Introduction to pulmonary function testing
The SpirXpert website aims at promoting understanding respiratory physiology and pathophysiology. The emphasis is on the measurement and interpretation of spirometric test results. The final evaluation of spirometric data, and any decisions about diagnosis, treatment and other interventions in patients remain the sole responsibility of the physician in charge of the patient, who should come to a conclusion on the basis of information from various sources, of which spirometric data form a part.
- In a healthy population there is great variation in spirometric values even after taking into account age, height, gender and ethnic group. This underlines the need for putting great emphasis on clinical data and the patient’s previous medical history in interpreting spirometric data. The best predicted value for a patient is the personal reference value, i.e. the value obtained in a clinically optimal period; such personal best values may reveal that values which were within the normal range are not the patient’s optimal values.
- Inspiratory airway obstruction can only
be assessed from inspiratory maneuvers: the FEV1
and the FVC or IVC do not provide information about inspiratory
Spirometric findings are non-specific and therefore not pathognomonic for a certain diagnosis. Thus an obstructive expiratory syndrome or a restrictive ventilatory defect may be due to a variety of diseases of the respiratory tract.
- Spirometric data can be used to exclude a restrictive ventilatory defect. They should not be used to diagnose restrictive lung disease, because this requires measurement of the total lung capacity.
- The response to a bronchodilator drug provides a picture at a given moment in time, and may differ from day to day.
A quick tour of pulmonary function testing
It is recommended that you acquire basic background knowledge before embarking on performing spirometry or interpreting test results. Concise and essential information is available in the following chapters:
- Performing spirometric tests
- Expressing test results
- Lung function indices, study in particular the paragraphs on FEV1, and on VC, IVC and FVC
- Criteria for obstruction and bronchodilatation
A good working knowledge of the pathophysiology of flow limitation is indispensible for optimally performing spirometry and interpreting test results. Recommended reading: