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Author
Date
2019Type
- Doctoral Thesis
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Abstract
Patients suffering from heart failure cannot provide sufficient cardiac
output for organ perfusion, such that effective medical treatment is
required. Three therapies for the treatment of heart failure have been
clinically established: pharmacological treatment, heart transplantation,
and implantation of a left-ventricular assist device (LVAD). Despite
the efficacy of these therapies, survival rates remain unsatisfactorily
low. The continuous monitoring of hemodynamic parameters can
improve survival, as it supports timely and effective clinical decision
making. The hemodynamics of the healthy heart are very sensitive to
the left-ventricular (LV) volume. Hence, the LV volume is a promising
hemodynamic parameter for clinical decision making. In addition, an
LV volume measurement could be used for physiological feedback control
of an LVAD, presumably increasing his or her quality of life and
reducing the probability of adverse events. The aim of this thesis was
to identify key requirements for an LV volume sensor, investigate possible
measurement principles and evaluate the three most promising
sensor concepts in terms of their sensitivity and accuracy.
The LV volume cannot easily be measured remotely, because the
requirements for a real-time portable sensor are highly complex. An
LV volume sensor needs to be implemented in such a way that traumatic
injury is avoided and the areas of foreign surfaces in the body
are not increased. The sensor should be small enough to be safely
implanted or attached to the body surface. The LV volume measurement
should be continuous and robust to changes in heart geometry,
posture or hematocrit. Computer tomography, magnetic resonance
imaging, various forms of impedance measurement, pressure measurement,
echocardiography and strain sensors have been proposed to estimate
the LV volume. However, none of them meets all of the above
requirements. An implantable, biocompatible and robust LV volume
sensor remains to be developed.
Three concepts for the real-time LV volume measurement are proposed
in this thesis: Acoustic resonance, ultrasonic distance and the
QRS amplitude of the electrocardiogram. The concepts were evaluated
in a testing environment suitable to their current stage of development:
in-silico, in-vitro, in-vivo and in the setting of an experimental
clinical study. All measurement priniciples were sensitive to the
LV volume. The achievable LV volume accuracies were assessed using
a Bland-Altman analysis. The accuracies for the acoustic concept
could not be evaluated as the principle was only assessed in-silico and
lacked the possibility to account for noise. The ultrasonic distance approach
yielded estimation accuracies for the LV volume smaller than
20% in human heart phantoms in vitro. The QRS-amplitude in vivo
measurement rendered LV volume estimation accuracies smaller than
20%. The experimental clinical study revealed a small, but significant
correlation between the QRS amplitude on the body surface and the
mean pulmonary arterial pressure.
The three concepts presented are all atraumatic, small enough, capable
of real-time measurement and should be sufficiently robust as
they can be placed close to the heart. The QRS amplitude is the most
promising concept to be implemented in the near future, particularly
because of the electrode size. The ultrasonic distance measurement is
equally convincing in terms of accuracy, but requires more effort for
miniaturization and efficient data processing. The influence of hematocrit
changes on both measurement principles should be investigated
carefully in subsequent studies. In conclusion, continuous measurement
of LV volume is possible and will likely increase survival rates in
heart failure patients in the future. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000339587Publication status
publishedExternal links
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Contributors
Examiner: Meboldt, M
Examiner: Leonhardt, Steffen
Examiner: Hayward, Christopher
Examiner: Schmid Daners, Marianne

Publisher
ETH ZurichSubject
Sensor; Cardiac; Hemodynamic monitoring; Implantable devices; Ventricular assist device (VAD)Organisational unit
03943 - Meboldt, Mirko / Meboldt, Mirko
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