Session 6 - Responses of the whole system Flashcards
At a constant CO, falls in TPR do what to venous and arterial pressure?
- Decrease arterial pressure
- Increase venous pressure
At a constant TPR, increasing CO has what effect on venous and arterial pressure?
- Increases arterial pressure
- Decreases venous pressure
Increasing venous pressure increases…
-CO
Decreasing arterial pressure increases…
…CO
How do falls in arterial pressure effect the bloodflow to the gut and skin, and the veins? What is the benefit of this?
- Increases the flow resistance to divert blood from non-important tissues
- Venoconstriction
- Short-term defence to a decrease in AP as will counteract it
What happens if HR increases with no other change?
-Increased HR = increased CO -> increased AP and decreased VP -> SV falls (diastole shorter and VP decreased) -> CO decreased
How is it ensured that the left and right stroke volumes match?
-Starlings law, if the right pumps more the left fills more
What is the consequence of right heart stroke volume being greater than the left?
-Pulmonary oedema as blood becomes congested in the lungs increasing hydrostatic pressure -> forces fluid out into interstitial space =oedema
In what situation would the right heart SV be higher then the left?
-Anything which comprimises LV filling or ejection eg LHF
How is an extremely high VP and thus overfilling of the RH avoided during exercise?
-Increase in HR before VP starts to rise as this shortens the length of diastole and avoids overfilling
What transient problem is faced during standing up?
-Both venous pressure and arterial pressure decrease
What causes both venous pressure and arterial pressure to decrease transiently when standing up?
-Blood pools in the superficial veins of the legs -> reduction in central venous pressure -> reduced filling of RV -> decrease CO-> TPR remains the same so decrease in AP
What is the normal control mechanism of decreased AP?
-Increase CO through baroreceptors
Why would increasing CO to counteract the decreasing AP when standing not work?
-Venous pressure is already low -> would exacerbate the problem
How is the decrease in VP and AP on standing controlled?
-Bloodflow to the gut and skin shut down for a transient time to increase TPR which counteracts the decrease in CO and increases AP
Why does bloodflow to the gut and skin only need to be shut down temporarily on standing and not throughout the duration?
-When standing muscle pumping aids venous return to the heart so no need for decreased bloodflow to gut and skin
What is postural hypotension?
-A transient fall in blood pressure associated with moving to a vertical position
What can cause postural hypotension?
- Reflex of shutting down bloodflow to gut and skin dont work
- If VP is already low
- Fluid imbalance
- Problems with ANS adjusting TPR
What occurs to the volumes, pressures, CO and TPR during haemorrhage?
Less blood in veins -> decreased VP -> decreases end diastolic volume -> decreased SV -> decreased CO whilst TPR is the same -> decreased AP-> detected by baroreceptors -> increases HR -> more blood removed from veins -> VP drops more-> heart fills less -> signals to increase CO but heart filing inadequately so low force of contraction -> increase in TPR and blood diverted from skin and gut -> helps AP a little but lowers VP -> cycles
How can the CVS remain uncomprimised when loosing upto 1-1.5L of blood?
- Venoconstriction -> smooth muscle in veins normally relaxed -> contracts and helps venous ret5urn, increasing venous pressure
- Autotransfusion
What is autotransfusion?
-Tissue fluid moves from the interstitial space into the vessels due to low pressure in vessels
What is the first line of treatment in haemorrhage?
-Infusion of fluids (doesnt have to be RBCs at this stage just water salts and protein -> need to increase volume!!)
What controls blood volume in the long term?
-The kidneys through controlling Na/water reabsorption
What is the result of long term increase in blood volume on pressures, CO and TPR?
-Increased venous pressure -> increases CO (TPR unchanged as bodys need for blood unchanged)-> Increases arterial pressure -> Increased bloodflow to tissues -> vasodilator metabolites washed away-> TPR increases -> AP rises further (self-sustaining system)
What is average arterial pressure related to?
-Blood volume
What is the consequence of prolonged increased TPR in hypertension?
-Hypertrophy of smooth muscle in vessels leading to further vasoconstriction
TPR is inversely proportional to…
…the body’s need for blood
