Levels of the blood-forming hormone erythropoietin appear to be increased in patients with severe obstructive sleep apnea (OSA), a disorder in which breathing stops for short periods during sleep. This could help explain why high blood pressure, which is influenced by the hormone, is often seen in patients with OSA.

Erythropoietin is a hormone secreted by the kidneys in response to low oxygen levels in the blood. The hormone attempts to solve this problem by stimulating the production of red blood cells - the oxygen-carrying cells of the blood. However, in addition to this potentially useful effect, the hormone has been shown to increase blood pressure.

“We were interested in the mechanisms that cause blood pressure to go up with OSA,” senior author Dr. Virend K. Somers, from the Mayo Clinic in Rochester, told Reuters Health. “Once the mechanisms are identified, we can potentially focus treatments on those mechanisms.”

“Erythropoietin is known to raise blood pressure among other effects,” Somers pointed out. “We were interested in determining if erythropoietin levels rose with OSA,” a condition that can cause low blood oxygen levels, he added.

As reported in the American Journal of Hypertension, the researchers measured erythropoietin levels in 18 severe and 10 mild OSA patients before and after receiving a breathing treatment for their condition. The erythropoietin levels in these patients were compared with those seen in 12 healthy subjects.

Before sleep, OSA patients and healthy subjects had similar erythropoietin levels. However, after about 4 hours of sleep with no treatment, severe OSA patients experienced a 20-percent increase in erythropoietin levels. The breathing treatment caused their levels to return back to normal.

In contrast, mild OSA patients had erythropoietin levels that remained stable throughout the night and were comparable to those seen in healthy subjects.

The low blood oxygen levels that occur with “severe OSA seem to produce a modest rise in erythropoietin levels,” Somers observed. But, he added that further studies are needed to determine if “erythropoietin is actually involved in the high blood pressure seen with OSA.”