Normal spirometry predictive values for the Western Indian adult population.

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology
• Epidemiology

Background:

• Spirometry interpretation relies on comparing patient lung function to predicted values.
• Global Lung Function Initiative (GLI) equations exist but noted a need for Indian population-specific data.
• Existing GLI equations may not accurately reflect lung function in Western Indian adults.

Purpose of the Study:

• To derive new spirometry predictive equations for a rural Western Indian adult population.
• To assess the suitability of current GLI reference values for this demographic.

Main Methods:

• Utilized spirometry data from 1258 healthy adults (≥18 years) collected by the Vadu Health and Demographic Surveillance System (2008-2012).
• Developed sex-stratified prediction equations for forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and FEV1/FVC ratio.
• Employed the Generalised Additive Model for Location, Scale and Shape (GAMLSS) method, modeling outcomes against age and height.

Main Results:

• The Western Indian population exhibited lower average lung volumes (FEV1, FVC) compared to GLI Ethnicity Codes 1 and 5, with a comparable FEV1/FVC ratio.
• Both age and height significantly predicted mean FEV1 and FVC. Age also influenced response variability in females.
• A strong age-related effect on FEV1/FVC was observed, questioning the universal applicability of a fixed 0.7 cut-off.

Conclusions:

• Using current GLI normal values may lead to overdiagnosis of lung disease in Western Indian adults.
• The newly derived equations and values are recommended for clinical use in this population for accurate diagnosis and severity assessment.
• This study underscores the importance of population-specific reference equations for spirometry.