Transfer factor (diffusing capacity) standardized for alveolar volume: validation, reference values and applications...

Area of Science:

• Pulmonary Physiology
• Respiratory Medicine

Background:

• Transfer factor (TL) is known to vary with alveolar volume (VA).
• The standard carbon monoxide transfer coefficient (KCO) method (TL/VA) may not accurately reflect this relationship.
• Investigating alternative models to standardize TL for VA is crucial for accurate lung function assessment.

Purpose of the Study:

• To evaluate linear and exponential models for standardizing TL by VA.
• To determine appropriate reference values for these models.
• To assess the clinical utility of a validated model for TL standardization.

Main Methods:

• Compared within- and between-subject relationships of TL to VA at varying inspiration depths and lung sizes.
• Assessed asymptomatic, nonsmoking Caucasian adults (31 males in lab, 503 in population studies).
• Developed and validated new reference equations for TL standardization using linear regression.

Main Results:

• A linear model demonstrated consistent partial regression coefficients of TL on VA, standardized for height (H), across subjects and VA ranges.
• The exponential model did not show similar consistency.
• New SI unit reference equations were derived: TL = 11.52 H + 2.72 VA.H-2 - 0.051 Age -12.35 (males, RSD 1.17) and TL = 4.87 H + 2.29 VA.H-2 - 0.019 Age -3.03 (females, RSD 0.92).
• The linear model explained variations in published TL reference values and improved prediction accuracy compared to current methods.

Conclusions:

• A linear model effectively standardizes transfer factor (TL) for alveolar volume (VA) and height (H).
• The derived reference equations offer improved accuracy for predicting normal TL, particularly when VA deviates from the norm.
• This model provides a clinically useful alternative to the carbon monoxide transfer coefficient, simplifying lung function assessment.