Public Release: 

Study reveals sleepiness and performance impairment in commercial drivers

American Thoracic Society

Truck drivers who have severe sleep apnea or who sleep less than five hours each night while at home are more likely to suffer from sleepiness, performance impairment and decreased task vigilance while behind the wheel.

The results of this large study of commercial truck drivers appear in the second issue for August 2006 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.

Allan L. Pack, M.B., Ch.B., Ph.D., of the University of Pennsylvania, and six associates tested 247 commercial drivers at high risk for sleep apnea and 159 at lower risk for sleep impairment. They evaluated the role of short sleep duration at home over one week in 340 drivers, with 55 sleeping less than five hours. Of the 406 drivers examined for sleep apnea, 118 had mild to moderate forms of the disease, and 28 had severe sleep apnea.

"In the United States, approximately 5,600 people are killed annually in crashes involving commercial trucks," said Dr. Pack. "Falling asleep while driving is an important factor in serious crashes involving commercial vehicles, prompting the question, why?" According to the authors, the two culprits are chronically insufficient sleep and obstructive sleep apnea.

The researchers defined mild to moderate sleep apnea as "from 5 to less than 30 temporary breathing pauses per hour of sleep," a process that decreases the amount of oxygen in the blood. Severe sleep apnea, on the other hand, involves more than 30 breathing pauses per hour.

However, the investigators also found that 77 percent of those with mild sleep apnea and 56 percent of with moderate sleep apnea did not have what could be termed "pathologic sleepiness" as a result of their problem.

The authors used the Epworth Sleepiness Scale to assess subjective sleepiness, the Multiple Sleep Latency Test to objectively determine the driver's propensity to fall asleep, and the Psychomotor Vigilance Task to assess behavioral alertness and define vigilance lapses. These tests were administered in addition to a normal sleep test (polysomnography) to measure breathing pauses and movement disorders in the sleep laboratory.

"In this study, we showed that both subjective and objective sleepiness, as well as performance impairments are common in our sample of commercial driver's license holders," said Dr. Pack. "Our analyses reveal that chronic short sleep duration is a risk factor for subjective sleepiness, objectively measured sleepiness and performance impairments. The results for sleep apnea are less clear."

The percentage of drivers with two or three performance impairments among those with less than 5 hours of sleep was 49.5 percent.

Of the 406 drivers tested, 93.3 percent were male and were over 45 years old. At the time of the study, 81.6 percent were employed as drivers of a commercial vehicle. All participants had a commercial driver's license.

"When we examined definitions of impairment for Psychomotor Vigilance Task Performance lapses and Divided Attention Driving Task tracking error based on data comparing results with those produced by alcohol intoxication, we found that slightly over 29 percent for lapses and almost 37 percent for mean tracking error had performance decrements compared to that induced in control subjects, albeit in different populations, after alcohol intoxication," said Dr. Pack.

The authors noted that these results should encourage the Federal Motor Carrier Safety Administration to reduce sleepiness and potential crash risk in commercial drivers. They suggest that the agency should develop plans to implement ways of identifying "sleep-impaired" drivers through objective testing, to identify and treat individuals with severe sleep apnea and to monitor their adherence to therapy, and to promote increased sleep duration among commercial drivers.


Allan I. Pack
M.B., Ph.D., Ch.B.
125 South 31st Street, Suit 2100
Philadelphia, PA 19104-3403
Phone: (215) 746-4806

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