New research suggests that young people may experience changes to the sympathetic nervous system after recovering from COVID-19.
The sympathetic nervous system governs the “fight-or-flight” response.
A study suggests that young adults who recently recovered from COVID-19 have increased activity in this branch of their nervous system while at rest.
Compared with controls, they had higher sympathetic nerve activity and a faster heart rate in a test designed to simulate standing up.
If similar disturbances occur in older adults after COVID-19, there may be serious adverse effects on their cardiovascular health.
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Around a third of otherwise healthy people who have recovered from mild COVID-19 experience the lingering symptoms of long COVID.
The most common symptoms include fatigue and shortness of breath, but some individuals also report heart palpitations.
This may be a sign that their “autonomic nervous system” is out of balance.
The two wings of the autonomic nervous system act together automatically to regulate vital functions such as heart rate and breathing.
When the body perceives a life threatening situation, the sympathetic nervous system increases heart rate and breathing rate, a reaction that people call the “fight-or-flight response.”
By contrast, the parasympathetic nervous system restores the body to a more stable, restful state, known as “rest and digest.”
Individuals with hypertension (high blood pressure), diabetes, and obesity often have increased activity in their sympathetic nervous system, which COVID-19 may exacerbate. For the first time, researchers have now assessed sympathetic nerve activity in otherwise healthy young people recovering from the infection.
They ran a series of tests on 16 individuals aged approximately 20 years old who had tested positive for SARS-CoV-2, the virus that causes COVID-19, around 35 days previously.
Before the pandemic, the scientists carried out identical tests on an age-matched group of 14 healthy volunteers, who served as controls.
The tests revealed changes in the sympathetic nervous system of people recovering COVID-19, both at rest and in response to a stress test.
There were also differences in heart rate and sympathetic nerve activity in a test designed to simulate standing up.
The researchers believe that the same changes in older adults could have adverse effects on their cardiovascular health.
“This is because, with aging, we tend to lose some of the compensatory mechanisms in place to offset the blood-pressure-raising effects of high sympathetic activity,” said senior author Dr. Abigail Stickford, from the department of health and exercise science at Appalachian State University in Boone, NC.
“Ultimately, this could also place more strain on the heart,” she told Medical News Today. The research appears in The Journal of Physiology.
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Bursts of electrical activity
During the tests, the volunteers lay on their backs on a bed in the lab. To monitor changes in their sympathetic nerve activity, the researchers inserted a tiny needle into a nerve behind their knee.
An electrode at the end of the needle recorded the frequency and intensity of bursts of electrical activity in the nerve.
At rest, activity was higher in the participants recovering from COVID-19 compared with controls, though their blood pressure and heart rate were the same.
Next, the scientists asked the volunteers to plunge their hands into icy water for 2 minutes — a painful experience that provokes the fight-or-flight response.
Surprisingly, the individuals recovering from COVID-19 had a much less pronounced increase in their sympathetic nerve activity. They also reported less pain.
However, changes in their heart rate and blood pressure were similar to those in the controls. Finally, the researchers conducted a standard test designed to simulate the effects on the cardiovascular system of standing up, known as the “head-up tilt.”
They tilted the bed to an angle of 30 degrees for 5 minutes, then 60 degrees for a further 5 minutes.
There were larger increases in sympathetic nerve activity and heart rate among participants recovering from COVID-19 compared with controls.
The body normally compensates for the fall in blood pressure when a person sits up or stands up by increasing heart rate.
Doctors use the test to diagnose orthostasis — a fall in blood pressure that occurs when the body fails to compensate fully, which can cause dizziness, lightheadedness, and fainting. In a related condition that doctors call postural orthostatic tachycardia syndrome (POTS), individuals experience a racing heart or palpitations when they sit up or stand up. POTS is among the autonomic disturbances or “dysautonomia” that people with long COVID experience.
“We have been seeing patients with lingering symptoms of fatigue, palpitations, brain fog and exercise intolerance for months after resolution of acute COVID infection,” said Dr. Svetlana Blitshteyn, a neurologist at the State University of New York at Buffalo, NY, who also runs a clinic for patients with dysautonomia.
She recently published case studies of 20 patients who developed dysautonomia — mostly POTS — following COVID-19.
Dr. Blitshteyn told MNT that there was a sufficient heart rate increase in some of the recovering COVID-19 patients in the study’s head-up tilt test for a diagnosis of POTS.
She said the duration of POTS and other symptoms of long COVID remains unclear, but her clinic continues to monitor patients.
“In my published case series, most patients had lingering symptoms, with 60% unable to return to work 8 months after acute [SARS-CoV-2] infection,” she added.
Limitations of the study
A possible limitation of the new study is that control subjects received testing before the COVID-19 pandemic.
Research also suggests there were increases in anxiety and depression among college-age students during the pandemic, so in theory, this could explain some of the autonomic changes that the scientists observed.
Overall, the “cross-sectional” design of the study meant it could not establish whether COVID-19 actually caused changes in participants’ sympathetic nervous systems.
In addition, the relatively small numbers of participants limit the statistical reliability of the findings.
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