Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Year 3 Cardiac physiology > CC7: Cardiac Output 1 > Flashcards

CC7: Cardiac Output 1 Flashcards

1
Q

What is cardiac output?

A

-The flow per minute from the heart into the systemic circulation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How does flow compare between left and right side?

A

-Flow through left heart (systemic) = Flow through right heart (pulmonary)
Qs= Qp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Example where flow is not equal between left and right side

A

-Shunts
-ASD/VSD

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Effects of low cardiac output

A

-Cellular hypoxia
-Loss of cellular viability
Poor cerebral perfusion which leads to:
-agitation
-confusion
-unconsciousness
-metabolic acidosis
-rapid respiratory rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the formula for CO

A

CO = HR x SV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are features of autonomic innervation?

A

-Vagus nerves on SA and AV node (parasympathetic)
-Sympathetic on SA and AV node
-Autonomic tone (acetylcholine and noradrenaline)
-Cardiac reflexes (baroreceptors and chemoreceptors)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is stroke volume?

A

-Amount of blood pumped out of heart with each contraction
-SV=EDV-ESV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What factors affect SV?

A

-Preload (atrial pressure)
-Afterload (peripheral vascular resistance)
-Contractility (vigour of contraction)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the limitations of estimating SV by echo/angiogram?

A

-They are 2 dimensional
-This could impede accurate measurement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is preload?

A

-The load (stretch, filling) on the ventricle before ejection
-Regulated by venous return to the heart

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are measures of preload?

A

-EDV
-EDP
-Right atrial pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What happens as afterload increases?

A

-As afterload increases, it takes longer before SL valves open and thus less blood will be ejected: ESV increases and SV decreases
-Increased by any factor that restricts arterial blood flow (atherosclerosis)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is afterload?

A

-Tension the ventricle must produce to open the semilunar valve and eject blood to the great vessels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What causes increase and decrease in SV?

A

Increase:
-Slow heartbeat
-Exercise

Decrease:
-Blood loss
-Rapid heartbeat

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is EDV affected by?

A

-Filling time (duration of ventricular diastole)
-Rate of venous return (rate of blood flow during ventricular diastole)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is ESV affected by?

A

-Preload
-Afterload
-Contractility

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is contractility affected by?

A

Sympathetic activity
-Adrenaline and noradrenaline cause ventricles to contact with more force
-This increases EF and decreases ESV

Parasympathetic activity
-Acetylcholine released by Vagus nerve reduces force of contractions

Hormones

Drugs mimic hormone actions
-Stimulate/block beta 1 receptors (beta blockers)
-Affect calcium ions, decreasing contractility (CCBs)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How do EDV and stroke volume change with rest and exercise?

A

At rest:
-EDV is low
-myocardium stretches little (low preload)
-stroke volume is low, ESV is high

With exercise:
-EDV increases (increased venous return)
-myocardium stretches more
-stroke volume increases, ESV decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the unit of cardiac output?

A

L/min

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is EDV?

A

-max filling after atrial systole (~130ml)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is ESV?

A

-residual volume after ventricular systole (~50ml)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is EF?

A

-Percentage of EDV represented by SV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are the methods of measuring stroke volume?

A

Geometric methods
-Angiographic
-Echocardiographic (single/biplane)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Measuring SV on echo

A

-Relies upon simple shape modelling of LV
-Assumption of symmetry
-Limited regional wall motion abnormalities
-Can accurately detect contour edges

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What are other ways of measuring cardiac output?
Radionuclide gated studies -level of activity via volume Bioimpedance methods -electrical properties of the thorax alters with blood volume Ultrasound Doppler -Measure Time-velocity integral -B mode echo gives cross sectional area of conduit -calculate SV Respiratory rebreathing techniques -uses CO2 or acetylene Dye dilution -Indocyanine Green or Cardio blue Thermodilution -uses cold as a marker Oxygen uptake measurements -The Fick principle
26
What are the 3 principle phases of thermodilution for measuring cardiac output?
-Injection - indicator is brought into circulation -Mixing and dilution - indicator mixes with the bloodstream -Detection - Concentration of the indicator is determined downstream
27
What is the gold standard for CO measurement?
Thermodilution
28
How to do thermodilution in vascular system?
-Choose accessible injectate site (right atrium) -Choose practical sampling site (pulmonary artery) -Inject known dose of marker (idocyanine green) -Continuously monitor distal blood concentration via light absorbance
29
Describe the thermodilution method downstream
-Injectate of known volume and temperature injected into right atrium and cooled -Blood transverses a thermistor in a major vessel downstream over a duration of time -CO is inversely proportional to mean blood-temperature depression and duration of transit of cooled blood
30
What are the features of thermodilution kit?
-5% Dextrose in water injectate (D5W) -Swan-Ganz floatation catheter -Injectate system
31
What are the system connections in thermodilution kit?
-Cooling coil -Injectate thermistor connection -Insulated syringe -Valved 'T' piece -Distal thermistor connection
32
What is special about Swan Ganz catheter?
-It has 10cm depth markers to show how far in the body
33
What pressures are shown here?
-Right atrium -Right ventricle -Pulmonary artery -PCW -Systolic pressure between RV and PA should be the same -Diastolic pressure between RA and RV should be the same -Diastolic pressure between PA and PCW should be the same
34
List the steps for the procedure of thermodilution
-Use 10ml of 5% dextrose in water as injectate -Pass injectate through cooling coil into insulated syringe -Inject fairly rapidly through one-way valve into proximal (RA) catheter lumen -Distal thermistor (PA) records temperature changes -Temperature variables input to micro-computer which calculates parameters
35
How does thermodilution calculate CO?
-Area under dilution curve calculates cardiac output -Can't do too many thermodilutions as it lowers patient's temperature
36
Advantages of thermodilution?
-Readily repeatable -Injectate is non-toxic -Simple measurement technique -Good correlation with earlier methods -Gold standard for CO measurement
37
Limitations of thermodilution?
-Reproducibility of measurements -Limits on the frequency and number of measurements -Complications with PA catheter -PA based CO not clinically useful during periods of haemodynamic instability as it is not real-time
38
Sources of measurement error and variability in thermodilution?
-Variation of injectate temperature and volume -Loss of indicator prior/during/after injection -Cyclic changes in CO -Truncation and extrapolation of of TD curves -Decreased HR during cold indicator injection
39
What are some problems and errors in thermodilution?
Technical factors with injectate -errors in injectate temperature -errors in injectate volume -injection too slow Physiologic and pathophysiologic variations -Changes in pulmonary temperature with respiration -Arrhythmia -Tricuspid regurgitation Analytic factors -Low CO -Changes in baseline core temperature -Position of wedge catheter
40
What are 4 causes of shunt?
-ASD -VSD -PFO (patent foramen ovale) -PDA (patent ductus arteriosus)
41
What is a shunt?
-Movement of blood between the left and right side of the heart -Blood flows from high pressure to low -Blood flows to region of high compliance
42
Where is the shunt?
-Right ventricle
43
3 causes of a bi-directional shunt?
-Eisenmenger -Coughing -Valsalva
44
3 way to detect intra-cardiac shunts?
-Indicator dilution method -Contrast angiography -Oximetry run
45
Explain Oximetry run
-Measured by taking O2 saturations from varying chambers and vessels of the heart -Samples acquired from patients breathing room air, <30% O2 -If shunt exists, arterial and venous blood mixes, altering SO2 measurement
46
How is shunt expressed?
-Ratio of the pulmonary flow to the systemic flow (e.g. 2:1, 3:1) -Qp to Qs
47
What is a basic technique for detecting shunts?
-Measuring O2 saturation of blood samples drawn sequentially from PA->RV->RA->SCV/IVC -Left to right shunt may be detected if there is significant increase in O2 saturation
48
Mechanism of right to left shunt
Needs downstream obstruction -Valvular (pulmonary stenosis, RVOT obstruction) -Vascular (pulmonary hypertension) Causes desaturation in systemic circulation -Cyanosis -Causes increase in Hb level
49
Is Qp/Qs affected by haemoglobin?
No
50
How many binding sites does one molecule of Hb have?
-4 binding sites for O2 -Hb molecule is saturated when all 4 sites are bound to O2
51
What is the formula for Qp/Qs?
Systemic arterial - Mixed venous /Pulmonary vein - Pulmonary artery (OXYGEN SATS)
52
What is the formula for Mixed venous?
53
What step-up value indicates left to right shunt?
-Step up in O2 Sat more than 7%
54
What is the criteria for Qp:Qs ratio?
Qp:Qs<1.5 Surgery not necessary Qp:Qs 1.5-3.0 Mild to moderate shunt Qp:Qs>3.0 Significant shunting
55
What are the limitations of shunting?
-Loses accuracy when calculating small shunts -Step up can vary -High CO underestimates AVO2 difference
56
Where is step up?
-right atrium
57
What is the Qp/Qs
1.5:1 left to right
58
What is Qp/Qs value in right to left shunt?
Qp/Qs < 1 (e.g. 1:1.5) <1.5 = small shunt >2.0 = significant
59
In what case could you have right to left shunt and what are signs?
-Eisenmenger syndrome Primary detection -Presence of cyanosis -Arterial hypoxaemia
60
What are the normal saturations?
-Right side = 60-75 -Left side = 95-99
61
What factors can affect CO
-Autonomic nervous system: sympathetic and parasympathetic affect HR -Circulating hormones: catecholamines affect HR -Venous return and stretch receptors: Preload, afterload and contactility affect SV

Year 3 Cardiac physiology (30 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions