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Volume 11 No. 04
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Accepted Papers





Scientific Investigations

Obstructive Sleep Apnea, Health-Related Factors, and Long Distance Heavy Vehicle Crashes in Western Australia: A Case Control Study

Lynn Meuleners, PhD1; Michelle L. Fraser, MPhil1; Matthew H. Govorko, MPH1; Mark R. Stevenson, PhD2
1Curtin-Monash Accident Research Centre (C-MARC), Curtin University, Perth, Australia; 2Monash University Accident Research Centre (MUARC), Monash Injury Research Institute, Monash University, Melbourne, Australia

ABSTRACT

Study Objectives:

To determine the association between obstructive sleep apnea (OSA), health-related factors and the likelihood of heavy vehicle crashes in Western Australia (WA).

Methods:

This case-control study included 100 long-haul heavy vehicle drivers who were involved in a police-reported crash in WA during the study period (cases) and 100 long-haul heavy vehicle drivers recruited from WA truck stops, who were not involved in a crash during the past year (controls). Driver demographics, health, and fatigue-related characteristics were obtained using an interviewer administered questionnaire. Drivers were tested for OSA using a diagnostic Flow Wizard. Logistic regression was used to determine health-related factors associated with crash involvement among long distance heavy vehicle drivers.

Results:

Heavy vehicle drivers diagnosed with OSA through the use of the FlowWizard were over three times more likely to be involved in a crash than drivers without OSA (adjusted OR: 3.42, 95% CI: 1.34–8.72). The risk of crash was significantly increased if heavy vehicle drivers reported a diagnosis of depression (adjusted OR: 6.59, 95% CI: 1.30–33.24) or had not completed fatigue management training (adjusted OR: 6.05, 95% CI: 1.80–20.24). Crash risk was 74% lower among older drivers (> 35 years) than younger drivers (adjusted OR: 0.25, 95% CI: 0.08–0.82).

Conclusion:

The results suggest that more rigorous screening and subsequent treatment of OSA and depression by clinicians as well as compulsory fatigue management training may reduce crashes among heavy vehicle drivers.

Commentary:

A commentary on this article appears in this issue on page 409.

Citation:

Meuleners L, Fraser ML, Govorko MH, Stevenson MR. Obstructive sleep apnea, health-related factors, and long distance heavy vehicle crashes in western Australia: a case control study. J Clin Sleep Med 2015;11(4):413–418.


Heavy vehicle crashes contribute significantly to the burden of death and injury on Australian roads. During the 12 months to the end of March 2010, 245 people died from crashes involving heavy vehicles in Australia.1 Previous research has indicated that heavy vehicle drivers are at an increased risk of chronic conditions as well as reporting a higher prevalence of risk factors such as cigarette smoking and physical inactivity.2,3 However, few studies have examined the association between specific health factors and a heavy vehicle crash.

There is considerable evidence linking fatigue and safety outcomes in the transport industry. In Australia, of 461 heavy vehicle crashes occurring during 2011 that resulted in losses greater than AUS$50,000, fatigue was established as the principal cause for 11.9%.4 Fatigue was also found to be the second most common cause of a heavy vehicle crash after speeding.4 In Western Australia (WA) specifically, an increase in fatigue-related incidents consistently occurred between 2003 and 2011.4 Similarly, results from the United States and New Zealand indicated driver fatigue was the main factor in 13% and 18% of truck crashes, respectively.5,6

A frequently recommended fatigue countermeasure is driver education, however the efficacy of such training is seldom evaluated.7 Despite comprehensive literature citing fatigue as a significant contributing factor in heavy vehicle crashes, no studies have examined the relationship between fatigue management training and subsequent risk of crash involvement.

BRIEF SUMMARY

Current Knowledge/Study Rationale: Evidence suggests that heavy vehicle drivers are at increased risk of obstructive sleep apnea and other chronic conditions. However, few studies have examined the association between obstructive sleep apnea, specific health conditions, and crashes among long-haul heavy vehicle drivers.

Study Impact: This study found that long-haul heavy vehicle drivers with obstructive sleep apnea, depression and those who had not undertaken fatigue management training were at a significantly increased risk of crash involvement. More rigorous screening and subsequent treatment of OSA and depression by clinicians as well as compulsory fatigue management training may reduce crashes among heavy vehicle drivers.

Recently, a large case-control study of long distance heavy vehicle drivers was conducted in New South Wales (NSW) and WA.811 However, WA has a unique road environment with vast distances between locations, extreme temperatures and weather conditions, and monotonous scenery.12 WA is also governed by different fatigue regulations from the rest of Australia and faces specific challenges for heavy vehicle safety. To date, little research has been conducted into risk factors for heavy vehicle crashes in WA. Therefore the aim of this study was to examine the association between OSA, health-related factors and the likelihood of heavy vehicle crash involvement in WA.

METHODS

Study Design and Participants

This paper describes results from the WA component of a case-control study conducted in WA and NSW, Australia. All participants were driving a commercial vehicle of ≥ 12 tonnes in tare weight and were undertaking a trip ≥ 200 km from their WA truck-base at the time of a crash (cases) or being approached for an interview (controls).

Cases consisted of 100 long distance heavy vehicle drivers who were involved in a police-reported crash in WA between January 2009 and November 2011. Potential cases were excluded if the crash resulted in a fatality, the heavy vehicle driver was seriously injured (admitted to hospital for two or more weeks or lost consciousness), or if they were driving a bus or coach.

Controls consisted of 100 long distance heavy vehicle drivers who had not been involved in a police-reported crash in the previous 12 months. Controls were also excluded if they were driving a bus or coach. The study was approved by the Curtin University Human Research Ethics Committee, Perth WA.

Case Recruitment

The WA Police sent contact details of commercial drivers involved in a police-attended crash in WA to the study team weekly. Drivers were then sent a letter of invitation to participate in the study, and trained interviewers made telephone contact with the potential participants. Of the 1,155 heavy vehicle drivers identified from Police records, 977 were not eligible to participate in the study due to weight/type of vehicle, length of trip, or missing contact details. While 178 drivers met the eligibility criteria for the study, 100 agreed to participate (56%).

Control Recruitment

Control drivers were recruited from 4 truck stops across WA between July 2009 and November 2011. The truck stops were chosen to cover all major trucking routes in WA. Recruitment took place across different days and months to ensure varied travel patterns of heavy vehicle drivers. Interviewers approached heavy vehicle drivers entering the truck stop. Those drivers who agreed to participate were interviewed at the truck stop or by phone at a later convenient date.

A total of 256 heavy vehicle drivers were approached to participate in the study. Eligibility status was obtained for 83% (n = 215) of drivers, and 136 met the inclusion criteria. Reasons for ineligibility (n = 79) included weight/type of vehicle, length of trip, or involvement in a heavy vehicle crash in the previous 12 months. A total of 100 controls were recruited from 4 truck stops, 50 from Kewdale, 20 from Upper Swan, 17 from Meekatharra, and 13 from Overlander, yielding a response rate of 73.5%.

Data Collection

Data collection consisted of 2 parts; a 40-min interviewer-administered questionnaire and sleep monitoring. All participants received study information sheets and provided informed consent.

Driver body mass index (BMI) was calculated from self-reported height and weight data. Health conditions diagnosed by a doctor (including depression), regular prescription medication usage, exercise participation in the past month, and smoking status were also self-reported. Consumption patterns of caffeinated substances consumed for the purpose of staying awake during the past month were recorded, including coffee, energy drinks, tea, soft drinks, and caffeine tablets. Participants were also asked whether they had undertaken any fatigue management training. Finally, drivers reported how many police-reported crashes they were involved in as a heavy vehicle driver during the last 5 years, regardless of fault.

In order to test for OSA, drivers who consented were sent a diagnostic Flow Wizard (DiagnoseIT, Sydney, Australia) device to wear overnight during their sleep. This device is a validated nasal pressure transducer that noninvasively measures an individual's airflow during sleep. Wong et al.13 previously validated the diagnostic accuracy of Flow Wizard (used at home) for correctly identifying OSA compared with polysomnography administered under full laboratory conditions. The flow monitor device was demonstrated to have good accuracy in detecting the presence of OSA, with an area under the curve (AUC) of 0.96, and at its apnea hypopnea index (AHI) threshold of 18; the sensitivity was 0.85–0.92, and specificity 0.81–0.86. In detecting severe OSA, reported sensitivity is 0.80–0.91 and specificity 0.75–0.89 at an AHI threshold of 30.13 It should be noted that the measure of sleep time is based on the length of recording only. Participants are asked to press a button on the recorder to turn it on and off, or it automatically turns off after 8 hours. Periods of no or poor signal are excluded from the sleep time (for example, if the device is turned on but is not being worn). This method may overestimate the sleep time, and this is a source of measurement error for the device. The devices provided an apnea-hypopnea index (AHI), and drivers with an index greater than 17 were considered to have OSA.8

Statistical Analysis

Descriptive statistics and unadjusted odds ratios (ORs) were used to compare case and control drivers. Logistic regression was then used to determine health-related factors associated with crash involvement among long distance heavy vehicle drivers, while controlling for confounding factors. Factors included in the model were age, (≤ 35 years, > 35 years), BMI (overweight or obese, normal), smoking status (smoker, non-smoker), diagnosed health conditions (yes, no), diagnosis of depression (yes, no), use of prescription medications (yes, no), use of caffeine to stay awake (yes, no), regular exercise (yes, no), completed fatigue training (yes, no), involved in a crash in previous 5 years (yes, no), and OSA as indicated by the Flow Wizard (yes, no).

RESULTS

Control drivers ranged from 22 to 68 years of age, with a mean age of 45.1 years (SD 9.5). Case drivers ranged in age from 22 to 74 years of age, with a mean age of 44.8 years (SD 11.8). Eighty-five percent of controls and 74% of cases were aged > 35 years (Table 1). The majority of controls (98.0%) and cases (99.0%) were male.

Demographic and health characteristics of long distance heavy vehicle drivers who crashed (cases) and those who did not crash (controls) during the previous 12 months in Western Australia, 2009–2011.

 

jcsm.11.4.413.t01.jpg

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Table 1

Demographic and health characteristics of long distance heavy vehicle drivers who crashed (cases) and those who did not crash (controls) during the previous 12 months in Western Australia, 2009–2011.

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Control drivers had a mean BMI of 29.2 (SD 4.8), and cases had a mean BMI of 30.6 (SD 5.5). The majority of control (85.0%) and case (81.0%) drivers were either overweight or obese (BMI ≥ 25). Nearly half of the control (46.0%) and case (49.0%) drivers were cigarette smokers (Table 1).

A large proportion of control (65.3%) and case (62.0%) drivers reported that they did not participate in any regular exercise during the previous month (Table 1). Among control drivers, 44.0% reported that they had at least one health condition, the most common conditions being high blood pressure (16.0%), diabetes (10.0%), and gastric disorders (7.0%). Three percent of control drivers reported they had a diagnosis of depression. Among case drivers, 45.0% reported at least one health condition, the most common being high blood pressure (16.0%), depression (12.0%) gastric disorders (8.0%), and heart disease (7.0%). A similar proportion of case (20.0%) and control (22.0%) drivers self-reported taking prescription medication on a regular basis (Table 1).

Eighteen percent of control drivers and 15.0% of cases reported consuming caffeine for the purpose of staying awake during the past month. A larger proportion of controls (92.0%) than cases (72.0%) reported that they had received driver fatigue training (Table 1).

In total, 65 controls and 63 case drivers wore the diagnostic Flow Wizard device overnight. Of these, 23 control and 31 case drivers had an AHI > 17 and were therefore considered to have OSA (Table 1).

Table 2 presents the multivariate model of OSA and health-related factors associated with crashes among long distance heavy vehicle drivers in WA.

Association between obstructive sleep apnea, health-related factors and crashes among long distance heavy vehicle drivers in Western Australia.

 

jcsm.11.4.413.t02.jpg

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Table 2

Association between obstructive sleep apnea, health-related factors and crashes among long distance heavy vehicle drivers in Western Australia.

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Heavy vehicle drivers diagnosed with OSA were over 3 times more likely to be involved in a crash than drivers without OSA (adjusted OR: 3.42, 95% CI: 1.34–8.72) after accounting for potential confounders. Drivers diagnosed with depression were almost 7 times more likely to be involved in a crash than those without depression (adjusted OR: 6.59, 95% CI: 1.30–33.24). Drivers who had not completed fatigue management training were also 6 times more likely to have been involved in a crash (adjusted OR: 6.05, 95% CI: 1.80–20.24). Crash risk was 74% lower among older drivers (> 35 years) than younger drivers (adjusted OR: 0.25, 95% CI: 0.08–0.82).

DISCUSSION

This study identified several sleep and health-related factors associated with involvement in long-haul heavy vehicle crashes in WA. The study found that heavy vehicle drivers diagnosed with OSA were at increased risk of a crash. While several studies and a systematic review have reported increased rates of motor vehicle crashes in patients with OSA in the general population,1416 minimal evidence exists specifically for heavy vehicle drivers. Our findings are consistent with Howard et al.,17 who reported NSW commercial truck drivers with a diagnosis of OSA had a 30% greater risk of self-reporting a crash in the previous 3 years. Interestingly however, the pooled analysis of data from the NSW and WA portions of the current study found that OSA was not associated with the risk of a crash.11 While reasons for this difference require further investigation, it is possible that OSA has a greater impact on crash risk for WA drivers due to the vast distances they travel, isolation, monotonous scenery, and harsh climate of WA—all factors which exacerbate the effects of fatigue.

This study confirmed that a much higher proportion of WA heavy vehicle drivers were identified as having OSA (42.2%) than estimated among the general population (approximately 5%).18 It is well known that excess bodyweight and cigarette smoking are 2 major risk factors for OSA.18 Therefore it is not surprising that OSA was more prevalent in this occupational population. In WA, long-distance heavy vehicle drivers must undergo the Health Assessment for Fitness to Drive including a driver health questionnaire and clinical assessment by a doctor. The questionnaire responses are reviewed by the examining doctor and used to guide the clinical examination and any further testing. The driver health questionnaire currently asks drivers to self-report OSA diagnoses as well as symptoms using the Epworth Sleepiness Scale.19 However, findings from the current study suggest that due to the very high prevalence of undiagnosed OSA among heavy vehicle drivers and the association with crash risk, more rigorous screening of OSA using take-home diagnostic devices and subsequent OSA management plans are paramount for reducing crashes among this population.

This is one of the first studies to report that long-distance heavy vehicle drivers who had not undertaken fatigue management training were at significantly increased risk of a non-severe crash. Compulsory fatigue training for long-haul heavy vehicle drivers may therefore represent a relatively simple and potentially effective crash countermeasure. While is it possible that fatigue management training is particularly relevant for heavy vehicle drivers in WA who travel very vast distances in monotonous conditions, it is likely that it would also improve safety for drivers in other States and countries. Further research is also required to determine the most effective type and frequency of fatigue management training for this population.

The current study also found that long-distance heavy-vehicle drivers with a diagnosis of depression were over six times more likely to be involved in a crash than those without depression. This finding is supported by a study of heavy vehicle drivers in NSW that reported severe or very severe depression was associated with an increased risk of a crash.20 Shattell et al. found that a large proportion of drivers with depression do not seek professional treatment.21 Bulmash et al. also reported that patients with untreated depression displayed significantly slower steering reaction times and experienced a significantly increased number of crashes in a driving simulator compared to those without depression.22

In Australia, the 12-month prevalence of affective disorders, including depression in adults aged 16 to 85 years is 6.2% overall and 5.3% for males.23 In the present study, 7.5% of long-distance heavy vehicle drivers (12% cases vs 3% controls) reported a diagnosis of depression. This finding is consistent with previous research undertaken by Meuleners at al., who found heavy vehicle drivers were characterized by numerous health issues including mental health disorders.24 The Health Assessment for Fitness to Drive in WA asks heavy vehicle drivers to simply self-report any “psychiatric disorders.” However, the findings of this study suggest more rigorous assessment using screening tools for depressive symptoms by clinicians might be necessary in order to diagnose and subsequently treat heavy vehicle drivers with depression.

This study also found that heavy vehicle drivers older than 35 years of age had a lower risk of crash involvement than younger drivers and is consistent with previous research.25 This finding suggests that younger drivers may require additional training to improve safety.

This study has several limitations. It used self-reported data, which may have resulted in under-reporting of diagnosed medical conditions including depression and medication usage. However, any under-reporting would likely have been present in a similar degree for both cases and controls. The sample size was also too small to analyze the association between the use of particular types of medication and crash risk. Future research should use larger samples to examine this. Clinical measures including neck circumference and blood pressure could also not be included, since non–face-to-face methods of data collection were used in order to maximize the study response rate. Oxygen saturation could not be measured with the Flow Wizard device, meaning some events may have been incorrectly classified as hypopnea. In addition, details on type, mode, delivery, and frequency of fatigue training were not collected. Information on severity of depression and whether the driver was undergoing treatment are also unknown. These are areas for future research. Finally, missing data pose a limitation on the OSA results.

Despite limitations, this study provides important information about the association between OSA and health-related factors among long-haul heavy vehicle drivers and crash risk. While further research is required, findings from this study suggest that policies requiring mandatory fatigue management training are essential for improving safety in the heavy vehicle industry. In addition, due the high prevalence of OSA and depression among heavy vehicle drivers and their association with increased crash risk, clinicians treating or assessing the fitness to drive of heavy vehicle drivers should undertake more rigorous and accurate assessments of these disorders, in order to reduce heavy vehicle crashes.

DISCLOSURE STATEMENT

This was not an industry supported study. This work was supported by Australian Research Council Linkage grant [LP 0776308]. This study was performed through the Curtin-Monash Accident Research Centre, Curtin University, Western Australia and the Monash University Accident Research Centre, Monash University, Victoria, Australia. The authors have indicated no financial conflicts of interest.

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