Lecture 29. Physiological Responses of the CV System: In Health and Injury Flashcards
What is a haemorrhage?
Rapid loss of blood
What maintains cardiac output?
Blood pressure
What happens to cardiac output during a haemorrhage?
Loss of pressure leads to lower cardiac output
Dangerously rapid loss of blood: Fall in blood volume → fall venous return
What causes initial corrections during a haemorrhage?
Baroreceptor complexes
What does increasing cardiac output do to a haemorrhage?
Increases rate of haemorrhage
What does an increased drive to vasculature (sympathetic) cause during a haemorrhage?
Stops blood flow to metabolising tissue
What does oncotic pressure recruit as hydrostatic pressure decreases?
Insterstitial fluid
Reabsorption of fluid throughout the capillary bed at the expense of viscosity
What is secreted to correct loss of blood volume?
Renin and Angiotensin II
What is secreted to correct for loss of red blood cells?
Erythropoietin
How many classes of haemorrhage are there?
4
What are class I haemorrhages?
15% of blood volume lost
No change in vital signs (i.e. blood donation)
What are class II haemorrhages?
15-30% of total blood volume lost
Tachycardia, narrowing of the difference between the systolic and diastolic blood pressures, peripheral vasoconstriction
Skin looks pale and is cool to the touch
The patient may exhibit changes in behaviour
What are class III haemorrhages?
30-40% of blood volume lost
Heart rate increases, blood pressure drops, the peripheral hypoperfusion (shock), mental status worsens
Fluid resuscitation with crystalloid and blood transfusion are necessary
What are class IV haemorrhages?
> 40% of blood volume lost
The limit of the body’s compensation is reached and aggressive resuscitation is required to prevent death
What does exercise require?
Redistribution of blood supply to skeletal muscles
How is blood redistributed to the skeletal muscles?
Vasoconstriction in peripheral tissues and vasodilatation in muscle blood vessels
How does vasoconstriction occur?
Through sympathetic release of noradrenaline or adrenaline acting at α-receptors
What effects override any sympathetic vasoconstriction?
Local vasodilator metabolites which match blood flow to metabolic needs
When do Starling’s laws not apply?
During exercise
What would an increase in filling pressure during exercise result in?
Overstretching of cardiac muscles
If filling pressure becomes very large, cardiac output fails
Why is there a reduction in diastole during exercise?
Protects the heart from overfilling
What contributes to thermoregulation during exercise?
Cutaneous vasodilation
Need to get rid of excess heat during exercise
1) Sweating
2) Cutaneous vasodilation
What is the problem that can arise from cutaneous vasodilation being used for thermoregulation?
Cutaneous vasodilation reduces peripheral resistance and will divert blood from muscles
Initially thermoregulation wins out
If central venous pressure falls sufficiently than thermoregulation is abandoned
When does coronary circulation cease?
During systole
What change occurs in arterial pressure during exercise?
Rises slightly
What change occurs in heart rate during exercise?
Rises susbtantially
What change occurs in stroke volume during exercise?
Rises 10-20%
What change occurs in cardiac output during exercise?
Rises substantially
What change occurs in total peripheral resistance during exercise?
Falls - Increased blood flow to skeletal muscle and heart
What change occurs in oxygen consumption during exercise?
Rises
