Effect on pulmonary functions of dust exposed rice mill workers in comparison to an unexposed population

2.1 Selection of subjects

The subjects were divided into two groups: exposed and unexposed groups. The exposed group volunteers were rice mill workers who remained exposed to the dust during their work. A total of 218 exposed volunteers (168 males and 50 females) from 25 old rice mills of three districts, namely North-Lakhimpur, Dhemaji and Sonitpur of Assam, were included in the study. The unexposed group included those volunteers who were not exposed to dust during their work. This group included 377 volunteers (291 males and 86 females) from the NERIST academic institutions, both students and faculty, who were not consistently exposed to dust related environments for any length of time.

The volunteers from both groups were selected in the age range of 18-60 years and with a minimum one year’s work experience. Volunteers were excluded from the study if they (a) could not perform spirometry as per American Thoracic Society (ATS) guidelines, (b) had a history of asthma, chronic bronchitis, chronic cough, exposure to any toxic chemicals, or surgery involving the chest wall or spine, and had ongoing respiratory symptoms, (c) smoked at least 1 cigarette/day for more than a year [12]. Demographic characteristics such as age, body height and body weight were documented for all selected subjects before testing. The demographic factors played an important role in comparing the pulmonary function tests (PFT) between the different groups. Body surface area was calculated from the recorded data using the Dubois formula [13]. The study was approved by the institutional ethics committee and written informed consent was obtained from all participants. The study took place between July 2015 and August 2018.

2.2 Pulmonary function test

Pulmonary function tests (PFT) were conducted for each volunteer for both groups. In order to assure better test results, some trial measurements were taken before performing pulmonary function tests. Volunteers were instructed (a) not to have a heavy meal at least two hours before performing the tests (PFT), (b) not to take drugs/drinks containing caffeine before the test, and (c) not to smoke or undertake heavy physical activity on the day of the test.

The PFT was conducted using calibrated portable micro-quark spirometer, with Omnia 1.2 software (COSMED the metabolic company, Italy). The apparatus was calibrated daily and operated within the ambient temperature range of 18-27⁰ C. The PFT parameters included forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), forced expiratory ratio (FEV₁/FVC, %), peak expiratory flow (PEF) and force expiratory flow fraction between 25 to 75% (FEF_25-75%). FVC is the amount of air which can be forcibly exhaled from the lungs after taking the deepest possible breath. The FEV₁/FVC is used to determine the presence and severity of lung diseases. The test was performed with the subject in sitting position using a nose clip, and repeated three times after adequate rest, and the best of three was taken for subsequent analysis.

2.3 Data analysis

Descriptive statistical analysis was carried out for pulmonary function test parameters using IBM SPSS version 22. Using Shapiro-Wilk test, the body height of the selected volunteers was found normally distributed for all groups except females of the exposed group. The measured FVC and FEV₁ were also found normally distributed (p > 0.05) for exposed and unexposed group for both male and female volunteers.

3.1 Demographic comparison of volunteers between groups

Demographic factors of the exposed and unexposed volunteers are given in Table 1. The mean age of exposed volunteers was nearly 2 and 3 years higher than the unexposed male and female volunteers, respectively. However, the age was found statistically insignificant (P > 0.05) between exposed and unexposed groups for both genders. Similarly, body height was also found insignificant between the groups for male and female. The average height was 164 and 154 cm for male and female volunteers, respectively which are close to the reported average heights for the study region [17].

Further, weight and BMI of the selected subjects were also analyzed and found significant between exposed and unexposed groups for males and non-significant for females. This clearly indicates that weight/height ratio of the unexposed group of male workers was greater than the exposed group. However, the BMI of exposed and unexposed groups of volunteers was found in the normal range (18.5-24.9 kg/m²). The normal range of BMI of the selected volunteers indicates the correct selection of the volunteers. Further, the significance of weight of selected volunteers between groups did not affect the selection because body weight has a limited role on lung function [16, 19].

The collected PFT parameters (FVC, FEV₁, FEV₁/FVC(%), PEF and FEF_25-75%) for exposed and unexposed were separated for male and female and presented in Table 2. The FVC of the exposed group of volunteers was found less compared to the unexposed group for both genders. It was found that mean FVC was 19.24 and 21.6% lower than the unexposed group for male and female volunteers, respectively. The average of FVC including males and females was 2.37 L, which is lower than the value reported by Ghosh et al. [20] (3.44 L) and more than reported by Dhillon and Kaur [21] (1.3 L) for rice mill workers. The FEV₁ was found to be significant in a test for equality of means between exposed and unexposed groups for both genders. The EFV₁ was 22.2% and 20.5% lower in the exposed group compared to the unexposed group for males and females respectively. Also, the mean value of FEV₁ of this study lies between the values reported by Ghosh et al. [20] and Dhillon and Kaur [21]. The PEF and FEF_25-75% for males was 60% and 47.2% lower for the exposed group respectively, and 57.94% and 9.20% lower for females. All PFT parameters were found significant except FEF_25-75% for females. For rice mills, the PEF was reported as 5.08 and 4.29 L/s by Ghosh et al. [20] and Dhillon and Kaur [21] and FEF_25-75% was reported as 2.82 L/s by Dhillon and Kaur [21]. For other industries also the range of PEF lies between 3.32 to 6.96 L/s and for FEF_25-75% lies between 2.39 to 3.13 L/s as reported earlier [21–25]. Decrease in PEF is probably due to hypertrophy of mucosal cells due to irritation by grain dust resulting in the increased secretion of mucous and formation of mucosal plugs which cause obstruction to the exhaled air [26]. Some previous studies [24, 28] also showed the decrease in FEF_25-75% as collaborated by our study.

The PFT parameters, such as FVC, FEV₁, FEV₁/FVC%, PEF and FEF_25-75% were compared between groups, as shown in Fig. 1. These graphs represent the minimum, mean, standard deviation and maximum value.

OPEN IN VIEWER

Fig. 1

PFT parameters of male and female subjects in age-wise distribution.

FVC: It is evident that mean FVC of exposed volunteers was less compared to unexposed volunteers for lower and higher aged sub-groups in both genders. The percentage differences were 22 and 19 for males and 13 and 24 for females between the two groups for 18-40 and 41-60 years, respectively. These differences are statistically significant (p < 0.001) between exposed and unexposed for both age sub-groups and genders. This analysis clearly indicates that the dust exposed male volunteers were affected more in the group 18-40 years; however, female volunteers were more affected in the higher age group (41-60 years). Finally, it can be concluded that the effect of dust in FVC was persistent in younger ages as well as higher age groups for both males and females.

FEV₁: It was further observed that FEV₁ of the exposed group was also lower than the unexposed group for both age sub-groups as well as gender. In the age group of 18-40 years, the values of FEV₁ in the unexposed group of male and female volunteers were varied from 1.64 to 4.62 and 1.29 to 2.86 L/s, respectively. In the case of exposed group volunteers, the values of FEV₁ ranged from 1.17 to 3.11 L/s for males and 0.77 to 2.59 L/s for females in the age group of 18-40 years. In the other age group, the ranges were 0.76 to 3.24 l/s for exposed males, 0.85 to 1.80 L/s for exposed females, 1.02 to 3.56 L/s for unexposed males and 1.11 to 2.24 L/s for unexposed females. Figure 1 shows the mean value of FEV₁ along with minimum, maximum and standard deviation.

FEV₁/FVC: It was highly significant (p < 0.01) between exposed and unexposed groups of volunteers for males, however, for females it was not found significant (p > 0.05) in any of the age groups.

PEF: In exposed group volunteers, the mean values of PEF were 4.47 L/s for males and 3.44 L/s for females, in unexposed volunteers, it was 7.56 L/s for males and 5.42 L/s for females, respectively in the age group 18-40 years. In the 41-60 years age group, the mean values were 4.49 L/s for exposed males, 2.96 L/s for exposed females, 6.50 L/s for unexposed males and 4.58 L/s for unexposed females. It was observed that the mean value of PEF the unexposed group was higher for both genders and age groups compared to exposed volunteers.

FEF_25-75%: The mean value of PEF_25-75% for males and females in the age group of 18-40 years for exposed volunteers was 37% and 5% lower than unexposed volunteers, respectively. However in the age group of 41-60 years, exposed volunteers had 22% and 11% reduced FEF_25-75% compared to unexposed volunteers for males and females. The difference in FEF_25-75% between exposed and unexposed was statistically significant in both age groups for male volunteers. For female volunteers, no significant difference (p > 0.05) was found for either age group.

The comparison of PFT parameters between two levels of experience for males is given in Table 3. It is evident from the table that the mean values of FVC, FEV₁ and FEF_25-75% are 18.5%, 14.3% and 18.2% lower for second level of experience compared to first level of experience. This indicates that workers who had been working for a longer period had poorer PFT than those who had worked less. The difference of these PFT parameters between levels of experience were significant as p value was lower than 0.05. Further, FVC and FEV₁ were found highly significant (p < 0.001) between two levels of experience [29]. Souza et al. [30] also reported similar results for mining industries. Two other PFT parameters, namely FEV₁/FVC% and PEF (L/s), were not found significant (P > 0.05) because these parameters are dependent on FVC which may not show an effect based on length of work experience.

Similar analysis was carried out for females and presented in Table 4. For females also FVC, FEV₁ and FEF_25-75% were found lower in second level (6-10 years) than first level (1-5 years) of experience and significant as P < 0.05. This indicates that longer duration of work in dust exposed environments results in deterioration in pulmonary function for both males and females. Singh et al. [31] reported that decreasing FVC, FEV₁ and PEF are directly associated with increasing duration of exposure to rice husk dust.

The total 218 selected rice mill workers were considered as either normal or having lung disease. Those with lung disease were further divided into two types: (i) obstructive (pure obstructive and mixed obstructive and restrictive) and (ii) restrictive. It was observed that 48.22% and 32% of the total male and female volunteers, respectively, were suffering from lung disease as given in Table 5. Ratnaprabha and Majunath [32] reported that about 50% of rice mill workers suffer obstructive respiratory disease who have worked < 5 years and restrictive disease who have worked for 5-10 years. The disease percentage of females was found lower than males because of three main reasons: (i) generally females were working in the packaging section where dust concentration was less, (ii) the selected female volunteers had less work experience in terms of number of years with respect to male volunteers and (iii) females were covering their nose, most of the time, by their saree (wearing cloth). Further, the male workers were suffering more from obstructive lung disease (26.78%) compared to restrictive (21.43%), whereas in females, the restrictive pattern was reversed. This trend was mainly because of less work experience of females compared to males as the obstructive pattern is more susceptible with the work experience. The pure obstruction was found much higher than the mixed restrictive and obstructive for both genders. The pure obstruction was found four times higher than the mixed restrictive and obstructive for males however, no mixed pattern was found in the selected female volunteers. Irrespective of gender, total 44.5 % workers were suffering from lung diseases either restrictive (21.1%) or obstructive (23.4%). The result of the study verifies that the decline in FVC indicates restrictive and decline in FEV_l and PEF along with other flow rates indicates obstructive pulmonary impairment, as also reported by Singh et al. [31], Mathur et al. [33], Rana et al. [34] and Rao et al. [35].

The severity of obstructive lung disease was analyzed as mild, moderate, severe and very severe as per Global Initiative for Chronic Obstructive Lung Diseases (GOLD) criteria [36]. It was observed that 36 out of 45 males and 5 out of 10 females were suffering from mild obstructive lung disease. The remaining 9 and 1 were in the moderate category for males and females, respectively. None of the volunteers were in the severe or very severe categories in either gender. Hence, it was calculated that 21.43% of male rice mill workers were suffering from mild disease and 5.35% from moderate obstructive lung disease. However for females, 10% were suffering mild disease and only one volunteer out of 50 (2%) was moderate.