CVS Flashcards
What is the rate of diffusion limited by?
Area available for exchange Diffusion resistance - nature of barrier and molecules, path length Concentration gradient
What is capacitance?
Ability to cope with changes in cardiac output - a store of blood
Define flow
Volume of fluid passing a particular point per unit time Flow = volume/time (L/min-1)
Define velocity
The rate of movement of fluid particles along the tube Velocity = distance/time (m/min-1)
What is laminar flow?
Gradient of velocity from the middle to the edge of a vessel. Velocity is highest in the centre, fluid is stationary at edge
What is turbulent flow?
Velocity gradient breaks down due to increased mean velocity. Fluid tumbles over, increasing flow resistance
What is viscosity?
Extent to which fluid layers resist sliding over one another
What is the equation for resistance?
Resistance = Pressure/Flow
If flow is fixed, how does pressure change if resistance is increased?
Increase in pressure
If pressure is fixed, how does flow change if resistance is increased?
Decrease in flow
What is systolic pressure?
Maximum arterial pressure
What is systolic pressure affected by?
Heart contractility Total peripheral resistance Compliance of arteries
What is diastolic pressure?
Minimum arterial pressure
What is diastolic pressure affected by?
Systolic pressure Total peripheral resistance
What is pulse pressure?
Difference between systolic and diastolic pressure
What is equation to work our average arterial pressure?
= 2/3 diastolic pressure + 1/3 systolic pressure
Define total peripheral resistance
Sum of the resistance of all the peripheral vasculature in systemic circulation
What is the dicrotic notch?
Occurs when left ventricular pressure falls below aortic pressure and there is a subsequent backflow of blood closing aortic value
What is the dicrotic wave?
Occurs as the aortic valve closes causing a slight increase in pressure and blood recoils off valve
How do arteries act to reduce arterial pressure flucuations in systole and diastole?
They have distensible walls allowing them to stretch in systole so pressure does not change that much
How do arterioles act as resistance vessels?
Walls contain smooth muscle and state of contraction determines lumen diameter
What is vasomotor tone?
Smooth muscle does not actively relax so even under maximum flow there is always some vasoconstriction. This continuous contraction is vasomotor tone. Vasodilation is actually a reduction in vasconstriction
How do vasodilator metabolites modify vasomotor activity?
Metabolically active tissues produce vasodilator metabolites which cause relaxation of local smooth muscle.
State the vasodilator metabolites
H+ K+ Adenosine
What occurs in reactive hyperaemia?
When circulation is cut off from a organ or limb for a short period, the organ/limb continues metabolising so when blood flow is restored the local arterioles dilate maximally and flow is very high.
What is auto-regulation in relation to blood flow?
At most levels of metabolic activity most organs can automatically take the blood flow that they need, as long as arterial pressure is kept within certain range
Define central venous pressure
The pressure in the great veins supplying the heart
Define venous return
The rate of flow of blood back to the heart - limits cardiac output
Define pre-load
End diastolic stretch of myocardium. Determined by venous pressure
Define after-load
Force necessary to expel blood into arteries. Determined by systemic vascular resistance and ventricular wall tension
Define contractility
The stroke volume for a given venous pressure. Slope of the Starling Curve
What happens to cardiac output if venous pressure rises?
Cardiac output rises
Increased pre-load
What happens to cardiac output when venous pressure falls?
Cardiac output falls
Decreased pre-load
What happens to cardiac output when arterial pressure rises?
Cardiac output falls
Increased afterload
What happens to cardiac output when arterial pressure falls?
Cardiac output increases
Decreased afterload
Describe what happens to CVS system after eating a meal
- Increased activity of gut leads to release of metabolites = local vasodilation
- Causes decrease in TPR =
- Fall in arterial pressure = baroreceptors = increased HR via sympathetic activation = increased cardiac output
- Rise of venous pressure = increased pre-load = increased contractility = increased cardiac output
- Increased cardiac output decreases venous pressure and increases arterial pressure
What is the difference between NSTEMI and STEMI
- NSTEMI - Infarct is not full thickness of myocardium
- STEMI - full thickness of myocardium
What is acute coronary syndrome?
- Group of symptoms attributed to the obstruction of coronary arteries
- Includes STEMI, NSTEMI, unstable angina
What is a pathological Q wave?
- Deepened Q wave
- Indicated previous MI
Define heart failure
Heart failure is a state in which the heart fails to maintain cardiac output to meet metabolic need of the body despite an adequate filling pressure.
- Heart can no longer produce same amount of force for given level of filling
List some causes of heart failure
- Ischaemic heart disease
- Hypertension
- Dilated cardiomyopathy - infections, drugs, pregnancy
- Valvular heart disease
- Arrhythmia
List compensary mechanisms activated in heart failure
- Sympathetic nervous system - baroreceptors detecting low pressure
- Increases HR, contractility
- Vasoconstriction
- RAAS - decreased renal perfusion
- ATII causes vasoconstriction
- Aldosterone and ADH increases Na/H2O reabsorption
- Myocardial hypertrophy and remodelling
What are the types of shock? Give an cause for that type of shock
- Cardiogenic shock - inability of heart to eject enough blood (ischaemic cardiac damage, heart failure, arrhythmias)
- Mechanical shock - restriction on heart of the filling of the heart (cardiac tamponade) or obstruction to flow through lungs (PE)
- Hypovolaemic shock - loss of circulating volume (haemorrhage, burns)
- Norovolaemic (distributive) shock - fall in peripheral resistance (sepsis, anaphylaxis)
What are the acyanotic heart defects?
All those where left side pressure > right side pressure
- Atrial septal defect
- Patent foramen ovale
- Ventricular septal defect
- Patent ductus arteriosus
- Coarctation of aorta
What are the cyanotic heart defects?
- Tetralogy of Fallot - placing outflow portion of interventricular spetum too far in anterior and cephalad direction
- Tricuspid atresia - no development of tricuspid valve
- Transposition of great arteries - results in two unconnected parallel circulations
What is tetralogy of fallot?
Placing outflow portion of interventricular septum too far in anterior and cephalad direction
- Pulmonary stenosis
- Right ventricular hypertrophy
- Overriding aorta
- Ventricular septum defect
