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. 2023 May 16;148:104551. doi: 10.1016/j.mvr.2023.104551

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Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

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Fig. 1 — (A/B) Tissue oxygenation is altered in patients with Post COVID-19 Syndrome.

(A) Changes of tissue oxygenation determined by near infrared spectroscopy (NIRS) before, during, and after standardized arterial occlusion. Inserts (A1) and (A2) show statistical comparison of linear regression slopes between patients with Post COVID-19 Syndrome (PCS), cardiovascular disease patients (CVD) and healthy controls during ischemia (3 min) and reperfusion. Respective linear regression slopes during ischemia are given as 1/slope for visualization indicating significantly slower oxygen consumption in PCS patients. (B) Comparison of tissue oxygenation before and after ischemia and reperfusion by tissue saturation index (TSI) between PCS and CVD patients and healthy controls. Individual data is presented with group mean and standard deviation. (C/D) Analyses of the effect of comorbidities on altered tissue oxygenation in PCS patients. (C) PCS patients were grouped by presence of arterial hypertension (HPT). Inserts (C1) and (C2) show statistical comparison of linear regression slopes between PCS patients (+) with (n = 18) and without (−) HPT (n = 12), and CVD patients during ischemia. Respective linear regression slopes during ischemia indicated significantly slower oxygen consumption in PCS patients with HPT compared to PCS patients without HPT and CVD patients. (D) PCS patients were grouped by BMI (≤/> median BMI = 31.0 kg ∗ m⁻²). Inserts (D1) and (D2) show statistical comparison of linear regression slopes between PCS patients with higher BMI compared to PCS patients with lower BMI and CVD patients during ischemia. Respective linear regression slopes during ischemia indicated significantly slower oxygen consumption in PCS patients with HPT compared to PCS patients without HPT and CVD patients. Data is presented as group mean values with 95 % confidence interval. Tissue saturation index was calculated as O₂Hb/(O₂Hb + HHb) × 100. P-values were calculated by comparison of linear regression slopes (in A, C, D) or one-way ANOVA corrected for multiple comparison (in B). ↓ start of ischemic phase (3 min), ↑ end of occlusion. ^#p < 0.05 for three-group comparison; *p = 0.01, ***p < 0.0001 for two-group comparison; ns, not significant.