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13.1 Are all the negative lllt studies really negative? |
The authors of this book have performed an analysis of a number of frequently cited studies on the effects of low-power-laser therapy. In many of these studies, analysis uncovered one or more reasons for the negative findings reported, the most common being the use of extremely low doses. Other reasons are: faulty inclusion criteria, inaccurate control group definition, ineffective methods of therapy, inadequate attention to systemic effects and tissue condition, and low power density. A weakness often encountered in these studies is their failure to provide sufficient data on laser parameters. Since negatively inclined studies such as these are often quoted as "proof" of the ineffectiveness of LLLT, it is important that they be subjected to a proper critical analysis. 1.400 articles were reviewed for this analysis, the emphasis being on double-blind studies. Of the 135 localised double-blind studies, 85 reported positive findings. Though important, the critical examination of scientific literature is decidedly unglamorous. It involves hours and days of searching through a wide variety of different sources, and by no means all information is yet available on-line. There are numerous pitfalls, too, especially for those who opt to read abstracts only - criticism of sources is impossible unless an article can be studied in its entirety. Basing an opinion from abstracts obtained from e.g. Medline is risky. In addition, only a minority of the early LLLT research reports are available from the major databases. In the following analysis of the available literature, we have chosen to analyse those studies unable to demonstrate the effectiveness of LLLT. Although priority was given to double-blind studies, non-double-blind studies were also included in certain typical cases. Certain studies were also included merely on the grounds that they are among the most frequently cited. The 1.400 articles reviewed for this analysis are now being stored in computerised form. |
"I heard it through the grapewine" |
A recognisable pattern is often distinguishable in the bibliographies accompanying scientific reports. The manner in which these patterns arise goes something like this: Researcher A is the man or woman behind some pioneering achievement and is therefore extensively quoted by researcher B, as well as by C, D, E and several others. Researcher K, however, is content to read what E has written about A and B, while researcher Z treats the work of A and B as a simple historical reference point previously described by researcher P. And, like a rumour, word spreads: everyone knows about A, B and C, but no-one has actually read their published work. Although generally known, therefore, older studies are not always relevant and it may sometimes be rewarding to go back and review them in detail. Often, especially in the light of new findings, the impression given is quite unlike that suggested in later, second-hand reports. |
Positive from negative |
Having traditionally concentrated on studies positive to LLLT, over the last few years we found ourselves becoming more and more interested in those studies with a negative spin: provided they have been properly carried out, they may be able to show us the parameters that do not appear to work. Naturally, negative reports must always be taken seriously, but the fact that a given study has been unable to demonstrate the effectiveness of LLLT does not necessarily mean that the method studied is incapable per se of producing results within the indication in question. All that it shows is that the parameters selected for the study were not sufficiently effective. Therefore, it is illogical to conclude that LLLT is ineffective simply because no effect was reported in that particular study. A number of studies reporting negative results are marred by such startling illogicality. |
Negative from negative |
LLLT is a relatively young science that has only just emerged from
its Sturm und Drang period, and it might perhaps be unfair to criticise
the earlier negative studies. Many medical researchers then had - and
indeed still have - a rather diffuse knowledge of physics, and qualified
books on the physics of laser therapy were long in appearing. In many
cases, the only information available to researchers on doses, methods
of treatment and suitable indications came from the manufacturers or
agents, while over-optimistic, ignorant salesmen often laid traps that
would ensnare both themselves and the researchers. |
Important parameters |
A. Wavelength That biological effect is significantly related to the wavelength of the light emitted by the laser has been demonstrated in numerous studies. Today, the wavelengths most commonly used for therapeutic purposes are 633 nm (HeNe lasers), 635 nm, 650 nm, 660 nm, 670 nm (InGaAIP lasers), 780 nm, 820 nm, 830 nm (GaAIAs lasers), 904 nm (GaAs lasers), and 10600 nm (CO2 lasers). Except for GaAs and CO2 lasers, all these lasers usually produce a continuous beam but may also be pulsed. |
B. Dose The most important parameter in LLLT is always the dose, often referred to as "fluence". By dose (D) is meant the energy (E) of the light directed at a given unit of area (A) during a given session of therapy. The energy is measured in J (joules), the area in cm2, and, consequently, the dose in J/cm2. Mathematically, this may be expressed as follows: E D = ---- [J/cm2] A Assuming that the power (P) output of the laser probe remains constant during treatment, the energy (E) of the light will be equal to the power multiplied by the time (t) during which the light is emitted. The dose may then be calculated as follows: P t D = ---- [J/cm2] A Sometimes, however, the power output is not constant, such as when the laser is pulsed or modulated, which may be achieved in several ways. The preferred method of pulsing a HeNe laser is to use some form of mechanical switching device or shutter, such as a rotating pierced disc, the useful proportion of the time during which light is emitted by the laser normally being fixed at a given value (duty cycle), most often 50%. In other words, light is permitted to pass through the disc for 50% of the total operating time (and is blocked for the remaining 50%). This enables use of the concepts of mean power (Pm) and maximum power. In the example given here, the mean power is 50% of the maximum power. If the laser is pulsed at mean power, the above formula will apply, giving: Pm t D = ------- [J/cm2] A GaAs lasers always pulse, the duration of each pulse being extremely short, and in these lasers the maximum power is always much, much greater than the mean power. This type of pulsing is often referred to as super-pulsing. In GaAs lasers, the duration of the pulse is normally in the region of 100-200 ns (nanoseconds) and the maximum power is typically 1 - 20 W (watts). Assuming, for example, that the duration of the pulse is 150 ns and that the maximum power is 10 W, each pulse emitted by the laser will have an energy of 1.5 µ J (microjoules). If the laser emits 100 such pulses per second (a pulse frequency of 100 Hz), its mean power output will be 0.15 mW (milliwatts). A pulse frequency of 1000 Hz gives a mean output of 1.5 mW, etc. In other words, the mean power output varies with the number of pulses emitted per second. By applying these relationships, it is often possible to obtains doses or other parameters not explicitly stated in the article under review. |
C. Power density Typical traditional laser instruments |
Dose development |
Pitfalls |
1. Low outputs In the following we review some of the studies in which low dose can plainly be identified as the most significant negative factor. We have also listed the parameters that we consider should always be specified in studies of this nature. It is not unusual for an author to criticise previous studies for inadequate specification of parameters, then himself to be found guilty of the same sort of omission. In the following examples, the parameters are summarised in tabular form. It should be noted that the power output is here to be understood as mean output on pulsing, since this is the figure required in order to calculate the dose. |
Author: | Waylonis G.W. et al: | Ref no: [E6] | |
Title: | Chronic Myofascial Pain: Management by Low-Output Helium-Neon Laser Therapy. | ||
Published in: | Arch Phys Med Rehab. 1988; 69: 1017-1020. | ||
Laser type: | HeNe-laser (633 nm) | Output: | Not specified |
Pulsing: | Not specified | Pulse frequency: | Not specified |
Dose: | Not specified | ||
Power density: | Not specified | Treatment distance: | Not specified |
Laser model: | Dynatron (model 1120), with fiberoptics | ||
Treated area: | All together 12 acupuncture points | ||
Treatment time: | 15 sek per point | No of patientes: | 62 |
No of treatments: | 2 x 5 (6 weeks inbetween) | Time between treatm: | Not specified |
Our comments: This study is frequently quoted. No dose is specified. However, other sources state that the tube output of the HeNe laser (Dynatron 1120) is less than 1 mW. Assuming that losses in the fibre-optic set-up reduce this to 0.5 mW, and given an irradiation time per point of 15 seconds, the dose will be 0.5 mW x 15 sec = 0.0075 J. Since a normal dose today is 0.5 - 2 J per acupuncture point and 1 - 4 J per trigger point, it is hardly surprising that no significant effect was observed. And since the instrument used can be pulsed, the dose and the effect may actually have been reduced still further. The study is said to have been double-blind, although there is no description of how this was achieved. This would, in fact, have been valuable information, since double-blind studies are normally quite difficult to carry out with HeNe lasers - they use red, visible light that is immediately distinguishable from conventional red light by its characteristic laser speckles. |
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Author: | Jensen H. et al: | Ref no: [E7] | |
Title: | Is Infrared laser effective in painful arthroses of the knee? | ||
Published in: | Ugeskr L¾ ger. 1987; 149: 3102-3106. | ||
Laser type: | GaAs-laser (904 nm) | Output: | 0,3 mW |
Pulsing: | Yes. 200 ns puls width | Pulse frequency: | 190-250 Hz |
Dose: | Not specified | ||
Power density: | Not specified | Treatment distance: | Not specified |
Laser model: | Space Laser IR CEB | ||
Treated area: | All together 4 points per knee | ||
Treatment time: | 180 sek per point | No of patientes: | 29 |
No of treatments: | 5 | Time between treatm: | 1 day |
Our comments: Although the dose is not explicitly stated, approximate figures may be calculated from other data. The power output is given as 0.3 mW, although in Space's instruments (as in many other GaAs lasers), the output is directly proportional to the pulse frequency. At 1000 Hz, these Space instruments usually produce an output of 1 mW. The pulse frequency interval is stated as being 195 - 250 Hz. On the basis of the power output stated, the dose may be estimated as 0.0003 W x 3 x 60 sec = 0.054 J. Four points were treated on each knee, giving a total dosage per session of 0.2 J. This dose is totally inadequate for a part of the body as large as the knee. This was a double-blind cross-over study. |
Author: | Basford J R et al: | Ref no: [E9] | |
Title: | Low-energy Helium Neon laser treatment of thumb osteoarthritis. | ||
Published in: | Arch Phys Med Rehab. 1987; 68: 794-797. | ||
Laser type: | HeNe-laser (633 nm) | Output: | 0.9 mW |
Pulsing: | Continuous | Pulse frequency: | - |
Dose: | Not specified | ||
Power density: | Not specified | Treatment distance: | Not specified |
Laser model: | Dynatronics (modell not specified), via fiberoptics | ||
Treated area: | 4 different points around 3 joints (All together 12 points) | ||
Treatment time: | 180 sek per point | No of patientes: | Not specified |
No of treatments: | 9 | Time between treatm: | Not specified |
Our comments: Assuming that the fibre loss is about 50%, the dose will here be 15 sec x 0.9 mW x 0.50 = 0.007 J per point. No obvious effect can be expected from such a low dose. This was a single-blind study. |
Author: | Taube S et al: | Ref no: [E10] | |
Title: | Helium-neon laser therapy in the prevention of postoperative swelling and pain after wisdom tooth extraction | ||
Published in: | Proc. Finn Dent Soc. 1990 (86) 1: 23-27 | ||
Laser type: | HeNe-laser (633 nm) | Output: | 8 mW (tube) |
Pulsing: | Pulsed | Pulse frequency: | 50 Hz |
Dose: | Not specified | ||
Power density: | Not specified | Treatment distance: | Not specified |
Laser model: | Biotronical Laser MC-8 | ||
Treated area: | Not specified | ||
Treatment time: | 120 sek before suturing and day 2 | No of patientes: | 17 |
No of treatments: | 2 | Time between treatm: | 24 hrs |
Our comments: Assuming a 50% fibre loss and a 50% pulsing loss, the total dose will be 2 mW x 120 sec x 2= 0.48 J. This is a low total dose for such major surgery. Also the number of treatments are low. |
Author: | Lundeberg T, Haker E, Thomas M | Ref no: [E11] | |
Title: | Effect of laser versus placebo in tennis elbow | ||
Published in: | Scand J Rehab Med. 1987; 19: 135-138. | ||
Laser type: | HeNe-laser (633 nm) | Output: | 1.56 mW |
Pulsing: | Continuous | Pulse frequency: | - |
Laser type2: | GaAs-laser (904) | Output: | 0.07 mW |
Pulsing: | Pulsed | Pulse frequency: | 73 Hz |
Dose: | 0.09 J/point (HeNe), 0,004 J/point (GaAs) | ||
Power density: | Not specified | Treatment distance: | 1 mm |
Laser model: | Modell was not specified, nor if fiberoptics was used | ||
Treated area: | 10 different acupuncture points through a 1 mm transparent plastic disc | ||
Treatment time: | 60 sek per point | No of patientes: | 82 |
No of treatments: | 10 per point | Time between treatm: | 2 treatm / week |
Our comments: The doses are so low that significant effects can hardly be expected. |
Author: | Masse J-F et al | Ref no: [E12] | |
Title: | Effectiveness of soft laser treatment in periodontal surgery | ||
Published in: | Internat Den J. 1993; 43: 121-127. | ||
Laser type: | HeNe-laser (633 nm) | Output: | 0.27 mW |
Pulsing: | Continuous | Pulse frequency: | - |
Laser type2: | GaAs-laser (904 nm) | Output: | 0.8 mW |
Pulsing: | Pulsed, 200 ns pulse width | Pulse frequency: | 47.5-3040 |
Dose: | Not specified | ||
Power density: | Not specified | Treatment distance: | 1 mm |
Laser model: | Stomalaser, independent measuring of power | ||
Treated area: | Not specified | ||
Treatment time: | 2 min 30 sek | No of patientes: | 28 |
No of treatments: | 1 | Time between treatm: |
Our comments: In this report, the authors studied the effect of combined HeNe/GaAs therapy on bilateral free autogenous gingival grafts and, commendably, performed independent measurement of the output specified by the manufacturer. The HeNe output, specified as 4 mW, proved actually to be 2 mW and a mere 0.27 mW after sustaining heavy losses in the fibre-optic rig. The maximum peak power output of the GaAs laser, given as 2 watts, was found to be only 0.8 watts. The size of the area treated is not specified, but assuming it was 1 cm2, the dose will be 0.0022 J/cm2 GaAs, plus 0.04 J/cm2 HeNe, that is, a total dose of 0.0422 J/cm2. Further, a single treatment is not likely to give significant results. |
Author: | Smith R J et al | Ref no: [E13] | |
Title: | The effect of low-energy laser on skin-flap survival in the rat and porcaine animal model | ||
Published in: | Plastic and Reconstructive Surgery, 1992; 89 (2): 306-309 | ||
Laser type: | HeNe-laser (633 nm) | Output: | 2.75 mW |
Pulsing: | Continuous | Pulse frequency: | - |
Dose: | Not specified | ||
Power density: | 310 mW/cm2 at probe tip | Treatment distance: | 1 mm |
Laser model: | Biostim 2000 | ||
Treated area: | Four dorsally based skin flaps with distal demarcation of necrosis | ||
Treatment time: | 30 sek/cm2 | No of patientes: | 82 |
No of treatments: | 5 | Time between treatm: | 24 hours |
Our comments: This study specifies just about everything but the dose, although this may be calculated as being 0.0825 J/cm2 per day. Five sessions of treatment were given before the skin flaps were prepared, five afterwards. Therapeutic treatment carried out before surgical invasion of healthy tissue is probably of questionable value. The total dose per flap will therefore be 5 x 0.0825 J/cm2 = 0.4125 J/cm2. This dose is quite low. The control procedure may also be called into question since symmetrical flaps were prepared on the right and left sides of the animal and only one side was irradiated. This procedure ignores the systemic effects of laser treatment (see below). |
Author: | Klein R G et al | Ref no: [E14 ] | |
Title: | Low-energy laser treatment and exercise for chronic low back pain: double-blind controlled trial. | ||
Published in: | Arch Phys Med Rehab. 1990; 71: 34-37 | ||
Laser type: | GaAs (904 nm) | Output: | 10 diodes of each 0.4 mW |
Pulsing: | Pulsed | Pulse frequency: | 1000 Hz |
Dose: | Stated : 1.3 J/cm2 per point. Calculated: 0.1 J/cm2 | ||
Power density: | Not specified | Treatment distance: | Not specified |
Laser model: | Omniprobe | ||
Treated area: | Not specified | ||
Treatment time: | 4 min per point | No of patientes: | 20 |
No of treatments: | 12 | Time between treatm: | Three times per week |
Our comments: The authors state that a GaAs laser was used to produce a point dose of 1.3 J/cm2, the indication being the heterogeneous diagnosis of "low back pain". However, analysis of the parameters given show that the dose was in fact only 0.1 J/cm2 (Pm = 2 W x 2 x 10 -7 sec x 1000 Hz = 0.4 mW; t = 240 sec; D = Pm x t = 0.1 J/cm2) and that the total dose was 5 J. In our experience, this recalcitrant indication calls for 2 - 4 J/cm2. |
Author: | Seichert N. et al: | Ref no: [E8] | |
Title: | Wirkung einer Infrarot-Laser-Therapie bei weichteilrheumatischen Beschwerden | ||
Published in: | Therapiewoche, 1987; 37: 1375-1379. | ||
Laser type1: | GaAs-laser (904 nm) | Output: | (each of 5 diodes): 1.2 mW |
Pulsing: | Yes. 200 ns pulse width | Pulse frequency: | 1200 Hz |
Laser type2: | HeNe-laser (633 nm) | Output: | 6.5 mW |
Pulsing: | Continuous | Pulse frequency: | - |
Dose: | Not specified | ||
Power density: | Not specified | Treatment distance: | 15 cm |
Laser model: | Space Laser MIX 5 | ||
Treated area: | Circular area, 6 cm diameter = 28 cm2 | ||
Treatment time: | 10 min = 600 sek | No of patientes: | 18 |
No of treatments: | 5 | Time between treatm: | Once per day |
Our comments: Although the author claims that his instrument is a GaAlAs laser, it is clear from the wavelength (as from the brand) that it is actually a GaAs laser. The dose is not explicitly stated, but, for the GaAs laser, can be calculated to 600 x 0.0012 x 5/28=0.128 J/cm2. On top of this comes the NeHe dose, which is more or less the same (0.139 J/cm2). See below for the purported double-blind procedure. |
Author: | Mulcahy D et al | Ref no: [E41] | |
Title: | Low level laser therpy: a prospective double blind trial of its use in an orthopaedich population. | ||
Published in: | Injury. 1995; 26 (5): 315-317. | ||
Laser type: | Not stated | Output: | 35 mW |
Pulsing: | Not stated | Pulse frequency: | Not stated |
Dose: | 1 J/cm2 “of skin” | ||
Power density: | Not specified | Treatment distance: | Not specified |
Laser model: | Not stated | ||
Treated area: | Not specified | ||
Treatment time: | Not stated | No of patientes: | 20 |
No of treatments: | 8 | Time between treatm: | 2-4 days |
Our comments:
It is interesting to quote the abstract of the negative study by Siebert
[E40] and then compare it to the analysis made by Baxter [E35]. |
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