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added to facilitate a
    greater HR response for the test.33 Low-dose DSE has the capacity
    to evaluate the contractile response of the impaired myocardium.
    Bellardinelli et al." have demonstrated that improvements in functional capacity after exercise can be predicted by low dose DSE.
    Patients with a positive contractile response to dobutamine were
    more likely to increase their Vo,max after a 1 0-week exercise program. Having a positive contractile response on the low-dose DSE
    had a positive predictive value of 84% and a negative predictive
    value of 59%.35 With research such as this study beginning to demonstrate the prognostic value of certain medical tests for determining functional prognosis, physical therapists will need to be prepared to critically assess this area of literature in order to assist
    the medical team in determining the level of rehabilitative care for a
    patient during his or her recovery.
    Exercise Testing
    Exercise testing, or stress testing, is a noninvasive method of
    assessing cardiovascular responses to increased activity. The use of
    exercise testing in cardiac patients can serve multiple purposes,
    which are not mutually exclusive. The most widespread use of
    exercise testing is as a diagnostic tool for the presence of coronary
    artery disease. Other uses include determining prognosis and
    severity of disease, evaluating the effectiveness of treatment, early

    34 ACUTE CARE HANDBOOK FOR I'HYSICAl THERAPISTS
    deteclion of labile hypertension, evalualion of CHF, evalualion of
    arrhythmias, and evaluation of functional capacity.33 Exercise testing involves the systematic and progressive increase in intensity of activity (e.g., treadmill walking, bicycling, stair climbing, arm
    ergometry). These lests are accompanied by simultaneous ECG
    analysis, BP measurements, and subjective reports, commonly
    using Borg's Rating of Perceived Exertion ( RPE).36,37 Occasionally,
    the use of expired gas analysis can provide useful information
    about pulmonary function and maximal oxygen consumption.33
    Submaximal tests, such as the 12- and 6-minute walk leSlS, can be
    performed to assess a patient's function. For further discussion of
    the 6-minute walk test, refer to Appendix IX.
    Submaximal tests differ from maximal tests because the patient is
    not pushed to his or her maximum HR; instead, the test is terminated at a predetermined end point, usually at 75% of Ihe palient's predicted maximum HR J8 For a comparison of rwo widely used
    exercise test protocols and funclional activities, refer to Table ·1 - 12.
    For a more thorough description of submaximal exercise testing, the
    reader is referred to Noonan and Dean.38
    Contraindications 10 exercise testing include the following39;
    • Recent MI (less Ihan 48 hours earlier)
    • Acute pericarditis
    •
    Unstable angina
    •
    Ventricular or rapid arrhythmias
    •
    Untreated second- or third-degree heart block
    •
    Decompensated CHF
    • Acute illness
    Exercise test results can be used for the design of an exercise
    prescription. Based on the results, the patient's actual or extrapolated maximum HR can be used 10 delermine the patient's target HR range and a safe aClivity intensity. RPE with symptoms during
    the exercise test can also be used to gauge exercise or activity
    intensilY. (Especially in subjects on beta-blockers-please refer to
    Ihe Physical Therapy Intervention section of this chapter for a discussion on the use of RPE.)

    CARDIAC SYSTEM
    35
    Table 1-12. Comparison of Exercise Test Protocols and Functional Tasks
    Energy Demands
    Oxygen
    Require-
    Treadmill:
    Bike Ergometer:
    mems (ml
    Metabolic
    Bruce PrOtocol
    for 70 kg of
    O,Jkr/
    EquivaJenrs
    Functional
    3·Min Stages
    Body Weight
    min)
    (METS)
    Tasks
    (mph/elevation)
    (kr/min)
    52.5
    1 5
    49.5
    14
    45.5
    1 3
    4.2/16.0
    1,500
    42.0
    1 2
    1,350
    38.5
    1 1
    1,200
    35.0
    10
    jogglg
    j 3.4114.0
    1,050
    3 1 .5
    9
    900
    28.0
    8
    750
    24.5
    7
    S t
    2.5112.0
    21.0
    6
    talr
    600
    climbing
    17.5
    5
    1