Renal resistance index in patients with obstructive sleep apnea

Background and objective: Previous studies have demonstrated renal dysfunction in patients with obstructive sleep apnea (OSA). The renal resistance index (RI) measured by renal duplexsonography (RI = 1 - [enddiastolic velocity/peak systolic velocity]) is at the same time a marker of parenchymal renal damage and predictor of the progression of renal dysfunction. It was the aim of this study to test the influence of OSA on RI. Patients and Methods: RI was compared between patients with (n = 97) and those without OSA (n = 61). The impact of OSA on the RI was analysed by adjusting for age. Thus, the difference between the measured RI and the age-based RI was expressed as a percentage of the normal age-adjusted value (RI%). Results: OSA patients showed a trend towards an increase in RI (69.1 +/- 8.8 vs. 66.5 +/- 8.3%, p = 0.068) and RI% (10.2 +/- 12.9 vs. 6.4 +/- 11.4%, p = 0.060), respectively. In patients with mild or moderate OSA (apnea-hypopnea-index [AHI] 5 - 30/h) this difference was significant (RI: 70.5 +/- 9.1 vs. 66.5 +/- 8.2, p = 0.012; RI%: 12.1 +/- 13,4 vs. 6.5 +/- 11.4%, p = 0.012). RI of patients with severe OSA did not significantly differ from those without OSA. In patients with mild and moderate OSA there was a significant linear association between AHI and RI or RI%. This association was independent of hypertension or diabetes. Conclusion: An impairment of renal perfusion and renal parenchymal damage due to increased sympathetic activity may promote renal dysfunction in patients with obstructive sleep apnea.