In the last decade the applications of the laser in surgery and medicine have increased dramatically. With the increase of indications has come a concomitant increase in possible classification of laser reactions. The author presents a classification which is based on the laser/tissue reaction rather than on the hardware used to produce the laser beam. Laser/tissue reactions fall into two broad groups. When the tissue reaction to absorption of the incident laser energy results in photodestruction of, or an irreversible photomodulated change to the tissue architecture, then the level of reaction is higher than the survival threshold of the target cells. The author refers to this as high reactive-level laser treatment (HLLT), or more generally as laser surgery. On the other hand, the level of tissue reactivity to very low incident power and energy densities is well below the cells’ survival threshold so that instead of being damaged the cells are directly activated by the low incident photon density. In this case the changes in the irradiated tissue are photoactivative and reversible: the author refers to this group of reactions as low reactive-level laser therapy (LLLT), or more generally as laser therapy. Both of these groups can be classed under the general heading of laser treatment (LT). LT is further subdivided into three main types: mono-type LT (Mo-LT, single laser treatment; multi-type LT (Mu-LT, multi-laser treatment); and concomitant LT (Cc-LT), in which any of the above LT types can be used in combination with conventional treatment methods. Mo-LT in turn contains pure LT (Pu-LT) single laser, single reaction; and auto-simultaneous LT (ASi-LT), single laser with a range of reaction types, each of which has its own abbreviation. Mu-LT contains two main sub-types, combined LT (Cb-LT) and compound LT (Cp-LT). Cb-LT concerns the same disease whereas Cp-LT is used to describe 2 or more diseases treated with the same or different lasers. Both Cb-LT and Cp-LT are further subclassified into the homogeneous and xenogeneous types, referring to the use of the same or different types of laser, respectively. If the lasers are applied at the same time, that is homo- or xeno-simultaneous laser treatment (HoSi-LT, XeSi-LT), and if at different times the term is homo- or xeno-succesive laser treatment (HoSu-LT, XeSu-LT). The various sub-sets of Mono-type and Multi-type laser treatment are further expanded, to give an accurate, treatment-based categorization of laser treatment. In addition to the above classification, the author has devised a graphical representation of laser surgical and therapeutic beams whereby the laser type, parameters, penetration depth, and tissue reaction can all be shown in a single illustration, which the author has termed the ‘Laser Apple’, due to the typical pattern generated when a laser beam is incident on tissue. Apple types fall into two main subdivisions, destructive or D-Apples (HLLT) which include the C-Apple (carbonization), V-Apple (vaporization) and so on, and the activative or A-Apple type (LLLT). When the above classification is combined and illustrated with the appropriate laser apple type or types, the author feels this offers an accurate and simple method of classifying laser/tissue reactions by the reaction, rather than by the laser used to produce the reaction.

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Extracellular field potentials were recorded in the stratum pyramidale of CA3 in hippocampal slices prepared from male Sprague-Dawley rats. Electrical stimuli were delivered to s. radiatum of CA3. After stable responses were established, stimulus trains were delivered every 5 mm until stable triggered and spontaneous population bursts were elicited. The slices were then irradiated with a low power (25 mW) argon laser. No changes in the morphology or number of epileptiform bursts were found while the laser was on. However, when the laser was turned off, there was a highly significant reduction in frequency and morphology of bursts. These results indicate that exposure to light alters epileptiform activity within the hippocampus in vitro, and provides evidence indicating that the central nervous system is photosensitive.

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Macrophage-like U-937 cells were exposed in vitro to noncoherent 660 nm wavelength light produced by a superluminous diode at a power density of 120 mW/cm² over a range of energy densities from 2.4 - 9.6 J/cm². Twelve hours after irradiation, the medium in which the macrophages had been growing and which contained growth factors secreted by them was added to 3T3 fibroblasts, also growing in vitro, and its effect on fibroblast proliferation assessed. It was found that by 96 h after addition of the macrophage-conditioned medium there was a statistically significant increase in fibroblast proliferation in the cells exposed to supernatants from the experimental compared with the sham-irradiated macrophages. The most effective energy density was found to be 7.2 J/cm² and the least effective 9.6 J/cm².

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Chemiluminescence (CL) of peripheral blood from the same donor was recorded after irradiation with various individual laser and superluminous diodes (660, 820, 880 and 950 nm, pulse repetition rates 16, 292 and 5000 Hz) during two periods of acute viral respiratory illness and in normal conditions of health. It was found that precise and statistically significant effects of laser radiation on CL (suppression of the CL) depend on wavelength, pulse repetition rate and dose and can be recorded only in the period of acute illness (i.e. at a certain immunological status of the organism) and there are practically no effects of laser radiation when the blood of a healthy donor is irradiated. The optimal irradiation parameters for suppression of free radical processes in human blood were as follows: dose range 10³-10⁴ J/m2, pulse repetition rate 292 and 5000 Hz (16 Hz was ineffective). All wavelengths under study had the effect but λ = 660 nm was found to be most effective (65% of CL was suppressed).

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The increasing use of phototherapy (for example in wound healing) has led to a great interest in the mechanism of light-biosystem interaction. Therefore, recent observations on the enhancement of the proliferation of irradiated skin cells (fibroblasts and keratinocytes) by visible light are important to understand phototherapy at the cellular level. In the present communication we show that at the doses appropriate for enhanced fibroblast proliferation, HeNe irradiation produces transiently increasing calcium concentration in the target cells. Fibroblasts were irradiated with 1, 3 and 5 J/cm²HeNe (633 nm) laser and intracellular Ca²⁺ concentration ([Ca²⁺ ]i) in single cells was analyzed by Fluo-3/AM using a dynamic video imaging system with frame-grabbing soft ware. Such observations can explain photobiostimulation because of the well-known vital role played by calcium in important biological processes such as proliferation and exocytosis.

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Low-level Laser Therapy (LLLT) has been suggested as an effective adjuvant in the healing of bone fractures. However, the mechanisms of the effects of laser bioactivation on tissue are still not completely clear. The present study was designed and performed to investigate the effect of LLLT doses of CO₂ laser irradiation on the bone healing of rabbits that had undergone bilateral mandibular hole-like osteotomies. The calcium, phosphorus and collagen hydroxyproline contents in the bone callus were determined respectively on different postoperative days. After exposure to a CO₂ laser beam at a power density of 225 mW/cm², it was demonstrated that the calcium, phosphorus and hydroxyproline quantities in the irradiated side bone callus were significantly higher than the contralateral unirradiated control callus. This may partially explain the bioeffects of LLLT on the speed and quality of bone repair. It is concluded that LLLT using theCO₂ laser has the potential of promoting metabolism and mineralization of bone callus, thus accelerating bone healing.

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The mechanism by which laser phototherapy (Low Level Laser Therapy - LLLT) induces analgesia in the treatment of chronic pain is not understood. To investigate a possible role for opioids in this treatment, a double-blind, placebo-controlled study was designed to compare the effect of two dosages (1 J/cm₂ and 5 J/cm₂) of an infrared (IR) laser (820 nm), a visible red laser (670 nm) and a near-monochromatic light emitting device (660 nm, 30 nm bandwidth) on trigger points. Fifty-six consenting subjects with chronic pain conditions exhibiting myofascial trigger points in the neck and upper trunk region underwent six experimental sessions over a two week period. Blood samples were withdrawn before and after treatment on three of six appointments. Plasma was assayed for β-endorphin (radioimmunoassay, RIA) and adrenocorticotropic hormone (ACTH - two-site immunoradiometric assay, IRMA) to assess opioid response. ACTH was shown to have a cumulative response to treatment with a significant response to a 1 J/cm₂ infrared laser (p ‹ 0.001) and a 5 J/cm² red laser (p ‹ 0.05). β-endorphin was noted to be significantly elevated between days one and four (p ‹ 0.05) in subjects who received IR (5 J/cm²) laser therapy. Results indicated that the analgesic response to phototherapy may be mediated through hormonal/opioid mechanisms, and that responses to LLLT are dose and wavelength dependent. A mechanism is proposed by which peripheral stimulation using LLLT may elicit activity in the central pathways.

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A laser speckle flowmetry technique has been developed to enable visualization of the distribution of skin blood flow and has been used to measure the microcirculation in various angiopathies as well as to monitor blood flow changes and other haemodynamics in skin flaps. The principal author’s institute has recently acquired such a laser speckle flowmetry system. The present preliminary study was designed to test the efficacy of the gallium aluminium arsenide (GaAlAs) diode laser on flap survival in the rat model using laser speckle flowmetry. Caudal-based random pattern flaps were raised on the back of two groups of Wistar rats, 10 rats in each group. The first group served as the control and underwent sham irradiation, otherwise they were handled in exactly the same way as the second group. The blood flow in all flaps was measured with laser blood flowmetry using the laser speckle method. Blood flow was measured in the flaps of the experimental animals and the unirradiated controls preirradiation, and the flaps were sutured back in place. The experimental group received laser irradiation from a GaAlAs diode laser (60 mW, 830 nm, continuous wave) for one minute on a point at the centre of the flap base (energy density ≅ 36 J/cm²). Laser speckle flowmetry was then performed on all animals immediately postirradiation and 30 minutes postirradiation. The following points were noted. There was no significant change in the flow rate of the flaps in the unirradiated animals. Immediately following the one minute irradiation in the experimental animals a decrease in the blood flow rate was seen compared with the unirradiated controls, but at 30 minutes postirradiation the blood flow rate in the flaps increased in the irradiated animals compared with controls. Five days postirradiation the survival area of the diode laser irradiated flaps was greater than the control flaps (≅1.12 : 1). It was concluded that GaAlAs diode LLLT increased early perfusion of the experimental flaps, thereby possibly accelerating early stage wound repair while at the same time controlling the inflammatory response, thus giving the irradiated flaps a better and earlier ‘take’.

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Postherpetic neuralgia (PHN) can be an extremely painful condition which in many cases proves resistant to all the accepted forms of treatment. It is frequently most severe in the elderly and may persist for years with no predictable course. This trial was designed as a double blind assessment of the efficacy of low level laser therapy (LLLT) with an 830 nm diode laser in the relief of the pain of PHN with patients acting as their own controls. Admission to the trial was limited to patients with established PHN of at least six months duration and who had shown little or no response to conventional methods of treatment. Measurements of pain intensity and distribution were noted over a period of eight treatments in two groups of patients each of which received four consecutive laser treatments. The results demonstrate a significant reduction in both PHN pain intensity and distribution following a course of LLLT.

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The clinical use of low reactive level laser therapy (LLLT) has been reported in several aspects of bioactivation. This study reports an investigation into the possible application of LLLT for the treatment of male infertility. Four azoospermic and 16 oligospermic male patients were treated with a 6 mW HeNe12.5 mW pulsed GaAs diode laser with a dose of 1.3 i/cm2. Although no improvement was noted in the azoospermic subjects. the sperm count increased from 2 to 5 times in the oligospermic subjects. In addition, ejaculation of abnormal spermatozoa decreased in several subjects. Libido also increased in 15 of the 20 patients. From these findings it was concluded that LLLT offers a possible treatment for the oligospermic patient, particularly for the subfertile.

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Degenerative joint disease (DJD), in particular in the knee, is difficult to cure successfully at present, often requiring surgical intervention. In addition, the chronic DJD patient often exhibits symptoms of both a physiological and psychological nature. A study is presented using low reactive-level laser therapy (LLLT) with an 830 nm infrared continuous wave gallium aluminium arsenide (GaAlAs) diode laser, with an output power of 60 mW, in light contact laser therapy for a population of 40 patients (incident power density of approximately 3 W/cm²). Four points around the patella were irradiated for 60 s each (energy density of 180 J/cm² per point) two sessions per week for eight weeks. Radiological, pain score and joint mobility assessments were made before the first session, immediately after, and at 4 months after the final LLLT session. All other medication and physical therapy was discontinued at least 15 days prior to the first treatment session. Thirty-three patients (82%) reported significant removal of pain and recovery of articular joint mobility. The remaining seven patients felt there was no significant effect following LLLT, and returned to their original pretherapy medication. The side effects were minimal. LLLT is concluded to be a safe, effective and noninvasive alternative to conventional surgical and medical treatment modalities for DJD patients.

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In rehabilitative training and treatment of patients with cerebral palsy, return and maintenance of good muscle tonicity and suppression of tonic muscle spasm is crucial. However, an effective method that is reliable, simple, painless and noninvasive has yet to be reported. In the present study, 150 cerebral palsy patients were treated on their limbs and trunk with infrared diode low reactive-level laser therapy (LLLT) (810 nm. 60 mW and 100 mW, continuous wave). The treatment sites were those normally associated with conventional therapies such as nerve block or acupuncture, and where muscular hyperspasm was particularly evident. In the majority of the patients, spasm was successfully suppressed by LLLT, with the notable exception of those patients suffering from severe joint contracture. Compared with conventional methodology, laser therapy has proved to be a simple, reliable and noninvasive method which enabled painless suppression of spasm. Another of the advantages of LLLT is that multiple repeated application is possible on any site selected by the physician, with an almost unlimited choice of treatment sites. The effect of LLLT lasted from one to several hours in patients with severe spasticity. Although it may be argued that this variable length of effect is one of the limitations of LLLT, the authors feel that LLLT is particularly useful as a supplementary or adjunctive therapeutic modality to improve the overall efficacy of physical rehabilitation and functional training in children with cerebral palsy.

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The purpose of this randomized, double-blind study was to examine the effect of GaAs laser therapy for tendinitis and myofascial pain in a sample from the general population of Åkersberga in the northern part of Greater Stockholm. 176 patients (of an original group of 200) completed the scheduled course of treatment. The patients were assigned randomly to either a laser group (92 patients, of whom 74 had tendinitis, completed the study) or a placebo group (84 patients, of whom 68 had tendinitis, completed the study). All 176 patients received six treatments during a period of 3-4 weeks. Their pain was estimated objectively using a pain threshold meter, and subjectively with a visual analogue scale before, at the end of, and four weeks after the end of treatment. Laser therapy had a significant, positive effect compared with placebo measured from the first assessment to the third assessment, four weeks after the end of treatment. Laser treatment was most effective on acute tendinitis.

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