Expiratory time constant patterns reveal obstructive lung mechanics in non-obstructive spirometry

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology
• Data Science in Healthcare

Background:

• Airway resistance is linked to prolonged expiratory time constant (TC).
• Investigating TC patterns may reveal signatures of airway obstruction.
• Spirometry is a key tool for diagnosing respiratory conditions.

Purpose of the Study:

• To determine if expiratory time constant (TC) patterns can serve as a signature for airway obstruction.
• To identify and characterize distinct TC patterns within a large spirometry dataset.
• To assess the prevalence and clinical significance of identified TC patterns.

Main Methods:

• Cross-sectional, multicenter study of 19,937 validated spirometry records.
• Division of expiratory flow-volume curves into five equal volume segments to derive consecutive TCs.
• Application of K-means clustering algorithm to define data-driven TC patterns.

Main Results:

• Two distinct TC patterns were identified: 'normal' (stable TCs) and 'obstructive' (progressively prolonging TCs).
• The obstructive pattern was found in 7% of normal spirometry, 13% of possible restriction, and 33% of nonspecific FEV1 reduction.
• Individuals with the obstructive TC pattern exhibited significantly lower FEV1, FEV1/FVC, MMEF25-75, and FEV3/FEV6 compared to those with normal patterns.

Conclusions:

• The obstructive TC pattern represents a distinct physiological phenotype indicative of obstructive lung mechanics.
• This obstructive TC pattern is highly prevalent across common spirometric categories, including those with normal spirometry.
• TC pattern analysis offers a novel approach to identifying and characterizing obstructive lung disease.