Personally, I increase lung capacity with HIIT (I enjoy the endorphins). However, the exercise will work for the average athlete as well. Physiologically, the body has 'beyond conscious control' sensors that require deep, full breathing when the carbon dioxide in the blood rises, utilizing the autonomic nervous system. It is possible, therefore, to use the body's own reactions to access lung capacity that is not used for any number of reasons (and there can be quite a few, even in 'normal' people - tight pectorals, for example). The exercise was originally designed for those with partial paralysis, namely polio victims who had lost the use of the voluntary chest and abdominal musculature and could not voluntarily exercise to improve lung capacity.
It would also work extremely well in the sedentary elderly, who are also at risk for stroke and pneumonia due to diminished lung function.
SilverShadow, the exercise should work well for you and improved lung capacity can only help. As with any exercise, it requires regular use (6x day, spaced in time, every day) Just don't use it during an acute attack - I'm sure you know that the issue in the middle of an attack is getting the air OUT, not IN! (overinflation, lack of respiratory transfer)