Low Blood Pressure

By: Maia Oelschlager

Heart Structure

4 Chambers of the Heart: Left Atrium, Right Atrium, Left Ventricle, Right Ventricle

4 Valves of the Heart: Atrioventricular valves (tricuspid and bicuspid) separate atrial chambers from ventricles.

Semilunar valves separate ventricular chambers from ventricular chambers.

  • Blood is pumped into arteries and out of veins
  • Named according to location


2 layers of fibrous tissue surrounding the heart.

Systemic Circulation

  • Blood is pumped from the left side of the heart to all other body tissues.

Pulmonary Blood Flow

  • Blood is pumped from the right side of the heart to the gas exchange tissues of the lungs

Conduction System of the Heart

Specialized cells rapidly conduct electrical impulses throughout the heart.
Conduction System The Heart's Conduction System Heartbeat Pacemaker Video

Arteries, Veins, and Capilaries

  • Arteries: Carry oxygenated blood away from the heart
  • Veins: Carry blood toward the heart
  • Capillaries: Microscopic, Connect arterioles and venules

ECG Test (Electrocardiogram)

An ECG Test is a test that checks for problems with the electrical activity of your heart.

  • P wave - atrial contractions
  • QRS wave - ventricular contractions
  • T wave - electrical activity produced when the ventricles are recharging for the next contraction

Blood Pressure

The pressure of blood as it flows through the cardiovascular system.

5 Factors that Influence Blood Pressure

  • Blood Volume - The more blood there is in the arteries, the higher the blood pressure will be. The less blood there is in the arteries, the lower the blood pressure will be.
  • Strength of Heart Contractions - The strength and rate of the heart affect cardiac output and therefore blood pressure.
  • Heart Rate - When the heart beats faster, more blood enters the aorta, increasing blood volume and blood pressure. ( only if stroke volume doesn't decrease when heart rate increases)
  • Blood Viscosity - If blood becomes less viscous (thinner) than normal, blood pressure decreases. Usually in high altitudes, the number of red blood cells increases beyond normal, increasing the viscosity and blood pressure.
  • Resistance to Blood Flow - Any factor that changes the blood's resistance to flow has a huge impact on blood pressure.

The Cardiac Cycle

  • Each complete heartbeat, including contraction and relaxation of the atria and ventricles

Stroke Volume

  • The amount of blood that is ejected from the heart with each beat


  • The alternating expansion and recoil of the arterial walls produced by the alternate contraction and relaxation of the ventricles, travels as a wave away from the heart.

Normal Heart Sounds

Types of Blood Tests

Lub Dup

  • Lub is caused by the vibration and abrupt closure of the AV valves as the ventricles contract. The first sound is of longer duration and has a lower pitch.
  • Dup is caused by the closing of the SL valves when the ventricles relax.

Types of Blood Tests

  • Hematocrit Test: The portion of your total blood volume that is composed of red blood cells. It indicates whether you have too little or too many blood cells. A lab technician puts a sample of your blood into a centrifuge, which spins your blood in a test tube and separates the blood into three parts. The three parts are plasma, red blood cells, and other blood cells.
  • WBC Count: Part of the Complete Blood Count Test. A blood sample is drawn from a vein to screen for diseases and conditions.
  • Platelet Count: Also part of the Complete Blood Count test. Used to detect a low or high number of platelets in the blood, also to screen for diseases.

Case Study: Low Blood Pressure

Hypotension; blood pressure of 90 mmhg or below systolic and 60 mmhg or below diastolic. Low blood pressure can be broken down to different categories according to causes and factors.


  • Blurred Vision
  • Fainting
  • Dizziness
  • Fatigue
  • Nausea
  • General Feeling of Weakness
  • Thirst
  • Rapid, Shallow Breathing


  • Pregnancy
  • Heart Problems
  • Endocrine Problems
  • Dehydration
  • Blood Loss
  • Severe Infection
  • Severe Allergic Reaction
  • Lack of Nutrients
Some drugs and medications can also cause hypotension.

  • Diuretics, some antidepressants, alpha and beta blockers, drugs for Parkinson's disease, and sildenafil.

Test Results of a Patient with Hypotension

  • EKG - Sometimes heart rythym abnormalities come and go, so if it doesn't detect any abnormalities your doctor may ask you to wear a Holter Monitor to record your heart's electrical activity as you go about your day.
  • Pulse - Increased
  • Blood Pressure - 90/60 mmhg or lower
  • Stroke Volume - decreased
  • Cardiac Output - decreased
  • Heart Sounds - unaffected
  • Blood Tests - can show possible causes


Low blood pressure that causes no symptoms or mild symptoms rarely needs to be treated.

If the low blood pressure is caused by medications, the doctor will change the dose of the medication or stop it completely.

If the cause is unclear or there is no treatment, the goal is to raise the blood pressure. You can do that by increasing salt intake, drinking more fluids, or taking certain medications.

The best treatment depends on the cause of the low blood pressure. Doctors usually try to address the underlying problem, rather than the low blood pressure itself.