Pranayama, the Yoga breathing technique is a very important part of the science of Yoga. It goes arm in arm with asanas or poses. In the Yoga Sutras of Patanjali, asana and pranayama are described as the highest form of purification and self discipline, mentally and physically.
The practices engender physical sensations such as heat, also called the inner fire of purification. Yoga teaches that this heat is part of the purification process of the Nadis. These are subtle nerve channels in the subtle body.
This renders an extremely healthy state to of mind and body.
In Pranayama you concentrate on your breath. Hence, when practising Pranayama it is very important to keep your mind alert. This is because the processes being observed are extremely subtle. In Pranayama, there is no perceptible body movement as in asanas. You will have to sense acutely and feel the movement of the breath within your respiratory tract, for a start - later, throughout your body. The only animated process will be breathing. Patanjali, in his treatise, the Yoga sutras, makes a couple of practical suggestions top help keep your attention on your breath.
For a start, you can concentrate on a part of your body, where you feel or hear your breath. Or else, you could try following the movement of breath in your body. Feel the inhale extend from the center of your collarbone, down through your rib cage to your diaphragm. Then follow your exhalation upwards from your abdomen. Another way to for pay attention to your breath is by feeling where it enters and leaves your body around the region of your nostrils. You can also listen to your breath, particularly if you tend make a b noise by gently tightening your vocal chords. This is a Pranayama techniques called Ujjayi.
Pranayama doesn't aim at bringing the inhale and exhale into some kind of a relationship with each other. Nor does it intend to establish a certain specified length of breath. If these exercises can help you focus on your Breath, it is wonderful. However the ultimate aim of breath ratios in Pranayama is, primarily, to give you as many different options of following your breath as possible. When you follow your breath, your mind will automatically be drawn to your breath. This way Pranayama gets you ready us for the stillness of meditation that is to come.