When the Korotokoff sounds are first heard (tapping noises)
How is diastolic pressure determined using a pressure cuff?
Pressure at which the Korotokoff sounds stop being heard
(Turbulent flow is now laminar/silent)
What is the role of gravity in blood pressure?
Maintains a pressure gradient allowing blood to flow from heart to the feet
Is blood pressure above the heart greater than below the heart?
Blood pressure above the heart is less than below it
What is postural hypotension?
When blood pools in your feet/ venous system below your heart as you are sitting down
Reduces blood flow to head when you stand up (may faint)
What is postural hypotension?
When blood pools in your feet/ venous system below your heart as you are sitting down
Reduces blood flow to head when you stand up (may faint)
What is the average cardiac output for the average 70kg male?
5 L/min
