CO and venous return

Question 1

What are two equations to calculate CO?

Answer 1

CO = SV x HR
CO = MAP/TPR

Question 2

How is CO maintained during the early stages of exercise?

Answer 2

An increase in HR and an increase in SV

Question 3

How is CO maintained during the late stages of exercise and why?

Answer 3

HR only as SV plateaus

Question 4

What are the invasive methods for measuring CO?

Answer 4

Fick principle
Indicator dilution method
Thermodilution method

Question 5

What are the non-invasive methods of measuring CO?

Answer 5

Doppler US
Impedence cardiography
Electrical cardiometry
MRI

Question 6

What are the 2 equations related to the Fick principle?

Answer 6

CO = rate of O2 consumption / (arterial O2 content/venous O2 content)
O2 content or AV difference = 0.0136 x Hgb x O2 saturation difference

Question 7

What is the principle behind the dilution methods for measuring CO?

Answer 7

Rate of blood flow can be determined from the rate of change in the concentration of a substance after a known amount of it has been added to the bloodstream

Question 8

What also increases with increased contractility of the heart?

Answer 8

SV

Question 9

What increases contractility of heart?

Answer 9

Catecholamines
Insulin and glucagon
Growth hormone
Thyroid hormone
Increased intracellular Ca++
Decreased activity of Na/Ca exchanger
Digitalis

Question 10

How does digitalis work?

Answer 10

Blocks Na/K pump to increase intracellular Na, which decreases Na/Ca exchange to increase intracellular Ca

Question 11

What decreases contractility of heart?

Answer 11

beta1 blockade –> decreases cAMP
systolic HF
Acidosis
Hypoxia and hypercapnia
Non-dihydropyridine Ca channel blockers

Question 12

What factors increase myocardial oxygen demand?

Answer 12

Increased afterload
Increased contractility
Increased HR
Increased diameter of ventricle (increased wall tension)
Sympathetic activity

Question 13

What is the equation for EF?

Answer 13

EF = SV/EDV = (EDV-ESV)/EDV

Question 14

What is a normal EF?

Answer 14

> 55%

Question 15

What is the equation for cardiac index?

Answer 15

cardiac index = CO/body surface area

Question 16

What is the purpose of the cardiac index?

Answer 16

Relates heart performance to the size of the individual

Question 17

Changes in what result in changes in EDV?

Answer 17

Venous return

Question 18

What factors increase CO?

Answer 18

Anxiety and excitement
Eating
Exercise
High environment temp
Pregnancy
Epinephrine
Hyperthyroidism

Question 19

What factors decrease CO?

Answer 19

Sitting/standing from supine
Rapid arrhythmias
Heart disease

Question 20

How does sleep effect CO?

Answer 20

There is no change in CO during sleep

Question 21

What is the normal value for CO?

Answer 21

5 L/mmHg

Question 22

At what value does CO normally plateau?

Answer 22

13 L/mmHg

Question 23

What can increase CO plateau to 25 L/mmHg?

Answer 23

Combination of SyNS stimulation and PsNS inhibition that increases HR and contractility

Question 24

What is cardiac reserve?

Answer 24

The maximum percentage that the CO can increase above normal

Question 25

What is the normal cardiac reserve in healthy adult?

Answer 25

300-400%

Question 26

What is the cardiac reserve in trained athletes?

Answer 26

500-600%

Question 27

What is the cardiac reserve in pts with HF?

Answer 27

None

Question 28

What factors influence venous return?

Answer 28

Posture
Ventilation - thoracic pump
Skeletal muscle activity
Vena cavae compression
Hyperviscosity
Venous compliance

Question 29

What factors increase venous return?

Answer 29

Increased venous pressure
Decreases R atrial pressure
Decreases venous resistance

Question 30

What are two causes of hyperviscosity?

Answer 30

Polycythemia
Hyperproteinaemia

Question 31

At what R atrial pressure does venous return become zero normally?

Answer 31

7 mmHg

Question 32

At what atrial pressure will venous return reach a plateau normally?

Answer 32

Less than or equal to -2 mmHg