The development of biomedical instrumentation using backscattered laser light.
This thesis is concerned with the measurement of blood flow
and oxygen saturation in the microcirculation using the
techniques of laser Doppler flowmetry and pulse oximetry.
An investigation of the responses of Doppler flowmeters
using different signal processing bandwidths and laser
sources revealed two major findings. Firstly, that careful
choice of processing bandwidth is required in order to
sample the whole range of possible Doppler frequencies
present in the backscattered light. Secondly, that the
choice of laser source is important in governing the output
stability of a flowmeter. Another investigation focused on
the evaluation of a dual channel laser Doppler flowmeter
using both in vitro and in vivo models. It was demonstrated
that the instrument permitted a useful method of obtaining
flow information by comparing simultaneous responses at
experimental and control sites.
The choice of laser wavelength was investigated in a study
to determine whether blood flow measurements are obtained
from different depths within the skin tissue. The results
indicate that some depth discrimination is obtainable using
instruments operating at different wavelengths, however it
is difficult to demonstrate the effect in vivo.
In a separate study it was shown that pressure applied to
the skin surface greatly affects the underlying blood flow.
It is recommended that care has to be taken when positioning
Doppler probes on the skin.
A reflection pulse oximeter was developed using laser light
backscattered from the skin. The instrument was evaluated in
vitro and in vivo by comparing desaturation responses with
a commercial transmission pulse oximeter. The reflection
oximeter was demonstrated to reliably follow trends in
oxygen saturation but several problems prevented instrument
Finally, a device combining laser Doppler flowmetry with
reflection pulse oximetry was developed and used in vivo to
follow trends in blood flow and oxygen saturation from the
same tissue sample.