Changes In Hydrostatic Pressure Research Articles

Diffusion profiles of Na+-fluorescein in frog ventricular muscle

Frog ventricular muscle strips were placed in a single sucrose-gap chamber to measure the interdiffusion of solutes across the sucrose-Ringer's solution partition. Steady-state diffusion profiles of fluorescein sodium developed along the axis of the muscle in the physiological node by continuously perfusing the sucrose pool with 210-mM sucrose plus fluorescein (5-10 mM). Fluorescein was found to diffuse freely through the extracellular space of the ventricular muscle without binding to the tissue. The fluorescence of Na+-fluorescein in the muscle (measured at 530 +/- 30 nm) varied linearly with the dye concentration in the sucrose perfusate. The diffusion profiles of dye in the test node depended on the tightness or snaring of the muscle strip by the latex diaphragms, the diameter of the muscle strip, and changes in hydrostatic pressure between the sucrose and Ringer's solution pools. Fluorescein concentration in the cross section of test node closest to the latex partition (sucrose-Ringer's solution interface) ranged between 4-13% of the dye concentration in the sucrose pool. These values are more than five times smaller than those estimated theoretically, assuming free diffusion. The experimental findings indicate that the presence of a physical barrier, such as a rubber diaphragm, limits free interdiffusion of solutes across the sucrose gap. The presence of such a barrier thus prevents large concentration gradients from occurring in the extracellular spaces along the physiological node.

Bubble Nucleation and Growth in Open-Cycle OTEC Subsystems

Bubble nucleation and growth in the evaporator, condenser, upcomers, and feedwater distribution systems of open-cycle ocean thermal energy conversion (OTEC) power plants are examined. The phenomenon that will probably have the most impact on system design is cavitation in the warm water feed near the entrance of the evaporator. The critical bubble size for cavitation is about 105 μm. Sources of bubbles in the warm water feed are those entering from the ocean, those nucleating on suspended particles, and those nucleating on the upcomer wall. Analyses of bubble growth induced by changes in hydrostatic pressure, mass transfer, and coalescence are presented. Using available information for bubble size distribution in seawater at California locations, it is shown that cavitation will probably have a significant impact on evaporator performance unless a debubbler is provided upstream of the evaporator entrance.

Role of hydrostatic and oncotic pressures in renal sodium reabsorption.

Physical factors, and renal interstitial hydrostatic pressure in particular, have an important effect on sodium excretion by the kidney. Changes in hydrostatic and oncotic pressures in the peritubular microcirculation may have effects on proximal tubule reabsorption under some, but not all, circumstances. In regard to control of sodium excretion, the loop of Henle may be a particularly important segment which is sensitive to transepithelial hydrostatic pressure changes. There is little evidence to support an effect of physical factors on sodium reabsorption by the distal tubule. The collecting tubule may be another pressure-sensitive site; however, changes in sodium reabsorption by deep nephrons in the kidney may account for changes that have been attributed to the collecting duct. Changes in intrarenal pressure may be an important link in the regulation of sodium excretion, particularly in pathological circumstances, such as the exaggerated natriuresis of hypertension and the sodium retention seen in congestive heart failure.

Clinical Implications of Experiments on Alteration of the Labyrinthine Fluid Pressures

Hearing is affected by changes in hydrostatic pressure of the perilymph, but very high pressures are required to produce a significant loss. Among the observed findings in cats are a rapidly reversible decrease in the sensitivity of the cochlear microphonic that is greater for low frequencies, harmonic distortion and reduction of dynamic range as measured by the input-output function for the cochlear microphonic, and a change in the summating potential from negative to positive. These changes are attributed to a temporary reduction in the size of the cochlear duct due to a shift of water molecules out of the cochlear duct into the blood until the resulting increase in osmotic pressure balances the increase in hydrostatic pressure. Consequently, the organ of Corti is biased "upward" away from the scala tympani. Increasing the hydrostatic pressure of the endolymph produces a "downward" biasing of the organ of Corti and has an opposite effect upon the summating potential. Presumably this is what happens in Meniere's disease. Because of the presence of the perilymphatic canaliculi, the locus of the hydrostatic pressure effect is assumed to be in the region of the reticular lamina. A theory has been developed to explain why cochlear function is very sensitive to relative differences between the hydrostatic pressures of the perilymph and the endolymph but is resistant to large variations in the absolute magnitudes of those pressures. Some of the clinical implications of this theory are discussed.

The Feeding Behaviour of a Cleaner and Scale, Skin and Fin Eater From Lake Malawi (Docimodus Evelynae; Pisces, Cichlidae)

Adult Docimodus evelynae feed upon scales, skin and fins of other fishes. Juveniles feed mainly on Aufwuchs and plankton, but small individuals (less than 50 mm SL) also clean fungi from other cichlids. The change from juvenile to adult diet takes place when individuals are between 60-80 mm SL. At this stage dentition alters: juvenile tricuspid teeth are replaced by adult unicuspid teeth. D. evelynae lives in predominantly rocky habitats where it occurs from the extreme shallows to depths of at least 91 m. Field observations indicated that it can tolerate marked changes in hydrostatic pressure. This was confirmed experimentally and it was also shown that this species can compensate physiologically for pressure changes more rapidly than all the other cichlids studied.

Thermoelastic temperature changes in poly(methyl methacrylate) at high hydrostatic pressure: Experimental

Temperature changes as a result of large rapid hydrostatic pressure changes were measured for poly(methyl methacrylate) at various temperatures from ambient to 95 °C and for various pressure increments from 14 to 207 MN/m2. We observe complete reversibility of the measurements over the pressure range studied. The value of the incremental ratio ΔT/ΔP was a function of both temperature and pressure, ranging from 0.04 to 0.09 K/MNm−2 from 298 to 368 K at low pressures, and 0.03–0.05 at 200 MN/m2 over the same temperature range. The largest variation of ΔT/ΔP with pressure was at low pressures, the ratio becoming nearly constant above about 200 MN/M2.

The Effect of Hydrostatic Pressure Cycles on the Activity of Young Plaice Pleuronectes Platessa

The responses of marine animals to changes in hydrostatic pressure have been widely studied (see reviews by Knight-Jones & Morgan, 1966; Fliigel, 1972; Nay lor & Atkinson, 1972). Most of these studies, however, have been concerned with invertebrates, particularly Crustacea, and few deal with fish (Gordon, 1970). Blaxter's (1978) review of baroreception summarizes recent work in this field and points out that a limitation of many experiments has been the use of sudden, rather than gradual, pressure changes. The limitation is especially true with respect to fish. This paper describes the results of experiments in which young plaice (Pleuronectes platessa L.) were subjected to hydrostatic pressure cycles of varying amplitude and frequency in order to describe the response to such pressure cycles, to determine the threshold of the response and to relate the response to the fish's behaviour in the sea.

Methodologic considerations in the study of glomerular ultrafiltration.

Over the past decade numerous studies have detailed the dynamics of glomerular ultrafiltration. Observations in a unique strain of Munich-Wistar rats, which afford the direct measurement of intraglomerular capillary hydrostatic pressure, have determined that under normal physiologic conditions these animals are in a state of filtration equilibrium. Both mathematical models based on this observation and experimental evidence indicate that under these circumstances the primary determinant of glomerular filtration rate (GFR) is the rate of glomerular plasma flow. In addition, this state of filtration equilibrium provides a condition in which changes in the product of glomerular surface area and glomerular capillary hydraulic conductivity (ultrafiltration coefficient) have no influence on glomerular filtration rate. Similarly, changes in glomerular hydrostatic pressure have a relatively small influence on GFR. These conclusions represent a marked alteration of the previously held concepts of the determinants of GFR. Unfortunately, studies in other strains of rats and in other animal species, particularly the dog, have led to the conclusion that filtration disequilibrium is the normal physiologic condition. The validity of this conclusion, however, is made uncertain by methodologic necessities that may lead to erroneous physiologic measurements of the determinants of GFR. In the present Editorial Review we examine the data reflecting on the applicability of filtration equilibrium to mammalian species. In addition, we summarize two new in vitro techniques for the further study of the dynamics of glomerular ultrafiltration.

Response of the soft tissue microcirculation to prostacyclin infusion

We studied the effect of prostacyclin infusion on the soft tissue microcirculation. We used lymph flow Q L and the lymph/plasma L/P protein ratio to reflect transvascular fluid flux and changes in microvescular hydrostatic pressure, Pmv. Unanesthetized sheep with prefemoral lymph fistulae were infused with PGI 2 (0.2 ug/kg/min) for two hours. Changes in Q L and L/P were compared to animals in which P mv was increased by volume loading. During PGI 2, Q L was significantly increased, as was cardiac output while mean aortic pressure decreased. The UP ratio did not decrease to the degree seen with a comparable increase in Q L, due to an increase in P mv. The increase in Q L was most likely due to an increase in microvescular surface area. Q L remained significantly increased for several hours after infusion and L/P decreased to the same degree as seen with an increase in P mv. This indicates that Pmv is increased for several hours in soft tissue after PGI 2 infusion, due to a relative increase in venous resistance probably secondary to activation of the renin-angiotensin system.

Cement distribution during post cementation

The distribution of the cement around parallel-sided and tapered posts coated with cement, and when cement was inserted into the prepared post hole, have been compared. In every case coating the post with cement gave rise to an incomplete cement film. Rough-surfaced posts and tapered posts retained more cement than smooth parallel posts. The method of post cementation may have an important bearing on retention in vivo. Further studies to measure intra-radicular hydrostatic pressure changes and post retention are required before an optimum method of post cementation can be promulgated.

The auditory bullae–swimbladder system in late stage herring larvae

Herring larvae, when they are about 30 mm long, swallow air and fill their auditory bullae with gas. It has been shown earlier that this is associated with a great increase in sensitivity to changes in hydrostatic pressure. Here we show that it is also associated with the appearance of a startle response to noises.At this stage of development, the utricular maculae are fully developed. However, the bullae are bounded by thin walls which are poorly calcified and the bulla membranes are thin and contain little elastic tissue. None the less the high-frequency cut-off in the mechanical responses to oscillating pressures is as high as that of the adult.

Frontal bodies: Novel structures involved in water vapour absorption by the desert burrowing cockroach, Arenivaga investigata

Above 83% relative humidity, nymphs and adult females of the desert cockroach can condense water vapour on to a fluid layer covering protruded hypopharyngeal bladders. This fluid is produced by a pair of spheroidal bodies situated beneath the frons. Each such frontal body is connected by to the corresponding bladder by a groove in the epipharynx. During absorption, contraction of muscles connecting the frontal bodies to the frons causes them to move dorsally from the mandibles. Oscillation frequency increases with relative humidity or the application of nanoliter quantities of water to the bladders. Frontal bodies appear to be derived from invaginations of the integument, and consist of a mass of tough fibres containing protein and chitin. Fibres embed in a permeable plate which gives rise to the epipharyngeal groove. Tonofibrillae connect the fibres to elongate epidermal cells which are composed primarily of microtubules. The myoepidermal junction is characterized by fascia adherens. Frontal bodies resist tensile forces, but undergo changes in shape as they oscillate. Accompanying changes in hydrostatic pressure may move extracellular fluid across the plate and into the epipharyngeal groove. Possible roles of the fluid in the absorption process are discussed.

Generic Predominance Facies Among Deep-Water Benthic Foraminifera of Gulf of Mexico: ABSTRACT

A synthesis of published and unpublished records of benthic foraminifera from the continental slope, rise, and the abyssal plains of the Gulf of Mexico reveals environmentally influenced facies of generic predominance. Circum-Gulf facies of predominant Brizalina, Uvigerina, and Bulimina are present on the continental slope and appear to be associated with water mass patterns or hydrostatic pressure changes. The Glomospira facies, which is patchily distributed on the continental slope and rise appears to be a result of geochemical conditions on bottom prominences. In abyssal depths, the Eponides-Nuttallides and Cibicides facies are associated with contrasting substrates on the Sigsbee Plain and Mississippi fan, respectively. Trends in the diversity of generic predominance acies mimic species diversity trends in other silled basins, and decrease from seven facies on the slope, to two facies on the Sigsbee Plain. End_of_Article - Last_Page 973------------

Hematologic response of fish to changes in gas or hydrostatic pressure.

Hematologic changes were studied in fingering salmon after rapid decompression from combined or independent exposure to gas and hydrostatic pressure. After decompression, fingerling salmon saturated with excess gas under pressure (10.1-40.6 m of seawater) suffered a decrease in thrombocyte counts and fibrinogen, prolonged prothrombin (PT) times, and increased fibrinolytic activity, plasma proteins, and erythrocyte counts in proportion to severity of the dive. After decompression, fingerling salmon exposed to increased pressure experienced an increase in thrombocyte counts and available fibrinogen, shortened PT times, increased erythrocyte counts, and decreased plasma protein levels. It appeared that pressure causes activation of the blood coagulation system of fish. This activation may predispose the fish to increased susceptibility to bubble-induced diffuse intravascular coagulation after rapid decompression. Furthermore, hemoconcentration after decompression may be a pressure-related phenomenon and not a response to bubble-induced anoxia.

Hydrostatic pressure changes related to paracellular shunt ultrastructure in proximal tubule

We examined the effets of changes in hydrostatic pressures on the ultrastructural geometry of the lateral intercellular space and tight junctions in proximal tubules of contrtol (C) and volume-expanded (VE) Necturus kidney. The following groups of tubules were studied: (1) C, free-flow pressure, (2) C, stopped-flow, high-luminal pressure, (3) C, stopped-flow, low-luminal pressure, (4) VE, free-flow pressure, and (5) VE, stopped-flow, high-luminal pressure. Intratubular and peritubular capillary pressures were monitored before and during standardized perfusion-fixation for electron microscopy, and complete cross-sections of all sampled tubules were subjected to morphometric analysis. Average lateral intercellular space widths decreased significantly in C and VE stopped-flow tubules with high-luminal pressures but widened greatly in C stopped-flow tubules with low-luminal pressures. The length or width of the tight junctions did not change between the five experimental conditions. The ultrastructural changes correlate with the applied transepithelial pressure gradients rather than with transepithelial volume fluxes. The narrowing of lateral intercellular spaces in high pressure tubules correlate with the previously described increase in electrical resistance expressed per unit length tubule indicating that in these conditions part of the paracellular resistance is located in the free interspaces. The geometry of the lateral intercellular space in the proximal tubule of Necturus favors models of near-isotonic transport that do not depend on long and narrow interspaces.

Observations and speculations on the alate processes of the ascidicolous copepod Notopterophoms papilio (Cyclopoida: Notodelphyidae)

The alate processes (“wings”) of the notodelphyid copepod Notopterophoms papilio Hesse have been studied at light microscope and electron microscope (scanning and transmission) level. General cuticular structure and three integumental organs occurring on the wings are described. These latter comprise a glandular pore, a bulb‐like protrusion and a long, hair‐like seta. It is suggested that all three may be concerned with maximising naupliar release and safe extrusion of young from the potentially hazardous confines of the ascidian host's pharynx. The proposed mechanism involves rheoreception and the detection of small changes in hydrostatic pressure through the medium of electrode action in the cuticle.

Renal perfusion and intratubular pressure during ureteral occlusion in the rat.

To define the interrelationship between changes in total renal blood flow (TRBF) and proximal tubular hydrostatic pressure (PTP), rats were studied 2, 3, 4, 6, 12, 18, and 24 h after bilateral ureteral occlusion (BUO). In control animals, a peak rise in both TRBF (3.52 +/- 0.26 ml . min-1 . 100 g body wt-1 . kidney-1) and PTP (28.6 +/- 1.3 mmHg) occurred 3 h after BUO. At each subsequent time interval, both TRBF and PTP fell, so that by 24 h after BUO, TRBF was 1.53 +/- 0.34 and PTP was 16.5 +/- 0.6, while in sham-operated rats the values were 2.52 +/- 0.22 ml . min-1 . g body wt-1 . kidney-1 and 12.8 +/- 0.2 mmHg, respectively. In animals treated with indomethacin (10 mg/kg) at the time of BUO, the alterations in both TRBF and PTP were completely ameliorated. At 3 h, TRBF was 1.8 +/- 0.32 ml . min-1 . 100 g body wt-1 . kidney-1 and PTP was 15.3 +/- 1.0 mmHg. TRBF and PTP remained essentially unchanged at each subsequent time period. These data indicate that 1) alterations in TRBF and PTP follow a similar and parallel pattern during BUO; 2) the pattern of changes in TRBF and PTP can be eliminated by treatment with indomethacin; and 3) renal hemodynamics appear to be the dominant factor in producing these changes during the first 12 h after BUO, whereas a sustained increase in tubular hydrostatic pressure may play a primary role in decreasing TRBF 12-24 h after ureteral occlusion.

An Apparatus to Record the Hydrostatic Pressure Changes Occurring during the Cementation of Dowel-Retained Prostheses

A new apparatus to measure the hydrostatic pressures developed during the cementation of dowel-retained prostheses has been developed and is described. The initial results obtained using this apparatus have been shown to vary from zero if the dowel is coated with cement, to 1.1 times 104 kN/m2 when cement is placed into the prepared hole for an optimally fitting dowel. Avenues of further research using this apparatus are mentioned.

Bulk flow of brain interstitial fluid under normal and hyperosmolar conditions.

Although bulk flow of brain interstitial fluid (ISF) occurs with changes in hydrostatic and osmotic pressures, under normal conditions only diffusion of molecules in the ISF has been reported. Extrachoroidal cerebrospinal fluid (CSF) production and intracerebral injection studies, however, provide indirect evidence for the bulk flow of ISF under normal conditions. We studied tissue penetration profiles of an extracellular molecule in gray and white matter after 1-, 2-, 3-, and 4-h ventriculocisternal perfusions. Gray matter apparent diffusion coefficients were similar at different times as expected with diffusion; however, white matter coefficients decreased significantly with time, suggesting bulk flow of ISF. White matter data was reanalyzed for both bulk flow and diffusion; we calculated a diffusion coefficient of 3.00 x 10(-6) cm2/s and a velocity for ISF of 10.5 micrometers/min toward the ventricle. Additional animals were given 20% mannitol (1.5--3 g/kg) intravenously prior to a /-h ventriculocisternal perfusion. Mannitol produced a significant bulk flow of ISF away from the ventricle in gray matter. We estimate that 30% of extrachoroidal CSF production is from flow of ISF in white matter.

The effect of rapid changes of hydrostatic pressure on the Atlantic herring Clupea harengus L. I. Larval survival and behaviour

Larval Atlantic herring ( Clupea harengus L.) from 11–39 mm total body length were subjected to different series of pressure changes intended to simulate passage through the cooling water of a thermal power station. This involved both acclimation and rapid pressure increases to 5 atmospheres pressure, followed by rapid decompression. Subsequent mortality, feeding and depth-compensating behaviour were checked as well as the integrity of the gas-filled auditory bulla-swimbladder system which develops between 23–35 mm. There was no evidence of increases in mortality in larvae up to about 20 mm. Larvae from about 25–29 mm showed increased mortality over controls; still larger larvae did not. Larvae which survived the pressure treatment fed as well as controls. There was strong evidence that larvae of all ages attempted to compensate for pressure changes by making appropriate vertical swimming movements. Some of the mortality of the intermediate-sized larvae may be attributed to hyperactivity in a restricted (experimental) space. The bulla membrane in some older larvae was ruptured by the pressure changes. Although this was not immediately a cause of mortality, it would impair mechanical reception in the long term.