Airway obstructions can contribute to the problem, so children who have sleep apnea are more prone to PH. Fix the apnea and the PH may not advance. When the PH is the result of a heart defect that was subsequently successfully repaired, the PH might go away over time. Or it might not. Ditto in premature babies whose lungs and hearts improve as they get bigger. It's hard to predict what course PH will take, Day says.

It can include pulmonary arterial hypertension (which Katy has), pulmonary venous hypertension caused by diseases of the heart's left side, PH associated with disorders of the respiratory system or hypoxia, PH caused by chronic thrombotic or embolic disease or something different. Because early symptoms like shortness of breath are not uncommon and could have a number of causes, diagnosis is often delayed. Once it is diagnosed, other tests to find the cause may be helpful. But often, the cause is never found.

In Katy's case, doctors first considered whether she had seizure problems but discounted that. Next, they sent her to Primary's cardiology department, where Christina Doak says the diagnosis was made immediately. The sooner a diagnosis is made and treatment begun, the better, "so we were lucky in that way."

Katy had abdominal pain that was likely caused because she wasn't getting good blood flow to her bowels. But that can lead doctors to look at entirely different things until they can be ruled out. Such symptoms may delay a valid diagnosis, Day says. Correct diagnosis and effective treatment require health-care providers with some expertise in PH.

The prognosis is as varied as the patients and the details of their disease. Katy had severe pulmonary blood pressure. Mom Christina describes the disease as generally progressive and terminal over time.

"It depends on the health of the patient and how much damage has been done to the lungs and heart by the time it's diagnosed." It also depends, adds cardiologist Day, who sees most Utah children with PH, on how they respond to treatment.

The Doak family from the beginning opted for an aggressive treatment program, traveling out of state for some of Katy's care, including an intravenous medication that she's been on continuously for many years now. Not all patients require or opt for that level of treatment.

Doctors use a heart catheterization to determine actual pressure, going in through the lung or neck. That also allows a test to see how well the patient responds to oxygen, which may be the primary or even sole treatment for some with PH.

But some patients do not respond to oxygen, Day says. Treatment may require some trial and error to see what works in an individual case. Some patients may respond positively to a tiny dose of nitric oxide to help keep vessels relaxed — not to be confused with nitrous oxide, the so-called laughing gas.