What does significant variability in lung function on pulmonary function tests indicate?

From the Guidelines

Significant variability in lung function on pulmonary function tests indicates a potential underlying condition with reversible airflow obstruction, such as asthma, and warrants further evaluation and monitoring. The provided pulmonary function test results show variability in measurements like FEV1, FVC, and MEF, which can be indicative of conditions like asthma or COPD with a reversible component 1.

Key Points to Consider:

• The coefficient of repeatability (CR) is a useful measure to determine the significance of changes in lung function over time, with values outside the CR indicating a potential real change in pulmonary status 1.
• The presence of airflow limitation is recognized by a reduction in the ratio of FEV1 to vital capacity (VC) or forced vital capacity (FVC), and the FEV1/VC ratio is a relatively sensitive index of mild COPD 1.
• A positive bronchodilator response, defined as an improvement in FEV1 of at least 12% and 200mL after administering a short-acting bronchodilator, strongly suggests asthma.
• Serial PFTs over time are valuable for monitoring disease progression and treatment response in patients with variable lung function.

Recommendations:

• Further evaluation, including a thorough medical history, physical examination, and additional diagnostic tests, is necessary to determine the underlying cause of the variability in lung function.
• Monitoring of lung function over time, using serial PFTs, can help determine the severity of the condition and the effectiveness of treatment.
• Treatment approaches, such as bronchodilators and anti-inflammatory medications, may be beneficial for patients with significant variability in lung function, and should be guided by the results of serial PFTs and clinical evaluation.

From the FDA Drug Label

The primary endpoint was the comparison of pre-bronchodilator FEV1 in the groups receiving fluticasone propionate and salmeterol inhalation powder 500 mcg/50 mcg or placebo Subjects treated with fluticasone propionate and salmeterol inhalation powder 500 mcg/50 mcg had greater improvements in FEV1 (113 mL, 10%) compared with fluticasone propionate 500 mcg (7 mL, 2%), salmeterol (15 mL, 2%), and placebo (-60 mL, -3%)

Significant variability in lung function on pulmonary function tests may indicate an unstable respiratory condition.

• FEV1 is an important measure of lung function, and significant changes in FEV1 can indicate a change in the patient's condition.
• The provided data shows variability in FEV1 and other lung function parameters, but the FDA drug label does not directly address the question of what significant variability in lung function indicates.
• However, based on the information provided, it can be inferred that significant variability in lung function may be related to the effectiveness of treatment or the progression of the disease.
• It is essential to consult the FDA drug label 2 for more information on the specific treatment and disease being discussed.

From the Research

Interpretation of Pulmonary Function Tests

Significant variability in lung function on pulmonary function tests can indicate various conditions, including:

• Obstructive defects, such as chronic obstructive pulmonary disease (COPD) 3
• Restrictive defects, such as decrease in total lung capacity 4
• Thoracic hyperinflation, such as increase in static volumes 4
• Respiratory insufficiency, which can be assessed through arterial blood gas analysis 4
• Alveolar-capillary wall and capillary blood volume abnormalities, which can be assessed through diffusing capacity of the lung for CO (DLCO) measurement 4

Factors Influencing Interpretation

The interpretation of pulmonary function tests depends on several factors, including:

• Clinical context 5
• Selection of reference standards 5
• Arbitrary choice of cut-off values 5
• Laboratory methodology 5
• Understanding of the consequences of a normal or abnormal designation 5

Diagnostic and Management Implications

Pulmonary function testing plays a crucial role in the diagnosis and management of various respiratory conditions, including:

• COPD, where spirometry is regarded as the standard for diagnosis, but other tests such as diffusing capacity and imaging studies may also be useful 3
• Chronic obstructive pulmonary disease, where lung function testing has undisputed value in comprehensive assessment and individualized management 6
• Dyspnea, where pulmonary function tests can help quantify the symptom and diagnose underlying respiratory or non-respiratory disorders 7