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How much physical pressure is required when applying LASER?

When using LASER, it is my understanding that pressure should be applied via the LASER head. I believe this is to essentially "push" the blood cells away from the surface and improve penetration of the light energy. There was some debate amongst our team this morning as to how much pressure needs to be applied. Any thoughts/guidance would be apprecaited

Greg Noonan

1 year ago

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Dr Ethne Nussbaum
Dr Ethne Nussbaum

All the facts pointed out by Liisa are important reminders for clinical practice. I agree with her final conclusion that pressure should be considered in order to optimize penetration. The need for this has in fact been demonstrated, at least for superluminous diodes assembled in an array. See Physiotherapy Canada 59; 3, 194-207 Nussbaum EL, van Zuylen J, Jing F.

Cliff Eaton
Cliff Eaton

A late responder Liisa but a response well worth awiting for :)

L.Laakso335
L.Laakso335

Hi all. Sorry I have come in so late on this one. (Yes, one year is VERY late!) Others have noted that there is no evidence and as far as I can tell, this is the case although recently some have started to look at penetration relative to laxity or stretch of tendons subjected to light. But let's look at the physical characteristics of tissue and combine that with the theoretical and mathematical modelling of photon penetration and absorption. Theoretically:

  • red light and similar wavelengths in the visible range of the electromagnetic spectrum are absorbed well superficially (i.e., do not penetrate far - perhaps a few millimetres at most)
  • invisible (infrared) wavelengths penetrate better (small percentage up to a few centimetres according to MonteCarlo modelling)
  • photons / wavelengths of light energy are subject to the principles of physics and so penetration is 'inverse' to absorption
  • effect of photons on cells is subject not only to the direct action of the photons that reach target cells but also to the effect of stimulated cells communicating with other cells nearby or remotely (i.e., in theory, you do not have to stimulate every cell to achieve a response - a response can occur indirectly by the activation of only some cells in the target area that then transmit the effect from cell to cell) - this is the abscopal effect

So, in theory we needn't apply photobiomodulation (PBM) therapy with pressure at all except to ensure that we reduce reflection and scatter - so keep the laser probe in contact where possible and ensure that the entire diode face is in contact and preferably at 90 degrees to your target tissue. However, any EPA is going to have its best effect if you try to optimise all facets of the treatment. If you truly wish to optimise the amount of photons reaching a deeper target lesion or anatomical site, compression of overlying tissue (assuming it's not painful to the patient) may help reduce the depth of overlying tissue and to situate photons closer to your target tissue. This then is the applied theory of what was originally called the 'woodpecker' technique suggested in some of the earliest clinical papers. It's a technique I still use - why not.

Liisa Laakso

Dr Ethne Nussbaum
Dr Ethne Nussbaum

Thanks for the SPIE reference Tim. SPIE format allows for not much more than a summary of ones research. A fuller discussion of findings & explanatory figures can be found in the article at Physiotherapy Canada 59; 3, 194-207 Nussbaum EL, van Zuylen J, Jing F. Transmission of light through human skin folds during phototherapy: effects of physical characteristics, irradiation wavelength & skin diode coupling.

Dinesh Verma
Dinesh Verma

Applying pressure over the surface in conditions where - there is Fluid accumulation / swelling - may be effective way to apply LASER ... Even Class 4 lasers are used with pressure application techniques. One of the established USA Class 4 laser uses a Crystal ball ROLLER applicator and is very commonly used technique.

Prof Tim Watson
Prof Tim Watson

Thanks for that Ethne. The article is at : http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1276117 and the citation that I have is :
Transmission of phototherapy through human skin: dosimetry adjustment for effects of skin color, body composition, wavelength, and light coupling to skin Ethne L. Nussbaum ; Jeff Van Zuylen Proc. SPIE 6140, Mechanisms for Low-Light Therapy, 61400H (February 28, 2006); doi:10.1117/12.647201 for those who want to follow it up

Dr Ethne Nussbaum
Dr Ethne Nussbaum

Please have a read of Nussbaum EL & van Zuylen J in Physiotherapy Canada for the evidence - I think 2007 on transmission of LLLT. Red blood cells are highly scattering elements. In addition to absorbing in the therapeutic waveband. Pressure enough to blanche skin reduces perfusion immediately under the laser probe thereby increasing penetration. Additional effects depending on configuration of the diode.

Prof Tim Watson
Prof Tim Watson

Interesting in the comment that Cliff made re High Power laser (Class 4) and not needing pressure - it was a Class 4 laser presentation to which I refer!!! I do not think anything by way of pressure is 'needed' unless there is evidence to say that it makes a difference. All I can see from the material I read is anecdotal - it might sound logical and appealing - but that is not the same thing

Cliff Eaton
Cliff Eaton

While there is no apparent evidence to support it manufacturers do suggest in their handbooks that pressure be applied to shunt the blood flow. It is considered that the blood flow will 'take the energy away from the treatment area'. One if the major claims for laser though is that it knocks off the oxygen molecules from HBO and which are taken up in repairing tissue and used to make ATP. If this is the case then we shouldn't be using pressure.
High Power laser, which is still light albeit with increased power and wavelength combination, does not require you to use pressure. So why for LLLT? If you do use pressure then how much? If you are looking to shunt blood then you will need a lot more presssure on a 'well insulated' patient than a thin one. On balance I would suggest enough pressure to ensure good contact with LLLT and testing pressure with HPL

Prof Tim Watson
Prof Tim Watson

Interesting question. Like Sandy, I can see the logic and indeed, I head the very same thing mentioned in a laser presentation just the other day BUT no evidence at all was provided to back up the claim - even when challenged. I have never seen anything by way of an evaluation in the literature - though of course I may have missed it. Maybe one of our LLLT expert people know of some tests that have been done??

Dr Sandy Rennie
Dr Sandy Rennie

I believe your rationale for applying pressure to the laser aperture makes sense, however I have not seen any research literature to support this. I do recall one LLLT paper where the patient had some bruises on the skin because of potentially too much pressure placed on the laser aperture.

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