Initial Orthostatic Hypotension

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Definition

A transient fall in blood pressure and increase in heart rate during rapid standing.

True 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. 

Transient initial orthostatic hypotension is a normal phenomenon which may be mistaken for orthostatic intolerance. When we and others measured peripheral blood flow and venous pressure in the arms and legs the data showed that healthy subjects with normal vasoconstrictive responses to sustained upright tilt, almost always experience a transient fall in blood pressure during standing and to a lesser extent during 70o upright tilt. The response  varies from almost undetectable BP changes to large decreases in blood pressure easily exceeding the 20mmHg threshold for orthostatic hypotension. Rarely there is fainting. 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.

 

Representative beat-to-beat arterial blood pressure changes are shown. Systolic blood pressure can normally decrease up to 40 mmHg during the first minute of upright tilt. This "Initial orthostatic Hypotension" is most often completely normal and is caused by rapid translocation of blood from the central circulation to the lower body upon rapid standing. There is a lag  in neurovascular  compensation that usually results in a trough of BP at 15-20 after standing and that is typically resolved with normal BP by 1 minute of standing. 
Averaged heart rates and blood pressure for normal healthy control subjects aged 162 years are shown in the upper and lower panels respectively. Blood pressure decreases while heart rate increases (via vagal baroreflex efferents) during standing. Stable  HR and BP are achieved within one minute
The decrease in arterial BP correlates well with the increase in blood flow in the leg (but not arm).

 

 


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Initial Orthostatic Hypotension
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Fainting and Related Phenomena a Lay Review
Orthostatic Intolerance
Orthostatic Hypotension