A spirometer is a medical device used to measure and record lung function parameters of respiratory air volume and flow rate. Modern spirometers use a variety of techniques, including turbine, pneumotachograph, and ultrasound. The procedure, called spirometry, is commonly used in general practices and by pulmonary specialists (pneumologists or pulmonologists) as part of a pulmonary function test.
What is a spirometer?
Spirometers are medical devices that allow indications of current lung function within spirometry. Spirometers are medical devices that allow indications of current lung function within spirometry. With their help, lung parameters can be measured and recorded. The main parameters that can be measured by spirometers can be divided into dynamic flow parameters and static volume parameters. In the case of dynamic flow parameters, the one second capacity (FEV1, Forced Expiratory Volume in 1 second) and peak flow (PF) are of particular interest. FEV1 corresponds to the volume of air exhaled with the greatest force within the first second after maximum inspiration, i.e. the greatest possible filling of the lungs with air. Peak flow corresponds to the maximum expiratory air flow achieved during exhalation. Both parameters are automatically calculated and stored by the spirometer. The way modern spirometers work – regardless of the physical mode of operation – is conducive to determining the values, because no air volumes are measured, only the flow rate of the air stream, and the absolute volumes are calculated by taking pressure, temperature and humidity into account. The static values reported by spirometers are vital capacity (VC), respiratory volume, and inspiratory and expiratory reserve volume. Vital capacity refers to the volume of air that is the difference between maximal inspiration and maximal expiration, whereas respiratory volume refers to the air inhaled and exhaled per breath during normal respiration.
Forms, types, and species
Original spirometers were based on volume measurements of inhaled and exhaled air via a vessel floating in liquid, which was immersed in the liquid to a greater or lesser degree depending on the volume of air and displayed on a measurement scale. The changes in volumes as a function of time could be recorded in a diagram, so that conclusions could also be drawn about dynamic parameters. Modern spirometers measure the flow rate, temperature and humidity of the inhaled and exhaled air and thus calculate the volume. To prevent hypercapnia, oversaturation and overacidification of the blood with carbon dioxide, from occurring when the previously exhaled air is re-inhaled, a large proportion of the carbon dioxide could be bound and rendered harmless by means of lime filters. Small handy spirometers with practicality use the physical laws of a small turbine, a pneumotachograph or ultrasound to measure the flow rate of the air breathed. The exhaled air is not collected, but escapes as it does during normal breathing. In devices with a free-running turbine, the flow rate can be measured from its rotational speed. Spirometers with a pneumotachograph use the difference in pressure between incoming and outgoing air at a short piece of lamellae to calculate and display the desired parameters. State-of-the-art devices use ultrasound to measure the flow velocity of the air. All methods have certain advantages and disadvantages, with the advantages clearly outweighing those of ultrasonic devices. However, they are also in the upper price range.
Structure and mode of operation
Simple turbine spirometers contain a reusable or a “single-use” turbine located in a tube with a defined cross-section. The patient breathes in and out through a disposable mouthpiece as instructed by the operator. The turbine speed is automatically detected by the device and converted into the main flow and volume parameters. The devices are usually only the size of a pocket calculator or cell phone. On the one hand, turbine spirometers are available in compact versions in which the calculator and turbine sections with mouthpiece are integrated into a single unit. On the other hand, the calculator – also possible with its own small printer – can be separated from the turbine part with mouthpiece and is connected via a thin cable.Spirometers based on the pneumotachograph principle are also generally small and handy. They manage entirely without moving parts. The heart of the device is a system of lamellae in the breathing tube through which the breath is exhaled. The lamella system opposes the airflow with a small resistance, which correlates positively with the strength of the respiratory airflow. During exhalation, the differential pressure between the lamella inlet and outlet is measured and the necessary parameters are automatically calculated from this. In ultrasonic spirometers, the integrated core consists of two ultrasonic transmitters and receivers facing each other at an angle to the airflow in the breathing tube. The device automatically determines the known parameters from transit time differences of the ultrasonic pulses as the airflow moves. Ultrasonic spirometers are very accurate and easy to use and can be operated with various bacterial filter systems.
Medical and health benefits
Parameters that deviate from the norm, diagnosed and confirmed by spirometry as part of a pulmonary function test, can cost-effectively provide initial indications of specific functional impairment or cardiopulmonary disease. Spirometry is particularly common in cases of narrowed airways that make breathing difficult. For example, when bronchial asthma or chronic obstructive pulmonary disease (COPD) is suspected. Chronic cough and shortness of breath with breathing sounds can also be clarified, as can a disorder of the respiratory muscles or the neuronal respiratory center in the brain. Long-time smokers can also determine the degree of restriction of their lung function by means of spirometry. If positive, the examination can also provide evidence of certain minimum lung function requirements, such as before performing major surgery or to prove fitness to fly for pilots. As a partial health screening examination, spirometry is not part of routine health screenings and must be ordered separately.
