S1) Haemodynamics Flashcards
What is haemodynamics?
Haemodynamics is the study of how pressure affects blood flow in blood vessels
Define infarction
Infarction is tissue death due to inadequate blood supply
Distinguish between the blood flow to different tissues of the body:
- Brain
- Kidneys
- Heart
- Skeletal muscle
- Gut
- Brain needs high, constant flow
- Kidneys need high, constant flow
- Heart muscle needs high flow which can vary
- Blood flow to skeletal muscle increases during exercise
- Blood flow to gut increases after a meal
What is perfusion rate?
Perfusion rate is the rate of blood flow (l.min-1)
Increases in metabolism are met by increases in blood flow.
Compare and contrast the perfusion rate at rest and during exercise
- At rest - total blood flow is about 5 l.min-1
- During exercise - total blood flow can rise to 25 l.min-1
State the factors that affect the rate of diffusion
- Area available for exchange
- Diffusion resistance
- Concentration gradient
Describe what determines the area available for exchange in diffusion
- Area available for exchange between capillaries and tissues depends on capillary density
- A tissue which is more metabolically active will have more capillaries & a higher capillary density
Identify the 3 factors which affect diffusion resistance
- Nature of the molecule
- The barrier
- Distance
Describe what determines the concentration gradient in diffusion
The perfusion rate determines the concentration gradient driving O2 diffusion into the cells
What is pericardial effusion?
Pericardial effusion is when excess fluid accumulates in the pericardial cavity, compressing the heart due to the inextensible fibrous pericardial layer
What is the danger associated with pericardial effusion?
Compression of the heart can lead to cardiac tamponade as the heart cannot fill during diastole
How can excess fluid be removed from the pericardial cavity?
Through a procedure called pericardiocentesis, excess fluid is removed for testing / to relieve compression
What is coronary circulation?
Coronary circulation is the circulation of blood in the blood vessels of the heart muscle (myocardium)
What are coronary arteries?
Coronary arteries are the vessels which deliver oxygen-rich blood to the myocardium
What are cardiac veins?
Cardiac veins are the vessels that remove the deoxygenated blood from the myocardium
Describe the general origins and location of the left and right coronary arteries and their branches
- Origins: base of the aorta from openings (coronary ostia) located behind the aortic valve leaflets
- Location: lie on the surface of the heart
State the specific origins of the left and right coronary arteries
- Right coronary artery rises in the right aortic sinus
- Left coronary artery rises in the left aortic sinus
What is the problem associated with coronary arteries?
Coronary arteries are vital to supply well oxygenated blood to the myocardium however, they are prone to atheroma wherein a thrombus forms and can block the artery
Which artery is commonly blocked in an AMI and which regions does it supply?
- Left anterior descending artery (LAD)
- Supplies the apex of the heart, the septum and the left ventricle and a bit of right ventricle
Discuss the relationship between pathology in the aortic and mitral valves
- The aortic and mitral valves are closely associated
- Hence, if a disease affects one it will likely affect the other
What is serum?
Serum is plasma minus the clotting factors
What is the main clotting factor in the body?
The main clotting factor is fibrinogen
What are the contents of buffy coat?
Buffy coat contains white blood cells and a few platelets
Differentiate between the different types of fluid collected from blood
- The fluid collected from unclotted blood = plasma
- The fluid collected from clotted blood = serum
Identify 4 factors which increase whole blood viscosity
- Increase in plasma viscosity
- Polycythaemia: increase in red blood cells
- Leukaemia: increase in white blood cells
- Thrombocythaemia: increase in platelets
What is the effect of increases in whole blood viscosity?
Increased whole blood viscosity leads to sludging in the peripheries
Identify the commonest cause for increases in plasma viscosity leading to increased whole blood viscosity
Multiple myeloma
In terms of plasma viscosity, how can one attempt to measure inflammation?
- Results from raised levels of acute phase plasma proteins e.g. fibrinogen, complement factors and CRP which increase in response to inflammation
- Hence, minor changes in plasma viscosity can be used to ‘measure’ the inflammatory response
Explain the difference between flow and velocity of blood
- Velocity is the distance blood has moved per unit of time (cm/sec)
- Flow is the volume of blood that is moving per unit of time (l/min)
Explain the difference between laminar and turbulent flow
- Laminar flow: blood usually flows in streamlines with each layer of blood remaining the same distance from the wall
- Turbulent flow: blood flows in all directions in the vessel and continually mixing within the vessel
Identify 5 situations wherein turbulent blood flow could happen
- When the perfusion rate becomes too great
- When the blood passes by an obstruction in a vessel
- When the blood makes a sharp turn
- When the blood passes over a rough surface
- Where there’s increased resistance to blood flow
What is peripheral resistance?
Peripheral resistance is the totality of the resistance being posed to the blood pumped from the heart
What is the impact of low peripheral resistance?
Low peripheral resistance lowers diastolic pressure and therefore increases pulse pressure due to the vasolidation of arterioles e.g. hot bath, exercise, pregnancy
What is the impact of high peripheral resistance?
High peripheral resistance raises diastolic pressure and therefore decreases pulse pressure due to the vasoconstriction of arterioles e.g. cold, thirsty
What is a pulse?
A pulse is a rhythmical throbbing of the arteries as blood is propelled through them, typically as felt in the wrists or neck
Differentiate between the terminology for weak and strong pulses
- A weak pulse is often described as “thready”
- A strong pulse is often described as “bounding”
Which 2 factors determine the strength (volume) of a pulse?
- The force with which the left ventricle is able to eject blood into the arterial system and thus develop a normal shock wave
- The pulse pressure
Identify conditions which lead to a stronger/weaker pulse
- Weaker pulses can result from left ventricular failure, aortic valve stenosis, hypovolaemia (severe dehydration, bleeding)
- Stronger pulses can result from bradycardia seen in conditions such as heart block
Explain what Phase I and Phase 5 are when measuring blood pressure
- Phase 1 – the point at which the first sound appears
- Phase 5 – the point at which the sounds disappear
What is pulse pressure?
Pulse pressure is peak systolic pressure – end diastolic pressure
120mm Hg – 80 mm Hg = 40mm Hg
Describe the impact of pulse pressure on the volume of the pulse
The greater the pulse pressure the stronger the pulse
Define mean arterial pressure
- Mean arterial pressure is estimated as diastolic pressure + 1/3 of the pulse pressure
- Therefore, most commonly, mean arterial pressure is 80 mmHg + 13 mmHg = 93 mm Hg
