After the peak of the COVID-19 pandemic, examining the long-term consequences of post-discharge COVID-19 survivors got a lot of attention, this study is the first cohort study in Iran that evaluates lung volumes and respiratory outcomes in adult patients who are discharged from the hospital after recovering from COVID-19. According to the present study, a significant percentage of people had restrictions in terms of lung function one year after being discharged from the hospital due to COVID-19. In similar studies, the most remarkable finding in one year after discharge is the high proportion of patients with lung damage. COVID-19, respiratory disorder, and a decrease in lung function have been expressed as permanent symptoms (20). According to previous outbreaks of coronaviruses, such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), or H7N9 influenza, survivors also suffered from pulmonary dysfunction (21, 22, 23).
In the present study, in the first follow-up (eight months after discharge), according to the spirometry results of the patients, more than two-thirds of the patients had lung dysfunction, and restrictive lung diseases accounted for the largest share. In a retrospective study that Eight weeks after hospital discharge, Maurizio Marvisibro conducted a study on 90 patients admitted to the respiratory department of the Istituto Figlie di San Camillo, Cremona (Northern Italy) with SARS-CoV-2 pneumonia. Evidence in favor of early lung fibrosis in 25% of patients was shown (24) and in another study, in the examination of patients three months after discharge, according to the fibrotic bands that were seen in the CT scan of one-fifth of the patients, it was suggested that some lung injuries may be stable and lead to become stable fibrotic changes in the lung (25), which can justify the high percentage of patients with dysfunction, especially patients of the restrictive type, in the second follow-up, which was done one year after the disease, 54.8% of pulmonary dysfunction was 17.1% less than the first time, which was more than the reduction in obstructive diseases. During the autopsy of lung tissues from 38 patients who died of COVID-19, pathological changes in the lungs of the patients in the form of diffuse alveolar damage, formation of hyaline membrane, interstitial edema, and type 2 alveolar epithelial cells were identified may be able to justify the results obtained. In other similar studies, a significant percentage of patients had lung function disorders between three and six months after discharge (5, 8, 15, 26), but the percentage of pulmonary function disorders in our study is significantly higher than this. It was studied that one of the reasons it seems that a significant number of hospitalized patients were workers who previously worked in the steel, iron, copper, and cement industries, which can increase the susceptibility to chronic lung diseases (38). Also, a study conducted in Kerman in 2013 showed that high occupational exposure to dust particles leads to respiratory symptoms, radiographic abnormalities, and decreased lung function (39), so many of these patients may have already had lung problems due to occupational exposure. On the other hand, Kerman is one of the desert cities in the southeast of Iran, which faces sandstorms and increased dust in the air during certain seasons of the year (40). According to a study conducted in Iran between 1990 and 2019, the province (Kerman) had the highest age-standardized mortality rate due to chronic respiratory diseases four times higher than the province (Tehran) and the attributable risk factors that caused the most DALYs, Smoking, Air pollution, and Body Mass Index were high (41). In our study, 47.2% of patients were housewives, according to a study conducted on rural housewives in Isfahan. Baking bread, weaving carpets, and using fossil fuels were significant risk factors for all lung diseases (42).
Also, in our first follow-up, 67.2% of patients had some degree of Dyspnea, and more than half of the patients had exertional dyspnea, which was higher in severe groups of patients who were hospitalized in the ICU and the second follow-up, the percentage of patients with Dyspnea was reduced by almost half, and exertional dyspnea was almost two-thirds of the first time. In other similar studies, Dyspnea or continuous exertional dyspnea was one of the main complaints of patients with COVID-19 after discharge from the hospital (7, 26, 28, 29, 30, 31). However, in the study of Mattia Bellan and his colleagues, the proportion of patients with Dyspnea and chest pain did not change from 4 months to 12 months of follow-up (27). Also, patients who recovered from SARS complained of Dyspnea in the early rehabilitation phase (32). Of course, there is a possibility that Dyspnea in these patients can be caused by lung, heart, and neuromuscular problems, except for the effects of the coronavirus (33, 34).
In addition, a higher BMI was associated with persistent Dyspnea one year after discharge (31), and in our study, both groups of patients with severe and moderate disease were overweight. Other studies showed that patients with CT Abnormally had a higher BMI, obese patients were more likely to be infected with severe COVID-19, and a significant proportion of patients with severe disease severity had a BMI of 30 or higher (23, 30, 31). In our study, in both groups of patients with moderate and severe disease severity, high blood pressure was more common than other underlying diseases, and this result was consistent with many studies (27, 30, 31, 33). Above, it was considered as one of the risk factors for the lasting consequences of COVID-19 (27). Also, in our study, in the group of patients with severe disease severity, the percentage of people with diabetes, kidney disease, and malignancy was higher than in patients with moderate disease severity, and in other studies, the prevalence of diabetes in the severe group was significantly higher than in the moderate group. (26, 30, 37). Therefore, when treating severe patients, doctors need to keep in mind the control of diabetes in a balanced way along with the treatment of viral infection, so it is necessary to follow up and control diabetes in the management of patients with COVID-19 after discharge (26).
In the current study, patients with more severe diseases were older than patients with moderate disease severity, which was consistent with Qian Wu’s study (26), in a study conducted in one of Iran's hospitals, it also showed that most of the patients hospitalized due to COVID-19 and Most of the patients with critical conditions were more than or equal to 75 years old (35) and another study also confirms this fact that older patients are more likely to be affected by the more severe COVID-19 (36).
One of the strong points of this study is the follow-up of two time points after discharge, which allows for comparison over time.
This study has several limitations:
We didn't have any information about lung function (spirometry test results) before COVID-19, The observed pulmonary dysfunction cannot be directly attributed to COVID-19, It is possible that a large number of patients who agreed to performed the spirometry test were people who had more pulmonary problems before. A significant 4% of the participants did not want to do a spirometry test.