Sean McCarraher hits the gym or does yoga several times a week, and he lays off fatty and sugary foods. At 5'11" and 194 pounds, he is technically a bit overweight, but it is mainly muscle. The 44-year-old has hereditary high blood pressure but keeps it under control with medicine. All good for his heart.

Yet there is one constant presence in his life that may have the opposite effect: The pager on his belt.

McCarraher is a volunteer firefighter with Limerick Fire Co., one of two dozen emergency responders who took part in an unusual Ursinus College study this year, wearing a cuff that automatically measured blood pressure every 30 minutes while on call. When their pagers went off, the participants' blood pressure readings spiked — a result of that well known "fight-or-flight" response that happens to anyone confronting danger.

But for firefighters, who face the added stresses of breathing hot, smoky air and lugging heavy gear, these adrenaline-fueled spikes in blood pressure can be cause for concern. Half of all on-the-job firefighter deaths are caused by a heart problem, in most cases a sudden cardiac arrest.

The Ursinus study was unusual for another reason. It was conducted by one of McCarraher's fellow Limerick firefighters: Deborah Feairheller, an assistant professor of health and exercise physiology at the liberal-arts school in Collegeville.

A firefighter for five years, Feairheller likes to remind her peers that the heart is a pump, which needs care and maintenance just like the pumps on Limerick's signature green fire trucks with the shamrock logo.

"And our blood vessels are the fire hose," she said.

Her goals are to identify risk factors that may make certain firefighters prone to higher blood-pressure spikes, and to recommend exercise programs and other lifestyle changes to keep them healthy and fit for duty.

Blood pressure is in the spotlight lately, with the announcement this month of stricter national guidelines that mean millions of additional Americans are now defined as having hypertension. Readings of at least 130 for systolic pressure or above 80 for diastolic pressure are considered to increase the risk of heart attack and stroke.

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But that is baseline blood pressure. A short-term rise to those levels, in response to a threat, poses no problem for someone in good health. The danger arises when obesity and other heart disease risk factors are present.

While Feairheller’s study is continuing, so far she and colleagues have found that when the alarm goes off, the systolic blood pressure number rises by about 23 and diastolic pressure by 15. Those with higher surges in diastolic pressure also had higher blood glucose levels, on average — a potential sign that those firefighters need to pay extra attention to their cardiovascular health. In several cases, blood pressure readings remained elevated for more than an hour following an alarm, another worrisome sign.

Four bags of I.V. fluid

And during a long, grueling effort to put out a fire, blood pressure can actually go down, but not in a good way. A previous study found that after just 18 minutes of battling a fire, a firefighter can sweat so much that plasma volume declines by 15 percent, thickening the blood into a clot-prone “pro-coagulatory” state.

So drinking water is crucial, as McCarraher knows all too well. On a hot summer day in 1993, he pushed himself too hard on a fire at the old B.F. Goodrich tire plant in Oaks, and collapsed. He was taken to a nearby hospital and given four bags of I.V. fluid.

For Feairheller’s study, McCarraher wore a blood-pressure cuff for several uneventful days in April. When he finally got a call one evening, his readings surged to 138 over 84, up from an average of 112 over 63 during the 10 hours before that.

It turned out to be a false alarm, and his readings soon returned to normal. But that initial surge was a familiar feeling after 28 years of experience.

“With the adrenaline rush, when your pager goes off, you jump on the truck,” he said. “Your heart just races, no matter how many years you’ve been in the service.”

Most study participants were firefighters from Montgomery and Chester Counties; several emergency medical technicians and paramedics took part as well.

The findings drew a thumbs-up from Harvard Medical School professor Stefanos Kales, who has studied firefighter health for 25 years.

“It’s nice work,” he said. “It underlines the fact that these people, they’re doing a great public service, but we have to keep them in good health.”

As obese as the rest of us

Kales stressed that on-duty death from heart disease is not a big risk for firefighters who are in good shape. Among the 50 or so firefighters who die on the job from a heart “event” each year — a sudden cardiac arrest or, less often, a heart attack — most have underlying heart disease, he said.

And in that respect, the firefighting population mirrors the rest of the United States. At least one-third of career firefighters are obese, which can lead to an enlarged heart and a risk of abnormal rhythm. Among volunteer firefighters, many of whom work in sedentary day jobs, close to half are obese, said Kales, chief of occupational medicine at Cambridge Health Alliance in Massachusetts.

The Limerick Fire Co. takes the matter seriously, requiring regular physicals for its members and adding a gym to a new firehouse that opened this year. A volunteer nutritionist helps them plan meals.

Meanwhile in Philadelphia, the fire department began requiring physical exams for its members in 2016 for the first time in decades. Designated members of the firefighters union also serve as personal trainers, available to work with any of their peers upon request.

Functional fitness

Exercise is a smart idea, said Feairheller, who also volunteers for a fire squad in Collegeville. She conducted a separate study of “functional fitness,” putting firefighters through a series of six job-related exercises over a period of four weeks — such as carrying a 40-pound, rolled-up hose for 100 feet and climbing a ladder while lugging a 20-pound tool.

Even after that short intervention, average blood pressure declined in study participants, she and her colleagues reported. That was a good sign, as chronic high blood pressure suggests the heart is working too hard and may become enlarged.

Among the participants was McCarraher, who is driven partly by the memory of his late father — also a longtime volunteer firefighter — who suffered three heart attacks before dying of cancer. In addition to his yoga and gym sessions, McCarraher stays active in his job in quality control for a medical-device maker, walking back and forth between company buildings 10 times a day. And he follows the study results from his fellow firefighter, whom he calls “Dr. Deb.”

After all, his heart depends on it.

“The last thing I want to do,” McCarraher said, “is become a victim to my crew on the fire scene.”