Objective: We hypothesized that transient hypotension associated with the symptom of lightheadedness with standing is a common phenomenon in healthy adolescents but may be mistaken for orthostatic intolerance.

Methods: We studied 23 healthy adolescents, combining upright tilt to 70 degrees and to 35 degrees (in 12 patients) with continuous heart rate and blood pressure (BP) measurements. We measured peripheral blood flow and venous pressure in the arms and legs by using venous plethysmography.

Results: Healthy subjects with normal vasoconstrictive responses to sustained upright tilt uniformly have a transient fall in BP during 70 degrees upright tilt that varies from almost undetectable to large decreases in BP easily exceeding the 20-mm Hg threshold for orthostatic hypotension. Large decreases are associated with short-lived symptoms of lightheadedness and are most marked in those with the largest calf blood flow. The higher the flow, the lower the BP falls. There is appropriate reflex tachycardia.

Conclusions: We conclude that transient orthostatic hypotension is common in many healthy adolescents, especially after prolonged recumbency, and is related to dependent vascular tone.