A dog's body temperature is close to 100 degrees F. The breath might be slightly cooler, but this is still approximately 30 degrees higher than your room temperature. Air conditioned room air is also very dry. Since your dog has been coughing up fluid from his lungs this additional moisture in his breath is obviously easier to see.
Additionally, Cushing's Syndrome causes increased panting.
The two or three Cushing's disease tests are not injurious or invasive to your dog, so I think that they should be performed if Cushing's is suspected. If your vet is concerned about the Cushing's treatment then use alternative, holistic treatments for the Cushing's syndrome, such as: Chinese Herbal Remedies, Melatonin, Flax Seed Lignans, etc.
Thank you very much! That is very informative. I didn't know about the Herbal remedies, it sounds much better than other medication that is pharmecutical...at least less chance of a side effect. We will get the test done..(demanding it).
Thanks again.