European Journal of Cardiovascular Medicine

Globally occupational health sector is demanding more attention from the health care authorities by each passing day, since the occupation of professional drivers take a toll on their respiratory health through exposure to the environment at work.¹ The economic growth in India is being marked by an inevitable increase in transportation activities of all sectors. In case of total passenger transportation, almost 80% of the load is shared by the road transport sector. In Maharashtra state, MSRTC buses also referred to as S.T. buses, are a popular mode of public transportation. ST bus vehicle population has increased from 2019 till 2024 by about 10.6 % in state.² Number of vehicles per km road length in the State is 98.10. The vehicle density per 1000 population is expected to grow by 65 times till 2030.³ 

 A four stroke (4T) diesel engine usually powers buses. These vehicles are typically high contributors to air pollution due to poor maintenance, design misuse of lubricants and use of mineral oils other than specially formulated 4T oil recommended by vehicle manufacturers, taking extra passenger load etc. Particle concentrations in transportation microenvironments, near roadways and inside vehicles often exceed nearby ambient levels.⁴ Contaminated air can flow into enclosed microenvironments, including vehicle compartments⁵. Furthermore, drivers of open cabin buses are affected by the pollutants more than air-conditioned vehicle drivers. Evidence suggests that exposure to TRAP (traffic related air pollution) is correlated with the rising rates of allergic respiratory diseases.^6,7 Professional bus drivers are more likely to experience a range of respiratory (upper respiratory tract problems, airway inflammation, asthma, chronic bronchitis, chronic obstructive pulmonary diseases and hospital admissions) and a range of other health problems including cardio vascular, gastrointestinal, musculoskeletal disorders, headaches and sore eyes.⁸

Professional drivers working in transport sector spend more than 8-10 hours a day in traffic which is polluted, noisy and dangerous and have a sedentary lifestyle that is not conducive to good health.⁵ The hazards of occupational exposure to air pollutants pose a greater challenge to the health care sector; are justified with a very limited amount is literature. With this background, this study aims to understand the level of deterioration of respiratory health of professional bus drivers due to their occupation.

Aims and objectives:

To compare pulmonary functions & respiratory health among state transport bus drivers and a comparison group.

A case control study was carried out in a sub urban area of the city of central India over a period of 6 months where the randomly selected State Road Transport Corporation bus depot. Bus drivers within the age range of 18-50 years, who started driving bus for at least 5 years continuously and currently working in same profession, registered with the union, consenting to participate in study were included. Employees of a tertiary health care center working in any profession other than driving fulfilling the relevant inclusion criteria formed the comparison group. The baseline characters which are potential confounders affecting the readings of pulmonary function parameters, such as age (within ± 2 standard deviation range), gender and smoking habits (group matching) were matched between the two groups. The participants were excluded from the study who were found to report any of the following complains:

Exclusion criteria:

1. Those with previous history or taking treatment of any respiratory, cardio-vascular ailments before joining the profession.
2. Those with history of chest injuries, congenital thoracic deformities, previous thoracic surgery, hernia, and those with severe obesity.
3. Those with any contraindications for performing spirometry test.

Proper training of investigators under the supervision of spirometry technician and associate professor of pulmonary medicine was conducted for 15 days beforehand to carry out the Pulmonary Function Testing by the spirometer. Mespiror, a portable, computerized, electronic, dry type of spirometry machine was used. Instructions for participants were provided a day before performing the spirometric evaluation. A single full expiratory maneuver gives many parameters in Medspiror. Three consecutive trials were given and the best of three readings of the test were noted in the case record form. The values of all tests were taken as percent of predicted as per age, gender and height of each participant⁹. Following parameters were selected for the study.

% Predicted reading = (Test reading)/ (Expected for the age, sex, BMI of individual)

1. FVC (Forced Vital Capacity),
2. FEV1 (Forced Expiratory Volume in First second of FVC),
3. Ratio of FEV1/FVC (FEV1/FVC %)

The results of univariate analysis which described the characteristics of the study population was represented in tabular as well as graphical format. With the help of the results of bivariate analysis, the association between proposed risk factors and the outcome was tested using student’s t test for continuous variable and Pearson’s chi square test for categorical variables.

While testing the association the p-value of < 0.05 was considered significant, p-value < 0.01 was considered highly significant, p-value < 0.001 was considered as very highly significant. Odds ratio with 95% C.I. of OR/mean difference was calculated to state the strength of association.

Mean age of bus drivers & controls were 38.23± 9.05 years & 38.4± 9.39 years respectively. None of the participants in both the groups were below 20 years of age. When classified according to the WHO classification of BMI for Asian population, none of the participants were present in the underweight category of BMI in both groups. About 36.4% bus drivers reported current tobacco smoking habit while 31.2% participants from comparison group were current tobacco smokers. Prevalence of physical activity reported by bus drivers and comparison groups was 29.4% & 22.5% respectively (table 1). None of the drivers were illiterate with majority of them having education till high school (35.5%). There were no drivers found belonging to the Class I socio economic status of the modified B.G. Prasad’s classification while majority of them (51.1%) belonged to Class IV.

Table 1: Distribution of bus drivers (n=231) and participants in comparison group (n=231) according to their baseline characteristics.

About 90.8% drivers were not using any kind of personal protective equipments (PPE) (cloth, mask, etc.) while working. Majority of the non-users felt no need of using PPE (184, 84.8%), while about 24 (11.1%) reported using PPE as uncomfortable.

About 58% drivers worked for > 48 hours/week with mean hours of work per week = 53.64 ± 6.8 hours.  The parameters among the drivers working for > 48 hours/week were FVC (73.63±4.67), FEV1 (79.58±14.2) when compared with those drivers working for < 48 hours/week FVC (81.24±13.49), FEV1 (87.51±12.74) which had a very highly significant difference with p value < 0.000.

Average years of work as a bus driver were 18.54 ± 9.25 years where majority of the participants had been working for 11-20 years (35.1%) as bus drivers. Among the drivers, the prevalence of drivers working for > 20 years was 37.2%. When PFT parameters were compared between drivers working for > 20 years (FVC = 70.95 ± 2.84, FEV1 = 77.79 ± 13.26) with those drivers working for ≤ 20 years (FVC = 80.31 ± 4.58, FEV1 = 85.94 ± 13.79) a very high significant difference was observed with p value < 0.000, as shown in table 2.

Table 2: Distribution of bus drivers (n=231) according to their occupational characteristics & association between PFT parameters.

The prevalence of deranged FVC (<70% of the predicted reading) among drivers was 40.69%, with mean value of 76.83±14.45 whereas in comparison group the prevalence was 7.79%, with mean value 88.5±14.44 (p < 0.001, 95% C.I. mean difference = -14.33 to -9.011). The prevalence of deranged FEV1(<70% of the predicted reading) among drivers was 18.18%, with mean value of 82.9 ± 14.13 whereas in controls the prevalence was 10.39%, with mean value = 88.23 ± 14.02 (p < 0.001, 95% C.I. mean difference = -7.894 to -2.747). The ratio of FEV1 and FVC (FEV1/FVC %) remained mostly unchanged among drivers as well as participants in the comparison group. However, its mean value was significantly increased among drivers (108.68 ± 13.1) as compared to comparison group (100.19 ± 9.74) (p < 0.001, 95% C.I. = 6.382 to 10.598, table 3).

Table 3: association of parameters of pulmonary function tests (PFT) between bus drivers (n=231) and participants in comparison group (n=231).

The prevalence of restrictive changes in lung functions was 24.67% among drivers which was much higher as compared to 4.33% among comparison group (p < 0.001, OR = 7.24, 95% C.I. OR = 3.59 – 14.59, table 4).

df= 1, x² (1) = 36.94, p= 0.000, OR = 7.24 (95% C.I. of odds ratio =3.59 – 14.59)

Table 4: association of restrictive impairment between bus drivers and participants in comparison group.

The obstructive changes in lung functions among drivers were 2.16% which was slightly lower as compared to 6.93% among comparison group. When association was tested, there was a significant difference (p < 0.05, OR = 0.3, 95% C.I. OR = 0.11 – 0.83) found in the obstructive changes between these two groups (table 5).

df= 1, x² (1) = 4.989, p= 0.012, OR = 0.3 (95% C.I. of odds ratio =0.11 – 0.83)

Table 5: association of obstructive impairment between bus drivers and participants in comparison group.

About 16.08% of the bus drivers had mixed (restrictive and obstructive) respiratory impairment, while only 3.46% of the participants in comparison group had mixed impairments. About 70.18% drivers had moderate and 22.81% drivers had moderately severe restrictive impairment. Only 7% of them had mild restrictive impairment. The participants of comparison group 10% had mild and 90% had moderate restrictive impairment.

The prevalence of respiratory symptoms among drivers was 67.1% while among comparison group it was 21.2%. About 25.1% of the drivers reported absence from work due to respiratory symptoms during last 12 months while only 2.6%reported the same. A very highly significant association was seen in most of the respiratory symptoms among drivers and comparison group (p < 0.001, OR= 7.58, 95% C.I. OR = 4.99 – 11.51) (table 6).

Table 6: association of perceived respiratory symptoms during last 12 months between auto rickshaw drivers (ADs, n=231) and participants in comparison group (n=231).

Age, BMI, physical activity are well known physiological factor affecting the pulmonary functions there was no significant difference in the age of participants in both groups (p > 0.05). About 36.4% drivers had history of smoking whereas 31.2% participants of the comparison group were smokers. Very few the studies conducted among bus drivers had included both smoker as well as non-smoker drivers as participants. To eliminate this effect of smoking habit on pulmonary functions both groups were matched for history of smoking habits (p >0.05).

The finding regarding weekly work hours clearly states the violation of 48 hours/week standards. A very highly significant difference was observed in the predicted readings of FVC, FEV1 of drivers working for different work hours and total duration of work. This suggests that those drivers spending more than >48 hours/week and who were working for > 20 years in the work environment have reduced lung functions.  This signifies the risk of working as bus drivers for longer periods and its effects on the respiratory functions. Chattopadhyay B.P. et al¹⁰ studied the effect of air pollution in bus drivers also reported that gradual decrement in lung functions has been found as the duration of exposure to the occupation increases. Pal A. et al,¹¹ Patel AJ et al¹² concluded that the drivers working for extended years have more derangement in their flow rates when compared with the garage workers.

A very highly significant difference found between the mean FVC & FEV1 values of drivers and participants in comparison group indicate significant reduction in lung functions because of occupational exposure to traffic related air pollution among drivers mostly to combination of PM10 and NO2 as a result of traffic related air pollution. Higher degree of restrictive changes in drivers can be attributing to the level and duration of exposure to particulate matter (PM10) and carbon monoxide (CO) both of which are the byproducts of incomplete combustion of fuel in addition to dust and ultrafine particulate matter.^{13, 14} These findings point towards. And these changes can be attributed to increased SO2 concentrations in microenvironment airflow as well as in ambient air leading to irreversible changes in larger alveoli diameter leading to obstructive disease. In a study done by Zuskin E et al¹⁵, Knibbs LD et al,¹⁶ Patel AJ. et al,¹² Mohandas S. et al¹⁷ concluded that the professional bus drivers had deranged pulmonary functions compared to non drivers.

The ratio of FEV1 and FVC (FEV1/FVC %) remained mostly unchanged among drivers as well as participants in the comparison group. However, its mean value was significantly increased among drivers as compared to comparison group. In addition to particulate matter, other gaseous pollutants like SO2 and NO2 have greater chances of reaching the deeper parts of lungs. These gaseous pollutants might also alter the properties and concentration of surfactant and contribute to early closure of small airways. Much of the terminal bronchioles are compromised before other pulmonary functions such as FEV1 are affected.¹⁸ This fact can be considered as an explanatory argument for the lesser prevalence of obstructive changes among drivers.

The mixed pattern [restrictive (reduced FVC) & obstructive (reduced FEV1)] of impairment among drivers is an effect of continuous exposure to ambient air pollution as well as smoking habit in drivers on small as well as larger airways of lungs respectively. Many studies conducted among similar study groups have shown similar results. Kumar P. et al,¹⁴ Chattopadhyay B.P. et al,¹⁰ Nitta H. et al²⁰ quoted that the majority of the  professional drivers had restrictive impairment

A common conclusion was derived by several studies conducted among bus drivers in different settings that the statistically significant reduction in pulmonary functions in this occupational group was due to exposure to air pollutants derived from traffic as well as other sources^15,18. Increase in severity of respiratory impairments can be attributed to exposure to higher level of vehicular pollutants suggesting a negative correlation between exposure level of pollution and derangement in PFT.

It was found that drivers had increased chance of having respiratory symptoms which might be due to longer duration of exposure to the fine and ultrafine particulate matter. Patel AJ. et al,¹² Bener A. et al,²⁰ Mohandas S. et al ¹⁷ have concluded that acute effects of diesel exhaust exposure includes irritation of the eyes and nose, changes in lung functions. While, chronic exposures are associated with cough, excessive sputum production and pulmonary function decrements. These studies included bus drivers using diesel as fuel and reported a higher prevalence of respiratory symptoms among them when compared to blue-collar workers.

Results of this study revealed that bus drivers had statistically significant decreased values of pulmonary functions i.e. FVC & FEV1 when compared to the administrative workers with matched age and smoking habit. The most common respiratory impairment being of restrictive type, increased prevalence of respiratory symptoms and decrement in the pulmonary functions among them can be attributed to the long duration of exposure to traffic related air pollution with a possible additional effect of tobacco smoking on their lung function. The findings of this study are conclusive in revealing that bus drivers are at an increased risk of developing impairments in respiratory health as a direct effect of the occupational environment.

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