Sleep Hypoxemia and Urinary Free Cortisol in Patients with Obstructive Sleep Apnea
Objective: This study evaluated the influence of obstructive sleep apnea (OSA) on hypothalamic–pituitary–adrenal (HPA) axis aiming to identify the polysomnographic data associated with cortisol abnormalities.
Methods: Forty-one men referred for suspected OSA underwent polysomnography and were classified according to the apneahypopnea index (AHI) into control group (n=16) and OSA group (n=25). The assessment of the HPA axis function included low-dose (0.25 mg) dexamethasone suppression test, the circadian rhythm of salivary cortisol secretion and the measurement of urinary free cortisol (UFC) excretion in a 24-hour urine collection.
Results: No differences were found between groups for age (p=0.112), body mass index (BMI) (p=0.617), waist circumference (WC) (p=0.358). UFC was higher in the OSA group compared with the control group (p=0.013). There was no correlation between the UFC and BMI. There was a negative correlation between UFC and minimum oxygen saturation (p=0.006) and positive correlations between UFC and rapid-eye-movement (REM) oxygen desaturation index (p=0.004), AHI (p=0.024) and arousal index (p=0.010). In a multivariable linear regression analysis, including, arousal index and minimum O2 saturation or REM ODI as independent variables and UFC as the dependent variable, only minimum O2 saturation or REM ODI were associated with high UFC levels.
Conclusion: Our results demonstrated that OSA is associated with increased UFC. The severity of hypoxemia is the major factor of this neuroendocrine dysregulation.