Interesting heart related observation on today's ride

Andre Jute writes:

On Tuesday, August 20, 2019 at 1:52:59 AM UTC+1, Radey Shouman wrote:

It seems possible that the pressure setpoint is somehow set by metabolic
requirements

Blood pressure operates exactly as an engineer would expect. If you
open up the blood vessels, say with oxygen intake or (somewhat
counterintuitively, with compression clothing which a lot of lycra
is), the blood flows faster and the pressure drops.

If I have a positive displacement pump running at constant speed pumping
fluid over a closed circuit, and the flow resistance changes, I don't
expect the flow rate to go up, I expect the power required by the pump
to go down. The question in my mind is how the speed (heart rate) is
actually controlled.