I have asthma. I heard that Pranayama is a remedy for asthma. So, what type of precautions would I need to take? And in how many days would you see expect to see the results?
I'm a physical therapist and do yoga in my free-time. So I'll provide some of the information I have.
Pranayama exercises and active/passive techniques that are used in physical therapy to treat asthma are very similar.
You cannot cure asthma with any of those two methods, but it can lead to bettering of the symptoms and it gets easier to deal with asthmatic attacks, when you know some techniques that help you get over an asthmatic attack.
Concepts, that are used:
Consciousness for your breathing - Pranayama uses different approaches to make you more conscious of your breathing (where do you feel movement, when you breath? stomach? ribcage? shoulders? how fast do you breath? do you breath through mouth or nose? ...) and helps you breath more deeply or let's say effectively.
Breathing techniques - Pranayama uses exercises to help you deepen your breath.
Body postures - differents asanas (well this is not pranayama itself, but yoga after all) stretch the respirational muscles (pectoralis major and minor, scm, and so on) and the intercostal muscles - this makes breathing easier and deeper. Your muscles get tense, when you have asthma/asthmatic attacks, so stretching helps your muscles relax so they can work more efficiently. Example asanas: http://www.yogajournal.com/slideshow/tias-little-sidebending-sequence/ - but please find an instructor to help you with this.
Body in space - the way your body is seated in the 3 dimensions, affects your lungs. The lower half of the lung is supplied better with blood (due to gravity) and the upper half is better ventilated. So lying on your right side, doing some breathing exercises has a different effect on either side of your lungs. https://en.wikipedia.org/wiki/Ventilation/perfusion_ratio
I'd recomment to find a competent yoga instructor, who can provide you with more information and can lead you through some exercises.
I have worked with long-term patients, who profitted from weekly sessions and exercising at home daily. Sessions can last between only a few minutes up to an hour, where the above mentioned concepts are combined. E.g. you start on your back and get conscious of your breathing. afterwards you are lying on your right side, lay your arm over your head, so the left ribcage is stretched and you do a breathing technique(pranayama). after a few minutes you turn on your back and feel teh difference between your two body sides and how your breathing has changed. then do the same exercise for your other side. But again, find an instructor to help you with this.
As I said it does not provide a remedy, but helps you deal with the symptoms.