Dr. Ben Wedro practices emergency medicine at Gundersen Clinic, a regional trauma center in La Crosse, Wisconsin. His background includes undergraduate and medical studies at the University of Alberta, a Family Practice internship at Queen's University in Kingston, Ontario and residency training in Emergency Medicine at the University of Oklahoma Health Sciences Center.
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
Low blood pressure is a difficult clinical finding for a healthcare provider
to address. While high blood pressure is known as the "silent killer," because
it is associated with few acute symptoms, hypotension (hypo=low +
tension=pressure) may be normal for a patient if it is without symptoms, but can
be of great importance if it is associated with abnormal body function.
Sometimes low is good, a goal to be achieved in keeping blood pressure under
control. Sometimes low is bad because there is not enough pressure to provide
blood flow to the organs of the body.
Blood pressure readings have two parts and are expressed as a ratio:
blood pressure, for example is 120/80 (120 over 80) and measures the pressure
within the arteries of the body.
Systolic pressure, the upper number, measures
the pressure within the arteries when the heart is contracting (systole) to pump
blood to the body.
Diastole pressure, the lower number, measures resting pressures within
the arteries, when the heart is at rest.
You can think of the heart and the blood vessels
(arteries and veins) as a system to pump blood, just like the oil pump in your
car. Oil is pumped through rigid tubes. Pressure remains relatively constant throughout the pumping cycle
unless the pump fails or there is an oil leak. Then oil pressure will fall.
The body is similar, except that the tubes have pliable walls, meaning that
the space within the arteries can get bigger or smaller. If the space gets
bigger, there is effectively less fluid, and pressure falls. If the space gets
smaller, pressure goes up. Arteries have layers of muscles within their walls
that can contract and narrow the artery, making less space inside the vessels.
Alternatively, the muscles can relax and dilate the artery, making more room.
These muscles are under the control of the autonomic nervous system, the body's
automatic system that makes adjustments for moment-to-moment changes in the
relationship of the body to the world. The autonomic nervous system has two
pathways that balance each other.
The sympathetic nervous system uses adrenaline (epinephrine) to cause the
muscles to contract (sympathetic tone). The nerves that help with this control
are located in the sympathetic trunk, which is a group of nerves that runs
alongside the spinal column. The parasympathetic system uses acetylcholine to
make muscles in the blood vessel walls relax via the vagus nerve. As an example,
when you stand up, the blood vessels have to narrow just a little to cause a
slight increase in blood pressure, so that blood can travel uphill to the brain.
Without that change, you might feel lightheaded or pass out.
Normal blood pressure depends on many factors including age and body size.
Infants and children have lower normal readings than adults.
Smaller or petite
patients may have lower normal blood pressure ranges.
Based upon American Heart
Association guidelines, any reading greater than 120/80 is considered
pre-hypertension or early high blood pressure.
For low blood pressure to be a problem there needs to be a symptom associated
with that low number. Readings below 120/80 may be normal depending upon the
clinical situation. Many people have systolic blood pressures below 100, but
some people develop symptoms with pressures that low. Symptoms of low blood
pressure occur because one or more of the body's organs is not getting enough
Medical Author: Benjamin C. Wedro, MD, FAAEM
Medical Editor: Melissa Conrad Stöppler, MD
The ambulance call comes in.
"We're running lights and siren with a 67 year old male.
He's confused, lethargic, blood pressure 80 over 40, thready pulse and sweaty. We'll be at your
door in a couple of minutes."
The nurses start setting up the equipment to care for the patient. We've been
through this drill before when someone arrives at the ER with low blood
pressure. I hope it's an easy diagnosis and something that we can treat quickly.
IV's are set up, monitor pads ready. The respiratory tech arrives with her
machines just in case they are needed.
The EMTS unload a man in obvious distress, sweaty, struggling to breathe, and
"He's had a fever for a couple of days with a
cough. Past history of
COPD, heart problems, still smokes."
The diagnosis still could be easy, but there are a lot of things that could
be causing this man's condition. He is in shock; his low blood
pressure is not
enough to provide blood flow and oxygen to his brain. That's why he is
lethargic. No doubt the rest of his organs are at risk too. But why?