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Cardiovascular compensations 2 (Hypovolaemia (Possible causes (Haemorrhage…
Cardiovascular compensations 2
Hypovolaemia
Decreased volume of circulating blood
Acute drop in mean arterial pressure
Possible causes
Haemorrhage
Severe dehydration
Sequestration of blood (non-circulating blood)
Low blood pressure
Decreased preload -> Decreased CO -> Hypotension -> Perfusion failure and tissue hypoxia -> Organ failure
Perceived by atrial volume receptors and arterial baroreceptors
Baroreflex
Short term compensations
Starlings law of capillaries
Fluid from ISF -> Capillaries
RAAS (if persisting hypovolemia)
Splenic contraction
Cells and proteins
Takes weeks to fully replenish lost proteins and cells
Heart failure
Forward failure
Failure of cardiac output
Reduced cardiac output -> Reduced mean arterial pressure
Signs of reduced perfusion
Pale mucous membranes, increased capillary refill time, weak pulse, fast exhaustion during exercise
E.g. DHM, Cardiac taponade
Backward failure
Congestive heart failure (CHF)
Inability of heart to cope with preload
Leads to increased venous pressure -> Increased capillary pressure -> Oedema
e.g Degenerative valve disease
Left sided backwards failure
Fluid in pulmonary veins -> Pulmnoary oedema
Signs
Left sided failure
Strugle to breathe
Right sided failure
Increased venous pressure
Jugular distension
Effusion in abdomen (ascites)
Hepatomegally
Splenomegaly
Forward leads to backwards and vice versa.
Backwards start
Forward start
Endogenous compensatory mechanisms for heart failure
Backward
Starlings mechanism
Increased venous/atrial pressure
Atrial stretch
Reduced atrial systole
Mechanical pressure = cough
Increased preload
Oedema
Increased CO
Forward
Baroreflex
Decompensation
Persistent vasoconstriction of "non-essential" organs
Azotaemia
Uraemia and renal failure
GI ischaemia
Ulceration and sepsis
Fluid retention
Oedema
Myocardial hypoxia
Increased afterload and exposure to aldosterone
Myocardial remodelling
Fibrosis
Vicious circle
More retention of water and vasoconstriction
Increased workload on failing heart
Further stimulation of RAAS etc
Heart failure worsens
Compensatory mechanisms fail to correct cardiac output
More stimulus for compensatory mechanisms
Natriuretic peptides
ANP and BNP
Causes sodium loss at kidney
Looses water with sodium
Peripheral vasodilation
May reduce renin and aldosterone
Can test