How to Explain Cardiac Reserve

The heart is one of the hardest-working organs in your body. It is the chief organ in charge of blood circulation. This means it must pump in proportion to the oxygen needed. When running, for example, you need more oxygen. As a result, your heart must pump faster to keep up with the demand. Cardiac reserve is how how high this demand can go beyond what is normal for a human being.

Instructions

• 1

  Lay out the baseline first. This is the basic "normal" heart rate for a human being doing day-to-day activities such as walking, sitting or cooking. It is your regular heartbeat and doesn't involve anything strenuous like running or fighting. The baseline issue is central because you calculate cardiac reserve from this point.

• 2

  Define the concept of cardiac adjustment. Under some circumstances, your heart must adjust quickly from a fairly normal rate to a higher rate of activity. Breaking into a run quickly, working out in the gym or being frightened or shocked force your heart to adjust its rate of pumping quickly to bring more oxygen and nutrients to the rest of the body. The cardiac reserve is then defined as how far from the baseline rate the heart can move in times of stress. You may also find it useful to explain that the concept of adjustment also has much to do with the condition of your heart muscle. How much this muscle can stretch to accommodate more blood during the time of the diastole (that is, when the heart has to "push" blood into the veins) is a major part of calculating this adjustment and, therefore, reveals cardiac reserve.

• 3

  Bring together the two concepts to give a full definition of cardiac reserve. It is normally expressed as a percentage. For a healthy or young person, the normal reserve is between 300 and 400 percent. This means that the heart can adjust its pumping to accommodate three or four times the amount of strain the body is placed under in exceeding its normal rate. An example might work here: If you need to break into a run to get away from a hostile dog, your heart must compensate to pump more oxygen-rich blood through your body, which now is under increased stress. Healthy people can do this at a rate normally three or four times from that of a standing or sitting position. For older folks, the heart reserve is usually only 200 percent of normal.