Haemodynamics

Questão	Responda
Haemodynamics is the relationship between ________ _______, ______ ___________ and ___________ to _______.	Blood flow, Blood pressure, Resistance to flow
What does it depend on? (7)	1. Flow 2. Resistance 3. Velocity of blood 4. Force of ejection 5. Work of isovolumetric contraction and ejection 6. Pressure difference between arteries and veins 7. Compliance of arteries
What is blood flow?	The volume of blood flowing in a given time
What is perfusion?	The blood flow per mass of tissue
How do you calculate the blood velocity?	Velocity = blood flow/cross-sectional area of vessel
How does this affect the cardiovascular system?	As the vessel branch more and more (arteries to arterioles to capillaries), the area through which blood can flow INCREASES, meaning velocity DECREASES.
What is Darcy's Law of flow?	Flow (Q) = change in pressure/resistance
What does this mean?	As pressure increases, flow also increases
What are 3 types of blood flow?	1. Laminar 2. Turbulent 3. Bolus
What is laminar blood flow and where does it occur?	Occurs in most arteries, arterioles, venules and veins. Blood travels in a straight line, with that closest to the wall moving the slowest, allowing interaction with the vessel wall, and blood in the centre of the vessel to move quickest (constituents of blood are here e.g. RBCs).
What is turbulent flow and where does it occur?	Occurs in the ventricles of the heart, the aorta and around any atheromas. Blood flow is disrupted and is therefore not travelling in a straight line - can be heard through a stethoscope as it is noisy.
What is bolus flow and where does it occur?	Occurs in the capillaries. RBCs travel through vessel in single file, with columns of plasma in between. There is little friction here so resistance is low.
Which type of blood flow does Darcy's Law relate to?	Laminar
Darcy's Law only applies up to a certain point. What is it and what happens above this point?	Reynold's Number (Re). After this, flow is turbulent.
Name 4 determinants of blood pressure?	1. CO 2. Viscosity of blood (haematocrit) 3. TPR 4. Elasticity of large arteries
How is pulse pressure calculated? What is the average value?	pulse pressure = systolic BP - diastolic BP. Usually approx 40mmHg
What do changes in pulse pressure indicate?	Changes in stroke volume or compliance
How are these all connected?	Pulse pressure = SV/compliance
How can compliance be calculated?	Compliance = change in volume / change in pressure
If the volume increases to very high levels, what happens to the pressure?	It increases very rapidly, as arteries reach their 'stretch' limit.
When does this become a problem?	As we get older, arteries become harder and less compliant (arteriosclerosis), so cannot stretch in response to high volumes.
How is the mean BP calculated?	Mean BP = diastolic pressure + 1/3 pulse pressure
What is this equivalent to?	BP = CO x TPR
Name 9 factors that influence mean BP	1. Age 2. Presence of disease 3. Posture 4. Distance along arterial tree 5. Blood volume 6. Sexual activity 7. Wake/Sleep 8. Exercise 9. Emotions
What are 2 key characteristics of veins?	1. Collapsible 2. Contractile
What drives veins to return blood to the heart?	Pressure gradient - pressure in veins is higher than in the right atrium.
What is the thoracic pump?	It forces blood back up to the heart during inhalation. This is because during inhalation, the abdominal cavity gets smaller and so pressure increases and thus blood is forced back to the heart.
What is the skeletal muscle pump?	Muscles in the legs 'squeeze' veins as they contract which promotes venous return.
How do valves help?	Valves prevent retrograde flow of blood, and therefore lower capillary pressure in the feet and ankles. This helps less filtration to occur there and therefore less swelling.
Which 3 factors control vascular resistance?	1. Poiseuille's Law 2. Viscosity 3. Pressure-Flow curves
What is Poiseuille's Law?	An equation for blood flow which incorporates parameters which control resistance.
What is the key part of Poiseuille's Law, and what does it mean?	r^4. This means that a small change in the radius will causes a big change in the resistance.
What are the other parameters involved in Poiseuille's Law? (3)	1. Viscosity 2. Length of vessel 3. Pressure difference
Where is the main site of resistance and why?	Arterioles because their smooth muscle is tightly controlled by innervation from the sympathetic NS.
What is viscosity a measure of?	The internal friction on a vessel
What does it depend on? (4)	1. Velocity of blood 2. Haematocrit 3. Deformability of RBCs 4. Diameter of vessel
What are the extrinsic factors which can alter vascular tone to divert blood to/away from certai organs as it is needed? (2)	1. Neural control 2. Hormones (endocrine)
What are the intrinsic factors? (4)	1. Metabolites 2. Hormones (autocrine, paracrine) 3. Endothelial factors 4. Myogenic response
What is the myogenic response?	As arteries/arterioles fill, they distend, then constrict due to elastic recoil.
How does this help?	Maintains blood flow at any pressure, as the extent of distension of the vessel is proportional to the extent of constriction caused by elastic recoil. Therefore homeostasis is maintained.

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	Criado por Hannah Tribe mais de 10 anos atrás