3 - Haemodynamics Flashcards
Why does the viscosity of blood increase and what happens as a result of it?
- Major: Increased plasma proteins, e.g polycythaemia. Dry gangrene in the peripheries
- Minor: changes to amount of things like fibrinogen as result of inflammation. Can measure inflammation by viscosity of blood
How do you measure the level of inflammation?
Used to be done by viscosity of blood. Now measure amount of CRP
What is blood made up of?
It moves as a fluid but made up of cells and plasma
What is laminar and turbulent flow?
- Laminar flow is smooth, maintaing energy. Faster velocity in middle of vessel as friction at the edges. SILENT
- Turbulent flow is disorganised and energy is lost, pressure increase beyond what flow can match, e.g ventricles, branching vessels. NOISY
What is flow?
Volume transferred per unit time (L/min)
What is pressure?
Force per unit area (mmHg or Pa)
What is conductance (k) and resistance (r)
- Conductance is a measure of the ease of flow
- Resistance is a measure of the difficulty of flow (reciprocal of K)
If change in pressure is an indicator of a change in resistance, which areas of the CVS have the highest resistance?
- Arterioles give greatest peripheral resistance
- Resistance in systemic higher than in pulmonary circuit
What is velocity?
Distance per unit time that the blood moves (cm/s)
What is flow increased by?
Flow affected by diameter, length of vessel and viscosity
- Increase in pressure gradient
- Decrease in resistance
How much resistance does the aorta/arteries have?
- Very little, has large diameter and relatively short
- High compliance
What is the velocity of blood affected by?
- V is proportional to flow
- V is inversley proportion to r2
(therefore large surface area means slower velocity)
What does the blood pressure look like in the aorta over one cardiac cycle, draw a graph
What is pulse pressure and mean arterial pressure?
- PP = SBP - DBP
- MAP = DBP + 1/3 PP
If MAP <70mmHg organ perfusion is impaired, usually about 90/95
What factors is pulse pressure affected by?
- Compliance of arterial system
- Volume of blood ejected
e. g haemorraghe will decrease PP and age will increase PP as higher systolic
What is a pulse?
Shock wave of aortic expansion that travels down blood vessel and is amplified by tendons. Arrives slightly before the blood arrives
What happens when you increase pulse pressure and what causes this?
Bounding pulse
- Bradycardia
- Vasodilation as decreased TPR
- Elite athletes (systolic increase, diastolic decrease)
How can you work out mean arterial pressure?
MAP = DBP + 1/3 PP
or
MAP = CO X TPR
What is flow affected by the most?
- Diameter. Small changes in radius, big changes in flow as radius is to the power of 4
- Diameter also effects resistance the most
What is cushing’s reflex?
- Increased systolic BP
- Decreased HR
- Decreased respiratory rate
OCCURS DURING INCREASED INTRACRANIAL PRESSURE
What is cardiac output?
CO = SV X HR
How do you work of resistance?
Resistance is series is added, resistance in parallel
What happens to MAP when exercising?
Maintains, systolic increases and diastolic decreases as too high MAP would harm vessels. Therefore, TPR must be decreasing as CO is increasing
How do you measure blood pressure via auscultation?
- At level of heart, arm resting on table, legs uncrossed and flat on ground
- Sat down for 10-15 minutes before
- Several measurements of left and right, use the higher as reference. Take mean of two closest values
- Right size cuff
MEASURE SBP AT 1ST KOROTKOFF AND DBP WHEN NOISES DISAPPEAR
What effect does gravity have on blood pressure?
- Pressure below level of heart is greater and above is lower
- Pooling of blood in the venous system when you stand up
- Pooling decrease CO as less blood returned to heart so can lead to postural hypotension as lower SV.
Why does syncope occur when standing up?
Postural hypotension due to standing up so decreased SV, the heart goes into tachycardia to compensate for cardiac output so blood is not pumped to brain properly
Why can blood pressure be measured by ausculation?
Laminar to turbulent to laminar flow so silent to noisy to silent
What factors affect central venous pressure?
What mechanism ensures that the right and left side of the heart pump the same amount of blood per minute?
- The Frank-Starling mechanism matches venous return to cardiac output
- Increased cardiac output in one ventricle automatically increases the venous return to the other ventricle.
- The consequent increase in myocardial fibre length in this ventricle results in an increased output which would match the other side
