In a normal animal, on inspiration the chest is moving out a little and the diaphragm is trying to move caudally. As dyspnoea worsens more chest movement will occur. Because the chest wall is a rigid bony structure, if the muscles of inspiration try to pull the chest out, then will pretty much always be successful in expanding the chest. The diaphragm though, is only a muscle attached around its periphery. If the chest wall expands but the lungs can’t expand for whatever reason then the diaphragm will get pulled cranially against its will and the abdomen will go in. Paradoxical abdominal movement is usually a sign of more severe dyspnoea.There are only really 4 things that cause paradoxical abdominal movement: upper airway obstruction, really stiff lungs, a diaphragm that is not working or has a hole in it or very severe pleural space disease, usually fluid. Pretty much any parenchymal disease will make the lungs stiffer or to use the correct terminology, less compliant. Observing the animal and listening with and without your stethoscope can be a real help in differentiating these 4 conditions and we will cover later in this Big Picture and next week.This is an old fella with very stiff lungs. Chest rads were very suggestive of diffuse neoplasia. Watch his chest move and count In, In, In with his inspirations. Then look replay the video and look at his abdomen as well and you can see that instead of going out on inspiration it is going in. A lot. I would class this as severe paradoxical abdominal movement and severe dyspnoea.