Cardiovascular Flashcards
The equation for thermodilution measurement
- This uses the equation, V̇ = m/Ct, where:
o V̇ = flow, or cardiac output
o m = dose of the indicator,
o C = concentration, and
o t = time
Deranged 2014 march Q19
Define cardiac output. (10% of marks) Outline the factors that affect cardiac output. (60% of marks) Briefly describe the thermo dilution method of measuring cardiac output. (30% of marks)
Cardiac output Definition
Cardiac output is defined as the volume of blood ejected by the heart per unit time.
It is usually presented as [stroke volume × heart rate], in L/min
Deranged 2014 march Q19
Define cardiac output. (10% of marks) Outline the factors that affect cardiac output. (60% of marks) Briefly describe the thermo dilution method of measuring cardiac output. (30% of marks)
Thermodilution measurement of cardiac output:
* Rate of blood flow can be determined from the rate of change in the concentration of substance after a known amount of it has been added to the bloodstream
* This uses the equation, X
- In the case of thermodilution, the “indicator substance” is a known volume of X, and the equation
- The use of thermodilution for cardiac output measurement requires a modified version of the abovestated equation, otherwise known as the X, which incorporates correction factors for specific heat and specific gravity of both the indicator and the blood.
2014 march Q19, Define cardiac output. (10% of marks) Outline the factors that affect cardiac output. (60% of marks) Briefly describe the thermo dilution method of measuring cardiac output. (30% of marks
Thermodilution measurement of cardiac output:
* Rate of blood flow can be determined from the rate of change in the concentration of substance after a known amount of it has been added to the bloodstream
* This uses the equation, V̇ = m/Ct, where:
o V̇ = flow, or cardiac output
o m = dose of the indicator,
o C = concentration, and
o t = time
* In the case of thermodilution, the “indicator substance” is a known volume of cold saline (or heated blood), and the equation
* The use of thermodilution for cardiac output measurement requires a modified version of the abovestated equation, otherwise known as the Stewart-Hamilton equation, which incorporates correction factors for specific heat and specific gravity of both the indicator and the blood.
2014 march, Define cardiac output. (10% of marks) Outline the factors that affect cardiac output. (60% of marks) Briefly describe the thermo dilution method of measuring cardiac output. (30% of marks)
examiner comment
2014 march, Define cardiac output. (10% of marks) Outline the factors that affect cardiac output. (60% of marks) Briefly describe the thermo dilution method of measuring cardiac output. (30% of marks)
58% of candidates passed this question. This is a core question. It was expected candidates could provide a definition (heart rate x stroke volume) and then move on to outline factors that affect it (afterload, preload, contractility). Additional marks were awarded for descriptions of the relationship to mean systemic filling pressure and other influences beyond this. Most candidates described a thermodilution cardiac output curve but almost all described the technique as based on the “Fick equation or method” (which is used to estimate cardiac output from oxygen consumption). Very few candidates correctly identified the Stewart Hamilton equation as the integration method used to relate cardiac output (flow) to temperature change as an example of indicator dye dilution. Candidates seemed to lack depth and understanding on this topic.
Cardiac output measurement can be performed:
INVASIVELY
o Pulmonary Artery Catheter
▪ Thermodilution
▪ Fick Principle
o Indicator Dilution Technique
o TOE
o Arterial waveform analysis
▪ PiCCO
▪ Vigileo
Non-invasively
o TTE
o MRI
o Thoracic impedance
cicm wrecks 2017-2-10
note: i no longer thing the above is correct, so there is ficks method vs indicator dilulution (which relies on ficks principle), termodiluation is a subset of indicator dilution, not: ficks method requires PA catheter for mixed venous blood sampling, and indicator dilution needs either CVC or pa catheter
2011 mar Describe the principles, and limitations, of the measurement of cardiac output using an indicator dilution technique
what is this/
* V̇ = m/Ct,
2011 mar Describe the principles, and limitations, of the measurement of cardiac output using an indicator dilution technique
Stewart-Hamilton equation:
* V̇ = m/Ct,
where
o V̇ = flow, or cardiac output
o C = concentration
o m = dose of the indicator, and
o t = time
* or, Cardiac output = indicator dose / area under the concentration-time curve
2011 mar Describe the principles, and limitations, of the measurement of cardiac output using an indicator dilution technique
Advantages and limitations:
2011 mar Describe the principles, and limitations, of the measurement of cardiac output using an indicator dilution technique
Advantages and limitations:
* Access to mixed venous blood and arterial blood is not essential
* It is convenient: with electronic calculations, cardiac output measurement can be automated and continuous
* Good correlation with gold standard measurements of cardiac output
2011 mar Describe the principles, and limitations, of the measurement of cardiac output using an indicator dilution technique
However:
2011 mar Describe the principles, and limitations, of the measurement of cardiac output using an indicator dilution technique
However:
* Use of dye limits the frequency and repeatability of measurements, as it produces recirculation, and even the most rapidly cleared dyes are cleared after some minutes.
* Manual integration of the area under the concentration/time curve is laborious
* Automated calculation of cardiac output involves the use of correction factors and coefficients, which reduces its accuracy
* The method relies on uniform mixing of blood and unidirectional flow
* Thermodilution measurements have numerous potential sources of error
* Under laboratory conditions, agreement between this method and the direct Fick method is within a margin of 25%
2011 mar Describe the principles, and limitations, of the measurement of cardiac output using an indicator dilution technique
examiner comment
2011 mar Describe the principles, and limitations, of the measurement of cardiac output using an indicator dilution technique
Most candidates chose to describe the thermodilution technique of cardiac output measurement. Descriptions of other techniques and indicators such as dye dilution using indocyanine green were acceptable alternatives. Better answers included a description of the Fick Principle and the fact that it is based on the law of conservation of matter. For thermodilution, heat lost from the blood = heat gained from the injectate. Also required were an accurate description of the technique, a description of the indicator-time curve and errors encountered in the technique. For thermodilution these included the requirement for a Swan Ganz catheter, nature and temperature of the injectate, temperature measurement using a thermistor in the pulmonary artery and an appreciation that it is the curve of a decrease in temperature versus time that is being analysed.
“vasovagal” vs orthostatic hypotension
A “vasovagal” is from excessive
autonomic reflex activity in contrast to orthostatic hypotension which is a failure of the autonomic reflex response.
examiners comments 2017 august Q19
description of vasovagal syncope
description of vasovagal syncope, also known as
neurocardiogenic syncope.
benign,
self-limiting
caused by an abnormal or exaggerated
autonomic response to various stimuli
examiners comments 2017 august Q19
definition of vasovagal syncope
Description:
Vasovagal syncope, or neurocardiogenic syncope, is a transient loss of consciousness due to global cerebral hypoperfusion, which occurs as the result of an autonomic reflex response to various stimuli
deranged 2017 august Q19
4 phases of vasovagal
Vagal: bradycardia
Sympathetic: systemic vasodilation (mainly muscles)
Vasovagal syncope is thought to have four distint phases:
phase 1: early stabilization (by normal baroreceptor reflex)
phase 2: circulatory instability (baroreflex vasoconstriction)
phase 3: terminal hypotension (bradycardia, cerebral hypoperfusion, systemic vasodilation)
phase 4: recovery
deranged 2017 august Q19
vasovagal effects on vagal and sympathetic
Vagal: bradycardia
Sympathetic: systemic vasodilation (mainly muscles)
deranged 2017 august Q19
Amount of blood in pulmonary vs systemic circulation
About 500ml, in a 70kg person
About 4500ml, in a 70kg person; of which the majority is in capacitance vessels
2017 march Q7 dranged specific answer
Normal PA systolic pressure
Normal PA diastolic pressure
Normal mean pulmonary arterial pressure
Normal PA systolic pressure = 18-25 mmHg
Normal PA diastolic pressure = 8-15 mmHg
Normal mean pulmonary arterial pressure = 9-16 mmHg
2017 march Q7 dranged specific answer
pulmonary vs systemic
compare resistance
pulmonary Low resistance;
PVR = 100-200 dynes.sec.cm-5
systemic
High resistance;
SVR = 900-1200 dynes.sec.cm-5
Trans-systemic intravascular pressure gradient is around 100 mmHg
2017 march Q7 deranged specific answer
pulmonary circulation
Regional distribution of blood flow
Blood flow is affected by
* gravity
* alveolar recruitment
* hypoxic vasoconstriction
Little active regulation occurs
2017 march Q7 deranged specific answer
Systemic circulation
Regional distribution of blood flow
Significant active regulation of organ-specific regional blood flow, depending on organ demand
Blood flow is less affected by gravity
2017 march Q7 deranged specific answer
pulmonary circulation response to hypoxia
Vasoconstriction
2017 march Q7 deranged specific answer
systemic circulation response to hypoxia
Vasodilation
2017 march Q7 deranged specific answer
pulmonary circulation response to hypercapnia
Vasoconstriction
2017 march Q7 deranged specific answer
systemic circulation response to hypercapnia
Vasodilation
2017 march Q7 deranged specific answer
metabolic functions of the lungs
Metabolic functions Metabolism of -hydroxytryptamine, prostaglandins and substrates for angiotensin-converting enzyme (bradykinin and angiotensin I)
2017 march Q7 deranged specific answer