Caution in interpretation of abnormal carbon monoxide diffusion capacity in COVID-19 patients

Abstract

Reduced K_CO in discharged patients with COVID-19 suggests persistent abnormalities in gas exchange. Further research is required to understand why. https://bit.ly/2Hb00gq

FIGURE 1

The relationship between alveolar volume (V_A) and, a) diffusing capacity of the lung for carbon monoxide (D_LCO) and b) rate constant for carbon monoxide uptake (K_CO), are plotted as a percentage of the value at total lung capacity (TLC). The relationships are shown for two situations that result in reduced V_A: suboptimal alveolar expansion (D_LCO and K_CO measured at volumes below maximum TLC, solid line); and loss of alveolar units (e.g. theoretical removal of lobules or lobes with remaining lung expanded to its normal TLC, dashed line). The star represents the group mean data of the “severe pneumonia” from Mo et al. [1]. Mean V_A was calculated as mean percent predicted D_LCO/mean percent predicted K_CO. The relationship between V_A, D_LCO and K_CO was calculated using the equations as described in [3]; for suboptimal alveolar expansion, K_CO = 0.43 + (0.57/V_A); for loss of alveolar lung units, change in K_CO = 0.4x + 2.1, where x is the proportion of volume diverted to the remaining lung; for both scenarios, D_LCO = V_A × K_CO.