I also want to add that according to the website listed below exposure to cigarette smoke, chemical irritants or dust can contribute to collapsed trachea.
Collapsed Trachea in Dogs
For those that smoke, please do not smoke around your little dogs. Also, things such as plug-in air fresheners can cause breathing problems for some. Simple things that we take for granted, like perfume, burning candles or cleaning products can cause these little ones serious problems.