What Are The Causes Of An Elevated Heart Rate?

Very few signs of life are as obvious as a heartbeat. Both because human life can't exist for long in the absence of a beating heart, and because the heart provides such a convenient mechanism for assessing life and health status, heart rate is one of the most commonly monitored biological metrics. While the heart must beat to maintain life, however, it doesn't beat at a constant rate. Instead, the heart rate adjusts throughout life and many times each day in response to a variety of circumstances and stimuli. There are many factors that can cause a rapid heart rate.

Lower Blood Pressure

The primary job of the heart is to circulate blood to the body cells, as the blood carries the oxygen and nutrients the cells need to maintain function. Dr. Gary Thibodeau, in his book "Anatomy and Physiology," explains that the heart can adjust its rate in response to changes in blood pressure. Low blood pressure means that with each beat, the heart ejects a bit less blood. As a result, the heart must beat more rapidly in order to maintain the same flow volume as compared to what would be required if blood pressure were higher. Dehydration, therefore, which reduces blood pressure, can lead to rapid heart rate. Also, blood pressure typically drops momentarily upon standing up from a seated or reclining position---this is called orthostatic hypotension. In response, the heart may beat very rapidly for a time to make up for this drop in pressure.

Medication

National Jewish Health, an online medical information source, indicates that some medications also affect heart rate. Beta blockers, which are given for heart-related complications, reduce stress on the heart and slow heart rate. Conversely, beta agonists are medications that increase stress on the heart and elevate heart rate. While they're not given for the purpose of stressing the heart---in fact, there would be little therapeutic benefit in doing so---they have many other positive effects, including dilation of the small airways of the lungs. Beta agonists are commonly used to treat asthma and other chronic airway diseases. Elevated heart rate, while a consequence of taking beta agonists, is merely a side effect of the medication, albeit a noticeable one.

Inhalation

For the heart to ensure that oxygenated blood reaches body cells at a constant rate, it's necessary for blood to circulate through the lungs for oxygen before being sent to the cells. To maximize the exposure of blood to oxygen, the heart does respond somewhat to ventilation, or breathing, rate. In her book "Human Physiology," Dr. Lauralee Sherwood explains that during an inhalation and while fresh air is in the lungs, the exposure of blood passing through the lungs to oxygen is maximized. Blood passing through the lungs during exhalation or when the lungs are empty is not exposed to as much oxygen. To maximize oxygen exposure, therefore, heart rate increases slightly during inhalation and decreases during exhalation. This effect is most noticeable if an individual purposely slows his breathing and monitors his heart rate. During inhalation, the heart rate will increase by several beats per minute, while during exhalation, it slows significantly.