Download BME lecture 6 - pv loops (Sept 14, 2004)

BME Class (Lecture 6 – LV pressure-volume relationship)
September 14, 2004
Lecture #6 - Left Ventricular Pressure-Volume Relationship - (September 14, 2004)
A. P-V Loop
(a) Phase I (D – Diastolic Filling) - blood passively fills from atrium into ventricle,
followed by additional volume due to atrial contraction. Characteristics:
mitral/tricuspid valve open and aortic/pulmonic valve closed, low pressure changes,
high volume changes.
(b) Phase II (IC - Isovolumic Contraction) - Ventricle contracts generating high pressure
level within the ventricle. Characteristics: mitral/tricuspid valve and aortic/pulmonic
valve closed, high pressure changes, no volume changes.
(c) Phase III (EJ - Ejection) - Pressure in ventricle now higher than aorta/pulmonary
artery, opening aortic/pulmonic valve and blood flow to arterial system occurs.
Characteristics: mitral/tricuspid valve closed and aortic/pulmonic valve open, low
pressure changes, high volume changes.
(d) Phase IV (IR - Isovolumic Relaxation) - Ventricle relaxes. Characteristics:
mitral/tricuspid and aortic/pulmonic valves closed, high pressure changes
(decreases), and no volume changes.
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BME Class (Lecture 6 – LV pressure-volume relationship)
September 14, 2004
End - Systolic Elastance
Left Ventricular
Pressure, mmHg
Pes
Increasing
Elastance
External
Work
Diastolic Elastance
Vo
Stroke Volume
Ved
Ventricular Volume, cc
Figure 6-1. Illustration of key landmarks for the left ventricular pressure-volume loop, where Pes = left
ventricular end-systolic pressure; Vo = left ventricular volume at 0 mmHg; and Ved = left ventricular enddiastolic volume. The area inside the P-V loop represents the external work of the ventricle.
Figure 6-2. Illustration of key landmarks for the left ventricular pressure-volume relationship. The PV
loops are generated by performing a vena cava occlusion to reduce pre-load to the heart. The slope of
the line tangent to the PV loop at end-systole is called the End-Systolic Pressure Volume Relationship
(ESPVR or Ees) that has been used as a load independent index of ventricular contractility.
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BME Class (Lecture 6 – LV pressure-volume relationship)
September 14, 2004
Ea
Pes
Ees
EW
Vo
SV
Ved
Figure 6-3. Illustration of key landmarks for the left ventricular pressure-volume loop, where Pes = left
ventricular end-systolic pressure; Vo = left ventricular volume at 0 mmHg; and Ved = left ventricular enddiastolic volume. The area inside the P-V loop represents the external work of the ventricle.
Cardiovascular Coupling Theory:
(1) To maximize power transfer Ees = Ea
(2) Does the heart function to ‘maximize’ or ‘optimize’ power transfer?
REFERENCES:
Koenig SC, DL Ewert, DA Ludwig, JW Fanton, and VA Convertino. Effects of fluid
shifts during bed rest confinement on left ventricular and systemic arterial elastances.
Aviat. Space Environ. Med., 75:7-15, 2004.
Ewert DL, B Wheeler, C Doetkott, C Ionan, GM Pantalos, and SC Koenig. The effect
of heart rate, preload, and afterload on the visco-elastic properties of the swine
myocardium. Ann. Biomed. Eng. (in press).
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BME Class (Lecture 6 – LV pressure-volume relationship)
September 14, 2004
2. Applications
A. Heart Failure
Figure 6-4. Illustration of difference in P-V loops for normal and failing heart. In top figure, heart failure is
induced by (1) betablocker and (2) Monensin.
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BME Class (Lecture 6 – LV pressure-volume relationship)
September 14, 2004
B. Ventricular Assist Devices (VAD)
Figure 6-5. Comparison of pressure-volume loops between a normal and failing left ventricle (LV) without
assistance and a failing LV assisted by an (a) artificial vasculature device (AVD), and (b) continuous
(CVAD) and (c) asynchronous pulsatile (PVAD) flow ventricular assist devices. Unlike VAD, the AVD
produces counterpulsation to the circulation as can be seen in left ventricular (LVP) and aortic (AoP)
pressure waveforms (d).
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BME Class (Lecture 6 – LV pressure-volume relationship)
September 14, 2004
100
90
LV pressure (mm Hg)
80
70
60
baseline
cVAD 50%
cVAD 100%
50
40
30
20
10
0
0
50
100
150
200
250
300
350
400
450
LV volume (ml)
80
70
LV pressure (mm Hg)
60
50
40
baseline failure
75% bypass
100+% bypass
30
20
10
0
-10
-20
0
50
100
150
200
250
LV volume (ml)
Figure 6-6. Comparison of pressure-volume loops in calves with normal (top) and failing ventricles
(below) during continuous flow (CF) ventricular assist device (VAD) support at 75% and 100% bypass.
Notice that in normal ventricle model, the only effect is a leftward shift of PV loop.
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BME Class (Lecture 6 – LV pressure-volume relationship)
September 14, 2004
Assignment #6 – For each of the 5 data sets from lecture 4 assignment, plot the left
ventricular pressure-volume relationship and calculate the stroke volume and external
work of the ventricle. Again, indicate whether the heart is normal/failure, supported by
an assist device, and/or whether the therapy is effective. NOTE: LVV = left ventricular
volume and LVP = left ventricular pressure.
*Assignment 6 due in class on Tuesday, September 21, 2004
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