You have already studied the anatomy and physiology of breathing in first session, where you have learnt that breathing, i.e. inhalation and exhalation is achieved by the movements of the Ribs, Diaphragm and Abdominal walls. The movement of Ribs is more energy consuming and that of Diaphragm is more economical. This is because energy required to move the ribs is more as compared to the energy required to move the diaphragm. Also the extent, to which the lung volume increases, is less with ribs and is more with the diaphragm. The movement of abdominal wall is supporting the movements of diaphragm. This fact is considered in Pranayamic Breathing. You have to maintain the ribs in their position without making much movement but making maximum movement of the diaphragm.
Initially it is very difficult to control the movements of the diaphragm but it can be achieved with regular practice. Controlling the movement of abdominal wall will help to achieve the control over the diaphragm movements.
Please remember 2 points before the Study.

1. Try to relax physically, mentally and emotionally.
2. Try to concentrate fully on the respiratory organs and diaphragm in particular.

Finally you are advised to stop the practice if you feel uneasy or any change in your condition.