Is there is wheezing or fluid in the lungs? Perhaps the lining of his lungs are inflamed. Is there pain with breathing? Are his BLOOD GASES o.k.? Pulmonary Hypertention causes shortness of breath. But this is usually in older people. Thye would have picked up that with an echocardiogram. Is his coloring good? It could simply be an acid base imbalance from the vomitting and he is compensating with the breath to bring his PH level to normal. Hope this helps. I only have training about Cardiac care. Good luck.