Hypoxia, Sleep Apnea Linked in Diabetes

New evidence suggests an association between obstructive sleep apnea (OSA) and microvascular complications in patients with type 2 diabetes mellitus (DM).

In particular, various parameters of OSA were independently associated with diabetic neuropathy (DN) and renal function. Also, it appears that hypoxemia may be more representative in associations of OSA and microvascular complications in DM than the apnea–hypopnea index (AHI).

The AHI-the total number of episodes of apnea and hypopnea that occur during sleep divided by total sleep time-is the standardized parameter for diagnosis and assessment of OSA severity. Data about how differences in other parameters of OSA may predict chronic DM complications are limited.

Chinese researchers, led by senior author Linong Ji, MD, of the Department of Endocrinology and Metabolism at Peking University People’s Hospital, enrolled 880 hospitalized patients in a multicenter, cross-sectional study that involved 12 hospitals from 6 cities. The researchers used overnight sleep monitoring with a portable monitor to record respiratory parameters, including the AHI, the oxygen desaturation index, oxygen saturation (SPO₂), and the cumulative time of SPO₂ below 90% or 85% (CT90% and CT85%, respectively). Chronic DM complications were recorded from medical charts.

The direct indicators of hypoxemia severity, such as oxygen desaturation index and oxygen saturation, appeared to be more sensitive than AHI in association with DN, as well as different stages of DN.

“The average SPO₂ and CT90% were markedly associated with microalbuminuria, which was the early stage of DN and may be reversible if treated properly,” they stated. “Among all indicators, CT90% was the only parameter that was simultaneously associated with DN, microalbuminuria, and macroalbuminuria and may be the most promising parameter to study in the future.”

They added: “The lowest SPO₂ may be a more sensitive parameter compared with the other parameters, including AHI.”

The parameters of OSA appear to have different significance in association with diabetic complications. The researchers noted that AHI is used globally in the diagnostic criteria for OSA, but the indices of the degree of hypoxemia, such as CT90%, appear to play a stronger role than AHI.

“We postulate that for microvascular complications in diabetes, the direct indicators of nocturnal hypoxemia may contribute more to the progression of these indicators,” they stated. “Our finding that CT90% was markedly associated with DN and albuminuria may suggest that the total time of hypoxemia rather than the frequency of desaturation was more important to DN.”

The study has several limitations. The researchers noted that this was a post hoc analysis and a sample size was not calculated for any DM complication. Diagnoses were based on laboratory tests of different hospitals, which varied in consistency.

“Finally, we could not determine a causal relationship between diabetes complications and OSA in this cross-sectional study, and it is likely that preexisting peripheral vascular disease caused by diabetes can lead to the lower measurements of SPO₂ compared with the real SPO₂ in the blood,” they stated.

The researchers published their results online ahead of print March 31, 2016 in Diabetes Technology & Therapeutics.