Cardiopulmonary Exercise Tests
These are advanced diagnostic tests aimed at evaluating cardiac and pulmonary functions of a healthy individual or a patient during exercise. The basic objective is to find out adequacy of the heart and lungs under stress. As a matter of fact, a cardiopulmonary exercise test evaluates the entire body’s response to exercise, primarily that of the musculoskeletal system.
Respiratory function tests, which are used to evaluate treatment response or pulmonary function for diagnostic purposes, are of prime importance to pulmonary medicine. However, they are carried out at rest, which limits their capability of evaluating pulmonary reserve capacity. CPET, on the other hand, is able to provide clear information in this regard, as exercise actually activates the aforementioned capacity.
Why are cardiopulmonary exercise tests performed?
Cardiopulmonary exercise tests are most commonly performed in order to determine adequacy of pulmonary capacity for postoperative survival of patients, who are planned to undergo lung surgery (preoperative evaluation). This allows estimation of immediate risk of postoperative complications (adverse effects). In the long term, the patient’s expected quality of life may be estimated as well. Differential diagnosis of idiopathic dyspnea is another objective for which cardiopulmonary exercise test is employed. It is a test which assists not only in diagnosis of diseases but also in evaluation of exercise capacity among individuals, especially athletes.
How are cardiopulmonary exercise tests performed?
High-tech devices and an experienced team are required for cardiopulmonary exercise tests.
The patient is asked to work out on an exercise bike or treadmill specifically designed for this test. An exercise bike is preferable rather than a treadmill, if pulmonary function is to be evaluated.
Testing procedure is explained in detail to the patient before starting. Blood pressure, heart rate and blood oxygenation level, which are vital signs, are measured prior to initiating the test. Additionally pretest respiratory function tests are performed and a heart electrocardiogram is obtained. For the duration of the test, the patient remains fitted with an automatic device that monitors blood pressure, electrodes to follow electrocardiography status and a small clamp on the tip of a finger for blood oxygen readings. A mask that does not hinder comfortable respiration is also placed on the nose and mouth to constantly measure intake of oxygen and carbon dioxide output.
Testing begins once these pieces of equipment are in place and the patient is on the exercise bike, where they will be asked to pedal at a particular pace. Pedaling is initially easy, but becomes gradually difficult as per the requirements of a program drafted in advance in accordance with the patient’s age, weight and height.
Electrocardiography readings, oxygen level, blood pressure, heart rate, oxygen intake and carbon dioxide output are constantly measured, recorded and followed by a physician throughout the duration of exercise. If deemed necessary or if the patient reports inability to carry on, the physician may terminate the test. The patient’s maximum rate of oxygen consumption during the test (VO2
max) is one of the most notable indicators of reserve pulmonary capacity. Heart rate, blood pressure and electrocardiogram readings are also used to evaluate the heart’s response to exercise or any possible existing disease.
Respiratory Function Tests
Respiratory function tests are a series of evaluations aimed at determining how well the lungs function. Spirometry is one of the most basic and common methods. In this test, the patient is asked to inhale the maximum amount of air they can right after a round of normal and relaxed respiration, after which they are required to exhale it fully at full power. It is used in diagnosis and follow-up of pulmonary diseases such as:
- Chronic obstructive pulmonary disease (COPD)
- Interstitial pulmonary disease (hardening of pulmonary tissue)
As it is necessary to perform inhalation and exhalation maneuvers at maximum capacity and full power, some patients, little children, seniors and disabled patients in particular, tend to fail at correctly practicing test instructions. Those patients who cannot follow or accurately perform spirometry instructions are subjected to another test called impulse oscillometry (IOS), which is based on the principle of measuring one’s airway resistance during relaxed respiration. It is thought to be most useful especially for diseases like asthma and COPD. While spirometry is a relatively common test method, the number of medical centers that have an IOS device in their laboratories and offer this test is few in our country.
Diffusion test is another method practiced in follow-up of interstitial pulmonary diseases. It involves inhalation of air containing carbon monoxide by the patient and checking the concentration of carbon monoxide in exhaled air, which indicates the amount of this gas entering bloodstream from the lungs. This is known as pulmonary diffusion capacity. If hardened pulmonary tissues are present, as expected in cases of interstitial pulmonary disease, pulmonary diffusion capacity decreases. This, in that regard, is one of the most remarkable tests in evaluating treatment response in specific diseases and monitoring course of existing disease.
Pulmonary subvolume and intraoral pressure measurements are two other respiratory function tests, albeit less frequently used. Measuring intraoral pressure provides valuable findings especially for monitoring of neuromuscular disease (compromised nerves and muscles). These tests are available only at select medical centers such as our hospital.
6-Minute Walk Test
The 6-minute walk test (6MWT) is utilized to monitor status of several pulmonary diseases, as it provides information on disease progress and severity. It involves the patient walking along a corridor of specific length with preset start and finish lines for 6 minutes. For preparation purposes, the patient rests in a chair for 15 minutes beforehand, during which time blood pressure, heart rate, oxygen readings and dyspnea score at rest are measured and recorded. How the test will ensue, what the walking pace should be and that the patient is free to stop and rest in case of strain are all explained to the patient. Walking at a fast pace for 6 minutes under supervision of an observer is then requested. The observer may be a physician, nurse or physiotherapist. A chair should be made available within the confines of the walking track, should the patient feel the urge to sit down at any time. Exhaustion, severity of dyspnea and oxygen readings are monitored throughout the test. If the patient slows down during the walk, they are prompted by the observer to restore the initial pace. Sweating, pallor and marked reduction in oxygen readings are signs which warrant premature termination of the test. At the end of 6 minutes, blood pressure, heart rate, oxygen readings and dyspnea score are evaluated again. How much distance the patient covered in 6 minutes is recorded as well.
It is known that normal individuals are able to walk 400-700 meters for 6 minutes. However, the distance each patient is expected to walk during the test is calculated in accordance with their age, gender, height and body mass index. It is acknowledged that the distance recorded at the end of the test is indicative of a patient’s daily exercise capacity.
This test is commonly used to monitor progress of pulmonary hypertension and interstitial disease (hardening of pulmonary tissue). Reduced oxygen readings during the walk or less distance walked in comparison to previous tests suggests increased severity of disease or inadequate treatment response. Patients who display marked reduction in oxygenation during the walk test are recommended to use a mobile oxygen support system during exercise