Interesting query. I will do what I can - though as I was involved in the research you are citing, I appreciate that you might be 'wary' of my response. We have a CRET clinical trial about to come out (submitted) which might provide useful additional information.
How does CRMR/CRet) differ substantially from the old form of long wave diathermy which I understand was discontinued a long time ago?
^^ the old longwave diathermy was a NON CONTACT technique - more like current shortwave applications. The CRET is a similar radiofrequency (around 0.5MHz) BUT is delivered in CONTACT with the tissues - this (to me) is the critical difference. There IS a current flow through the tissues with CRET. There is an INDUCED current with longwave.
What are the physical principles that allow/require skin coupling agent for the active and inactive electrode for CRMR/CReT, whereas in the other therapeutic radiofrequency treatments of shortwave and microwave this is not allowed/required?
^^ as above - it is necessary as the energy delivered is effectively an electric current application. I have been thinking of it as a Radio Frequency Electric Current. Skin contact and electric coupling are therefore essential for the energy to get into the tissues
In most studies I have read using CRMR/CRet they seem to use 10-15 minutes of capacitive mode followed by 10-15 minutes of resistive mode. I have been unable to find any theoretical justification for the use of both modes in this way, although I understand that the capacitive and resistive modes may have similarities to the capacitive and inductive modes respectively, of short wave (Kumaran and Watson, 2015)
^^ my personal opinion (backed up by the Kumaran and Watson research that you cite) is that the RESISTIVE mode is probably the most 'effective'. The CAPACITIVE mode (we only used 5 mins) may serve to increase skin temp and blood flow making it 'easier' for the RESISTIVE energy to get into the tissue at depth. Our evidence would support that postulation.
If one was aiming for a deep thermal effect, are there any theoretical or practical reasons why this form of radiofrequency treatment could be better than continuous short wave diathermy
^^ our results (lab and clinical) included direct comparisons with shortwave - which we took to be the nearest equivalent existing therapy. The CRET results (using Indiba equipment at 448kHz) were significantly 'stronger' and certainly longer lasting than those with shortwave. I genuinely did not expect this result - thought they would be the same or at least very similar. The CRET effects were still in evidence 45mins + after end of treatment - WAY longer than shortwave effects.
??? Any help ???