key: cord-0811174-wn5ak1x2
authors: Chapman, David G.; Badal, Tanya; King, Gregory G.; Thamrin, Cindy
title: Caution in Interpretation of Abnormal Carbon Monoxide Diffusion Capacity in COVID-19 Patients
date: 2020-11-05
journal: Eur Respir J
DOI: 10.1183/13993003.03263-2020
sha: f593300453a0939faea86f667225aad57476dda1
doc_id: 811174
cord_uid: wn5ak1x2

Reduced KCO in discharged patients with COVID-19 suggests persistent abnormalities in gas exchange. Further research is required to understand why.

In response, Dr Nusair (2) contributed the interpretation that "low D LCO is caused mainly by reduced alveolar volume, and not residual interstitial abnormalities or pulmonary vascular abnormalities caused by COVID-19" i.e. normal capillaryalveolar units. However, we believe that this interpretation does not consider the complex relationship between VA, DLCO and KCO, and may prematurely rule out the presence of abnormal gas exchange. To demonstrate our point, Figure 1 illustrates the expected effect of a reduction in VA on DLCO and KCO due to either suboptimal alveolar expansion or loss of alveolar units (with normal expansion in communicating alveoli) (3). Firstly, it is evident that in the "severe pneumonia" patients in the study by Mo et al the impairment in DLCO (1) (represented by the star) is considerably greater than expected if a reduction in VA was the sole abnormality, regardless of the mechanism for the reduced VA. Secondly, a reduction in VA due to either aforementioned mechanism would be is associated with an increase in KCO, which is opposite to the reduced KCO in many of the discharged patients with severe COVID-19 (3). This reduction in KCO suggests that loss of alveolar units is not sufficient to cause the observed impairment in DLCO. 

Abnormal pulmonary function in COVID-19 patients at time of hospital discharge. The European respiratory journal

Abnormal carbon monoxide diffusion capacity in COVID-19 patients at time of hospital discharge. The European respiratory journal

Examination of the carbon monoxide diffusing capacity (DL(CO)) in relation to its KCO and VA components. American journal of respiratory and critical care medicine

Pulmonary fibrosis secondary to COVID-19: a call to arms? The Lancet Respiratory medicine

Novel insights on the pulmonary vascular consequences of COVID-19. American journal of physiology Lung cellular and molecular physiology

Assessment of Small Pulmonary Blood Vessels in COVID-19 Patients Using HRCT. Academic radiology