Unraveling Pathophysiologic Mechanisms Contributing to Symptoms in Patients with Post-acute Sequelae of COVID-19 (PASC): A Retrospective Study

Patients with post-acute sequelae of COVID-19 (PASC) present with a decrease in physical fitness. The aim of this paper is to reveal the relations between the remaining symptoms, blood volume distribution, exercise tolerance, static and dynamic lung volumes, and overall functioning. Patients with PASC were retrospectively studied. Pulmonary function tests (PFT), 6-minute walk test (6MWT), and cardiopulmonary exercise test were performed. Chest CT was taken and quantified. Patients were divided into two groups: minor functional limitations (MFL) and severe functional limitations (SFL) based on the completed Post-COVID-19 Functional Status scale (PCFS). Twenty one patients (3 M; 18 FM), mean age 44 (IQR 21) were studied. Eighteen completed the PCFS (8 MFL; 10 SFL). VO max was suboptimal in both groups (not significant). 6MWT was significantly higher in MFL-group (p = 0.043). Subjects with SFL, had significant lower TLC (p = 0.029). The MFL-group had more air trapping (p = 0.036). Throughout the sample, air trapping correlated significantly with residual volume (RV) in L (p < 0.001). An increase in air trapping was related to an increase in BV5 (p < 0.001). Mean BV5 was 65% (IQR 5%). BV5% in patients with PASC was higher than in patients with acute COVID-19 infection. This increase in BV5% in patients with PASC is thought to be driven by the air trapping in the lobes. This study reveals that symptoms are more driven by occlusion of the small airways. Patients with more physical complaints have significantly lower TLC. All subjects encounter physical limitations as indicated by suboptimal VO max. Treatment should focus on opening or re-opening of small airways by recruiting alveoli.