OxyFlo Pro User Manual
Revision 1.1 | May 2015
14
2.3
Laser Doppler flowmetry and the OxyFlo Pro
Laser Doppler Flowmetry (‘LDF’) is an established and reliable method for
the measurement of blood perfusion in microvascular research that in no
way harms or disturbs the normal physiological state of the microcirculation.
The OxyFlo Pro blood flow monitor implements this method by illuminating
tissue with low power laser light using a probe containing optical fibre light
guides. Laser light from one fibre is scattered within the tissue and some is
scattered back to the probe. A second optical fibre collects the
backscattered light from the tissue and returns it to the monitor. Most of the
light is scattered by tissue that is not moving but a small percentage of the
returned light is scattered by moving red blood cells. The light returned to
the monitor undergoes signal processing to extract the signal related to the
moving red blood cells.
Laser Doppler signals from the tissue are recorded in BPU (Blood Perfusion
Units) which is a relative units scale defined relative to a carefully controlled
motility standard comprising a suspension of latex spheres undergoing
Brownian motion.
Perfusion is also referred to as tissue blood flow, microvascular blood flow
or red blood cell flux.
In common with all LDF devices the OxyFlo Pro generates arbitrary, non-
absolute units of tissue blood flow since the tissue sampling volume cannot
be reliably established. Thus, LDF is best suited to observations of
continuous, acute changes in blood flow relative to a baseline (control)
obtained within the same experiment.
In other words, measurements obtained by LDF are intrinsically of a relative
nature; although such measurements are proportional to perfusion, the
factor of proportionality will be different for different tissues.
2.4
Measurement parameters generated by the OxyFlo Pro
The blood flow (BPU) parameter
The primary function of the OxyFlo Pro is to produce a tissue blood flow
output signal that is proportional to the red blood cell perfusion (or flux) in
the area of tissue being investigated. This represents the transport of blood
cells through the microvasculature and is defined as,
Tissue blood flow
=
Number of blood cells moving in
the tissue sampling volume
x
Mean
velocity of
these cells
Tissue blood flow therefore, is the product of mean blood cell velocity and
mean blood cell number (concentration) present in the measuring volume of
tissue under illumination from the probe.