Any opinions regarding this radiograph would be much appreciated.

This is from a 10 year old Tibetan Spaniel that travels regularly between the UK and Greece. The history is a bit vague, but he has had episodes of dyspnoea in the past that seem to have spontaneously resolved. 

2 days ago he developed fairly severe inspiratory dyspnoea and exercise intolerance. Coughing has never been a feature but he holds his neck outstretched. He has been eating and drinking well throughout. Unfortunately the dog is very aggressive, I am sure his heart sounds completely normal, the heart rate is approximately 60bpm and is regular with good pulse quality. Temperature is normal. 

The attached X-ray is the only one I have been able to obtain given his temperament. I am not sure whether the bronchial pattern is suggestive of lower airway disease, though the pattern of dyspnoea is more consistent with an upper airway problem? 

This image was first uploaded Oct 8 2014, re-uploaded Nov 26 2018 after site upgrade.