Bicycle Ergometry / Supine Ergometry

Relevant Social Security Medical Listings

  • Listing 4.04 Ischemic Heart Disease (Adults)

Type

Objective/EKG (Exercise)

Can SSA Purchase?

Yes. Also, results of this test should always be considered by the SSA if appearing in the evidence of record from a treating doctor. It should be noted that although the SSA frequently purchases stress testing in the evaluation of ischemic heart disease, it is less likely to do so in those individuals with a history of heart failure or simply to establish blood pressure response to exercise.

Purpose

  • Diagnose and evaluate severity of decreased blood flow to heart muscle (myocardial ischemia) secondary to the obstruction of coronary arteries.
  • Detect exercise-induced abnormalities in rate and rhythm (arrhythmias).
  • Evaluate exercise tolerance.
  • Evaluate blood pressure response to exercise.

Contraindications

See Treadmill Stress Testing (TST, TMST).

Technique

A physician should examine and clear the patient for bicycle stress testing (ergometry), and should be readily available if complications appear during testing. The patient should not eat or drink anything for several hours prior to testing, and dress appropriately for exercising. With proper screening of the patient, the risk of complications is low. Diabetics that miss their regularly scheduled meal should also skip that insulin dose. The testing facility should include oxygen, drugs, and equipment necessary to treat high or low blood pressure, respiratory distress, cardiac arrest, etc. During the testing the patient should always be under observation by at least a nurse with special training in heart disease, but preferably a physician.

The patient rides a stationary bicycle that can have tensions set on the wheels to control the work output required to turn the pedals. The exercise equipment is sometimes arranged so that the patient pedals an ergometer while lying in the supine position (supine ergometry) rather than sitting on a bicycle, but the tests are otherwise the same. Bicycles or other leg ergometers are useful for patients who would have difficulty walking on a moving treadmill, but can use their legs to pedal[1]; the test is also used with individuals with no difficulty ambulating. The patient pedals the stationary bicycle while EKGs and heart rate are continuously monitored.[2] As tolerated by the patient, the workload tension required to pedal the bicycle is gradually increased in 2 or 3 minute stages. Permanent records of heart rate, blood pressure and EKGs should be made at least once during each stage; blood pressure may be taken while the patient briefly stops exercising (no longer than 1 minute) and the tension on the wheels is set to the next higher stage. If possible, the patient continues exercising until at least 85% of their predicted maximal heart rate is reached.

A MET is a term used to describe oxygen utilization by the body, and stands for metabolic equivalents. One MET means use of 3.5 ml oxygen/minute/kilogram of body weight. METs allow standardization of exercise capacity, so that a certain physical performance on an cardiac exercise test can be deduced to represent a certain level of fitness. It requires one MET just to sit; sedentary to very light work requires about 5 METs. The ability to perform 7 METs is average exercise ability for a normal person who leads a sedentary lifestyle; normal individuals who exercise regularly can perform much better. Bicycle ergometer external workload[3] is measured in kilogram-meter/minute[4] (kgm/min). Energy expenditure is measured in kilopond-meter/minute or watts.[5] Kgm/minute, kpm/min, or watts can then be matched to various MET levels for a 70 kilogram person:

KGM/Minute Watts METs[6]
150 25 2.5
300 50 4.0
450 75 5.0
600 100 6.0
750 125 7.0
900 150 9.0
1050 175 10.0
1200 200 11.0
1350 225 12.0
1500 250 13.5
1650 275 14.5
1800 300 16.0

The above MET values represent those for a person weighing a standard 70 kilograms.[7] Thus, the actual METs used depends on the body weight of the individual when riding a bicycle ergometer and reference must be made to standard tables for expected oxygen consumption for various weight individuals in order to determine the METs used. However, individuals of different weights but performing the same external workload in kgm/minute on a bicycle have done the same amount of physical work even though METs are different. The heavier the patient, the less METs utilized for the same external workload, since METS are calculated on the basis of oxygen used per unit of body weight. This is in contrast to treadmill stress testing, in which METS and stage of exercise accomplished are the same for people of different weight. For example, a 70 kilogram (154 lb) person performing an external workload of 600 kgm/minute (100 watts energy output) by pedaling would require 6 METs, while a person weighing twice that much at 140 kilograms (308 lbs) would require 3 METs to perform the same external work. Thus, actual exercise capacity on bicycle ergometers should not be confused with METs.

However, the workloads attained on a bicycle ergometer utilizing the 70 kilogram weight values can be correlated with the same MET levels on a treadmill stress test, regardless of the weight of the patient. In other words, if the individual in the above example attained a workload of 600 kgm/minute on a bicycle at 6 METs (70 kilogram) or 3 METs (140 kilograms), the performance is the same in either instance as being able to perform at the 6 MET level on a treadmill.

Stress tests should also always be terminated at the request of the patient, even if there is no evidence medical reason for stopping; however, premature cessation by a patient may prevent a meaningful test. Stress tests should also be terminated if the patient becomes physically exhausted, but this fact is not in itself indicative of heart disease.

After termination of the test, the patient should be monitored (EKGs, blood pressure, heart rate, possible symptoms) until vital signs are clearly stable and returned to at least near-normal.

Interpretation

See Treadmill Stress Testing (TST, TMST).

Comments

See Treadmill Stress Testing (TST, TMST).

Footnotes

  1. For example, a patient might have such poor balance that walking on a treadmill is not possible.
  2. Baseline resting EKG tracings (lying and standing) are also performed prior to exercise, sometimes with voluntary hyperventilation to determine if such rapid breathing will influence the EKG tracings. Post-exercise tracings are also run, because abnormalities sometimes appear a few minutes after exercise has stopped although they were induced by exercise.
  3. External work output refers to physical work performed by the legs in contrast to metabolic work in the biochemistry of the body.
  4. One kilopond-meter (kpm) is the energy required to lift a 1 kilogram mass 1 meter against the normal gravitational force of the earth (kilogram-meter or kgm). One kpm is the energy necessary to perform a one kgm workload. In terms of exercise testing, 1 kpm/min energy expenditure or a 1 kgm/min workload amount to essentially the same thing.
  5. One watt energy expenditure is 6.12 kpm/minute.
  6. MET values are fairly accurate approximations; however, precise MET values would require actual measurement of oxygen consumption (VO2) during exercise.
  7. There are 2.2 pounds per kilogram.