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Exercise Stress Tests

Introduction

Exercise Stress Testing

What are the risks of exercise stress testing?

Procedures for Exercise Stress Tests

What happens when the test is abnormal?

Further Diagnostic Tests

References and Related Links


Introduction

Cardiopulmonary health is essential for emergency responders.  The physiologic burden of wearing bulky protective clothing and breathing through a self-contained breathing apparatus while performing physically demanding work at the incident scene places an enormous strain on the body.  Furthermore, the fire fighters work environment is known to contain toxic chemicals that may contribute to development of heart disease over time.  This is one reason why emergency response personnel should be provided a mandatory, annual, non-punitive and confidential wellness / fitness program.

The IAFF/IAFC Fire Service Joint Labor/Management Wellness-Fitness Initiative recommends cardiopulmonary testing for all emergency responders.  Such testing should be conducted as a part of pre-employment testing and annually thereafter.


Exercise Stress Testing

The term exercise stress test refers to stressing the body by putting an exercise load on it and measuring the response.  Exercise stress tests can come in many forms, however most people relate the term to just cardiovascular testing.  Exercise stress testing is an important tool used by physicians and exercise specialists to:

  • Determine whether an individual is physically fit to perform essential job duties without undue risk of harm to self or others
     

  • Monitor the effects of exposure to specific biological, physical, or chemical agents that may be related to hazardous working conditions
     

  • Detect any patterns of disease in the workforce that might indicate underlying work- related problems
     

  • Provide the fire fighter with information about his/her current health
     

  • Provide a cost-effective investment in the early detection, disease prevention, and health promotion of the fire fighter
     

  • Develop recommendations for exercise prescription and rehabilitation
     

  • Comply with federal, state, provincial, and local requirements

An exercise stress test is just one diagnostic test that a physician may use in the determination of a persons' fitness for duty.  The determination of fitness for duty must not be made on the basis of a single test, but rather on a comprehensive evaluation of the individual that includes diagnostic testing, personal medical history, and other indicators of health status. 

There are two levels of evaluating aerobic exercise capacity, either maximal or sub-maximal. 

Maximal aerobic exercise testing makes the fire fighter work until exhaustion in order to directly determine VO2 max  and maximum heart rate.  These tests must only be performed by qualified medical personnel under the supervision of the fire department physician and must be conducted in a medical care setting. 

 

Sub-maximal exercise stress testing makes the fire fighter work until a pre-determined heart rate is achieved.  The pre-determined heart rate is typically 85% of the predicted maximum heart rate.  Such testing only allows for a prediction of maximum exercise capacity.  The IAFF/IAFC Fire Service Joint Labor/Management Wellness-Fitness Initiative recommends a sub-maximal exercise stress test without EKG because of the safety of the test, they are relatively inexpensive, are easier to administer by an exercise specialist, and they provide the sufficient information needed for the evaluation of cardiopulmonary fitness.  (Note: The IAFF/IAFC Fire Service Joint Labor/Management Wellness-Fitness Initiative also recommends a resting EKG as part of an emergency responders annual medical evaluation.)
 

Exercise stress test can be administered in conjunction with many different physiologic monitoring devices.  Monitoring devices will be selected based upon the goal of the test and the depth of data necessary to achieve the goals.  

Exercise Stress Testing with heart rate monitoring measures the heart's performance and determines exercise capacity (VO2 max).  This information is used to determine safe levels of exercise.  Such testing may be either maximal or sub-maximal.  Maximal capacity testing must only be performed by qualified medical personnel under the supervision of the fire department physician and must be conducted in a medical care setting.


Exercise Stress Tests
with EKG allow the physician and exercise specialist to determine maximal exercise capacity (VO2 max), and also detect early signs of coronary artery disease.  An EKG (electrocardiogram, also called ECG) is a non-invasive test that records the heart’s electrical impulses.  It can identify abnormalities in heart rate and rhythm, and it can help to establish whether the heart muscle is receiving enough oxygen.  Some early signs of angina or myocardial infarctions can be seen on a 12-lead EKG.  Such testing can be either a sub-maximal or maximal test.  Maximal capacity testing must only be performed by qualified medical personnel under the supervision of the fire department physician and must be conducted in a medical care setting.

 

Exercise Stress Test with EKG and direct respiratory gas analysis allows the physician and exercise specialist to determine exercise capacity (VO2 max), determine safe levels of exercise, detect early signs of coronary artery disease and also to determine maximal oxygen consumption, respiratory gas exchange ratio, and ventilatory equivalent for oxygen.  Such testing will require the individual to breath into a tube during the test.  Such testing can be either a sub-maximal or maximal test.  Maximal capacity testing must only be performed by qualified medical personnel under the supervision of the fire department physician and must be conducted in a medical care setting.


What are the risks of exercise stress testing?

Exercise stress testing, as with any other type of activity, carries a certain degree of risk.  However, the percentage of individuals who have cardiovascular problems during an exercise stress test or other activity is extremely low.  When there are problems they are usually the result of insufficient blood flow to the heart muscle or problems with the heart's electrical signals.  If there are any symptoms of chest pain, chest tightness, shortness of breath, dizziness or signs of any poor perfusion, the test will be terminated and the individual will be allowed to rest.  The risk of death is very low, and careful monitoring during the test further adds to its safety.
 

Procedures For Exercise Stress Tests

There are many protocols that have been used to evaluate aerobic exercise capacity.  Some of these protocols differ in the use of evaluation equipment (treadmill, stairmill, stationary exercise bike, swimming pool, step test), rate of increasing work output, and the test end point (maximal or sub-maximal test). 

The IAFF/IAFC Fire Service Joint Labor/Management Wellness-Fitness Initiative  provides two protocols to determine the fire fighter's exercise capacity.  These two protocols were specifically developed and validated to measure the sub-maximal aerobic capacity of uniformed-personnel.   Both exercise stress tests are sub-maximal in nature and do not use either EKG or direct respiratory gas analysis. 

You can view the exercise stress test protocols and all other fitness protocols of the WFI 3rd Edition in PDF format by clicking here
 

What happens when the test is abnormal?

If  the test is terminated early because of chest pain, chest tightness, extreme shortness of breath, dizziness, lost of consciousness, or an abnormality in heart rate or blood pressure, you may have to undergo further diagnostic testing and evaluation.   Depending upon the reason for early termination of the test, the fire department physician will rest you until your blood pressure and heart rate stabilizes and may send you for one of the following diagnostic tests.
 

Further Diagnostic Tests

Further diagnostic testing may be required to determine the cause of the health condition or symptoms that resulted in early termination of the exercise stress test.  Further diagnostic testing is divided into noninvasive tests and invasive tests. For more information, consult the  Johns Hopkins Cardiology Division website.

Non-Invasive Tests:

Electrocardiogram: (ECG or “EKG”)  A non-invasive test that records the heart’s electrical impulses.  An EKG can identify abnormalities in heart rate and rhythm, and it can help to establish whether the heart muscle is receiving enough oxygen. Some early signs of angina or myocardial infarctions could be seen on a 12-lead EKG.  This test can be done at rest or as part of the exercise stress test.

Holter Monitoring:  A Holter monitor provides a continuous EKG recording, usually for 24-48 hours, while you go about your normal daily activities.  It is used to detect abnormalities that may not occur during a resting EKG.  Wires are attached to your chest and connected to a small recording device that you carry with you.  If you experience any symptoms, you push a button so that your heart rhythm at the time of your symptoms can be determined.  An doctor will later analyze the recordings of your heart to determine what your heart rhythm was while you were experiencing your symptoms and also whether any abnormal heart rhythms occurred while you were wearing the Holter monitor.

Event Monitors:  Event monitors are similar to Holter monitors. The difference is that event monitors only record the heart rhythm when you activate them.  They typically are used for one month, during which patients are instructed to trigger the device if symptoms occur.  Once a recording is obtained, the EKG tracing can be transmitted over the telephone to a monitoring station, which will analyze the EKG recording and send it to your doctor for interpretation.  This test allows a doctor to determine if symptoms are caused by an arrhythmia

Echocardiogram:  (also known as an "echo") A non-invasive test that uses high-frequency sound waves to produce a study of the motion of the heart's chamber and valves.  During this procedure, a sound transducer is placed on the chest and images of the heart are recorded for further analysis.  This is used to test resting cardiac function, and given the non-invasive nature of this test, it is usually use as one of the first diagnostic tests for heart function.

Stress EchocardiogramA stress echocardiogram, or "stress echo", is an exercise test that is combined with an ultrasound study of your heart.  This test allows your physician to see how well your heart pumps during increased activity.  A brief echocardiogram will first be performed while you are at rest.  A technician will then prepare you for your exercise test.  A physician will be present for the exercise portion of the test.  Immediately after exercise, you will lie down on a bed and a second set of ultrasound pictures will be recorded.  By comparing the pictures taken before exercise with the pictures taken after exercise, your physician will be able to see any changes in your heart function while under the stress of exercise

Dobutamine Stress Echocardiogram Test:  A dobutamine stress echocardiogram is an ultrasound study of the heart combined with a pharmaceutical (drug-induced) stress test.  The test allows your physician to see how your heart functions when it is required to work harder.  This test is used to determine whether there is clinically significant heart disease in individuals who are unable to adequately exercise on a treadmill.  The dobutamine stress echo can show your physician if an area of the heart does not pump properly due to an inadequate blood supply to the heart muscle

Thallium Stress Test:  This is a type of nuclear scanning test or myocardial perfusion imaging test.  It shows how well blood flows to the heart muscle.  It's usually done along with an exercise stress test on a treadmill or bicycle.  When the patient reaches his or her maximum level of exercise, a small amount of a radioactive substance called thallium is injected into the bloodstream.  Then the patient lies down on a special table under a camera ("gamma camera") that can see the thallium and make pictures.  The thallium mixes with the blood in the bloodstream and heart's arteries and enters heart muscle cells.  If a part of the heart muscle doesn't receive a normal blood supply, less than a normal amount of thallium will be in those heart muscle cells.  The first pictures are made shortly after the exercise test and show blood flow to the heart during exercise. The heart is "stressed" during the exercise test -- thus the name "stress test."  The patient then lies quietly for 2-3 hours and another series of pictures is made.  These show blood flow to the heart muscle during rest.

Ultrafast CT Scan:  A normal computed tomography (CT or CAT) scan uses an x-ray beam that moves in a circle around the body to capture images of the bodies structures.  Conventional CT scans have been of limited use in the diagnosis of heart disease because it is difficult to obtain clear images of the blood vessels around the heart due to constant motion.  An ultrafast CT scan uses new electron beam technology to take several images of the heart within the time of a single heartbeat, producing clear images of the heart and arteries.  Ultrafast CT scanning can detect very small amounts of calcium within the heart and coronary arteries.  This calcium has been shown to indicate lesions that may eventually block off an artery.  Ultrafast CT scanning is may be used by physicians as a means to diagnose early coronary artery disease, especially in people who have no symptoms of the disease.  A physician may also use the ultrafast CT scan to rule out false-positive test results in asymptomatic individuals with positive stress test results.  The amount of radiation in an ultrafast CT scan is similar to that of a screening mammogram. 

Tilt Table Test:  A tilt table test  may be prescribed for individuals that have a history of passing out.  This condition may be caused by an imbalance in the nerves that normally control heart rate and blood pressure.  The tilt table test involves monitoring an individual while they lie on a table that is slowly rotated to a vertical (standing) position in order to help diagnose an abnormality of blood pressure regulation. Based on the results, your doctor may be able to determine the cause of your symptoms and recommend treatment.

Positron Emission Tomography (PET) Scan:  A nuclear scan that provides information about the flow of blood through the coronary arteries to the heart.

Magnetic Resonance Angiography (MRA):  This test is more sensitive to blood vessel abnormalities than the standard echocardiographic studies.  MRA photographs, in conjunction with other information, pinpoint targeted treatment options.  For a virtual example of an MRA technique, click here

Other Invasive Tests

Transesophageal Echocardiogram (TEE):  A test in which a small transducer is passed down the esophagus, providing a clearer image of the heart structure.  The image is transmitted  from an ultrasound transducer inside the esophagus and provides a clear picture of the function of your heart.

Electrophysiology (EP) Study:  An EP test is a test performed in a lab, where electrodes are placed to measure the electrical conducting system of the heart.  This test may be advised for patients who have impaired heart function and intermittent extra heartbeats, even if the patient does not have symptoms.  In these cases, the test may identify patients at high risk of developing a serious arrhythmia.  Depending on the results, your doctors may recommend a change in medication, heart surgery, catheter ablation, implantation of a pacemaker or defibrillator to manage heart rhythm, or more diagnostic tests.

Cardiac Catheterization ("cath"):  A test in which a small catheter is guided through a vein or artery into the heart.  An iodine compound is provided through the catheter, and moving X-ray images are made as the compound travels through the heart.  This test shows narrowing in the arteries, outside heart size, inside chamber size, the heart's pumping ability, valves' ability to open and close, as well as measurement of the pressures within the heart.  The figure below demonstrates the diagram of the cardiac catheter's path. Click here for sample pictures of results from a cardiac catheterization.

Diagram of the path of cardiac catheterization.  Courtesy of the University of Iowa Department of Internal Medicine Virtual Hospital website.
 

For more information on coronary heart disease, click here.

 

References and Related Links:

1.  The Fire Service Joint Labor Management Wellness-Fitness Initiative. 1997, 2000 published by the International Association of Fire Fighters.

2.  http://www.hopkinsmedicine.org/heartdisease.html

3.  Levitt, Michael H., MD. MPH. editor.  Diagnostic Testing.  Occupational Medicine: State of the Art Reviews Vol. 12, No. 3, July-September 1997.

4.  http://www.americanheart.org

5.  http://www.nhlbi.nih.gov

6.  http://www.lungusa.org

7.  http://www.nhlbi.nih.gov/health/public/heart/other/angina.htm

8.  http://www.nhlbi.nih.gov/health/public/heart/other/chdfacts.htm

9.  http://www.vh.org

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