This is the first trial assessing the impact of optically modified PET garments on pain. The pain questionnaires employed have been validated in previous studies [1–7], and were modified only by asking subjects to consider foot pain in their replies (except for the SF-36). Although a placebo effect was observed for most questions (controls reported improvement in 7 out of 9, 3 significantly), more reduction in pain was reported by subjects wearing Celliant™. The response to MPQ question III, in particular, showed significantly greater reduction in pain for Celliant® compared to controls. In the DPN subgroup, two questions failed to show greater improvement with Celliant™ compared to placebo: MPQ questions Ib and Ia+b. These questions employ multiple complex scales and are designed more to measure sensory and affective aspects of pain rather than intensity. For all subjects, only question Ib on the MPQ did not display results favouring the Celliant™ group. Similarly, the BPI pain interference question does not address pain intensity and in the DPN subgroup, more improvement was found in the control group (p > 0.566). Table 3 shows the aggregate result for all pain questions.
Overall the data reported show more improvement in pain reported by subjects wearing the Celliant® socks compared to the controls. The lack of statistical significance for the differences in results with most of the questions may be due to the relatively low number of subjects in this pilot study as well as a lack of homogeneity in the subjects.
In our study each questionnaire was administered twice before and after dispensing the study garments with the results averaged, in the hopes of increasing the precision of the pain assessments. This might skew the data if the therapeutic effect of the Celliant™ socks changes with time – either increasing or decreasing. In future studies employing larger number of subjects this methodological problem should be avoided by administering each set of pain questionnaires only once.
In general, non-DPN subjects showed more sensitivity to the beneficial effect of Celliant™ than subjects with DPN. Assuming the effect of Celliant™ on tissue is relatively localized, one might expect less of an effect to be seen in neuropathy, as only a portion of the diseased neuron fibers are in close proximity to the plantar aspect of the socks, and thus likely subject to the effect of the modified fabric.
This raises the question of what mechanism could account for the apparent beneficial impact of optically modified fiber garments. Two unpublished studies, one in healthy subjects and one in diabetics, demonstrated significant increases in transcutaneous oxygen tensions in the skin of the hands and feet when Celliant™ garments were worn compared to placebo garments (Lavery LA, 2003; McClue GM and Lavery LA, 2003). The increased oxygen tensions were observed by 10 minutes and persisted during repeated measurements over 60 minutes. The increase in healthy subjects ranged from 10 to 24%; diabetic subjects showed an average increase of 10%. It is conceivable that some interaction of the Celliant™ particles with light increases reflection or transmission of light in the visible or near infrared portion of the spectrum into the skin, leading to vasodilation of the microcirculation and enhanced perfusion of tissue, which plausibly could ameliorate some causes of chronic pain. Alternatively, the enhanced illumination of the skin and underlying tissues could influence the biologic activity of endogenous chromophores (cytochromes, flavins, and poryphyrins) involved in energy metabolism in a manner leading to anti-inflammatory or anti-nocioceptive effects.
A large body of evidence suggests that short periods of illuminating skin, tissue, and cells with visible or infrared light has positive effects on pain, injury recovery, and wound healing. A number of studies have looked at joint pain such as temporomandibular joint pain , finding that near infrared light (810 nm) appears to reduce pain compared to sham illumination regimens. A meta-analysis of 20 trials employing laser therapy for chronic joint disorders found that when sufficiently intense light was employed, such therapy had a direct anti-inflammatory effect on the joint capsule . A study of the effects of infrared (950 nm) on sural nerve conduction showed significant impact of illumination on nerve conduction velocity and negative peak latency compared to sham illumination . Several studies on diabetic neuropathy showed a favourable impact of intermittent illumination with infrared at 890 nm on sensation and pain [11, 12]. Low level illumination of joints affected by osteoarthritis by infrared diodes emitting at 890 nm has also been reported as effective for alleviating pain, and the effect has been postulated to be related to stimulation of constitutive nitric oxide synthetase . Low intensity laser therapy at 810–820 nm combined with exercise regimens has been shown to benefit patients with chronic back pain and Achilles tendonopathy [14, 15]. Several studies using animal models of wound healing or cell cultures have examined the effects of short exposures to red (e.g., 632 nm, 670 nm) or infrared light (e.g., 830 nm), finding wound healing to be significantly accelerated or increased expression of genes and proteins associated with proliferation [16–21].
Previous studies generally entailed short illumination periods of a few minutes at intensities of 1 to 20 Joules/cm which are much higher than the presumptive low intensity optical effects of Celliant™ garments. Our subjects were wearing socks under ambient light conditions and often shoes. Past demonstrations of interactions between tissues and external light, nonetheless, support the possibility that Celliant™'s effect is due to prolonged exposure of underlying structures to an altered electromagnetic environment. Given the putative anti-inflammatory effects of infrared light, the ability of longer wavelengths to penetrate more deeply, and the likelihood that Celliant™ particles significantly reflect and scatter infrared light, plausibly the Celliant™ effect is mediated by perturbations in the infrared portion of the spectrum. Conceivably, but we think unlikely, the Celliant™ effect may be due to higher skin temperatures resulting from more efficient reflection of infrared energy, but this requires further investigation. We are now planning further studies employing thermography and hyperspectral imaging of skin blood flow to further characterize the effects of wearing Celliant™ garments.