A treadmill stress test is a screening tool doctors often use to assess heart health. Depending on whether the test is maximal or submaximal, a stress test can either help your doctor determine whether heart disease is present or enable her to assess the severity of damage already present. Although in many cases the process is generally the same, a submaximal treadmill stress test uses different timing and produces different results.
Identification
Your doctor will most often order a submaximal treadmill stress test if he already knows you suffer from coronary artery disease. This test is useful during an initial assessment of the degree of blockage, as a way to help monitor your condition and when setting exercise limitations. When performing a submaximal test, your doctor is looking for signs of ischemia, or reduced blood flow, before this condition causes a type of chest pain called angina. To prevent angina from developing, you will not exercise to your full capacity, but instead to a lower, or submaximal, level chosen by your doctor, the radiology department of the Greenville (South Carolina) Memorial Hospital explains on its website.
Types
The type of test your doctor chooses depends on preference and whether the test is predictive-based --- an assessment of your overall aerobic capacity --- or performance-based --- an assessment of your ability to perform a specific task or exercise. Two examples of predictive-based tests using only a treadmill include the modified Bruce treadmill test, a maximal test adapted for use as a submaximal test, and the single-stage walking test. Performance-based tests often include a combination of activities you perform both on and off a treadmill, such as the self-paced walking test, the modified shuttle walking test and the bag-and-carry test, according to the "Journal of the American Physical Therapy Association."
Performance Results
Although each type of test involves different procedures and ways of analyzing results, all accomplish objectives by measuring your heart rate and blood oxygen levels during the test, followed by applying standard mathematical equations with differing variables to evaluate your VO2 max, or your highest rate of oxygen consumption during the test. For example, if you perform the single-stage walking test, the test itself takes about eight minutes, four of which you perform at a zero grade, walking between 2 and 4.5 miles per hour, and four at a 5-percent grade using the same speed. At the end of part one, your doctor measures your heart rate and compares it to a rating scale, making sure you fall within acceptable limits. At the end of the test, your doctor uses equation variables that include your blood oxygen levels, speed of the treadmill, heart rate, age and gender to assess and analyze results.
Considerations
The American Academy of Family Physicians recommends that in some cases, your doctor perform additional tests that do not include exercise as a testing component to better interpret results. These tests, including echocardiographic studies and radionuclide scintigraphy, are especially helpful if your doctor performs a submaximal stress test when symptoms of heart disease are present but do not involve your heart, such as fatigue, or if a reduction in your capacity to exercise makes getting results difficult.
References
- Greenville Radiology: Cardiac Stress Test
- American Heart Association: Silent Ischemia and Ischemic Heart Disease
- "Journal of the American Physical Therapy Association"; Submaximal Exercise Testing: Clinical Application and Interpretation; Vanessa Noonan, Elizabeth Dean; August 2000
- "Journal of the American Physical Therapy Association"; Predictive Submaximal Exercise Tests; Vanessa Noonan, Elizabeth Dean; August 2000
- "American Family Physician"; Ordering and Understanding the Exercise Test; Mark. D. Darrow, M.D.; January 1999
