Spirometry (meaning the measuring of breath) is the most common of the pulmonary function tests (PFTs). It measures lung function, specifically the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is helpful in assessing breathing patterns that identify conditions such as asthma, pulmonary fibrosis, cystic fibrosis, and COPD. It is also helpful as part of a system of health surveillance, in which breathing patterns are measured over time. Spirometry generates volume-time curves and also flow-volume loops, which are charts that plot the volume and flow of air coming in and out of the lungs from one inhalation and one exhalation.
Testing
Spirometer The spirometry test is performed using a device called a spirometer, which comes in several different varieties. Most spirometers display the following graphs, called spirograms:
a volume-time curve, showing volume (litres) along the Y-axis and time (seconds) along the X-axis a flow-volume loop, which graphically depicts the rate of airflow on the Y-axis and the total volume inspired or expired on the X-axis
Procedure The basic forced volume vital capacity (FVC) test varies slightly depending on the equipment used. It can be in the form of either closed or open circuit. Regardless of differences in testing procedure providers are recommended to follow the ATS/ERS Standardisation of Spirometry. The standard procedure ensures an accurate and objectively collected set of data, based on a common reference, to reduce incompatibility of the results when shared across differing medical groups. The patient is asked to put on soft nose clips to prevent air escape and a breathing sensor in their mouth forming an air tight seal. Guided by a technician, the patient is given step by step instructions to take an abrupt maximum effort inhale, followed by a maximum effort exhale lasting for a target of at least 6 seconds. When assessing possible upper airway obstruction, the technician will direct the patient to make an additional rapid inhalation to complete the round. The timing of the second inhale can vary between persons depending on the length of the preceding exhale. In some cases each round of test will be preceded by a period of normal, gentle breathing for additional data.
Limitations Clinically useful results are highly dependent on patient cooperation and effort and must be repeated for a minimum of three times to ensure reproducibility with a general limit of ten attempts. Given variable rates of effort, the results can only be underestimated given an effort output greater than 100% is not possible. Due to the need for patient cooperation and an ability to understand and follow instructions, spirometry can typically only be done in cooperative children when they are at least 5 years old or adults without physical or mental impairment preventing effective diagnostic results. In addition, general anesthesia and various forms of sedation are not compatible with the testing process. Another limitation is that persons with intermittent or mild asthma can present normal spirometry values between acute exacerbation, reducing spirometry's effectiveness as a diagnostic tool in these circumstances.
Supplemental diagnostics Spirometry can also be part of a bronchial challenge test, used to determine bronchial hyperresponsiveness to either rigorous exercise, inhalation of cold/dry air, or with a pharmaceutical agent such as methacholine or histamine. To assess the reversibility of a particular condition, a bronchodilator can be administered before performing another round of tests for comparison. This is commonly referred to as a reversibility test, or a post bronchodilator test (Post BD), and is an important part in diagnosing asthma versus COPD. Other complementary lung functions tests include plethysmography and nitrogen washout.
Indications Spirometry is indicated for the following reasons:
to diagnose or manage asthma to detect respiratory disease in patients presenting with symptoms of breathlessness, and to distinguish respiratory from cardiac disease as the cause to measure bronchial responsiveness in patients suspected of having asthma to diagnose and differentiate between obstructive lung disease and restrictive lung disease to follow the natural history of disease in respiratory conditions to assess of impairment from occupational asthma to identify those at risk from pulmonary barotrauma while scuba diving to conduct pre-operative risk assessment before anaesthesia or cardiothoracic surgery to measure response to treatment of conditions which spirometry detects to diagnose the vocal cord dysfunction.
Contraindications Forced expiratory maneuvers may aggravate some medical conditions. Spirometry should not be performed when the individual presents with:
Hemoptysis of unknown origin Pneumothorax Unstable cardiovascular status (angina, recent myocardial infarction, etc.) Thoracic, abdominal, or cerebral aneurysms Cataracts or recent eye surgery Recent thoracic or abdominal surgery Nausea, vomiting, or acute illness Recent or current viral infection Undiagnosed hypertension
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