These two factors are related to truck crashes but researchers don't know why

When Matthew Thiese and his team set out to learn why truck drivers crash, they looked at about 25 different variables including age, gender, weight, experience, heart disease, feeling tense, low back pain as well as alcohol and tobacco use. After recruiting drivers at truck stops, truck shows and on line – and ultimately including 797 in their analysis – three factors consistently stood out: pulse pressure, feeling physically exhausted after work and cell phone use.

While cell phone use makes intuitive sense as a crash factor, because of the obvious distraction, the other two factors – pulse pressure and feeling physically exhausted after work - are baffling, says Thiese, Assistant Professor at the University of Utah’s Rocky Mountain Center for Occupational and Environmental Health. His work was supported by the federal government.

"In terms of looking at crash risk, I was surprised that feeling physically exhausted after work was related to being involved in a crash," he says, "but then I was also surprised at how many drivers had uncontrolled hypertension or uncontrolled high cholesterol, so those two were both surprising to me, too - more so the hypertension." He notes that many drivers who said they were on medication, about 100 of the participants, still had high blood pressure. "I was surprised by that. I would've thought there would be more  people who had it under control especially because they need certification every two years to drive. There are no outward signs of high blood pressure and some medications have side effects which affects compliance. I absolutely understand that, but it was still surprising."

The study, funded by the National Institute of Occupational Safety and Health, part of The Centers for Disease Control and Prevention, had a specific goal of looking at doing a large study of truck drivers to describe their health. "There's really not much out there looking at it," Thiese says. "To my knowledge this is the largest study that's ever address all of these different factors. Our objective was to look at these data and how they associate with crashes."

In future studies, Thiese wants to learn why pulse pressure and feeling physically exhausted correlated so high with crashes. "We know that these medical conditions occurred before the crash, so it's more suggestive of causation. We're working on a grant to actually perform a longitudinal study, where we enroll drivers and actually follow them through time, so that we can really get a handle on that strength of relationship between the predictive elements of a medical factor and having a subsequent crash."

[Note: Pulse pressure is different than blood pressure which reads the diastolic and systolic pressures like 120/80. Pulse pressure is the difference between the two and represents the force that the heart generates each time it contracts. A high pulse pressure is believed to be a predictor of cardiovascular disease.]

What can drivers take away from the study?

"I want drivers to consider that there is not one risk factor for being involved in a crash. There are a lot of different factors, which also gives drivers many opportunities to try and reduce their own crash risk. There's been a lot of focus on sleep apnea. There's increasing focus on diet and exercise, and for some drivers, positive changes are feasible. There are other things that they can do, but for some drivers, it's just really hard to eat healthy, or they don't for one reason or another."

He concludes: "Being physically exhausted after work, your pulse pressure, not talking on a cell phone - these are three very different things that, in theory, if you're able to address, you should be able to reduce your crash risk."

The study was published in the October, 2015 issue of Journal of Occupational & Environmental Medicine.

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