People who suffer from breathing disorders such as sleep apnea are usually at higher risk for cardiovascular disease. But an intriguing new study from Technion-Israel Institute of Technology scientists suggests that some heart attack patients with these conditions may actually benefit from mild to moderate sleep-disordered breathing.
Apnea and other types of sleep-disordered breathing can boost the numbers and functions of rare cells that help to repair and build new blood vessels, according to the Technion's Dr. Lena Lavie and her colleagues. They say the findings could help predict which patients are at a greater health risk after a heart attack, and may even suggest ways to rebuild damaged heart tissue.
Sleep-disordered breathing is characterized by cycles of apnea-induced hypoxia, where the sleeper experiences a temporary drop in oxygen levels. It occurs in about 5 to 10% of the general adult population, but is extremely common in patients with cardiovascular diseases - somewhere between 40-60%. Many studies have shown that sleep apnea is a risk factor for everything from high blood pressure to chronic heart failure, Lavie noted. Earlier studies by the Technion scientists suggest apnea increases oxygen-related stress and inflammation in the heart and blood vessels.
The scientists' study in the American Journal of Respiratory and Critical Care Medicine (vol. 187, no. 1) could help resolve a puzzling medical issue. If sleep disordered breathing is associated with cardiovascular disease, why is it that people who suffer from breathing disorders in sleep seem to do as well as healthy sleepers after a heart attack?
Lavie, along with researchers Dr. Slava Berger, Prof. Doron Aronson and Prof. Peretz Lavie, looked for clues to this puzzle in 40 male patients - a mix of healthy sleepers and those with sleep disordered breathing, who had had a heart attack just a few days earlier.
Blood samples drawn from these patients revealed that the sleep disordered breathing patients had markedly higher levels of endothelial progenitor cells (EPCs), which give rise to new blood vessels and repair the injured heart, than the healthy sleepers. They also had higher levels of other growth-promoting proteins and immune cells that stimulate blood vessel production.
The Technion researchers were able to trigger a similar increase in vessel-building activity in vascular cells taken from a second set of twelve healthy men and women, by withholding oxygen from the cells for short periods. "Indeed, our results point at the possibility that inducing mild-moderate intermittent hypoxia may have beneficial effects," Lena Lavie said.