Integration

Question 1

Changes in CO can be….

Answer 1

Physiological (exercise/posture) or pathophysiological (HF, haemorrhage)

Question 2

Why to we not just try increase the preload if someone has heart failure

Answer 2

Because although they need to raise their CO, they have ALREADY got volume overload.

Question 3

SO what do we focus on in HF patients

Answer 3

• Cardiac function
• Vascular function
• Blood volume (kidneys

Question 4

What are the differing factors that impact CO?

Answer 4

Cardiac Factors : HR and Myocardial contractility

Coupling Factors: preload and afterload (dependent of vascular function)

Question 5

CO =

Answer 5

CO = SV x HR
CO = change P x TPR

Although HR and SV do impact CO, we need to remember SV is dependent on venous return! Look at the bigger picture.

Question 6

CO is more becuase of the tissue needs, instead of the

Answer 6

heart pumping

Question 7

CO must match (within a beat or two) …

Answer 7

Venous return

Question 8

Draw and explain CO curve

Answer 8

…

Question 9

Three main determinants of Venous Return

Answer 9

1) Right atrial pressure (back pressure)
2) Degree of filling (blood volume and venous capacitance) ~ mean systemic filling pressure
3) Systemic vascular resistance

ie: the pressure gradient (Ps - Pv) and vascular resistance > “vascular function”

VR= Pa-Pv/ R

Question 10

Draw Venous function curve (venous return)

Answer 10

-as we change venous return the right atrial pressure (preload) is affected.

As Right atrial pressure increases, venous return decreases, due to pressure gradient driving flow (Pa-Pv)

-So as MRAP falls, flow increases but the curve level off due to the large veins collapsing (inc R), so no further increase in VR

Question 11

usually Pressure gradient =

Answer 11

PG = 102 (aortic) - 2 (venous)
= 100mmHg
this is required to ensure venous return is maintained!

Question 12

What happens when CO= 0L/min (when right atrial P = 7mmHg)

Answer 12

Arterial Pressure drops
Venous Pressure rises due to large diference in compliance (19mmHg drop in arterial P = 1mmHg rise in venous P)

This is because veins are very compliant and already have lots of blood in them, can handle volume change BUT arteries are not and so small volume change > big pressure change.

Meet at 7mmHg “mean systemic filling pressure”

Question 13

Main determinant of mean systemic filling pressure (Psf)

Answer 13

Blood volume (inc)
venous compliance (dec)

as MSFP increases, venous return increases at any given R atrial pressure

Question 14

What would an increase in vascular/resistance do to venous return

Answer 14

Drops venous return curve as its harder to get blood back to the heart.

Still plateau at 0/-2 right atrial pressure.

Question 15

An increase in blood volume leads to…

Answer 15

> increase in mean systemic filling pressure = increase in venous return > increased CO at a high right atrial pressure

eg) transfusions

Question 16

What happens in heart failure?

Answer 16

Heart is unable to effective pump. This decrease in peripheral perfusion > synmpathetic activation and increase in fluid retention > increased MSFP. CO remains normal

So the patient will have a higher Right atrial pressure just to compensate /maintain CO

Question 17

is the increase ing R atrial pressure/ MSFP a good thing

Answer 17

No as you have a higher workload on the heart!! Bad long term

Question 18

Because of increasing MSFP in heart failure, whats a good treatments

Answer 18

Diuretics:
-reduce venous pressure
-reduce oedema
BUT WILL REDUCE OUTPUT

ACE inhibitors

• Vasodilation
• reduces remodelling
• reduces bloodvolume

Beta-blocker
-Reduce energy demand