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Cardiac Pressure – Volume Relationship

Scisense Inc. (Canada)

The Theory and Significance of PV Loop Measurements

The Theory and Significance of PV Loop Measurements

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OVERVIEW

1. Background on Pressure-Volume (PV) Loops

2. Critical Analyses that can be performed

3. Application examples

4. Conductance technique as a method of measuring volume

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Background on Scisense

• Founded in 2002 to develop high fidelity pressure and pressure-volume sensors

• Products are manufactured in Canada and sold worldwide

• Minimally invasive tools for hemodynamic research:

– catheters for ventricular pressure, volume and ECG

– amplifiers & acquisition systems– analysis software

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Pressure Volume Loop

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What the Reviewers Say:

“When perusing the literature….if the ESPVR was not measured, I would personally ignore the article”

Source: William J. Mazzei, M.D. Lecture notes,Cardiac Physiology and Monitoring, July 18, 1999 (www.imhotep.net/lecture3.html)

Source: William J. Mazzei, M.D. Lecture notes,Cardiac Physiology and Monitoring, July 18, 1999 (www.imhotep.net/lecture3.html)

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Requirements for PV Loops

• High fidelity pressure measurements

• Ability to alter pre-load or after-load

• LV volume measurements (choose one:)– Conductance catheter (real time, load independent)– Sonomicrometer (invasive, for larger animals)– Echocardiography (cost, off-line, time resolution,

operator dependent)– MRI (cost, difficult, off-line analysis)

• Data Acquisition & Analysis Software

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Typical PV Catheter

Scisense1.2F

Millar1.4F

Photo Courtesy of: Dr. Marc Feldman, M.D., University of Texas at San Antonio

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PV Loop Parameters

Variable Description Variable Description Variable Description

HR Heart Rate Vmax Maximum Volume

CO Cardiac Output

Pmax Maximum Pressure

Vmin Minimum Volume

EF Ejection Fraction

Pmin Minimum Pressure

ESV End-Systolic Volume

dP/dt max

Maximum dP/dt

Pdev Developed Pressure

EDV End-Diastolic Volume

dP/dt min

Minimum dP/dt

ESP End-Systolic Pressure

SV Stroke Volume

dV/dt max

Maximum dV/dt

EDP End-Diastolic Pressure

SW Stroke Work dV/dt min

Minimum dV/dt

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PV Loop Parameters

• Stroke Work = Area in PV Loopo Work done by the ventricle to eject a volume of

blood

• Stroke Volume (SV) = EDV - ESVo Amount of blood ejected by the ventricle during each

beato Affected by changes in preload, afterload, inotropyo Failing hearts - SV highly sensitive to afterload

changes

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PV Loop Parameters

• Cardiac Output (CO) = SV x heart rateo Amount of blood pumped out by the LV in unit time

• Ejection Fraction (EF) = (SV/EDV) x100o Fraction of the End Diastolic Volume that is ejectedo Used as a clinical indicator of cardiac contractilityo Normal EF > 60%o Severe heart failure - EF < 20%o Low EF usually indicates systolic dysfunction

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PV Loop Parameters

• dP/dtmin & dP/dtmax

o Min and max rate of pressure change in LVo Requires high fidelity LV pressure measurementso Increase in contractility - increased dP/dtmax during

isovolumic contractiono dP/dtmin used in the calculation of Tau

• Isovolumic Relaxation Constant (Τau)o Index of diastolic function that is relatively load

independento Used in evaluation of heart failureo Requires high fidelity LV pressure measurements

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Types of PV Loop Analysis

•ESPVR – End Systolic Pressure-Volume Relationship

•EDPVR – End Diastolic Pressure-Volume Relationship

•Frank Starling Curve

•PRSW – Preload Recruitable Stroke Work

•Pressure-Volume Area (PVA) Analysis

•Effective Arterial Elastance (Ea)

•ESPVR – End Systolic Pressure-Volume Relationship

•EDPVR – End Diastolic Pressure-Volume Relationship

•Frank Starling Curve

•PRSW – Preload Recruitable Stroke Work

•Pressure-Volume Area (PVA) Analysis

•Effective Arterial Elastance (Ea)

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End Systolic Pressure Volume Relationship (ESPVR)

• changes in load alter the slope of the ESPVR

• Provides an index of myocardial contractility and systolic function

• Load independent, therefore better index than EF, CO or SV

• curve becomes steeper and shifts to the left as inotropy increases.

ESPVR = Maximal pressure developed by the ventricle for any given LV volume:ESPVR = Maximal pressure developed by the ventricle for any given LV volume:

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End Diastolic Pressure Volume Relationship (EDPVR)

Slope of EDPVR line is the reciprocal of Ventricular Compliance

Decreased Compliance = Ventricular Hypertrophy

Increased Compliance = Dilated Cardiomyopathy

EDPVR = Passive Filling Curve for the VentricleEDPVR = Passive Filling Curve for the Ventricle

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Frank Starling Curves

• If EDV increases, there is a corresponding increase in stroke volume, suggesting heart failure and inotropy

• Reduced stroke volume suggests increased preload and decreased ejection fraction

Ability of the heart to change force of contraction in response to changes in venous return

Ability of the heart to change force of contraction in response to changes in venous return

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Preload Recruitable Stroke Work (PRSW)

• Slope of PRSW line is a highly linear index of myocardial contractility

• NOT SENSITIVE to preload and afterload

Describes the relationship between stroke work and end-diastolic volume. Describes the relationship between stroke work and end-diastolic volume.

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Pressure Volume Area Analysis

• PVA = PE + SW

• Correlates with myocardial oxygen consumption (MVO2)

• Used to calculate cardiac efficiency and the energy requirements of the heart

Represents total mechanical energy generated by ventricular contractionRepresents total mechanical energy generated by ventricular contraction

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Effective Arterial Elastance

• Study of the interaction between the heart and the arterial system ventriculo-arterial coupling

• Ea characterizes both the ventricular and arterial systems in terms of pressure and stroke volume

A measure of Arterial Load (Ea = ESP/SV)A measure of Arterial Load (Ea = ESP/SV)

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Application Example Cardiomyopathies

LVP

(mm

Hg)

LVV (uL)

EDPVR:

ESPVR: Slope maintainedRightward Shift

Increased SlopeSW

Decreased

Restrictive

LVP

(mm

Hg)

LVV (uL)

EDPVR:

ESPVR: Decreased SlopeRightward Shift

Rightward Shift

SWDecreased/

Normal

Dilated

LVP

(mm

Hg)

LVV (uL)

EDPVR:

ESPVR: Increased SlopeLeftward Shift

Leftward Shift

SWDecreased

Hypertrophic

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PV loop Measurement Technique

• Miniature catheter advanced through the carotid artery into the Ventricle.

• Four metal rings on the catheter used for volume measurement

– Constant current applied acrossoutside 2 electrodes

– Voltage change across inside electrodes corresponds to conductance change

• Baan’s equation (1980’s) used to calculate volume

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Volume Cuvettes for Calibration

• Alternate method to determine true volume from conductance

• Conductance measurements made in known volumes of saline

• Saline conductivity matched to blood conductivity

• Directly relates measured conductance to absolute volume

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Volume Measurement - Theory

• Gmeas = Gblood + Gp

• Gp is parallel conductance of muscle and must be removed to estimate volume

• Hypertonic saline bolus injection– Conductance signal increases

– Gb-ED & Gb-ES both increase

• Conductivity of blood changes but not the conductivity of the muscle

23GEDV

GES

V

Gp

Hypertonic Saline Injection

• GEDV & GESV graphed on X-Y scatter plot

• Slope line superimposed on line of identity

• Point of intersection ofboth lines indicates parallel conductance (Gp)

• This technique can bedifficult in small animals like mice and rats

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NEW!! ADVantageTM System(only from Scisense Inc.)

• No more saline bolus

• No volume cuvette calibration

• Real time feedback on catheterposition in the LV

• Parallel conductance is subtracted in real time for more accurate volumes

• Absolute blood volumes are obtained– Lower standard deviation– Fewer animals required– Saves time and money

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Conclusion

•ESPVR – End Systolic Pressure-Volume Relationship•EDPVR – End Diastolic Pressure-Volume Relationship•Frank Starling Curve•PRSW – Preload Recruitable Stroke Work•PVA - Pressure-Volume Area Analysis•Ea - Effective Arterial Elastance

•ESPVR – End Systolic Pressure-Volume Relationship•EDPVR – End Diastolic Pressure-Volume Relationship•Frank Starling Curve•PRSW – Preload Recruitable Stroke Work•PVA - Pressure-Volume Area Analysis•Ea - Effective Arterial Elastance

The Study of PV Loops is an extremely useful method of assessing cardiac function and is being demanded by Peer Reviewers around the world

The Study of PV Loops is an extremely useful method of assessing cardiac function and is being demanded by Peer Reviewers around the world