Constant Pressure System Research Articles

Oxygen cost of stress development in hypertrophied and failing hearts from the spontaneously hypertensive rat.

Left ventricular isovolumic stress development and metabolic parameters were studied in 18-24-month-old spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto (WKY) rat controls using the isolated, isovolumic (balloon in left ventricle) buffer-perfused rat heart preparation. After WKY rats and all SHRs were compared, SHRs were divided into two groups: those animals with (SHR-F) and without (SHR-NF) evidence of heart failure. Hearts were perfused at 100 mm Hg using a constant pressure system at a temperature of 37 degrees C. In the baseline state, peak systolic pressure was greatest in the SHR-NF group and lowest in the SHR-F group. Peak midwall stress was greatest in the WKY group and, again, lowest in the SHR-F group. Oxygen consumption was lowest in the SHR-F group. When the oxygen cost of stress development was estimated by normalizing myocardial oxygen consumption by peak developed midwall stress, values were lowest in the WKY, greater in the SHR-NF, and greatest in the SHR-F group. Lactate production did not occur in the baseline state in any of the groups. Functional and metabolic responses to graded hypoxia, induced by changing the gas mixture of the perfusate from 95% to 50%, 25%, and 0% oxygen at perfusion pressures of 100 and 130 mm Hg, were studied. Increasing perfusion pressure generally resulted in small increases in peak systolic pressure and myocardial oxygen consumption but did not substantially reverse the contractile or metabolic deficit present in the SHR-F group.(ABSTRACT TRUNCATED AT 250 WORDS)

Criteria for analysis of arterial and venous occlusion

To provide a better understanding of analysis of arterial (AO) and venous occlusion (VO) tracings, using a constant and nonpulsatile perfusion pressure system, we set up an isolated in situ dog lobe preparation perfused with autologous blood. Four signals were recorded: arterial pressure, arterial inflow rate, venous pressure, and venous outflow rate. The four signals were recorded into the memory of a computer. When flow into the lobe was abruptly stopped (AO), flow out of the lung continued unchanged for approximately 150 ms and then decreased slowly to zero. Likewise, when flow out of the lung was abruptly stopped (VO), the flow into the lung continued unchanged for approximately 130 ms and then decreased slowly to zero. A monoexponential curve was fitted to different stretches of data between 0.1 and 5 s postocclusion and extrapolated to the instant of occlusion (defined here as the instant when flow at the site of occlusion becomes zero). The results indicate that 1) the first 150 ms postocclusion should be avoided because of the oscillatory artifacts generated by the occlusion maneuver, 2) use of a long segment of postocclusion data (5 s) tends to underestimate the middle pressure gradient and overestimate the arterial and venous pressure gradients, and 3) the changes in segmental vascular resistance under different experimental conditions were found to be unaffected by the criteria of analysis. Analysis of the postocclusion (AO and VO) tracings was found to be most compatible with the double-occlusion capillary pressure by fitting a stretch of data between 0.2 and 2.5 s postocclusion and extrapolating back to the instant when flow becomes zero at the site of occlusion but no earlier.

Substance P Enhances Desensitization of the Nicotinic Response in Bovine Chromaffin Cells but Enhances Secretion upon Removal

A fundamental process in neurosecretion is desensitization, or a declining response to a stimulus. The response of chromaffin cells to continuous nicotinic stimulation, secretion of catecholamines, desensitizes within a few minutes. The neuropeptide substance P (SP) has been reported to prevent desensitization in culture dish experiments and to enhance desensitization in patch clamp studies. In the present study, these contradictory responses have been demonstrated and the apparent contradictions resolved. We have measured catecholamine secretion by on-line electrochemical detection in a constant-pressure flow system. Isolated chromaffin cells cultured on quartz plates were stimulated with the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP) in the presence and absence of SP. SP inhibited secretion and increase the rate of desensitization compared with stimulation by DMPP alone. However, when the cells were stimulated a second time with DMPP alone immediately after 5-min stimulation with SP + DMPP, the rate of desensitization was markedly lower than the control. Removal of SP after a desensitizing stimulation with SP + DMPP caused a slow secondary release of catecholamine in response to the continued stimulation with DMPP. The kinetic analysis of the secretory response shows that the primary response to SP is enhanced desensitization, but that upon removal of SP the response to DMPP desensitizes less rapidly. We suggest that SP protects some receptors from nicotinic desensitization while holding them in an inactive state, and that upon removal of SP these receptors can slowly respond to DMPP.

Physical exercise and blood flow properties.

In 46 executive level managers at risk for cardiovascular disease, whole blood filterability through five micron pore Nuclepore filters was monitored using a constant flow positive pressure system before and after treadmill exercise and compared to our laboratory standard. Our results show regular exercise compensates not only for the potential damage risk factors represent but also for the physical stress provoked by vigorous exercise.

Physical and mechanical effects of cardioplegic injection on flow distribution and myocardial damage in hearts with normal coronary arteries

The physical and mechanical effects of injecting crystalloid cardioplegic solution under various pressures and flows was studied (in canine hearts) to establish a safe method for administering it in the presence of normal coronary arteries. A constant pressure system (300 mm Hg = 15 psi) was maintained in the solution reservoir, and flows and pressures were varied with the use of cannulas of different inner diameters: 0.8, 1.35, 1.6, 2.3, 2.58, and 2.80 mm. Cardioplegia distribution was measured by 15 microns radioactive microspheres. Peak flow rate, total flow, and mean flow rate per infusion were measured by an inline electromagnetic flowmeter probe. Direct aortic root pressure, time to standstill, and myocardial temperatures were recorded by continuous monitoring. Cardiac isoenzymes were measured in the coronary sinus, peripheral blood, and directly in the myocardial tissue. Histologic changes in the left ventricle were examined by light microscopy. The results showed that the higher the flow and pressure, the shorter the prearrest period, the better the flow distribution, and the faster the myocardial temperature drop. Mean aortic root pressures higher than 110 mm Hg and peak flow rates greater than 1500 ml/min caused a higher incidence of mechanical-physical trauma to the vascular endothelium and the endocardium, but cellular protection was good. Low pressure (less than 30 mm Hg) and peak flows (less than 125 ml/min) showed a higher incidence of cellular (myocardial) ischemia, focal necrosis, and uneven flow distribution. An aortic root pressure of 61 +/- 5 mm Hg, a mean peak flow rate of 622 +/- 52 ml/min, and a total flow of 600 ml for the first injection seem to offer the best cellular protection with minimal physical injury to the endothelium and endocardium for a mean canine heart weight of 236 gm.

Validation of transport measurements in skeletal muscle with N-13 amino acids using a rabbit isolated hindlimb model

We are studying the transport of C-11 and N-13 labeled amino acids in tumor-bearing rabbits to determine the role of amino acid transport in the pathogenesis of muscle wasting in cancer. To validate a new, in vivo, method for measuring transport in skeletal muscle with these compounds, an isolated hindlimb model was developed in rabbits. The limb was perfused with a non-recirculating, normothermic, constant pressure system and a cell-free perfusate. Hemodynamic and metabolic parameters were measured during the first 75 min. of pergusion and found to remain normal and stable. Flow varied directly with perfusion pressure over the normal range of resting flows in the intact rabbit hindlimb. Time-activity curves (TAC's) were recorded from the medial thigh following bolus co-injection of L-[amide N-13] glutamine or N-13 L-glutamate with Tc-99m human serum albumin (HSA) into the femoral artery. Regional plasma flow was determined from the Tc-99m data. The N-13 TAC's consistently manifested a three-phased washout with half times of approximately 30 sec., 5 min. and 2 hr. Capillary and cellular transport parameters were computed from the N-13 data using a double barrier, single capillary model of capillary and cellular transport and assuming that the three washout components result, respectively, from tracer throughput, extraction into the interstitial space and extraction into the intracellular space. This interpretation was validated and the sensitivity of the technique to transport processes demonstrated by examining the effects on the N-13 TAC's and computed transport parameters of several factors known to influence cellular transport of amino acids, viz., the insulin concentration, amino acid concentration and pH of the perfusate. Time-activity curves and transport parameters for N-13 L-glutamine in the isolated limb were very similar to those observed in the intact rabbit hindlimb, suggesting that studies in the perfused model are indicative of amino acid transport in vivo. The methodology described here is especially well suited for studying the specific effects on transport of factors which influence amino acid metabolism in skeletal muscle (e.g., hormones and monokines).

Studies on combustion of fuel spray injected from constant pressure system with single compression machine.

Studies on combustion of fuel spray injected from constant pressure system with single compression machine.

ChemInform Abstract: Palladium/Hydrogen Membrane Electrode for High Temperature/High Pressure Aqueous Solutions.

AbstractSeveral Pd‐Ag alloy membrane electrodes with suitable H2 partial pressure on the dry side (a detailed description of the electrode design is given) have been tested over the temp. range 100‐300 °C at a constant system pressure of 10000 kPa and a H2 pressure range of 300‐7000 kPa, in solutions with a pH range of 5‐11. The electrode is a suitable high temp./high pressure electrode.

Intracrystalline diffusion of benzene in ZSM—5 and silicalite

A gravimetric constant pressure system was used to investigate the sorption isotherms and diffusivities of benzene in monocrystals of ZSM—5 and silicalite in the temperature range 303–423 K. The corrected diffusivities decrease with increases in quantity. The absolute values of corrected diffusivities are lower within the channel system of ZSM—5 compared with silicalite. The corrected diffusivities in the system benzene—ZSM—5 were confirmed by independent measurements using a constant volume — variable pressure device.

Palladium/Hydrogen Membrane Electrode for High Temperature/High Pressure Aqueous Solutions

Several reference electrodes have been reported for high temperature/high pressure aqueous solutions, but none of them are fully satisfactory for fast relaxation measurements of electrode kinetics. The charged palladium electrode seems to fulfill all requirements at lower temperatures, but above 200°C the diffusional loss of hydrogen, into a solution not saturated with hydrogen, is very fast and the electrode must be recharged frequently. This problem can be overcome by use of a palladium‐silver alloy membrane as an electrode with suitable hydrogen partial pressure on the dry side. Several electrodes of this type were built and tested over the temperature range from 100° to 300°C at a constant system pressure of 10,000 kPa and a hydrogen pressure range of 300–7000 kPa, in boric acid/lithium hydroxide solutions with a pH range of 5–11. The palladium membrane electrode was found to operate as a classical hydrogen electrode and is usable either as apH electrode (combined with a pH‐independent reference electrode) or as a reference electrode (in a constant pH solution).

A NEW TECHNIQUE TO ASSESS THE DEFORMABILITY OF RED AND WHITE BLOOD CELLS

The pathological importance of abnormal blood cell rheology in ischaemic disorders has been widely investigated during the past decade. There continues to be a need for a simple, accurate and clinically applicable technique which can distinguish between transit and clogging of different blood cells in a filtration system. The St. George's Blood Filtrometer measures independently blood cell transit time and the clogging rate in a constant pressure system by accurately detecting the filtration rate of three successive small volumes (3 × 20 μl) of blood cell suspension at the beginning of filtration. From this data the initial cell filtration rate and transit time as well as the clogging rate are calculated automatically. The method is able to exclude some of the artefacts which have interfered with previous blood cell filtration techniques: (1) cell sedimentation on the surface of filter membrane, (2) early decrease of filter capacity by pore clogging, (3) unphysiologically high and varying perfusion pressure. The St. George's Blood Filtrometer gives reproducible results with a C.V. of less than 5%. This new technique has now been applied clinically and rheological abnormalities in the red and white cells have been demonstrated in different diseases.

Application of a low-pressure differential filtration technique to suspensions of red blood cells.

The paper describes a low-pressure 2 cm H2O, 5μm nuclepore filtration system for assessing red blood cell flexibility in suspensions of native plasma. Details are given of the white cell removal technique and filter handling methods for improved repeatability. Calibration of the system and filters using physiological saline controls is detailed and the advantages of a constant-pressure system are discussed. Data on filtration rates from normal controls and diabetics are given. Comparison of thisin votro system with literature data onin vivo systems is made.

Adsorption and diffusion of C 6 and C 8 hydrocarbons in silicalite

A constant-volume, constant-pressure system was employed to measure the adsorption isotherms and diffusion coefficients of C 6 (hexane, cyclohexane and benzene) and C 8 ( p-xylene, m-xylene, o-xylene and ethylbenzene) hydrocarbons in silicalite in the temperature range of 20°–200°C. The difference in equilibrium adsorption capacity and diffusion coefficient for these hydrocarbons is discussed in terms of the shape selective characteristics of the silicalite and size of the adsorbate molecules.

Effects of nitroprusside on pancreatic juice secretion in the blood-perfused canine pancreas

The effects of nitroprusside on the secretion of pancreatic juice were investigated in preparations of isolated and blood-perfused canine pancreas. Nitroprusside (10−30 μg/kg) injected intravenously elicited a dose-dependent increase in pancreatic secretion accompanied by a decrease in blood pressure. Intra-arterial administration of nitroprusside (3–300 μg) into the perfused pancreas also elicited an increased secretion in preparations of both constant pressure and constant flow perfusion system. The results suggest that nitroprusside-induced pancreatic secretion may not result from the peripheral vasodilation caused by nitroprusside. The effect of 100 μg of intra-arterial nitroprusside corresponded roughly to that of 0.1 units of secretin or 0.3 units of pancreozymin. Nitroprusside-induced secretion was inhibited by the infusion of ethacrynic acid (1 mg/min), but was not modified by phentolamine, propranolol, atropine, haloperidol, tetrodotoxin and metiamide. Nitroprussine produced a dose-dependent increase in the bicarbonate and protein concentrations in the juice, but had little effect on chloride concentration. This action was different from that of secretin or pancreozymin. It is concluded that nitroprusside may produce an increase in pancreatic secretion by acting directly on pancreatic cells, and that this action may be mediated at least in part through the increase of intracellular cyclic GMP concentration.

The Self-Regulated Hydrostatic Opposed-Pad Bearing in a Constant Pressure System

It is shown that a self-regulated hydrostatic opposed-pad bearing which allows for the continuous and automatic distribution of the total flow into two half-flows in the two recesses is highly efficient in a constant pressure system. Its performance is comparable to that of a conventional hydrostatic opposed-pad bearing compensated with flow control valves, and is superior to that of a conventional bearing compensated with orifices or capillary tubes. Its performance may be further improved if the self-regulated bearing itself is compensated with an orifice or a capillary tube.

Vascular perfusion of the isolated rat stomach with a fluorocarbon emulsion.

A constant-pressure system using a fluorocarbon (FC-75) containing artificial medium was used for vascular perfusion of the isolated rat stomach. A 10% emulsion of FC-75 in a modified Tyrode solution, containing 3.5% bovine serum albumin, amino acids, nucleosides, and beta-hydroxybutyrate appeared to allow an adequate perfusion for at least seven hours. The following criteria were used to estimate for functional state of the perfused stomach: (1) venous flow, (2) oxygen consumption, (3) leakage from the blood vessels to the gastric lumen, (4) ultrastructure, (5) secretion of H+ and pepsinogen after stimulation, and (6) transport of labelled macromolecules. During perfusion oxygen consumption and venous flow remained, after an initial high value, constant for at least seven hours. Leakage from the vascular bed was absent. Ultrastructure was preserved for at least seven hours. Administration of pilocarpine led to secretion of HCl ad pepsinogen. Pentagastrin and histamine stimulated HCl secretion in only some of the preparations. [3H]-galactose was incorporated into macromolecules and transported from the Golgi-region towards the apex of the cell. These observations led to the conclusion that the described vascular perfusion system in at least an appropriate model for studying glycoprotein synthesis.

Pressure-temperature-composition relationships for heated drawsalt systems

A molten nitrate salt mixture consisting of 60% NaNO 3 and 40% KNO 3 by weight is an attractive candidate for a heat transfer and thermal energy storage fluid in large-power solar systems. The relationships between pressure, temperature and composition (nitrate to nitrite ratio) have been determined for this salt mixture under two system configurations: constant volume (sealed containment) and constant pressure (open containment). For the first, families of pressure-temperature and composition-temperature curves were generated for initial salt volume fractions of 0.1 to 0.7. For the constant pressure system, composition-temperature curves were generated for oxygen pressures of 1, 0.2, 0.01 and 0.001 atm.

Glycoprotein synthesis in the mucous cells of the vascularly perfused rat stomach. I. Surface mucous cells.

We developed a constant-pressure vascular perfusion system of the isolated rat stomach, utilizing an artificial, fluorocarbon (FC-75)-containing medium. Perfusion could be maintained for at least six hours, as demonstrated by the ultrastructure of the mucosal cells and by the constant incorporation of [3H]-galactose in the surface mucous cells. Moreover all mucous cell types in tissue fixed after six hours of perfusion showed the same histochemical reactions for glycoproteins as in tissue fixed shortly after decapitation of the animal. The surface mucous cells of the antrum incorporated 30% less [3H]-galactose, [3H]-serine and [35S]-sulphate than those of the fundus. The amount of radioactivity incorporated per cell did not decrease during a subsequent 2 hour chase.

Bearings for Sulzer Slow‐Speed Diesel Engines

In a paper to the Institute of Marine Engineers in London on 14th November, Dr. P. E. A. Borgeaud (Technical Director, Diesel Engine Department, Sulzer Brothers Ltd., Winterthur) presented some detailed developments in the RND range of Sulzer slow‐speed Diesel engines which, a few years ago superseded the RD series. The main difference in the new range was in the super‐charging arrangement: pulse system for RD and constant pressure system for RND. Service experiences have caused various refinements and improvements, and in connection with bearings, the author had this to say.

Unsteady state operation of a reverse osmosis desalination unit

The effect of a variable power input on a reverse osmosis desalination system has been studied. Membranes were subjected to a continuous sinusoidal flow velocity change at a constant system pressure of 600 psi. Feed was a brackish water solution of sodium chloride and tap water. For the test period, it was found that constant variation in the feed velocity had no effect on the membrane performance. In fact, the product flux and salinity curves were similar to those obtained under steady state conditions.