Cardiac output

Question 1

What does end systolic volume depend on?

Answer 1

Preload, after load, heart rate and contractility

Question 2

Fick principle

Answer 2

Oxygen content of the pulmonary vein is derived from the pulmonary artery blood and oxygen uptake across the lungs. Measures cardiac output

Question 3

How is cardiac output measured from the Fick principle?

Answer 3

Q1- rate of delivery (cardiac output x oxygen conc in pulmonary artery)
Q2- rate of uptake across lungs
Q3- rate of removal (cardiac output x oxygen conc in pulmonary vein)
CO= O2 uptake / oxygen conc in pv - oxygen content in pa

Question 4

Methods for measuring the cardiac output of a patient

Answer 4

1- Measure O2 uptake rate by vol and O2 in expired air, measure oxygen in pa by pulmonary catheter and oxygen in pv by peripheral arterial blood
2-Indicator dilution
3- Thermodilution
4- Ultrasound

Question 5

How does indicator solution work to measure cardiac output?

Answer 5

Inject inert tracer into vein/ right ventricle e.g. inocyanine green, measure difference between colour of what you put in and what comes out in arterial blood, output is proportional to 1/ [tracer]

Question 6

How does thermodilution work to measure cardiac output?

Answer 6

Cold saline injected into right atrium, mies blood, moves to ventricle then pulmonary artery, sensor in artery measures temperature changes, this change with the vol put in is used to calculate cardiac output

Question 7

How does ultrasound measure cardiac output?

Answer 7

Measures changes in ventricular dimensions, stroke volume can be calculated

Question 8

Typical value for stroke volume

Answer 8

80ml, 5.5permin-1 at 69 bpm

Question 9

Cardiac index

Answer 9

Cardiac output/ body SA, 2.5-3.6lmin-1m-2

Question 10

How is cardiac output controlled?

Answer 10

By rate (mainly by innervation) and stroke volume changes (innervation and length tension relationship)

Question 11

What is heterometric control of cardiac output

Answer 11

The starling effect so is regulated by EDV which is regulated by venous return

Question 12

Give examples of heterometric control of cardiac output

Answer 12

Blood vol, vascular storage, haemorrhage, vascular resistance (increases VR), muscle pump action (increase VR), atrial sucking, gravity, inspiration, exercise –> all act of venous return which alters EDV

Question 13

How does the parasympathetic nervous system control cardiac output?

Answer 13

Left vagal nerve on AVN and right vagal nerve on SAN, primary chronotropic, Aah release on to M receptors which inhibit cAMP so decrease slope so longer to reach threshold causing bradycardia, slow conduction through AV node so decreases the force per beat

Question 14

How does sympathetic nervous system control cardiac output?

Answer 14

Both chronotropic and ionotopic effects, NA to B1 receptors on Nodes and myocardium which stimulate cAMP which stimulates PKA which activates L-type Calcium channels causing contraction, increase SA node firing and increases conduction velocity, decreases time for systole and diastole - due to increase in calcium increasing contractility

Question 15

Is parasympathetic or sympathetic control more dominant at rest?

Answer 15

Parasympathetic

Question 16

What humeral factors affect heart rate?

Answer 16

Thyroid hormones

Question 17

What can hyperthyroid result in?

Answer 17

Genomic actions- promotes cardiac gene expression e.g myosin, ATPase, non genomic actions on transport proteins, hypertrophy of heart

Question 18

What influences the period between SA node firing AP and the next?

Answer 18

Maximum diastolic potential, slope of diastolic depolarisation, threshold potential

Question 19

What does End diastolic volume depend on?

Answer 19

Filling pressure, filling time, ventricular compliance

Question 20

What must systemic venous return match?

Answer 20

Systemic cardiac output