The Coronavirus Disease 2019 (COVID-19), caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), rapidly evolved into a global pandemic, significantly burdening healthcare systems worldwide[1]. Although initially considered an acute respiratory illness, emerging evidence suggests that COVID-19 can have long-term sequelae, particularly affecting the respiratory system even after apparent clinical recovery[2].

Pulmonary complications such as pneumonia, acute respiratory distress syndrome (ARDS), and pulmonary fibrosis have been commonly reported in hospitalized COVID-19 patient[3]. Post-recovery, patients often continue to experience symptoms such as dyspnea, cough, and fatigue, indicating potential residual impairment in lung function. The underlying pathophysiology is believed to involve alveolar damage, inflammation, and fibrotic remodeling, which may lead to restrictive or obstructive ventilatory defects detectable via spirometry[4].

Assessing pulmonary function in patients recovered from COVID-19 is essential to identify subclinical abnormalities and guide rehabilitation strategies. Studies conducted globally have reported varying degrees of pulmonary dysfunction post-COVID-19, with restrictive patterns being the most prevalent. However, data from the Indian population, particularly from southern tertiary care centers, remain limited[5].

This study was conducted to evaluate pulmonary function changes in post-COVID-19 patients at a tertiary care hospital in Visakhapatnam, Andhra Pradesh. The study also aimed to correlate these spirometric abnormalities with the severity of the initial illness and residual radiological findings, thereby providing insight into the extent and nature of long-term respiratory impairment following COVID-19.

Study Design and Setting

This was a prospective observational study conducted at the Department of Pulmonary Medicine, Andhra Medical College, Visakhapatnam, a tertiary care teaching hospital catering to a large urban and semi-urban population in Andhra Pradesh, India.

Study Period

The study was carried out over a four-month period from March 2020 to June 2020.

Study Population

A total of 100 patients who had recovered from confirmed COVID-19 infection were enrolled. COVID-19 diagnosis was confirmed through RT-PCR during the acute phase of illness. Patients were evaluated for pulmonary function 4–6 weeks after discharge or clinical recovery. Written informed consent was obtained from all participants prior to enrolment.

Inclusion Criteria

Patients aged ≥18 years.

Confirmed COVID-19 positive by RT-PCR during acute illness.

Minimum of 4 weeks post-recovery at the time of pulmonary function testing.

Willing to provide informed consent.

Exclusion Criteria

Patients with pre-existing diagnosed chronic respiratory conditions (e.g., COPD, asthma, ILD).

Uncooperative or unable to perform spirometry.

Hemodynamically unstable patients at follow-up.

Data Collection and Assessment

Demographic details, severity of initial COVID-19 illness (categorized as mild, moderate, or severe based on ICMR/MOHFW guidelines), and presenting symptoms were recorded. Each participant underwent:

Pulmonary Function Test (PFT) using standard spirometry (FVC, FEV₁, FEV₁/FVC).

6-Minute Walk Test (6MWT) to assess exertional desaturation.

High-Resolution Computed Tomography (HRCT) Chest, if clinically indicated.

Statistical Analysis

Data were entered into Microsoft Excel and analyzed using SPSS software . Descriptive statistics were used to summarize the demographic and clinical characteristics. Results were presented as means, standard deviations, and percentages.

A total of 100 post-COVID-19 patients were enrolled in the study. The mean age of participants was 45.2 ± 13.6 years, with 57 males and 43 females, resulting in a male-to-female ratio of 1.3:1 (Table 1).

Table 1: Demographic Characteristics

Pulmonary Function Test (PFT) Findings

Pulmonary function was evaluated using spirometry between 4 to 6 weeks after clinical recovery from COVID-19. Among the 100 patients, 38% demonstrated normal pulmonary function, while 42% exhibited a restrictive pattern, 14% showed an obstructive pattern, and 6% had a mixed ventilatory defect (Table 2).

Table 2: Pulmonary Function Test (PFT) Patterns

Figure No:1. Pulmonary Function Test (PFT) Patterns

PFT Abnormalities in Relation to Initial COVID-19 Severity

PFT alterations varied with the severity of the initial COVID-19 infection. In the mild category (n = 50), 70% had normal spirometry findings, and 30% exhibited restrictive changes. Among patients with moderate illness (n = 30), restrictive and obstructive patterns were observed in 60% and 10% respectively. In severe cases (n = 20), 85% had abnormal PFTs, including 50% with restrictive, 20% with obstructive, and 15% with mixed patterns (Table 3).

Table 3: Severity of Initial COVID-19 Illness and PFT Abnormalities

Follow-Up Symptomatology

At the time of pulmonary function testing, 48% of patients reported exertional dyspnea, and 22% experienced a persistent cough, predominantly among those with obstructive or mixed patterns. Fatigue was the most commonly reported symptom, affecting 65% of patients irrespective of spirometric findings (Table 4).

Table 4: Symptomatology at Follow-Up

Figure No.2 Symptomatology at Follow-Up

Oxygen Saturation and Exercise Tolerance

Baseline oxygen saturation levels at rest were within normal limits (>95%) in 90% of the participants. However, during the 6-minute walk test (6MWT), 28% of patients demonstrated a desaturation of ≥4%, most of whom had underlying PFT abnormalities (Table 5).

Table 5: Oxygen Saturation and 6-Minute Walk Test (6MWT)

Figure No.3 Oxygen Saturation and 6-Minute Walk Test (6MWT)

Radiological Findings and Functional Correlation

High-resolution computed tomography (HRCT) scans revealed residual radiologic abnormalities (e.g., ground-glass opacities or fibrotic changes) in 35 patients. Of these, 85.7% (n = 30) exhibited restrictive defects on spirometry, indicating a strong correlation between radiological sequelae and impaired pulmonary function (Table 6).

Table 6: Radiological Findings and Restrictive Defects

This study evaluated pulmonary function abnormalities in post-COVID-19 patients 4–6 weeks after clinical recovery. Our findings indicate that a substantial proportion (62%) of recovered individuals had persistent respiratory impairments, with restrictive defects being the most common (42%), followed by obstructive (14%) and mixed patterns (6%). These findings are consistent with previous international studies which reported similar post-COVID sequelae in lung function, particularly restrictive ventilatory patterns, due to parenchymal damage and fibrotic changes [6,7].

The correlation between the severity of initial COVID-19 illness and pulmonary dysfunction was evident in our study. Patients with moderate and severe disease exhibited a significantly higher prevalence of spirometric abnormalities compared to those with mild illness. In particular, severe cases had the highest rate of mixed and obstructive defects, possibly reflecting airway remodeling or post-ARDS changes. This aligns with prior studies by Huang et al. and Mo et al., who reported that severe cases are more prone to long-term lung function impairment [8,9].

Exertional dyspnea, reported by nearly half of the patients, and fatigue (65%) persisted despite clinical recovery, underscoring the importance of follow-up care. Additionally, desaturation during the 6-minute walk test in 28% of patients suggests impaired gas exchange capacity, often associated with interstitial involvement[10].

The strong correlation between residual HRCT abnormalities and restrictive PFT patterns (85.7% among those with radiological changes) further emphasizes the role of imaging in evaluating post-COVID pulmonary recovery. Persistent ground-glass opacities and fibrotic bands likely contribute to decreased lung compliance and volume, explaining the restrictive patterns observed.

These findings highlight the need for routine spirometry and pulmonary rehabilitation in the post-COVID period, especially for those recovering from moderate to severe disease. Early identification of at-risk individuals can facilitate timely intervention and potentially improve quality of life and long-term outcomes.

This observational study highlights that a considerable number of post-COVID-19 patients experience persistent pulmonary function abnormalities, predominantly of the restrictive type, even 4–6 weeks after clinical recovery. The severity of the initial illness strongly correlates with the likelihood and extent of pulmonary dysfunction. Symptoms such as dyspnea, fatigue, and desaturation during exercise were common among those with abnormal spirometry. Additionally, residual radiological findings were significantly associated with restrictive defects. These findings underscore the importance of routine pulmonary follow-up, including spirometry and imaging, especially in patients who had moderate to severe COVID-19. Early identification and rehabilitation may improve long-term respiratory outcomes in this population.

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