Spirometers

Spirometers are devices that measure the volume of air inhaled and exhaled by the lungs and the speed of the air flow. They are used to assess lung function in clinical settings and, in some cases, for home monitoring.

Most spirometers determine volume by measuring flow and integrating it over time. The main outputs are volumes such as forced vital capacity (FVC) and expiratory and inspiratory volumes, and flow rates such as the forced expiratory volume in one second (FEV1). A common output is the flow-volume loop, which graphs airway flow against volume during a forced breath.

Devices vary in mechanism. Traditional volume-displacement spirometers rely on moving chambers or bell mechanisms. More common today are pneumotachograph-based spirometers, turbine-based spirometers, and devices using differential pressure sensors, hot-wire or ultrasonic technologies. Modern systems may be portable and connect to computers or mobile devices, and some consumer devices provide peak flow measurements rather than full spirometry.

Test procedures typically involve a maximal inhalation followed by a rapid, forceful exhalation through a mouthpiece, sometimes with nose clips. Reproducible results usually require several acceptable maneuvers. Quality control includes regular calibration, often with a 3-liter syringe, and adherence to guidelines from bodies such as ATS/ERS.

Interpretation focuses on comparing measured values with predicted normal values adjusted for age, sex, height, and ethnicity. A reduced FEV1/FVC ratio indicates obstructive disease, while reduced lung volumes with a normal or high FEV1/FVC ratio can suggest restriction. Spirometry cannot measure residual volume or total lung capacity directly.

Applications include diagnosis and assessment of asthma, COPD, and other lung conditions, preoperative evaluation, and monitoring response to therapy. While highly informative, spirometry requires effort and proper technique to ensure accuracy.