Relationship between dyspnea and respiratory function indicators after coronavirus pneumonia

Aim. To study the relationship between the probability and severity of dyspnea following COVID-19 pneumonia with the characteristics of lung ventilatory function (LVF), lung diffusion capacity (DCL), and respiratory muscle strength (RMS) impairments.

Materials and methods. A total of 108 patients (58% women, age 62 [52-66] years) who had recovered from COVID-19 pneumonia were examined. Spirometry, bodyplethysmography, DCL, and RMS assessments were conducted 75 (46-155) days after the onset of the disease. The severity of dyspnea was evaluated using the MRC (Medical Research Council Scale) and the 10-point Borg scale. Instrumental and laboratory data from the acute phase of COVID-19 were retrospectively obtained from medical records.

Results. The risk of dyspnea of any severity at the time of examination was statistically significantly higher in patients with reduced (z-score < -1.645) VC, FVC, FEV₁, DLCO, VA, and DLCO/VA. No correlation was found between the risk of dyspnea and acute COVID-19 indicators (maximum C-reactive protein, lactate dehydrogenase levels, lung tissue damage assessed by computed tomography, positive PCR test), sex, or body mass index. None of the patients had a Gensler index <70%; however, reduced FEV₁ was found in 10.3% of patients. Restrictive LVF impairments were observed in 8.3% of patients, and mixed impairments in 11.2%. Dyspnea severity was statistically significantly higher in patients with LVF impairments, especially with mixed type, compared to patients with normal respiratory biomechanics. The correlation between the risk of dyspnea and functional parameters persisted even when the sample was limited to patients with normal LVF (n=75) and without comorbidities (n=49). In patients with normal LVF and no comorbidities who did not report dyspnea, FEV₁, ITGV, DLCO, and DLCO/VA values (in % of predicted) were higher, and Raw and Rocc were lower than in those with any severity of dyspnea.

Conclusion. There is a correlation between the risk and severity of dyspnea and restrictive, obstructive VFL impairments, and reduced DCL in the post-COVID-19 period. Additionally, identified patterns suggest that subclinical bronchial obstruction and reduced RMS may be possible mechanisms of dyspnea in patients with a normal respiratory biomechanics pattern.

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