Physiological quotients and mortality: redefining lung function interpretation beyond FEV₁

Area of Science:

• Pulmonary Medicine
• Respiratory Physiology
• Biostatistics

Background:

• The FEV1Q (Forced Expiratory Volume in 1 second Quotient) is a physiological metric comparing measured FEV1 to a minimal survival threshold.
• Existing lung function metrics may not optimally predict mortality risk.
• Developing new physiological quotients could enhance patient outcome assessment.

Purpose of the Study:

• To derive physiological quotients for key lung function parameters.
• To evaluate the association of these novel quotients with all-cause mortality.
• To compare the discriminative performance of physiological quotients against traditional metrics.

Main Methods:

• Analysis of adult lung function data from Cambridge University Hospital and Royal Papworth Hospital (2016-2024).
• Investigation of 1st percentile stability for FEV1, FVC, FEV1/FVC, DLCO, KCO, VA, and TLC across age and sex.
• Calculation of physiological quotients (measured value/1st percentile) and association with all-cause mortality via Cox regression and Harrell's C statistics.

Main Results:

• Data from 13,771 patients analyzed; mean follow-up ranged from 5.5 to 5.8 years.
• 1st percentile values showed stability across age for most parameters, but sex differences were noted for FEV1, FVC, VA, and TLC.
• Physiological quotients demonstrated superior Harrell's C statistics compared to raw values, z-scores, and percent predicted, indicating enhanced survival discrimination.

Conclusions:

• Physiological quotients offer superior discriminative ability for predicting all-cause mortality.
• These quotients represent a potentially valuable alternative standard for interpreting lung function test results.
• The findings support the clinical utility of physiological quotients in risk stratification.