Gas exchange abnormalities in Long COVID are driven by the alteration of the vascular component

BACKGROUND

There are uncertainties whether the impairment of lung diffusing capacity in COVID-19 is due to an alteration in the diffusive conductance of the alveolar membrane (Dm), or an alteration of the alveolar capillary volume (Vc), or a combination of both. The combined measurement DLNO and DLCO diffusion, owing to NO higher affinity and faster reaction rate with haemoglobin compared to CO, enables the simultaneous and rapid determination of both Vc and Dm. The aim of the present study was to better identify the precise cause of post-COVID-19 diffusion impairment.

METHODS

Using the combined NO and CO gas transfer techniques (DLNO and DLCO), it is possible to better understand whether gas exchange abnormalities are due to membrane or alveolar capillary volume components. The present study was aimed at evaluating pulmonary gas exchange one year after severe COVID-19.  Results: The cohort included 33 survivors to severe COVID-19 (median age 67 years, 70% male) with no pre-existing lung disease, who underwent clinical, lung function and imaging assessments at 12 months due to persistence of respiratory symptoms or radiological impairment. The gas exchange abnormalities were mainly determined by the compromise of the vascular component as demonstrated by vascular pattern of gas exchange impairment (i.e., DLNO/DLCO≥110%, 76% of the sample), and by a reduction of the Vc (73%), while the Dm was reduced only in 9% of the entire sample. We did not find a correlation between the gas exchange impairment and the extent of the chest CT alterations (DLCO p = 0.059 and DLNO p = 0.054), which on average were found to be mild (11% of the parenchyma).

CONCLUSION

In COVID-19 survivors who are still symptomatic or have minimal CT findings at one year, gas exchange abnormalities are determined by impairment of the vascular component, rather than the diffusive component of the alveolar membrane.

Vaccination Recommendations in Solid Organ Transplant Adult Candidates and Recipients

Prevention of infections is crucial in solid organ transplant (SOT) candidates and recipients. These patients are exposed to an increased infectious risk due to previous organ insufficiency and to pharmacologic immunosuppression. Besides infectious-related morbidity and mortality, this vulnerable group of patients is also exposed to the risk of acute decompensation and organ rejection or failure in the pre- and post-transplant period, respectively, since antimicrobial treatments are less effective than in the immunocompetent patients. Vaccination represents a major preventive measure against specific infectious risks in this population but as responses to vaccines are reduced, especially in the early post-transplant period or after treatment for rejection, an optimal vaccination status should be obtained prior to transplantation whenever possible. This review reports the currently available data on the indications and protocols of vaccination in SOT adult candidates and recipients.