How does The Tread mill Stress Test compare to the Cardiopulmonary Exercise Test?
Doctors use exercise stress tests to assess how the body’s systems respond when they are stressed. Exercise stresses the cardiovascular, pulmonary, and muscular systems by making them work faster and harder. If these systems are affected by a medical condition they will not be able to function appropriately under the stress of exercise.
During a traditional treadmill stress test the patient walks on the treadmill as it gets faster and steeper. The blood pressure and electrocardiogram (EKG) are the only aspects of the cardiovascular system that are measured during this test.
Doctors primarily look at a specific part of the EKG to determine if there are blockages in the large blood vessels of the heart (coronary artery disease) preventing it from getting enough oxygen (ischemia is the condition when the heart is not getting enough oxygen). However, in many people with heart disease, this EKG abnormality never appears. Additionally, the body motion of walking often causes the EKG signal to have artifact and become unclear to read.
During a CPET the patient exercises on a stationary bicycle as it progressively becomes harder to pedal. Just like the treadmill stress test, the blood pressure and EKG are monitored. Additionally, the amount of oxygen the body is using, the amount of carbon dioxide it is producing, and the breathing pattern are measured. The heart and lungs function together to send oxygen to the muscles and body tissues, and to remove carbon dioxide produced by the body. These measurements allow the CPET to assess the cardiovascular, pulmonary, and muscular systems all at once. The pattern in which the body uses oxygen can indicate if the heart has a blockage causing ischemia. This is significantly more sensitive at detecting heart disease (blockages) than the treadmill stress test. Additionally, unlike the treadmill stress test, the CPET can detect blockages in the small blood vessels of the heart and it can detect the early stages of heart disease. This allows doctors to treat patients before their heart disease becomes irreversible and deadly.
The treadmill stress test can only detect ischemic heart disease of the large blood vessels, and it is not very accurate at doing this. Not only does a CPET do a better job of detecting ischemic heart disease, but it can also pick-up many other conditions that the treadmill stress test cannot. The conditions detected by CPET, but not treadmill stress test include:
- Heart Failure
- Myocardial Ischemia of the small blood vessels
- Cardiac valve dysfunction
- Chronotropic incompetence
- Pulmonary ventilation disorder
- Pulmonary circulation disorder
- Muscle metabolic disorders
Exercise mode: Treadmill vs Bicycle
During a CPET the exercise is performed on a stationary bicycle, which has several advantages over a treadmill. Some think that a treadmill is better for stress testing because people are more used to walking than riding a bicycle. However, walking on a treadmill is significantly different than walking down the street. When walking on a treadmill, the ground moves but the body does not. The patient has no control over the treadmill and if the patient cannot keep pace, there is a great chance for falling. This is why so many people are frightened of doing an exercise stress test. In reality, people are not any more used to walking on a treadmill than riding a stationary bicycle.
The main diagnostic tool of a treadmill stress test is the EKG. Unfortunately, the up and down body motion generated from walking on a treadmill can cause artifact in the EKG signal and make the EKG difficult to accurately interpret. This movement also makes it difficult to take an accurate blood pressure reading, especially if an automatic blood pressure cuff is used. During a CPET, the bicycle allows the upper body to remain stationary, which usually results in clear EKG and blood pressure recordings. Although the EKG and blood pressure are secondary measurements during the CPET they are often more accurate than when a treadmill is used.
Patients who are obese, use a cane or walker, and are elderly have difficulty walking on a treadmill. These patients are often unable to move their legs fast enough to keep-up with the increasing speed of the treadmill. This problem is usually not encountered on a bicycle because the patients keep their legs moving at the same speed for the entire test. This allows a wider range of people to be tested using the bicycle compared to the treadmill.
With the traditional stress test all patients exercise with the same increases in treadmill speed and incline. Young people can exercise for a long period of time, but patients with a heart, lung or metabolic condition, the elderly, the obese, and patients with a short height may only be able to exercise for a few minutes. This results in a very small amount of information being collected on many patients. During a CPET the increases in workload are adjusted for each patient so that almost everyone exercises for 8-12 minutes. This ensures that enough information is collected to make an accurate interpretation of the test results.
During a traditional stress test the speed and incline of the treadmill increases in large jumps, jolting the cardiovascular and pulmonary systems. This sudden increase in stress on the body can be too much for the patient to handle, causing some to stop the test early. In contrast, the bicycle allows for the exercise level to be increased very gradually, a little at a time. This gentle increase in work load lets the cardiovascular and pulmonary systems smoothly reach their maximal levels.
- Safer, less chance of falling
- Cleaner EKG and blood pressure measurements (less movement artifact)
- Detects multiple conditions affecting the heart, lungs, and muscles
- More accurate detection of ischemic heart disease
- Gradual increase in exercise level
- Exercise level adjusted for each individual
- Greater exercise time, more information
- Direct measurement of work performed
Treadmill stress test
- Intimidating for many
- Movement artifact on EKG and blood pressure
- Detects ischemic heart disease
- Same exercise level for each person
- Difficult to keep up with large jumps in speed and incline
- Improper use of hand support skews results
- Shorter exercise time, less information
Will I get the same results from CPET as I would with another test?
No, other tests use fewer measurements and assess cardiac and lung function separately. A treadmill stress test only looks at a specific part of your ECG during exercise that can indicate heart disease. However, in many people with heart disease, this ECG abnormality never appears. Nuclear stress testing uses a radioactive chemical that is injected into the bloodstream to estimate how blood flows around the heart. Pictures are taken with a special camera before and after exercise to show any abnormalities. This can detect an abnormality in main, large (macrovascular) blood vessels around the heart; however, it does not show any abnormalities in the small (microvascular) blood vessels of the heart. Nuclear stress testing can also miss patients with blockages in multiple blood vessels, or in blood vessels not easily seen by the camera due to their position on the heart. The CPET is not an imaging test, but a physiological test. It measures how your heart, lungs, and muscles are functioning during exercise. CPET takes into account multiple physiological variables that might limit your ability to exercise. No other test exists that can measure heart, lung, and muscle function all at once.