"but there is no current, concrete data on the effects that the rehabilitative training or manual approaches could have on the patient; in particular, on his/her cognitive and cerebral aspects in general."
Now try and find a reference population of people with "skill and desire to train breathing techniques to improve their health". Administer half of those people a "placebo" technique, where both the trainer and the subject are convinced they are working on the "correct breathing technique". Measure the improved health condition. Deliver "statistically significant results" showing how the placebo group improved less than the actual test group.