CVS 128 Chronic Stable Angina Flashcards
What is Angina?
Chest pain provoked by physical exertion, reversible ischaemia brought on my increased work load - subsides with rest
Why does angina occur?
Due to increased oxygen demand of the myocardium which exceeds the supply
How do you classify angina?
Stable - Class 1: predictable brought on by strenuous or protracted exercise
Class 2: slight limitation
Class 3: marked limitation
Unstable: unpredictable and should be treated as Acute Coronary Syndrome (ACS)
With chest pain, what a more localised pain indicate?
That the origin was pleuritic or to do with the chest wall? Ischaemic chest pain is diffuse
What are some causes of “chest pain” that may originate from below the diaphragm?
Acute cholecystitis radiating to right shoulder
Crushing pain through to bank think thoracic aorta
Why is cocaine and nicotine a risk factor for ischaemic heart disease?
They cause coronary artery spasm
How can you treat angina?
Treat and manage underlying disease/lifestyle GTN spray Beta blockers Calcium channel blockers Statins
What is GTN?
glycerol trinitrate - fast acting vasodilator
Why are beta blockers used to treat angina?
They reduce heart rate and contractility reducing work load
What do calcium channel blockers cause?
Vasodilation
What do statins do?
Inhibit cholesterol synthesis and encourage LDL uptake by the liver
Inhibit thrombosis - aspirin, clopidogrel
What is Darcy’s Law?
Perfusion = pressure difference/ resistance
can only be applied to laminar flow
What is Pouseille’s Law?
takes into account the resistance of a vessel
8 x viscosity x length / pi x radius^4
What is resistance due to in blood vessels? Describe the fluid flow?
Friction between fluid layers moving at different speeds
No slip condition: outermost layer doesn’t move as it is in contact with the epithelium
Fluid layers is arranged in concentric layers from Slow –> Fast
Where is viscosity of blood smallest? Why?
In the smallest vessels - due to axial streaming and bolus flow - the Fahraeus Lindqvist effect
What is axial streaming in the blood stream?
Where RBC’s migrate to the centre of the lumen leaving a cell free zone near the wall where friction is the greatest - which acts as a lubricant layer
RBC’s move through the microcirculation faster than the plasma therefore the haematocrit is lower here and blood has decreased viscosity
What is bolus flow in the blood stream?
Where the RBC diameter takes up the whole capilliary therefore “sweeps along” the plasma - so there is no slow moving plasma at the edge of vessels
Why is viscosity of blood lower at high flow rates?
RBC aggregation and shear thinning. When shear forces are low (low flow) the RBC’s aggregate in rouleaux (increased viscosity) whereas in high shear these are thinner to allow free flow and movement of RBC’s
What can a higher RBC count cause?
hypertension and heart failure
What are the 3 ways of measuring blood flow?
Tissue clearance
Plethysmography and Ficks principle
How do you measure tissue clearance?
Radioactive substance is injected into tissue and the time taken for the radioactivity to decline due to seepage into bloodstream is measured
How do you measure blood flow using plethysmography?
Measures blood flow through a limb - pressure cuff used to occlude venous drainage only and initial swelling in limb is measured
How do you measure blood flow using Fick’s Principle?
Measures blood flow through an organ - consituents of blood before and after passing through an organ are measured and compared to normal rates of increase/depletion of constituent organ
Why is autoregulation important for the control of distribution of blood flow?
As it is necessary in organs that require a near constant flow e.g. brain and kidneys - used to stabilise against BP changes
How does “active hyperaemia” control the distribution of blood flow?
It regulates local blood flow by how hard they’re working - the metabolic rate
It adjusts perfusion to demand and is controlled both intrinsically and extrinsically due to control of resistance vessels
Where is resistance most in what arteries?
systemic arterioles - small change in diameter is a huge change in resistance and therefore BP
What controls arteriole diameter?
Vascular smooth muscle contraction in response to various extrinsic and intrinsic factors
e.g. K+, CO2 and adenosine from respiration or NO from endothelium =vasodilation
What is NO released in response to ? and why?
Shear forces in the endothelium increase NO secretion to dilate organs upstream with a metabolic need
When are PG’s, histamine and bradykinin released and what is their function?
Released in response to damaged or inflamed tissue - act as vasodilators
What are the extrinsic neuronal and hormone regulators of distribution of blood flow?
Vasomotor nerves (NA and AcH) and adrenalin and the RAAS system
