lecture 21 - heart failure Flashcards
How does the Starling Curve shift during cardiac failure?
Reduced myocardial contractility shifts curve down
What is the equation for ejection fraction of the heart?
Stroke Volume / End diastolic volume
How does the ejection fraction change in heart failure?
It is reduced
What are the 2 compensatory mechanisms in cardiac failure?
Increased adrenergic activity, renal retention of sodium/water
How does increased adrenergic activity compensate for heart failure?
Causes vasoconstriction and increased total peripheral resistance, so MABP can be maintained.
How does renal retention compensate in heart failure?
Increases extracellular fluid volume causing an increase in end diastolic volume and therefore stroke volume and cardiac output
Why does fluid retention in chronic heart failure result in oedema?
Renal fluid retention increases plasma volume which elevates capillary pressure, leading to a shift from the capillaries to the interstitial space resulting in oedema
How is pulmonary oedema described on a chest xray?
‘Snowstorm’
At what time of the day is dyspnoea from pulmonary oedema worst?
At night - Paroxysmal Nocturnal Dyspnoea - because a supine position exacerbates
Is pulmonary oedema more likely to be caused by left or right heart failure?
Left heart failure
Is peripheral oedema more likely to be caused by left or right heart failure?
Right
Where is peripheral oedema most likely to be found?
In the ankles of ambulant patients or sacrum of bed ridden patients
What are the 3 key signs of peripheral oedema?
Swollen ankles/sacrum, elevated Jugular venous pulse, enlarged liver
What is Laplace’s law in terms of the heart?
Muscle tension = (ventricular pressure * ventricular radius)/(wall thickness)
How does LaPlace’s Law explain a gain in ventricular tension during heart failure?
As the left ventricle dilates during heart failure and the thickness decreases, the tension increases leading to increased myocardial O2 demand
