Instantaneous orthostatic hypotension in children and adolescents: a new entity of orthostatic intolerance.

We are the first to report clinical characteristics and circulatory and catecholamine responses to postural change in 44 children with instantaneous orthostatic hypotension (INOH). The symptoms include chronic fatigue, orthostatic dizziness, weakness, sleep disturbance, syncope or near syncope, headache, and loss of appetite. We divided the patients into two groups: group I (30 patients) had either a recovery time for mean arterial pressure of >25 s or a recovery time of >20 s with a 60% or greater decrease in mean arterial pressure at the initial decrease; group II (14 patients) had a prolonged reduction in systolic arterial pressure of > 15% during the later stage of standing (3-7 min) in addition to the criteria for group I. INOH was characterized by a marked reduction in blood pressure at the initial decrease (mean, -55/-27 mm Hg systolic/diastolic). Delayed recovery time of >60 s was found in 21 of 44 patients and orthostatic tachycardia (>35 beats per minute) in 20 of 44. Plasma noradrenaline responses were significantly lower in group I and II than in controls at 1 min of standing and were lower in group II at 5 min of standing. These results suggest that mechanisms responsible for INOH may depend on insufficient sympathetic activation during standing, possibly due to centrally mediated sympathetic inhibition, thus causing impairment of quality of life including school absenteeism. INOH is an important pathologic condition in children with complaints of orthostatic intolerance and can be an unrecognized cause of chronic fatigue. This condition can be identified by using a noninvasive beat-to-beat continuous blood pressure monitoring system.