Cardiovascular physiology

Question 1

What determines cardiac output?

Answer 1

Cardiac output = heart rate x stroke volume

Question 2

What is Darcy’s equation?

Answer 2

Flow = pressure / resistance
(cf Ohm’s law, i=v/r)
therefore,
Ventricular volume = BP / SVR

Question 3

Define stroke volume

Answer 3

Stroke volume = ventricular volume - residual volume (SV=EDV-ESV)

Question 4

How does hypoxia affect peripheral resistance?

Answer 4

It is a potent vasodilator

Question 5

What causes peripheral vasodilatation?

Answer 5

• hypoxia
• acidosis
  (therefore, tissue need for O2 → ↓PVR → ↑CO)

Question 6

What causes increased ventricular volume (blood flow back to heart)?

Answer 6

Hypoxia, acidosis, venostriction (sympathetic fight or flight response)

Question 7

How is ventricular residual volume decreased?

Answer 7

↑contractility

• Frank-Starling curve
• +ve inotropic agents

Question 8

What is Starling’s law of the heart?

Answer 8

Stroke volume increases in response to increase in volume of blood filling the heart (the end diastolic volume) when all other factors remain constant

Question 9

How does filling of ventricle increase contractility?

Answer 9

The stretching increases the affinity of troponin C for calcium, causing a greater number of actin-myosin cross-bridges to form within the muscle fibres

Question 10

What are the 3 effects of the sypathetic / adrenergic system on the heart?

Answer 10

• inotropic (contractility)
• chronotropic (heart rate via SA node ↑Na influx)
• dromotropic (↑AV nodal conduction)

Question 11

What is the parasympathetic effect on the heart?

Answer 11

↓heart rate via SA node, can be profound (→vasovagal)

Question 12

What are the 3 determinants of stroke volume?

Answer 12

Preload, afterload, inotropy

Question 13

Give 6 mechanisms of increased ventricular preload

Answer 13

1. ↑CVP [↓venous compliance (sympathetic), ↑volume (i.v., respiration, muscle pump, gravity)]
2. ↑ventricular compliance
3. ↑atrial force contraction (sympathetic, frank-Starling)
4. ↑ventricular filling time (↓HR)
5. ↑aortic afterload (secondary effect)
6. Pathological (poor LV, AS, AR)

Question 14

Give 6 mechanisms of reduced ventricular preload

Answer 14

1. ↓CVP (blood loss, gravity)
2. impaired atrial contraction (e.g. AFib)
3. ↑heart rate (↓filling time)
4. ↓afterload
5. ↓ventricular compliance (e.g. LVH, ↓relaxation)
6. inflow valve obstruction