Young people who are infected with the COVID-19 virus but are otherwise healthy have an impaired fight-or-flight response that can last for months, according to a new study.
In a six-month study in which 30 people took part (16 of whom contracted COVID-19), the results obtained by the researchers are largely in line with what many COVID-19 truckers are reporting.
Even at rest, the nerves of young survivors of COVID-19 are working much harder than those of those who have not contracted the virus.
In a study, a tiny electrode inserted into the back of the knee found reduced electrical activity in the muscles of people recovering from COVID-19.
These nerves receive messages from the sympathetic nervous system, which controls our fight-or-flight response, and in those recovering from the virus, this system is abnormally active.
For example, when moving from a prone position to an upright position, 16 COVID survivors experienced increased sympathetic activity followed by an exaggerated heart rate response to changes in blood pressure.
It's worth noting that this is only a small study, but even though the sample was tiny, the results are in line with recent reports that many truckers - people experiencing COVID-19 symptoms for months on end - are unable to keep their pulse in standing position from out of control.
In other cases, however, the sympathetic nervous system of COVID-19 patients does not appear to be active enough.
For example, when young participants dipped their hands into ice-cold water, their muscle nerves were less active and participants reported significantly less pain than 14 healthy controls.
This is not a perfect comparison; it would be better to test before and after contracting COVID-19 to see how their personal physiological responses might change over time. But given the astonishing nature of this disease, using healthy, unaffected participants as controls is our next best option.
The results show that SARS-CoV-2 may somehow disrupt the sympathetic nervous system, causing it to work too hard at rest and not hard enough in stressful situations, even in young people who are not as susceptible to severe illness.
"If a similar autonomic dysregulation, like that found in young adults, is present in older adults after infection with SARS-CoV-2," the authors write, "it could have significant negative effects on cardiovascular health."
But so far there are only many "ifs" and not many answers.
It is known that increased activity of the sympathetic nervous system at rest increases heart rate and cardiac output, possibly leading to stress on the cardiovascular system over time. But this is the first study that examined the activity of the nervous system after infection of the body with the SARS-CoV-2 virus.
Today, around 200 million people worldwide have experienced COVID-19, and if the new findings can be confirmed among much larger populations, that means millions of people may have suffered from an abnormal sympathetic nervous system for months during their recovery.
How long these symptoms lasted before they disappeared remains unknown. In the current study, participants were followed for six months, but some people who received long-term treatment continued to have high heart rates and other cardiovascular problems long after.
The authors are not convinced that SARS-CoV-2 affects the sympathetic nervous system of patients to such an extent, but they suspect that oxidative stress and inflammation are to blame.
High levels of sympathetic nervous activity in muscles in the past have been associated with increased arterial stiffness, and interestingly, young adults with COVID-19 showed increased arterial stiffness for three months after testing positive for the virus.
Decreased elasticity can alter the delivery of oxygen to the head or heart, which in turn can trigger the body's fight-or-flight response. On the other hand, inflammation caused by the immune system can also trigger the sympathetic nervous system.
"If, indeed, our [COVID positive] participants also had an increase in the diameter of the vessels at rest, then the increased activity [of the muscular sympathetic nervous system] may serve as an acute adaptation to systemic vasodilation," the authors suggest.
"Of course, we are limited in these interpretations given the cross-cutting nature and short time frame of this study."
It is difficult to draw any conclusions from the results obtained, but their implications are worrisome. Given the potential health problems that can arise from over-activity of the sympathetic nervous system, it is important to learn more.
The study was published in the Journal of Physiology.