Skin Penetration Time-Profiles for Continuous 810 nm and Superpulsed 904 nm Lasers in a Rat Model

Abstract

Objective: The purpose of this study was to investigate the rat skin penetration abilities of two commercially available low-level laser therapy (LLLT) devices during 150 sec of irradiation. Background data: Effective LLLT irradiation typically lasts from 20 sec up to a few minutes, but the LLLT time-profiles for skin penetration of light energy have not yet been investigated. Materials and methods: Sixty-two skin flaps overlaying rat's gastrocnemius muscles were harvested and immediately irradiated with LLLT devices. Irradiation was performed either with a 810 nm, 200 mW continuous wave laser, or with a 904 nm, 60 mW superpulsed laser, and the amount of penetrating light energy was measured by an optical power meter and registered at seven time points (range, 1-150 sec). Results: With the continuous wave 810 nm laser probe in skin contact, the amount of penetrating light energy was stable at *20% (SEM -0.6) of the initial optical output during 150 sec irradiation. However, irradiation with the superpulsed 904 nm, 60 mW laser showed a linear increase in penetrating energy from 38% (SEM -1.4) to 58% (SEM -3.5) during 150 sec of exposure. The skin penetration abilities were significantly different ( p < 0.01) between the two lasers at all measured time points. Conclusions: LLLT irradiation through rat skin leaves sufficient subdermal light energy to influence pathological processes and tissue repair. The finding that superpulsed 904 nm LLLT light energy penetrates 2-3 easier through the rat skin barrier than 810 nm continuous wave LLLT, corresponds well with results of LLLT dose analyses in systematic reviews of LLLT in musculoskeletal disorders. This may explain why the differentiation between these laser types has been needed in the clinical dosage recommendations of World Association for Laser Therapy.

Photobiomodulation with Pulsed and Continuous Wave Near-Infrared Laser (810 nm, Al-Ga-As) Augments Dermal Wound Healing in Immunosuppressed Rats

“…It has been further revealed that LLLT in PW mode can better penetrate through the melanin and other skin barriers, supporting the hypotheses that pulsing is beneficial in reaching deep target tissue and organs [25]. Some recent studies have demonstrated that PW mode is advantageous over the CW mode, particularly, in the context of repair of deep tissue injuries and stroke management [25–27]. Ilic et al, reported that pulsed light produced no neurological or tissue damage, whereas an equal power density delivered by CW caused marked neurological deficits [28].…”

Effectiveness of low-level laser therapy in patients with knee osteoarthritis: a systematic review and meta-analysis

“…The penetrability of certain wavelengths varies in different tissues. According to Joensen et al 36 , the amount of penetrating light energy is 20% for a wavelength of 810 nm and 58% for a wavelength of 904 nm. King et al 37 found that the penetration of laser irradiation into skin is limited to a few millimeters.…”

Low-Level Laser Therapy with 810 nm Wavelength Improves Skin Wound Healing in Rats with Streptozotocin-Induced Diabetes

“…From this perspective, the use of an infrared laser is justified, because of its greater depth of penetration. 26,27 The relationships between basic LLLT parameters and their relationships to wound healing are still not fully understood; therefore, the optimal wound type-specific treatment has not yet been determined. In an open wound model, we have previously shown that LLLT at wavelengths 635 and 670 nm was more effective when higher intensity was combined with shorter wavelength and/or lower intensity was combined with higher wavelength.…”