canine - collapsing trachea

[DCR]

Has anyone had experience working with dog with collapsing trachea (supposedly condition common to the breed)? Small older (15 years) dog was recently exposed to toxins (lawn treatment plus chemicals in the mulch in two separate events within 3 weeks). Heavy harsh hacking cough has been reduced to a spasmodic dry cough ( about the level of hiccups - but still lasting several minutes at a time) with appropriate remedies, but I am wondering what role the pre-existing condition might play in his recovery. Symptom of the trachea problem prior to the toxins were limited spasmodic dry cough only when excited or with extreme weather change and were very short duration.
Thank you in advance for sharing your experience.