Lecture 27: Integrated physiology

Question 1

In heart failure and other conditions of the heart what else is important to consider? (i.e the point of this lecture)

Answer 1

The effects on the vasculature

Question 2

What can drive changes in CO?

Answer 2

• Physiological i.e exercise or posture

- Pathophysiological i.e heart failure or heamorrhage

Question 3

What are the key components in CV regulation?

Answer 3

• Cardiac function
• Vascular function
• Blood volume

Question 4

Describe how the regulation of cardiac output demonstrates the integrated model:

Answer 4

Cardiac factors:
- HR and Inotropy

Vascular factors:

• Preload
• Afterload

Question 5

Whats the cardiocentric vs integrated view of CO eqauation?

Answer 5

Cardiocentric; CO = SV x HR

Integrated; CO = P(A-V) / TPR

Question 6

What linearly increases with CO?

Answer 6

• Work of the heart and oxygen consumption of the heart

Question 7

What is the plateau of CO determined by?

Answer 7

HR and contractility

Question 8

What is cardiac output dependent on?

Answer 8

Venous return i.e preload

Question 9

What determines venous return?

Answer 9

Pressure gradient (Pa-Pv) (in this case veins vs RA)
Vascular resistance

Question 10

What is right atrial pressure dependant on?

Answer 10

Blood volume and venous capacitance (this also determines mean systemic filling pressure; i.e the pressure across the entire system when the heart stops)

Question 11

What are normal Pa and Pv values?

Answer 11

100 and 0

Question 12

How do you calculate TPR?

Answer 12

MABP = CO x TPR

MABP / CO = TPR

Question 13

What if CO dropped to zero, what would happen to Pa and Pv?

Answer 13

They would drop to around 7mmHg as this is the mean systemic filling pressure because the veins would store most of the blood and are very compliant.

Question 14

What happens to Pv if CO increases?

Answer 14

It is reduced unless VR increases i.e VR must = CO

Question 15

On the VR vs RA pressure graph, whats of note?

Answer 15

• As RA increases, VR decreases (less gradient)\
• VR = 0 @ MSFP
• Plateau is caused by large veins collapsing due to pressure being negative
• RA pressure usually 0-2mmHg = 5l/min VR

Question 16

What are the determinants of MSFP?

Answer 16

• Venous tone (symp), increased tone = inc. MSFP

- Blood Volume

Question 17

What happens to VR if MSFP increases?

Answer 17

For any RA pressure, an increase in MSFP i.e increased blood, or (decreased capacitance because increased venous tone), then VR increases.

and vice versa

Question 18

How does vascular resistance influence venous return?

Do some research on this

Answer 18

Increased peripheral resistance decreases VR at any given RA pressure.

BUT doesnt influence MSFP

Question 19

What does the CO vs RA pressure cardiac function curve represent?

Answer 19

Frank-starling relationship i.e CO dep. on preload

Question 20

How does CO change for a given RA pressure following increased SNS drive?

Answer 20

Increased symp = increased CO b/c inotropy and HR

Question 21

What did the guyton analysis show?

Answer 21

CO = VR

Question 22

What happened on the guyton analysis when there was a blood transfusion?

Answer 22

BT = Inc MSFP -> Inc VR -> Inc CO at higher RA p

But very transient

Question 23

Describe the integrated approach of increased SYM drive?

Answer 23

CO increased

• Inc Inotropy
• Inc HR

VR increased

• Inc venous tone (inc MSFP)
• Inc resistance (dec slope) (may increase peripheral resistance, but local factors still cause dilation, so whilst VR is up, resistance does decrease this slightly)

i.e if VR didnt return then the change in CO would only be modest

Note symp: Increases venous tone which may increase vascular resistance but the increase in tone and vascular return is far greater.

Question 24

Describe what happens in lying to standing?

Answer 24

• Decreased VR b/c venous pooling
  = Dec CO
  = Baroreceptors dec. firing = symp stimulation
  = Inc CO and VR

i.e 3 stages of response / 3 curves

Question 25

Describe what happens in exercise;

Answer 25

Complex:
- Inc symp = Inc MSFP and venous tone
BUT
- Dec. systemic resistance 
- Muscle pumps assist VR

i.e Overally VR is increased and matches the increased CO

must know how to draw on the two different curves and what happens if VR isnt increased

Question 26

What happens in HF after MI?

Answer 26

A) Healthy VR/CO vs RA p curve
B) Post MI, Heart cant pump, CO dec, RA increases (backlog) thus VR decreases
D) Compensation = Inc symp and fluid retention, curves shift up but at a cost of increased RA pressure.

Question 27

Whats the aim for HF patients?

Answer 27

Reduce the pressure in the RA whilst maintaining best CO possible i.e decreasing cardiac work

Achieved by:

• Decreasing inotropy (Blood volume, VR, EDV, Careful balance)
• Decreased afterload
• Decrease symp drive i.e beta blockers

Aim, small reduction in CO for bigger decrease in RA pressure and work on the heart