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Coming as a surprise to the researchers, the recent study showed that people who did not have a large heart rate response to a stress task would experience more distress related to COVID-19. Previous work shows individuals with post-traumatic stress disorder (PTSD) have higher responses to stress.

But very few studies have examined heart rate responses to acute stress before the onset of a traumatic event, researchers said.

“The study shows that diminished biological arousal — how the body responds when it is exposed to something startling or stressful — before a global pandemic may predict PTSD symptoms related to the event,” said principal investigator Annie T. Ginty, Ph.D., assistant professor of psychology and neuroscience at Baylor University.

The biological reactions were measured by blood pressure and heart rate, said co-author Danielle Young, Psy.D., research coordinator in the Baylor Behavioral Medicine Lab.

The study, published in the journal Psychosomatic Medicine, grew out of an ongoing study of undergraduate students at Baylor University.

“The research also showed that some college students were experiencing distress related to the pandemic in its earliest stages, even when social distancing was just beginning,” Ginty said.

In the study’s first phase, with 120 participants, researchers measured their resting heart rate and blood pressure before and during a standard acute psychological stress test. They asked students to do mental math, rather than writing down figures or using a calculator, and give the scorers verbal responses.

In a four-minute test, they were asked to add consecutive single-digit numbers while remembering the most recent and adding it to the next number presented. They did this while being videotaped with a scorer present and looking at themselves in a mirror.

“The standard acute psychological stress task is meant to increase levels of stress by including requirements of cognitive effort, social evaluation, self-evaluation and competition. The task substantially increases heart rate and feelings of stress,” Ginty said.

The study’s first phase, which ended in February 2020, was done in Central Texas. After the pandemic’s onset, researchers launched a second phase between March 26 and April 5, sending participants a follow-up questionnaire about COVID-19.

The participants were in 22 states after early campus closure due to COVID-19. When asked, none had tested positive for COVID-19 and 87.5 percent were living in a city/state with a “shelter in place” order.

The questionnaire included standard items used to measure PTSD symptoms of intrusion (dreaming about the event and having trouble staying asleep), hyperarousal (irritability and having trouble concentrating) and avoidance (trying not to think or talk about the event) in the seven days before they responded to the questionnaire.

The findings are in line with a previous study of soldiers, which showed that a lower response of cortisol — the primary stress hormone — to an acute psychological stress task before deployment predicted greater PTSD symptoms post-deployment