Haemorrhage, Fainting, Exercise Flashcards
What is haemorrhage?
Severe blood loss
What does haemorrhage cause?
Hypovolaemia
What happens in hypovolaemia?
Reduction in venous return
Reduction in cardiac output
Reduction in MAP
Reduction in prefusion of regional circulations (circulatory shock)
What kind of shock is present if there is a pressure greater than 45mmHg?
Nonprogressive/compensatory shock
What happens during compensatory shock?
Bodily compensatory mechanism alone cause full recovery
What happens if pressure drops below 45mmHg?
Progressive shock which worsens until death without therapy
What will trigger sympathetic reflexes initiated by arterial baroreceptors and other vascular stretch receptors?
Initial haemorrhage and drop in MAP
What happens as a result of baroreceptor and vascular reflexes?
General systemic arteriolar constriction increases total peripheral resistance
Veins and venous reservoirs constrict; helps to maintain adequate venous return despite diminished blood volume
Heart rate increases to ~180bpm
When does the intensity of baroreceptor reflex plateau?
MAP<60mmHg
What will inadequate blood flow stimulate?
Strongly stimulates peripheral chemoreceptors
What does the chemoreceptor reflex do?
Increases rate and depth of respiration promoting venous return by reducing intrathoracic pressure
When does MAP plateau for a 2nd time?
~50mmHg
What causes the second plateau in MAP?
Activation of CNS ischaemic response resulting from increased PCO2 and decreased PO2
What does the CNS ischaemic response cause?
Extreme stimulation of the SNS which results in pronounced vasoconstriction and increased cardiac contractility
What decreases capillary hydrostatic pressure?
Reduced MAP
Increased TPR
Reduced venous pressure
What does decreased capillary hydrostatic pressure promote?
Reabsorption of large quantities of interstitial fluid
Why does colloid osmotic pressure of plasma decrease?
Dilution of blood by tissue fluid
When does the concentration of adrenaline in plasma increase greatly?
MAP of ~40mmHg
What is a potent vasoconstrictor?
Vasopressin/ADH
What stimulates the release of vasopressin?
Sensory input from baroreceptors and other vascular stretch receptors
What stimulates the release of vasopressin?
Sensory input from baroreceptors and other vascular stretch receptors
What does a reduction in MAP cause renally?
Reduces renal glomerular filtration rate
Increases renal sympathetic nerve activity
ADH promotes renal water reabsorption
What does increased renal sympathetic nerve activity do?
Increased production of angiotensin II stimulating the release of aldosterone
Increases salt and water reabsorption in the nephrons
How long after haemorrhage are sympathetic reflexes maximally activated?
30-60 sec after haemorrhage
What do the reflexes allow in regard to suvival?
Full recovery from blood loss of ~30-40%
How long does it take for angiotensin and vasopressin mechanisms to fully respond?
10-60 minutes
How long does the readjustment of blood volume by absorption of interstitial fluid take?
1hr to 48hrs
What is progressive shock?
Positive feedback mechanisms that further reduce cardiac output - decompensatory mechanisms
What dictates the outcome of a patient in progressive shock?
Relative strength of compensatory/decompensatory mechanisms