Was prescribed Oxygen for forced exertion (walking) on Nov 4/13 by my GP, Dated Nov 4/13

I have been very short of breath over the last year so my general practitioner prescribe oxygen for me, to be used only during forced exertion (walking). I am fine at rest as my oxygen saturation level is between 92 and 94 percent. On forced exertion, it has gone down to 85 percent. The proof that oxygen helped me was when I went to a shopping and walked without stopping for one half hour with my walker. This feat I have not been able to do for over a year. Unfortunately, I have to pay for it out of pocket as I do not qualify to have it subsidized by by the provincial assistive devices program (ADP). It cost me $ 398.00 per month or 4 4,728 per year.