In the UK, 50% of people will faint or blackout at some point in their lives. But what’s going on in the body that causes it to happen? Well, scientists think they’ve finally unearthed the answer.
Fainting or syncope, as it’s scientifically known, is when you pass out for a short time and usually happens after feeling dizzy; cold and sweaty; warm or hot; nauseous; or experiencing changes to vision.
It’s not a pleasant experience but, according to the NHS, it’s not usually a sign of anything serious either.
Until recently, the bodily mechanisms behind fainting weren’t entirely clear. It had been attributed to low blood pressure and a lack of blood flow and oxygen to the brain but that was about as much as we understood of this phenomenon.
So, why do we faint?
According to a study published in Nature, it’s quite literally our hearts ruling our heads, rather than the other way around.
That’s right, scientists have discovered a new nerve pathway which slightly changes our understanding of how the brain works.
Until now, it was believed that our brains sent out signals that the body responds to – but this pathway works in the opposite direction, with the heart sending signals to the brain and, in turn, restricting blood flow.
“There is blood-flow reduction, but, at the same time, there are dedicated circuits in the brain which manipulate this,” said Vineet Augustine, a neuroscientist at the University of California, San Diego, and co-author of the study.
Until recently, it was believed that a mechanism known as the Bezold-Jarisch Reflex (BJR) was likely related to fainting as it is connected to heart rate, blood pressure and breathing – but it’s been difficult to identify because the nerve pathways it uses aren’t entirely understood.
However, this study identified a cluster of neurons in the vagus nerve that are closely related to BJR. When these nerves were stimulated on lab mice, the mice fainted – yet just like humans, the mice quickly bounced back.
“This is all very exciting”
Jan Gert van Dijk, a clinical neurologist at Leiden University Medical Centre, who wasn’t involved in the study, said “neurons in the brain are very much like extremely spoiled children”.
“They need oxygen and they need sugar, and they need them now,” he explained.
Neurons stop working very quickly if you deprive them of oxygen or glucose, he added. These nerve cells do begin to die within 2-5 minutes without oxygen but a fainting spell typically lasts 60 seconds, causing the bounce-back.
“Coming from a clinical standpoint, this is all very exciting,” Richard Sutton, a clinical cardiologist at Imperial College London, told Nature.
The discovery of these neurons “doesn’t answer all questions immediately but I think it could answer, with future research, almost everything,” he concluded.
Kalyanam Shivkumar, a cardiologist at the University of California, Los Angeles, and another contributor to the study, added: “The study of these pathways could inspire new treatment approaches for cardiac causes of syncope.”