Pins and Needles: Why?

June 30, 2006 8:21 PM

What is the underlying physiological cause for paresthesia (tingling of the fingers) secondary to hyperventilation? Specifically, what metabolic or neurological process causes you to feel tingling in your fingers when you hyperventilate?
posted by scrump to Science & Nature (2 answers total)

Hyperventilating causes you to blow off CO2, which is usually in the blood at a partial pressure of 40 mmHg or so. You can blow this down to 20 or thereabouts, and raise your blood pH from 7.40 down to, what, 7.56? (There's an exact relation, but I can't recall it off the top of my head.)

Now, peripheral nerves rely on ion exchange over membranes to do their thing, and the ion channels that let the various ions in and out are pH-sensitive. They work right when the pH is 7.40; too broad a deviation from this and they get to malfunctioning, letting ions in or out when they hadn't ought to do so.

Apparently this can cause an aberrant potential to arise. Noise in the peripheral nerves looks, to the brain, like tingling; so there you go. You can achieve a similar effect by tourniqueting a limb briefly and then removing the tourniquet (not recommended); as the blood flows back in, the pH alters rapidly from acidic back to normal, and as the ion channels reequilibrate, you get tingling. Most people say "My foot fell asleep."
posted by ikkyu2 at 9:49 PM on June 30, 2006

ikkyu2 has it right, as usual. Hooray for respiratory alkalosis!
posted by oats at 10:42 PM on June 30, 2006