by Karla Gale

Last Updated: 2008-10-24 10:22:58 -0400 (Reuters Health)

New research from the UK shows that minimally symptomatic obstructive sleep apnea (OSA) is associated with endothelial dysfunction and increased arterial stiffness, suggesting that patients with this condition are at increased cardiovascular risk.

"In previous studies we found that measures of cardiovascular risk, such as blood pressure and arterial stiffness, are increased in patients with moderate to severe OSA, and that CPAP therapy improved these measures of cardiovascular risk," Dr. Malcolm Kohler told Reuters Health. "We hypothesized that this might also be the case in patients with mild OSA as well."

Dr. Kohler at Churchill Hospital in Oxford and colleagues studied 64 patients (ages 45-75 years) with minimally symptomatic OSA (> 7.5 oxygen desaturations exceeding 4% per hour with no daytime symptoms) and 15 control subjects matched for age, gender, body mass index, and cardiovascular risk profile. The British investigators report their findings in the American Journal of Respiratory and Critical Care Medicine for November 1.

According to ultrasonographic assessment of the brachial artery, OSA patients had flow-mediated dilatation that was significantly lower than in control subjects (mean 5.0% vs 7.5%, p = 0.003).

"The size of this difference has been shown to be of clinical significance in studies looking at the association between flow-mediated dilatation and subsequent cardiovascular events," the authors note.

Radial artery pulse waveforms recorded with a pressure tonometer showed that arterial stiffness was significantly higher in the OSA group (26% vs 21%, p = 0.04).

As to how OSA may damage vasculature, "the most likely explanation is that repetitive arousals from sleep lead to increased sympathetic nerve activity, higher levels of catecholamines and hypertension, all factors known to impair endothelial function and increase arterial stiffness," Dr. Kohler explained. "Alternatively, the intermittent hypoxia associated with apneas has been shown to induce atherosclerosis in animal models."

Based on their findings, he believes that patients with only mild OSA may be at increased cardiovascular risk and may therefore benefit from CPAP therapy. To test that theory, "the Oxford Centre for Respiratory Medicine is currently investigating the effects of 6 months of CPAP therapy on cardiovascular risk in patients with minimally symptomatic OSA in a large international randomized controlled trial."

In an accompanying editorial, Dr. Geraldo Lorenzi-Filho and Dr. Luciano F. Drager at the University of São Paulo in Brazil note that "the prevalence of OSA in the general population is extremely high," and conclude: "OSA is a leading health burden with major cardiovascular implications."

Am J Respir Crit Care Med 2008;178:892-893,984-988.