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Understanding Ventricular
Pressure-Volume Calibration
and Experimental Design
Dr. Dimitrios "Jim" Georgakopoulos
Chief Scientific Officer,
Sunshine Heart, Inc.
InsideScientific is an online educational environment
designed for life science researchers. Our goal is to aid in
the sharing and distribution of scientific information
regarding innovative technologies, protocols, research
tools and laboratory services.
Today’s Lecture…
1. Introduction to PV
2. Starting with the end in mind
3. Stroke Volume Calibration
4. Parallel Volume Correction
5. What does it all mean?
Why Pressure Volume?
LV Volume (µL)
2520151050
LVPressure(mmHg)
0
50
100
ESPVR: Pes = 6.857 * Ves + 29.165, r² = 0.9909
EDPVR: Ped = 0.1509 * exp(0.1488 * Ved), r² = 0.9512
LV Volume (µL)
2520151050
LVPressure(mmHg)
0
50
100
• Intrinsic cardiovascular condition can be
assessed during changing load conditions
• Load-Independent can be data important
when making hemodynamic assessment of
conditions that may effect preload or
afterload.
• Multi-segments useful assessing
dysynchrony
• The only method which provides the gold
standard of diastolic function, EDPVR.
Catheter-based Pressure-Volume studies provide
global assessment of the heart and vascular system.
• Catheters consist of a single
pressure sensor and 4 or more
electrodes for volume
measurement
• Outer electrodes provide
excitation to the ventricle, inner
electrodes measure conductance
between them.
• During diastole, blood volume
increases and conductance
increases. Both decrease during
systole.
Introduction
to PV Theory
Conductance to Volume…
A
L
R r=
2
R
L
R
L
LLAV rr ===
L A
R = Resistance
V = Volume
r = Blood Resistivity
Ohm’s Law:
where…
I = current (constant)
V∞ R
Why must we
calibrate PV?
Location…
Location…
Location!
The necessity of calibration is derived from the
variability inherent to the measurement, and
variability between animals
• Catheter placement is the most important variable
• The composition of the myocardium can vary between every animal,
especially in in disease conditions.
• Can directly effect the electrical properties of the myocardium, and
by extension the measured conductance
• Calibration is important if done correctly, reduces variability of the
data minimizing the number of animals required to show an effect,
or lack of it.
Calibration of Volume Signal
 Reference methods as MRI, Echo, Angio
 Parallel conductance by hypertonic saline (provide EF)
 SV calibration flow probe, thermodilution
Start With The End In Mind
• Care should be taken to understand which
parameters are needed for your study.
– What physiological changes are taking place?
And what PV parameters reflect these changes.
• Relative changes may be sufficient, depending on
your experimental requirements
(eg. Testing effects of a drug, acute changes in PV)
• All parameters, except EF, can be derived from SV
calibration alone
– EDV, ESV, Max and Min Vol must be used as relative
measures without parallel volume correction
?
• First, we attempt to quantify how
changes in the volume of the blood
pool affect the measured
conductance
– Converts the measured conductance
changes to stroke volume
– Can be derived from blood resistivity
only, or can be made more accurate
with adjustment based on a known
Stroke Volume reference.
LV Volume (µL)
40353025201510
LVPressure(mmHg)
-40
-20
0
20
40
60
80
100
120
LV Volume (µL)
40353025201510
LVPressure(mmHg)
-40
-20
0
20
40
60
80
100
120
How do we calibrate PV?
Blood Resistivity
• The simplest method to calibrate volume
is using a set of reference blood volumes.
– Conductance is measured in a known
cylindrical volume, this relationship is
applied to the data.
– This is the most common method for
calibrating stroke volume.
• May not account for all of the variability
inherent to Pressure Volume recording
Blood Resistivity
• Well volumes are recorded in
your software and a calibration
curve can be calculated
Blood Conductance/Resistivity
• Blood conductance will rarely change…
However, it may not always be possible to do a blood
conductance measurement on every animal
– Multiple doses of a compound known to alter blood resistivity
– Effective calibration grouping should be considered when appropriate
• You may consider an adjustment based on a second
measure of known stroke volume
• Consider using a secondary measurement of
SV or CO to provide further validation of your
data accuracy
• These methods attempt to adjust the
recorded SV, with or without a resistivity
measurement, and match it with another
known stroke volume
• Can be derived from Transit-Time Ultrasound
measurement, thermodilution, or
echocardiography
• Linear or non-linear approaches can be used
based on your resources
Methods for SV Adjustment
• Assumes a linear relationship
between conductance and blood
volume
• Favored when an alternative SV
measure is available only as a
discrete or single-sample value
(Echo, Thermodilution, Transit-
Time Ultrasound) KnownPV SVSV /=
Methods for SV Adjustment
Linear SV Adjustment
Favored when an alternative
method for continuous SV
measurement is available
(Transit-Time Ultrasound)
Non-Linear SV adjustment is
foundational to admittance
systems, and can be another
approach to SV correction.
Linear SV Adjustment
Favored when an alternative
method for continuous SV
measurement is available
(Transit-Time Ultrasound)
Non-Linear SV adjustment is
foundational to admittance
systems, and can be another
approach to SV correction.
What is a Known SV?
• Consider that a SV correction attempts to
fit your PV loop data to a known SV
• Fitting all of your animals, or all animals in
a group to a single SV value will invalidate
this approach
• It is imperative to understand the
variability in SV among groups
– Disease conditions often present a varying
degree of change from control
– SV can only be considered an input that
increases accuracy in Pressure-Volume
data when the SV for the specific animal is
known
“range of SV in control
mouse strains is 14-26 μL”
Measurement of cardiac function using
pressure–volume conductance catheter
technique in mice and rats
Pál Pacher, Takahiro Nagayama, Partha Mukhopadhyay, Sándor Bátkai, and David A Kass
Nat Protoc. 2008; 3(9): 1422–1434.
• This is the most critical part of your
calibration
– All outputs parameters of your PV Loops
are affected
• If using only resistivity as the calibration,
consider if that value may be transiently
affected by your interventions
• If SV adjustment is to be used, ensure
that the SV applied to the fit is based on
reasonable assumptions
Considerations for SV Calibration
• Next, we attempt to remove any
offset in the measurement
– The largest offset in the
measurement is typically due to the
conductance of the myocardium
contributing to the measured signal
– Termed parallel conductance or
parallel volume
LV Volume (µL)
40353025201510
LVPressure(mmHg)
-40
-20
0
20
40
60
80
100
120
LV Volume (µL)
40353025201510
LVPressure(mmHg)
-40
-20
0
20
40
60
80
100
120
How do we calibrate PV
Increased Conductivity
x xx xxx
x x x x x
End-diastolic Volume (µL)
80604020
End-systolicVolume(µL)
20
30
40
50
Ves = 0.4484 * Ved + 12.926, r² = 0.9973
End-diastolic Volume (µL)
80604020
End-systolicVolume(µL)
20
30
40
50
Saline Bolus Injection
Saline Bolus Data Quality
PV Loop Demo.adicht
0
50
100
40
60
56:02 56:03 56:04 56:056 7
7/28/2011 11:57:50.839 AM
SalineBolus
LV Volume (µL)
706050403020
LVPressure(mmHg)
0
50
100
LV Volume (µL)
706050403020
LVPressure(mmHg)
0
50
100
Vp throughout the cardiac cycle
• Change in constant current parallel
conductance has been shown to be
minimal throughout the cardiac cycle
– E.B. Lankford, et. al “Does volume catheter parallel conductance
vary during the cardiac cycle,” Am. J. Physiol. Heart Circ. Physiol.
258: H1933-H1942, 1990.
• The time-varying method used can be
applied to conductance data if desired
• Later work has shown that complex
admittance (using AC excitation) does
change throughout the cardiac cycle
– Cl Wei, et.al “Evidence of time-varying myocardial contribution
by in vivo magnitude and phase measurement in mice,” IEEE
Eng Med Biol Soc. 2004;5:3674-7.
Vp throughout the cardiac cycle
• Change in constant current parallel
conductance has been shown to be
minimal throughout the cardiac cycle
– E.B. Lankford, et. al “Does volume catheter parallel conductance
vary during the cardiac cycle,” Am. J. Physiol. Heart Circ. Physiol.
258: H1933-H1942, 1990.
• The time-varying method used can be
applied to conductance data if desired
• Later work has shown that complex
admittance (using AC excitation) does
change throughout the cardiac cycle
– Cl Wei, et.al “Evidence of time-varying myocardial contribution
by in vivo magnitude and phase measurement in mice,” IEEE
Eng Med Biol Soc. 2004;5:3674-7.
Considerations for Parallel Volume
• Ejection Fraction (EF) is the most important value for
which the parallel volume adjustment is critical
• Degree of remodeling in disease conditions, along
with individual variation in heart morphology and
muscle fitness makes introduce variability between
animals.
• Repeated saline calibrations can be difficult in some
disease models.
• Saline can effect the utilization of calcium in the
myocardium
• Consider whether transient changes in Vp could be
present in your study LV Volume (µL)
40353025201510
LVPressure(mmHg)
-40
-20
0
20
40
60
80
100
120
LV Volume (µL)
40353025201510
LVPressure(mmHg)
-40
-20
0
20
40
60
80
100
120
SV
EDV
EF = SV/EDV
Other affected parameters: all absolute Volume Parameters (ESV, EDV, Max and Min Vol, etc. (relative changes still meaningful)
∙ ∙ ∙ ∙
1. Making Analysis and
Calibration selections:
- Linear Sections vs. Non Linear
2. Double Check
Pressure Calibration
at the study’s end
Other Accuracy Considerations
Summary
• Ultimately, this is a hugely powerful set of data
• Important to consider the ultimate goal of your study in making decisions
about study design
• Understand how the intervention you are making might change the
calibration values
• Consider the inputs of your calibration, where do they come from, and
how can you minimize variability?
• Choose your calibration procedure accordingly…try to be consistent
• No matter the procedure used, proper calibration should be your default
procedure and should be done for each experiment
Proven within the research community
Millar Mikro-tip catheters
and the conductance
method of calibration have
been tested and validated
as an accurate and
trustworthy combination
for research.
Click on publications
to view online…
Thank You!
For additional information on ADInstruments solutions
for pressure-volume loops, including Millar catheters,
Pressure-Volume Hardware and associated data
acquisition and analysis software please visit:
www.adinstruments.com/partners/millar

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Understanding Ventricular Pressure-Volume Catheter Calibrations and Experimental Design

  • 1. Understanding Ventricular Pressure-Volume Calibration and Experimental Design Dr. Dimitrios "Jim" Georgakopoulos Chief Scientific Officer, Sunshine Heart, Inc.
  • 2. InsideScientific is an online educational environment designed for life science researchers. Our goal is to aid in the sharing and distribution of scientific information regarding innovative technologies, protocols, research tools and laboratory services.
  • 3. Today’s Lecture… 1. Introduction to PV 2. Starting with the end in mind 3. Stroke Volume Calibration 4. Parallel Volume Correction 5. What does it all mean?
  • 4. Why Pressure Volume? LV Volume (µL) 2520151050 LVPressure(mmHg) 0 50 100 ESPVR: Pes = 6.857 * Ves + 29.165, r² = 0.9909 EDPVR: Ped = 0.1509 * exp(0.1488 * Ved), r² = 0.9512 LV Volume (µL) 2520151050 LVPressure(mmHg) 0 50 100 • Intrinsic cardiovascular condition can be assessed during changing load conditions • Load-Independent can be data important when making hemodynamic assessment of conditions that may effect preload or afterload. • Multi-segments useful assessing dysynchrony • The only method which provides the gold standard of diastolic function, EDPVR. Catheter-based Pressure-Volume studies provide global assessment of the heart and vascular system.
  • 5. • Catheters consist of a single pressure sensor and 4 or more electrodes for volume measurement • Outer electrodes provide excitation to the ventricle, inner electrodes measure conductance between them. • During diastole, blood volume increases and conductance increases. Both decrease during systole. Introduction to PV Theory
  • 6. Conductance to Volume… A L R r= 2 R L R L LLAV rr === L A R = Resistance V = Volume r = Blood Resistivity Ohm’s Law: where… I = current (constant) V∞ R
  • 7. Why must we calibrate PV? Location… Location… Location!
  • 8. The necessity of calibration is derived from the variability inherent to the measurement, and variability between animals • Catheter placement is the most important variable • The composition of the myocardium can vary between every animal, especially in in disease conditions. • Can directly effect the electrical properties of the myocardium, and by extension the measured conductance • Calibration is important if done correctly, reduces variability of the data minimizing the number of animals required to show an effect, or lack of it.
  • 9. Calibration of Volume Signal  Reference methods as MRI, Echo, Angio  Parallel conductance by hypertonic saline (provide EF)  SV calibration flow probe, thermodilution
  • 10. Start With The End In Mind • Care should be taken to understand which parameters are needed for your study. – What physiological changes are taking place? And what PV parameters reflect these changes. • Relative changes may be sufficient, depending on your experimental requirements (eg. Testing effects of a drug, acute changes in PV) • All parameters, except EF, can be derived from SV calibration alone – EDV, ESV, Max and Min Vol must be used as relative measures without parallel volume correction ?
  • 11. • First, we attempt to quantify how changes in the volume of the blood pool affect the measured conductance – Converts the measured conductance changes to stroke volume – Can be derived from blood resistivity only, or can be made more accurate with adjustment based on a known Stroke Volume reference. LV Volume (µL) 40353025201510 LVPressure(mmHg) -40 -20 0 20 40 60 80 100 120 LV Volume (µL) 40353025201510 LVPressure(mmHg) -40 -20 0 20 40 60 80 100 120 How do we calibrate PV?
  • 12. Blood Resistivity • The simplest method to calibrate volume is using a set of reference blood volumes. – Conductance is measured in a known cylindrical volume, this relationship is applied to the data. – This is the most common method for calibrating stroke volume. • May not account for all of the variability inherent to Pressure Volume recording
  • 13. Blood Resistivity • Well volumes are recorded in your software and a calibration curve can be calculated
  • 14. Blood Conductance/Resistivity • Blood conductance will rarely change… However, it may not always be possible to do a blood conductance measurement on every animal – Multiple doses of a compound known to alter blood resistivity – Effective calibration grouping should be considered when appropriate • You may consider an adjustment based on a second measure of known stroke volume
  • 15. • Consider using a secondary measurement of SV or CO to provide further validation of your data accuracy • These methods attempt to adjust the recorded SV, with or without a resistivity measurement, and match it with another known stroke volume • Can be derived from Transit-Time Ultrasound measurement, thermodilution, or echocardiography • Linear or non-linear approaches can be used based on your resources Methods for SV Adjustment
  • 16. • Assumes a linear relationship between conductance and blood volume • Favored when an alternative SV measure is available only as a discrete or single-sample value (Echo, Thermodilution, Transit- Time Ultrasound) KnownPV SVSV /= Methods for SV Adjustment
  • 17. Linear SV Adjustment Favored when an alternative method for continuous SV measurement is available (Transit-Time Ultrasound) Non-Linear SV adjustment is foundational to admittance systems, and can be another approach to SV correction.
  • 18. Linear SV Adjustment Favored when an alternative method for continuous SV measurement is available (Transit-Time Ultrasound) Non-Linear SV adjustment is foundational to admittance systems, and can be another approach to SV correction.
  • 19. What is a Known SV? • Consider that a SV correction attempts to fit your PV loop data to a known SV • Fitting all of your animals, or all animals in a group to a single SV value will invalidate this approach • It is imperative to understand the variability in SV among groups – Disease conditions often present a varying degree of change from control – SV can only be considered an input that increases accuracy in Pressure-Volume data when the SV for the specific animal is known “range of SV in control mouse strains is 14-26 μL” Measurement of cardiac function using pressure–volume conductance catheter technique in mice and rats Pál Pacher, Takahiro Nagayama, Partha Mukhopadhyay, Sándor Bátkai, and David A Kass Nat Protoc. 2008; 3(9): 1422–1434.
  • 20. • This is the most critical part of your calibration – All outputs parameters of your PV Loops are affected • If using only resistivity as the calibration, consider if that value may be transiently affected by your interventions • If SV adjustment is to be used, ensure that the SV applied to the fit is based on reasonable assumptions Considerations for SV Calibration
  • 21. • Next, we attempt to remove any offset in the measurement – The largest offset in the measurement is typically due to the conductance of the myocardium contributing to the measured signal – Termed parallel conductance or parallel volume LV Volume (µL) 40353025201510 LVPressure(mmHg) -40 -20 0 20 40 60 80 100 120 LV Volume (µL) 40353025201510 LVPressure(mmHg) -40 -20 0 20 40 60 80 100 120 How do we calibrate PV
  • 22. Increased Conductivity x xx xxx x x x x x End-diastolic Volume (µL) 80604020 End-systolicVolume(µL) 20 30 40 50 Ves = 0.4484 * Ved + 12.926, r² = 0.9973 End-diastolic Volume (µL) 80604020 End-systolicVolume(µL) 20 30 40 50 Saline Bolus Injection
  • 23. Saline Bolus Data Quality PV Loop Demo.adicht 0 50 100 40 60 56:02 56:03 56:04 56:056 7 7/28/2011 11:57:50.839 AM SalineBolus LV Volume (µL) 706050403020 LVPressure(mmHg) 0 50 100 LV Volume (µL) 706050403020 LVPressure(mmHg) 0 50 100
  • 24. Vp throughout the cardiac cycle • Change in constant current parallel conductance has been shown to be minimal throughout the cardiac cycle – E.B. Lankford, et. al “Does volume catheter parallel conductance vary during the cardiac cycle,” Am. J. Physiol. Heart Circ. Physiol. 258: H1933-H1942, 1990. • The time-varying method used can be applied to conductance data if desired • Later work has shown that complex admittance (using AC excitation) does change throughout the cardiac cycle – Cl Wei, et.al “Evidence of time-varying myocardial contribution by in vivo magnitude and phase measurement in mice,” IEEE Eng Med Biol Soc. 2004;5:3674-7.
  • 25. Vp throughout the cardiac cycle • Change in constant current parallel conductance has been shown to be minimal throughout the cardiac cycle – E.B. Lankford, et. al “Does volume catheter parallel conductance vary during the cardiac cycle,” Am. J. Physiol. Heart Circ. Physiol. 258: H1933-H1942, 1990. • The time-varying method used can be applied to conductance data if desired • Later work has shown that complex admittance (using AC excitation) does change throughout the cardiac cycle – Cl Wei, et.al “Evidence of time-varying myocardial contribution by in vivo magnitude and phase measurement in mice,” IEEE Eng Med Biol Soc. 2004;5:3674-7.
  • 26. Considerations for Parallel Volume • Ejection Fraction (EF) is the most important value for which the parallel volume adjustment is critical • Degree of remodeling in disease conditions, along with individual variation in heart morphology and muscle fitness makes introduce variability between animals. • Repeated saline calibrations can be difficult in some disease models. • Saline can effect the utilization of calcium in the myocardium • Consider whether transient changes in Vp could be present in your study LV Volume (µL) 40353025201510 LVPressure(mmHg) -40 -20 0 20 40 60 80 100 120 LV Volume (µL) 40353025201510 LVPressure(mmHg) -40 -20 0 20 40 60 80 100 120 SV EDV EF = SV/EDV Other affected parameters: all absolute Volume Parameters (ESV, EDV, Max and Min Vol, etc. (relative changes still meaningful)
  • 27. ∙ ∙ ∙ ∙ 1. Making Analysis and Calibration selections: - Linear Sections vs. Non Linear 2. Double Check Pressure Calibration at the study’s end Other Accuracy Considerations
  • 28. Summary • Ultimately, this is a hugely powerful set of data • Important to consider the ultimate goal of your study in making decisions about study design • Understand how the intervention you are making might change the calibration values • Consider the inputs of your calibration, where do they come from, and how can you minimize variability? • Choose your calibration procedure accordingly…try to be consistent • No matter the procedure used, proper calibration should be your default procedure and should be done for each experiment
  • 29. Proven within the research community Millar Mikro-tip catheters and the conductance method of calibration have been tested and validated as an accurate and trustworthy combination for research. Click on publications to view online…
  • 30. Thank You! For additional information on ADInstruments solutions for pressure-volume loops, including Millar catheters, Pressure-Volume Hardware and associated data acquisition and analysis software please visit: www.adinstruments.com/partners/millar