Long-term reproducibility of tests of small airways function. Comparisons with spirometry

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology
• Longitudinal Cohort Studies

Background:

• Pulmonary function tests (PFTs) are crucial for assessing respiratory health.
• Understanding the reproducibility of PFTs is essential for accurate diagnosis and monitoring.
• Longitudinal studies provide valuable insights into the stability of PFT variables over time.

Purpose of the Study:

• To measure the reproducibility of single breath nitrogen washout (SBNW) and spirometric variables using a tracking index.
• To compare the characteristics of individuals with high versus low pulmonary function tracking.
• To evaluate the influence of smoking and respiratory conditions on PFT reproducibility.

Main Methods:

• Utilized a tracking index to assess reproducibility of SBNW (CV/VC, CC/TLC, delta N2/L) and spirometry (FEV1, FEV1/FVC) variables.
• Analyzed data from two longitudinal cohorts spanning 9-11 years.
• Adjusted all variables for age, sex, and height using Z-scores.

Main Results:

• FEV1 demonstrated the highest tracking index, indicating superior reproducibility among all measured variables.
• Delta N2/L and FEV1/FVC showed similar, slightly lower tracking indices, while CV/VC had the lowest.
• Tracking indices were generally higher in smokers than non-smokers, and CC/TLC reproducibility increased over time.

Conclusions:

• FEV1 is the most reproducible pulmonary function variable, both within and between individuals.
• Poor tracking or reproducibility of PFTs is not associated with smoking status, respiratory symptoms, or existing respiratory disease.
• The findings support the use of FEV1 as a reliable measure in longitudinal respiratory health assessments.