Heart Rate and Cardiac Output

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Posted on 24th March 2011 by admin in Uncategorized

The heart beats non stop day and night.  The number of heat beats that occur per minute is called the heart rate.  This rate is used to determine how much blood is pumped through the heart in a given amount of time.  The volume of blood pumped by the heart is called the cardiac output.  On average, a normal adult heart pumps about 5 liters of blood per minute through the body. A person’s heart rate can vary depending on activity.

However a marked and persistent rate change usually signals cardiovascular disease.

Some people have heart irregularities that affect the heart rate and rhythm.  A heart irregularity is called an arrhythmia.  There are several types of heart arrhythmias.  A person with a slow heart rate that is less than 60 beats per minute has a heart arrhythmia condition called bradycardia.  There are several potential causes of bradycardia that include low body temperature, certain drugs, or parasympathetic nervous activation.  Many endurance athletes have bradycardia because the physical and cardiovascular conditioning that they undergo causes the heart to hypertrophy and stroke volume to increase.  This change allows the resting heart rate to be lower while still providing the same cardiac output.

A fast heat rate over 100 beats per minute is called trachycardia.  This condition can result from elevated body temperature, stress, certain drugs, or heart disease.  It can commonly occur when someone has a high fever.  Persistent trachycardia is a pathological condition because it can promote fibrillation of the heart.  Heart fibrillation is a condition of rapid and irregular heart contractions that result when control of heart rhythm is taken away from the sinoatrial (SA) node due to rapid activity in other regions of the heart.  The rapid, uncoordinated contrations caused by heart fibrillations can result in lack of pumping action.

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