Cardiac output

Question 1

Afterload

Answer 1

the load/ pressure the heart must eject blood against.

roughly equal to aortic pressure

Question 2

Preload

Answer 2

amount ventricles are stretched (filled) in diastole

*related to sarcomere length, EDV and central venous pressure.

Question 3

central venous pressure

Answer 3

pressure in large veins draining to the heart

Question 4

arterial pressure

Answer 4

pressure in the large arteries

Question 5

total peripheral resistance

systemic vascular resistance

Answer 5

resistance to blood flow offered by all systemic vasculature

Question 6

what effect does constriction of arterioles have for the pressure? *refer to resistance

Answer 6

• increases resistance.
• cause pressure in capillaries and on venous side to fall as blood reaches it and pressure on arterial side to increase as sudden resistance.

Question 7

what is the relationship between cardiac output, SV and HR?

Answer 7

CO = SV X HR

Question 8

what determines the SV?

Answer 8

SV = end diastolic volume - end systolic volume

*increase SV by increasing EDV or decreasing ESV
( fill heart more or empty ventricle more ) OR BOTH

Question 9

what is the typical SV for an average man at rest?

Answer 9

70ml

- 2/3 of EDV

Question 10

when does ventricular filling happen?

Answer 10

• at diastole, when AV valves are open but aortic and pulmonary closed.
• ventricle fills until stretch enough to produce an Intraventricular pressure = venous pressure (no more flow).
• higher venous pressure more fills, more fills the higher the LV pressure.

Question 11

what does frank-starling law of heart state?

Answer 11

• if you stretch the cardiac fibres before contracting it will contract harder.
  AKA more it fills the harder it contracts.

*harder contract = more SV, higher venous pressure so more fill depending on compliance.

Question 12

how is cardiac input + output balance maintained with increased SV?

Answer 12

• increased SV balanced with increased filling of heart as an intrinsic control.
• pulmonary and systemic in series as same vol of blood pumped to body also pumped to lungs.

Question 13

why does starling’s curve eventually plateu? why doesn’t increasing LV EDV continue to increase SV?

Answer 13

• due to full stretch of cardiac fibres reached, increasing fluids or volume wont give greater SV beyond a certain point.

Question 14

what is contractility and what can increase it?

Answer 14

• force of contraction for given fibre length.
• extrinsic factors such as sympathetic stimulation and circulating adrenaline can increase it.

*decrease in BP causes activation of SNS and increase in HR and contractility.

Question 15

name some factors that determine cardiac output.

AKA how much ventricle empties

Answer 15

• how hard it contracts : down to contractility + EDV.

- how hard it is to eject blood : aortic impedance.

Question 16

what are the CVS consequences of eating a meal?

Answer 16

• local vasodilatation in gut decreases TPR and arterial pressure and increases venous pressure initially.
• increase HR and SV.
• increasing cardiac output so arterial pressure and decreasing venous.

Question 17

what are the CVS consequences of standing?

Answer 17

• blood pools due to gravity, decreasing venous, arterial pressure and output.
• Bararoreceptor (stretch receptors) reflex and ANS increase HR, contractility and TPR ensuring arterial pressure.

*if reflexes do not work you get postural hypertension

Question 18

what are the CVS consequences of exercise?

Answer 18

• initial increase in venous pressure as calf muscle pups and venoconstriction returns more blood.
• later decrease in TPR increases venous return, increasing SNS, increased contractility.
• combination of factors needed otherwise flat part of starlings curve.

Question 19

what is the jugular venous pulse? (JVP)

Answer 19

• a biphasic pulse in right internal jugular vein behind sternocleidomastoid muscle, due to direct column of blood connected to right atrium.
• also measured with central line into internal jugular vein or Superior vena cava to see waveform.

Question 20

what would increase JVP?

Answer 20

• Right heart doesn’t pump properly.
• volume overload with IV infusion.
• filling of heart impaired.
• stab to heart, distended neck veins, low arterial BP and loss on consciousness.