(This entry is cross-posted from Pat on The Boundary Layer)
I’m sure that you’ve all felt dizzy at least once in your life when standing up from a supine position. This sudden change in position is associated with a lowering in the amount of blood returning to your heart (venous return), the amount of blood going out of your heart (cardiac output) and blood pressure. Although the reduction in blood flow to your brain (and thus oxygen level) is limited because of its capacity of autoregulation, orthostatic intolerance with associated symptoms such as dizziness is not uncommon in healthy individuals like you and me. However, in healthy individuals, postural hypotension rarely leads to a loss of consciousness (syncope).
This being said, its not the same ball game for individuals prone to syncope. In these subjects, prolonged standing is associated with vasodilatation and a reduction heart rate (vasovagal reaction). These changes are triggered, in most part, by a lowering in central blood volume, a consequence of the pooling of blood in their legs. These individuals may experience numerous losses of consciousness, from several times a year to several times a day !
Are these individuals sentenced to lose consciousness their entire life? Is there a way to attenuate orthostatic intolerance? Some researchers have been interested in that issue and found that, in healthy volunteers, the reduction in brain blood flow (and oxygen level) is attenuated by muscle tensing (that is pressing the legs against each other). Interestingly, leg crossing and muscle tensing are also associated with increased orthostatic tolerance in individuals prone to syncope. So, a simple movement can delay, or even prevent, a loss of consciousness in these individuals.
So, next time you see a move like this…
and there is no boom box nearby, it’s not a new breakdance move, it’s most likely muscle tensing!