It is estimated that over 500,000 Americans are
afflicted with Orthostatic Intolerance. Despite the enormity of
the number, these conditions are among the least understood of
the autonomic disorders.
Affecting predominately younger individuals,
often in those under the age of thirty five, these syndromes
affect more women than men. The onset can be sudden, and the
impact can be significant on both lifestyle and on the capacity
Often, these conditions tend to be misdiagnosed
as either a psychiatric or anxiety - related disorders, due to
the nature of the symptoms.
Standing upright results in a series of reflexive
bodily responses, regulated by the Autonomic
Nervous System, to compensate for the effect of gravity upon
the distribution of blood. These conditions are a result of an
inappropriate response to this change in body position.
The normal response for a change in body
position, results in a stabilization to the upright position in
approximately sixty seconds. During this process, the normal
change in heart rate would include an increase in heart rate of
10 to 15 beats per minute, and an increase in diastolic pressure
of 10 mm Hg, with only a slight change in systolic pressure.
For those who are afflicted with Orthostatic
Intolerance, there is an excessive increase in heart rate upon
standing, resulting in the cardiovascular system working harder
to maintain blood pressure and blood flow to the brain.
Upright posture also brings about a neurohumoral
response, involving a change in the levels of vasopressin, renin,
angiotensin and aldosterone levels - all of which are involved in
the regulation of blood pressure.
Additionally, arterial baroreceptors, particularly those in
the carotid sinus area, play an important role in the regulation
of blood pressure and the response to positional changes. As the
heart pumps blood to the body, the left atrium is passively
filled with blood as a result of the force exerted by venous
blood pressure. The baroreceptors in the left atrium respond,
proportionately, to the pressure exerted by this venous blood
pressure. Thus, a drop in venous blood pressure will trigger a
compensatory response to increase blood pressure.
Any disruption in any of these processes, or their
coordination, can result in an inappropriate response to an
upright position, and can lead to a series of symptoms, and may
The inappropriate response to an upright position has been
observed and given a variety of names in medical literature.
These names have included:
Currently, there are three main categories used
to describe Orthostatic Intolerance Conditions:
These conditions are similar in presentation, and
in the ensuing treatment plans. The underlying mechanisms will
have to become better understood in order to alleviate some of
the overlap in the terminology used for these conditions.
Individualized treatment plans are often
necessary to manage these conditions.
The symptoms for these conditions may include the
Weakness - most noticeable in the legs
Shortness of Breath
Migraines and Other Headaches
There has been much new insight gained as to the
mechanisms of these disorders in the past several years, and as a
result, it can be confusing for both the affected individual, as
well as the physician, to get a clear understanding of these
conditions, and how to effectively manage them.
As a result, management of these conditions needs
to be highly individualized, and may include both pharmocologic
and non-pharmocologic methods.
The majority of individuals affected with Orthostatic
Intolerance Syndromes see an improvement in their condition, and
only experience mild symptoms. However, for some, the disorder
can be a debilitating condition, that poses a significant
challenge for effective treatment. Additional research into the
underlying causes of these disorders will be necessary to develop
more effective treatment plans.
For many, the effect of these disorders will be
short lived, while others tend to show a progressive nature to
their disorder, and a worsening of symptoms may occur.
In most cases, a well defined, individualized,
treatment plan needs to be developed. Since the underlying causes
for these disorders are not yet completely understood, no one
approach can be defined as the sole treatment plan. The
underlying causes for these disorders are probably multiple, and,
for some, may include an underlying autonomic nervous system
Continued research into these disorders will
result in more effective diagnostic tools and treatment plans.