Introduction
Tobacco, in both smoking and smokeless form, is a major cause of morbidity and mortality worldwide.1 India has a substantial share of the global burden of tobacco-induced disease and death, accounting for over a million deaths per year.2 In India, approximately half of tobacco consumption is in the form of bidis.Reference Chaudhry and Rath3 At present, India is the fourth largest producer of tobacco, and second largest cigarette and bidi producer in the world, after China.4
The prevalence of smoking bidi or the Indian cigar is quite high in rural India and among the lower socioeconomic status population.Reference Gupta, Ray, Narake, Palipudi, Sinha and Asma5 A bidi contains about 0.2 g sun-dried and processed tobacco flakes, rolled in a tendu leaf (Diospyros melanoxylon) and tied together by a cotton thread.Reference Prabhakar, Narake and Pednekar6 Apart from causing an incredible number of diseases, including oral and lung cancer, chronic bronchitis, emphysema, cerebrovascular accidents, and numerous potentially malignant diseases, the components of smoke, such as nicotine, hexamine, ammonia and formaldehyde, are held to be widely responsible for the phenomenon of cilia toxicity.Reference Bombick, Bombick, Ayres, Putnam, Avalos and Borgerding7–Reference Hecht9
Cilia are rod-shaped organelles that are present in almost all the cells in the human body, primarily in the respiratory tract, lungs and middle ear. They are only about 0.1 mm in length, and possess a rhythmic waving or beating motion, with a frequency of 7–16 Hz.Reference Satir and Sleigh10 Nasal mucociliary clearance is essentially a protective feature, in which the cilia present in the nasal mucosa are instrumental in eliminating dust particles and other foreign bodies from the nasal cavity towards the nasopharynx. They work successfully to keep the airways free of mucus and dirt, allowing individuals to breathe easily without irritation.
Apart from smoking, disruption in nasal mucociliary clearance is seen in those with diseases such as chronic obstructive pulmonary disease (COPD), bronchial asthma, cystic fibrosis, rhinosinusitis and deviated nasal septum. It is also known that tobacco smoke alters the viscoelastic nature of mucus and further decreases nasal mucociliary clearance.Reference Navarrette, Sisson, Nance, Gipson, Hanes and Wyatt11
Studies by Stanley et al.Reference Stanley, Wilson, Greenstone, MacWilliam and Cole12 and Baby et al.Reference Baby, Muthu, Johnson and Kannan13 observed the mean nasal mucociliary clearance time (saccharine transit time) as 12 minutes. A nasal mucociliary clearance time of over 30 minutes was considered abnormal and signalled an increased chance of morbidity. EwertReference Ewert14 observed a decreased rate of dye transportation across a specified area of anterior septal mucosa in healthy smokers compared to non-smokers. However, Quinlan et al.Reference Quinlan, Salman, Swift, Wagner and Proctor15 reported no distinction between smokers and non-smokers in the mucociliary clearance of insoluble radiolabelled resin particles placed on the inferior nasal turbinate.
The existing literature does not show any conclusive evidence of the effect of bidi smoke on nasal mucociliary clearance. This study aimed to compare nasal mucociliary clearance in adult non-smokers, cigarette smokers and bidi smokers using the methylene blue dye test.
Materials and methods
This cross-sectional study was carried out in the Department of Otorhinolaryngology at Kasturba Medical College, Manipal, in India, between August 2016 and September 2017. Participants were classified into three categories depending on whether they were a non-smoker, cigarette smoker or bidi smoker.
Sample size calculation was determined by estimating a 10 per cent difference in the nasal mucociliary clearance values of each group, as evident from previous studies.Reference Stanley, Wilson, Greenstone, MacWilliam and Cole12 Based on a power of 0.80 and a 0.05 type I error, a sample size of 60 participants (20 each in the non-smoker, cigarette smoker and bidi smoker groups) was deemed adequate to detect a statistically significant difference between the groups.
The study protocol was reviewed and approved by the Institutional Ethics Committee of Manipal Academy of Higher Education in accordance with the Helsinki declaration.16 Participants were included only after providing informed written consent.
Sixty male participants aged 20–40 years, residing in the Udupi district, Karnataka, were incorporated into our study. The primary reason for including only males was because smoking is more prevalent among males in the study region than in females.Reference Jha, Jacob, Gajalakshmi, Gupta, Dhingra and Kumar17 It was also assumed that male participants would be more forthcoming about their tobacco addiction history than females.
Participants taking medications such as decongestants, anti-histamines, saline drops and anticholinergics were excluded. Participants were screened for related nasal and systemic pathologies, such as rhinosinusitis, nasal polyps, allergic rhinitis and COPD, to rule out any confounding effect. A detailed case history and spirometry were used to screen for COPD. The clinical examination was conducted by an ENT specialist with a speculum and a nasal endoscope. Participants were excluded if any of these pathologies were clinically present.
The addiction history of participants was assessed with the help of a standard proforma, which recorded age, education, marital status and occupation, and included a detailed column on tobacco habits.Reference Heatherton, Kozlowski and Fagerström18
Nasal mucociliary clearance was measured with methylene blue dye, in accordance with the procedure described by Ewert.Reference Ewert14 The tests were performed in an air-conditioned room (temperature, 24.9 ± 0.30 °C) between 4:00 pm and 5:00 pm. The participants were asked to rest for 30 minutes before the procedure commenced. One drop of the methylene blue dye was applied, with a 24-gauge needle, to the anterior end of the inferior turbinate of the participants’ nasal cavity, with the help of a nasal speculum. After application of the dye, participants were instructed not to sniff or sneeze, and to maintain a sitting posture for a period of 15 minutes, following which the participants were asked to recline on a bed. The distance that the methylene blue dye traversed inside the nasal cavity was recorded in millimetres with a nasal endoscope and a standard 6 inch (15.24 cm) metal scale.
Statistical analysis
The SPSS statistical software program, version 20.0 (SPSS, Chicago, Illinois, USA), was used for data analysis. Demographic data were stated as numbers, while the quantitative data were presented as means ± standard deviations. The distribution of the residuals corresponding to nasal mucociliary clearance was considered non-parametric, and the Kruskal Wallis test was used to examine the difference between the nasal mucociliary clearance readings of the three groups. A p-value of less than 0.05 was considered as statistically significant.
The variables of smoking status, number of years’ formal education, marital status, occupation, and number of bidis or cigarettes smoked in a day were categorised according to their distribution in the sample, whereas age, age of smoking onset and pack-years were treated as continuous variables. The dependent variable nasal mucociliary clearance was dichotomised according to the distance covered by the dye inside the nasal cavity (less than 70 mm was scored as 0, and equal to 70 mm was scored as 1). Initially, a bivariate log regression analysis was conducted to assess the effects of the various parameters on nasal mucociliary clearance. Following this, all variables that indicated associations (wherein p < 0.20) were considered for multivariate binomial log regression analysis. Crude and adjusted odds ratios and 95 per cent confidence intervals (CIs) were calculated and reported.
Results
The demographic and socioeconomic characteristics and tobacco exposure history of the 60 participants are shown in Table 1. The mean age of participants was 30.23 ± 6.12 years, with an age range of 20–40 years. The mean age of non-smokers, cigarette smokers and bidi smokers was 29.3 ± 6.25 years, 31.2 ± 5.42 years and 30.2 ± 6.77 years, respectively. The mean number of years of formal education (n = 60) was 15.38 ± 4.02 years. The mean number of years of formal education of non-smokers, cigarette smokers and bidi smokers was 16.5 ± 4.2 years, 18.05 ± 2.14 years and 11.6 ± 2.01 years, respectively. Among the participants, 30 were married and 30 were unmarried; 25 were professionals or semi-professionals, 24 were semi-skilled or unskilled workers, and 11 were students. The mean age of smoking onset was 18.55 ± 1.76 years for cigarette smokers and 16.25 ± 1.29 years for bidi smokers, while the mean pack-years among these groups were 4.63 ± 2.74 and 7.5 ± 5.1 respectively. The mean nasal mucociliary clearance for the non-smokers, cigarette smokers and bidi smokers was 67.89 ± 4.10 mm, 67 ± 5.48 mm and 59.25 ± 12.38 mm, respectively. Among all the variables compared, only age and marital status were not found to be statistically significantly different between groups.
Table 1. Demographic, socioeconomic and tobacco exposure data, by group
SD = standard deviation. *n = 20; †n = 20; ‡n = 20. **P < 0.05 considered statistically significant
As the data were not normally distributed, the medians were derived. The median nasal mucociliary clearance of the 60 participants was 70 mm (95 per cent CI = 65.00–70.00), with a range of 35 mm. The median nasal mucociliary clearance of non-smokers and cigarette smokers was 70 mm each, whereas it was 65 mm for bidi smokers. The difference in nasal mucociliary clearance between bidi smokers, non-smokers and cigarette smokers was found to be statistically significant (p < 0.05, Kruskal Wallis test).
Table 2 shows the association, on bivariate analysis, between nasal mucociliary clearance and the demographic, socioeconomic and tobacco exposure variables recorded. In the bivariate analysis, a variable with a p-value of less than 0.2 was considered for inclusion in the adjusted model. Smoking status, number of years’ formal education, occupation, number of cigarettes or bidis smoked per day, and number of pack-years were thus included.
Table 2. Bivariate regression analysis results*
*Examining the association between nasal mucociliary clearance and demographic, socioeconomic and tobacco exposure variables. †Variables where p < 0.20 were considered for inclusion in the adjusted model. The dependent variable nasal mucociliary clearance was dichotomised according to the distance covered by the dye inside the nasal cavity (less than 70 mm scored as ‘0’ and equal to 70 mm as ‘1’). OR = odds ratio; CI = confidence interval
Table 3 shows the association, on multivariate regression analysis, between nasal mucociliary clearance and the covariates included from the bivariate analysis. In the unadjusted multivariate regression analysis, a statistically significant association (p < 0.05) was seen between nasal mucociliary clearance and smoking status, number of cigarettes or bidis smoked per day, and pack-years. However, when adjusted for age, number of years’ formal education, marital status and occupation, a statistically significant association (p < 0.05) was only seen between nasal mucociliary clearance and smoking status and number of pack-years.
Table 3. Crude and adjusted multivariate regression analysis results*
*Examining the association between nasal mucociliary clearance and demographic, socioeconomic and tobacco exposure variables. The dependent variable nasal mucociliary clearance was dichotomised according to the distance covered by the dye inside the nasal cavity (less than 70 mm scored as ‘0’ and equal to 70 mm as ‘1’). †Adjusted for age, number of years’ formal education, marital status and occupation. ‡P < 0.05 considered statistically significant. OR = odds ratio; CI = confidence interval
Discussion
This cross-sectional study determined the nasal mucociliary clearance values of non-smokers, cigarette smokers and bidi smokers, and evaluated the association with demographic, socioeconomic and tobacco exposure variables. The results indicated that nasal mucociliary clearance after 15 minutes was significantly decreased among bidi smokers, in comparison to cigarette smokers and non-smokers. A significant inverse association was also seen between bidi smoking, number of pack-years and nasal mucociliary clearance.
• The components of cigarette tobacco smoke cause cilia toxicity
• Nasal mucociliary clearance is a protective feature for eliminating dust particles and foreign bodies from the nasal cavity towards the nasopharynx
• The prevalence of smoking bidi or the Indian cigar is quite high in rural India
• Bidi smoking is more harmful to ciliary movement in the nasal mucosa than cigarette smoking
• Bidi smoking was associated with a higher number of pack-years as compared to cigarette smoking
• Bidi smokers mainly belonged to the lower socioeconomic strata of society
Various factors might have played a role in the outcome. The true biological reasons for the findings are yet to be ascertained; however, the most important explanation could be the chronicity or duration of the smoking habit, denoted by the number of pack-years. As the bidi smokers had a significantly higher number of pack-years, it was assumed that cilia toxicity would develop much earlier relative to cigarette smokers and non-smokers.
One factor that could have affected the results is the nature of the bidi sticks. Bidis are traditionally hand rolled and they are devoid of a filter, unlike cigarettes. The filter of a cigarette functions as a barrier, by preventing the noxious fumes from reaching the nasal cavity. Although a bidi contains a lower amount of tobacco compared to a cigarette, when tested on a standard smoking machine, it produces higher levels of nicotine, carbon monoxide, tar, phenols and ammonia, resulting in a higher degree of addiction. It has been shown that bidis produce three times the amount of carbon monoxide and nicotine, and five times the amount of tar, than cigarettes.Reference Jayant, Pakhale, Sanghwi and Notani P19 Given the low combustibility of the tendu leaf wrapper, bidi smokers must take more frequent and deeper puffs, resulting in the inhalation of more smoke, which is disseminated deeper into the lungs.Reference Bhonsle, Murti, Gupta, Gupta, Hamner and Murti20 Unlike the thin, single-layer paper wrapper used in Western-style cigarettes, leaf wrappers add considerably to the total mass of a bidi and contribute significantly to the amount of total particulate matter produced during smoking.Reference Pakhale, Dolas and Maru21
As with all tobacco products, bidis are carcinogenic and mutagenic. Bidi smokers have an increased risk of: coronary heart disease, and cancers of the larynx, pharynx, oral cavity, oesophagus, liver, stomach and lungs. Bidi use during pregnancy is associated with high perinatal mortality.Reference Malson, Sims, Murty and Pickworth22–Reference Dempsey and Benowitz24 Given its relatively lower cost and widespread availability, it is widely perceived that a bidi causes more harm to the respiratory system than a cigarette.
The socioeconomic status of the participants, as denoted by the number of years’ formal education and occupation, though not statistically significant, could have played a mediatory role in the difference observed between the bidi smokers and the other two groups. In our study, bidi smokers predominantly belonged to the lower socioeconomic strata; hence, it is possible there was a lack of awareness about the deleterious effects of bidi smoking, as indicated by the significantly higher number of pack-years.
The results obtained from our study are comparable to those of various other studies. Kim et al.,Reference Kim, Kim, Lee, Kim, Lim and Lee25 observed a significant increase in methylene blue nasal mucociliary clearance time in smokers compared with non-smokers. EwertReference Ewert14 also demonstrated a significant reduction in nasal mucociliary clearance in cigarette smokers compared with non-smokers. However, Quinlan et al.,Reference Quinlan, Salman, Swift, Wagner and Proctor15 observed no such distinction between smokers and non-smokers in the mucociliary clearance of insoluble radiolabelled resin particles placed on the inferior nasal turbinate. We too could not demonstrate a statistically significant difference in nasal mucociliary clearance between non-smokers and cigarette smokers. It is possible that ciliary damage was less among smokers given the relatively younger age of the study participants (21–40 years). Another possible reason could be the time interval (15 minutes) used to assess nasal mucociliary clearance. It has been postulated that nasal mucociliary clearance time (the time taken for the dye to travel the length of the nasopharynx) could be as low as 12 minutes among healthy people.Reference Stanley, Wilson, Greenstone, MacWilliam and Cole12 It is possible that given the longer interval used in our study, the difference in distance travelled by the methylene blue in both groups was reduced, thus affecting the findings.
Few studies utilising saccharin crystals as the nasal mucociliary clearance time indicator showed similar outcomes.Reference Baby, Muthu, Johnson and Kannan13, Reference Proenca, Xavier, Ramos, Cavalheri, Pitta and Cipulo Ramos26 The primary advantage of the methylene blue test over a saccharin test is the objectivity in study design and the shorter time required to perform the test. The need for objectivity is important; not all participants will have the same level of susceptibility towards the sweet sensation of saccharin, which is mandatory to calculate the nasal mucociliary clearance time.
Nasal mucociliary clearance is affected by various diseases and pathologies.Reference Karnitzki, Mlynski and Mlynski27–Reference Altuntas, Kaya, Uysal, Cevit, Içağasioğlu and Müderris29 Hence, careful screening was required to rule out those participants considered unsuitable for inclusion in the study. The main limitation of our study is that participants’ age ranged only from 20 to 40 years. In addition, the extent of passive smoking that each of the three groups of participants might have been subjected to was not explored. The methylene blue dye occasionally caused a mild burning sensation, adding to participants’ discomfort.
As we observed a significant association between pack-years and nasal mucociliary clearance, in the future participants with a wider age range (of more than 40 years) should be recruited to explore the effects of bidi and cigarette smoking on nasal mucociliary clearance. In order to arrive at more accurate results, the beating frequency of cilia and the viscoelastic nature of mucus secretion should also be considered.Reference Liote, Zahm, Pierrot and Puchelle30
Nasal mucociliary clearance measurement is an elementary and precise procedure for evaluating the effect of smoking on the mucociliary activity of nasal mucosa. The decreased nasal mucociliary clearance detected in the bidi smokers of our study may be due to reduced ciliary beat frequency, a decline in the number of cilia or alterations in the viscoelastic properties of mucus. Our study emphasises the vital contribution of nasal mucociliary clearance as an indicator of respiratory system health and the general health of an individual.
Acknowledgements
The authors wish to acknowledge Dr Vasudeva Gudattu and Ms Maria Matthews for their commendable contribution towards the sample size calculation and statistical analysis.
Competing interests
None declared
