21 March 2019 What are respiratory function tests? Respiratory function tests assess the capacity of the respiratory system to perform its normal physiological functions. Individually, they can provide a variety of functional information on the upper or lower airways, which contributes to the diagnosis of: Respiratory diseases; Respiratory impact of other diseases. As well as diagnosis, they can also help assess the response to treatment. What are the characteristics of respiratory function tests? Respiratory function tests: Are simple and painless; Usually require the cooperation of the person being tested; Do not need any specific preparation. There are certain rules that must be followed in the days before the tests are carried out, some of which depend on the individual characteristics of the person being tested. Overall, respiratory function tests make it possible to study: Respiratory volume and rate; Effectiveness of pulmonary ventilation; Gas exchange; Airway reactivity. What are the different types of respiratory function tests? Respiratory function tests comprise several different examinations. The most frequently performed are: Spirometry; Plethysmography; Inhalation provocation tests; Diffusion test; Cardiopulmonary exercise test. Spirometry Spirometry is a study of lung volume and output ; that is, the volume of air that the lungs are able to take in and expel. It also seeks to study the speed at which the air moves through the respiratory tract during the processes of inspiration and expiration, both normal and forced. Spirometry is done by using a pneumotachograph - a device that measures the flow of air and categorises it numerically, thereby allowing for the calculation of various parameters that are then compared with reference values. Spirometry results can help diagnose reductions in the size of the airways (due to narrowing or obstruction) and the inability of the lungs to inhale and force out sufficient volumes of air during respiratory processes. In specific cases, the spirometry may be repeated after administration of a bronchodilator , which allows the assessment of bronchial response to treatment. Plethysmography Plethysmography also enables the assessment of lung volume , but in a way that is more detailed than with spirometry , as it also estimates the total lung capacity and the residual volume (the volume of air left in the lungs after maximum expiration). It has a particularly important role in assessing the effectiveness of the respiratory mechanisms , by: Studying the capacity to transport air; Strength of the muscles involved in breathing; Airway resistance. The plethysmography is carried out in a plethysmograph - a sealed chamber with a known volume, into which the patient is placed for the duration of the examination. While in the plethysmograph, the patient breathes through a nozzle and is asked to perform various breathing manoeuvres of varying force, which cause pressure changes in the cabin. These pressure variations make it possible to calculate the variations in pulmonary volumes that are necessary to calculate the various parameters being studied. Inhalation provocation tests Inhalation provocation tests are used to study the reaction of the airways to specific compounds or situations. They are usually carried out as part of the diagnosis of allergic diseases and airway sensitivity problems. They involve the application of a stimulus (physical or pharmacological) and evaluation of the response by means of spirometry . Lung diffusion test Gas exchange occurs in the pulmonary alveoli of the lungs. It involves the transferral of oxygen and removal of carbon dioxide from venous blood, turning it into arterial blood. The lung diffusion test allows assessment of the capacity of the lungs in diffusing gases. In this test, patients inhale a gas (which competes with the oxygen in binding to red blood cell haemoglobin) for a determined period. Subsequently, the concentration of this gas in the expired air is quantified , making it possible to assess the alveolar surface area available for gas exchanges. Some diseases can affect the functionality of the pulmonary alveoli. Cardiopulmonary exercise testing Cardiopulmonary exercise testing has a wider application than the previous tests. It can be used to help diagnose respiratory, cardiovascular or muscle diseases , as well as to differentiate between varying causes of respiratory distress. With regard to its use in the diagnosis of respiratory diseases , it enables assessment of: Functionality of the pulmonary alveoli to meet the requirements imposed by physical exercise; Gas exchange; The degree of any existing limitation. Patients start the cardiopulmonary exercise testing by performing a standard type and level of exercise for a fixed period of time. They are then subjected to situations of increasing effort. At the end of the test, information on the following areas is available: Level of effort supported; Reason for discontinuing the test; Oxygen consumption; Carbon dioxide production; Changes in heart rate, blood pressure and respiratory rate. This article was written with the support of physicians and other clinical professionals from the Hospital da Luz network . The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
