Thursday, September 26, 2013

Study: Sleep Apnea and Kidney Disease Linked

A study claims that obstructive sleep apnea and kidney disease are linked disorders.

Severe hypoxic events in obstructive sleep apnea (OSA) might lead to kidney damage, though the sleep disorder appeared to be only a minor contributor overall, an observational study showed.
The lowest oxygen saturation level reached at night modestly but significantly predicted chronic kidney disease as indicated by a below-normal estimated glomerular filtration rate (eGFR), Oreste Marrone, MD, of the Institute of Biomedicine and Molecular Immunology of the National Research Council in Palermo, Italy, and colleagues found.
Mean oxygen saturation wasn't a significant predictor overall in the multivariate analysis, nor were there consistent correlations between eGFR and Apnea-Hypopnea Index, the researchers reported here at the European Respiratory Society meeting.
"We don't have to expect a major effect on kidney function," Marrone told MedPage Today. "But we can expect that if a patient has very important drops in oxygen saturation, it may in some way worsen his kidney function, especially if he has comorbidities."
Predictors of a low estimated glomerular filtration rate (eGFR) included older age, female gender, and higher body mass index across most models, while diabetes was significant in polysomnography-tested patients, and hypertension was significant in nocturnal cardiorespiratory polygraphy-tested patients.
In such more susceptible patients, "OSA could give a minor contribution to reduce eGFR by means of nocturnal hypoxia," the researchers noted in the poster presentation.
Potential mechanisms for a causal link to kidney damage could be intermittent hypoxia, metabolic abnormalities, hypertension, and sympathetic hyperactivity, Marrone noted.
The most likely explanation is via vascular damage in the kidneys from hypoxic events, Jan Hedner, MD, of the University of Gothenburg, Sweden, noted in an interview with MedPage Today at the poster discussion session he chaired.
"It's a vulnerable area of the body," he said. "If you already have comorbid conditions like diabetes and hypertension, it could well be that you accelerate the deleterious effect on the renal system."
Marrone's group analyzed 8,112 patients in the European Sleep Apnea Database (ESADA)seen for suspected OSA at 24 centers with polysomnography or cardiorespiratory polygraphy and who had data available to calculate eGFR.
Overall, 8.5% of the cohort had an eGFR below 60 ml/min/1.73 m2, all in the range of stage 3 kidney disease. Participants with the highest creatinine levels -- indicating severe kidney disease -- were excluded from the study, as their condition was unlikely to have been caused by sleep disordered breathing.
That measure of kidney function correlated with Apnea-Hypopnea Index by home polygraphy (P=0.008) but not by the more rigorous sleep study.
The opposite was true for oxygen desaturation index, which correlated with eGFR on polysomnography (P=0.013) but not polygraphy.
Mean and lowest oxygen saturation were significantly linked with eGFR by both types of sleep study.
"The strength of this data is that it represents the biggest studied cohort so far of patients addressing renal function, so from that perspective I think it's useful and important work," Hedner noted. Hedner was involved in ESADA as a sleep medicine specialist but not in Marrone's analysis.
However, the study couldn't determine causality, and Hedner pointed out that it couldn't answer questions that require a longitudinal approach either.
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