ESTIMATING VENTRICULAR STROKE WORK FROM AORTIC
PRESSURE WAVEFORM
S.Kamoi1, C.G.Pretty1, Y.S.Chiew1, A.Pironet2, T.Desaive2, G.M.Shaw3, J.G.Chase1
of Mechanical Engineering, University of Canterbury, New Zealand
2GIGA
Cardiovascular Science, University of Liege, Belgium
3Intensive
Care Unit, Christchurch Hospital, New Zealand
1. Introduction
Ventricular Stroke Work (VSW) is an important
physiological parameter when assessing patient
cardiovascular performance. Decreased VSW
occurs during many states of cardiovascular
dysfunction. However, quantifying VSW normally
requires ventricular pressure and volume
measurements, which are highly invasive and
thus typically unavailable clinically. This research
presents a model-based analysis of aortic
pressure contours to estimate beat-to-beat VSW
trends through the aortic pressure-velocity
gradient (ρc).
Figure 2 shows a time-series of measured VSW
and estimated ρc during hemodynamic changes
induced via alterations to mechanical ventilation
pressure during an experiment (stepwise PEEP
recruitment maneuver).Clearly, ρc captures
trends in VSW very well.
The methods presented in this study show the
potential for continuous, accurate monitoring of
VSW trends by estimating pressure-velocity
relationship in the aortic compartment.
Importantly, this method only requires an aortic
pressure measurement, which is often available
in intensive care patients.
2. Methods
0.4
Figure 1 illustrates the method used for
identifying ρc from measured data for each beat.
Identify physiological parameters from
aortic pressure contour (τ = RC)
Separate Pao into excess and reservoir pressure
using identified parameters [1].
Identify Pulse Wave Velocity (PWV) using
Bramwell & Hill Equation [2].
Calculate pressure-velocity gradient, ρc in aortic
compartment using Joukowsky Equation [3].
Figure 1 - Schematic of estimation procedure
Data from porcine experiments were used to
validate the accuracy of ρc to estimate VSW
using measured ventricular pressures and
volumes.
3. Results and Discussion
The correlation coefficient between measured
VSW calculated from a Pressure-Volume loop
and model-based estimate of ρc from aortic
pressure showed good agreement with R = 0.71.
VSW (Joule)
Measured aortic pressure waveform (Pao)
0.35
2.4
VSW
pc
2.3
0.3
2.2
0.25
2.1
0.2
2
0.15
0.1
0
pc (kPas/m)
1Department
1.9
500
1000
1500
1.8
2000
Figure 2 – Time-series plot of measured VSW
and estimated pc from model based analysis of
aortic pressure contour
References
[1] S. Kamoi, et al., "Continuous stroke volume
estimation from aortic pressure using zero
dimensional aortic model," PLOS ONE, 9(7),
2014.
[2] J. C. Bramwell, et al., "The velocity of the
pulse wave in man," Proceedings of the Royal
Society of London. Series B, 93(652), 1922.
[3] A. S. Tijsseling et al., "The Joukowsky
equation for fluids and solids," Proceedings of
the 9th Intl. Conf. on Pressure Surges, 2004.
Keyword(s): biomechanics - biosignals
13th Belgian Day on Biomedical Engineering – joint meeting with IEEE EMBS Benelux Chapter
November 28, 2014