is Neurally Mediated Syncope (NMS) and why do these
patients pass out? NMS is a condition that
can occur in a wide range of people, many of whom
do not have any other associated cardiovascular problems.
These patients give a history of repeatedly having
syncope (passing out spells) over the course of several
years. Some of these spells may be preceded by a hot
sensation or nausea but many come on without any warning.
The patient may fall to the ground and recover consciousness
quickly and without any further problems. The episodes
of syncope may occur at church, in the grocery store,
while a blood specimen is being drawn, or while sitting
quietly at home, etc. Surprisingly, the majority of
the patients never sustain serious injuries and the
diagnosis may go undetected for decades. Patient's
get used to having "faints" and life goes
on! The availability of the Tilt Test, its wide success
in establishing the diagnosis of NMS, and effective
treatment for NMS has resulted in the well deserved
popularity of the test.
understand this phenomenon, we must first examine
how the nervous system of the body functions. During
our daily activities, our heart rate (HR) and blood
pressure (BP) constantly rise and fall to meet the
needs of the body. The HR and BP are lower at rest,
while the HR picks up and BP is elevated during emotional
stress and exercise. The control of the HR and BP
are under the domain of the sympathetic (pronounced
sim-pa-thetic) and parasympathetic nervous system.
The former increases the HR and BP while the latter
reduces them. To simplify this concept, let us imagine
that the body is an automobile. Pressing the accelerator
pedal would make the car work harder and go faster.
In contrast, pressing the brake pedal would slow the
car down. Thus, the sympathetic nervous system behaves
like an accelerator for the body while the parasympathetic
system functions like a braking system. You with me?
Normally, the sympathetic and parasympathetic
nervous system work together in a very efficient and
cooperative manner. Just like a good driver, the accelerator
and brake pedals are used efficiently (one being slowly
pressed while the other is smoothly released). The
car slows down and speeds up so smoothly that one
does not recognize the change. Similarly, our HR and
BP goes up and down without us being aware of it.
From time to time, this system breaks down in people
with NMS. It is almost as if the accelerator pedal
remains in the control of the car driver while the
braking system is occasionally turned over to an extremely
nervous "back seat driver." This spells
trouble! Now, if the "car" accelerates too
rapidly (HR and BP goes up), the back seat driver
panics and SLAMS the brake. The HR and BP (either
singly or together) drop suddenly and severely. This
reduces blood supply to the brain and the patient
passes out. The back seat driver then steps off the
brake pedal, the HR and BP increases, blood flow is
restored and the patient awakens.
The condition may be diagnosed
by performing a tilt test.
Effective treatment is available for patients with
a positive test.