title: Bernoulli's Principle Applied to Brain Fluids: Intracranial Pressure Does Not Drive Cerebral Perfusion or CSF Flow.
abstract: In line with the first law of thermodynamics, Bernoulli's principle states that the total energy in a fluid is the same at all points. We applied Bernoulli's principle to understand the relationship between intracranial pressure (ICP) and intracranial fluids. We analyzed simple fluid physics along a tube to describe the interplay between pressure and velocity. Bernoulli's equation demonstrates that a fluid does not flow along a gradient of pressure or velocity; a fluid flows along a gradient of energy from a high-energy region to a low-energy region. A fluid can even flow against a pressure gradient or a velocity gradient. Pressure and velocity represent part of the total energy. Cerebral blood perfusion is not driven by pressure but by energy: the blood flows from high-energy to lower-energy regions. Hydrocephalus is related to increased cerebrospinal fluid (CSF) resistance (i.e., energy transfer) at various points. Identification of the energy transfer within the CSF circuit is important in understanding and treating CSF-related disorders. Bernoulli's principle is not an abstract concept far from clinical practice. We should be aware that pressure is easy to measure, but it does not induce resumption of fluid flow. Even at the bedside, energy is the key to understanding ICP and fluid dynamics.
authors.affiliation: Department of Neurosurgery, Hôpital Purpan, Place du Dr Baylac TSA 40031, Toulouse, 31059, France. schmidt.e@chu-toulouse.fr.
authors.forename: Eric
authors.initials: E
authors.lastname: Schmidt
authors.affiliation: Department of Neurosurgery, Hôpital Purpan, Place du Dr Baylac TSA 40031, Toulouse, 31059, France.
authors.forename: Maxime
authors.initials: M
authors.lastname: Ros
authors.affiliation: Department of Neurosurgery, Hôpital Purpan, Place du Dr Baylac TSA 40031, Toulouse, 31059, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Moyse
authors.affiliation: Department of Porous Media, Institute of Fluid Mechanics of Toulouse, Toulouse, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Lorthois
authors.affiliation: Department of Porous Media, Institute of Fluid Mechanics of Toulouse, Toulouse, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Swider
mesh_terms: D002555:Cerebrospinal Fluid / Q000502:physiology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006801:Humans; D057446:Hydrodynamics; D007427:Intracranial Pressure / Q000502:physiology*; D013816:Thermodynamics
keywords: Bernoulli’s principle; Cerebrospinal fluid; Energy; Fluid mechanics; Hydrocephalus; Intracranial pressure; Velocity