Evaluation of diffusing capacity of the lung for carbon monoxide normalized per liter alveolar volume as a parameter for assessment of interstitial lung diseases

The single-breath (SB) diffusing capacity for carbon monoxide (DLCO) is the most clinically useful routine pulmonary function test after spirometry and lung volumes. The DLCO is the product of two measurements during breath holding at full inflation: (i) the rate constant for carbon monoxide uptake from alveolar gas and (ii) the accessible alveolar volume (VA). DLCO divided by VA (DLCO/VA), also called Krogh factor, reflects physiology more appropriately. It reflects the diffusing capacity in the available alveolar spaces. The aim of the study was to assess the validity of DLCO/VA interpretation in patients with interstitial lung diseases. This study involved 53 patients diagnosed as interstitial lung disease who presented to our pulmonary function laboratory in the Chest Department at Ain Shams University Hospital. Spirometry and DLCO-SB technique were performed. Fifty-three patients with mean age of 47.11 ± 13.7 years were included, 20 women and 33 men. The study showed positive correlation between age and forced vital capacity (FVC) and negative correlation between age and residual volume (RV). Height was significantly statistically related to DLCO, DLCO/VA, and total lung capacity (TLC)-SB. FVC showed no correlation with both DLCO and DLCO/VA. However, it was positively correlated with TLC-SB, VA, RV, and functional residual capacity. The mean of DLCO was 45.62 ± 17.19 and of DLCO/VA was 76.5 ± 31.7. DLCO showed a significant relationship with the following parameters: DLCO/VA, TLC, and RV/TLC. DLCO/VA showed positive statistical correlation with DLCO and TLC and negative correlation with VA. VA was positively correlated with TLC, FVC, and RV. However, it was negatively correlated with DLCO/VA. DLCO and DLCO/VA should be interpreted coherently with each other especially in restrictive lung diseases; in addition, VA and TLC-SB give a good guide for lung volume in interstitial lung disease. Egypt J Broncho 2014 8:51–56