Hyperviscosity as a possible cause of positive acoustic evoked potential findings in patients with sleep apnea: A dual electrophysiological and hemorheological study

Objective: To test the hypothesis that blood hyperviscosity could account for the controversial results observed during electrophysiological evaluation of the brain stem in sleep apnea syndrome. Methods: This was a prospective study of a sample of patients with sleep apnea who were participating in a stroke prevention evaluation. Participants were 610 male patients with obstructive sleep apnea, aged 30-55 years, without large vessel disease on Magnetic Resonance Angiography and neck Doppler sonography, and an infratentorial lesion on head magnetic resonance imaging. Brainstem auditory-evoked potential and hemorheological investigations were carried out. Results: Forty-six percent (N = 282) of the patients evidenced hyperviscosity and 53% (N = 328) had normal rheological findings. Evoked potential changes appeared only in the hyperviscosity positive subgroup. Of these, 84% (N = 239) evidenced BAEP changes with 24% (N = 57) demonstrating sensorineuronal and 76% (N = 182) demonstrating brain stem type abnormalities. After six months of CPAP therapy, hyperviscosity was normalized in 66% (N = 159) of patients. BAEP wave III latency values were normalized in 70% (N = 112) of these patients. Conclusions: Viscosity changes play an important role in the brainstem electrophysiological abnormalities in apnea patients. These abnormalities can be normalized after six months of CPAP therapy.