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Power is defined as the ratio at which energy is emitted, received or transferred, or the efficacy or speed with which that energy is supplied.
In laser therapy, power is measured in watts (W) and it is one of the decisive factors for tissue penetration. Another decisive factor for tissue penetration is wavelength (the distance between two successive peaks of a periodic wave in the same phase).
With this definition in mind, power therefore helps carry photons deeper and reduce treatment times; i.e., we supply more photons over a shorter time with weaker lasers by applying a formula in which the energy (in joules) is equal to the power (in watts) multiplied by the time (in seconds):
E (J) = P(W) x t (s)
Lasers can be categorised by their power, with the IIIB laser (maximum power of 0.5W) and the class IV laser (maximum power of more than 0.5W) being the most commonly used at present. Eye protection is necessary when using both these laser types, as damage can be caused by direct and reflected contact.
The stronger power of the latter can also cause skin damage in the form of burns. Caution is essential when using class IV lasers and the properties of the device must be known in order to determine the best application technique to prevent injuries.
Here is an example to demonstrate power and its impact on application times. When wishing to supply a total of 1,200 joules to a hip, the total treatment time when using a IIIB laser with a maximum power of 0.5W would be 2,400 seconds (40 minutes). When using a class IV laser with an average power of 4W, this treatment time would be 300 seconds (5 minutes).
The current debate surrounding therapeutic laser is about deciding whether it is best to use a IIIB or class IV laser (see Blog 6, Power: Studies Demonstrating its Importance).
Power is not only important to treatment time and penetration depth but also to the application technique. Depending on the power characteristics of the device, a scanning and/or spot technique can be used. The speed of a scanning technique is highly important and may vary according to power and the various treatment heads used with the device. It is therefore essential for the various laser therapy devices to train and inform their users about the best application technique.
Laser devices are becoming increasingly more powerful and that means we might now ask ourselves how powerful these devices might become in the future. We might also wonder how much energy a body is capable of absorbing over a given period of time. This is because it has been shown that excess doses can inhibit the reparatory effects.
Some authors believe that damaged cells are more sensitive to exposure to laser light. This would mean that they need a lower dose over a shorter period of time. Furthermore, the option to supply this energy in pulsed or continuous mode also plays an important role. In the study conducted by Ilic et al (2006), they looked at the effects of different power densities (the amount of power within a specific area, expressed in W/cm2) and doses in the brains of healthy rats.
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They observed that transcranial application at a power density of 750 mW/cm2 in continuous mode caused injury (associated with the thermal effect produced), while this same power density in pulsed mode caused no negative effects.
Although further studies on power are needed (relating different variables), it is indeed clear that shorter treatment times can be achieved with different lasers because the energy can be supplied over the course of shorter treatment times. Furthermore, power helps to reach deeper tissues. As photons penetrate tissue, their concentration is reduced to such a point that photon density (i.e., the concentration of photons) is so low that no photobiomodulation effects are observed.
DoctorVet is a class IV laser therapy device (i.e., above 0.5W) with an average power of 8W and a peak power of 16W. Different power options are available according to the location of the wound and the size of the patient.
The choice is based on time optimisation and the target tissue depth, while avoiding the creation of protocols that supply excessive energy over too short a time period so as to be harmful, especially for damaged tissues that may be more sensitive.
These power levels have been selected by biophysicists with years of experience in laser therapy for veterinary medicine, who have created protocols with optimum power levels to help our pets.
They are safe and effective for the various pathologies that arise in day-to-day clinical practice.
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