It’s not that simple. Physiology is a very dynamic system so I appreciate any corrections. But, basically the venous system has a lot of compliance and capacitance holding 70% or so of your blood volume in a euvolemic state. You can easily maintain blood pressure and arterial volume while dehydrated.
Orthostatics refers to change in blood pressure when standing. Every time you stand up you lengthen a large column of blood that gravity wants to pull to the bottom of your feet. Pressure sensors in your neck (where blood goes to the brain) immediately tell the autonomic nervous system about the sudden drop which sends a response to increase heart rate and increase resistance in the arterial system to maintain output and arterial pressure so you don’t pass out. To accommodate this you pull extra volume from the large venous pool to continue optimally filling the heart with each stroke. If your venous pool is low, the extra refill volume and venous pressure isn’t available to keep up with the sudden demand and the arterial pressure drops.
We have different medication classes that can selectively slow the heart down or decrease blood pressure by preventing increased resistance in the arterial system and those folks are also at risk of orthostatic hypotension because of blocking those compensatory mechanisms.
Orthostatics refers to change in blood pressure when standing. Every time you stand up you lengthen a large column of blood that gravity wants to pull to the bottom of your feet. Pressure sensors in your neck (where blood goes to the brain) immediately tell the autonomic nervous system about the sudden drop which sends a response to increase heart rate and increase resistance in the arterial system to maintain output and arterial pressure so you don’t pass out. To accommodate this you pull extra volume from the large venous pool to continue optimally filling the heart with each stroke. If your venous pool is low, the extra refill volume and venous pressure isn’t available to keep up with the sudden demand and the arterial pressure drops.
We have different medication classes that can selectively slow the heart down or decrease blood pressure by preventing increased resistance in the arterial system and those folks are also at risk of orthostatic hypotension because of blocking those compensatory mechanisms.