Longitudinal Examination of the Shape of the Maximum Expiratory Flow‐Volume Curve in Young Adults Following SARS‐CoV‐2 Infection

Stickford, Jonathon; Augenreich, Marc; Province, Valesha; Stute, Nina; Stickford, Abigail; Ratchford, Stephen

Examination of the shape of the maximum expiratory flow‐volume curve represents a method to noninvasively describe lung and airway function in health and disease. Severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection can result in pulmonary dysfunction and may result in changes to the shape of the maximum expiratory flow‐volume curve during the recovery period following SARS‐CoV‐2 infection. PURPOSE: The purpose of this study was to quantitatively examine the shape and the area of the maximum expiratory flow volume curve in otherwise healthy, young adults during the three months following SARS‐CoV‐2 infection. METHODS: Otherwise healthy, young adults (4M/3F, age: 21 ± 1 y, height: 174.9 ± 11.2 cm, body mass index: 23.6 ± 1.6 kgᐧm(‐2)) who tested positive for SARS‐CoV‐2 completed spirometry testing on three occasions. The first visit (BL) took place three‐to‐four weeks after positive test confirmation. Approximately four weeks separated each subsequent visit (1M and 2M, respectively). Following each spirometry test, the flow‐volume loop with the greatest sum of forced vital capacity (FVC) and forced expiratory volume in one second was chosen for analysis. The angle beta (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 area under the maximum expiratory flow‐volume curve was calculated. Data were compared using repeated measures analysis of variance. Statistical significance was set at p = 0.05. RESULTS: FVC remained similar over the study period (p > 0.05). The β° was significantly reduced at 2M compared with BL (BL: 188.8 ± 15.7°, 1M: 180.9 ± 6.9°; 2M: 176.8 ± 5.0°, p = 0.012). Flow ratios were similar between visits (BL: 20.3 ± 11.7%, 1M: 13.0 ± 6.4%, 2M: 18.1 ± 5.9%; p = 0.53). Additionally, the slope ratios at each lung volume were similar between visits. However, while not statistically different, the slope ratio at 80% FVC approached significance (BL: 1.22 ± 0.98, 1M: 2.37 ± 1.00, 2M: 2.13 ± 0.86; p = 0.07). The total area under the maximum flow‐volume curve was not different between visits (BL: 21.0 ± 5.1 L(2)∙s(‐1), 1M: 21.5 ± 4.5 L(2)∙s(‐1); 2M: 21.9 ± 4.7 L(2)∙s(‐1); p = 0.49). The percentages of the total area under the curve that were contained between peak expiratory flow (PEF) and 75% FVC and between 50% FVC and 25% FVC were altered at 1M and 2M compared with BL (p < 0.05). PEF tended to be greater during 2M compared with BL (BL: 8.49 ± 1.34 L(2)∙s(‐1), 1M: 9.34 ± 1.92 L(2)∙s(‐1), 2M: 9.44 ± 1.53 L(2)∙s(‐1); p = 0.056) and the changes in PEF from BL to 2M were significantly correlated with the changes in β° and area under the curve subdivisions over the same time period (p < 0.05). CONCLUSION: These data demonstrate that the shape of the maximum expiratory flow‐volume curve changes marginally during the initial three months following SARS‐CoV‐2 infection. Yet, the changes appear to be largely driven by increases in peak expiratory flow and suggests that SARS‐CoV‐2 infection is acutely involved in large airway dysfunction.