Risk factors for obstructive sleep apnea among train drivers

1 Introduction

Risk factors such as obesity and high blood pressure make drivers more prone to diseases such as obstructive sleep apnea (OSA). The disease is a result of partial or complete obstruction of the upper airway thus resulting in its dysfunction [1]. OSA is associated with excessive sleepiness, impaired cognition and increased risk of accidents [1]. Other associated diseases are hypertension, diabetes, obesity, and cardiovascular diseases [2].

OSA is prevalent among drivers of vehicles including locomotives [3]. Therefore, studying the risk factors associated with OSA in locomotive drivers would provide a better understanding of the diseases’ prevalence and subsequent outcomes in the case of patients to whom no diagnostic label can be attached. Australia has included risk factors such as obesity, high blood pressure, and diabetes as the screening risk factors for OSA to whom further investigations are required [2]. In a study of railway workers in Australia, only 4% of male workers had a body mass index (BMI) under 35, of which only a small subset was identified not to have OSA. More objective measurements in this population than the self-reported questionnaire of sleepiness such as Epworth Sleepiness Scale (ESS) provides better estimate of at-risk individuals for OSA. OSA has been associated with several train accidents in the USA. On the same basis, further attention should be paid to the locomotive drivers susceptible to OSA. Several train drivers have been reported to have undiagnosed apnea [4, 5]. In an evaluation of railway in Indonesia, 22% of accidents were associated with train operators’ act indicating importance of train drivers’ health in railway accidents [6].

Currently, there is no information/data available with regard to the risk factors of OSA in locomotive drivers in Iran. Screening and appropriate management for sleep apnea is not included in current annual examination of train drivers. There is urgent need to highlight the high-risk population of obstructive sleep apnea for authorities. Assessing the common risk factors of this incapacitating chronic disease would help health care providers to accurately screen for individuals at risk of apnea which is one of the major risk factors of traffic accidents. This study aimed to assess major known risk factors of sleep apnea among railroad workers.

2 Materials and methods

The present research is a cross-sectional study conducted in Baharloo Hospital, Tehran University of Medical Sciences, Iran. The study population included 281 locomotive drivers referred for their annual physical examination during 2016-2017. Prior to the study, all necessary ethical approvals were obtained from the appropriate research committee of Tehran University of Medical Sciences and all study participants signed written consent forms. All contacted participants accepted participation into the study. Sampling of participants was consecutive. All of the participants had no previous history of a known medical disease and were in good health prior to working as a locomotive driver.

Demographic characteristics included age, marital status, educational level, working shifts, and smoking. Daytime sleepiness was assessed using a validated Persian version of ESS-IR [7]. The questionnaire consisted of eight items measuring participants’ sleepiness in different situations with a 0 to 3 Likert scale. ESS score ranges from 0 to 21. In this study, ESS≥10 was assumed as excessive daytime sleepiness.

The participants’ physical examination was performed by a trained physician. Neck and waist circumference, weight, height, and BMI were measured for each participant accordingly. Systolic and diastolic blood pressures were recorded using a sphygmomanometer. Individuals were asked to undertake 14 h fasting prior to their physical examination at the laboratory of the hospital. Blood samples were obtained to measure FBS, triglyceride, Cholesterol, low-density lipoprotein cholesterol (LDL), and high-density lipoprotein cholesterol (HDL).

Demographic characteristics, blood pressure, BMI, neck and waist circumference, and other parameters including fasting blood sugar (FBS), cholesterol, HDL, and LDL were recorded for all study participants.

Blood pressure ≥140/90 mmHg or history of drug use (P), BMI > 35 kg/m² (B), age >50 years (A), and neck circumference >40 cm (N) (P-BANG) were defined as risk factors for OSA-RFs. The aforementioned OSA-RFs are the known ones for this sleep problem [8, 9]. More than two OSA-RFs was considered as high risk for sleep apnea. BANG and P-BANG scores were calculated for estimating risk of sleep apnea in our participants. Participants who had abnormal laboratory tests or were at a high risk for sleep apnea were recommended to visit a related physician.

SPSS version 16 was used for data analysis. Data were analyzed using descriptive and analytical statistics.

3 Results

In this cross-sectional study, 281 participants were recruited and evaluated having undergone periodic occupational health examination. All participants completed written consent forms and the response rate was 100%. All the participants were male with a mean age of 43(10.1) years and BMI of 26.06 (3.67) kg/m².

The mean neck circumference was approximately high with a standard deviation value of 2.6 (see Table 1). About half of the participants were unmarried; and 58.06% had upper diploma education. Most (53.5%) of the participants were not shift workers.

64 (21.5) participants aged more than 50 years old; 112 (37.7) of them had neck circumference of more than 40 cm. The frequency of apnea risk factors according to BANG and P-BANG scores are presented in Table 2. No statistically significant association was found between risk factors of sleep apnea and participants’ sleepiness (ESS > 10) (P value >0.05).

Out of the 281 workers studied, about half (47%) showed at least two risk factors of OSA. Although, half of the population were estimated to be at risk of sleep apnea, only 18 participants reported sleepiness during daytime (ESS > 10). However, no statistically significant association was found between risk factors of sleep apnea and ESS > 10 among study participants. Subjective and non-honest reports of symptoms in occupational settings could be considered as the cause of this non-significant association. It is previously showed that in drivers seeking health license, subjective self-reported problems such as drowsiness or fatigue could not be considered as a reliable risk factor for OSA [9].

Ample evidence exists with regards to the prevalence of OSA and its associated factors among professional drivers. Saberi et al. reported that a high proportion of professional drivers have hypertension [10]. In addition, a plethora of literature has reported a much higher prevalence in larger sample sizes. They reported hypertension in 42% of their samples compared to 27% in the present study. Nevertheless, different measurement tools, definitions, and number of study participants may be the cause of lower hypertension prevalence rate obtained in this study. Most of the participants in this study had BMI less than 35 kg/m². In addition, the mean BMI was 26 kg/m². However, 27% of participants in the study of Saberi et al. were reported to be obese. Truck drivers’ lifestyle may predispose them more to obesity compared to railroad drivers [10]. Higher triglyceride level and diastolic blood pressure are also attributed to sleep complaints of drivers in one study [11]. Izadi et al. also reported a high prevalence of overweight, obesity, and hypertension among a population of 1903 professional drivers referred for obtaining their health license [12].

The results from the present study supported a relatively high prevalence of apnea risk factors (>2) including high blood pressure, BMI, age, neck circumference, and male gender (P-BANG) among the studied participants. Professional drivers diagnosed with sleep apnea are at an increased risk of motor vehicle accidents due to sleepiness, impaired attention and cognition as well as performance [13]. However, a small subset of individuals reported daytime sleepiness. In a Greek population of railroad drivers, Nena et al. reported a higher mean (BMI = 28). Consistent with the present study, a small subset of train drivers reported daytime impairment [13]. The frequency of high ESS and mean standard deviation of ESS was higher in a study conducted by Nena et al. The fear of losing job and employment issues may force drivers to not be honest in their subjective evaluations, thereby the inclusion of objective parameters for apnea screening is warranted. Accordingly, we did not observe an association between daytime sleepiness and risk factors of sleep apnea which may be due to non-honest report of symptoms. In that study by using polysomnography, a higher prevalence of apnea was recorded among participants. In another study of 745 railroad workers, 35% were diagnosed with OSA [13]. The identified risk factors of apnea in Brazilian railroad workers were age, BMI, neck, waist circumference and alcohol use [3]. Along with Koyama et al.’s study, the prevalence of three risk factors including high neck and waist circumference as well as age were high in this study. In this vein, further evaluation of the population is required for sleep apnea using objective measurements such as polysomnography. 43% of the studied participants reported ESS≥10 which was inconsistent with findings of the present results. High employment security, different cultural issues and also the fact that this study was performed during the periodic annual examination of drivers may be the causes of lower reported rates of sleepiness. Larger sample size and performing separate screening for apnea symptoms through occupational examinations may help participants to be more honest with regards to their symptoms.

High prevalence of apnea risk factors is reported in the present study. It is hoped that these results will encourage authorities to pay more attention to the risk factors of chronic diseases such as apnea in the population. An approach that includes individual, group, and organizational intervention to control blood pressure, impaired glucose and lipid metabolism as well as obesity would be a sophisticated approach to abate the risk factors of apnea. Such an approach would benefit the staff individually and would entail lower health costs and increased productivity as railroad driving is considered a safety-sensitive job.

It is worth noting that sleep apnea and its subsequent sleepiness is identified as a risk factor of road traffic accidents among professional drivers. Philip et al. identified sleep disorders to be the leading cause of 20% of traffic accidents, a major cause of death among Iranian youths [1, 14]. Currently, professional truck and out-of- urban drivers are evaluated for apnea risk factors and referred for further examination and treatment by health care authorities [14, 15]. Meanwhile, currently, there is no screening protocol available for determining the risk factors of sleep apnea among train drivers in Iran. The findings of this study could provide baseline data for more detailed evaluation of apnea risk factors among this group of individuals (drivers). According to a report released by the National Transportation Safety Board of Washington a train accident in New York City with four deaths and 59 injured survivors occurred due to the undiagnosed sleep apnea in the operating train engineer [4]. This report highlighted the importance of screening, diagnosis, and accurate treatment of sleep apnea among workers, as such an impairment of their physical and cognitive capacities may lead to serious harm to the public [4]. Another train crash in New York City in 2017 and a train crash at Hoboken Terminal of New Jersey in 2016 which resulted to the death of a woman were also linked to sleep issues after accident investigations [5]. However, the drivers were not investigated after the crashes nor screened for sleep apnea. Due to limited evidence and information in this regard, more investigation into train drivers’ health is warranted.

This is a cross sectional study that did not have as its objective the evaluation of participants’ sleep disordered breathing. The evaluation of subjective symptoms during annual occupational health assessments may be inconclusive and requires objective assessments and or execution of such evaluations in. Thus, one limitation of the present study is that the participants were not evaluated in terms of breathing disorders. The examination of participants during annual occupational health assessment is done subjectively without objective assessment such as overnight polysomnography test as a gold standard for diagnosis of sleep apnea. As well, the study samples should have also been evaluated in non-occupational settings.

It is recommended that future investigations should be conducted with a larger sample size and screening of train drivers for sleep apnea risk factors and also the ways which can enhance their sleep quality through interventions in sleep postures or sleep platform [16, 17] using objective measurements and subsequent sleep laboratory evaluations.

5 Conclusions

The findings indicate that locomotive drivers have a high prevalence of OSA-RFs. According to available evidence regarding important role of sleep apnea in accidents of transportation system and along with lack of criteria for screening of OSA among locomotive drivers, the revision of current examination standards in this population seems necessary. Sleep apnea is considered an important preventable risk factor for traffic accidents. Therefore, further research is required to re-evaluate the current screening regulations for sleep apnea diagnosis among locomotive drivers.

Conflict of interest

None to report.