3 - Haemodynamics Flashcards
What is the difference between plasma and serum?
Serum is plasma without the clotting factors
What is polycythaemia?
Excess red blood cells leading to increased blood viscosity
What is thrombocythaemia?
Excess platelets leading to increased blood viscosity
What is leukaemia?
A cancer which starts in blood-forming tissue, usually the bone marrow. It leads to the over-production of abnormal white blood cells
Whole blood viscosity changes are uncommon (e.g. polycythaemia), minor changes to viscosity of the plasma are more typical. What plasma proteins typically change?
- Fibrinogen
- Compliment
- C-reactive protein (CRP)
What vessel has the largest diameter lumen?
Vena cava
What vessel has the highest thickness wall?
Aorta
What type of liquid flow is found in the majority of blood vessels? Describe this type of flow?
Laminar flow
Smooth, fast flow (fastest in the centre due to more resistance around the edges of the vessel). Most energy efficient.
What causes turbulent flow?
An obstruction/constriction in the vessel, leading to disorganised flow after the obstruction. Energy is lost.
E.g. stenosed arteries, changing direction of vessels (branching)
In laminar flow, flow is …….. ……………. to perfusion pressure.
Directly proportional
The point at which laminar flow becomes turbulent flow as pressure increases is called the critical ………….. number.
Reynolds
What is the SI unit of pressure?
Pascal
What is conductance?
Measure of the ease of flow
What is resistance?
Measure of the difficulty of flow, reciprocal of conductance.
What is the relationship between flow, pressure and resistance (Darcy’s Law)?
Flow = ΔP / R
ΔP = pressure gradient
When blood supply to an organ needs to be changed how is flow altered?
- By changing the vascular resistance.
- Blood pressure does not change
What factors affect vascular resistance?
Which is most important physiologically?
- Diameter of vessel
- Length of vessel
- Viscosity of blood
Vessel length and viscosity don’t change so diameter is the most important.
The radius of a vessel has a large impact on flow. Flow is proportional to radius to what power?
4
Flow α r^4
In which artery is resistance the lowest?
The aorta - large diameter and relatively short
Which vessels contribute the most to total peripheral resistance?
The arterioles
- Play the biggest role in resistance of the systemic circulation
- Biggest drop in pressure
Resistance in the pulmonary circulation is ………. than in the systemic system. Why is this?
Lower - due to shorter and wider vessels
How is flow related to the velocity of the blood in the vessel?
F = V x A
- A is the cross-sectional area of the vessel
- In constant flow, V is inversely proportional to r^2
Velocity of blood flow depends on the total ………………… ……….
Cross-sectional area
In what type of vessel is blood flow the slowest?
The capillaries
- Very large cross-sectional area
- Velocity is reduced and increases again as they merge into veins
What is the pulse pressure?
Systolic BP - diastolic BP
How is mean arterial pressure calculated?
Mean arterial pressure = diastolic BP - (pulse pressure / 3)
- Time-weighted mean
How is mean arterial pressure related to cardiac output and total peripheral resistance?
MAP = CO x TPR
How is cardiac output calculated?
Heart rate x Stroke volume
What factors affect the pulse pressure?
- Volume of blood ejected (stroke volume)
- Compliance (stretch) of the arterial system
During exercise, what changes to increase the pulse pressure?
Stroke volume increases
What is the effect on pulse pressure of:
a) Haemorrhage?
b) Age?
a) blood volume loss = decreased PP
b) atherosclerosis reduces compliance of vessels - less stretch to account for the pressure change = increase PP
What is the pulse?
The shock wave that arrives slightly before the blood in a vessel
An increased pulse pressure is described as having a …………… pulse
Bounding
What can cause a bounding pulse?
- Heart block (reduced electrical transmission between atria and ventricles) - bradycardia
- Vasodilation - decreases peripheral resistance (occurs in pregnancy)
- Elite athletes - systolic BP increases and diastolic BP decreases (large PP)
In pathological turbulent flow, what is the effect on:
a) velocity?
b) flow?
a) Velocity increases
b) Flow decreases
In terms of turbulent flow is vessels, what is:
a) Thrill?
b) Bruit?
Thrill - the feeling of turbulent flow
Bruit - the sound in the vessel of turbulent flow
When measuring blood pressure, turbulent flow is created intentionally by compressing a vessel. What type of sounds can be heard?
Korotkoff sounds
What is the name for a blood pressure cuff?
Sphygmomanometer
Which artery is used to auscultate for blood pressure?
Brachial artery
If the blood pressure cuff is too small, what will happen to the estimate of blood pressure?
Will overestimate the blood pressure (too high)
If the blood pressure cuff is too big, what will happen to the estimate of blood pressure?
Will underestimate the blood pressure (too low)
How should a patient be positioned for blood pressure measurement?
- Taken at rest
- Sat comfortably upright, legs uncrossed and feet flat on the floor
- Arm supported
- Measurement taken at level of the heart
What effect does gravity have on blood pressure?
- Pressure below the level of the heart is greater than above
- Gravity maintains a pressure gradient that allows blood to flow from the heart to the feet
- Pooling of blood occurs in the venous system when standing
What is postural hypotension?
- Dizziness upon standing due to transient arterial hypotension
- When standing there is a delay in constriction of resistance vessels in the lower body, blood pools in the lower limbs
- Less blood returns to the heart causing a transient reduction in cardiac output (Starling’s Law)
- Less blood is pumped to the brain (dizziness, nausea, fainting)
