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Low Blood Pressure (cont.)

The Arterial Wall

The space within the intravascular space is variable, based upon the muscle tension in the walls of the arteries. Adrenalin (epinephrine) increases tension and causes the arteries to narrow and support blood pressure. Acetylcholine dilates blood vessels and will lower pressure. Normally, the two are in balance.

Loss of the sympathetic tone may occur with injuries to the spine and damage to the sympathetic trunk, resulting in dilation of the blood vessels and lowered blood pressure.
Over stimulation of the vagus nerve can cause dilation of the blood vessels as well. A temporary, self-limiting situation called vasovagal syncope (passing out from low blood pressure due to overstimulation of the vagus nerve) is often seen when a patient receives a noxious stimulus. This can be physical, like a broken bone, or emotional like a medical student seeing their first operation.