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|Title: ||Non-invasive vascular assessment using photoplethysmography|
|Authors: ||Crabtree, Vincent P.|
|Issue Date: ||2003|
|Publisher: ||© Vincent Peter Crabtree|
|Abstract: ||Photoplethysmography (PPG) has become widely accepted as a valuable clinical tool
for performing non-invasive biomedical monitoring. The dominant clinical application
of PPG has been pulse oximetry, which uses spectral analysis of the peripheral blood
supply to establish haemoglobin saturation. PPG has also found success in screening for
venous dysfunction, though to a limited degree.
Arterial Disease (AD) is a condition where blood flow in the arteries of the body is
reduced,a condition known as ischaernia. Ischaernia can result in pain in the affected
areas, such as chest pain for an ischearnic heart, but does not always produce symptoms.
The most common form of AD is arteriosclerosis, which affects around 5% of the population over 50 years old. Arteriosclerosis, more commonly known as 'hardening of the arteries' is a condition that results in a gradual thickening, hardening and loss of
elasticity in the walls of the arteries, reducing overall blood flow. This thesis investigates the possibility of employing PPG to perform vascular assessment, specifically arterial assessment, in two ways. PPG based perfusion monitoring may allow identification of ischaernia in the periphery. To further investigate this premise, prospective experimental trials are performed, firstly to assess the viability of PPG based perfusion monitoring and culminating in the development of
a more objective method for determining ABPI using PPG based vascular assessment. A complex interaction between the heart and the connective vasculature, detected at the
measuring site, generates the PPG signal. The haemodynamic properties of the
vasculature will affect the shape of the PPG waveform, characterising the PPG signal
with the properties of the intermediary vasculature. This thesis investigates the
feasibility of deriving quantitative vascular parameters from the PPG signal. A
quantitative approach allows direct identification of pathology, simplifying vascular assessment. Both forward and inverse models are developed in order to investigate this topic. Application of the models in prospective experimental trials with both normal subjects and subjects suffering PVD have shown encouraging results.
It is concluded that the PPG signal contains information on the connective vasculature
of the subject. PPG may be used to perform vascular assessment using either perfusion based techniques, where the magnitude of the PPG signal is of interest, or by directly
assessing the connective vasculature using PPG, where the shape of the PPG signal is of
it is argued that PPG perfusion based techniques for performing the ABPI diagnosis
protocol can offer greater sensitivity to the onset of PAD, compared to more
conventional methods. It is speculated that the PPG based ABPI diagnosis protocol
could provide enhanced PAD diagnosis, detecting the onset of the disease and allowing a treatmenpt lan to be formed soonert han was possible previously. The determination of quantitative vascular parameters using PPG shape could allow
direct vascular diagnosis, reducing subjectivity due to interpretation. The prospective trials investigating PPG shape analysis concentrated on PVD diagnosis, but it is speculated that quantitative PPG shaped based vascular assessment could be a powerful tool in the diagnosis of many vascular based pathological conditions.|
|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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