What is the Stress Test?
The controlled exercise stress test is used to monitor a patient’s heart electrical signals (an electrocardiogram, referred to as an ECG) as well as their blood pressure while they perform a progressive exercise protocol lasting 6–15 minutes, either on a treadmill (ergometry) or on a stationary bicycle (cycloergometry).
How it is performed?
Electrodes are placed onto the individual’s chest area to perform an ECG at rest and to monitor the electrical signals of their heart during exercise. The patient also wears a pressure cuff which is kept in place throughout the stress test. A baseline blood pressure reading is recorded and is compared to the person’s blood pressure measurements at the end of each exercise stage.
After the initial preparation, the exercise test begins. Where a treadmill is used (ergometry), the most commonly used exercise procedure is the Bruce protocol, which consists of three-minute stages in which the steepness and walking speed of the treadmill are progressively increased. The test ends when the target maximum heart rate has been reached, in which the patient is unable to continue exercising, presents symptoms, or when changes in their electrocardiogram or blood pressure are observed.
Where a bicycle test is used (cycloergometry), the most commonly implemented protocol is the OMS in which, like the ergometry test, each stage consists of three minutes, and the bicycle load is increased by 25 W each stage.
What is the stress test for?
The stress test is a technique widely used in the field of cardiology. It is used to diagnose coronary artery disease. When a patient has a blockage in their arteries, the blood flows properly under resting conditions, but when physical exercise is performed, the work the heart must perform and the oxygen demand of the coronary arteries increase, and so the obstruction manifests itself, primarily as chest pain (angina pectoris), shortness of breath (dyspnea), or as intense fatigue. In this case, the symptoms are accompanied by alterations in the ST segment of the electrocardiogram.
Stress tests also provide information about the person’s blood pressure response, any exercise-induced heart rhythm disturbances, and the person’s functional capacity. This data is essential for giving a diagnosis and prognosis for other cardiac diseases such as arterial hypertension, myocardiopathies, or congenital heart diseases.
How should you prepare?
Before carrying out the test, consider the following points:
- Wear comfortable clothes and sports shoes (or similar). For comfort, it is advisable to wear a wireless bra.
- To ensure good adhesion of the electrodes, do not apply moisturizer for a few hours before taking the test.
- Avoid eating food for two hours before the test.
- Do not perform high-intensity exercise 12 hours before the test.
- Continue or stop taking your normal medication according to the instructions given by the professional who requested the test.
Patients with low functional capacity. Because of heart disease and/or other non-cardiological diseases, some patients have a very low physical exercise capacity, which is why they do not tolerate the usual exercise protocols well. In these cases, and where ergometry is used, a modified Bruce protocol is implemented in which the treadmill slope increase is more progressive, and the speed does not vary between the first and third stage. Where cycloergometry is used, the protocol is the same, but the power (Watts) is adapted based on each person’s ability to perform the activity. The health personnel responsible for carrying out the tests will individually assess each patient to decide the most appropriate protocol in each case. When the patient is unable to perform physical exercise on a treadmill or bicycle, an effortless ischemia test is performed in which a drug is used to simulate the changes that would normally occur with the performance of exercise. This is the case when myocardial SPECT with the administration of drugs and pharmacological stress echocardiography are used.
Athletes The stress test, together with the ECG and the echocardiogram, are common tests in the assessment of cardiovascular health in athletes. The data provided by the stress test includes information about potentially undiagnosed coronary disease, the person’s blood pressure response to exercise, exercise-induced arrhythmias, and the patient’s functional capacity.
When ergometry is used, the protocol most used for athletes is a constant 3% slope and a progressive treadmill speed increase of 6 km/h for women or 8 km/h for men at a rate of 1 km/hour until the maximum tolerated speed is reached. For athletes that practice mountain sports disciplines in which there is usually a pronounced slope, the Bruce protocol is also a common option. For cycloergometry, the protocol is used with the general population, either with progressive and continuous power-increase protocols in which the power is progressively increased by 5–20 W every minute, depending on the patient’s weight and age.
What is the stress test with evaluation of the consumption of expired gases?
In this stress test, aside from monitoring only the electrical signal of the heart with an electrocardiogram and blood pressure, expired gases are also continuously evaluated while the physical exercise is performed.
In this case, in addition to wearing electrodes and a blood pressure cuff, an adapted mask with a large tube and two small tubes attached is worn during exercise, and the data obtained from this analysis is recorded and displayed on a monitor.
This allows the direct evaluation of the relationship between the respiratory, cardiovascular, and blood systems, and in the case of shortness of breath (dyspnea), doctors can understand if these symptoms stem from a heart problem, respiratory disease, muscular issues, or combinations of the above problems.
This test can be done either on treadmill or a static bicycle. The intensity of the exercise protocols is progressively incremented by increasing the speed for treadmill-based tests and the power (Watts) for the bicycle test.
The parameters of this test are:
- Maximum oxygen consumption (V02 max.). The maximum functional capacity of the person is measured directly. It represents the amount of oxygen a person can extract, transport, and use from exhaled air while they are under maximum physical effort. The higher the V02 max, the greater the person’s functional capacity.
- Metabolic thresholds:
- Aerobic threshold (VT1). This indicates the point at which the intensity of the exercise requires the person to increase their ventilation rate. Before reaching the aerobic threshold, the patient obtains all their energy from aerobic metabolism, in other words, from oxygen. When the VT1 threshold is reached, the body begins to resort to a different system (anaerobic) in which lactic acid is generated during exercise, although this is still easily eliminated by the person’s increased respiration rate.
- Anaerobic threshold (VT2). This threshold indicates the intensity zone in which the exercise the person is performing results in such a high energy demand that the person’s lungs are unable to eliminate the excess carbon dioxide (C02) resulting from the exercise, and this causes the accumulation of lactic acid.
- The respiratory-equivalent C02 slope shows the relationship between ventilation (VE) and C02 generation (VE/VC02). It evaluates cardiorespiratory efficiency. The higher the ratio, the worse the cardiorespiratory efficiency. Values less than 30 are considered normal.
The V02max and respiratory thresholds are very useful parameters for the prescription of exercise, in people with cardiological problems, in healthy people and also in athletes because it allows us to establish directly the different training zones are known directly. In the case of patients with respiratory and / or cardiac diseases, V02max and VE / VC02 are also parameters of great prognostic value.