Effects of Alcohol and Sleep Restriction on Simulated Driving Performance in Untreated Patients With Obstructive Sleep Apnea

Context Obstructive sleep apnea (OSA) is associated with sleepiness and poor concentration, symptoms that could impair driving performance. Contribution This study evaluated simulated driving performance in 38 patients with untreated OSA and 20 control participants under 3 conditions: unrestricted sleep, sleep restriction, and consumption of alcohol. Compared with control participants, patients with untreated OSA had worse simulated driving performance. Patients with OSA also had greater decrements in driving performance after sleep restriction and after alcohol consumption. Implication Consider alerting patients about the potential negative influence of untreated OSA on driving performance and their heightened vulnerability after sleep deprivation and alcohol consumption. The Editors Obstructive sleep apnea (OSA) causes excessive daytime somnolence and reduced vigilance, concentration, and neurocognitive function (1, 2). Patients with OSA, particularly those with moderate to severe disease, have a 2- to 7-fold increased risk for motor vehicle accidents (310). Community surveys have shown that approximately 7% of the middle-aged population has at least mild OSA (>10 obstructive events per hour of sleep) (1113), and up to 80% of these cases are undiagnosed (1416). For patients whose condition is diagnosed, delays in instituting treatment are common (17). Between 46% and 83% of patients do not adhere to treatment over the long term (18). The many patients with undiagnosed or untreated OSA represent a serious public health concern with respect to road safety. Accidents related to OSA result in an estimated 1400 road fatalities and cost $15.9 billion annually in the United States alone (19). Improving access to diagnosis and treatment may help reduce this public health burden. However, even with improved sleep medicine services, many unidentified or untreated patients with OSA will probably remain at increased risk for motor vehicle accidents. A better understanding of the factors contributing to motor vehicle accidents among patients with OSA is therefore needed to develop cost-effective prevention strategies. This study was designed to compare the effects of 2 common lifestyle factors, low-dose alcohol and acute partial sleep deprivation, on driving simulator performance between untreated patients with OSA and healthy matched control participants. We postulated that because of previous chronic sleep disruption and possible hypoxia-induced brain damage (2, 2026), patients with OSA would be more vulnerable to the effects of these common, mild central nervous system stressors and would experience significantly greater decrements in driving performance. Methods The study was approved by the Human Research Ethics Committees of the Repatriation General Hospital, University of South Australia, and University of Adelaide. Participants were introduced to the study objectives and protocol during an introductory session, gave written informed consent, and were remunerated for their participation. Study Design Patients with OSA and control participants underwent driving simulator assessments under 3 conditions that were presented in random and counterbalanced order: after a normal nighttime sleep, after a single night of sleep restriction (4 hours in bed from 2:00 a.m. to 6:00 a.m.), and after acute administration of low-dose alcohol (target blood alcohol concentration, 0.05 g/dL). All driving simulator sessions began at 2:00 p.m. and were conducted at least 5 days apart to avoid carryover effects from the previous interventions. Participant Selection Thirty-eight untreated patients with OSA of varying severity were recruited after diagnostic polysomnography. Neither they nor their referring physician had specific concerns about their driving. To minimize selection bias, patients were told that the study objective was to investigate general neurocognitive performance; they were unaware that the trial measured driving performance until after they agreed to attend an introductory session. Twenty healthy control participants matched for age and sex were recruited from the general population through newspaper advertisements, which only generally described the study and did not mention driving performance measures. Exclusion criteria were employment as a professional driver or shift worker; history of driving less than 2 years or less than 2 hours per week; notable medical comorbid conditions (such as cardiac or respiratory failure), periodic limb movement disorder (periodic limb movement arousal index >5 per hour), or past head injury or depression; use of alertness-altering prescription medications that may change neurocognitive function (such as antihistamines, opiates, or antidepressants); and history of alcohol abuse or current use of recreational drugs. Control participants were also excluded if they had higher-than-normal scores on sleep quality and daytime drowsiness questionnaires. Baseline Measures Before the driving simulator assessment, all participants completed questionnaires that evaluated general health (medical conditions, medication, alcohol intake, caffeine and drug use), sleep quality and habits, and daytime drowsiness using the Pittsburgh Sleep Quality Index (27) and the Epworth Sleepiness Scale (28). All participants underwent overnight standard diagnostic polysomnography with the following recordings: electroencephalography (C3/A2, C4/A1 lead placements), left and right electrooculography, submental electromyography, nasal cannulization to measure nasal pressure, limb movement sensors, inductive plethysmography for thoracoabdominal motion, lead II electrocardiography, and finger pulse oximetry (to measure arterial oxygen saturation). All signals were digitized and stored by using a Compumedics-E Series sleep system (Melbourne, Australia). Sleep and sleep arousals were scored by using standardized methods (29, 30). Apneas and hypopneas were scored according to internationally agreed-on criteria (30). All studies were scored by 1 staff member certified by the Board of Registered Polysomnographic Technicians. Table 1 shows participant characteristics, sleep study results, caffeine and alcohol consumption, and medication use. Table 1. Patient Characteristics, Polysomnography Results, and Medication Use Main Outcome Measures The main outcome measures were performance on the driving simulator, including lateral steering deviation, braking reaction time, crash frequency, and precrash electroencephalography and electrooculography results. Driving performance was assessed by using the AusEd driving simulator (Woolcock Institute for Medical Research, Sydney, Australia), which ran on a purpose-built Windows 2000 workstation (Microsoft, Redmond, Washington) with a 19-inch FP937s monitor (BenQ, Taipei, Taiwan); the MOMO steering wheel and pedals (Logitech, Fremont, California) were used to assess the driving variables. Steering deviation was measured as the average deviation in centimeters from the driver's median lane position sampled at 30 Hz. Participants were instructed to maintain speed within 60 to 80 km/h but to apply the brakes as quickly as possible whenever a slow-moving truck appeared ahead in the driving lane. The latter occurred 7 times during the drive, and the mean braking reaction time was computed for the 7 truck-ahead incidents. Crashes occurring throughout the driving task were defined as follows: car deviating from the road (all 4 wheels completely off the road), collision with a truck, or stationary position of the car for more than 3 seconds. The main outcome measure for crashes was the number of control participants and patients with OSA who experienced at least 1 crash incident. A secondary crash analysis was undertaken to determine whether crashes were associated with brief falling-asleep episodes and prolonged eye closures. Fifteen-second epochs of electroencephalography, electrooculography, and synchronized video (head and shoulders) before each crash (crash epoch) were scored for the presence of prolonged eye closure (>2 seconds) and microsleeps (>2 seconds of continuous electroencephalographic theta activity) within each crash epoch. A random sample of an equal number of 15-second noncrash epochs was selected and matched within participants and condition so that they could be compared with the crash epochs. The simulated driving task used in the study consisted of a 90-minute country nighttime drive on a predominantly straight dual-lane road with bends occurring at 10-minute intervals, each taking approximately 30 seconds to negotiate. There was no oncoming traffic or traffic lights. Driving simulator studies have been shown to correlate reasonably well with on-road driving (31, 32), and the AusEd simulator has been validated and shown to be sensitive to fatigue in a range of experimental settings (3337). Detailed Experimental Procedures For all 3 conditions, participants' sleep patterns and duration were monitored throughout the study by using actigraphy monitors (Actiwatch Model-AW64, Mini-Mitter Co., Bend, Oregon) worn from at least 5 days before the experiments began until study completion to estimate sleep/wake timing, to ensure adherence to the sleep restriction protocol, and to ensure that patients did not nap in the 24 hours before the experiments (38). In addition, during the night of sleep restriction, participants left a message on a time- and date-stamped answering machine at bedtime (2:00 a.m.) and wake time (6:00 a.m.), again to ensure adherence to the protocol. Participants were instructed to abstain from alcohol and caffeinated beverages, not to nap for 24 hours before each experimental session, and to consume breakfast before 9:00 a.m. on the day of each experiment. They were transported by taxi to and from the laboratory. Upon arrival at the laboratory at 12:00 p.m. , each participant's blood alcohol concentration was estimated by using a calibrated breathalyzer (Alcotest7