Stress testing consists of a graded exercise test (GXT) that is performed to provide an objective evaluation of cardiorespiratory fitness and heart health.
Stress testing can be performed in apparently healthy men or women. Alternatively, stress testing can also be executed in those individuals diagnosed with cardiovascular, pulmonary, or metabolic disease. Stress-testing procedures, monitoring, protocols, and indications for test termination will all vary depending on the health status of the test participant.
Resting heart rate and blood pressure should be obtained at baseline prior to commencing a stress test. Heart rate, blood pressure, and rating of perceived exertion (RPE) measures should be obtained throughout the stress test. Each of these measures should be recorded near the end of each stage of the stress test. ECG and expired gases can also be collected continuously during stress testing. All of these parameters should be assessed by the test administrator to ensure the response to exercise is normal. Additionally, the test administrator should also constantly monitor the test participant for physical appearance and possible appearance of adverse symptoms (e.g., shortness of breath, tachycardia).
Almost all stress-testing protocols are performed on either a treadmill or cycle ergometer. Popular treadmill and cycle ergometer stress-testing protocols include the Astrand, Bruce, Balke, Fox, Modified Balke, and Naughton. Each modality has advantages and disadvantages.
Approximately 75% of all stress testing is done on a treadmill. There are numerous advantages to this modality. Walking and running are familiar activities for most people. Treadmill exercise recruits substantial muscle mass and will increase the likelihood of obtaining maximal heart rate, blood pressure, and maximal oxygen uptake (VO2max). It is also easy to control the workload on the treadmill. Nevertheless, there are also a few drawbacks to using the treadmill. Higher-quality treadmills can be expensive. Additionally, some physiological measurements are more difficult to obtain on the treadmill, including exercise blood pressure and exercise ECG.
The cycle ergometer is an excellent alternative to the treadmill as a modality for stress testing and has many advantages. Cycle ergometers are less expensive and more portable as compared to treadmills. It can also be easier to obtain physiological measurements, such as exercise blood pressure and exercise ECG, on the cycle ergometer. The cycle ergometer is an excellent option for those individuals performing a stress test with orthopedic problems. Disadvantages to use of the cycle ergometer include cadence problems and premature fatigue due to localized fatigue in the quadriceps region. This latter point is one of the reasons that maximal heart rate and VO2max values tend to be 5%–10% lower on the cycler ergometer as compared to the treadmill.
Prior to stress testing, individuals should undergo adequate preparticipation health screening and risk stratification to optimize safety. The purposes of the screening process are as follows: (1) to identify and exclude individuals with contraindications to exercise testing; (2) to identify the need for medical supervision of exercise tests; and (3) to identify individuals with other special needs. Two commonly used prescreening instruments include the Physical Activity Readiness Questionnaire (PAR-Q) and a Health History Questionnaire (HHQ). The PAR-Q evaluates one's health risks in a series of seven yes/no questions and encourages test-takers to seek medical attention prior to exercise testing if any question results in a “yes” response. Likewise, an HHQ can assist in the identification of existent diseases or medical conditions (e.g., cardiovascular disease, type 2 diabetes).
To minimize risk and obtain valid results, the test participant should be adequately prepared for the stress test. Accordingly, it is recommended that the following pretesting instructions be communicated to the test participant in advance of the appointment:
Stress testing typically continues until the participant reaches voluntary maximal exertion. Test administrators, however, must be vigilant for various indicators that may signify an adverse exercise response. The following are some common indications for terminating a stress test:
After the stress test has concluded, monitoring the heart rate, blood pressure, and ECG should continue for at least five minutes to ensure a gradual return to baseline values.
Risk stratification of an individual into categories of low, moderate, or high prior to stress testing provides insight into the degree of medical supervision required. The presence of positive cardiovascular disease risk factors provides a framework for riskstratifying individuals. The overall number of positive risk factors should be totaled. In the event no information is available for a specific positive cardiovascular disease risk factor, it has been recommended to assume the worst-case scenario and count the risk factor. Participants with positive risk factors for cardiovascular disease are at increased risk for ultimately developing cardiovascular disease and/or experiencing a stress-testing-related cardiac event. Positive risk factors are elements that contribute toward developing a disease. Similarly, individuals with known signs and/or symptoms of cardiovascular, pulmonary, and/or metabolic disease are at increased risk of an exerciserelated cardiac event or other complication.
After the preparticipation health screening process it is possible to risk-stratify individuals into one of three classifications (low, moderate, or high). It is recommended that individuals who are risk stratified into either the moderate- or high-risk category have physician supervision of the stress test. The criteria for low, moderate, and high risk are as follows:
Stress testing yields many important results. Arguably, the most important is that stress testing provides an accurate assessment of cardiorespiratory fitness. Indeed, cardiorespiratory fitness has been coined the ultimate heart-health outcome.
The level of an individual's cardiorespiratory fitness revealed during a stress test is dependent on numerous variables including age, sex, race, training status, and genetics. Normative values for VO2max with specific reference to age and sex are available at the Cooper Institute website. Because low cardiorespiratory fitness is a powerful risk factor for CVD, it is important to assess how low is too low. It has been demonstrated that the highest relative risk of CVD exists for those individuals with cardiorespiratory fitness levels below the 20th percentile. Therefore, moving individuals out of the lowest 20th percentile of cardiorespiratory fitness is an important goal of prevention and rehabilitation exercise programs. In fact, it has been shown that the most substantial drop in CVD risk occurs when individuals move from the 20th to 30th percentile of cardiorespiratory fitness.
One of the very first studies to explore the connection between cardiorespiratory fitness and heart health was published in 1989 in a hallmark paper. It was reported that an inverse relationship existed between VO2max values and risk for CVD. It was also shown that this relationship held true for individuals with no other risk factors for CVD, one risk factor for CVD, and two or more CVD risk factors. In 2001, the question of whether cardiorespiratory fitness should be considered a separate risk factor for CVD, in addition to lack of physical activity, was addressed in a metaanalysis. The author noted that both increased cardiorespiratory fitness and increased physical activity were associated with decreased risk for CVD events. Moreover, it was also found that higher cardiorespiratory fitness levels yielded greater reductions in CVD risk compared to those imparted from increased physical activity levels. It was concluded that being unfit warrants consideration as a separate CVD risk factor, independent of physical inactivity and other traditional CVD risk factors. Perhaps the strongest case to support cardiorespiratory fitness as the ultimate heart-health outcome was made in a paper published in 2009. The author presented data to show that low cardiorespiratory fitness accounted for more overall deaths, including those from CVD, when compared to deaths that could be attributed to traditional risk factors, such as obesity, smoking, hypertension, dyslipidemia, and type 2 diabetes.
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Lance C. Dalleck, PhD