Radu Sigheti/ReutersAs a neonatologist, I worry about patients with pulmonary hypertension. This unforgiving disease, sometimes seen after premature birth, can end with sudden death from constricting blood vessels in the lungs. One minute a baby in the neonatal ICU may be sleeping comfortably; moments later, doctors and nurses are giving chest compressions and rescue medications. A pulmonary hypertension crisis, as these frightening episodes are called, starts with a drop in the blood oxygen level.