Changes In Chamber Pressure Research Articles

Measurements of the Rate of Gas Diffusion in Rigid Cellular Plastics

This paper describes a method for measuring gas diffusion through cellular plastics A specimen is placed in a chamber, which is then scaled and pressur ized with the test gas. The pressure increase causes some gas to enter the specicmen, and this entry results in a reduction of the chamber pressure By following the change in chamber pressure with time an appropriate transport characteristic for the material is determined An application of this method to a core specimen of an extruded polystyrene board is presented.

Carotid baroreflex resetting during drug-induced arterial pressure changes in humans.

We studied human baroreflex resetting during 25 min of drug-induced arterial pressure changes in 10 healthy volunteers. Average (+/- SE) base-line systolic pressure of 113 +/- 4 fell to 102 +/- 3 during nitroprusside infusions and rose to 135 +/- 6 mmHg during phenylephrine infusions. Average base-line R-R intervals of 932 +/- 37 shortened to 820 +/- 39 during nitroprusside infusions and lengthened to 1,251 +/- 61 ms during phenylephrine infusions. Carotid baroreceptor-cardiac reflex responses were evaluated with a complex series of neck chamber pressure changes, and R-R intervals were plotted as functions of carotid distending pressure. Baroreceptor-cardiac reflex relations shifted on both R-R interval and arterial pressure axes during drug infusions, but there was no significant change of the maximum slope or range of R-R interval responses. The position of baseline R-R intervals on the reflex relation (operational point) changed significantly. Resting R-R intervals were closer to threshold during pressure reductions and closer to saturation for baroreceptor-cardiac responses during pressure elevations. These results document short-term partial resetting of human baroreceptor-cardiac reflex responses as early as 25 min after the onset of arterial pressure changes.

Continuous resetting of the human carotid baroreceptor-cardiac reflex.

Although human baroreflex responses have been studied during night as well as day, there has been no attempt to distinguish circadian changes of baroreflex function from those related to sleep. We measured carotid baroreceptor-cardiac reflex responses serially during a 24-h period in 11 normotensive volunteers who were awake and cooperative during testing. We applied sequences of ramped R-wave-triggered neck chamber pressure changes from +40 to -65 mmHg, during held expiration, at 3-h intervals. Subjects maintained their usual sleep-wake cycles but were awakened for three 30-min periods for night testing. There was no systematic change of baroreflex slope during the 24-h period. There were, however, parallel shifts of the entire sigmoid baroreceptor-cardiac reflex response relation along its R-R interval and arterial pressure axes associated with small, but significant, circadian changes of baseline R-R intervals and arterial pressures. Thus, although our data do not point toward major circadian variability of baro-reflex responsiveness, they provide evidence for an ongoing process of human baroreflex resetting.

Device for rapid quantification of human carotid baroreceptor-cardiac reflex responses.

We designed, constructed, and evaluated a new device to characterize the human carotid baroreceptor-cardiac reflex response relation rapidly. We designed this system for study of reflex responses of astronauts before, during, and after space travel. The system comprises a new tightly sealing silicone rubber neck chamber, a stepping motor-driven electro-deposited nickel bellows pressure system, capable of delivering sequential R-wave-triggered neck chamber pressure changes between +40 and -65 mmHg, and a microprocessor-based electronics system for control of pressure steps and analysis and display of responses. This new system provokes classic sigmoid baroreceptor-cardiac reflex responses with threshold, linear, and saturation ranges in most human volunteers during one held expiration.

A model-based system for assessing ventricular chamber pressure-volume-dimension relationship: regional and global deformation.

A system has been developed for measuring and relating in a non-beating isolated canine left ventricle dynamic changes in chamber pressure, volume, diameter, regional segment length, and wall thickness. The measurement system consists of a pulsatile blood pump whose stroke-volume and frequency can be adjusted selectively. The external pump system is used as a primary means for controlling instantaneous intraventricular volume. The relationship between left ventricular volume change, intraventricular pressure, minor axis diameter, and regional dimensions were studied as a function of pump rate. In addition to the basic constitutive properties, this system provided the means for measuring and comparing regional and global pressure-strain relationship including the effect of strain rate and its relationship to viscoelastic myocardial muscle model. The dynamic relationship between global dimensions and regional dimensions, circumferential segment length, and wall thickness were also investigated. The instantaneous relationship between intraventricular pressure resulting from periodic oscillations of chamber volume, including minor equator diameter, wall thickness, and regional segment dimensions were plotted and fitted to an exponential pressure-strain model, assuming a quasi-static large deformation. The observed difference between global and regional pressure-dimension strain stiffness coefficients can be attributed in part to basic constitutive and geometric considerations and not necessarily to the complex anisotropic or heterogeneous nature of cardiac muscle properties. This methodology provides indices which appropriately characterize the regional and global left ventricular chamber deformation and stiffness.

The effect of pressure change rate on the eustachian tube function in pressure chamber tests.

The capacity of the Eustachian tube to equilibrate pressure differences across the eardrum was tested repeatedly at different rates of pressure change with the aid of a quantitative impedance method in a pressure chamber. Three recordings of the active and passive pressure equilibration functions were made during chamber pressure changes of 0.3, 0.7 and 1.5 kPa-1s in 53 ears in 28 otologically healthy subjects. The middle ear pressures at which the active and passive equilibrations were achieved increased with increasing rates. The test-retest reliability was not rate dependent as regards the passive pressure equilibration functions, but tended to deteriorate with increasing rates for the active equilibration functions. Advantages and disadvantages of the different rates in such tests are discussed.

Motion of Air Bubbles in Mineral Oils Subject to Sudden Change in Chamber Pressure : 1st Report, Experimental Analysis of Single Spherical Bubbles

This paper deals with an experimental and a theoretical analysis of growth and decay of a spherical air bubble rising in a stationary oil closed in a chamber subject to such a rapid rate of pressure variation as one bar during two or several milliseconds. The oils used were two kinds of base oils for hydraulic fluids with low and high viscosities, and base oils including a small quantity of silicon-type deforming agent were also used. The following are discussed from the comparison of the measured bubble motion with the numerical analysis: (1) mass transfer effect on expansion or compression of the bubble boundary. (2) effect of deforming agents added to the oil on the mass transfer through the bubble boundary, and (3) effect of surface dilational viscosity on violent bubble oscillation in a low viscosity oil.

Motion of Air Bubbles in Mineral Oils Subject to Sudden Change in Chamber Pressure : 1st Report, Experimental Analysis for Single Bubbles

油中の単一気ほうが急激な圧力変化を受けて膨張・収縮する際の気ほう径と圧力との関係を実験的に調べ、これを理論解と比較してつぎのことを明らかにした。(I)油圧油の基油中では数ms内に1気圧という急激な圧力変化を受ける場合にも、気ほう界面に拡散による相変化が生じる。(ii)基油に微量の界面活性剤を添加すると拡散現象は抑制される。(iii)気ほうの理論解析には表面粘性による界面変形抵抗を考慮する必要がある。

Experimental status of high frequency liquid rocket combustion instability

Experimental status of high frequency liquid rocket combustion instability