The nonspecific pulmonary function test: longitudinal follow-up and outcomes

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology

Background:

• Nonspecific (NS) pulmonary function (PF) pattern is defined by normal total lung capacity (TLC), normal FEV₁/FVC ratio, and reduced FEV₁, FVC, or both.
• Long-term stability and predictive factors for NS PF patterns are not well-established.

Purpose of the Study:

• To assess the long-term stability of the NS PF pattern.
• To identify variables that predict changes in PF patterns from an initial NS classification.

Main Methods:

• Analysis of pulmonary function tests from 1,284 subjects with an initial NS pattern and at least one follow-up test (≥6 months).
• Evaluation of lung volumes, diffusing capacity, and spirometry data.
• Multivariate, multinomial logistic regression to determine associations with final PF patterns.

Main Results:

• 64% of subjects maintained the NS PF pattern at last follow-up after a median of 3 years.
• 16% developed a restrictive pattern, 15% an obstructive pattern, 3% a normal pattern, and 2% a mixed pattern.
• Increased specific airway resistance and TLC-alveolar volume difference predicted a shift to an obstructive pattern.

Conclusions:

• The NS PF pattern is a distinct and stable classification in respiratory testing.
• Current interpretation guidelines may inaccurately label NS patterns as obstructive and require revision based on these findings.