Effect of pulsing in low‐level light therapy

Abstract

Background and Objective Low level light (or laser) therapy (LLLT) is a rapidly growing modality used in physical therapy, chiropractic, sports medicine and increasingly in mainstream medicine. LLLT is used to increase wound healing and tissue regeneration, to relieve pain and inflammation, to prevent tissue death, to mitigate degeneration in many neurological indications. While some agreement has emerged on the best wavelengths of light and a range of acceptable dosages to be used (irradiance and fluence), there is no agreement on whether continuous wave or pulsed light is best and on what factors govern the pulse parameters to be chosen. Study Design/Materials and Methods The published peer-reviewed literature was reviewed between 1970 and 2010. Results The basic molecular and cellular mechanisms of LLLT are discussed. The type of pulsed light sources available and the parameters that govern their pulse structure are outlined. Studies that have compared continuous wave and pulsed light in both animals and patients are reviewed. Frequencies used in other pulsed modalities used in physical therapy and biomedicine are compared to those used in LLLT. Conclusion There is some evidence that pulsed light does have effects that are different from those of continuous wave light. However further work is needed to define these effects for different disease conditions and pulse structures.

Fundamental Information

“…A 2010 literature review by Hashmi et al examined CW versus pulsed light and concluded that more evidence is needed: "It was impossible to draw any meaningful correlations between pulse frequency and pathological condition, due to the wide-ranging and disparate data. " The authors concluded, "there is no consensus on the effects of different frequencies and pulse parameters on the physiology and therapeutic response of the various disease states that are often treated with laser therapy" (Hashmi et al, 2010). CW emission, as illustrated in Figure 2.4, is the simplest form of output to understand.…”

Development of an Optical Tissue Clearing Laser Probe System

“…However, it was generally confirmed that the PW laser may penetrate deeper into soft tissue as compared to the CW [26,27]. The PW from 2.5 to 10,000 Hz on LLLT was frequently used in the clinic due to the deep light penetration depth in soft tissue [26].…”

“…Liu et al investigated various light irradiations to increase permeability of chemical agents and, therefore, enhance the efficacy of OTC [25]. Although many studies have been reported to evaluate the effect of laser pulse frequency (LPF) on LLLT [26], the efficacy of LPF [continuous wave (CW) or pulsed wave (PW)] on LLLT is still unclear, and there is no complete consensus for the mechanism of LLLT. However, it was generally confirmed that the PW laser may penetrate deeper into soft tissue as compared to the CW [26,27].…”

“…Although many studies have been reported to evaluate the effect of laser pulse frequency (LPF) on LLLT [26], the efficacy of LPF [continuous wave (CW) or pulsed wave (PW)] on LLLT is still unclear, and there is no complete consensus for the mechanism of LLLT. However, it was generally confirmed that the PW laser may penetrate deeper into soft tissue as compared to the CW [26,27]. The PW from 2.5 to 10,000 Hz on LLLT was frequently used in the clinic due to the deep light penetration depth in soft tissue [26].…”

The Framework of a Mathematical Model of the Autonomic Nervous System and Physiological Systems: Using the Neuroregulation of Blood Glucose as an Example

“…The random flashing of lights could stimulate a photosensitive event e.g. a migraine, yet techniques based upon this principle [158] have been approved for use as a treatment for migraines [149]. There is a significant scientific principle involved.…”