Study Links Low Levels of Oxygen in Blood to Poor Pulmonary Hypertension Patient Outlook

Low levels of oxygen in the blood of people with idiopathic or heritable pulmonary arterial hypertension (IPAH or HPAH) are associated with secondary diseases and a poor patient outlook, a study shows.

IPAH and HPAH patients can have hypoxemia, or low levels of oxygen in the blood, either at rest or during physical activities. Secondary diseases can contribute to hypoxemia, studies have shown.

But researchers had never categorized the prevalence of hypoxemia in these patients or its association with a specific patient’s characteristics and outlook.

A Cleveland Clinic team examined records in the Cleveland Clinic Pulmonary Hypertension Registry to identify IPAH and HPAP patients diagnosed between January 2000 and July 2015.

Their study, “Hypoxemia in patients with idiopathic or heritable pulmonary arterial hypertension,” appeared in the journal Plos One.

Two hundred fifty-six, or 88 percent, of the 292 people in the study had IPAH and 36, or 12 percent, HPAH.

The mean age of the patients was 50 1/2 years, and 214, or 73 percent, were women. Two-thirds had not received any previous PAH treatment.

Researchers checked patients’ six-minute walk distance test, a measure of exercise capacity, and their pulse oximetry reading, which measures blood oxygen levels.

The pulse oximetry readings were taken when patients were at rest and during the walking test. A less than 89 percent pulse oximetry reading equated to hypoxemia, researchers said. They also considered a patient to have hypoxemia if doctors had decided they needed continuous supplementary oxygen.

Half of the patients showed some degree of hypoxemia. Eighty-nine, or 31 percent, displayed it during the walking test and 60, or 20 percent, when they were at rest.

Hypoxemia patients were older, heavier, had worse scores on the walking test, and more cardiovascular and secondary respiratory diseases. But they also seemed to have better PAH measurements, suggesting a less severe condition.

A key finding was that hypoxemia, either at rest or during the walking test, was associated with worse long-term survival.

But since hypoxemia can be alleviated with supplementary oxygen, the team wrote that “it is unlikely that this condition per se significantly affected survival to the degree observed in our study.”

“It is more probable that the hypoxemia represents one of the characteristics of a phenotype [profile] linked to worse survival,” they concluded.