Pranayam means breath control. Though breathing is an involuntary body function in yoga we practise Pranayam that is a form of controlled breathing where in we can control the inhalation and exhalation process to a certain extent.
While practising Pranayam it is important that your respiratory tract is open; lungs are relaxed but not tired or exhausted. Blood pressure should be within normal limits. With practice of pranayam one can increase the oxygen level in the body and eliminate carbon di oxide with other toxins. This gives energy to each and every cell of the body. However it has to be practised not as technique but with intellectual and emotional involvement (Bhava) with relaxation in between. Then only one can really enjoy the benefits of Pranayam ie balance at emotional level, peace of mind as a result of cleansing of thought process.
During Pranayam one needs to open ones lungs to its maximum capacity. To bear the pressure you need to have good flexible chest muscles and flexible rib cage. We can achieve this by good practice of back bends, side bends and twisting asanas. After this you can inhale and exhale to maximum lung capacity for a longer time and enjoy physical, mental, emotional and intellectual benefits.
For normal people before practicing Pranayam, practicing of the asanas is very essential.