Intro and haemodynamics Flashcards
What is infarction?
Death of cells
Capillaries are the sight of diffusion, what do they consist of?
A single layer of endothelial cells surrounded by basal lamina.
Name 3 factors which affect diffusion
- Area available for exchange - depends on capillary density.
- Diffusion resistance - nature of molecule, barrier, path length.
- Concentration gradient - depends on rate of use by tissues and rate of blood flow through capillary bed.
What is capillary density?
Amount of capillaries in a tissue - higher capillary density at more metabolically active tissues.
How does blood flow affect the concentration gradient?
Substances used by tissues have higher concentrations in arteries than capillaries. The lower the blood flow, lower capillary concentration. Blood flow has to be high enough to maintain a concentration gradient to drive oxygen diffusion into cells.
What is perfusion rate?
Rate of blood flow.
What type of blood flow is needed for: the brain, the heart, the kidneys and skeletal muscle and the gut.
The brain needs a constant high flow.
The heart needs a high flow which increases during exercise.
The kidneys need a high, constant flow.
The skeletal muscles can have a very high flow during exercise and the gut blood flow is highest just after a meal.
What is the average cardiac output for a 70kg man?
5L/min at rest and can rise up to 25L/min during exercise.
Where does the heart lie?
Between the 2nd and 5th intercostal spaces, behind the sternum in the pericardial sac situated in the media stinum (between lungs). The apex lines up with the left midclavicle line.
What are the layers of the pericardial sac?
3 layers: outer fibrous layer attached to the first serous membrane of the parietal layer, then there’s the pericardial cavity containing a thin fluid for lubrication and then the visceral serous membrane (pericardium) which is attached to the myocardium.
What is cardiac tamponade and what may need to be done in response to it?
If excess fluid builds up rapidly in the pericardial cavity, the heart is suppressed due to the inextensible fibrous layer of the pericardial sac. The heart won’t be able to relax and refill during diastole - medical emergency. Fluid may need to be removed to relieve pressure or for testing - pericardiocentesis.
Where is the transverse pericardial sinus and what’s it’s use clinically? (Also, what’s the oblique sinus?)
The transverse pericardial sinus is the space behind the aorta and pulmonary trunk which is clamped when there’s a bypass machinery in use. (The oblique sinus is a dead end near the pulmonary veins at the posterior surface of the heart.)
List 3 features of coronary arteries.
They’re end arteries, prone to a thermos and vital to supply well oxygenated blood to myocardium.
Picture the heart and some of the coronary arteries and cardiac veins.
Check picture on images. Left and right coronary arteries, marginal arteries and circumflex branch round at the back. Anterior interventricular artery aka left anterior descending artery (widow maker). Posterior interventricular comes from right. Veins: anteriorly - small cardiac vein on left and great cardiac vein on right, posteriorly - all feed into coronary sinus, which drains into right atrium, as do the inferior and superior vena cava.
What’s the difference between plasma and serum?
Serum is fluid collected from clotted blood, so serum = plasma - clotting factors (particularly fibrinogen).
What is peripheral resistance?
Resistance of arteries to blood flow/totality of opposition to pumping heart.
A marked increase in plasma viscosity can lead to an increase in whole blood viscosity and sludging at the peripheries (blood is more viscous when cool), what is the commonest cause?
Multiple myeloma - cancer of the bone marrow.
What do the following terms mean and what can they all lead to? Polycythaemia, thrombocythaemia and leukaemia.
Polycythaemia is an increased number of red blood cells, thrombocythaemia is the same for platelets and leukaemia is the same for white blood cells. All three can lead to an increase in whole blood viscosity and sludging in the peripheries.
Recently, C-reactive protein has been used as a measure for inflammation, why?
CRP is an acute phase proteins which increase in the blood in response to inflammation, producing a minor change in blood viscosity.
Why does blood move from an area of high pressure to an area of low pressure.
It is a mixture of cells and plasma and considered a fluid.
What is laminar flow of blood?
Blood flowing in stream lines with each layer remaining the same distance from the vessel walls. Blood in the centre has the highest velocity.
Turbulent flow sees blood flowing in all directions and constantly mixing in a vessel, what 5 situations might cause it?
The rate of blood flow may be too great. Blood may pass through an obstructed vessel. It may make a sharp turn. It may pass over a rough surface. There may be an increased resistance to blood flow.
What’s the difference between velocity and flow?
Velocity is the distance an object moves over time and is measured in distance/time, whereas flow is volume of liquid/gas moving over time and is measure in volume/time.
What effect may stenosis have on flow?
Increase pressure (PSI - pounds per square inch) and so decrease flow, may lead to critical ischaemia.
What’s the difference between a stenosis and an occlusion?
A stenosis is a narrowing whereas an occlusion is a blockage.
How may a stenosis be noticed?
An abnormal sound through a stethoscope/murmur - bruit.
Thrill - buzz that you feel.
In a pressure time graph of the descending aorta, what is the area under the curve and what can you tell from it? How else is it estimated? (MAP)
MAP - mean arterial pressure, estimated as diastolic pressure + 1/3 pulse pressure, so commonly 93mmHg. If it falls below 70mmHg, organ perfusion impaired.
What are the anacrotic and dicrotic limbs on a graph?when does the dicrotic notch occur.
The anacrotic limb is the upstroke and the dicrotic limb is the line going down. The dicrotic notch occurs when the aortic valve shuts, at the end of systole.
What is pulse pressure?
Peak systolic pressure - end diastolic pressure. Most commonly 120-80= 40mmHg. Determines how strong a pulse is.
What is retrograde flow in arteries?
Blood moves backwards - greatest when peripheral resistance is high.
What determines strength of pulse?
Force with with left ventricle pumps out blood into arterial system, creating shock wave.
How is a weak pulse referred to and what can cause it?
A weak pulse is known as ‘thready’ and can occur if there is left ventricle failure, stenosis in the aorta or hypovolaemia (dehydration, blood loss).
What is a strong pulse known as and what may cause it?
A strong pulse is ‘bounding’ and may be caused by bradycardia which widens pulse pressure by lowering diastolic pressure, as does low peripheral resistance e.g. from pregnancy, exercise or a hot bath.
Explain Karotkoff sound phase 1.
External pressure>systolic pressure, so no flow and there is silence. Pulse obliteration.
Explain what happens when diastolic pressure
There is partial flow and a sound is heard.
Explain what happens at Karotkoff sound phase 5.
Sound disappears indicating that external pressure
What can cause a falsely high BP reading?
The cuff being too small - it must cover at least 80% of the arm.
What innervates the pericardium?
The phrenic nerve (on the way down to the diaphragm).
