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|Title: ||Artefact reduction in photoplethysmography|
|Authors: ||Hayes, Matthew J.|
|Keywords: ||Biomedical monitoring|
|Issue Date: ||1998|
|Publisher: ||© Matthew James Hayes|
|Abstract: ||The use of optical techniques in biomedical monitoring and diagnosis is becoming
increasingly widespread, primarily because of the non-invasive nature of optically
derived measurements. Physiological analysis is usually achieved by characterisation
of the spectral or temporal properties of the interaction between light and the
anatomy. Although some optical measurements require complex instrumentation and
protocols, recent technological advances have resulted in robust and compact
equipment that is now used routinely in a multitude of clinical contexts.
Unfortunately, these measurements are inherently sensitive to corruption from
dynamic physical conditions or external sources of light, inducing signal artefact.
Artefact is the primary restriction in the applicability of many optical measurements,
especially for ambulatory monitoring and tele-medicine.
The most widely used optical measurement is photoplethysmography, a technique
that registers dynamic changes in blood volume throughout the peripheral vasculature
and can be used to screen for a number of venous disorders, as well as monitoring the
cardio-vascular pulse wave. Although photoplethysmographic devices are now
incorporated into many patient-monitoring systems, the prevalent application is a
measurement known as pulse oximetry, which utilises spectral analysis of the
peripheral blood to estimate the arterial haernoglobin oxygen saturation. Pulse
oximetry is well established as an early warning for hypoxia and is now mandatory
under anaesthesia in many countries. The problem of artefact is prominent in these
continuous monitoring techniques, where it is often impossible to control the physical
conditions during use.
This thesis investigates the possibility of reducing artefact corruption of
photoplethysmographic signals in real time, using an electronic processing
methodology that is based upon inversion of a physical artefact model. The
consequences of this non-linear artefact reduction technique for subsequent signal
analysis are discussed, culminating in a modified formulation for pulse oximetry that
not only has reduced sensitivity to artefact but also possesses increased generality.
The design and construction of a practical electronic system is then used to explore
both the implementation issues and the scope of this technique. The performance of
artefact reduction obtained is then quantified under realistic experimental conditions,
demonstrating that this methodology is successful in removing or reducing a large
proportion of artefact encountered in clinically relevant situations.
It is concluded that non-linear artefact reduction can be applied to any
photoplethysmographic technology, reducing interpretation inaccuracies that would
otherwise be induced by signal artefact. It is also speculated that this technology
could enable the use of photoplethysmographic systems in applications that are
currently precluded by the inherent severity of artefact.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Mechanical, Electrical and Manufacturing Engineering)|
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