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C HAPTER 1 9 / Exercise Testing 423
a treadmill test may be inappropriate for a patient who has diffi- for diagnostic purposes, for functional assessment, or for risk
culty with balance or gait, such as someone who has had a stroke stratification. An often ignored but nevertheless consistent recom-
or is otherwise neurologically impaired, or someone who has se- mendation in the recent exercise testing guidelines is that the pro-
vere peripheral vascular disease, which causes difficulty in walk- tocol be individualized for the patient being tested. 4,8,27,28 For
ing. A bicycle ergometer would be a more appropriate choice for example, a maximal, symptom-limited test on a relatively de-
such patients. Test specificity should also be considered. For ex- manding protocol would not be appropriate (or very informative)
ample, it would be more appropriate to use a cycle ergometer to for a patient with severe limitations. Likewise, a very gradual pro-
assess physiologic responses to a cycling program. Likewise, if a tocol might not be useful for an apparently healthy, active person.
person is being assessed for readiness for return to work that re- Use of submaximal testing, gas exchange techniques, the presence
quires arm strength, an arm ergometer test may provide more ap- of a physician, and the exercise mode and protocol should be de-
propriate information than will a treadmill test. termined by considering the person being tested and the goals of
the test.
Modalities Commonly used exercise protocols, their stages, and the meta-
bolic equivalent task (MET) level (metabolic equivalents; an esti-
An ideal exercise mode increases total body and myocardial oxygen mated value representing a multiple of the resting metabolic rate)
demand to its highest level safely and in moderate, continuous, and for each stage are outlined in Figure 19-2. The most suitable pro-
equal increments. This requires a dynamic exercise device that uses tocols for clinical testing should include a low-intensity warm-up
major muscle groups, permitting large increases in cardiac output, phase followed by progressive, continuous exercise in which the
oxygen delivery, and gas exchange. Many modalities have been used demand is elevated to a patient’s maximal level within a total du-
for diagnostic testing, including cycle ergometers, treadmills, arm ration of 8 to 12 minutes. 3,4,8,22,25,27 In the absence of gas ex-
ergometers, steps, and, more recently, pharmacologic agents. Iso- change techniques, it is important to report exercise capacity in
metric exercise, or static exercise, which involves muscle contraction METs rather than exercise time, so that exercise capacity can be
without movement of the corresponding joint, causes a greater in- compared uniformly between protocols. METs can be estimated
crease in systolic blood pressure and heart rate in relation to total from any protocol using standardized equations that have been
body oxygen uptake and therefore a greater pressure load on the put into tabular form. 4,8,29 In general, 1 MET represents an in-
heart compared with dynamic exercise. Thus, it is not preferred for crement on the treadmill of approximately 1.0 mph or 2.5%
diagnostic exercise testing. However, isometric exercise has been grade. On a cycle ergometer, 1 MET represents an increment of
used to provide occupation-specific information for patients whose approximately 20 W (120 kg ⋅ m/min) for a person weighing
job requires an extensive amount of isometric activity. 70 kg. The assumptions necessary for predicting MET levels from
The bicycle ergometer and the treadmill are the most com- treadmill or cycle ergometer work rates (including not holding the
monly used dynamic exercise devices. Bicycle ergometer testing is handrails, that oxygen uptake is constant [i.e., steady-state exercise
more commonly used in Europe, whereas the treadmill is more of- is performed], that the subject is healthy, and that all people are
ten used in the United States. The bicycle is usually less expensive, similar in their walking efficiency) raise uncertainties as to the ac-
occupies less space, and is quieter. Upper body motion is de- curacy of estimating the work performed for an individual pa-
creased, making blood pressure and electrocardiographic record- tient. For example, the steady-state requirement is rarely met for
ings easier. The workload administered by simple, mechanically most patients on most exercise protocols; most clinical testing is
braked bicycle ergometers is not always accurate and depends on performed among patients with varying degrees of cardiovascular
pedaling speed, causing variations in the work performed. These or pulmonary disease; and people vary widely in their walking ef-
29
have largely been replaced by electronically braked bicycle er- ficiency. It has therefore been recommended that a patient be as-
gometers, which maintain the workload at a specified level over a cribed an MET level only for stages in which all or most of a given
wide range of pedaling speeds, and are therefore more accurate. stage duration has been completed. 30
Bicycle ergometer work is commonly expressed in kilogram-
meters per minute (kg ⋅ m/min) or watts. The treadmill is usually Bruce Treadmill Protocol
more expensive than the cycle ergometer, is relatively immobile, Surveys have shown that the Bruce protocol is the most widely
and makes more noise. Studies comparing treadmill and bicycle used in North America. 14,31 An advantage of using this test is that
ergometer exercise tests have reported the maximal oxygen uptake a great deal of functional and prognostic data have been generated
to be approximately 10% to 20% higher and maximal heart rate over several decades using the Bruce protocol, and many pub-
5% to 20% higher on the treadmill. 22–26 Significant ST-segment lished normative values have been derived from it. For example,
changes have been reported to be more frequent and angina is some of the most robust databases on the use of the exercise test
elicited more frequently during treadmill testing compared with for assessing prognosis, such as those from the Coronary Artery
the cycle ergometer. 25,26 In addition, exercise-induced myocardial Surgery Study (CASS) 32 and the Duke Treadmill Score, 33 were
ischemia by thallium scintigraphy was reported to be greater after generated from patients who underwent exercise testing using the
treadmill testing than after cycle ergometry. 23 Although most of Bruce test. Numerous studies have shown that patients who are
these differences are minor, if assessing the functional limits of the unable to complete the first stage of this protocol (approximately
patient and eliciting subjective or objective signs of ischemia are 5 METs) have an extremely poor prognosis. 32,34,35 However, the
important goals of the test, the treadmill may be preferable. disadvantages of the Bruce protocol include its large and unequal
increments in work, which have been shown to result in less ac-
Protocols curate estimates of exercise capacity, particularly for patients with
cardiac disease. Investigations have demonstrated that work rate
The purpose of the test and the person tested are important consid- increments that are too large or rapid result in a tendency to over-
erations in selecting the protocol. Exercise testing may be performed estimate exercise capacity, less reliability for studying the effects of