The markovchain package aims to provide S4 classes and methods to easily handle Discrete Time Markov Chains (DTMCs), filling the gap with what is currently available in the CRAN repository. In this work, I provide an exhaustive description of the main functions included in the package, as well as hands-on examples.

Background: Endothelial dysfunction has a key role in the pathogenesis of coronavirus disease 2019 (COVID-19) and its disabling complications. We designed a case-control study to assess the alterations of endothelium-dependent flow-mediated dilation (FMD) among convalescent COVID-19 patients. Methods: COVID-19 patients referred to a Pulmonary Rehabilitation Unit within 2 months from swab test negativization were consecutively evaluated for inclusion and compared to controls matched for age, gender, and cardiovascular risk factors. Results: A total of 133 convalescent COVID-19 patients (81.2% males, mean age 61.6 years) and 133 matched controls (80.5% males, mean age 60.4 years) were included. A significantly lower FMD was documented in convalescent COVID-19 patients as compared to controls (3.2% ± 2.6 vs. 6.4% ± 4.1 p < 0.001), confirmed when stratifying the study population according to age and major clinical variables. Among cases, females exhibited significantly higher FMD values as compared to males (6.1% ± 2.9 vs. 2.5% ± 1.9, p < 0.001). Thus, no significant difference was observed between cases and controls in the subgroup analysis on females (6.1% ± 2.9 vs. 5.3% ± 3.4, p = 0.362). Among convalescent COVID-19 patients, FMD showed a direct correlation with arterial oxygen tension (rho = 0.247, p = 0.004), forced expiratory volume in 1 s (rho = 0.436, p < 0.001), forced vital capacity (rho = 0.406, p < 0.001), and diffusing capacity for carbon monoxide (rho = 0.280, p = 0.008). Overall, after adjusting for major confounders, a recent COVID-19 was a major and independent predictor of FMD values (β = −0.427, p < 0.001). Conclusions: Post-acute COVID-19 syndrome is associated with a persistent and sex-biased endothelial dysfunction, directly correlated with the severity of pulmonary impairment.

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Background: To investigate and compare the gap (i.e. fit) and thickness of six aligner systems (Airnivol, ALL IN, Arc Angel, F22, Invisalign and Nuvola) using industrial computed tomography (CT). The null hypothesis was that there would be no detectable differences in either measurement between the aligners investigated. Materials and methods: Passive aligners of each brand were fitted to one single resin cast prototyped from an STL file from a single patient. The samples obtained were examined under high-resolution micro-CT, and the resulting tomographic microphotographs and volumetric data were compared. 3D analysis investigated the gap volume, the mean gap width and the maximum gap width of each sample. A total of 204 linear 2D measurements were made on 18 microtomographic images to investigate the aligner gap and thickness among different systems. Investigated regions were the central incisor, canine and first molar. The resulting measurements were analysed by ANOVA and compared using Tukey's post hoc analysis (P < 0.05). Results: 3D analysis revealed that the F22 displayed lower gap volume and mean gap width, followed by Airnivol and Invisalign, whereas Airnivol the lowest maximum gap width. 2D analysis showed that F22 had the lowest mean gap and aligner thickness at all teeth investigated. Comparison of the 2D point values revealed statistically significant differences between brands in terms of both measurements (P < 0.05), with the exception of six points in the gap analysis and one in the thickness analysis. Conclusions: There are differences between the six aligner systems examined in terms of 2D and 3D measurements of aligner thickness and gap.

Background: Complications of coronavirus disease 2019 (COVID-19) include coagulopathy. We performed a meta-analysis on the association of COVID-19 severity with changes in hemostatic parameters. Methods: Data on prothrombin time (PT), activated partial thromboplastin time (aPTT), D-Dimer, platelets (PLT), or fibrinogen in severe versus mild COVID-19 patients, and/or in non-survivors to COVID-19 versus survivors were systematically searched. The standardized mean difference (SMD) was calculated. Results: Sixty studies comparing 5487 subjects with severe and 9670 subjects with mild COVID-19 documented higher PT (SMD: 0.41; 95%CI: 0.21, 0.60), D-Dimer (SMD: 0.67; 95%CI: 0.52, 0.82), and fibrinogen values (SMD: 1.84; 95%CI: 1.21, 2.47), with lower PLT count (SMD: −0.74; 95%CI: −1.01, −0.47) among severe patients. Twenty-five studies on 1511 COVID-19 non-survivors and 6287 survivors showed higher PT (SMD: 0.67; 95%CI: 0.39, 0.96) and D-Dimer values (SMD: 3.88; 95%CI: 2.70, 5.07), with lower PLT count (SMD: −0.60, 95%CI: −0.82, −0.38) among non-survivors. Regression models showed that C-reactive protein values were directly correlated with the difference in PT and fibrinogen. Conclusions: Significant hemostatic changes are associated with COVID-19 severity. Considering the risk of fatal complications with residual chronic disability and poor long-term outcomes, further studies should investigate the prognostic role of hemostatic parameters in COVID-19 patients.