In this study, we characterized the respiratory symptoms in survivors of the Bhopal gas disaster and assessed their lung functions by both FOT and spirometry. The majority complained of breathlessness. Abnormalities in spirometry were observed in nearly half of those who performed acceptable spirometry. The abnormalities in FOT, suggestive of SAD, were independent of abnormalities in spirometry.
After any toxic inhalational disaster, population-based studies are vital in understanding the pathophysiological mechanisms of lung injury, long-term sequel, and developing appropriate medical management. Besides the Bhopal gas disaster, many individuals were exposed to the dust of building materials during the World Trade Center (WTC) attack. The gases of the Bhopal gas disaster were lethal compared to the dust of the WTC attack. Extensive research and long-term follow-up of the exposed population in the WTC attack helped us understand lung injury pathogenesis following toxic inhalation. However, long-term follow-up lung function in the Bhopal gas disaster survivors is lacking.
Aftermath any disaster, over or under-reporting of symptoms in the exposed population is anticipated due to various medical and non-medical causes. Most of our study population mentioned having at least one respiratory symptom. The morbidity data of the ongoing long-term epidemiological study of the ICMR are collected either from the head of the family or any adult family member available during the surveys. In contrast, the morbidity data of the current study were collected through face-to-face interaction. This might be a possible reason for observing higher respiratory morbidity than previous reports of long-term epidemiological study.1–3
Lung function assessment is essential to evaluate the adverse effects of toxic inhalations. Immediately after the disaster and subsequently, several studies were conducted to estimate the lung function abnormalities in survivors of the Bhopal gas disaster. Spirometry was mostly used to assess lung functions. The type, severity, and distribution of abnormalities in spirometry were widely variable across those studies.11 We also observed new abnormalities in spirometry and rapid decline in spirometry parameters in survivors with respiratory symptoms.12 The last publication on lung function of the Bhopal gas disaster survivors was a retrospective analysis of spirometry reports of those who consulted a particular hospital for their respiratory problems.12 That study reported an obstructive pattern as the predominant abnormality (50.8%), followed by a restrictive pattern (13.3%). The current study being a community-based might be the reason for the different distribution of abnormalities in spirometry. Cullinan et al. were the first to report reduced MMEF, a subtle spirometry marker of SAD in the Bhopal Gas Disaster exposed population.13 They observed that those were living near the pesticide plant had significantly reduced MMEF. However, they had not reported the prevalence of MMEF abnormalities. Nearly one-third of our population had MMEF < LLN.
The individuals exposed to the WTC attack had persistent respiratory morbidity and lung function abnormalities over decades.14,15 Therefore, lung function abnormalities in the exposed population of the Bhopal gas disaster, even over thirty years after the exposure, were not surprising. We observed that the lung function abnormalities were less in those exposed in their early life than older ones. This was possibly due to the wane of exposure effects as the children grown.
FEV1 predominantly reflects the obstruction of medium to large-sized airways. A significant amount of small airway resistance must be built up to make FEV1 abnormal.16 Spirometry fails to detect complex heterogeneous pathology of airways, especially if subtle abnormalities are present in the small airways. FOT and Impulse Oscillometry (IOS) are two noninvasive techniques used to assess small airway function. Both these techniques measure respiratory system resistance (Rrs) and reactance (Xrs), the two components of respiratory impedance. Rrs represent impedance to airflow, primarily reflecting overall airway caliber. Whereas, Xrs represents impedance to volume changes and encompasses both the respiratory system's inertial and elastic properties. The evaluation of small airway function in participants exposed to WTC attack provided valuable information that was rarely apparent in the spirometry.14,15 Oppenheimer et al. highlighted IOS as a better way of identifying SAD in subjects exposed to the WTC attack.17 The association of small airway dysfunctions in the exposed population of the WTC attack with persistent respiratory symptoms is well established.14,19 Breathlessness in our study population had a significant association with the abnormalities of both FOT and spirometry. Like the WTC attack exposed population, we also found abnormalities in IOS parameters independent of spirometry abnormalities. Sriramachari histopathologically documented the involvement of small airways in lung autopsies of the exposed population of the Bhopal gas disaster.18 He showed necrotizing bronchiolitis with denudation of the epithelium, in addition to severe tracheitis and bronchitis. Our study is the first to investigate and document SAD in survivors of the Bhopal gas disaster.
The restrictive spirometry of the WTC disaster was attributed to the involvement of small airways.20 SAD closes small airways at tidal volume, leading to restrictive spirometry. We also observed the presence of SAD in participants with restrictive spirometry. Few individuals with restrictive spirometry in our study also undergone radiological evaluations; however, no evidence of fibrosis or scarring was found in their chest X-rays.
The major limitations of this study were cross-sectional design, low participation, recruitment was restricted to only severely exposed cohort, no comparator group, and nearly half of the recruited individuals participated in lung function assessment. Therefore, the observation of this study may not be generalized to the survivors of the Bhopal gas disaster. The causes of low participation were busy with livelihood, lack of interest, no financial benefits for participation, change of residence, local migration, etc. We were also unable to establish contact with the individuals who are usually at work during our study visits, and they were probably healthier. There was a potential risk of selection bias, as those with relatively fewer respiratory symptoms participated in lung function assessments. This study was conducted over thirty years after the exposure, and some participants were also exposed to occupational and ambient air pollution in the succeeding years. In the absence of longitudinal lung function assessments, we cannot attribute the observed lung function abnormalities to exposure only. Post-bronchodilator spirometry and FOT were not performed due to logistics issues. Lung volume estimation of participants with restrictive spirometry was also not performed to confirm reduced total lung capacity. The strength of this study was that participants were part of the original cohort of the long-term epidemiological study. Therefore, their exposure to the disaster was undoubted.
In conclusion, this study highlighted self-reported respiratory morbidity and abnormalities in lung functions. Those who were exposed in early childhood had lesser lung function abnormalities compared to older ones. Lung function abnormalities are complex, and small airway dysfunction was independent of spirometry. A comprehensive lung function assessment by both spirometry and FOT is indispensable in assessing the effects of inhalational exposures.