Evaluating the Heart and Lungs at Work

Are you all worked up because your physician has ordered you to have a stress test?

A stress test, more accurately called a cardiopulmonary exercise test (CPX), is typically performed on a treadmill or bicycle. You exercise at a gradually increasing intensity until fatigue sets in or other changes indicative of a problem become evident. A CPX might be performed as part of a routine physical to assess physical fitness or test for hidden heart disease.

What Does a Stress Test Test?

Symptoms that occur during the test are perhaps the most important and informative variable monitored by a CPX.

Symptoms such as excessive shortness of breath, chest pain or confusion can indicate a heart problem, and the test should be stopped.

Stress tests also make use of another measure called the rating of perceived exertion (RPE). This measure is an indicator of your subjective perception of effort; how you are feeling during the test and in conjunction with the physiological variables gives a more complete picture of your tolerance for the test.

Another important variable is your level of exertion, determined by increasing the speed or incline on the treadmill or the resistance and pedal rate on the bicycle. This variable indicates not only your level of fitness but
also your chances of survival after an event such as a heart attack. Work output is measured in units called METs, or metabolic equivalent of task.

Heart rate is measured in beats per minute and should increase with increasing levels of exercise. Maximum heart rate is figured by subtracting your age from 220 (for men) and from 226 (for women); this provides only an estimate, however.

Resting heart rate typically ranges from 60 to 80 beats per minute. If you take beta blockers for your blood pressure or for other reasons, your heart rate will not be affected the same way by exercise and will tend to be lower while at rest.

Systolic blood pressure, along with heart rate, is the force that delivers blood to the working muscles. Systolic blood pressure is the top number of a blood pressure measurement and should increase with increasing exercise. Diastolic blood pressure is the bottom number and represents the time during which the heart is filling with blood for the next delivery. Diastolic blood pressure should stay the same or perhaps decrease during exercise.

The electrocardiogram (EKG) is monitored throughout the test, and while there will be many changes to it, the most relevant to the CPX is that of the ST segment. Changes in position of this segment during the CPX can indicate a blockage in the blood vessels of the heart, impacting the vessels’ ability to deliver nutrients to the heart muscle.

All of the above factors should be considered when evaluating the results of a CPX.

If you have any questions about your stress test or the results, be sure to ask the members of the testing team or your physician. They are there to help you understand and get the most benefit possible from your CPX.

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What are normal responses for heart rate and blood pressure during a stress test?

Age- and gender related standards for heart rate and blood pressure have been developed by reviewing thousands of stress test results. In general, an excessive rise in heart rate or blood pressure may indicate reduced cardiovascular fitness, while too low of a response may indicate a failing heart.

I have heard the term “METs” used to describe work output during a stress test. What are “METs”?

“MET” stands for “metabolic equivalents of task,” which is shorthand for the amount of energy needed to perform a given level of work. Extensive tables have been developed defining the MET level for various activities ranging from walking, running, grocery shopping and driving a truck.

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