Superficial Cold And Heat Application During Transcutaneous Electrical Stimulation May Not Change Perceived Sensation Of Pain

摘要

Transcutaneous electrical stimulation is commonly applied in clinical practice to provide pain relief. Due to the discomfort associated with high intensity electrical stimulation, cold or heat is often applied to the area to allow higher stimulus intensity based on suggestions that the application of cold or heat alters the sensory pain perception through sensory nociceptive pathways. It is therefore of clinical relevance to investigate whether application of superficial heat or cold changes perceived pain sensation as a function of stimulation threshold. Twenty-six participants volunteered for this study. Constant voltage electrical stimulation with a frequency of 5 Hz, and a pulse width of 300 microseconds was applied to the tibialis anterior. The intensity of the electrical stimulation varied from zero to 200 volts peak to peak. Participants were requested to state when they first perceived any sensation of the electrical stimulation and when stimulus intensity became intolerable. Paired t-test analysis indicated no significant difference in the baseline peak current and the peak current following the application of either superficial heat or cold at the sensory threshold or limit of tolerance. There was a significant difference in the plateau current at baseline compared to the plateau current following the application of superficial heat and cold at the sensory threshold and limit of tolerance. From the experimental results this finding appears to be an artefact of altered skin impedance resulting from changing skin temperature. Thus, it is unlikely that the application of superficial heat or cold significantly changes the way transcutaneous electrical stimulation normally interacts with the sensory or pain systems. Introduction Transcutaneous electrical stimulation is commonly applied in clinical practice to provide pain relief.(Van Swearingen, 1999) However sensory perception including discomfort and pain often accompanies subcutaneous electrical stimulation (Low and Reed, 2000; Van Swearingen, 1999) and although extended analgesia is sometimes advantageous, the pain associated with sensory fibre activity frequently makes high intensity electric stimulation intolerable.(Walsh, 1997) Electrical stimulation applied in combination with the simultaneous application of superficial heat or cold may reduce perceived pain and pain thresholds. However limited evidence is available on how these modalities interact with one another and whether there is any benefit. This research project investigated the interaction between superficial cold and heat and transcutaneous electrical stimulation, when these modalities are combined under experimental conditions. Superficial coolingSuperficial cooling decreases skin temperature rapidly and involves the application of a cooling agent such as ice, cold gel packs, ethylchloride or other cooling sprays to the skin surface, and immersion in a cold water bath.(Ernst and Fialka, 1994; Johnson et al., 1989) An early study on the effect of skin temperature had no effect on subjective sensory sensation when a finger was electrically stimulated (0.2msec, 1Hz) at baseline skin temperature and again after the application of a cold water bag to 17oC threshold.(Todnem et al., 1989) Whereas other reports using superficial cold application suggested the opposite.(Bugaj, 1975; Ernst and Fialka, 1994) However pain increases linearly with decreasing skin temperature and is consistently perceived at temperatures below 0oC.(Chen et al., 1996; Simone, 1997)Superficial heatSkin temperature increases rapidly following the application of a superficial heat source. The effect of superficial heat on perception and subjective sensory thresholds to transcutaneous electrical stimulation respectively has been examined with results showing no significant effect with increased temperature.(Hawkes, 1962; Todnem et al., 1989) Innocuous heat is widely used clinically for analgesic purposes.(Low and Reed, 2000; Williams et al