| Research Abstract |
We determined the criteria for instantaneous orthostatic hypotension (INOH), a typical form of orthostatic dysregulation, from the reference data of 173 healthy children, aged 6 to 18 years. Also reported were clinical characteristics, circulatory and catecholamine responses to postural change in 44 children and young adults with instantaneous orthostatic hypotension (INOH) compared with 73 age matched controls. The criteria for INOH was as follows : group I (mild type), a 60% or greater decrease in mean blood pressure during the initial phase of standing, or blood pressure recovery time of more than 25 sec evaluated by a non-invasive finger arterial pressure monitoring system ; group II (severe type), prolonged reduction in systolic arterial pressure of more than 15% during the later stage of standing in addition to the criteria for group I.Sensitivity and specificity of this criteria were as high as 100% and 90.4%, respectively. Group I and group II showed significantly more pronounc
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ed reduction in BP) than normal controls at the initial drop (% reduction for systolic BP : -53+-12, -50+-6 vs.-32+-16, respectively, p<0.001), one minute of standing (-6+-10, -24+-18 vs.6+-12, p<0.001) and five minute of standing (-5+13, -21+-11 vs.8+-9, p<0.05). Plasma noradrenaline responses to standing were significantly lower in group I and group II than in controls after one minute of standing (50+-63,33+-39 vs.99+-56 pg/ml, respevtively), and were kept lower in group II after five minutes (218+-122,115+-78 vs.193+-98 pg/ml, respectively). The physical complaints included chronic fatigue (91% of the patients), orthostatic dizziness (88%), weakness (84%), sleep disturbance (73%), syncope or near syncope (68%), headache (68%), loss of apprtite (57%), abdominal pain (55%). Among these complaints chronic fatigue, loss of appetite, orthostatic dizziness, syncope and morning tiredness were specific for INOH.These results suggest that mechanisms responsible for INOH may depend on reduced noradrenaline secretion during orthostatic stress, associated with centrally mediated sympathetic inhibition. The patients in group II seemed to have more decreased sympathetic activation and thus more impaired quality of life than those in group I including school absenteeism. INOH is an important pathological condition in children with complaints of orthostatic intolerance and chronic fatigue. This can be identified when using a non-invasive beat-to-beat continuous blood pressure monitoring system. Less
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