A comparison of single breath and re-breathe diffusing capacity in emphysema patients and controls

In emphysema patients, gas dilutional alveolar volume is underestimated by a 10s single breath maneuver at total lung capacity (TLC) compared with re-breathing at functional residual capacity (FRC); corresponding underestimation of single breath diffusing capacity (DLCO) in emphysema has not been demonstrated. The purpose of this study was to quantify the degree to which re-breathe DLCO at FRC (DLCO _RB) differs from single breath DLCO at TLC (DLCO _SB) in emphysema.In 37 consecutively recruited patients with moderate to severe emphysema (FEV ₁/FVC 40%±10% predicted), DLCO _RB as % predicted of 91 controls without cardiopulmonary disease was 79%±24%, significantly greater than % predicted DLCO _SB (44%±19%; p<0.0001). DLCO _RB/DLCO _SB was inversely proportional to FEV ₁% predicted (R=-0.47, p=0.004), and FEV ₁/FVC (R=-0.54, p<0.001).These data indicate that a 10. s single breath DLCO maneuver progressively under-represents re-breathe lung diffusing capacity in emphysema as airflow obstruction increases.