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Bronchodilator reversibility testing in post-COVID-19 patients undergoing pulmonary rehabilitation

Background The usefulness of bronchodilators in coronavirus diseases 2019 (COVID-19) survivors is still uncertain, especially for patients with a concomitant obstructive lung disease. We aimed at verifying the level of bronchodilator reversibility in COVID-19 patients undergoing multidisciplinary pulmonary rehabilitation after the acute phase. Methods We enrolled 105 consecutive patients referring to the Pulmonary Rehabilitation Unit of Istituti Clinici Scientifici Maugeri Spa SB, IRCCS of Telese Terme, Benevento, Italy after being discharged from the COVID-19 acute care ward and after recovering from acute COVID-19 pneumonia. All subjects performed a spirometry before and after inhalation of salbutamol 400 μg to determine the bronchodilation response within 48 h of admission to the unit. Results All patients had suffered from a moderate to severe COVID-19, classified 3 or 4 according to the WHO classification, Seventeen patients had concomitant obstructive lung disease (14 suffering from COPD and 3 from asthma). FEV1 after salbutamol improved on average by 41.7 mL in the entire examined sample, by 29.4 mL in subjects without concomitant obstructive lung diseases, by 59.3 mL in COPD patients and by 320.0 mL in asthma patients. Mean FVC after salbutamol improved by 65.7 mL in the entire examined sample, by 52.5 mL in subjects without concomitant obstructive lung diseases, by 120.0 mL in COPD patients, and by 200.0 mL in asthma patients. Conclusions This study suggests that a treatment with bronchodilators must always be taken into consideration in post-COVID-19 patients because it can induce a functional improvement that, even if small, can facilitate the breathing of these patients.


Introduction
Currently, there is no data that can help us to clarify the usefulness of bronchodilators in coronavirus diseases 2019 (COVID- 19) survivors, especially in patients with a concomitant obstructive lung disease. In particular, the clinical criteria for identifying post-COVID-19 patients who may benefit from bronchodilators are unclear.
Although mentioned in the current treatment recommendations for asthma [1] but not in those for chronic obstructive pulmonary disease (COPD) [2], bronchodilator reversibility testing is commonly used in clinical practice to predict the usefulness of a bronchodilator treatment [3]. However, levels of bronchial reversibility seem to be associated also with functional exercise performance, quality of life, exacerbation frequency, dyspnea, and radiological airway measures and, when focused on forced vital capacity (FVC) instead of forced expiratory volume in 1 s (FEV 1 ), they indicate further clinical and radiological characteristics [4].
The aim of this study was to verify the level of bronchodilator reversibility in post-COVID-19 patients undergoing multidisciplinary pulmonary rehabilitation and to compare the data obtained from patients without a previous pulmonary disease with those from patients who had a history of obstructive lung disease.

Materials and methods
This study included consecutive patients admitted to the Pulmonary Rehabilitation Unit of Istituti Clinici Scientifici Maugeri Spa SB, IRCCS of Telese Terme, Benevento, Italy soon after being discharged from the COVID-19 acute care wards of several hospitals in which they were hospitalized for acute pneumonia COVID-19, and always less than 2 months after the onset of COVID-19. All patients had two consecutive negative SARS-CoV-2 swab tests before their admission in our unit. Main demographic and clinical characteristics were collected. We excluded from the subsequent clinical study patients who were unable to perform technically acceptable spirometry upon entering the ward.
At recruitment, which occurred within 48 h of admission to the unit, measurements were made of FEV 1 and FVC, and reversibility to salbutamol was assessed irrespective of baseline FEV 1 and FVC using an automated equipment (Vyasis FlowScreen II Spirometer, Milan, Italy).
After an initial spirometry in which three FEV 1 and FVC measurements were taken, and for analysis the best FEV 1 and FVC were chosen regardless of the curve, all subjects inhaled salbutamol 400 μg through a spacer device as recommended by the American Thoracic Society/European Respiratory Sociery Task Force [5] after withdrawing short-acting β 2 -agonists for ≥6 h, long-acting β 2 -agonists for 12 h, and long-acting antimuscarinic agents and/or ultra long-acting β 2 -agonists for 24 h. Subjects then remained seated for 20 min, without smoking or consuming beverages other than water. Then, a repeated spirometry was performed in an identical fashion to determine the bronchodilation response.
The study was conducted in accordance with the Declaration of Helsinki of the World Medical Association. The Institutional Review Board of Istituto Nazionale Tumori, Fondazione Pascale, Naples, Italy approved this study with reference number ICS11/20. All patients provided written informed consent to use their de-identified data for future research.
Statistical analysis was performed with Prism 8 software package (GraphPad Software Inc, USA). Continuous data were expressed as mean and 95% confidence interval (CI) (standard errors have been reported in figures). Analysis of spirometric data for each treatment was performed using the Student's t-test for paired variables. Relationships between continuous variables were examined using simple regressions with Pearson's correlation coefficient (r). All results were expressed as 2tailed values, and a probability level of P < 0.05 was considered as being of significance for all tests.

Results
We recruited 105 patients, 90 men and 15 women. All were Caucasians. Regarding the age groups, 17 were under the age of 50 years, 64 were aged 51-70 years, and 24 were over 70 years. There were 12 current smokers, 44 ex-smokers and 49 never-smokers. The World Health Organization (WHO) cut-off point of body mass index (BMI) for obesity (i.e. 30 kg/m 2 ) [6] indicated that 48 of 105 patients were obese. In particular, 24 had a BMI between 30.00 and 34.99 (obese class I, moderate), 18 a BMI between 35.00 and 39.99 (obese class II, severe), and 6 were suffering from very severe obesity (obese class III, BMI ≥40.00).
All patients had suffered from a moderate to severe COVID-19, classified 3 or 4 by using the WHO classification, which separates patients affected by COVID 19 according to the gravity of their clinical scenario [7]. Seventeen patients had concomitant obstructive lung disease (14 suffering from COPD and 3 from asthma).
We found a statistically significant positive correlation between the changes of FEV 1 and those of FVC (Pearson r = 0.62, P < 0.001), being confirmed also in no OLD subjects (Pearson r = 0.68, P < 0.001) (Fig. 6). However, when specifically considering patients with a concomitant obstructive lung disease, no significant correlation between FEV 1 and FVC was found both among COPD (Pearson r = 0.38, P = 0.17) and asthma (Pearson r = 0.68, P = 0.52) patients.

Discussion
Our data confirm that COVID-19 pneumonia may result in significant alterations in lung function. Although it has been suggested that in post-COVID-19 patients impairment of carbon monoxide diffusion capacity (D LCO ) is the most common abnormality of lung function followed by restrictive ventilatory defect, which are both associated with the severity of the disease [10,11], bronchial obstruction can also be present.
It has been shown that, among COVID-19 survivors, 47% had normal findings, 41% presented a restrictive pattern, and 12% an obstructive pattern after 3 months from hospital discharge [12]. Another study revealed that 54% of COVID-19 survivors had abnormal lung function 10 weeks after diagnosis [13]. Restriction was the most prevalent pulmonary function abnormality, with critically ill patients being more prone to this condition and pulmonary function impairment being not related to abnormal imaging results or residual symptoms. A systematic review on five databases aimed at determining the prevalence of restrictive and obstructive patterns in post-COVID-19 patients documented a 15% prevalence of the restrictive pattern and a 7% prevalence of the obstructive pattern, with the diffusion capacity being impaired in close to 40% of patients [14]. In particular, the reduction in D LCO and also dynamic volumes, such as FEV 1 , seems to be correlated with disease severity and associated with the presence of lung consolidations both during the acute phase and after 6 weeks of follow up [15].
In any case, the reversible restrictive pattern on spirometry can to be a variant of the obstructive lung disease in which early airway closure results in air trapping and low FVC [16]. It has been suggested that the low D LCO characterizing the restrictive pattern is mainly determined by a reduced alveolar volume and not by the residual interstitial lung abnormalities or pulmonary vascular abnormalities caused by COVID-19     [17]. Apparently, in some subjects with airway reversibility, salbutamol tends to significantly affect alveolar volume [18]. However, it also known that β 2 -agonists can induce an increase in heart rate, and consequently volume per minute, cardiac output and right ventricular ejection also increase, raising D LCO [19]. For this reason we preferred not to measure D LCO before and after the reversibility test although we must admit that, by doing so, we were unable to verify the presence or absence of a correlation between changes in FEV 1 induced by salbutamol and values D LCO .
In our study, in which the reversibility tests were conducted less than 2 months after the onset of COVID-19, normal findings were recorded in 32% of the study subjects. Both restrictive and obstructive patterns were found in 6% of the examined subjects, but in the majority of our patients (56%) a mixed obstructive-restrictive lung syndrome was present. The presence of an obstructive component suggested that bronchial reversibility evaluation of post-COVID-19 patients could be clinically important for the treatment planning.
The mean increase in FEV 1 after salbutamol in the patient group we studied was 41.8 mL. The increase was lower when we separately considered the previously healthy asymptomatic non-smokers (39.6 mL) and subjects without concomitant obstructive lung diseases (29.6 mL). Contrariwise, in COPD patients, it was larger (59.3 mL). Patients with concomitant asthma showed a good reversibility, although no conclusions can be drawn for them, as in our series only 3 subjects had asthma.
These figures appear to be lower than those reported in large studies conducted in the past, when COVID- 19 had not yet appeared, in both the general population and COPD patients. Actually, FEV 1 improved on average by 77.2 mL in a general adult urban population and by 62.0 mL in healthy asymptomatic non-smokers [20]. In another study, the mean change in FEV 1 after salbutamol was 80 mL in healthy non-smoker controls and 120 mL in COPD patients [21]. A third large worldwide study reported a FEV 1 improvement of 72 mL after salbutamol (200 μg) in a healthy general population. The improvement was larger in patients with a concomitant obstructive lung disease without asthma (104 mL) and in patients in which asthma was included (114 mL) [22].
It is likely that the lower values in our series are the expression of persistent lung damage. At present, the long-term pulmonary consequences of COVID-19 remain speculative. We still do not know whether survivors may be truly at risk of developing chronic pulmonary sequelae, although organizing pneumonia and diffuse alveolar damage seem to be, by far, the most common forms of lung injury associated with COVID-19 [23]. It has been reported that breathlessness is an anticipated symptom that can persist long-term after discharge [24] in survivors with COVID-19, and a large proportion of hospitalized patients with COVID-19 have reduction in the functional status 6 months after hospitalization [25].
Looking at our data, it is also worth mentioning that the change in FEV 1 induced by salbutamol in subjects who had undergone mechanical ventilation was significantly lower than in those who did not need this procedure, while mechanical ventilation did not change the magnitude of the increases in FVC. It is difficult to determine whether this response was the consequence of COVID-19 severity, thus requiring mechanical ventilation or, instead, mechanical ventilation caused lung damage or, more likely, weakness of the respiratory muscles.
We believe that the positive response we have recorded in patients with previous COPD or asthma or in those where the obstructive component was probably prevalent is very interesting. Although some data suggest a lower than expected prevalence of COVID-19 in patients with asthma and COPD, they are still at greater risk from the long-term consequences of infection [26]. When a patient with asthma or COPD develops COVID-19, the obstructive disease with the possibility of pulmonary emphysema overlaps with pulmonary fibrosis. In such cases, doubts arise about the usefulness of bronchodilators. Regardless of the possible impact of COVID-19, inhaled bronchodilators may be prescribed as for COPD, although the benefit of bronchodilators in combined pulmonary fibrosis and emphysema has not been adequately demonstrated [27]. In any case, several reports suggest that about 50% of patients with combined pulmonary fibrosis and emphysema receive bronchodilators [28,29]. This therapeutic choice is not without foundation if we consider that idiopathic pulmonary fibrosis (IPF) may be comorbid with obstructive lung diseases and furthermore, reversible airflow limitation co-exists in a subgroup of patients with IPF [30].
Our study has however some limitations. First of all, the lack of information on the functional pulmonary status of each patient before the onset of COVID-19, either because the patient had never performed spirometry or because he/she could not provide us with the previous spirometric tests, makes it impossible to establish the real impact of COVID-19 on lung function. The number of patients who were previously suffering from obstructive lung diseases was very small, especially with regard to asthma, and does not allow us to formulate solid conclusions. It could be argued that the number of COPD patients (14 out of 105) in our study resulted in a much higher COPD rate than in the general population [31]. However, the small absolute number led to a large dispersion of the data. Furthermore only one bronchodilator reversibility test was performed in each subject and there is a well-known between-day variability in the classification of the patients as reversible or not [32].
Lung function and bronchial reversibility must be evaluated over time, ideally after 6 months. Since COVID-19 survivors can have an impairment of muscular performance [33], and a decline in muscle strength initiates a chain of events that leads to a reduced pulmonary function [34], it will be important to understand if the multidisciplinary respiratory rehabilitation program will have resulted in an improvement in lung function including bronchial reversibility. Right now, however, this study suggests that a treatment with bronchodilators must always be taken into consideration because it can still induce a functional improvement that, even if small, can facilitate the breathing of post-COVID-19 patients.