The effect of conductive ventilation heterogeneity on diffusing capacity measurement.

Area of Science:

• Pulmonary Physiology
• Respiratory Medicine
• Lung Function Testing

Background:

• Ventilation heterogeneity is a known factor in lung diseases.
• Its direct impact on carbon monoxide transfer factor (Dl(CO)) measurements has been debated.
• Conductive ventilation heterogeneity involves larger airways and flow asynchrony.

Purpose of the Study:

• To investigate estimation errors in carbon monoxide diffusing capacity (Dl(CO)) measurements.
• Specifically focusing on errors caused by conductive ventilation heterogeneity.
• To understand the interplay between ventilation heterogeneity, flow asynchrony, and Dl(CO) in healthy lungs.

Main Methods:

• Induced conductive airway ventilation heterogeneity in 35 healthy, non-smoking subjects using histamine provocation.
• Measured changes in conductive ventilation heterogeneity via multiple-breath washout tests.
• Assessed corresponding changes in Dl(CO), alveolar volume, and inspired vital capacity using single-breath methods.

Main Results:

• Conductive ventilation heterogeneity doubled, while Dl(CO) decreased by 6% (p < 0.001) with no individual correlation.
• Inspired vital capacity and alveolar volume decreased by 6% and 3% respectively.
• Individual changes in alveolar volume and heterogeneity correlated (r = -0.46; p = 0.006), suggesting error cancellation.

Conclusions:

• Histamine-induced conductive ventilation heterogeneity did not significantly bias Dl(CO) estimation in healthy subjects.
• Observed errors appeared to largely cancel out due to opposing effects of volume distribution.
• Identified potential combinations of heterogeneity and asynchrony that could substantially affect Dl(CO) in diseased lungs.