Spirometry and Upper Respiratory Tract

Spirometry is a fundamental lung function examination. It informs about lung volumes and inspiratory and expiratory flows, which reflect airway patency and stability. Forced vital capacity (FVC), forced expired volume in 1s (FEV1) and Tiffeneau index (FEV1/FVC) are the most important spirometry parameters. These parameters are primarily intended to detect lower airway obstruction. Additionally, they may raise suspicion about restrictive disorder (which needs estimation of total lung capacity to confirm). Although the sensitivity and specificity of spirometry for upper airway pathology are limited, there are visual and quantitative criteria, which may help in detecting upper airway obstruction. Visual criteria are based on the evaluation of flow-volume loop shape both in inspiration and expiration. The ‘knee’ shape is one of the most typical findings. The quantitative criteria include the Empey index (ratio of FEV1 and peak expiratory flow) and others that use parameters characterising inspiratory flows, expiratory flow at different levels of FVC and others. Nevertheless, spirometry is just supportive method for the first-line assessment of upper airway function and requires further confirmation. Spirometry may also inform on the concomitant lower airway pathology and trigger a more detailed investigation.