By japah is meant the practice of yoga-vidyaa in its preliminary stage. The practice of japah leads the practioner to the practice of tapah and then to yoga, which should result in the realization of saakshaatkaara, paramapadavi and brahmatva
Japah is a bio-technique, very closely following the process of respiration, serves four functional aspects of the living organisms.

Pulmonary ventilation, which means the inflow and outflow of air between the atmosphere and the living alveoli.

Diffusion of oxygen and carbon dioxide between alveoli and blood.

Transport of the above (O2 and CO2) in the blood and the body fluids to and from the cells, and Regulation of respiration.
 

Almost all life depends on chemical reaction with oxygen to produce energy. Organisms receive oxygen from the atmospheric air, which is 20.84% by volume. The air is drawn in through the nasal cavities, and it enters the lung alveoli through nasopharynx, larynx, trachea, bronchi, bronchioles. Oxygen is carried to the different tissues in the form of oxyhemoglobin of the red blood.

Under normal conditions about 5ml of oxygen is transported by each 100ml of blood, and the normal cardiac output is about 5000ml per minute. Therefore the total quantity of oxygen delivered to the tissues each minute is about 250ml.

There are about 75 trillion cells in the human body and the quantity of oxygen available for their optimal activity seems to be inadequate. Also, it is likely, that a number of cells, particularly the brain cells, may not be within the reach of the oxygen supply.

The organism within it contains a technique meant to augment the oxygen supply to the tissues manifold. The human intelligence consists in noticing this technique and then employ it for the welfare of one\92s own organism.

This bio-technique is named as japah.
How does japah augment the supply of oxygen? What else does it do other than this?
Japah is a multifaceted bio-technique. In its initial stage it concerns air and respiration.
Japah starts with vaayumathana, meaning the churning of air; vaayu means air.

The air (vaayu) is put to rhythmic upward and downward movement in the posterior part of the nasopharynx, just behind and above the uvula region. The vigorous movement (gataagati) of air produces an audible sound. Uvula is a soft extension of the soft palate that hangs from the roof of the mouth above the root of the tongue. Its vibration produces sound.