© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

4.3.3.3 Fluid Acceleration Sensors

Biological fluid accelerations may also be inferred from measurements of spatial pressure gradients. Ignoring frictional and gravitational forces and assuming laminar flow, fluid acceleration a_fluid is given by

{Eqn. 4.15}

where r = fluid density (e.g., blood plasma is an almost incompressible Newtonian fluid, with r ~ 1025 kg/m³ at 310 K) and DP is the measured change in pressure over a distance Dx. The mitral and aortic valves in the heart (DP / Dx ~ 10⁵ N/m³, a_fluid ~ 10 g's,⁴⁷⁴ Dx ~ a few cm), as well as valves in the veins and lymphatics, operate as bistable analog decelerometers employing this principle.⁴⁴⁴ Micron-scale medical nanorobots traveling across blood vessel surfaces could use pressure sensors capable of 10^-6 atm resolution (Section 4.5.1) to infer local blood flow accelerations to an accuracy of ± 0.01 g from sequential measurements taken 1 mm apart.

Last updated on 17 February 2003