The June study, which was published in The Journal of Physiology, studied 16 young adults who had a COVID-19 diagnosis several weeks before.
Those patients were put through a series of tests to measure their muscle sympathetic nerve activity (their fight or flight response), blood pressure, heart rate, lung function, and exercise capacity. Their results were compared with young, healthy patients who did not have a previous COVID-19 diagnosis.
The researchers found that the sympathetic nervous system, which oversees the fight or flight response, was overactive in some patients who previously had COVID-19 and underactive in others.
There were a few notable differences in patients who had COVID-19 versus those who hadn’t contracted the virus. Subjects did a “cold pressor test,” where they put their hand in an ice water mixture for two minutes.
Those who didn’t have COVID-19 had a significant increase in their fight or flight activity and blood pressure, while those who had the virus rated their pain as substantially lower than their counterparts.
Researchers also put patients through a test that moved them into an upright position to see how well their body responds. Those who had COVID-19 had a large increase in heart rate during the test and more sympathetic nerve activity than other healthy, young adults who didn’t have COVID-19.
The researchers concluded that the fight or flight response in people who have had COVID-19 may be altered, at least for a period of time afterward, which could be a sign of post-COVID conditions.
“Through our collaborative project, we have been following this cohort of COVID-19 subjects for six months following their positive test results,” senior author Abigail Stickford, PhD, a postdoctoral research fellow at Appalachian State University, said in a press release. “This work was representative of short-term data, so the next steps for us are to wrap up data collection and interpret how the subjects have changed over this time.”
Doctors Say More Research Is Needed
Research previously suggested a link between postural tachycardia syndrome (POTS), a condition that causes an abnormal increase in heart rate that happens after someone sits or stands, and long COVID.
These findings only add to that, infectious disease expert Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security, tells Verywell.
“It’s becoming evident that there is some dysfunction with the autonomic nervous system in certain patients with COVID,” Adalja says. “This might be occurring because of a direct effect of the virus on those parts of the central nervous system responsible for sympathetic activity.”
It could also happen due to inflammation, the impact of the virus on the vascular system, or a combination of these factors, he says.
Adalja points out that some people who developed POTS after a COVID-19 infection have seen “some improvement” with proper treatment. “It will be important to see if those treatments have an impact here and what the prognosis is,” he says.
But John Sellick, DO, an infectious disease expert and professor of medicine at the University at Buffalo/SUNY in New York, tells Verywell that the findings are difficult to parse out.
“You can’t deny any of it,” he says. “The problem is that there’s so much variability from person to person with the sympathetic nervous system.”
Meaning, the way one person’s sympathetic nervous system reacts to a stimulus can be very different from how another person’s sympathetic nervous system reacts, regardless of whether they previously had COVID-19.
“We have to be careful that we don’t over-extrapolate too much from this,” he says. Still, Sellick anticipates that more people will study this association.
“This is probably going to be a first step in what will wind up being even more research,” he says.
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