Research
LASER DOPPLER FLOMMETRY
Introduction
Laser Doppler
flowmetry is a new technique used in other species to measure microcirculatory
blood flow in many different tissues. We have adapted this technique to measure
laminar microcirculatory blood flow within the hoof wall in the standing,
non-sedate horse. This technique is physiologic, is non-invasive, and permits
continuous measurement of microcirculatory blood flow. Of particular bearing are
the facts that laser Doppler flowmetry is non-invasive and that the disease is
ultimately occurring at the microcirculatory level.
Principle of Technique
Laser doppler flowmetry (LDF) is a non-invasive,
continuous measure of microcirculatory blood flow. Laser doppler flowmetry has
been used to measure microcirculatory blood flow in many tissues including
neural, muscle, skin, bone and intestine. The principle of this method is to
measure the Doppler shift - the frequency change that light undergoes when
reflected by moving objects, such as red blood cells. Laser doppler flowmetry
uses monochromatic light emitted from a low power laser. The light emitted and
reflected is fed through optical fibers from the target to the
analyzer-recorder. Measurement of the RBC motion is recorded continuously in the
outer layer of the tissue under study, with little or no influence on
physiologic blood flow. This output value constitutes the flux of red cells,
defined as the number of red cells times their velocity and is reported as
microcirculatory perfusion units. 
No
direct information concerning oxygen, nutrient or waste metabolite exchange in
the surrounding tissue is obtained with this technique. The relationship between
the flowmeter output signal and the flux of red blood cells, is linear. The beam
can penetrate unbroken, non-pigmented tissue to a depth of 1-2 mm. We have
adapted this technique to measure laminar microcirculatory blood flow in the
standing, non-sedate horse.
Current Areas of Research
Currently our research is directed toward the study of
founder in the horse. Founder is a severely crippling and many times fatal
disease. Even though there are many different causes of founder, death of the
laminae, resulting from low blood flow within the hoof, ultimately leads to the
signs that are seen. The most critical time in the development of founder is
from the time of the insult to the time that clinical sign's first appear. This
is the time when treatment must be started to stop the horse from foundering.
Treating a horse that is already showing clinical signs is often times
unrewarding. Documenting the changes in blood flow during the development of
founder has been a challenge. This is partly because the hoof vessels are
encased within the hoof wall and are inaccessible. Various techniques, using the
live horse, have been used to study hoof blood flow during the development of
founder. Although important information has been gathered, these techniques do
not allow for the continuous, non-invasive measurement of blood flow. 
Changes
in the digital pulses and coronary band temperature during the development of
founder suggest that the blood flow changes are dynamic. It is believed that a
period of little or no blood flow occurs before clinical signs occur. Knowing
when this period of low blood flow occurs would allow us to more effectively
treat and perhaps prevent the horse from foundering. We have adapted LDF to
measure laminar microcirculatory blood flow within the hoof wall in the
standing, non-sedate horse. This technique is physiologic, is non-invasive,
non-painful and permits continuous measurement of microcirculatory blood flow.
Of particular bearing are the facts that laser Doppler flowmetry is non-invasive
and that the disease is ultimately occurring at the microcirculatory level.
Evaluation of the changes that occur during the development of laminitis is
critical for identifying effective treatments and applying them at the
appropriate time.
Henry
S. Adair, M.S., D.V.M.
Associate Professor of Surgery
Diplomate of the American College of Veterinary Surgeons