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PubMed1985

Vascular basis for regulation of nasal heat exchange in reindeer.

A hypothesis for the operation and control of nasal heat exchange in reindeer is presented that originated from studies of the nasal vascular anatomy and has been supported by physiological measurements as well as test experiments on a physical prototype model of the reindeer nose. A central theme of our hypothesis is that the nasal mucosa possesses arterial and venous retia that communicate by way of capillaries and arteriovenous anastomoses. During heat conservation the blood runs countercurrent in these retia, whereby a temperature gradient along the nasal mucosa can be maintained. During heat dissipation, however, the retia are perfused unidirectionally in the anterior direction, whereby the temperature gradient along the nasal mucosa is reduced and heat loss facilitated. In this situation cooled venous blood, routed by way of the dorsal nasal vein, may be distributed either to the caval veins directly, for general body cooling, or, by way of the cavernous sinus that encases the carotid rete, for selective cooling of the brain.

Animals↗

PubMed1980

Microbiology of acute otitis media with particular reference to the feasibility of pneumococcal immunization.

Middle-ear fluid was aspirated in 103 episodes of acute otitis media occurring in 100 South Australian children aged from four months to 14 years in 1977, and in 1978. Bacteria were cultured from the middle-ear fluid in 66% of cases, and viruses were grown in three cases in conjunction with bacteria. The bacteria grown were pneumococci in 30 cases (29%), Haemophilus influenzae in 26 cases (25%), beta-haemolytic streptococci in 12 cases (12%) and Neisseria spp. in six cases (6%). Pneumococci and H. influenzae were cultured from children of all ages, whereas beta-haemolytic streptococci were more frequently isolated in children aged five years and older. Countercurrent immunoelectrophoresis yielded positive results in 35% of culture-positive pneumococcal infections and gave additionally the positive reaction for pneumococci in two cases where culture produced negative results. The pneumococci which were isolated belonged to 12 serotypes; 26 of the 30 isolates were serotypes for which pneumococcal vaccines are currently available. There were appreciable differences in the distribution of serotypes from that encountered in a study of nasal carriage amongst healthy schoolchildren living in the same district.

Acute Disease↗

PubMed1979

Tamm-Horsfall glycoprotein: ultrastructural immunoperoxidase localization in rat kidney.

Tamm-Horsfall urinary glycoprotein (TH) is the primary constituent of urinary casts. The intracellular distribution of TH in normal rat kidney was determined by immunoelectron microscopy using horseradish peroxidase-labeled antibodies and compared with morphologic localization of TH by immunofluorescence and light immunoperoxidase microscopy. Electron microscopy revealed an intracellular localization of TH restricted to the thick ascending limb of the loop of Henle (ALH). In this nephron segment, TH was distributed on and between adjacent intercellular membranes and infolding intracellular membranes at the base of these cells, within Golgi vacuoles, apical vesicles, and on the luminal membranes. Macula densa cells were negative, although typical ALH cells across the lumen of the same tubular segment were positive. Other renal segments were negative for intracellular TH. The unique distribution of TH is consistent with the known function of the ALH as the diluting segment of the nephron. We speculate that the aggregation and gel formation of TH on and between ALH surface membranes may restrict water movement across the ALH. This influence on permeability would be an important role for TH in the generation of concentration gradients for the countercurrent multiplier system of the kidney.

Animals↗

PubMed1986

Contribution of angiotensin to the control of medullary hemodynamics.

The unique architecture and organization of medullary vasculature permit regional regulation of medullary hemodynamics by vasoactive hormones and are conducive to the operation of the countercurrent multiplication system. Recent studies suggest that an increase in inner medullary blood flow causes medullary solute washout, which in turn decreases passive sodium transport in the thin ascending limb of Henle's loop. In canine models of chronic sodium retention accompanied by activation of the renin-angiotensin system, glomerular filtration rate (GFR), renal blood flow (RBF), and intracortical blood flow distribution were similar to those in normal dogs; however, papillary plasma flow (PPF) was markedly reduced and papillary tissue solute content was increased significantly both during hydropenia and after saline loading. During euvolemic diuresis with loop diuretics, there was an increased renin release associated with a marked reduction in PPF, despite an increase in total RBF. Direct intrarenal infusion of angiotensin II (AngII) (at a dose not affecting GFR and RBF) induced ipsilateral sodium retention, conservation of urinary concentration, and papillary ischemia. These studies provide evidence for regional regulation of medullary hemodynamics by AngII, possibly contributing to sodium retention in chronic salt-retaining states.

Angiotensin II↗

PubMed1988

A combined macro and microvascular model for whole limb heat transfer.

A new prototype model for whole limb heat transfer is proposed wherein the countercurrent heat exchange from the large central arteries and veins in the core of the limb is coupled to microvascular models for the surrounding muscle and the cutaneous tissue layers. The local microvascular temperature field in the muscle tissue is described by the bioheat equation of Weinbaum and Jiji. The new model allows for an arbitrary axial variation of cross-sectional area and blood distribution between the muscle and cutaneous tissue, accounts for the blood flow to and heat loss from the hand and treats the venous return temperature and surface temperature distribution as unknowns that are determined as part of the solution to the overall boundary value problem. Representative solutions are presented for a wide range of environmental conditions for a limb in both the resting state and during exercise.

Arm↗

PubMed2005

Perfusion-diffusion compartmental models describe cerebral helium kinetics at high and low cerebral blood flows in sheep.

This study evaluated the relative importance of perfusion and diffusion mechanisms in compartmental models of blood:tissue helium exchange in the brain. Helium has different physiochemical properties from previously studied gases, and is a common diluent gas in underwater diving where decompression schedules are based on theoretical models of inert gas kinetics. Helium kinetics across the cerebrum were determined during and after 15 min of helium inhalation, at separate low and high steady states of cerebral blood flow in seven sheep under isoflurane anaesthesia. Helium concentrations in arterial and sagittal sinus venous blood were determined using gas chromatographic analysis, and sagittal sinus blood flow was monitored continuously. Parameters and model selection criteria of various perfusion-limited or perfusion-diffusion compartmental models of the brain were estimated by simultaneous fitting of the models to the sagittal sinus helium concentrations for both blood flow states. Purely perfusion-limited models fitted the data poorly. Models that allowed a diffusion-limited exchange of helium between a perfusion-limited tissue compartment and an unperfused deep compartment provided better overall fit of the data and credible parameter estimates. Fit to the data was also improved by allowing countercurrent diffusion shunt of helium between arterial and venous blood. These results suggest a role of diffusion in blood:tissue helium equilibration in brain.

Animals↗

PubMed1984

Theory and experiment for the effect of vascular microstructure on surface tissue heat transfer--Part II: Model formulation and solution.

In this paper the conceptual three-layer representation of surface tissue heat transfer proposed in Weinbaum, Jiji and Lemons [1], is developed into a detailed quantitative model. This model takes into consideration the variation of the number density, size and flow velocity of the countercurrent arterio-venous vessels as a function of depth from the skin surface, the directionality of blood perfusion in the transverse vessel layer and the superficial shunting of blood to the cutaneous layer. A closed form analytic solution for the boundary value problem coupling the three layers is obtained. This solution is in terms of numerically evaluated integrals describing the detailed vascular geometry, a capillary bleed-off distribution function and parameters describing the shunting of blood to the cutaneous layer. Representative heat transfer results for typical physiological conditions are presented.

Animals↗

PubMed2003

Effects of novel manufacturing technology on blood and dialysate flow distribution in a new low flux "alpha Polysulfone" hemodialyzer.

The main target for low flux hemodialyzers is an efficient low molecular weight solutes clearance. Such efficiency is largely dependent on the optimization of diffusion between blood and dialysis solution. The diffusion process can be impaired if there is a mismatch between blood and dialysate flow distribution in the dialyzer. Thus optimized flow distribution both in the blood and dialysate compartment becomes quintessential for the maximal efficiency of the diffusion process within the hemodialyzer. The present paper describes the distribution of the blood and dialysate flows in a new low flux polysulfone hollow fiber hemodialyzer characterized by a specific undulation of the fibers and a new cutting technology of the fibers for an improved micro-flow condition in the blood compartment headers. Twelve Diacap alpha Polysulfone LO PS 15 (1.5 sqm) (B. Braun Medizintechnologie, Melsungen Germany) were employed for the study. Six were analyzed in vitro and six were studied in vivo. Blood flow distribution was studied in vitro by dye injection in the blood compartment during experimental extracorporeal circulation utilizing human blood with hematocrit adjusted at 33%. Sequential images were obtained with a helical scanner in a fixed longitudinal section of the dialyzer 1 cm thick. Average and regional blood flow velocities were measured utilizing the reconstructed imaging sequence. The method allowed the calculation of single fiber blood flow (SF Qb) and the mass transfer zone (MTR) definition in digitally subtracted images. The patterns 20-10 and 40-30 were utilized. The same technology was used to evaluate flow distribution in the dialysate compartment after dye injection in the Hansen's connector. Regional dialysate flow was calculated in central and peripheral sample areas of 1 cm2. Six in vivo hemodialysis treatments on patients with end stage renal disease were performed at three different blood flow rates (250-350 and 450 ml/min) in order to measure urea, creatinine and phosphate clearance. Macroscopic and densitometrical analysis revealed that flow distribution was homogeneous in the blood compartment while in the dialysate compartment a slight difference between the peripheral and central regions in terms of flow velocity was observed. This however was not generating channeling phenomena. Urea creatinine and phosphate clearances were remarkably high and so were the Kt/V observed in all sessions, especially in relation to the studied blood flows. In conclusion, a significant blood to dialysate flow match with optimized countercurrent flow condition was observed in the studied hollow fiber hemodialyzers. Such optimization might be due both to the improved dialyzer design at the level of the blood header and to the specific fiber undulation that prevents dialysate channeling.

Biocompatible Materials↗

PubMed1985

The elasmobranch kidney. I. Gross anatomy and general distribution of the nephrons.

The morphology of the little skate (Raja erinacea) and spiny dogfish shark (Squalus acanthias) nephron has been investigated in sexually mature females by 1) gross observations of the kidney surfaces, 2) vascular injections, 3) scanning electron microscopy, 4) light microscopy. In the little skate, each nephron is highly complex and begins at the urinary pole of the renal corpuscle, which is located between a thin, dorsal bundle zone and a thicker, ventral sinus zone. The nephron loops back and forth, repeatedly entering and exiting each zone. In the bundle zone, segments from each nephron form a bundle of 5 tubules (tubular bundle) which are arranged in a countercurrent loop fashion. A peritubular sheath composed of closely packed, squamous cells wraps the 5 nephron segments of the tubular bundle together and separates each bundle from the next. In the sinus zone the tubules from many nephrons mix freely with each other in large blood sinuses. In the spiny dogfish, the nephron displays a complex pattern similar to that of the skate. Renal corpuscles are adjacent to a bundle zone composed of tubular bundles, each wrapped by a peritubular sheath in a cell-rich connective tissue matrix. However, the bundle zone is not limited to the dorsal region of the shark kidney but extends ventrally along deep interlobular septa. The sinus zone of the shark is like that of the skate except that it is not limited to the ventral regions of the kidney.

Animals↗

PubMed1975

Intrarenal distribution of citrate in the dog during antidiuresis and diuresis.

The intrarenal distribution of citrate was evaluated in the dog during antidiuresis and osmotic diuresis, by using the specific citrate assay method of Moellering and Gruber. The measurements were made on tissue samples taken from four different regions throughout the kidney: cortex, outer and inner medulla, and papilla. During antidiuresis, a characteristic distribution of citrate was observed with highest levels in the papilla and lowest ones in the outer medulla. A medullary concentration gradient for citrate was found. Mannitol greatly decreased papillary citrate and sodium, but no changes in outer and inner medullary citrate occured. The results could not be explained by the citrate contained either in the trapped urine or blood in the tissue. It is suggested that citrate accumulation in the inner regions of renal medulla may be accounted for by countercurrent mechanisms or regional differences in renal citrate metabolism.

Animals↗

PubMed1990

An electrospray-ionization mass spectrometer with new features.

The construction and performance of an electrospray-ionization mass spectrometer with new features are described. The mass spectrometer consists of a newly designed electrospray ion-source that is plugged directly into a modified commercial quadrupole mass spectrometer with the ions entering the mass analyzer through a long metal capillary tube and three stages of differential pumping. The present ion source differs from previous designs in the combination of techniques employed in the transportation and desolvation of solvated biomolecule ions, prior to mass analysis. Transport of ionized entities between atmospheric pressure and vacuum is carried out through a 203 mm long stainless steel capillary tube with a 0.5 mm bore. Desolvation is effected by the use of controlled heat transfer through the long capillary tube and collisional activation in a region of reduced pressure between the capillary tube exit and the skimmer. Desolvation with this system is convenient and effective and does not involve the strong countercurrent flows of gases that have been used by all previous workers. The effects on the spectra of peptides of capillary tube temperature and desolvation collision energy are investigated. Electrospray-ionization mass spectrometric results are described for thirteen proteins with molecular masses ranging from 5000 to 77,000 Da. The performance of the present instrument, with respect to mass accuracy and sensitivity, is comparable with previously reported systems. The effect of protein concentration in solution on the electrospray mass spectrometric response and charge-state distribution is discussed.

Mass Spectrometry↗

PubMed1989

A compartmental model for oxygen transport in brain microcirculation.

A compartmental model is formulated for oxygen transport in the cerebrovascular bed of the brain. The model considers the arteriolar, capillary and venular vessels. The vascular bed is represented as a series of compartments on the basis of blood vessel diameter. The formulation takes into account such parameters as hematocrit, vascular diameter, blood viscosity, blood flow, metabolic rate, the nonlinear oxygen dissociation curve, arterial PO2, P50 (oxygen tension at 50% hemoglobin saturation with O2) and carbon monoxide concentration. The countercurrent diffusional exchange between paired arterioles and venules is incorporated into the model. The model predicts significant longitudinal PO2 gradients in the precapillary vessels. However, gradients of hemoglobin saturation with oxygen remain fairly small. The longitudinal PO2 gradients in the postcapillary vessels are found to be very small. The effect of the following variables on tissue PO2 is studied: blood flow, PO2 in the arterial blood, hematocrit, P50, concentration of carbon monoxide, metabolic rate, arterial diameter, and the number of perfused capillaries. The qualitative features of PO2 distribution in the vascular network are not altered with moderate variation of these parameters. Finally, the various types of hypoxia, namely hypoxic, anemic and carbon monoxide hypoxia, are discussed in light of the above sensitivity analysis.

Animals↗

PubMedDate not supplied

Surface markers and biological functions of PMNC fractionated by countercurrent centrifugal elutriation.

Peripheral blood mononuclear cells (PMNC) were separated by countercurrent centrifugal elutriation (CCE) in PBS-EDTA medium into 13 fractions. Properties associated with B cells were restricted mainly to the first fractions (F2 and F4) while those associated with T cells were confined to fractions F4, F6 and F8. The final fraction (FF) contained more than 90% monocytes while fraction F10 contained 40% monocytes and 60% null cells, and F12 contained 50% monocytes and 50% null cells. Natural killer (NK) cell activity against K-562, a human erythroleukaemia cell line, and against an adherent undifferentiated sarcoma target, was distributed between fractions F6 and F8. Using electron and scanning microscopy and a new single cell liquid cytotoxic assay, we studied membrane interaction and binding of the CCE fractionated cells with the 2 targets. Effector/target cell conjugates revealed interdigitations in the area of cell contact but no membrane fusion, although certain effector cells had a distinct large granulocytic lymphocyte morphology. Furthermore, different cell types from different fractions were able to bind to the targets although the killing was associated with certain fractions only. When purified monocytes from fraction FF were added to F6 and F8, NK activity against both targets was depressed. This inhibition was not reversed by indomethacin, and binding of the targets to the effector cells was unaffected. CCE is a powerful technique which allows the fractionation of PMNC without altering their biological functions, contrary to what is seen with nylon wool or dextran fractionation. In this report, the activity associated with CCE fractions is studied and discussed.

Antibody-Producing Cells↗

PubMed2004

Preparative enantiomer separation of dichlorprop with a cinchona-derived chiral selector employing centrifugal partition chromatography and high-performance liquid chromatography: a comparative study.

A countercurrent chromatography protocol for support-free preparative enantiomer separation of the herbicidal agent 2-(2,4-dichlorphenoxy)propionic acid (dichlorprop) was developed utilizing a purposefully designed, highly enantioselective chiral stationary-phase additive (CSPA) derived from bis-1,4-(dihydroquinidinyl)phthalazine. Guided by liquid-liquid extraction experiments, a solvent system consisting of 10 mM CSPA in methyl tert-butyl ether and 100 mM sodium phosphate buffer (pH 8.0) was identified as a suitable stationary/mobile-phase combination. This solvent system provided an ideal compromise among stationary-phase retention, enantioselectivity, and well-balanced analyte distribution behavior. Using a commercial centrifugal partition chromatography instrument, complete enantiomer separations of up to 366 mg of racemic dichlorprop could be achieved, corresponding to a sample load being equivalent to the molar amount of CSPA employed. Comparison of the preparative performance characteristics of the CPC protocol with that of a HPLC separation using a silica-supported bis-1,4-(dihydroquinidinyl)phthalazine chiral stationary phase CSP revealed comparable loading capacities for both techniques but a significantly lower solvent consumption for CPC. With respect to productivity, HPLC was found to be superior, mainly due to inherent flow rate restrictions of the CPC instrument. Given that further progress in instrumental design and engineering of dedicated, highly enantioselective CSPAs can be achieved, CPC may offer a viable alternative to CSP-based HPLC for preparative-scale enantiomer separation.

2,4-Dichlorophenoxyacetic Acid↗

PubMed1992

A three-dimensional variable geometry countercurrent model for whole limb heat transfer.

A new formulation of the combined macro and microvascular model for heat transfer in a human arm developed in Song et al. [1] is proposed using a recently developed approximate theory for the heat exchange between countercurrent vessels embedded in a tissue cylinder with surface convection [2]. The latter theory is generalized herein to treat an arm with an arbitrary variation in cross-sectional area and continuous bleed off from the axial vessels to the muscle and cutaneous tissue. The local microvascular temperature field is described by a "hybrid" model which applies the Weinbaum-Jiji [3] and Pennes [4] equations in the peripheral and deeper tissue layers, respectively. To obtain reliable end conditions at the wrist and other model input parameters, a plethysmograph-calorimeter has been used to measure the blood flow distribution between the arm and hand circulations, and hand heat loss. The predictions of the model show good agreement with measurements for the axial surface temperature distribution in the arm and confirm the minimum in the axial temperature variation first observed by Pennes [4] for an arm in a warm environment.

Arm↗

PubMed1984

Effects of dihydroergotamine on the feline cardiovascular response to intravenous infusion of live Escherichia coli bacteria.

A septic shock state was induced in cats by intravenous infusion of live Escherichia coli bacteria. Cats pretreated with an unspecific 5-HT blocker, dihydroergotamine (DHE), or with a specific 5-HT blocker, ketanserin, were compared with a series receiving bacteria without pretreatment. DHE pretreatment prevented the reduction in systemic arterial blood pressure found in the other series during the 2-hour period of septic shock. Pretreatment could not influence the increased vascular resistance in the pulmonary vascular bed or the early increase in pulmonary arterial blood pressure. Peripheral blood flow distribution was studied using radioactive labelled microspheres. Compared to bacteremia without pretreatment, the 5-HT blockers increased CNS blood flow and ketanserin also prevented the reduction in pancreatic blood flow. Gastric blood flow and gastric mucosal blood flow remained unchanged in all series as did the small intestinal total blood flow. Small intestinal mucosal blood flow, however, was reduced after 2 h of bacteremia. Microscopy revealed no gastric epithelial damage while the jejunal mucosa was characteristically damaged. There was no correlation between the changes in the small intestinal blood flow and the degree of mucosal damage, however, supporting the countercurrent theory for the pathogenesis of these lesions.

Animals↗

PubMed2000

The renal medullary microcirculation.

Blood flow to the renal medulla is supplied through descending vasa recta (DVR), which are derived from the efferent arterioles of juxtamedullary glomeruli. In addition to their role as conduits for blood flow, it is accepted that the vasa recta are countercurrent exchangers. That process, however, involves events which are more complicated than paracellular diffusive exchange of NaCl and urea. Urea transport in DVR is accommodated through the combined expression of endothelial and erythrocyte facilitated carriers while transport of water involves solute driven efflux across water channels. Unlike DVR, which have a continuous endothelium, ascending vasa recta (AVR) are fenestrated with a very high hydraulic conductivity. Transport of water in AVR is probably governed by transmural hydraulic and oncotic pressure gradients. The parallel arrangement of DVR in outer medullary vascular bundles coupled with their capacity for vasomotion implies a role for regulation of the regional distribution of blood flow within the medulla The importance of the latter process in the urinary concentrating mechanism and the exchange of nutrients and O2 is poorly defined. The large number of hormones and autacoids that influence DVR vasomotion, however, suggests that DVR have evolved to optimize the functions of the renal medulla.

Animals↗

PubMedDate not supplied

Transvaginal progesterone: evidence for a new functional 'portal system' flowing from the vagina to the uterus.

The results of many recent experimental and clinical studies support the hypothesis that progesterone administered vaginally is distributed selectively to the uterus where tissue concentrations and effects exceed expectations. This phenomenon has multiple clinical implications in several fields of gynaecological endocrinology, notably in assisted reproductive treatments and new forms of hormone replacement therapy. Yet, the actual mechanisms by which vaginal administration of progesterone can induce higher concentrations in the uterus, despite low concentrations in the systemic circulation, remain obscure and most puzzling to many gynaecologists. This review aims to muster ideas and propose different mechanisms to explain the observed phenomenon. In particular, we will summarize data that support the various putative modes of transport including, direct diffusion through tissue, intracervical aspiration, absorption into the venous or lymphatic circulatory systems and countercurrent vascular exchange with diffusion from utero-vaginal veins/lymph vessels to arteries. All these mechanisms may concur to various extents to the uterine specificity of vaginal progesterone.

Administration, Intravaginal↗