Obstructive sleep apnea and the kidney.

Recent studies of obstructive sleep apnea and its comorbidity with other systemic diseases have stimulated interest in the relationship of apnea to renal disease and hypertension. Polysomnographic sleep studies in patients on dialysis who complain of day-time fatigue or sleepiness reveal significant apnea in up to 73% of those studied. Abnormalities in respiratory controller mechanisms from chronic hypocarbia, metabolic acidosis, and uremic toxins have been blamed for the occurrence of apnea in this setting. Proteinuria and sometimes nephrotic syndrome have been recognized in morbidly obese patients with sleep apnea syndrome. Renal biopsies of such patients have shown glomerulomegaly and focal segmental sclerosis. It is postulated that these lesions may result from increased glomerular filtration and blood flow. Elevated urine output, sodium and chloride excretion, and atrial natriuretic peptide have been well demonstrated in obstructive apnea patients and correct to control levels with treatment of the apnea. Both acute (with each apnea) and chronic daytime blood pressure elevation are frequently observed in sleep apnea patients, and occult sleep apnea is postulated as one possible cause of "primary" hypertension in middle-aged men. In younger patients, such hypertension seems to be more reversible with the elimination of apnea. In older patients, however, the cure of systemic hypertension cannot be guaranteed with the elimination of the apnea, and asymptomatic apnea patients tend not to tolerate the bother and discomfort of apnea treatment with nasal continuous positive airway pressure. Therefore, aside from a careful history regarding sleep symptomatology, polysomnographic studies of clinic populations with primary hypertension to search for apnea as a cause cannot be recommended.