Orthostatic Hypotension
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Definition Defined by the consensus group of the American Autonomic Society as a sustained decrease in blood pressure exceeding 20 mmHg systolic or 10 mmHg diastolic occurring within 3 minutes of upright tilt. Orthostatic hypotension is a sign of autonomic dysfunction and dysautonomia in adults and in children. It may also occur with reductions of blood or plasma volume. However, the experience of transient hypotension often associated with the symptom of lightheadedness with standing is common among teenagers and is familiar to pediatricians. Transient orthostatic hypotension in children and teenagers is a normal phenomenon related to the relative rapidity of blood translocating from the thorax to the dependent parts of the body during orthostasis. This may be sufficiently rapid that there is not sufficient time for neurovascular compensation and blood pressure falls. We hypothesized that transient hypotension is a normal phenomenon which may be mistaken for orthostatic intolerance. We measured peripheral blood flow and venous pressure in the arms and legs using venous plethysmography. Data indicate that healthy subjects with normal vasoconstrictive responses to sustained upright tilt, uniformly experience a transient fall in blood pressure during 70o upright tilt which varies from almost undetectable to large decreases in blood pressure easily exceeding the 20mmHg threshold for orthostatic hypotension. Large decreases are associated with short-lived symptoms of dizziness and are most marked in those with the largest calf blood flow. The higher the flow, the lower the blood pressure falls. There is appropriate reflex tachycardia.
Orthostatic hypotension and lightheadedness which lasts for more than a minute is probably abnormal. |
