Features of respiratory tests (hydrogen + methane), indirect liver elastometry data in COVID-19 convalescents (pilot study)

Purpose of the work: to study liver elasticity indicators, hydrogen and methane levels in exhaled air, and their associations with clinical and biochemical parameters for patients who underwent COVID-19. Materials and methods. We examined 30 patients (mean age 51.8±2.91) who underwent COVID-19 (confirmed by SARS-CoV-2 RNA test or SARS-CoV-2 antigen) 12-16 weeks after the onset of the first symptoms, of which 11 were diagnosed with pneumonia. 19 people (mean age 47.1±3.09) who did not have COVID-19 made up the comparison group. The patients underwent a clinical and biochemical study, the degree of liver fibrosis was determined (FibroScan® 502 Echosens, France), the levels of hydrogen (H2) and methane (CH4) in the exhaled air were measured (baseline and after taking lactulose solution) (GastroCheck Gastrolyzer, Bedfont Scientific Ltd., England). Results. Past COVID-19 infection was directly correlated with age (r=0.331, p=0.022), male gender (r=0.324, p=0.025), and presence of liver fibrosis (r=0.291, p=0.044). COVID-19 survivors were more likely to have liver fibrosis (p<0.001) and higher liver elasticity in kPa (p=0.018) with overweight and obesity (63.3%) and elevated body mass index (p= 0.03) compared with the control group. The presence of liver fibrosis was associated with moderate pneumonia (p<0.001). Among those who had COVID-19, there were significantly more non-producers of methane (p=0.02), fewer people with an average level of methane in exhaled air (p=0.016). In COVID-19 convalescents, bacterial overgrowth syndrome (BOS) was detected less frequently than in controls (p=0.04), but signs of delayed intestinal transit were more often recorded (p<0.05). The presence of liver fibrosis in survivors of COVID-19 is associated with BOS detection (23.3% vs. 5.2%, p<0.001), which probably contributes to the pathogenesis of liver damage. Hydrogen levels at 120 min and methane at 60 min after ingestion of lactulose solution distinguished between COVID-19 convalescents and COVID-19 survivors with an AUC of 0.683 and 0.660, respectively. The associations of the levels of gases in the exhaled air with clinical and biochemical parameters were revealed: the presence of overweight and obesity showed inverse associations with the level of methane production (r= -0.342, p<0.05), its concentration after taking lactulose at various time intervals, and also the basic level of hydrogen (r= -0.313, p<0.05); the degree of obesity was also inversely correlated with the level of methane emission (r= -0.368, p=0.038). Direct links were established between indicators of liver elasticity in kPa and the level of hydrogen production (r=0.275, p<0.05). Conclusions. Obtained indirect signs of pronounced changes in the intestinal microbiome, which obviously contribute to a more severe course of COVID-19, the development of liver fibrosis, so the impact on the intestinal microflora can be considered as a potential target in the treatment of patients with COVID-19.

COVID-19 convalescents, liver fibrosis, hydrogen, methane, exhaled air

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