(Circulation. 1995;91:912-921.)
© 1995 American Heart Association, Inc.
Articles |
| Introduction |
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This statement provides a guide to initiating and maintaining a high quality clinical laboratory for administering graded exercise tests to adults. Pediatric testing is addressed separately.1
| Testing Room |
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The laboratory should be well lighted, clean, and well ventilated with temperature and humidity control. Including posters or pictures of outdoor scenes can reduce boredom and anxiety, particularly if the room has no windows. A wall-mounted clock with a "sweep" second hand or a digital counter is useful. The examining table should have space for towels, tape, and other items needed for patient preparation and testing. A curtain for privacy during patient preparation is useful. Minimizing interruptions and maintaining privacy allows the patient and laboratory personnel to concentrate on the testing procedure.
To assess
the level of effort, a large-print scale of perceived
exertion2 (Table 1
) should be
mounted on the wall in clear view of the patient. The same scale has
been used to assess symptoms of fatigue, dyspnea, or leg
fatigue/pain.3 Dyspnea can also be measured by means
of a visual analog scale that is valid and reliable.4
In addition, a hand-held symptom scale is useful during cardiopulmonary
testing when the mouthpiece or mask may prevent speech. This should be
clearly explained to the patient.
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A thermometer, barometer, and hygrometer should be kept in the room. Heart rate and perceived exertion rise with an increase in ambient temperature.5 6 Furthermore, cardiovascular responses become variable when humidity exceeds 60%. The combination of heat and humidity will lower maximum performance.7 In general, a temperature of 22°C (71.6°F) is considered comfortable for exercise. With short exercise periods, however, a temperature as high as 26°C (78.8°F) is acceptable as long as there is adequate air movement.8 A cool, dry environment (50% humidity) enhances cutaneous heat exchange or loss and serves to dissipate excessive heat provoked by exercise.7 Circulating fans can assist in controlling room temperature and ventilation. If gas exchange measurements are being performed, barometric pressure and temperature should be measured since gases expand with heat and/or low barometric pressures and contract with cold and/or high barometric pressures. Most modern automated cardiopulmonary testing systems will make adjustments for ambient conditions.
Equipment
Electrocardiogram
A suitable
electrocardiographic (ECG) recording system is
essential for continuous monitoring of heart rhythm and evaluation of
ischemic ECG changes during exercise and recovery. Equipment ranges
from more sophisticated and costly computerized systems to simpler,
more conventional types. Nonetheless, the instrument should meet the
specifications set by the American Heart
Association.9 10
When purchasing a highly specialized computer system, care must be taken to ensure that the frequency response accurately reflects ST segment changes. It is necessary therefore to compare raw analog data with computer-generated data for validity. Continuous oscilloscopic monitoring of a minimum of three leads is recommended to optimally identify arrhythmia patterns. Furthermore, the ability to produce a 12-lead hard copy will enhance interpretation.11 The Mason-Likar adaptation of the 12-lead ECG has been commonly used in the clinical setting.12 ECG systems with built-in automatic arrhythmia sensing, which alerts the user to the occurrence of arrhythmias, are commercially available. Although not essential in every laboratory, these automatic arrhythmia detectors may be practical when the population being tested is at high risk.
Silversilver chloride electrodes are recommended as the most dependable for minimizing motion artifact. Commercially available disposable electrodes vary in size and adhesive preparation. However, the importance of adequate skin preparation cannot be overlooked, regardless of the size or type of electrode used. Lightweight, shielded cables will lessen motion artifact. In addition, cable systems that arise from a central box can be worn around the waist and further stabilize the ECG signal. Flexible knit "tube" shirts for stabilizing the electrodes and cables are also available.
Blood Pressure Monitoring
Manual auscultation is
still the most feasible method of
monitoring blood pressure during exercise and the easiest to
use.11 A variety of automated blood pressure units
are available, but these devices are expensive and may perform
erratically at high exercise intensities because of motion. In
addition, diastolic blood pressure may not be
accurate.13 If such systems are used, their
reliability should be validated against manual cuff measurements within
each respective laboratory before routine use, and distinctly abnormal
hypertensive or hypotensive blood pressure recordings during exercise
should be corroborated by manual recordings. A second staff member
should check abnormally high or low blood pressure readings.
The laboratory should have cuffs of various sizes, including large and pediatric.13 The mercury manometer is recommended instead of the aneroid manometer because it is more accurate and easier to maintain and calibrate.13 The manometer should be placed at the level of the patient's heart. Sphygmomanometers and cuffs, along with other testing equipment, should be cleaned and inspected on a regular schedule.
Ergometry
Treadmill. A treadmill should be electrically driven
and should accommodate a variety of body weights up to at least 157.5
kg (350 lb). In addition, it should have a wide range of speeds, from a
low of 1.6 km (1 mph) to a high of at least 12.8 km (8 mph). Elevation
should be electronically controlled and should offer a variety of
settings, from no elevation to 20% elevation. A dedicated 220-volt
outlet may be required along with heavy electrical cables that meet
electrical safety standards. The treadmill platform should be a minimum
of 127 cm (50 in) in length and 40.64 cm (16 in) in width. Models are
available with side platforms to allow the patient to adapt to the
moving belt before fully stepping onto it. For patient safety and
stability, padded front and side rails are recommended. An emergency
stop button must be easily visible and readily accessible to the staff
and the patient when needed.
Bicycle. Cycle ergometry is an alternative to treadmill testing for those patients who have orthopedic, peripheral vascular, or neurological limitations that restrict weight bearing. It can also serve as a less expensive, portable substitute for testing. Work intensity can be adjusted by variations in resistance and cycling rate. Work rate can be calculated in watts or kilopond-meters per min-1 (kpm/min).
Two types of stationary bicycles are used for testing: mechanically braked and electronically braked. Mechanically braked ergometers require that a specified cycling rate be maintained to keep the work rate constant. Electronically braked ergometers are more expensive and less portable but automatically adjust internal resistance to maintain specified work rates according to the cycling rate. Regardless of the type of stationary bicycle used, the ergometer must have the capability to adjust the work rate in increments either automatically or manually.
The cycle ergometer must include handle bars and a seat that adjusts for height. At the ideal seat height the knee should be slightly flexed at full extension. For safety purposes, adaptable pedal grips should be included. In addition, meters, dials, or digital displays should be appropriately sized and placed for easy reading.
Physiological
responses to exercise on a cycle ergometer differ from
those obtained on a treadmill.14 15 Moreover, maximum
oxygen uptake is 5% to 20% lower than on the treadmill.3
Table 2
lists the approximate oxygen cost in
metabolic equivalents (METs) for cycle ergometry relative to
weight.
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Arm Ergometer. Arm exercise testing is a useful alternative for diagnostic testing of patients with lower extremity impairment caused by vascular, orthopedic, or neurological conditions. In addition, arm ergometry is helpful for performing occupational evaluation in patients whose work primarily involves the arms and upper body. Dynamic arm exercise involves a smaller muscle mass than does leg ergometry for a given workload. However, arm exercise often necessitates the use of other muscles in the chest, back, buttocks, and legs for body stabilization, depending on exercise position and intensity.16
Arm exercise testing can be performed with either mechanically braked or electronically braked arm ergometers. The former can be purchased separately as a specifically designed unit for graded arm cycling or can be adapted from standard bicycle ergometers by replacing the pedals with handles for cranking.17 18
Recommended protocols for arm ergometry testing require that the subject be seated in the upright position, with the fulcrum of the handle adjusted at shoulder height. The arm should be slightly bent at the elbow during farthest extension movements. Cycling speeds of 60 to 75 revolutions per minute must be maintained. Work rate increments of 10 W per 2-minute stage are suggested. Testing end points are similar to those of other types of ergometry. Vo2 requirements during arm cycle ergometry can be determined from formulas that take into account work rate, gender, and subject body weight19 and can be estimated easily using data in Tables 3 and 4. Other techniques used to test the upper body include rowing machines and air-braked arm/leg ergometers.20 21
Oxygen uptake during any equivalent submaximal level (eg, 50 W) of arm work exceeds that of leg work. Accordingly, the rates of increase of heart rate and blood pressure responses during arm ergometry are more rapid.19 Other physiological responses to dynamic arm exercise, eg, stroke volume and diastolic blood pressure, also differ from those of leg exercise.22 23 24
The sensitivity of arm exercise testing for detection of significant coronary artery disease is less than that of treadmill testing and is discussed elsewhere.25
Equipment for
Ventilatory Gas Exchange Analysis
Recent technological advances have
made it easier to perform gas
exchange analysis during exercise testing, and this technology is
being used with increasing frequency in the clinical setting. The use
of gas exchange analysis techniques can greatly enhance both
precision and reproducibility for assessing cardiopulmonary function
compared with indirectly estimating oxygen uptake from work
rate.26 27 Gas exchange analysis is essential for
accurately quantifying the effects of medical interventions. For this
reason, gas exchange analysis techniques are being used in an
increasing number of clinical research trials. However, the additional
accuracy and information provided by this technology is dependent on
some basic skills required of both the technician, who must properly
calibrate the system and perform the test, and the physician, who must
interpret the results and communicate them to the patient. In addition,
the equipment must meet certain specifications, and specific
calibration procedures must be followed.
Equipment Calibration (see Appendix 4)
Ancillary Imaging
If ancillary imaging is to be
performed in conjunction with the
stress test, certain modifications should be considered. The use of a
gamma camera for radionuclide images or a cardiac ultrasound
machine for stress echocardiograms will require increased space to
accommodate this equipment. Dedicated electrical outlets or a 220-V
line may be necessary as well. Institutional radiation safety committee
guidelines must be carefully followed.
If a large volume of stress echocardiograms are to be performed, a platform or bed with a "cut away" mattress for easier imaging can be helpful. A wide variety of systems are available for display of continuous loop rest and stress images in a side-by-side format. For laboratories performing pharmacologic stress tests such as those using dobutamine or dipyridamole, a precision intravenous delivery system (eg, IVAC) is also needed.
Personnel
Staff members may include exercise physiologists,
exercise
specialists, physical therapists, ECG technicians, nurses, and
physicians' assistants. Appropriate training and performance skills
for exercise testing personnel are available in published
guidelines.3 All staff members must have received
training in basic life support. Training in advanced cardiac life
support is strongly encouraged.28
The degree of exercise testing supervision required is primarily dependent on the type of patients being tested. For patients who are at a higher risk (eg, unstable angina after stabilization, heart failure, or high-grade arrhythmia), a physician must directly monitor the test. In other cases, another properly trained healthcare professional (ie, nurse or exercise physiologist/specialist) can conduct the test and directly monitor patient status throughout testing and recovery. However, the supervising physician must be readily available.
The medical director of the exercise laboratory is responsible for the structure of the laboratory and its policies. The physician should also ensure that the laboratory is properly equipped and that the staff is appropriately qualified and trained.
The physician is responsible for interpreting the data, suggesting further evaluation or additional techniques for testing, if needed, and delivering appropriate emergency care when necessary.29 Requirements for physician competency in this area are clearly outlined in the American College of Physicians/American College of Cardiology/American Heart Association statement on clinical competence29 and include successful completion of an AHA-sponsored course in advanced cardiac life support.
Accurate and timely written interpretation of the exercise test results should be available, ideally in 72 hours or less. A preliminary test reading, however, should be available immediately. If the test results are highly abnormal, the referring physician should be notified as soon as possible.
| Emergency Preparation |
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An exercise laboratory should have a written emergency plan appropriate to the individual facility. All personnel should know and review the planned procedures at least quarterly. The plan must allow for evacuation of unstable patients by a specified route for rapid transfer to hospital emergency facilities. AHA protocols for basic and advanced life support should be followed as appropriate.33
Equipment and Drugs
Table 5
lists the minimum
emergency
equipment necessary in any testing laboratory. If intubation becomes
necessary, suction equipment, laryngoscope with blades of various
sizes, and intubation equipment should be readily available. If a more
extensive equipment cart is located in an area other than the testing
area, a specific plan for rapid accessibility to the cart should be
clearly defined. A defibrillator should be in every exercise testing
laboratory and should be tested on a daily basis.
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The AHA's
classification of drugs most commonly used in a
life-threatening emergency33 is listed in Table 6
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| Patient Preparation |
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Before Testing
In the current practice environment, a written
request for
exercise testing should be provided by the referring physician with a
brief description of the diagnosis (confirmed or suspected), the reason
for testing, and, if possible, a list of the patient's medications.
With regard to medications, dose and time taken should be recorded. To
standardize the response to testing and minimize patient anxiety, both
written instructions given before the test and verbal instructions at
the time of the test are recommended. A detailed set of instructions
should be provided to the patient when the testing appointment is made.
The instructions should include abstinence from food and smoking for 3
hours before regular testing and 8 hours before a nuclear imaging
study. Clothing should be comfortable and loose, and footwear should be
sturdy and comfortable.
If the patient is receiving multiple medications, the instructions should include a request for a list of drugs and dosing to be brought to the testing center. Tests are usually performed even if patients are receiving drug therapy, but withdrawal of certain medications such as ß blockers or calcium blockers34 should be considered if the physiological response may be altered and thus lessen diagnostic accuracy. The physician ordering the test should make the decision to taper or discontinue medications, because rebound effects can occur.
At the Time of Testing
A brief history and physical exam with
a focus on the
cardiovascular system should be conducted before testing to elicit any
signs and symptoms of peripheral vascular disease, orthopedic, or
neurological restrictions that may limit performance. Information about
usual physical activity will aid the laboratory staff in selecting an
appropriate testing protocol. A sample history and physical form is
shown in Appendix 2. The patient's questions must be
thoroughly
answered before the test. Informed consent may be obtained and
witnessed by personnel who can accurately describe the tests and
potential risks. The informed consent should be included in the
exercise test record. Five informed consent samples are included as
Appendix 1A27 and Appendixes 1B through 1E. These
can be modified to fit the needs of a particular laboratory.
Specific instructions should be given on how to perform the exercise
test, with a brief demonstration of the test procedure.
Skin Preparation
To obtain the best interpretation of an ECG,
the interface between
the skin and the electrode must be optimal. Resistance should be
reduced to 5000
or less.3 To achieve this, the
superficial layer of skin must be removed. The areas where electrodes
will be applied should be shaved with a battery-operated trimming
device, to decrease the incidence of abrasions, or with a standard
razor. Alcohol-saturated gauze should be used to clean and remove oil
from the skin. When the skin is dry, the electrode-placement areas
should be marked with a felt-tipped pen and rubbed with fine sandpaper
or commercially prepared abrasive tape to remove the superficial layer
of skin. After electrode placement, the technician can lightly tap the
electrode to assess adequacy of skin preparation. A flexible tubing
"vest" may be necessary to reduce cable motion.
Resting Data
A standard 12-lead ECG should be recorded
initially, followed by
an exercise 12-lead ECG. Resting ECG, heart rate, and blood pressure
should be taken in both supine and standing positions before testing.
This is necessary to determine the presence of any ECG abnormalities
that might contraindicate the test and to determine any changes that
occur due to body position.
Changes in T waves with hyperventilation can be common. ST segment depression can also occur with hyperventilation but is less common.35 The decision to perform hyperventilation pretesting can be made by the physician supervising the test, based on the clinical evaluation of the patient. If gas exchange analysis is being performed, resting values should be recorded with the patient at rest for at least 2 minutes or until a stable baseline is achieved.
Exercise Data
Exercise testing protocols can be chosen by the
supervising
physician or laboratory staff. It is recommended that protocols be
selected and/or adapted based on the limitations of the individual.
Ideally, the desired testing end point should be reached within 8 to 12
minutes of testing.28 Longer protocols do not yield
additional diagnostic information and result in reduced values for
exercise capacity.36
Measurements recorded during testing should include heart rate and blood pressure at rest and at each workload level, ECG recording each minute, arrhythmias, abnormal ECG responses, and patient symptoms. Furthermore, the patient's appearance should not be overlooked: changes in skin color, alertness, coordination, and strength during exercise should be noted and recorded. End points for testing usually include symptoms such as chest pain, shortness of breath or fatigue, ECG changes, arrhythmias, and abnormal blood pressure responses. Specific definitions and interpretation of these observations are discussed in the AHA's exercise standards.28 A sample data recording form is shown as Appendix 3. Recovery data are included since abnormalities that occur during exercise can persist after exercise. In addition, symptoms, ECG abnormalities, and arrhythmias can first appear after exercise has been completed.11 35 The patient should be carefully monitored until heart rate, blood pressure, and ECG have returned to near-baseline levels. Moreover, if the patient has experienced any discomfort, monitoring should continue until significant symptoms have resolved. If symptoms and/or abnormal signs persist beyond 15 minutes in recovery, the supervising physician should evaluate the patient and recommend further observation or treatment.
| Report of Test Results |
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| Quality Control |
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| Footnotes |
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Requests for reprints should be sent to the Office of Scientific Affairs, American Heart Association, 7272 Greenville Avenue, Dallas, TX 75231-4596.
| Appendix 1A |
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To determine my cardiovascular response to exercise, I voluntarily agree to engage in an exercise test. The information obtained about my heart and circulation will be used to help my doctor understand more about any problems related to my heart and advise me about activities in which I may engage.
I have been told that before I undergo the test, I will be evaluated either by a physician or by another member of the healthcare team in an attempt to determine if I have a condition indicating that I should not engage in this test.
I am told that the test I will undergo will be performed on a _____ (description), with gradually increasing effort until symptoms such as fatigue, shortness of breath, or chest discomfort may appear, indicating to me or to my physician that I should stop. I have been told certain changes may occur during the test, including abnormal blood pressure, fainting, an abnormal ECG, disorders of heart beat (too rapid, too low, or ineffective), and, possibly, heart attack and death.
I have read the above and understand it, and my questions have been answered to my satisfaction. Patient _____ Date_____ Physician Supervising the Test _____Witness _____
| Appendix 1B |
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Your physician has asked that you undergo an exercise test to evaluate the functional capacity of your heart, lungs, and/or blood vessels. The information obtained will be important for your diagnostic and future healthcare management. The test will measure your tolerance of exercise until fatigue, breathlessness, chest discomfort, or other symptoms occur, which will stop the test. The electrocardiogram will be monitored by a physician, and precautions for your safety will be observed. Risks of the testing procedure are minimal and rare and include fainting, falling, irregularities of heart beat, and, very rarely, heart attack or death (less than l in 10 000 cases). Professional staff will be present during testing and emergency treatment will be available if it becomes necessary. You understand that in the event of physical injury resulting from this procedure, physician services will be provided without charge but not compensation or costs of any required hospitalization. _____
I have read and fully understand the above and voluntarily consent to perform this exercise test at the _____Hospital or center. Signed _____Witness _____Date _____
| Appendix 1C |
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To determine an appropriate plan of treatment to assist in my recovery from my heart illness, I hereby consent to voluntarily engage in an exercise test to determine the state of my heart and circulation. The information obtained will aid my physician in advising me about activities in which I may engage.
Before I undergo the test, I will have an interview with a physician. I will also be examined by a physician to determine if I have any condition that could indicate that I should not engage in this test.
The test that I will undergo will be performed on a treadmill or bicycle with the amount of effort increasing gradually. This increase in effort will continue until symptoms such as fatigue, shortness of breath, or chest discomfort may appear, which would indicate to me to stop.
During the performance of the test, a physician or trained observer will monitor my pulse, blood pressure, and electrocardiogram. Oxygen intake may also be measured and _____tests performed.
Certain changes may occur during the tests. These changes include abnormal blood pressure, fainting, disorders of heart beat (too rapid, too slow, or ineffective), and, in very rare instances, heart attack. Every effort will be made to minimize such changes through the preliminary examination and observations during testing. Emergency equipment and trained personnel will be available to deal with unusual situations that may arise.
The information obtained will be treated as privileged and confidential and will not be released or revealed to any person without my expressed written consent. The information obtained, however, may be used for a statistical or scientific purpose with my right of privacy retained. _____
I have read the foregoing and I understand it, and any questions that may have occurred to me have been answered to my satisfaction. _____Signed: _____Date Patient _____ _____ Physician supervising test Witness
| Appendix 1D |
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To determine my cardiovascular status and state of physical condition, I hereby consent to perform an exercise test.
Based on the results of this exercise test and evaluation, I will be given a prescription for an exercise program. It is my decision to select either a supervised group exercise program, to exercise on my own, or not to exercise. In any event, I do not hold Emory University, the George W. Woodruff Physical Education Center, or the Emory Health Enhancement Program responsible for any cardiovascular event and/or other accidents connected with either testing or training.
This consent remains valid as long as I remain in the supervised exercise program at the Emory Health Enhancement Program and includes all exercise tests and other evaluations. The Emory Health Enhancement Program, the George W. Woodruff Physical Education Center, and Emory University are not responsible for any cardiovascular event and/or other accidents occurring apart from the supervised exercise programs and/or testing. Signed _____ _____ _____ Date _____ _____ _____
| Appendix 1E |
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Potential risks are associated with exercise testing. These include dizziness, fainting, orthopedic problems, chest discomfort, disorders of heart rhythm, heart attack, and death.
I understand these risks, though rare, can occur and I voluntarily accept the risks associated with the procedure. In addition, I understand that I may ask that the test be discontinued at any time.
*A cardiologist is available at all times should a problem arise. Date _____Patient _____ Witness _____
| Appendix 2 |
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Name _____ Study Date _____MR No. _____ Referring MD _____Test indication: Follow-up _____ Pre-op _____Chest pain Yes/no
Typical/atypical; New/changing pattern/chronic;
Exertional/rest/nocturnal Comments: _____Past medical history Myocardial infarction: Yes/no; date: _____; region: _____; complicated by: _____ Coronary artery bypass graft: Yes/no; date: _____; number of vessels _____ Other cardiac disease: CHF/valvular _____ arrhythmias _____ Percutaneous transluminal coronary angioplasty: Yes/no;
date: _____; vessels: _____Other: _____Risk factors: Smoking/family history/hypertension/obesity/
high cholesterol/insulin-dependent diabetes mellitus or
noninsulin-dependent diabetes mellitus/
peripheral vascular disease Prior workup Cardiac catheterization: Yes/no; Date: _____; Results: _____Endotracheal tube: Yes/no; Date: _____; Results: _____Nuclear tracer study: Yes/no; Date: _____; Results:_____
Cardiovascular medications
ß-blocker: Yes/no; last
taken: _____
Ca2+-blocker: Yes/no; last taken: _____
Digoxin: Yes/no; last taken: _____
Theophylline Dipyridamole: Yes/no; last taken: _____
Converting enzyme inhibitors: Yes/no; last taken: _____Physical exam: Heart: murmur, S3, S4 Pretest _____ posttest _____ Lungs: clear _____ crackles _____ wheezes _____ Peripheral pulses __________Precordial dyskinetic areas by palpation: _____Resting ECG _____ _____ _____Comments: _____ _____ _____
| Appendix 3 |
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Type of test: Maximal Submaximal Dipyridamole Canceled Treadmill: Protocol _____Cycle: _____ kpm/min or W per stage Arm: _____ Leg: _____
Rest and Exercise![]()
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Symptoms: C indicates chest pain; S, dyspnea; D,
dizzy; PVD, peripheral vascular disease; CP, calf pain; F, flushing; H,
headache; M, musculoskeletal pain; 0, no symptoms
Exercise time: _____ minutes Highest stage
(no.): _____ Time: _____Peak
Vo2: _____ METs _____Ventilatory
threshold: _____ ST depression: Yes No
Time turned positive: _____ min.
Heart rate at ischemic threshold: _____
ST depression: H indicates horizontal; D, downsloping;
U, upsloping
Type _____ lead(s) _____ amount (mm) _____
ST elevation: Lead(s) _____ amount (mm) _____
ST depression
5 leads? Yes _____ No _____
ST depression persisted
5 min in recovery?
Yes _____ No _____
_____ mg aminophylline given (dipyridamole test)
Adenosine dose reduced? Yes _____ No _____
| Appendix 4 |
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Calibration of the treadmill and cycle ergometer (both leg and arm) should be performed on a monthly basis, or more frequently if a large number of tests are performed.3 Specific directions for calibration and preventive maintenance are included in the treadmill or ergometer operation manual provided by the manufacturer. Each laboratory should record dates that calibrations are performed. These records are an important part of quality assurance procedures.
Treadmill Speed
Calibration of treadmill
speed requires knowledge of the
belt length, which can be obtained from the manufacturer or measured
with a tape. The treadmill speed can be calibrated by counting the
number of rotations of the treadmill belt per unit of time. Using a
mark on the treadmill belt as a reference, the number of belt
revolutions in 1 minute can be counted, and, knowing the length of the
belt, the actual miles per hour calculated by:
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(1056 = conversion of inches per minute to miles per hour)
The value obtained is the treadmill speed in miles per hour. If the speed indicator does not agree with this value, adjust the meter to the proper setting. Frequently a calibration adjustment screw is found in a small opening in the front of the control panel. If not available, the manufacturer should be contacted. The calibration procedure should be repeated for several different speeds to ascertain accuracy across commonly used protocols in a given laboratory.
Treadmill Elevation
Treadmill elevation is
calibrated by measuring a fixed distance
on the floor and determining the difference in height of the treadmill
over the fixed distance. The following specific procedures are
performed:
1. With the use of a carpenter's level, ensure that the treadmill is resting on a level surface. Set the treadmill elevation to 0% grade. If the elevation does not read 0% when it is level, adjust the potentiometer until it does.
2. Mark 2 points 50 cm (20 in) apart along the length of the treadmill.
3. Elevate the treadmill to its metered reading of 20% grade and measure the distance of each of the 2 points to the floor.
4. Divide the difference between the two heights by 20. The results should be .20 or 20% when the elevation is properly calibrated. If the result is not 20%, adjust the elevation meter potentiometer so that it displays the calculated elevation percentage. A check of 5%, 10%, and 15% grade readings is recommended to ensure the validity of intermediate positions.
Speed and elevation should be calibrated without a subject on the treadmill. It is recommended, however, that after calibration a moderately heavy subject (75 to 100 kg) walk on the treadmill to ensure that the calibrations remain accurate when in use. Speed should remain unchanged regardless of the weight of the individual on the treadmill.
After approximately 1000 hours of use, the treadmill should be serviced, which should include lubricating the motor bearings, checking the variable speed belt for wear, centering the belt, greasing the chain drive, and cleaning and lubricating the gears. Service and maintenance schedules should be available from the manufacturer.
Bicycle Ergometer Calibration
Since the work rate
on a mechanically braked ergometer depends
not only on the resistance but also on the cycling rate in revolutions
per minute, it is essential that a counter quantify this factor. It is
also important that the belt tension be adjusted appropriately and that
the flywheel be cleaned to ensure smooth operation. Electronically
braked ergometers are more difficult to calibrate and require special
instruments generally not available to the individual purchaser, so
calibration is usually provided by the manufacturer or by the
institutional biomedical engineering department.
To check the calibration on a mechanically braked cycle ergometer, the belt should be removed from the wheel. The mark on the pendulum weight should be set at "0," and a weight that is known to be accurate should be attached to the belt. The weight should hang freely. A reading of that weight should be given accurately on the scale. If all conditions are met and the scale continues to show an incorrect reading for the known weight, the adjusting screw should be turned until the scale reads the appropriate weight.
When calibrating an ergometer that is braked by a lateral friction device, the ergometer is placed on two chairs so that the brake scale plate is vertical. After releasing the brake regulator knob on the handlebar, a known metric weight is hung on the brake arm using a wire S-hook. After loosening the fastening screw of the shock absorber at one end, the scale should read, in kiloponds, the exact amount of the weight attached to the brake arm. The pointer should always be read from directly above. If the scale does not accurately read the weight, the regulating nut should be turned. When the pointer indicates the same figure as the weight attached, the ergometer is correctly calibrated.
Mechanically braked ergometers can be delicate and may lose adjustment from frequent use or if they are transported. Before using an ergometer, the chain should be checked for tightness and lubrication, and the braking surfaces of the flywheel should be free of any dirt that has gathered. A fine sandpaper pressed against the braking surface while pedaling the ergometer will smooth the surface.
Arm
Ergometry
Mechanically braked arm ergometers should be manually
calibrated
routinely as recommended for bicycle ergometers. Electronically braked
models require periodic calibration by experienced biomedical
technicians as recommended by the specific equipment manufacturer.
Gas Exchange Systems
The metabolic system should be
calibrated just before and
immediately after each test. This should include calibration of airflow
and both the oxygen (O2) and carbon dioxide
(CO2) analyzers. Gas analyzers and flow meters are prone to
drift, which can lead to serious errors. Today, nearly all commercially
available systems have convenient calibration procedures controlled by
a microprocessor. Validation studies have been performed on a number of
the computerized systems.37 38 Because ambient
conditions affect the concentration of O2 in the inspired
air, it is necessary to have a thermometer, barometer, and hygrometer
in the room. A copy of the calibration report should be printed before
and after each test and should be attached to the test report. Valid
interpretation of test results is possible only if calibration values
are appropriate.
Gas exchange measurements are highly reproducible
within a given
subject if testing methods are consistent. One method often used for
validating a system's performance is to test laboratory staff members
at a matched submaximal workload on a periodic basis. It is recommended
that several staff members participate in this process, each using a
slightly different steady-state submaximal workload.
Jones39 has outlined the limits of variation in
oxygen uptake and hemodynamic data for a given steady-state work rate
(Table 7
). In addition to being
reproducible, the data should approximate the predicted
oxygen cost of a given steady-state work load (±10%).3
The following specific calibration procedures should be performed to
ensure that valid data are obtained:
1. Room air should read 20.93±0.03% O2 at 0% humidity. However, the precise fraction is dependent on humidity and should be adjusted accordingly. A calibration source containing 100% nitrogen should read 0% O2. The analyzer should be checked further by simulating the fraction of expired O2 (FEO2) during the test, ie, approximately 16% O2. The exercise laboratory should be well-ventilated to assure a representative fraction of inspired O2; a fan is helpful for this purpose.
2. The CO2 analyzer should read a room air fraction of 0.03±0.02% and should not change when the 100% N2 or 16% O2 fractions are sampled from the calibration tanks. The CO2 analyzer should be checked further by simulating the fraction of expired CO2 (FECO2) during exercise, ie, approximately 4% CO2.
3. For both the O2 and CO2 analyzers, it is also preferable to check the analyzer response time or "delay." It is important that the system meets the specifications outlined by the manufacturers; this feature is available in most systems.
4. Once limited to large weather balloons and tissots, great strides have been made in the measurement of ventilatory volume, and numerous flow devices are now available, including small turbines, propellers, and even disposable pneumotachometers. All can be validated before testing by ascertaining a stable baseline (0 L/min) and injecting a known volume (usually 3 or 4 L) from a syringe. It is preferable to perform several injections at different flow rates to ensure stability; the average error should be within ±3% of the known volume.
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