Orthostatic Hypotension

Orthostatic hypotension is the condition where standing up is accompanied by a large drop in 
blood pressure, decreasing the amount of blood the heart is able to deliver to the brain, 
possibly resulting in dizziness or fainting.  In a normal person, this effect is compensated 
for by a reflex mechanism in the autonomic nervous system that increases the heart rate and 
further compensates for the blood pressure, to restore it to it's normal levels. 

The force of gravity overpowers the system initially, and fills the veins of the legs with 
blood, a process termed venous pooling.  This is not simply an effect of gravity 
impeding the return of blood, but involves distension of the veins due to competing forces of 
gravity and atrial pressure.

Sample Problems:

1.	Hypotension means: _______________________.

2.	The mechanism behind orthostatic hypotension is:
		a) weakening of the veins
		b) gravity preventing blood from reaching the brain
		c) gravity impeding blood flow while atrial pressure pushes blood
		d) the left ventricle pumping more than the right ventricle

Answers:

1.	Hypotension means low (blood) pressure.

2.	(c) The combined opposing forces cause the veins to distend, increasing their volume
	and decreasing the amount of blood reaching the heart and brain.

For more information on this topic, please refer to Berne & Levy , 216

Also, check out the following links that may be helpful:

• MetriCor - Orthostatic Hypotension
• National Organization of Rare Disorders (NORD) - Hypotension, Orthostatic
• And, as always, if you have questions, or if you can suggest a helpful link, please e-mail me.

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This page was written by Jason Jopling, a student in this course.

BME 403 Pages maintained by the T.A., Douglas Miles.