Cutaneous Laser Doppler Flowmetry: Applications and Findings
Section snippets
NEED FOR NONINVASIVE TESTING OF CBF
A noninvasive, objective means of assessing CBF is important in the evaluation of vasospasm, ischemia, wound and ulcer healing, postoperative survival of grafts, therapeutic trials, and various pathologic conditions. The ideal technique should be reliable and inexpensive as well as provide a direct measurement of CBF. Unfortunately, currently available objective measurements, including arteriography, electromagnetic flow probes, radioactive microsphere deposition, quantitative fluorometry, and
CURRENT METHODS FOR TESTING CBF
The currently available tests for assessing CBF are summarized in Table 1. Each method relies on different physiologic principles; most tests are indirect indices of flow. Of note, LDF is the only technique for direct CBF measurement. Radioisotope washout is specific for CBF but is invasive, indirect, and unamenable to the study of small areas of tissue because of regional averaging. The inability of washout techniques to measure flow in small and discrete regions of skin is a particular
THEORY OF LDF AND CONTROVERSIES
The theory of LDF is that the emitted laser light penetrates tissue to a depth that is dependent on the light frequency. The light is reflected after it strikes either immobile or moving tissues; the portion of this light reflected from moving blood cells undergoes a Doppler shift.17 By sampling all reflected light, the device can calculate flux of erythrocytes within the sample volume.17, 18, 19 Flux is calculated by multiplying the percentage of reflected light returning from moving blood
APPLICATIONS
Throughout the years, a wide variety of clinical applications have been developed for LDF, most for assessing CBF. Disagreements about the technique have resulted from an earlier lack of understanding about the variables that LDF actually detects and how to control for them.
Cutaneous microvascular diseases can be categorized into vasospastic diseases and fixed arterial obstructive diseases.
CONCLUSION
LDF measures Doppler-shifted quantities of reflected laser light at a superficial level to determine cutaneous and noncutaneous microcirculatory flux of erythrocytes, a perhaps useful measure of blood flow and volume. It is noninvasive and inexpensive and has been in clinical use since 1977. Early conclusions about LDF were unfavorable because of comparisons against inadequate standards and a poor understanding of the microvascular physiology. Elements such as rapid and frequent fluctuations in
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