Originally Posted by
Dolamite02
Any of y'all have issues with blackouts when you get up from sitting for a while? I've been experiencing this with increasing frequency recently. It's only vision, and every now and then, light-headedness/dizzynes. It seems to happen regardless of whether I've been eating or drinking recently. Never lasts long, just a few seconds, but it hits pretty strongly sometimes.
Blood Pressure. Basically you are changing the hydrostatic pressure at brain level when you stand quickly. Under normal circumstances, your body accommodates 1) by having enough blood that there is plenty of return all the time. i.e. you stand, pressure goes down, but there's "nowhere" for blood to go in your lower body, so it keeps being delivered to your head. and 2) your vessels have smooth muscles surrounding them, when there are sudden changes in blood pressure, these muscles constrict and effectively "boost" blood pressure, but reducing the total vascular volume.
When we ride a lot we end up with 1) low blood volumes - chronic dehydration and 2) low blood pressures. The extent to which these are related/the same thing, I'm not sure. But the effect of both are seen when we stand quickly - blackouts/whiteouts/fainting. When there's low blood volume/pressure our body's mechanisms are much less effective and maintaining blood return to the brain. Brain doesn't get blood = pass the f*ck out.