Hello, Monika. I agree with Dr. Rennie that there is not a lot of research specifically assessing the effects of HVPC on pain. What little has been done appears to suggest that either would be effective.
I agree with Professor Hoens regarding the effect of cathodal HVPC on edema. The elegant series of papers by Fish & Mendel and colleagues demonstrated that cathodal HVPC was more effective than anodal, albeit using rat and frog models (there has been little work published on humans, and it is equivocal). Based on aspects of their research designs over their research series, Fish & Mendel believed that the polarity effect was not due to the cathode repelling negatively charged serum proteins. There is not a demonstrated, established mechanism for the effect. However, they showed that the cathode must be placed over the site of tissue damage (not necessarily where the fluid has extravasated).
Since there appears to be no differential effect of polarity on pain relief, HVPC could be used for a pain relief effect in a similar manner as with other types of current/waveforms (i.e., those that are biphasic and balanced). I, respectfully, disagree with the hypothesis expressed by Dinesh Varma regarding inability for HVPC to modulate pain relief via neural activation. One can use HVPC to produce a sensory response (the patient will feel tingling) as well as a motor response, depending on the amplitude of the stimulation, even though the pulse duration on such devices are fixed and relatively low. These responses would occur, necessarily, via neural stimulation; supporting the similarity among various current types for the more classical, neural mechanism of pain relief. Regarding circulatory effects of ES, biphasic balanced currents have also been reported to be beneficial.