Epidural versus subdural spinal cord cooling: cerebrospinal fluid temperature and pressure changes

The three fundamental principles for the variation of static pressure p throughout a body of fluid at rest are (a) the pressure at a point is the same in all directions (Pascal’s law), (b) the pressure is the same at all points on the same horizontal level, and (c) the pressure increases with depth z according to the hydrostatic equation. dp/dz= ρ‎g For a fluid with constant density ρ‎, the increase in pressure over a depth increase h is ρ‎gh, a result which can be used to analyse the response of simple barometers and manometers to applied pressure changes and differences. In situations where very large changes in pressure occur an equation of state may be required to relate pressure and density together with an assumption about the fluid temperature. The hydrostatic equation is still valid but more difficult to integrate, as illustrated by consideration of the earth’s atmosphere.

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Pressure Gradients Affecting the Labyrinth during Hypobaric Pressure

Annals of Otology Rhinology & Laryngology ◽

10.1177/000348949710600610 ◽

1997 ◽

Vol 106 (6) ◽

pp. 495-502 ◽

Cited By ~ 10

Author(s):

Konrád S. Konrádsson ◽

Björn I. R. Carlborg ◽

Joseph C. Farmer

Keyword(s):

Cerebrospinal Fluid ◽

Eustachian Tube ◽

Ambient Pressure ◽

Pressure Gradients ◽

Cochlear Aqueduct ◽

Fluid Compartment ◽

Large Pressure ◽

Fluid Compartments ◽

Pressure Changes ◽

Considerable Pressure

Hypobaric effects on the perilymph pressure were investigated in 18 cats. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to the atmospheric pressure. The pressure equilibration of the eustachian tube and the cochlear aqueduct was studied, as well as the effects of blocking these channels. During ascent, the physiologic opening of the eustachian tube reduced the pressure gradients across the tympanic membrane. The patent cochlear aqueduct equilibrated perilymph pressure to cerebrospinal fluid compartment levels with a considerable pressure gradient across the oval and round windows. With the aqueduct blocked, the pressure decrease within the labyrinth and tympanic cavities was limited, resulting in large pressure gradients toward the chamber and the cerebrospinal fluid compartments, respectively. We conclude that closed cavities with limited pressure release capacities are the cause of the pressure gradients. The strain exerted by these pressure gradients is potentially harmful to the ear.

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Assessment of Piezoelectric Sensors for the Acquisition of Steady Melt Pressures in Polymer Extrusion

Fluids ◽

10.3390/fluids4020066 ◽

2019 ◽

Vol 4 (2) ◽

pp. 66

Author(s):

Sónia Costa ◽

Paulo Teixeira ◽

José Covas ◽

Loic Hilliou

Keyword(s):

Polymer Processing ◽

Piezoelectric Transducers ◽

Piezoelectric Sensors ◽

Flow Curves ◽

Signal Drift ◽

Temperature And Pressure ◽

Pressure Independent ◽

Pressure Changes ◽

Different Levels ◽

Slit Die

Piezoelectric sensors have made their way into polymer processing and rheometry applications, in particular when small pressure changes with very fast dynamics are to be measured. However, no validation of their use for steady shear rheometry is available in the literature. Here, a rheological slit die was designed and constructed to allow for the direct comparison of pressure data measured with conventional and piezoelectric transducers. The calibration of piezoelectric sensors is presented together with a methodology to correct the data from the inherent signal drift, which is shown to be temperature and pressure independent. Flow curves are measured for polymers showing different levels of viscoelasticity. Piezoelectric slit rheometry is validated and its advantage for the rheology of thermodegradable materials with viscosity below 100 Pa·s is highlighted.

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Compensation of phase drifts caused by ambient humidity, temperature and pressure changes for continuously operating interferometers

Journal of Instrumentation ◽

10.1088/1748-0221/14/11/p11016 ◽

2019 ◽

Vol 14 (11) ◽

pp. P11016-P11016

Author(s):

K.J. Brunner ◽

J. Knauer ◽

J. Meineke ◽

M. Stern ◽

M. Hirsch ◽

...

Keyword(s):

Ambient Humidity ◽

Temperature And Pressure ◽

Pressure Changes

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DECOMPOSITION PRESSURES OF FERRIC SULPHATE AND ALUMINUM SULPHATE

Canadian Journal of Chemistry ◽

10.1139/v60-297 ◽

1960 ◽

Vol 38 (11) ◽

pp. 2196-2202 ◽

Cited By ~ 17

Author(s):

N. A. Warner ◽

T. R. Ingraham

Keyword(s):

Gas Phase ◽

Static System ◽

Ferric Sulphate ◽

Kcal Mole ◽

Aluminum Sulphate ◽

Temperature And Pressure ◽

Pressure Changes ◽

Mercury Manometer ◽

Decomposition Pressure ◽

Gas Pressures

The gas pressures over samples of anhydrous ferric sulphate and anhydrous aluminum sulphate have been measured in a static system, using a mercury manometer in which the exposed surface was covered with a flexible Pyrex bellows. The calculated ΔH for the decomposition of Fe2(SO4)3 was +135.4 kcal/mole. It was not possible to calculate the ΔH for the Al2(SO4)3 decomposition, because a discrete aluminum oxide with singular thermodynamic properties was not obtained.In the Fe2(SO4)3 system, the fraction of SO3 in the gas phase was found to be almost constant over the range of temperature and pressure changes used in the study.At any given temperature, the decomposition pressure over a ferric sulphate sample is greater than that over an aluminum sulphate sample, thus indicating that preferential decomposition of ferric sulphate should be thermodynamically feasible in mixtures of ferric sulphate and aluminum sulphate.

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