Pathophysiology of Heart Failure Flashcards
What is heart failure?
the inability of the heart to pump blood out therefore reduced stroke volume hence reduced cardiac output
what are starlings forces?
forces that determine whether fluid will move in to or out of the capillary.
what direction does hydrostatic pressure force fluid?
out of the capillary
where is hydrostatic pressure the highest, arteriole or venuole end?
arteriole
what is oncotic pressure?
osmotic pressure doe to protein, albumin
what direction does oncotic pressure force fluid?
into the capillary from extracellular tissue fluid
what is oedma?
when there is an inbalance in the hydrostatic and oncotic pressure so the hydrostatic pressure is higher forcing fluid out of the capillary
what is the capillary filtration coefficient ?
a value denoting the permeability of the capillary. The higher the permeability, the higher the coefficient
how do we calculate net pressure?
hydrostatic pressure gradient + colloid osmotic (oncotic) pressure gradient
what is the net flow of fluid through the capillary?
3L a day
where does the 3L of fluid that leaves the capillary go?
it enters the lymphatic system and is returned to the venule end
what are the classifications of heart failure?
- Acute or Chronic
- Left or Right sided failure
- biventricular failure
what can be used to detect a reduction in ejection fraction of the heart?
an echocardiogram
what are clinical features of heart failure (i.e. symptoms)
- reduced ejection fraction (reduced fraction of blood pumped out in comparison to volume of blood in the ventricles)
- hypotension (causing tiredness and dizziness)
- reduced urine flow
- cold peripheries - less blood to fingers and toes
- breathlessness (co of oedema (especially in lungs)
- atrial fibrilation (due to pressure on atrium causing electrical disturbances)
why do patients have reduced urine flow with heart failure?
- because there will be less flow of blood to the kidneys hence less blood filtered to produce urine.
- also, fluid is lost at the capillary end so less fluid in systemic circulation for urine
what are the 4 categories for factors causing heart failure?
- impaired contractility
- pressure overload
- left ventricular diastolic dysfunction
- obstruction of left ventricular filling
what diseases cause a pressure overload to cause heart failure?
- aortic stenosis
2. uncontrolled hypertension
how does aortic stenosis cause heart failure?
narrowing of the aorta hence causing increased aortic pressure therefore it becomes more difficult to move blood through the aorta
how does uncontrolled hypertension cause heart failure?
when the ventricles have to overcome high pressure hence increasing workload on the ventricular muscles therefore resulting in heart failure
what diseases cause impaired contractility to cause heart failure?
- myocardial infarction
- transient myocardial ischemia
- chronic volume overload (mitral and aortic regurgitation)
- dilated cardiomyopathy
what is dilated cardiomyopathy?
a muscle disorder causing a lack of contraction hence heart failure
what is chronic volume overload?
two types: mitral and aortic regurgitation.
- mitral: backflow of blood from high pressure pulmonary artery into right ventricles
- aortic: backflow of blood from high pressure aorta into left ventricles
what diseases cause left ventricular diastolic dysfunction to cause heart failure?
- left ventricular hypertrophy
- hypertrophic cardiomyopathy
- restrictive cardiomyopathy
- transient myocardial ischemia
what diseases cause obstruction of left ventricular filling to cause heart failure?
- mitral stenosis
2. pericardial constriction or tamponade
what causes a rise in atrial pressure?
a rise in end-diastolic volume coupled with increased myocardial hypertrophy
when the contractility of the ventricles reduces (heart failure), what happens?
- less ventricular emptying
- causing an increase in end-diastolic volume
- so the fall in stroke volume is less than it would have otherwise been
- more left ventricular filling leads to pulmonary congestion
what is activated when stroke volume and cardiac output is reduced?
- sympathetic reflexes
- Renin-angiotensin system
- ADH release
what drugs are used to treat heart failure?
- diuretics
- positive inotropes
- vasodilators
- beta adrenorector antagonists
give examples of positive inotropes?
- adrenoreceptor agonists
- cardiac glycosides
give examples of vasodilators?
- RAAS antagonists (ACEI)
- Nitrates
- Alpha adrenoreceptor antagonists
Explain how drugs work to treat heart failure?
- Failing heart with reduced stroke volume and left ventricular end diastolic pressure causes pulmonary congestion
- diuretics reduce pulmonary congestion without increasing stroke volume
- excessive diuresis or venous dilation may cause fall in stroke volume hence hypotension
- end diastolic pressure of left ventricles reduced by ionotropic therapy causing arterial dilation
- this represents the potential of combining vasodilators and ionotropic therapy
