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Concept: Combined gas law


We introduce a simple residual pressure self-measurement method for the Fabry-Perot (F-P) cavity of optical MEMS pressure sensor. No extra installation is required and the structure of the sensor is unchanged. In the method, the relationship between residual pressure and external pressure under the same diaphragm deflection condition at different temperatures is analyzed by using the deflection formula of the circular plate with clamped edges and the ideal gas law. Based on this, the residual pressure under the flat condition can be obtained by pressure scanning process and calculation process. We carried out the experiment to compare the residual pressures of two batches MEMS sensors fabricated by two kinds of bonding process. The measurement result indicates that our approach is reliable enough for the measurement.

Concepts: Pressure, Gas, Sensor, Ideal gas, Pressure sensor, Ideal gas law, Gas laws, Combined gas law


In this study, a new algorithm was developed for estimating the pump outflow of a pneumatic ventricular assist device (p-VAD). The pump outflow estimation algorithm was derived from the ideal gas equation and determined the change in blood-sac volume of a p-VAD using two external pressure sensors.

Concepts: Fundamental physics concepts, Volume, Pressure, Gas, Ideal gas, Ideal gas law, Gas laws, Combined gas law


High injection pressure is one of the warning signs of intraneural injection, with animal models suggesting pressures higher than 69 or 176 kPa as high risk, and is normally detected subjectively and inaccurately. We describe a system improvised from common clinical components that uses Boyle’s law to objectively measure injection pressure. The objectives of the study were to (1) Validate our improvised pressure gauge (IPG) by comparing the injection pressure as calculated by Boyle’s law against the measured pressure and (2) Use the IPG to measure the range of injection pressures by two groups of anesthetic professionals using the “syringe feel” technique. Our IPG system consists of an extended 1 ml syringe attached to a 3-way stopcock, inserted between the syringe containing the local anesthetic injectate and the needle. The IPG was validated against a pressure calibration reference. 20 anesthesiologists and 20 anesthetic assistants were recruited to apply pressure to the 20 ml syringe in vitro while blinded to the attached IPG. The pressures were measured on three separate occasions for each participant. There was good agreement (<8 percent difference) between the measured and theoretical pressure values. Anesthesiologists exceeded the threshold of 69 kPa in 18 of a total of 60 attempts whereas anesthetic assistants exceeded the threshold in 30 attempts out of 60 attempts. Anesthetic assistants exerted a higher overall pressure of 80 kPa compared to 51 kPa for anesthesiologists-this was statistically significant (p = 0.027). Our improvised system is easily and rapidly assembled from common clinical equipment and shows promise as a monitor for inadvertent intraneural injection.

Concepts: Pressure, Vacuum, Hypodermic needle, Ideal gas law, Boyle's law, Combined gas law


ImportanceIt is well known that altitude ascent with intravitreal gas can cause expansion of gas and intraocular pressure (IOP) elevation. According to Boyle’s law, the gas bubble will not expand unless a higher altitude than the gas insertion site has been reached. We report four cases in which intravitreal gas was injected at an altitude of 790 m (Jerusalem). All four cases developed high IOP even though they did not reach a higher altitude in their post-operative period.ObservationsA report of four patients following vitrectomy with 12% mixture of perfluoropropane and air are presented. All four patients arrived with ocular pain following the ascent by car of 765-1100 m to Jerusalem where the vitrectomy and gas insertion was conducted. Upon examination, all four patients had high IOP (30-55 mm Hg). IOP was well controlled with IOP-lowering medications. None of the patients suffered from long-term complications.Conclusions and RelevanceCaution should be taken with altitude changes in patients with intravitreal gas even if there was no ascent from the altitude in which the vitrectomy was performed.Eye advance online publication, 2 May 2014; doi:10.1038/eye.2014.83.

Concepts: Intraocular pressure, Pressure, Altitude, Ideal gas law, Octafluoropropane, Boyle's law, Combined gas law, The Ascent