Comparison of the effect of multiwavelength light produced by a cluster of semiconductor diodes and of each individual diode on mast cell number and degranulation in intact and injured skin
Authors: El Sayed Salah O. , Dyson Mary 
Published: March 2007

Intact skin and partial thickness wounds in adult male Wistar rats were irradiated by pulsed, monochromatic light of different spectral wavelength peaks simultaneously and the effects on mast cell number and degranulation were assessed. The light was produced by a Biotherapy 3ML (Omega Universal Technologies) device utilizing a 21 semiconductor diode cluster probe emitting 6 different wavelengths in the red and near infrared part of the spectrum simultaneously, only one of the wavelengths (820 nm) being coherent. The duration of treatment was 4 minutes. The average power density, distributed over the surface area of the probe (19.62 cm2) was 45 mW/cm2. The average energy density at the wound site was 10.8 J/cm2. The effect of each of the wavelengths incorporated in the cluster probe was then examined separately. The average power density for each single probe was 120 mW/cm2, except for the 820 nm diode which was 400 mW/cm2. The average energy density was maintained at 10.8 J/cm2 as with the cluster probe. After 2 hours the rats were killed and the skin was removed, processed for light microscopy, and stained with tolu‐idine blue to identify the mast cells. The numbers of the intact and degranulated mast cells were counted in 100 high power fields (i.e., over a total area of 20 mm2) in each irradiated specimen and compared to the sham‐irradiated and untreated groups. To avoid bias, the slides examined were coded and evaluated blind. In intact skin, the cluster probe irradiation was followed by a statistically significant increase in the total number of mast cells compared to the sham‐irradiated group, but the percentage of the degranulated mast cells was not affected. In the partial thickness wound, the cluster probe. irradiation was also followed by a statistically significant increase in the total number of mast cells compared to the sham‐irradiated group; however, there was, in addition, a significant increase in the percentage of degranulated mast cells. Concerning the single probes, only the 660, 820, 940, and 950 nm wavelength emitters produced statistically significant increases in both mast cell number and degranulation in partial thickness wounds. However, when intact skin was irradiated with probes emitting these wavelengths, although the total number of mast cells was increased significantly, there was no change in degranulation compared with the sham‐irradiated group. The effects observed were less than those of the cluster probe. No significant differences were found between the 870 and 880 nm wavelength‐irradiated, sham‐ irradiated, and untreated groups in either intact or injured skin. Since the cluster probe produced a rise in temperature of about 1.8°C in 4 minutes, the effect of the same rise in temperature over the same duration of time was investigated on mast cells in both intact and injured skin. It was found that this level of heating did not produce any statistically significant effects on either mast cell number or on mast cell degranulation.