Pulmonary function testing encompasses a variety of techniques and tests. The indications for pulmonary function testing include: (1) documenting the presence of obstructive or restrictive abnormalities in the course of establishing a diagnosis, (2) monitoring the course of a known pulmonary disease (e.g. cystic fibrosis, asthma), (3) monitoring for pulmonary toxicity related to treatment (e.g. amiodarone, radiation, chemotherapy), (4) monitoring response to therapy, and (5) describing normal and abnormal lung growth.
INPATIENT APPLICATIONS OF PULMONARY FUNCTION TESTING
A common use of pulmonary function tests in the inpatient setting is to monitor response to therapy. For example, patients with cystic fibrosis receiving intravenous antibiotics for a pulmonary exacerbation of their disease are usually monitored weekly with spirometry. The patient’s prior baseline (or previous best) lung function is a helpful target when determining the duration of therapy. Measurement of spirometry or exhaled nitric oxide may help determine duration of prednisone therapy for an acute exacerbation of asthma. Pulmonary function tests may also assist in preoperative planning, such as for patients with restrictive lung disease undergoing scoliosis repair. A less common scenario would be to monitor the progression of muscle weakness in a patient with Guillain-Barre syndrome. Additionally, these tests have important uses in the evaluation of respiratory symptoms (shortness of breath, cough, wheeze) when there is no specific diagnosis.
PULMONARY FUNCTION LABORATORY
The tests described herein require specialized equipment and experienced personnel. The equipment and laboratory should conform to the standards published by the American Thoracic Society,1 including daily calibration, biologic controls, and infection control practices. A stadiometer for accurate height measurement is required. The personnel should be patient, have the appropriate training, and be comfortable working with children of a variety of ages, who often require different coaching strategies. Most children by the age of 6 years, are able to follow directions and perform spirometry maneuvers. Some children as young as 3 to 4 years are able to perform spirometry.2 The space for testing should be quiet and free of distractions. Recently, some primary care physicians have begun to use spirometry in the office setting for patients with asthma or chronic obstructive pulmonary disease. The accuracy of testing in this situation is not well documented.
The values measured in the laboratory are usually normalized with the use of reference equations, most commonly based on the subject’s height, gender, age and ethnicity. With these equations, a predicted value can be calculated for each parameter, and the measured flows can be reported as a percentage of the predicted value or as a standardized deviation score (Z-score). Test results from different pulmonary function laboratories may not be directly comparable if different reference equations are used.
Spirometry is the measurement of airflow during a maximally forced exhalation. The test is informative because airflow rates are inversely proportional to the fourth power of ...