Cardiac Output

Question 1

define cardiac output

Answer 1

The volume of blood ejected from one ventricle in one minute.

Question 2

Direct Fick Method:

Answer 2

–Calculations require the following information:
i. Oxygen concentration of arterial blood
ii. Oxygen concentration of mixed venous blood:
• mixed venous blood - if all systemic venous blood were to be pooled, mixed and sampled for oxygen concentration, this would represent a “mixed” venous oxygen concentration.
• a mixed venous blood sample is typically sampled from the pulmonary artery.
iii. Oxygen consumption of the patient.
iv. Analogous procedures that use CO2 instead of O2 can be employed.

Question 3

Indicator Dilution (Dye Dilution Method):

Answer 3

• -Theory:
  i. Add a known mass of dye to an unknown volume of liquid (water).
  ii. Measure the concentration of dye in liquid and calculate the volume of the liquid.
  d. Application:
  i. Inject a known quantity of dye into the right ventricle,
  ii. Measure the concentration of dye in blood downstream for an increment of time.
  iii. Calculate volume/time.

Question 4

thermal dilution relevant to indicator dilution method or direct fick method?

Answer 4

indicator dilution

Question 5

Frank-Starling Curve relationship

Answer 5

• relationship is linear. For a given loading (in terms of volume), a force of contraction (in terms of pressure) is measured. Within this linear region, an increase in the load yields a proportional increase in contractile force.
• As venous return is increased, the left ventricle is filled to a greater degree. In turn, a greater displacement (stretch) is produced prior to stimulation - and the resultant force of contraction is increased.
• At some point above this maximum, there will be a decrease in force of contraction.

Question 6

Cardiac Output =

Answer 6

Heart Rate x Stroke Volume,

Question 7

While heart rate is increased, stroke volume is ____. Net effect is to ____.

Answer 7

is REDUCED.

Maintain constant CO.

Question 8

Positive inotropic effect on force of contraction?

Answer 8

INCREASED FORCE - NE and E

Question 9

Negative inotropic effect on force of contraction?

Answer 9

DECREASED FORCE - ACH

Question 10

autonomic influence and relationship to volume?

Answer 10

They change independently!

Question 11

effect of increased force of contraction?

Answer 11

reduced LVESV

Question 12

During exercise LVEDV is…

Answer 12

is reduced bc the HR is increased so there is less time to fill the ventricle up as compared with filling during rest.

Question 13

During exercise LVESV is…

Answer 13

is reduced bc the LVEDV is also reduced so the heart needs to pump more of what it has out (inc force of contraction). LVESV is what is left after the heart pumps out - this amount is smaller during exercise than during rest (LESS RESERVE BLOOD)
-THEREFORE … OVERALL STROKE VOLUME IS INCREASED

Question 14

NE and E effects on heart: (SYSTOLIC EVENTS)

Answer 14

-increase HR by decreasing time spent in diastole
-increase glycogenolysis = more energy = inc in atrial and ventricular contractility = increased stroke volume
-increase membrane permeability to Ca = more Ca entry in phase 2 = inc in atrial and ventricular contractility = increased stroke volume
========>ALL INCREASE CARDIAC OUTPUT

Question 15

SYSTOLIC EVENTS: When exercising, sympathetic tone is ____ and ____ is released to activate ___ receptors on ventricular muscle cells. NE stimulates release of ___ which acts on ___ receptors to increase force of contraction.

Answer 15

• SYMP TONE IS INCREASED
• NE RELEASED TO ACTIVATE B1 RECEPTORS
• RELEASE OF E TO ACTIVATE B1 RECEPTORS

====> OVERALL–> INC HR

Question 16

NE and E effects on heart: (DIASTOLIC EVENTS)

Answer 16

• inc HR and dec time in diasole
• inc rate of pumping of Ca out of cardiac muscles during diastole = shorter relaxation time and more efficient/faster filling of ventricles
• inc rate of uptake of Ca by sacoplasmic reticulum during diastolic periods= shorter relaxation time and more efficient/faster filling of ventricles

Question 17

Coronary blood flow to heart during exercise…

Answer 17

increases— duh

Question 18

inc coronary blood flow to heart mechanism:

Answer 18

1) increased sympathetic tone= increase in metabolism = slight hypoxia of the cardiac cell.
2) Hypoxia disturbs the ratio of breakdown to synthesis of ATP=there will be an increase in AMP within the cardiac cell.
3) Enzymes within the cardiac cell dephosphorylate AMP to Adenosine=increased adenosine diffusson out of the cell. Note that the cardiac cell is fairly permeable to adenosine.
4) Adenosine causes a vasodilation of the coronary circuit. Vasodilation results in increased blood flow which ultimately corrects the hypoxia.

Question 19

Adenosine present due to what and does what to coronary circuit and results in what?

Answer 19

• Present due to hypoxia
• VASODILATION
• increased coronary blood flow

Question 20

for healthy indiv what is the major limiting factor that determines cardiac output?

Answer 20

rate of venous return - determined by Mean Systemic Filling

Question 21

Mean Systemic Filling definition:

Answer 21

the driving force that determines the rate at which blood is returned to the heart.

Question 22

factors that alter Mean Systemic Filling

Answer 22

1. Factors that increase Psf:
   a. Increased blood volume,
   b. Increased sympathetic tone (causing venoconstriction): Venoconstriction has a great effect in increasing Psf because 75% of the blood volume is in the venous system.
   c. Increased massage of veins by skeletal muscle.
2. Factors that decrease Psf:
   a. decrease in blood volume
   b. decrease in sympathetic tone
   c. decrease massage of veins

Question 23

Factors that control venous return:

Answer 23

• Mean Systemic Filling Pressure (Psf)
• Atrial pressure represents a resistance of sorts to venous return. It is precisely this pressure that must be overcome in order to fill the heart.

Question 24

How do we recognize myocardial ischemia or injury on ECG?

Answer 24

-elevated and depressed ST segment (but elevation trumps depression)

Question 25

pulmonary valve slower to close on exhalation or inhalation?

Answer 25

inhalation

Question 26

thermal dilution: the more the temperature changes the better or worse cardiac output?

Answer 26

the less change = GREATER CO

the more change = LESS CO

Question 27

What slows conduction through the AV node - for example to fix atrial fibrilation and why?

Answer 27

beta blockers or calcium channel –> heart is beating so fast and not enough time to fill. this will slow conduction through the AV node which will give the ventricles enough time to fill up

Question 28

increased contractility=

Answer 28

greater force for the SAME end disatolic volume

Question 29

during exercise your heart increases force of contraction or increased contractility?

Answer 29

• DONT FILL TO A GREATER END DIASTOLIC VOLUME BUT YOU PUMP MORE OUT
• INCREASED CONTRACTILITY - end systolic volume is lowered!