Hypotension - Physiological Response
Cardiovascular response & Orthostasis
Cardiovascular response
A simple way to test the cardiovascular response is by varying your pulse.
Take your pulse and get a good sense of your heart rate.
Then, take a deep breath and hold it for 5 or 6 seconds.
Your heart rate should speed up because when you inhale deeply, you open up lung tissue and shunt blood into the lung capillaries, which reduces your effective circulating blood volume (ie, your stroke volume).
Cardiac output is stroke volume multiplied by heart rate; therefore, to compensate for a decreased stroke volume, your heart rate increases (typically by 8 beats per minute).
Orthostasis
An additional, slower response to a reduced stroke volume is to increase the effective circulating blood volume, itself.
For instance, when we stand, blood pools in our veins, so after we stand upright for a full minute, T5 sympathetic splanchnic fibers command our abdominal vessels to shunt roughly 1.5 units of blood from our abdomen into our peripheral vasculature.
Because there is a delay in the shunting of blood between systems, when we check orthostatic blood pressure, we must wait at least a few minutes in between measuring supine and standing blood pressure (and possibly longer, even).