In discussing fluids, we turn to Bernoulli’s equation:
ΔP + ρgΔy = ½ (υ² – ν²)
This is where ΔP is the pressure of the fluid, Δy is the change in height from the initial to the final position of the fluid, ρ is the density of the fluid, and g is the acceleration due to gravity (9.81 m/s²).
Now, if the fluid’s initial velocity (υ) is equal to the fluid’s velocity after its change in height (ν), the fluid’s pressure must change such that:
ρgΔy = -ΔP
This explains what happens in moving the transducer: the flush solution, which creates the blood pressure readings, has a different change in height by moving the transducer, which creates a different pressure from the transducer, and thus, a different returned blood pressure reading.