Indians have worse lung function post COVID-19 compared to other populations: CMC study

A new study assessed lung impairment in Indians post-COVID-19 recovery and found that the prevalence of residual lung damage was much higher compared to the Europeans and Chinese. This might have been influenced by the higher rate of comorbidities in the Indian population, the researchers said.

The study published in the PLOS Global Public Health Journal by the Christian Medical College (CMC) in Vellore analysed lung impairment in patients that persisted 63 days after the onset of the disease during the first wave of the pandemic. The trial was conducted with 207 subjects by the Department of Pulmonary Medicine at CMC between  August 11, 2020, to January 14, 2021.

“In a large Indian cohort, we have reported the presence of post-COVID-19 residual lung damage, as assessed by lung function tests, exercise capacity, chest radiography, and quality of life measurement,” the paper highlighted.

The doctors at CMC used a pulmonary function test to determine the working capacity of the lung called the diffusing capacity for carbon monoxide (DLCO). It measures the amount of oxygen that is transferred from the lungs to the bloodstream when a gas containing trace amounts of carbon monoxide is inhaled.

In the cohort, overall 44.4 per cent had diminished DLCO with less than 80 per cent diffusing capacity. Among the remaining subjects, 35 per cent had a restrictive lung defect and 8.3 per cent had an obstructive defect, both conditions also restrict the volume of air the lungs take in and out.

The research was led by Dr DJ Christopher, professor of pulmonary medicine at CMC. He told Down to Earth, “In the long run, these patients might end up with a lung that functions less than optimally. Patients are immediately symptomatic if the impairment is severe. If the impairment is relatively smaller, they will carry on normal activities of life. But they might not be able to run or participate in sports. When the activities increase, they may not be able to perform. Also, their lungs would age faster and cause breathing difficulties much sooner than normal people.”

Further, the study compared the rate of comorbidities in several countries. “Our population reported relatively higher symptomatology and comorbidities and greater lung function impairment, compared to most published studies,” the paper said.

“Overall, 72.5 per cent of subjects had underlying comorbidities, of which 40.1 per cent had two or more comorbidities. Common comorbidities included diabetes mellitus (37.7 per cent), systemic hypertension (33.3 per cent), chronic respiratory diseases (29 per cent), ischemic heart disease (8.2 per cent), malignancy (4.3 per cent) and chronic kidney disease (1.9 per cent),” the paper added.

Comparatively, the number of patients who reported comorbidities was much lower in a 2020 study published in the European Respiratory Journal. The study said that 40 per cent of the Chinese subjects had at least one underlying comorbidity, 23.6 per cent had hypertension and 8.2 per cent had diabetes. Only 2.7 per cent were reported as having chronic respiratory diseases.

“Comorbidities may be a factor contributing to lung damage. If people had comorbidities, the impact of the disease could have been worse,” Christopher told DTE. 

The 207 subjects were categorised into the WHO disease severity groups: Mild 124 (59.9 per cent), moderate 41 (19.8 per cent), severe and critical 42 (20.3 per cent).

Overall, the Indian population also fared poorly when it came to lung function post COVID-19 infection. A study by the University Hospitals Birmingham in  2021 found that the DLCO was low in 152 patients (20.3 per cent) with mild disease, 435 patients (32 per cent) with moderate disease and 181 patients (59.5 per cent) with severe disease.

In contrast, in the Indian population, low DLCO results were observed denoting lung impairment in 31.5 per cent of mild patients, 54.8 per cent of moderate patients and 73.3 per cent in the severe group. It is equivalent to an average of 44 per cent of low DLCO across the board in all three categories, the study calculated, juxtaposing the higher rate of poor lung functioning among Indians.

Christopher added, “Across every category of disease, our population had worse lung function. It is clear that the lung function is affected more in the Indian population compared to the international data.”

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