Abstract

The aim of this study was to determine reference equations for the combined measurement of diffusing capacity of the lung for carbon monoxide (CO) and nitric oxide (NO) (D_LCONO). In

addition, we wanted to appeal for consensus regarding methodology of the measurement including calculation of diffusing capacity of the alveolo-capillary membrane (D_m) and pulmonary capillary volume (V_c).

D_LCONO was measured in 282 healthy individuals aged 18–97 years using the single-breath technique and a breath-hold time of 5 s (true apnoea period). The following values were used: 1) specific conductance of nitric oxide (θ_NO)=4.5 mL_NO·mL_blood⁻¹·min⁻¹·mmHg⁻¹; 2) ratio of diffusing capacity of the membrane for NO and CO (D_mNO/D_mCO)=1.97; and 3) 1/red cell CO conductance (1/θ_CO)=(1.30+0.0041·mean capillary oxygen pressure)·(14.6/Hb concentration in g·dL⁻¹).

Reference equations were established for the outcomes of D_LCONO, including D_LCO and D_LNO and the calculated values D_m and V_c. Independent variables were age, sex, height and age squared.

By providing new reference equations and by appealing for consensus regarding the methodology, we hope to provide a basis for future studies and clinical use of this novel and interesting method.