METHODS:Otherwise healthy, young adults (COV+: 6M/6F, 21 ± 1 y, 24 ± 3 kgᐧm -2 ) who tested positive for SARS-CoV-2 three-to-four weeks prior to the testing date completed standardized spirometry. Subsequently, the flow-volume loop with the greatest sum of forced vital capacity (FVC) and forced expiratory volume in one second was chosen for analyses. The angle β and flow ratio were calculated using standard pulmonary function parameters. Slope ratios at increments of 5% of FVC were determined from 80% to 20% FVC. Additionally, the total area under the maximum expiratory flow-volume curve was calculated. Data were compared to sex-, age-, and BMI-matched control participants (CON: 6M/6F, 21 ± 2 y, 23 ± 3 kgᐧm -2 ). RESULTS: The angle β was significantly lower in COV+ compared with CON (COV+: 182.1 ± 10.6°, CON: 194.8 ± 15.3°; p = 0.02). Flow ratios were similar between groups (COV+: 20.5 ± 25.9%, CON: 12.9 ± 19.1%; p = 0.42). With exception at 75% FVC (COV+: 1.42 ± 0.92, CON: 0.76 ± 0.40; p = 0.047), the slope ratios were similar between groups. While not statistically different, the slope ratio at 80% FVC approached significance (p = 0.06). The total area under the maximum flow-volume curve was not different between COV+ and CON participants (COV+: 21.1 ± 6.2, CON: 24.8 ± 9.4; p = 0.27). CONCLUSIONS: These data suggest that SARS-CoV-2 infection may result in damage, albeit minor, to the airways, which may result in alterations to the shape of the maximum expiratory flow-volume curve, especially at higher lung volumes. However, the data still may be classified as normal, and thus, longitudinal investigation may be warranted to examine if these parameters change throughout recovery following SARS-CoV-2 infection.

Purpose Kinetics of cardiorespiratory parameters (CRP) in response to work rate (WR) changes are evaluated by pseudo-random binary sequences (PRBS testing). In this study, two algorithms were applied to convert responses from PRBS testing into appropriate impulse responses to predict steady states values and responses to incremental increases in exercise intensity. Methods 13 individuals (age: 41 ± 9 years, BMI: 23.8 ± 3.7 kg m−2), completing an exercise test protocol, comprising a section of randomized changes of 30 W and 80 W (PRBS), two phases of constant WR at 30 W and 80 W and incremental WR until subjective fatigue, were included in the analysis. Ventilation ($$\dot{V}_{{\text{E}}}$$ V ˙ E ), O2 uptake ($$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 ), CO2 output ($$\dot{V}{\text{CO}}_{2}$$ V ˙ CO 2 ) and heart rate (HR) were monitored. Impulse responses were calculated in the time domain and in the frequency domain from the cross-correlations of WR and the respective CRP. Results The algorithm in the time domain allows better prediction for $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 and $$\dot{V}{\text{CO}}_{2}$$ V ˙ CO 2 , whereas for $$\dot{V}_{{\text{E}}}$$ V ˙ E and HR the results were similar for both algorithms. Best predictions were found for $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 and HR with higher (3–4%) 30 W steady states and lower (1–4%) values for 80 W. Tendencies were found in the residuals between predicted and measured data. Conclusion The CRP kinetics, resulting from PRBS testing, are qualified to assess steady states within the applied WR range. Below the ventilatory threshold, $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 and HR responses to incrementally increasing exercise intensities can be sufficiently predicted.