LASER DOPPLER FLOMMETRY
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..
S. Adair, M.S., D.V.M.
Associate Professor of Surgery
Diplomate of the American College of Veterinary Surgeons