Its like this.
When they see that I might get hypoed, they will set the machine to give me some sodium or salt. It will in effect raise my blood because in effect I will absorb more water, then the BP will rise.
In cases where my BP is too high, they will set the machine to take more sodium from my body/blood, the reverse will happen and it will lower my BP.
At the back of every machine there is a supply of salt that it takes when needed.
Sometimes I am annoyed because my BP is not high enough for them but I am feeling relaxed, then they will do those things to raise my BP and will make my heart jumpy in the process.