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Running Men
VacuMed
4538 Westinghouse Street
Ventura, CA 93003
(800) 235-3333
 

Helpful Hints for Setting up an
Exercise Stress Testing Laboratory

(C) Copyright VacuMed 1998 - 2006

When most lay people hear the word STRESS TEST, they visualize a person running on a treadmill or pedaling on a stationary bicycle while all kinds of wires are attached.

What they think of is the Cardiac Stress Test.

It is not immediately obvious to everyone, that a deficiency in the performance of the heart may be caused by an insufficiency of the lung. So we now know that a Stress Test may mean either, or both, a Cardiac and/or Pulmonary evaluation.

Cardiac Stress testing in a clinical setting is fairly well understood and the equipment required is well known. This is not necessarily so for Pulmonary Stress Testing.

Simple, computerized equipment for pulmonary stress testing (gas exchange analysis) has only become available since the introduction of the Personal Computer (PC). Prior to that, it was a cumbersome procedure requiring the collection of exhaled gases in Douglas bags or large Tissot spirometers and then determining the gas concentrations by various gas analysis instruments.

Pulmonary stress test systems go by a number of names: VO2 Measurement System, Metabolic Cart, CPX System, or Ergospirometry System as they are called in Europe.

To keep it short, we will use CPX hereafter.

Now, a number of companies offer automatic and computerized data acquisition and analysis.

While a cardiac stress test is almost exclusively conducted for the purpose of evaluating a problem or suspected problem with the heart, there are several reasons for measuring oxygen consumption:

  1. To test a patient with a suspected illness or deficiency
  2. To measure the progress of "Rehab"
  3. To measure the progress of a weight loss program
  4. Fitness Evaluation: Physical performance of athletes
  5. Nutritional assessment

Perhaps the most important differences we find between labs testing "patients" vs. labs testing so-called "normal" subjects is the use of the 12-lead ECG and the availability of resuscitation equipment and personnel trained in it's use.

2. Equipment for the Cardiac Stress Test

The equipment required is usually obvious and well understood, but you should be aware that there is a big price differential between Resting ECG and Stress Testing ECG. In evaluating competing systems, be sure you understand software options, such as "Full Disclosure", "Automatic Arrhythmia Detection", "ST Segment Analysis" and others, which may affect the cost of the system.

Minimum requirements are a 12-lead system with STRESS TEST software.
See ECG Menu

Other equipment required:

Exercise Devices: Treadmills or ergometer , more details in chapter 5.

Blood pressure sphygmomanometer (e.g. Baumanometer) or
Electronic non-invasive blood pressure meter, see VacuMed number "Tango"

Emergency Resuscitation Equipment
Defibrillator
Crash cart, Ambu bags, 100% oxygen with face mask,
Resuscitation mask, e.g. CPR Micro Shield

3. Equipment for the Pulmonary Stress Test Lab

The instrumentation here can vary greatly depending on the type of testing to be performed, the reason for the test, the mission of the laboratory and the desired accuracy. For example, a college teaching laboratory might be more interested in a basic low cost system, while a lab planning to publish their findings would be more interested in accuracy. Listed in approximate order of importance
  1. Oxygen Consumption (VO2, VCO2) Measurement System (or CPX)
  2. Calibration Gases & Pressure Regulators Should include a true "Zero" gas, usually 100% N2 and a "Span" gas, such as 16% O2 and 4%CO2.
  3. Calibration Syringe , usually a 3-liter volume syringe
  4. Exercise Device: Treadmills , Ergometers , rowing machine, etc.,
    more details in chapter 5.
  5. Patient Interface:
    a. Mouthpiece , 2-way valve and nose clip
    b. Stress Test Face Mask with headgear
    Consider the V-Mask or Air Cushion Masks ("KM-Mask")
  6. Heart Rate Measurements or EKG system One channel (3-lead) minimum
  7. Barometer
  8. Hygrometer and Thermometer to measure relative humidity
  9. Metabolic Calibrator / Simulator
  10. Spirometer
  11. Lactate Analyzer
  12. Weight Scale and Height Measure
  13. Valve Balancer, hangs breathing valve from overhead support
  14. Body fat Measurement Method:
    The Gold Standard: Underwater Weighing System
    Electronic Systems: Impedance measurements
    Body fat Calipers
  15. Metronome: For use when the exercising subject needs to maintain a steady cadence (Such as when using non-isopower ergometer).

4. The VO2 System: What to look for

All CPX's (VO2 Measurement Systems) contain the same basic building blocks:

Oxygen and CO2 analyzers, a ventilation measurement device, interfacing electronics, gas sampling system, data acquisition system and some kind of computer and software.

Most CPX manufacturers do not make their own gas analyzers, instead they buy them from companies that specialize in making nothing but gas analysis equipment. This is actually good news, because better quality can often be achieved by specialization.

The other major component is the ventilation measurement device or flow sensor. The chart below may help you select a desirable flow sensor.

Almost all companies use a PC now, so very little differentiation can be expected there.

The final and perhaps most important component is the software. It is the software that ultimately determines the accuracy of the VO2 measurement. You may have the world's best gas analyzers, but if the software does not correctly align gas data with flow data, or if the compensation for barometric pressure, temperature and humidity is not handled correctly, then the system cannot report accurate VO2's.

To our knowledge only a Metabolic Simulator(1,2) can accurately verify if the system operates correctly.

Here are some other questions you may want to ask before you buy:

  • Can you look at a demo disk of the software before you buy?
  • Can the system be interfaced to a notebook computer in case you need a portable system?
  • If you need options such as EtCO2 or SAO2, are they available, can they be added later?
  • Is software available for test interpretation, data base analysis or exercise prescription?

5. Exercise Devices

There are a lot of exercise devices on the market and this listing is not intended to be complete.

Treadmills

In our opinion, for testing you should not consider a treadmill costing less than $4000. The desirable, higher priced machines should include motorized elevation, built-in and programmable exercise protocols and/or the ability to be remotely programmed by your stress test software.

VacuMed's models 13610 and 13620 meet this description and also include a "Kill Switch" that automatically shuts of the treadmill if the runner gets too far away from the control console. Model 13610 is a heavy duty research type treadmill. Most manufacturers of exercise stress testing devices offer treadmills with their own name on them but manufactured by other companies specializing in treadmill manufacturing.

Ergometers

Ergometers, in principle, are more desireable for exercise stress testing because they allow the direct determination of braking power in watts, while treadmills only allow an indirect approximation. However, if you are testing runners, then a treadmill will be the preferred device.

In our opinion, for CPX testing you should not consider an ergometer costing less than $2000. Ergometers are stationary bicycles that have some kind of braking mechanism that can be calibrated in Watts, Joules or KPM. Braking mechanisms using belts, brake pads tend to be less accurate. Modern braking mechanisms use electro-magnetic brakes (eddy current). For more advise on selecting ergometers, go back to Dr Andrew's Corner.

Rowing Machines and Stairclimber are sports-specific and are almost never used in a clinical setting.

6. Accessories & Supplies

Typical cardiac supplies:
  • ECG chart paper
  • Electrodes
  • Electrode Gel
  • Skin Prep
  • Stress Test Shirt
    Keeps electrodes and electrode cables in place to minimizes movement artifacts. Bandages and tape to keep electrodes in place. Wipes to remove electrode gel after test.

    Basic emergency response supplies:

    Typical pulmonary test supplies:

  • Mouthpieces and Noseclips Note # 109NT mouthpiece works well with subjects wearing dental braces
  • Nose clips , disposable Nose clip, permanent
  • Breathing Tubes , to connect the exhalation valve to the mixing chamber. (In mixing chamber systems)
  • Sample Tubing , to connect the gas sample port to the gas analyzer input 1/8" ID and 1/16" ID respectively (In breath-by-breath systems)
  • Sterilizing/Disinfecting Solution to clean mouthpieces and breathing valves
  • Silicone Grease to lubricate valve threads and tubing joints
  • Pulmonary Function Test Filters
  • Towels
  • Drink: Access to drinking water or juice
  • Capsaisin (available in the US as "Zostrix") promotes blood flow to the earlobe in case of problems with SAO2 or heart rate sensors.
    (Read CAUTION label!)

7. Laboratory Setup

Make sure large equipment, such as treadmills and underwater weighing tanks will fit through doors, hallways or windows.

The layout should consider the number of people likely to be present during testing. In a teaching environment you may want a large number of students to witness the test. This may require secondary monitors to be placed in visible locations.

Do you want the test subject to see the computer screen during test?

Provide for adequate ventilation, install a fan in front of the test subject to cool him during exercise.

The laboratory should have a sink to wash hands, clean mouthpieces, masks, etc.

We have seen labs placing a mattress behind a treadmill to minimize injuries in case of a fall. A treadmill with a "Kill Switch" is a useful safety feature.

If you are using an ergometer, make sure the seat is adjusted high enough so the knee of the test subject is fully extended on the down stroke.

Place a RPE (Rate of Perceived Exertion) chart (if desired) within convenient reach of the test subject.

Prominently post instructions for emergency procedures, phone numbers for emergency assistance. Spell out instructions to emergency personnel how to find you.

Decide where your data files will be stored; institute computer backup procedures.

Verify the accuracy of your barometer by calling the local weather bureau or the nearest airport control tower, they have accurate instruments.

8. Test Precautions

Consult the publications listed on the next page.

Know the symptoms that require test termination.

Read the instruction manual that comes with your instruments.

Some additional comments:

Develop a questionnaire even for "normal" subjects to determine risk factors.

Conduct a simple spirometer test to detect respiratory impairment.

Tell your test subject to wear comfortable clothing, such as shorts and T-shirt, as well as walking or running shoes.

If you are using a treadmill, demonstrate how to get on and off the running treadmill.

Make sure tubing connections and electrode cables are secure to avoid having to repeat the test.

If you are using a face mask block off the exhalation port and ask the subject to pressurize the mask (exhale) to check for leaks.

Some people produce insufficient signals with earlobe SAO2 or heart rate sensors.

Keep some capsaicin (Zostix) on hand to apply to earlobe, but wash hands immediately to prevent getting it into eyes or other sensitive body areas.

9. What are the reasons for Exercise (CPX) Stress Testing
and what can you teach with a CPX System?

9.1 Exercise Physiology

Exercise requires the integration of physiological mechanisms to enable both, the respiratory and cardiovascular systems to support the increased metabolic demands.

During exercise, both ventilatory and cardiovascular systems are under stress. The ability to respond adequately to this stress is a measure of physiological health and fitness.

Exercise testing evaluates the respiratory and cardiovascular responses to increased gradual workloads in order to define the level of physical work capacity, and to determine the limiting factors to the increased metabolic demands of exercise.

Serial exercise studies help define the effects of treatment or fitness programs on the physiological response to physical work.

Here are some examples of exercise related study subjects:

  • Metabolism, Physiologic Responses to Various Stimuli: Exercise, diet or food groups.
  • Respiratory Gas Exchange (VO2, VCO2), Oxygen debt, effect of CO2 retention (hypoventilation) on the regulation of CO2 stores in the body.
  • Assessment of Physical Fitness: VO2max, Anaerobic (lactic) Threshold (AT or LT) as a percentage of VO2max. VO2 dynamics, t* (tau)
  • Assessment of a Training or Weight Loss Program. Lowering of VCO2 and HR at a given exercise level as a result of training. Reduction of t for VO2 and VO2 drift for constant load heavy exercise.
  • Progress of Post-Injury Rehabilitation. Improvement in VO2max, AT and t*.
  • Cardiac Output: CO2 rebreathing as a method for estimating Cardiac Output (C.O.). Fick Method.
  • Pulmonary Function Testing, Lung Volumes Measurement Vital Capacity (Spirometry) Residual Volumes with VacuMed system Residual Volume or Nitrogen Washout by Wilmore Method(3)
  • Rehabilitation

9.2 Studies of Metabolism

This involves the measurement of VO2 and VCO2 at rest for the determination of :

  • Basal Metabolism (Basal Metabolic Rate) Research studies of metabolic and endocrine disorders, such as diabetes Effect of training on Basal Metabolic Rate and Heart Rate
  • Resting Energy Expenditures (REE) which is useful for studies involving nutrition and also has important application in weight loss programs and studies of eating disorders. For example, is a subject in a weight loss program really reducing his/her calorie intake?
  • Substrate Utilization
  • Nutritional Assessment, effect of a fat vs. carbohydrate diet on RQ
  • Testing of drugs affecting metabolism or weight control
VacuMed offers a specific instrument for studies of metabolism: MX-REE

See also Dr. Andrew's Corner

9.3 Occupational Applications

Exercise Stress (CPX) Testing is frequently used in professions that require high physical demands, such as
Firefighters
Police
Military
Rescue & Disaster Response Teams
Miners
Steel Mill Workers
Divers
Professional Athletes
Pilots

CPX testing in such professions may be used for:

  • Pre-employment screening
  • Routine fitness assessment
  • Disability assessment and documentation
  • Rehabilitation assessment and documentation

9.4 Clinical Applications

  1. Diagnosis of causes of exercise limitation

  2. Responses of cardiopulmonary variables in patients with cardiovascular disease or pulmonary disease

RESPONSE TO EXERCISE IN CARDIAC OR PULMONARY DISEASE (5)*
Variable Cardiac Disease Lung Disease
VO2 Peak Decreased Decreased
Anaerobic Threshold Decreased Low or Normal
Heart Rate Reserve Decreased Increased
Breathing Reserve Normal or Increased Decreased
O2 Pulse Decreased Normal or Low**
Exercise PaO2 Normal Normal or Decreased
Exercise P(A-a)O2 Normal or High*** Increased
Exercise VD/VT Falls Normally Fails to fall normally
ECG During Exercise Abnormal Normal

3. Exercise-induced asthma
(See also Turboaire Challenger cold air generator)

4. Pre- and post-operative evaluation

5. Disability assessment Functional capacity testing (METs)

6. Assessment of supplemental O2 requirement Assessment of oxygen desaturation (SAO2) during exercise

7. Evaluation of level of fitness / exercise prescription
Occupational fitness assessment (e.g. police or firefighters) Pre-clearance for exercise/fitness/weight loss program

8. Evaluation of cardiac and/or pulmonary rehab

9. Evaluation of Metabolic Disorders

10. Evaluation of Muscular Disorders

11. Nutritional Assessment

12. Resting Energy Expenditure (REE)

13. Fick Cardiac Output Calculations

14. Cardiopulmonary Rehabilitation

15. Measurement of physiological dead space and determination of the VD/VT ratio (Requires the EtCO2 option).

10. What is measured during a CPX test?

1. Oxygen Uptake Response

VO2max: This is the gold standard to measure functional capacity of the cardiovascular system to transport oxygen.

VO2max depends on the mode of exercise, the degree of training and the integrity of cardiovascular function.

It is usually reduced in any sort of cardiopulmonary disease. In most cases, except in athletes, the presence of a normal or elevated VO2max virtually ensures the absence of any major cardiovascular or pulmonary diseases.

VO2max is expressed in ml/kg of body weight and relates to exercise tolerance.

2. Haemodynamic Responses

The behavior of heart rate, systolic and diastolic pressures and cardiac output, during exercise provides insight into cardiovascular response.

3. Ventilatory Responses

Changes in Minute ventilation (VE), Tidal Volume (TV) and breathing frequency (f) reflect the magnitude of ventilatory response to exercise. The pattern of increase in tidal volume and breathing frequency may provide information about certain pulmonary and circulatory disorders.

4. Metabolic Response

This usually involves the measurement of VO2 and VCO2 at rest. Metabolism is affected be diet, exercise, disease, climate variations, etc.

5. Electrocardiographic Response

This represents the main focus of conventional ECG Stress testing. It is useful in defining the presence or absence of exercise induced ischemias as well as the presence or absence of dysrhythmias.

Clinical exercise testing requires monitoring of ECG and prompt termination of exercise testing is mandatory when a patient develops signs of distress, such as changes of PQRST pattern.

11. Other Publication

1. GUIDELINES FOR EXERCISE TESTING (4) A Report of the American College of Cardiology/American Heart Association Task Force on Assessment of cardiovascular Procedures (Subcommittee on Exercise Testing) Reprints: Mr. David J Feild, Assistant Executive Vice President, American College of Cardiology, 9111 Old Georgetown Road, Bethesda MD 20814

2. Books PRINCIPLES OF EXERCISE TESTING AND INTERPRETATION By Karlman Wasserman, MD, PhD., James E Hanson, MD., Darryl Y Sue, MD., Brian J Whipp, PhD., Richard Casaburi MD, UCLA Medical Center, 274 pp, illus., 1994, 2nd ed.

3. Books RESOURCE MANUAL FOR GUIDELINES FOR EXERCISE TESTING AND PRESCRIPTION Edited by the AMERICAN COLLEGE OF SPORTS MEDICINE, Indianapolis, IN. (64 Contributors) 580 pp, 205 illus., 1993

4. Books GUIDELINES FOR EXERCISE TESTING AND PRESCRIPTION, 4th ed. Edited by the AMERICAN COLLEGE OF SPORTS MEDICINE, Indianapolis, IN. 314 pp, paperback, 1991

5. Books EXERCISE PHYSIOLOGY LABORATORY MANUAL Basic principles of field and laboratory testing, includes forms for data collection and typical calculations. By Gene M Adams, California State University-Fullerton 304 pp, illus, wirecoil, 1993, 2nd ed.

6. Books EXERCISE PHYSIOLOGY Energy, Nutrition, And Human Performance William D McArdle PhD, Frank I Katch EdD and Victor L Katch EdD 853 pp, illustrations, 1991, Third Edition

7. Books EXERCISE IN HEALTH & DISEASE Evaluation & Prescription for Prevention and Rehabilitation, 2nd ed. By Michael L Pollock & Jack H Willmore, 754 pg, 367 illus, 1990

8. Books PRINCIPLES AND PRACTICE OF PULMONARY REHABILITATION Up-to-date info about diagnostic techniques & rehabilitation By Richard Casaburi MD PhD & Thomas L Petty MD. 510 pp, 190 illus, 1993

References:

(1) Huszczuk, A., B.J. Whipp, and K.Wasserman. A respiratory gas exchange simulator for routine calibration in metabolic studies. Eur. Respir. J. 3:465-468, 1990

(2) Gore, C.J., P.G. Catcheside, S.N. French, J.M. Bennett, and J. Laforgia. Automated VO2 max calibrator for open-circuit indirect calorimetry systems. Med. Sci. Sports Exerc 29:1095-1103, 1997

(3) Wilmore, J.A., P.A. Vodak, R.B. Parr, R.N. Girandola an J.E. Billing. Further simplification of a method for determination of residual lung volume. Medicine and Science in Sports and Exercise Vol. 12, No. 3.

(4) SPECIAL REPORT: Guidelines for Exercise Testing. JACC Vol. 8, No. 3. Sept 1986:725-38

(5) ACCP, San Francisco1991, A Pulmonary Approach to Exercise Testing, Idelle M. Weisman, FCCP, El Paso, TX

    Last Updated: 25 July 2006
    The Metabolic (Lung) Simulator
    Calibration of Metabolic Systems
    Stress Testing
    Resting Energy Expenditure "REE"
    Why Calibrate Ergometers
    How to select a Cycle Erometer
    Deception of the Douglas Bag