Chronic cardiac failure Flashcards
What is Chronic heart failure
The inability to perfuse tissue at normal filling pressures
What is heart failure a result of
Reduced heart contractility
How does heart failure effect exercise and how can this cause toxic products to build up in the plasma
Stroke volume can’t be increased due to a decrease in the catecholamine response - low levels of local noradrenaline as well as a reduced receptor density
Adrenal gland tries to compensate by releasing noradrenaline into the bloodstream - can build up to toxic levels
What is the early compensation mechanism for heart failure
Peripheral vasoconstriction
Increased sympathetic activity
Increased angiotensin II in circulation
How is the renal system affected by short term compensation of heart failure
Reduced renal blood flow evokes sodium and water retention - raising BP
This increases filling pressure and therefore output
What is cardiac dilation
The heart becomes enlarged - impairs muscle and valve function - can’t pump blood efficiently
How does increased vasopressin lead to a reduction in plasma colloid osmotic pressure
More water retention - reduces concentration of protein in the plasma - can lead to an oedema
How is heart failure treated
- Diuretics - vaso and venodilators - amiloride
- Digoxin - improve contractility - Na/KATPase inhibitor - less Na/Ca exchanger functionality so builds up intracellular calcium
What role does the lymphatic system play in preventing oedemas
Fluid formation per day exceeds absorption by 2-4l
Excess is taken up by the lymphatic system
How does capillary damage lead to an oedema
Increases the concentration of tissue fluid protein which also increases the colloid osmotic pressure at the venous end (was essentially 0) this creates a small difference in pressures so less fluid is likely to be reabsorbed into the capillary
How does an increase in venous blood pressure (due to venous obstruction/ heart failure) lead to an oedema
TF hydrostatic pressure is around 1mmHg - at the venous end if the HP is greater, more fluid is going to move into the tissue fluid as a result of the increased gradient between the two compartments -
How does hypoproteinemia (due to starvation/ fall in plasma proteins in nephrosis) lead to an oedema
Fall in plasma protein reduces colloid osmotic pressure in the capillary - so reduced driving force of fluid back into the capillary at the venous end
How does exercise cause oedemas
Hydrostatic pressure increase at arterial end creating a higher pressure gradient forcing fluid out the capillary - increase up to 25%
