Heart disease kills firefighters. This one is also a scientist, and she is fighting back.

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.