1. Cardiac stroke volume and sympathetic/parasympathetic measurements increase the sensitivity and specificity of HUTT in children and adolescents Mohammed. T. Numan, Jeremy.E. Lankford, RawanAlnajjar Anand. Gourishankar, Ian. J. Butler Introduction: Head up tilt table test (HUTT) is the gold standard in evaluating autonomic dysfunction and syncope in children and adolescents. Limitations of conventional HUTT, cycling blood pressure (BP) every one to two minutes, with heart rate (HR) correlated with patient symptoms, has low sensitivity and specificity (~ 60% and 70% respectively). Conventional HUTT has low reproducibility because the test depends mainly on the occurrence of severe symptoms to call the test positive. Investigators have evaluated more reliable and sensitive physiological parameters to increase predictability of HUTT Methods: From May 2009 to May 2012 we performed 422 HUTT evaluations on children and adolescents. The first group of 152 patients had conventional HUTT, including HR, arm cuff BP, and oxygen saturation recorded every minute for 10 minutes while supine, for 30 minutes while head up 70⁰ and for 10 minutes with supine reposition while recording patient symptoms. The second group included 270 patients with HUTT using Task Force Monitor® with display and storage of continuous BP, HR, cardiac stroke volume (SV) by trans-thoracic impedance and calculated sympathetic and parasympathetic activity correlated with symptoms and signs. Median ages were 12.5 years and 13.2 years in group one and two, respectively. Patients from both groups were referred by pediatric neurologists, cardiologists, gastroenterologists and rheumatologists with syncope (63%), dizziness (88%), light headedness and headaches (52%), chronic nausea and stomach pains (32%), chronic fatigue (42%), convulsions (6%), fibromyalgia (2%), palpitations and chest tightness (12%) and metabolic disorders (10%). Heart Rate Continuous BP Cardiac Stroke Volume Head up tilt Results: A positive test was defined in group one as severe symptoms of syncope, blackout, vomiting, severe headache, excessive fatigue and tremors or convulsions accompanied by changes in HR (tachycardia, bradycardia) and/or blood pressure. In group two, similar symptoms were accompanied by significant changes in HR, BP, cardiac SV and sympathetic/parasympathetic activity. There was increased ability to correlate clinical manifestations with physiological abnormalities on HUTT in the second cohort of subjects and also an increased sensitivity of the test to determine whether there was orthostatic intolerance Sympathetic over activity Parasympathetic activity Tilt up Conclusion: HUTT using added parameters of cardiac Stroke volume, sympathetic and parasympathetic activity increase the clinical correlation with this test. Conventional test dependent on the severe symptoms to conclude it positive will exclude several positive patients with dysautonomia and decrease the positive predictive value. While several patients who were tested using the added parameters were showing significant changes even with lack of severe symptoms like syncope and sinus pauses. Start tilt Blue for vagal Red for sympathetic Dizzy and palpitation Nausea and bradycardia Figure 1: continuous BP, HR and stroke volume during supine, head up and reposition to supine Figure 3: Fourier analysis of HR variability with low frequency harmonics showed sympathetic activity and high frequency harmonics for parasympathetic Figure 3: Upper lines showed sympathetic and parasympathetic tone collected from HR variability and diastolic BP variability. Lower line showed the balance activity between the two autonomic tones