Autonomic stress tests in obstructive sleep apnea syndrome and snoring

Apneic events in the obstructive sleep apnea syndrome (OSAS) are associated with cardiovascular responses mediated through the autonomic nervous system. We examined autonomic cardiovascular responses in 33 patients (median age = 50 years, range = 20-72 years) undergoing polysomnography for suspected OSAS. We examined these responses in the evening and at arousal in the morning. Tests consisted of heart rate responses to Valsalva maneuver, deep breathing and change from lying down to standing. In addition, systolic blood pressure (BP) response to standing and diastolic BP response to handgrip were studied. Each abnormal test scored +1 and each marginal result +0.5. Autonomic nervous system (ANS) test results were scored as abnormal if a subject had a score > 1 which included at least one abnormal test. The total scores for evening and morning tests combined showed 11/24 sets of scores > 1 in 12 severe OSAS patients [median RDI (apnea+hypopnea per hour slept) = 44 (range = 31-74)] compared to 3/22 in non-OSAS (p = 0.04). The response to deep breathing, expressed as an expiratory to inspiratory ratio (E/I), was the test most often found abnormal. A significant difference between normal abnormal autonomic stress test (AST) groups was observed in the evening and the morning as regards cumulative time spent under 90% SaO2 and minimal SaO2. We conclude that abnormal autonomic stress responses are common in OSAS and are probably a secondary defect.