These triggers set off a reflex in our nervous system that cause our hearts to paradoxically slow instead of speed up, and our blood vessels to dilate instead of constrict. Blood pressure and brain blood flow plummet, and we faint.
Excessive heat plays a role, too, as it makes it more difficult for the body to maintain blood pressure. With the weather warming across the country, now is a good time to know signs and symptoms that lead to fainting. As a physiologist, I can offer some pointers.
Blood pressure regulation harder in summer
Physiologists, neurologists and cardiologists have long studied how people regulate blood pressure and maintain consciousness while standing. Upon standing, there is an immediate decline in blood pressure, and the body must respond to this decline. The normal response includes constriction of blood vessels, increased heart rate and the release of various hormones into the bloodstream.
Together these responses help to maintain blood pressure. By protecting blood pressure, our oxygen-thirsty brain ensures that it will continue to be adequately nourished. Usually the response is flawless – we can stand without any trouble.
But various triggers sometimes mess up this finely tuned response, and the summer heat makes it more challenging to regulate blood pressure.
Ultimately, if blood pressure is not maintained, brain blood flow will decline. The fancy term for this is cerebral hypoperfusion – the defining characteristic of fainting (i.e., syncope), whatever the cause or trigger.
The symptoms that precede syncope vary but may include sweating, nausea, paleness and abdominal discomfort.