Cardiac Output and Venous Return

Question 1

normal cardiac output in a 70 Kg man

Answer 1

5-6 L/min

Question 2

Flick Method

Answer 2

Based on conservation of mass. The amount of blood entering the pulmonary artery each minute plus the amount of oxygen entering from the alveoli must equal the amount leaving (oxygen entering= oxygen leaving)

Question 3

CO Flick equation (basic concept)

Answer 3

CO = oxygen exhaled (out) / (Concentration of arterial o2) - (concentration of venous o2)

Question 4

what assumptions are made when using indicator dilution

Answer 4

1.) Constant flow 2.) No loos of indicator 3.) no recirculation

Question 5

how does the indicator dilution curve change with exercise

Answer 5

smaller- flow is faster and there is a higher cardiac output

Question 6

Dilution idicator equation

Answer 6

CO = Bolus injected/area under the concentration curve OR CO= Bolus injected/Avg dye under curve x duration of curve

Question 7

describe the “permissive role” of the heart

Answer 7

it normally pumps out (CO) all the blood it receives (VR)

Question 8

Role played by systemic vasculatire in determining cardiac output

Answer 8

1.) Relative Filling of the vasculature (most critical) 2.) Total peripheral resistance

Question 9

Cardiac output

Answer 9

amount of blood leaving the left ventricle each minute

Question 10

Venous Return

Answer 10

the amount of blood entering the right atrium each minute

Question 11

Factors that cause hypoeffective heart

Answer 11

Sympathetic decrease. MI, Myocardial damage, Impaired pump function (valcular, congenital, tamponade, pericarditis)

Question 12

Factors that cause hypereffective heart

Answer 12

sympathetic increase (Vagal decrease), increased circulating catecholamines (positive ionotropic agents) , hypertrophy

Question 13

Mean Circulatory Filling Pressure

Answer 13

pressure that would exist in all vessels of the systemic and pulmonary circulations if the heart were stopped and blood were allowed to re-equilibrate

Question 14

What is the normal MSFP

Answer 14

7 mmHg

Question 15

when the heart is stopped how does pressure change in the arteries and veins

Answer 15

venous pressure rises (normally low pressure due to compliance) and arterial pressure falls ( normally very high due to low compliance)

Question 16

during circulation where does pressure equal the mean systemic filling pressure? What is the significance of this location?

Answer 16

small post capillary veins. This is wjere we thing of venous return starting

Question 17

Factors that increase MSFP

Answer 17

increased blood volumes, increased sympathetic tone (vasoconstriction- same blood volume in a smaller container) increased abdominal compression, increased skeletal muscle tone (exercise)

Question 18

Factors that decrease MSFP

Answer 18

Hemorrhage (low volume state), Spinal anesthesia (blocks sympathetic traffic to blood vessels)

Question 19

what happesn to the VR curve at -4

Answer 19

becomes flat- due to vena cava colalpse (-4 is intrathoracic pressure - below this the vena cava collapse)

Question 20

Describe the direction the venous return curve shifts when resistance changes

Answer 20

Increase resistance - counterclockwise shift from hinge point Decreased resistance - clockwise shift from hinge point

Question 21

factors that increase resistance in the venous system

Answer 21

increased sympathetic tine, polycythemia (increase viscosity) , circulating catecholamines

Question 22

factors that decrease resistance to venous return

Answer 22

decreased sympathetic tone, anemia (decreased viscosity) , AV fistula