Pitfalls of venous occlusion method for determination of capillary pressure in humans

We tested the method of estimating capillary pressure from venous pressure transients obtained after sudden venous clamping in a hydrodynamic model. The basic principles were confirmed in the model, but it was found that when occlusion was caused over a relatively wide distance or in a predistended vessel, capillary pressure was overrated. This problem was due to volume backflow from the occlusion site, since it could be eliminated by placing a one-way valve upstream from the occlusion site. Upstream from the valve, the venous pressure transient accurately followed capillary pressure. Downstream, however, the reading of capillary pressure was impaired by the backflow volume squeezed between valve and occlusion clamp, which caused an immediate large pressure elevation. We also tested the method recently advanced to estimate capillary pressure in humans from venous pressure curves obtained after rapid venous occlusion with an air-filled compression cuff. With the cuff around the upper arm, venous pressure was recorded at different levels along the forearm. The tracings obtained from the dorsum of the hand and halfway along the forearm did not show the initial rapid upstrokes that might indicate the capillary pressure. Tracings obtained slightly below or above the cubital fossa were similar to those seen downstream from the one-way valve in the model. Extrapolation to zero-time, using the distally recorded curves as a template, yielded values equal to venous pressure. We conclude that although the problem of backflow can be circumvented by pressure recording distal from venous valves, the method of venous occlusion by a circular upper-arm cuff may not be appropriate to estimate capillary pressure in humans.     

Exogenous bacterial contamination of donor blood.

The Canadian Red Cross blood transfusion service has followed a set protocol for phlebotomy and collection of a unit of blood. Recent requirements for automated testing have necessitated that a second tube of blood be obtained from the blood line following collection of the unit. Evaluation of the techniques used, however, has indicated the possibility of bacterial contamination from the skin of donors, from insertion of the needle through an unsterile rubber stopper, and through backflow from a nonsterile vacuum tube. To test these possibilities swabs were taken from skin and stoppers of vacuum tubes. Further, vacuum tubes were deliberately contaminated with Escherichia coli. The normal sampling procedure, which involves stripping the donor line to refill and mix the blood, was then followed. This resulted in contamination of the segments and even the blood bag. These findings led to modification of the standard bleeding technique, whereby stripping was eliminated and sterile vacuum tubes were to be used at all times.     

With a system in turmoil,will there be enough blood?

In a short time Canadians won''t be able to recognize their blood-collection system. With the Red Cross getting out of the blood business and the government and business moving in, what will the changes mean for Canadians and their physicians?     

Plasma-collection plant has to overcome tainted-blood fallout in search for donors

Canada''s lack of self-sufficiency in blood products has led to the opening of a blood-plasma collection centre in Thunder Bay, Ont.--the first of its type in Canada. In convincing donors to donate plasma, the new centre had to overcome some lingering public concern about the safety of the blood-collection system.     

Comparative study of the amount of backflow produced by four types of aortic valve prostheses

To determine the extent of backflow encountered with currently used prosthetic valves, four types of aortic valves with comparable orifice diameters were tested in a pulse duplicating system. These were a Hancock porcine valve, a Lillehei-Kaster pivoting disk valve, a St. Jude bileaflet valve and a Bj?rk-Shiley tilting disk valve. Mean aortic pressure was sequentially increased from 83 to 147 mmHg, keeping the pump rate essentially constant (69-73 strokes/min). The porcine valve produced the least amount of total backflow (backflow due to closure plus leakage backflow) (1.6 to 2.4 mL/stroke). Among the mechanical valves the Bj?rk-Shiley valve showed the least amount of total backflow (5.0 to 6.0 mL/stroke). At a mean aortic pressure of 100 mmHg and a low cardiac output of 2 L/min, the total backflow with the porcine valve was only 6 percent of forward flow; whereas it was 19 percent with the Lillehei-Kaster valve, 22 percent with the St. Jude valve and 18 percent with the Bj?rk-Shiley valve. Leakage backflow at a given level of mean aortic pressure was, as expected, directly related to the annular clearance area. It is concluded that the Hancock valve showed the least amount of backward flow, which would be particularly beneficial in low output states. In the presence of normal hemodynamics, the amount of backflow with the three mechanical valves appeared to be well below the level of backflow considered to be clinically significant.     

"Cash-for-blood" companies still thriving in US

Unlike Canada''s voluntary blood-collection system, the US system routinely makes use of donations from paid donors. Milan Korcok reports that this is starting to cause some concern, since infection levels tend to be higher among those who are paid for their blood.     

Influence of needle insertion speed on backflow for convection-enhanced delivery

Fluid flow back along the outer surface of a needle (backflow) can be a significant problem during the direct infusion of drugs into brain tissues for procedures such as convection-enhanced delivery (CED). This study evaluates the effects of needle insertion speed (0.2 and 1.8 mm/s) as well as needle diameter and flow rate on the extent of backflow and local damage to surrounding tissues. Infusion experiments were conducted on a transparent tissue phantom, 0.6% (w/v) agarose hydrogel, to visualize backflow. Needle insertion experiments were also performed to evaluate local damage at the needle tip and to back out the prestress in the surrounding media for speed conditions where localized damage was not excessive. Prestress values were then used in an analytical model of backflow. At the higher insertion speed (1.8 mm/s), local insertion damage was found to be reduced and backflow was decreased. The compressive prestress at the needle-tissue interface was estimated to be approximately constant (0.812 kPa), and backflow distances were similar regardless of needle gauge (22, 26, and 32 gauge). The analytical model underestimated backflow distances at low infusion flow rates and overestimated backflow at higher flow rates. At the lower insertion speed (0.2 mm/s), significant backflow was measured. This corresponded to an observed accumulation of material at the needle tip which produced a gap between the needle and the surrounding media. Local tissue damage was also evaluated in excised rat brain tissues, and insertion tests show similar rate-dependent accumulation of tissue at the needle tip at the lower insertion speed. These results indicate that local tissue damage and backflow may be avoided by using an appropriate insertion speed.     

Xylem, Phloem and Transpiration Flows in a Grape: Application of a Technique for Measuring the Volume of Attached Fruits to High Resolution Using Archimedes' Principle

The minute changes in volume of a grape berry which occur fromhour to hour were measured non-destructively in the field usingreadily available and cheap laboratory equipment and a modernelectronic balance. The method, applicable even to small (approximately10 g) fruits, is based on Archimedes' principle and gave a resolutionof about 1 part in 1 000 by measuring the buoyant upthrust experiencedby a berry when immersed in water. Volume data from control,pedicel-steamed, and detached berries were used to calculatethe magnitudes and directions of the fluid flows which tookplace through the stalk of the phloem and xylem streams andthrough the skin in the transpiration stream. In the latter stages of fruit development, after the onset ofripening, net volume growth more or less ceases in grapes althoughtheir rate of sugar import is at its strongest. Cessation ofvolume growth comes about because the strong inflow of sugarywater in the phloem is closely balanced in part by transpirationalwater loss through the skin and in part by the backflow of xylemwater to the parent vine. This xylem backflow appears to persistthroughout the diurnal cycle. The net backflow direction of the xylem stream, together withthe inability of the phloem stream to carry certain ions (notablycalcium), may explain how some mineral imbalance disorders arisein the later stages of fruit development. The intense manner in which fruiting sinks compete with vegetativesinks in Vitis finds its explanation in the breakdown of apoplast:symplast compartmentation in the berry which occurs around thetime of onset of ripening. The breakdown exposes the terminalsieve tubes of the berry to a highly negative water potentialenvironment, serving to increase both the speed and the concentrationof the translocation stream. Key words: Archimedes' principle, volume measurement, mineral nutrition, xylem, phloem, assimilate partitioning, fruit splitting     

A radioimmunoassay for bovine parathyroid hormone.

A radioimmunoassay for bovine parathyroid hormone (bPTH) has been developed. An antibody was raised in a goat against 1-84 b PTH which was directed against the carboxy-terminal part of the molecule (no cross-reactivity with synthetic 1-34 b PTH fragment). 1-84 b PTH was labelled with 125I using the chloramine-T method. The tubes were incubated at 4 degrees C for 6 days in an equilibrium system with 25% protein concentration. Separation was performed using plasma-coated charcoal. Jugular venous plasma PTH levels were shown to be increased in hypocalcemic parturient cows.     

Avulsion injuries of the thumb

Avulsion amputations of the thumb are generally thought to have a worse prognosis after replantation than other amputations. We report the results of 17 thumbs that had an avulsion amputation and were replanted. Fourteen of the 17 survived (82 percent). Our experience indicated that the survival rate was improved by restoring continuity of at least two veins and two arteries, using a Y-shaped vein graft and the princeps pollicis artery for the source of arterial circulation. Nerve grafts were used to bridge defects in avulsed digital nerves. When possible, avulsed tendons were reattached to their muscle. Key pinch strength was 60 percent of normal, and grip strength was always less than that of the normal hand. The age of the patients and the cold ischemia time had no significant effect on either survival or function of the replanted thumb. When excellent venous backflow occurred immediately after the vessel repair and continued for at least 20 minutes, the thumb always survived without complications.     

Semen backflow after insemination and its effect on fertilisation results in sows

The aim of the present study was to investigate the volume of and number of spermatozoa in semen backflow during and after insemination, and the effect of backflow on fertilisation results assessed at day 5 of pregnancy. Multiparous sows (n=140) were artificially inseminated with either (1, 3 or 6)×10⁹ mixed spermatozoa from three boars in a constant volume of 80 ml. Backflow of semen was measured three times: during insemination (M1); during the first half hour after insemination (M2); and from 0.5 h until about 2.5 h after insemination (M3). Transrectal ultrasonography was performed at intervals of 4 h to determine the time of ovulation. Sows were sacrificed at 120±0.4 h after ovulation to assess the results of fertilisation. Every sow had some backflow and the variation in volume, and number of spermatozoa within the backflow was high. The average semen backflow within 2.5 h after insemination was 70±3.4% of the volume and 25±1.4% of the spermatozoa of the inseminated dosage. The concentration of the backflow (% of the inseminated dosage) decreased with time after insemination from 65% at M1 to 40% and 26% at M2 and M3, respectively. The correlations between volume and number of spermatozoa were high: r=0.97, r=0.73 and r=0.81 in M1, M2 and M3, respectively. More than 5% of the inseminated spermatozoa in backflow during insemination affected fertilisation negatively in those sows inseminated with 1×10⁹ spermatozoa (P<0.05). Backflow after insemination had no effect on fertilisation results (P>0.05). Timing of insemination relative to ovulation and oestrus were not related to backflow during or after insemination (P>0.05). Of the sows which had backflow, those of parity 1 tended to have the highest proportion of sows with more than 5 ml backflow (47%; n=8 of 17) compared with sows from parity 2 and higher (24%; n=14 of 59) (P=0.075). It was concluded that excessive backflow of semen during insemination had a negative effect on fertilisation results when sows where inseminated with only 1×10⁹ spermatozoa. Causes of variation in backflow between sows were not clearly identifiable.     

Designing and testing of backflow-free catheters

Convection-enhanced delivery (CED) is a drug delivery technique used to target specific regions of the central nervous system (CNS) for the treatment of neurodegenerative diseases and cancer while bypassing the blood-brain barrier (BBB). The application of CED is limited by low volumetric flow rate infusions in order to prevent the possibility of backflow. Consequently, a small convective flow produces poor drug distribution inside the treatment region, which can render CED treatment ineffective. Novel catheter designs and CED protocols are needed in order to improve the drug distribution inside the treatment region and prevent backflow. In order to develop novel backflow-free catheter designs, the impact of the micro-fluid injection into deformable porous media was investigated experimentally as well as numerically. Fluid injection into the porous media has a considerable effect on local transport properties such as porosity and hydraulic conductivity because of the local media deformation. These phenomena not only alter the bulk flow velocity distribution of the micro-fluid flow due to the changing porosity, but significantly modify the flow direction, and even the volumetric flow distribution, due to induced local hydraulic conductivity anisotropy. These findings help us to design backflow-free catheters with safe volumetric flow rates up to 10 μl/min. A first catheter design reduces porous media deformation in order to improve catheter performance and control an agent volumetric distribution. A second design prevents the backflow by reducing the porosity and hydraulic conductivity along a catheter's shaft. A third synergistic catheter design is a combination of two previous designs. Novel channel-inducing and dual-action catheters, as well as a synergistic catheter, were successfully tested without the occurrence of backflow and are recommended for future animal experiments.     

Ultrastructure of feeding tubes formed in giant-cells induced in plants by the root-knot nematodeMeloidogyne incognita

Summary The plant pathogenic nematodeMeloidogyne incognita forms conspicuous tubular structures referred to as feeding tubes in special food cells, called giant-cells, induced and maintained in susceptible host roots by feeding nematodes. Feeding tubes are formed by nematode secretions injected into giant-cells via a stylet and apparently function to facilitate withdrawal of soluble assimilates by the parasite. In giant-cells in roots of the four host species examined in this study, feeding tube morphology was identical. Tubes were straight to slightly curved structures just less than 1 μm wide and up to slightly more than 70 μm long. At the ultrastructural level, each tube consisted of a 190–290 nm thick, electron-dense, crystalline wall surrounding an electron-transparent lumen with a diameter of 340–510 nm. The distal end of the tube was sealed with wall material. Older tubes were found free in the host cytoplasm while the proximal ends of young tubes were attached to the host cell wall via short wall ingrowths through which the nematode's stylet was inserted. An elaborate membrane system was associated with the feeding tubes and was most extensive around newly formed tubes. Contiguous to the feeding tube wall, this membrane system consisted of strands of smooth endoplasmic reticulum while rough endoplasmic reticulum predominated toward the outer margin of the membrane system. Vacuoles and mitochondria were excluded from a zone of cytoplasm surrounding feeding tubes. This zone of exclusion, as well as the membrane system noted above, tended to be less pronounced or absent around older tubes no longer being used by the nematode.     

Finite Element Model to Reproduce the Effect of Pre-Stress and Needle Insertion Velocity During Infusions into Brain Phantom Gel

Convection-enhanced delivery (CED) is a technique to bypass the blood-brain barrier and deliver therapeutic agents into the brain. However, animal studies and preliminary clinical trials have reported reduced efficacy to transport drugs in specific regions, attributed mainly to backflow, in which an annular zone is formed outside the catheter and the fluid preferentially flows toward the surface of the brain rather than through the tissue toward the targeted area. In this study, a finite element model of backflow was updated by implementing the pre-stress generated during needle insertion, which allows considering the effect of needle insertion velocity during CED infusions in agarose gel. The nonlinear mechanical properties of the agarose solutions were obtained by fitting experimental data from stress-relaxation tests. Additional experimental measurements of backflow lengths were used to adjust the pre-stress model. The developed model was able to reproduce changes of backflow length under different insertions velocities and flow rates. These findings reveal the relevance of considering the pre-stress in the tissue located around the needle surface during CED infusions into the brain.     

Effect of Needle Insertion Speed on Tissue Injury,Stress, and Backflow Distribution for Convection-Enhanced Delivery in the Rat Brain

Flow back along a needle track (backflow) can be a problem during direct infusion, e.g. convection-enhanced delivery (CED), of drugs into soft tissues such as brain. In this study, the effect of needle insertion speed on local tissue injury and backflow was evaluated in vivo in the rat brain. Needles were introduced at three insertion speeds (0.2, 2, and 10 mm/s) followed by CED of Evans blue albumin (EBA) tracer. Holes left in tissue slices were used to reconstruct penetration damage. These measurements were also input into a hyperelastic model to estimate radial stress at the needle-tissue interface (pre-stress) before infusion. Fast insertion speeds were found to produce more tissue bleeding and disruption; average hole area at 10 mm/s was 1.87-fold the area at 0.2 mm/s. Hole measurements also differed at two fixation time points after needle retraction, 10 and 25 min, indicating that pre-stresses are influenced by time-dependent tissue swelling. Calculated pre-stresses were compressive (0 to 485 Pa) and varied along the length of the needle with smaller average values within white matter (116 Pa) than gray matter (301 Pa) regions. Average pre-stress at 0.2 mm/s (351.7 Pa) was calculated to be 1.46-fold the value at 10 mm/s. For CED backflow experiments (0.5, 1, and 2 µL/min), measured EBA backflow increased as much as 2.46-fold between 10 and 0.2 mm/s insertion speeds. Thus, insertion rate-dependent damage and changes in pre-stress were found to directly contribute to the extent of backflow, with slower insertion resulting in less damage and improved targeting.     

Effect of oxygen supply on growth ofKlebsiella aerogenes in a multistage tower fermentor

The effect of the rate of oxygen supply on biomass growth, consumption of carbon source formation of metabolic by-products, biomass yeilds referred to C-source and oxygen, respiration rate and the respiratory quotient was studied in a multistage tower fermentor with an interstage backflow, i.e. with a continuous reinoculation of the preceding stages. Experiments were done with Klebsiella aerogenes CCM 2318 in a synthetic glucose medium with constant glucose concentration in the feed, at pH 7.0. temperature 30 degrees C, and dilution rates 0.6 and 0.178 h-1 (referred to one stage). Different behavior of the culture was found at different dilution rates both with oxygen and under oxygen limitation. As compared with the chemostat system, the regime with an interstage backflow exhibited differences in respiration rate and CO2 formation; this attests to a considerably different physiological state of the cells.     

Sinus-parenchyma border of the human kidney as the site of origin of intracanalicular and extravascular diffusion of fluids

Injecting fluids into the kidney against the physiological direction of flow leads to a passage of liquid across the border-line between the renal sinus and the parenchyma. This event, caused by a sudden raising of pressure during the injection is called pyelorenal backflow. It can be divided into a number of subtypes, as there are: pyelocanalicular backflow, pyelosinous backflow, pyelovenous backflow, pyelolymphatic backflow. Among all these phenomena only the pyelocanalicular backflow can be interpreted as a genuine backflow in the fullest sense of the word, while the others never can happen before the fornix had been mutilated. In the case of pyelocanalicular backflow, the contents of the renal pelvis regurgitate into the Ducts of Bellini, but the fluid never goes beyond the collecting ducts in the pyramids. Neither a rupture of the tubuli, followed by an interstitial spreading up to under the capsule, nor a direct penetration into the medullary veins are possible, because the pressure necessary for it causes a rupture of the fornix earlier. This rupture happens step by step as an oblique dissection of the calyx from the papilla. The big calices at the poles show an increased tendency to rupture because they are attached along a line which is shaped like an "8" or like a clover leaf, and so do calices the angle of which is acute. Depending on whether a vein is torn simultaneously with the fornix or not, the contents of the pelvis transflow into the vein (pyelovenous backflow) or into the sinus (pyelosinous backflow). In spite of a previous pyelocanalicular backflow the pelvis is not relieved of pressure to such an extent that there could not occur an additional rupture of the fornix, nevertheless. The pyelosinous backflow leads to a sinus-extravasation which can ascend towards the parenchyma and descend towards the hilum. The ascending sinus-extravasation spreads out within the vascular canals of the kidney. These canals, strictly situated between cortex and medulla, enclose a pyramid (Canales peripyramidales) and contain the interlobar and arcuate bloodvessels. The space between the bloodvessels and the wall of a peripyramidal canal (perivascular space) is filled with connective tissue consisting of 3 components: tunica adventitia of the bloodvessels themselves and fibres originating from the inner capsule and the wall of the calyx. The ascending sinus-extravasation proceeds into the perivascular space by pushing off the bloodvessels from the medulla.(ABSTRACT TRUNCATED AT 400 WORDS)     

Determination of the bacteriostatic capacity of neutrophils and monocytes in mixed cell populations.

Cline [1, 2] described a method of determining the phagocytic and bacteriostatic activity of individual types of leukocytes within mixed cell populations. We tried to improve the applicability of this method for the investigation of clinical problems.--Bacteria in the log-phase of growth were incubated in test tubes with leukocytes separated from venous blood. After a short period of phagocytosis 3H-thymidine was added to label DNA-synthesizing organisms. Smears were prepared and processed by autoradiography. The labeling indices of extracellular bacteria and of those phagocytized by neutrophils and monocytes were determined microscopically. The intracellular inhibition of DNA-synthesis was taken as indicative of the bacteriostatic activity of the leukocytes. The proposed modification of Cline's assay is suited to investigate clinical problems of phagocyte dysfunction.     

Oxidant and antioxidant status of Turkish marasmic children: A single center study

The aim of this study was to investigate plasma oxidant and antioxidant status in Turkish marasmic children. The study population consisted of 38 marasmic children (group I) and 28 age-matched children (group II) who were apparently well, with weight-forage >80% of the standards in the same region. After overnight fasting, venous blood samples were drawn and immediately transferred to heparinized and normal tubes. Plasma antioxidant potential (AOP), and malondialdehyde (MDA) levels were measured in both groups. The plasma MDA levels were found to be higher in group I than in group II. However, plasma AOP values were lower in group I than in group II. The present study suggests that AOP is reduced due to an impaired antioxidant system in the plasma of malnourished patients. This oxidant stress causes significant peroxidation. Also, the antioxidant defense system of the patients is deteriorated in marasmus.     

Effects of biocide treatment and backflow pressure on the permeability of microbially fouled model cores

Summary Sintered glass bead cores were plugged until the permeability was reduced to 1% or less of the original permeability by the injection of a slime-producing bacterium isolated from produced water. Scanning electron microscopy of fractured core sections showed that the bacteria were predominantly located in the uppermost sections, around the core inlet. Killing the bacterial cells in the plugging biofilm, using a biocide, had little effect on core permeability. The dead cells were only removed when backflow pressure, simulated by inversion of the test core followed by fluid injection, was applied and maintained at 55–69 kPa. Backflow of plugged cores containing live bacteria produced transient pressure-dependent increases in permeability that were proportional to the backflow pressure applied. We conclude that only sustained backflow procedures reduced permeability: such operations are not effective for oil recovery in field conditions.