BOSTON - People with obstructive sleep apnea syndrome showed poorer vigilance while driving than did normal controls, a result that could not be predicted by pretest measures of disease severity or subjective reports of sleepiness, according to a poster presented by Dr. Jon Tippin at the annual meeting of the American Academy of Neurology.
“[Obstructive sleep apnea syndrome] can now be added to the list of diseases, including dementing illnesses like Alzheimer's disease and Parkinson's disease, that cause vigilance problems [during driving],” said Dr. Tippin, a neurologist at the University of Iowa, Iowa City.
Vigilance was assessed using the Simulator for Interdisciplinary Research in Ergonomics and Neuroscience (SIREN), an interactive driving simulator adapted from a car fitted with projection screens in front of and behind the driver. Drivers were asked to respond by clicking the high-beam control as soon as they detected light targets flashed at unpredictable temporal intervals (average one per minute) at seven locations across the forward horizon. Hit rates (HR) and reaction times (RT) were the outcome measures. The hour-long test was administered in the late afternoon.
The overall hit rate was lower in drivers with obstructive sleep apnea syndrome (OSAS) (n = 25) than in normal controls (n = 41) (P = .018).
The data also suggested that peripheral targets were more likely to be missed by people with OSAS than were those located in the central field of vision (P = .0862). “These people do not have visual field impairments but rather they show inattention to things in the peripheral field. As [drivers] becomes more inattentive, they focus more on the things right in front of them,” said Dr. Tippin.
Although slower reaction times predicted poorer driving performance in all drivers (P is less than.03), there was no difference in mean reaction times between the groups.
People with OSAS were not sleepier than controls before the test, as indicated by the predrive Stanford Sleepiness Scale test. OSAS drivers were sleepier than controls at the end of the drive (P = .027), but only in OSAS drivers did the increased sleepiness correlate with poorer vigilance (as measured by lower hit rates, P = .0135). Objective tests of sleepiness, such as polysomnography and the Multiple Sleep Latency Test done on the evening of and day after the drive, respectively, also did not correlate with vigilance or driving performance.
“For patients with OSAS, the problem is less one of falling asleep than maintaining attention,” said Dr. Tippin.
Factors such as age, obesity, and a sedentary lifestyle raise the risk for OSAS.
For truck drivers, many of whom have several of these risk factors, the likelihood of OSAS may be elevated to four times that of the general population, said Dr. Tippin. Sleep deprivation and fragmentation may compound the problem in this population.
Stakeholders such as the Federal Motor Carrier Safety Administration (FMCSA), the trucking industry, and insurance carriers are working to develop guidelines regarding illness and driving.
Dr. Tippin suggested that OSA should be added to the list of conditions that compromise driving capability.