Yet, the underlying principles of Hatha Yoga can be fully understood through training. Practise and realise. Swatmarama enumerated the methods and as well as the basic instructions. The intricacies would still have to come from a practical teacher.
The bhastrika pranayama directly affects the nervous and circulatory systems. The intracranial pressure abruptly increases through each inhalation which, in turn, magnetises the cerebrospinal fluid.