The last of the six shatkarma is kapalbhati. The words 'kapal' mean the 'cranium' or 'forehead'. 'Bhati' means 'light' or 'splendour', but also 'perception and knowledge'. Kapalbhati is a pranayama technique which invigorates the entire brain and awakens the dormant centres which are responsible for subtle perception. In English it is referred to as the 'frontal brain purification' technique.
Normal breathing is characterised by active contraction of only the inspiratory muscles, such as the diaphragm and external intercostals. Expiration occurs passively on the cessation of this contraction of the internal intercostals. Kapalbhati reverses this process -exhalation is active while inhalation is passive. This induces a reversal in the flow of the nerve impulses to and from the brain bringing about stimulation and awakening of the brain centres.
There are three forms of Kapalbhati: Vatakrama, Vyatkrama and Sheetkrama.
In this practice inhalation is passive and exhalation is active, just opposite of normal breathing. We do short inhale and exhale rapidly. To practice this Kapalbhati please visit this page - https://yog.dev/en/pranayama/kapalbhati.html
'Vyutkmma' means 'expelling system' and for this practice you require a bowl of warm saline water. Sniff the water through the nostrils - let the water flow down into the mouth and then spit out the water.
This is the reverse of vyutkrama. The word 'sheet' means 'cool' or 'passive'. In this practice we take a mouthful of warm salty water, but instead of swallowing it you expel it through the nose.