Just work up the time, perhaps the first time just being 1 inhalation keeping it 6 inches from the mouth. Probably overkill in terms of safety, but certainly you can work up cautiously and feel confident you are being totally safe.
If the increased difficulty breathing was temporary, please also be sure to consider the possibility it was a herx. I had increased asthma for an hour once, and I recognized it as a herx from the nebulized silver. ~David
