Wick Fluid Research Articles

Low-Gradient Magnetophoresis of Nanospheres and Nanorods through a Single Layer of Paper.

The possible magnetophoretic migration of iron oxide nanoparticles through the cellulosic matrix within a single layer of paper is challenging with its underlying mechanism remained unclear. Even with the recent advancements of theoretical understanding on magnetophoresis, mainly driven by cooperative and hydrodynamics phenomena, the contributions of these two mechanisms on possible penetration of magnetic nanoparticles through cellulosic matrix of paper have yet been proven. Here, by using iron oxide nanoparticles (IONPs), both nanospheres and nanorods, we have investigated the migration kinetics of these nanoparticles through grade 4 Whatman filter paper with a particle retention of 20-25 μm. By performing droplet tracking experiments, the real-time stained area growth of the particle droplet on the filter paper, under the influences of a grade N40 NdFeB magnet, were recorded. Our results show that the spatial and temporal expansion of the IONP stain is biased toward the magnet and such an effect is dependent on (i) particle concentration and (ii) particle shape. The kinetics data were first analyzed by treating it as a radial wicking fluid, and later the IONP distribution within the cellulosic matrix was investigated by optical microscopy. The macroscopic flow front velocities of the stained area ranged from 259 μm/s to 16 040 μm/s. Moreover, the microscopic magnetophoretic velocity of nanorod cluster was also successfully measured as ∼214 μm/s. Findings in this work have indirectly revealed the strong influence of cooperative magnetophoresis and the engineering feasibility of paper-based magnetophoretic technology by taking advantage of magnetoshape anisotropy effect of the particles.

Moulding of micropatterned nanocellulose films and their application in fluid handling

HypothesisWell-controlled micropatterned nanocellulose films are able to be fabricated via spray coating onto a micropatterned impermeable moulded surface. The micropattern size is able control the directionality of wicking fluid flow. ExperimentsUsing photolithography and etching techniques, silicon moulds with channel widths of 5–500 µm and depths of 6, 12 and 18 µm were fabricated. Micropatterned nanocellulose sheets were formed by spray coating nanofibre suspensions onto the moulds. We also investigate the effect the dimensions of these micropatterned nanocellulose films have on wicking fluids. FindingsMicropatterns were imparted on the surface of nanocellulose films which resulted in three well-defined regimes of conformation with the moulds: full, partial and no conformation. These regimes were driven by the aspect ratio (channel depth/width) of the moulds. Achieved channel widths and depths were compared to those possible with other micropattern fabrication techniques. The directionality of the wicking water droplets can be controlled with the micropatterned channel. Channels within the full conformation regime resulted in increased directionality of fluid flow compared with those not within this regime. This research demonstrates the industrially scalable process of spray coating has potential to serve as the foundation for a new generation of paper-based microfluidic devices.

A fractional approach to wicking fluid flow in nonwoven porous fabric

Purpose – The purpose of this paper is to employ a fractional approach to predict the permeability of nonwoven fabrics by simulating diffusion process. Design/methodology/approach – The method described here follows a similar approach to anomalous diffusion process. The relationship between viscous hydraulic permeability and electrical conductivity of porous material is applied in the derivation of fractional power law of permeability. Findings – The presented power law predicted by fractional method is validated by the results obtained from simulation of fluid flow around a 3D nonwoven porous material by using the lattice-Boltzmann approach. A relation between the fluid permeability and the fluid content (filling fraction), namely, following the power law of the form, was derived via a scaling argument. The exponent n is predominantly a function of pore-size distribution dimension and random walk dimension of the fluid. Originality/value – The fractional scheme by simulating diffusion process presented in this paper is a new method to predict wicking fluid flow through nonwoven fabrics. The forecast approach can be applied to the prediction of the permeability of other porous materials.

One-way wicking in open micro-channels controlled by channel topography

One-way wicking (microfluidic diode) behaviors of a range of IPA–water mixtures on internally structured PDMS-based open micro-channels were experimentally demonstrated and quantified. The open microfluidic channels, each internally decorated with an array of angled fin-like-structure pairs, were fabricated using a combined photolithography and soft molding procedure. Propagations of wetting fluids were found to be much more impeded on the fin-tilting direction, or the hard wicking direction, comparing to the opposite direction, or the easy wicking direction. This asymmetric wicking behaviors were attributed to the structure-induced direction-dependent Laplace pressure. Two key parameters – the contact angle of the wicking fluid and the tilting angle of the fin-like structures – were studied. The effects of preferential evaporation and wetting instability were also investigated. The findings of this study are expected to provide a better understanding of how fluids interact with micro-scaled structures and to offer a new way of manipulating fluids at the micron and nanometer scales.

Effects of bending on heat transfer performance of axial micro-grooved heat pipe

Heat pipe is always bent in the typical application of electronic heat dissipation at high heat flux, which greatly affects its heat transfer performance. The capillary limit of heat transport in the bent micro-grooved heat pipes was analyzed in the vapor pressure drop, the liquid pressure drop and the interaction of the vapor with wick fluid. The bent heat pipes were fabricated and tested from the bending angle, the bending position and the bending radius. The results show that temperature difference and thermal resistance increase while the heat transfer capacity of the heat pipe decreases, with the increase of the bending angles and the bending position closer to the vapor section. However, the effects of bending radius can be ignored. The result agrees well with the predicted equations.

Acute Peritoneal Dialysis in Rats Results in a Marked Reduction of Interstitial Colloid Osmotic Pressure

The aim of this study was to investigate whether the interstitial colloid osmotic pressure (COP(i)) of peritoneum is of importance for peritoneal fluid reabsorption during peritoneal dialysis (PD). For testing this hypothesis, a method to isolate interstitial fluid from the peritoneal membrane and to measure the interstitial COP(i) in the normal peritoneum and directly after the initiation of PD needed to be developed and validated. Eighteen female rats were anesthetized subcutaneously in the neck region with fentanyl-midazolam (1:1). Nylon wicks were implanted postmortem by means of a plastic catheter in the tissue just underneath the peritoneal surface. The characteristics of this fluid were compared with that isolated from wicks that were implanted in intermuscular spaces in hindlimb muscle and back subcutis. All wicks were removed after 20 min and centrifuged. The wick fluid was collected and analyzed in a colloid osmometer constructed for submicroliter samples, and interstitial fluid COP was compared with that of plasma. PD was initiated by injecting 20 ml of 3.86% glucose-containing PD fluid (Dianeal) into the peritoneal cavity, over a dwell time of 4 h. Control rats received no PD. The ratio of COP(i) to that of plasma (COP(p)) during control was 0.65 +/- 0.05 in peritoneum, 0.53 +/- 0.04 in muscle, and 0.59 +/- 0.05 in skin. After a PD dwell, the ratio was 0.29 +/- 0.03 in peritoneum, 0.54 +/- 0.08 in muscle, and 0.41 +/- 0.06 in skin. Thus, the COP ratio in peritoneum fell by 55% (P = 0.014) and in skin by 30% (P = 0.03), whereas the COP ratio in muscle was unchanged. The results suggest that acute PD results in a marked fall of the COP(i) in the peritoneal membrane, shifting the Starling equilibrium toward an absorptive state. The effect was restricted to the peritoneal membrane and, to some extent, the skin. It is speculated that the increase in peritoneal hydrostatic pressure after PD causes an increase in interstitial tissue volume, with primarily a dilution of interstitial colloids.

Isolation of interstitial fluid from skeletal muscle and subcutis in mice using a wick method.

Until recent years, mice were sparsely used in physiological experiments, and therefore, data on the basic cardiovascular parameters of mice are lacking. Our aim was to gain access to interstitial fluid and thereby study transcapillary fluid dynamics in this species. Using a modified wick method, we were able to isolate interstitial fluid from subcutis and skeletal muscle in mice. Three-stranded, dry, nylon wicks were inserted post mortem in an attempt to avoid local inflammation and thus eliminate protein extravasation and wick contamination. Colloid osmotic pressure (COP) was measured with a colloid osmometer for submicroliter samples and averaged (means +/- SE) 18.7 +/- 0.4 in plasma, 9.1 +/- 0.4 in subcutis, and 12.3 +/- 0.5 mmHg in muscle. HPLC of plasma and wick fluid showed similar patterns except for some minor peaks eluting in the <40-kDa region. Plasma protein extravasation as determined by 125I-labeled human serum albumin showed that contamination of wick fluid by plasma proteins was negligible (<2%). Capillary hyperfiltration induced by intravenous infusion of saline (10% of body wt) was reflected in tissue fluid isolated by wicks as shown by the average postinfusion COP values of 14.5 +/- 0.6, 6.8 +/- 0.3, and 7.7 +/- 0.4 mmHg in plasma, subcutis, and muscle, respectively. We conclude that the wick technique can be easily adapted for use in mice and may represent a reliable method to isolate interstitial fluid and study transcapillary fluid flux in this species.

Interstitial exclusion of albumin in rabbit lung measured with the continuous infusion method in combination with the wick technique.

To determine albumin exclusion from the pulmonary perivascular interstitium by using the continuous infusion methods coupled with direct samples of pulmonary interstitial fluid via the wick technique. To evaluate extracellular albumin distribution volume, radioactive ((125)I) rabbit serum albumin (RSA) was delivered intravenously until reaching a steady-state tissue concentration. In anesthetized rabbits with ligated kidney pedicles, extracellular (V(x)) and intravascular (V(v)) fluid volumes were measured as the distribution volumes of (51)Cr-ethylenediaminetetraacetic a id and (131)I-RSA, respectively. Post mortem, lung samples and interstitial fluid collected via implanted wicks were assayed for isotope activity. The extravascular wick fluid equivalent albumin distribution volume (V(a,w)) was calculated assuming equal concentrations of (125)I-RSA in interstitial and wick fluid. The mean (+/-SE) V(x), V(v), and interstitial fluid volumes (V(i) = V(x) - V(v)) were 1896 +/- 61 (n = 8), 556.8 +/- 19, and 1329 +/- 73 microL/g of blood-free dry lung tissue weight, respectively. The mean albumin-excluded volume (V(e,a) = V(i) - V(a,w) and the excluded fraction (V(e,a)/V(i)) were 875.8 microL/g +/- 58 and 0.66 +/- 0.05, respectively. At variance with previous indirect reports, the present data indicate that normal pulmonary parenchyma displays a tight fibrous structure that is highly restrictive with respect to plasma protein distribution.

Interstitial exclusion of positively and negatively charged IgG in rat skin and muscle.

Volume exclusion, i.e., the space not available for a specific probe, may be dependent on the probe charge. Therefore, interstitial exclusion was measured for positively and negatively charged immunoglobulin (IgG) in skin and muscle of rats by using a continuous infusion method (30). Steady-state concentration of (125)I-labeled IgG 1 (pI = 8.7) and (131)I- labeled IgG 4 (pI = 6.6) was maintained by infusion of tracer for 120-168 h with an implanted osmotic pump. At the end of the infusion period and before tissue sampling, the rat was anesthetized and nephrectomized, and (51)Cr-labeled EDTA was injected and allowed 4 h for equilibration to measure interstitial fluid volume (V(i)). Interstitial fluid was isolated from skin and muscle by using nylon wicks implanted post mortem. The relative IgG available space was measured as the ratio between labeled IgG and (51)Cr-labeled EDTA wick fluid equivalent spaces, and relative excluded volume fraction (V(e)/V(i)) was calculated as 1--V(a)/V(i). V(e)/V(i) in hindlimb skin averaged 0.37 +/- 0.05 (SE) and 0.65 +/- 0.06 (P < 0.01) for IgG 1 and 4, respectively, with corresponding figures of 0.24 +/- 0.05 and 0.51 +/- 0.04 (P < 0.01) in hindlimb muscle (n = 9 for both tissues). These experiments suggest that fixed negative charges, most likely glycosaminoglycans, influence distribution of macromolecules in the interstitium and therefore affect interstitial fluid balance.

Sampling of interstitial fluid and measurement of colloid osmotic pressure (COPi) in pigs: evaluation of the wick method.

The wick method for sampling of interstitial fluid from subcutis was applied in fluid balance studies in young pigs. Colloid osmotic pressure was measured in serum (COPs) and interstitial fluid (COPi) using a membrane colloid osmometer. Our aims were to determine the 'true' COPi, and to find the optimal duration of wick implantation. In series I (n = 6) a 'crossover' experiment was performed using wicks soaked in different priming solutions (non-diluted and diluted serum protein solutions or isotonic salt solution). Circulatory arrest was induced just before wick insertion in order to eliminate the vascular part of the acute inflammation. In series II (n = 6) wicks were removed in sequence after 60, 90, 120 and 180 min sampling time in anaesthetized pigs in vivo. COPs, COPi and haematocrit (HCT) together with haemoglobin (Hgb), serum albumin and total protein concentrations were determined in the same animals. In series I average COPs and COPi were 13.7 (1.4) and 7.2 (1.4) mmHg respectively (SD). In series II the optimal wick implantation times were estimated to be 60-90 min for wicks soaked in diluted protein solution, and 90-120 min for dry and saline-soaked wicks. COPs averaged 13.0 (0.7) mmHg, HCT 30.0 (1.6)%, Hgb 8.3 (0.9) g/dl, s-albumin 22.7 (0.6) g/l and s-protein 47.3 (2.3) g/l. Compared to commonly reported reference values, we found surprisingly low values for most of the measured variables. This may be related to the fact that we used immature pigs. An analysis of the validity of the wick method based on our own results and published reports is presented. We conclude that sampling of interstitial fluid with subcutaneous wicks is easy to perform in young pigs. However, the COP-values measured in wick fluid have to be carefully evaluated especially when sampling is performed in vivo.

Effect of venous stasis and hypoproteinemia in gingival fluid formation in rats.

Experiments were performed to provide information on the mechanisms of the formation of gingival fluid in rats and on the determinants of its flow and composition. For this purpose we studied the effect of increasing net capillary filtration by venous stasis induced by multiple ligations of the jugular vein or by hypoproteinemia induced through puromycine nephrosis. A 1 microliter glass capillary was placed in the sulcus of the first maxillary molar for collection of gingival fluid (GF). Colloid osmotic pressure (COP) was determined in GF, in wick fluid from attached gingiva and buccal mucosa, and in plasma. Interstitial fluid hydrostatic pressure (Pi) was measured by micropuncture technique and the fractional removal rate of radio-labelled human serum albumin (kAlb) was recorded in attached gingiva and buccal mucosa. During venous stasis the gingival fluid flow increased from 1.7 microliters/h to 3.8 microliters/h, whereas COPGF fell from 14.1 mmHg to 8.8 mmHg. COP in wick fluid from gingiva was reduced from 10.3 to 4.3 mmHg. Pi increased from 6.8 to 13.1 mmHg, and kAlb in sham-operated controls increased from 0.068 to 0.189 h-1. In buccal mucosa COPi was significantly decreased to 7.1 mmHg in rats with venous stasis, whereas Pi and kAlb remained unchanged compared to the sham-operated controls. In hypoproteinemic rats COPGF was 5.0 mmHg and COPp was reduced from 18.9 to 8.0 mmHg. COPi declined from 8.9 mmHg to 2.4 mmHg in gingiva and from 8.1 mmHg to 2.7 mmHg in buccal mucosa.(ABSTRACT TRUNCATED AT 250 WORDS)

Change in Macro Molecular Composition of Interstitial Fluid from Swollen Arms after Breast Cancer Treatment, and Its Implications

1. The pathophysiology of chronic arm oedema after treatment of breast cancer was investigated by collecting serum and subcutaneous interstitial fluid from the affected and contralateral arms by the wick method (both arms) and by aspiration (oedematous arm). The fluids were analysed for total protein, albumin, glycosaminoglycan and viscosity, and arm volume was measured. 2. Total protein concentration in the aspirated oedema fluid was 32.4 +/- 7.5 g/l (mean +/- SD throughout; n = 39). Protein concentration in wick fluid from the oedematous arm (35.8 +/- 7.3 g/l, n = 14) was not significantly different from that in aspirated fluid. The oedema protein concentrations were significantly lower than in wick fluid from the non-swollen arm (41.4 +/- 6.7 cmH2O, n = 13, P < 0.01, analysis of variance). This was surprising in view of the common assumption that, the condition being of lymphatic origin, the oedema protein concentration should be raised. 3. The ratio of aspirate protein concentration to serum protein concentration showed a weak but highly significant negative correlation with the percentage increase in arm volume (r = -0.47, n = 35, P < 0.005), again in contrast to conventional expectation. The demonstration of a reduced protein concentration in the swollen arm did not therefore depend solely on a comparison with the wick control results. The volume increased by on average 33% and the ratio of aspirate protein concentration to serum protein concentration averaged 0.52 +/- 0.11 on the swollen side and 0.64 +/- 0.13 on the unaffected side. 4. Serum protein concentration in the patients with arm swelling (61.2 +/- 4.9 g/l) was significantly lower than that in postmastectomy patients without this complication (65.0 +/- 6.2 g/l). Most of the decrease occurred in the albumin fraction (oedema patients, 38.3 +/- 5.1 g/l; control patients, 42.0 +/- 2.1 g/l). In oedema patients receiving the anti-oestrogen tamoxifen serum albumin concentration was on average 2.3 g/l lower than in oedema patients not under medication (P < 0.05, t-test). 5. Glycosaminoglycan concentration in oedema fluid was 0.8 +/- 0.14 g/l (n = 21) and 75% was sulphated. Along with the plasma protein this raised the relative viscosity of the fluid to 1.34 +/- 0.16 (n = 11). 6. The reduction in interstitial protein concentration in the swollen arm, contrary to expectation in lymphoedema, could be explained in several ways. One possible hypothesis in light of reported haemodynamic abnormalities in such arms is that capillary pressure rises, increasing capillary filtration rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Fluid exchanges across the parietal peritoneal and pleural mesothelia

In 31 anesthetized rabbits, after removal of superficial tissues, glass micropipettes filled with 0.5 M NaCl solution and connected to an electrohydraulic servo-null system were used to measure extraperitoneal interstitial fluid pressure (Pi,per) and peritoneal liquid pressure (Pliq,per) at various heights. Linear regressions relating pressure to recording height (H) were Pi,per = 1.07 - 0.27H and Pliq,per = 0.9 - 0.64H, respectively. Protein concentration (Cp;g/dl) and colloid osmotic pressure (II; cmH2O) of plasma and of peritoneal and pleural liquids were 5.48 +/- 0.38 and 24.61 +/- 3.23, 3.07 +/- 0.5 and 13.29 +/- 1.87, and 1.76 +/- 0.42 and 8.45 +/- 2, respectively. The equation relating II to Cp was II = 4.64Cp + 0.0027Cp2. Tissue fluid samples were collected with saline-soaked wicks implanted in vivo or dry wicks inserted postmortem in extraperitoneal and extrapleural interstitial spaces. After 60 and 15 min, respectively, wicks were withdrawn and centrifuged; wick fluid was analyzed in colloid osmometer for small samples. Average extraperitoneal and extrapleural II values were 14.2 +/- 2.49 and 11.94 +/- 1.52 cmH2O, corresponding to Cp of 3.07 and 2.57 g/dl, respectively. The average net pressure gradient, assuming reflection coefficient and hydraulic conductivity (Negrini et al. J. Appl. Physiol. 69: 625-630, 1990; 71: 2543-2547, 1991), was 1.18 and 0.98 cmH2O for parietal peritoneal and pleural mesothelia, respectively, favoring filtration from the extraserosal interstitia into the serosal cavities. Total parietal peritoneal filtration was 1.49 ml.kg-1.h-1, approximately 15-fold higher than that for pleural mesothelium.

Sampling interstitial fluid from rat skeletal muscles by intermuscular wicks

A modification of the implanted wick method (K. Aukland and H. O. Fadnes. Acta Physiol. Scand. 88: 350-358, 1973) was devised to sample interstitial fluid from rat muscles. Dry nylon wicks were inserted postmortem into intermuscular spaces between leg muscles by means of a plastic catheter, which was subsequently withdrawn. Inserting the wicks postmortem avoids contaminating wick fluid with proteins extravasated as a result of local inflammatory reactions; placing them intermuscularly avoids contamination by fluid and proteins from damaged muscle cells. Wick fluid protein concentrations (mg/ml) averaged 24.1 +/- 1.1 and 28.5 +/- 1.5 (means +/- SE) in medial and lateral hindlimbs muscles, respectively. The corresponding albumin concentrations were 13.0 +/- 0.7 and 13.9 +/- 0.7 mg/ml. Total protein and albumin concentrations in plasma were 54.1 +/- 0.8 and 22.5 +/- 0.3 mg/ml. Electrophoresis of wick fluid showed a pattern of peaks similar to that of plasma, with albumin relatively high and larger molecules relatively low. Proteins from muscle cells were not detected. Isotope studies (125I-labeled albumin, 51Cr-EDTA) showed that less than 2% of the albumin in wick fluid came directly from plasma and that wick fluid was not concentrated by cell swelling postmortem. Wick fluid from intermuscular wicks implanted in anesthetized rats in vivo had nearly the same total protein concentration as fluid from postmortem wicks, but albumin-to-globulin (A/G) ratios were slightly lower (1.22 +/- 0.07 vs. 1.53 +/- 0.21 measured by gel electrophoresis), and more significantly, nearly 50% of the albumin leaked to wick fluid from plasma as a result of wick implantation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of longstanding venous stasis and hypoproteinaemia on lymph flow in the rat tail

This study was performed to provide information on the determinants of lymph flow by comparing the effect of venous stasis and hypoproteinaemia in the rat tail. This low-compliant tissue was chosen in an attempt to induce preferential changes in interstitial pressure or volume. The removal rate (kAlb) of 125I-labelled human serum albumin (I-HSA) injected subcutaneously was monitored with external gamma-counting equipment and used as a measure of lymph flow. Interstitial fluid hydrostatic pressure (Pi) was measured with wick-in-needle technique, and interstitial fluid was collected post mortem by dry wicks. Colloid osmotic pressure of plasma (COPp) and wick fluid (COPi) was measured with a colloid osmometer. In a separate group of experiments, 51Cr-EDTA and [125I]HSA were used to measure the interstitial fluid volume. Venous stasis, induced by bilateral ligation of the external tail veins, increased interstitial fluid hydrostatic pressure from 1.7 to 16 mmHg and kAlb from 0.030 to 0.063 h-1, whereas tail circumference was nearly constant. Interstitial volume averaged 1.17 ml/g dry weight in control animals and 1.27 ml/g during increased venous pressure. Daily injections of aminonucleoside in salt-loaded rats (0.3% NaCl as drinking water) reduced colloid osmotic pressure of plasma from 19.1 to 8.5 mmHg and of wick fluid from 11.2 to 2.9 mmHg, while interstitial fluid hydrostatic pressure increased to 5.2 mmHg. The removal rate of 125I-labelled human serum albumin increased to 0.113 h-1, compared to 0.051 h-1 in salt-loaded controls. The interstitial volume showed a marked increase in salt-loaded hypoproteinaemic rats, 1.75 ml/g dry weight, compared to 1.30 ml/g in salt-loaded controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Edema-preventing mechanisms in rat gingiva

The long-term effect of increased local venous pressure (Pv) on interstitial fluid pressure (Pi), colloid osmotic pressure (COPi), and fractional removal rate of 125I-labeled human serum albumin (kAlb) was studied in rat gingiva. Measurements were performed on experimental animals and sham-operated controls up to 4 days after ligation of jugular veins. On the day of ligation Pv in the facial veins rose from 2.5 +/- 0.3 (SD) to 15.8 +/- 2.8 mm Hg and stayed at about this level for 2 days before a decrease to 7.4 +/- 0.9 mm Hg on day 4. In free gingiva Pi rose from an average of 3.5 +/- 0.4 to a maximum of 6.3 +/- 0.7 mm Hg, whereas in attached gingiva the corresponding increase in Pi was from 6.0 +/- 0.7 to 11.1 +/- 2.1 mm Hg. One day after the ligation COPi in wick fluid from gingiva was reduced from the control level of 10.6 +/- 1.4 to 4.5 +/- 0.9 mm Hg. COP in plasma and COPi in subcutaneous tissue on the back were unaffected. The removal rate of 125I-labeled albumin (kAlb) from the gingiva showed a nearly threefold increase after venous ligation, from 0.073 +/- 0.01 to 0.211 +/- 0.06 h-1. It is concluded that in free and attached gingiva, both a rise in Pi and a decrease in COPi will counteract the increased filtration pressure and thus prevent edema formation during venous stasis. The fall in COPi is most likely due to increased lymph flow and not dilution, as venous stasis significantly increased kAlb without any visible increase in gingival volume.

Wick technique: reference method for implanted glucose sensors.

The control of function of experimentally implanted glucose sensors needs an independent reference method. Employing saline-impregnated cotton threads, an implanted wick-technique was adopted in dogs to obtain analytical specimen from the subcutaneous interstitial fluid compartment. By measuring the contents of potassium, calcium, and hemoglobin, the centrifuged wick fluid was validated to contain the interstitial concentrations of solutes after an equilibration time of approximately 15 min. Between 2 and 25 mmol/L, the steady state subcutaneous glucose concentration is nearly identical to circulating glycemia. Slow alterations, as during an oral glucose tolerance test, (OGTT) are well paralleled by the levels in the wick fluid. During alterations, however, a distinct delay is observed. The wick-based glucose levels are mirrored by the output of electrochemical sensors implanted at the same site. This method may be used in checking implanted sensors that can otherwise not be calibrated in situ.

Mechanisms behind increased dermal imbibition pressure in acute burn edema.

We have measured tissue pressures in excised rat skin subjected to in vitro burn injury and investigated the mechanisms behind the increased imbibition (swelling) pressure in burned skin. Skin pieces wrapped in aluminum paper were immersed into boiling hot water for 10, 30, or 60 s. Dermal imbibition pressure was measured with micropipettes and tissue osmometry as interstitial fluid hydrostatic pressure (Pif) and/or interstitial fluid colloid osmotic pressure (COPif). COPif was also measured in interstitial fluid sampled with intradermal wicks. Control values of Pif (micropipettes) and of COPif (wick fluid) averaged -1.5 mmHg and -17.5 mmHg, respectively. An increase in imbibition pressure was seen after thermal injury. After 10 s of heat exposure, the imbibition pressure gain was mainly due to a strongly negative hydrostatic pressure (Pif mean value -33.3 mmHg). Pif became slightly positive and COPif increasingly negative after longer exposure (mean Pif 0.3 and mean COPif -133 mmHg after 60-s exposure). Collagen degradation and water solubility increased with extension of the heat exposure time. Thermal degradation of collagen seems to be the main mechanism responsible for the generation of increased imbibition pressure.

Colloid osmotic pressure of interstitial fluid in rat subcutis and skeletal muscle: comparison of various wick sampling techniques.

Interstitial fluid for measurement of colloid osmotic pressure (COPi) was collected from rat subcutis and skeletal muscle with three wick methods; saline-soaked wicks implanted in vivo, titration with wicks preloaded with serial dilutions of rat plasma implanted postmortem (crossover method) and dry wicks implanted in vivo and post-mortem. When compared in 12 rats, the mean subcutaneous COPi of 14.2 and 13.3 mmHg as estimated with the crossover method and dry wick method, respectively, both exceeded the 10.7 mmHg obtained in saline-soaked wicks implanted for 60 min. Colloid osmotic pressure (COP) in fluid from dry wicks implanted subcutaneously was slightly lower than in plasma 5 min after implantation in vivo, then fell gradually, but remained stable the last 30 min of the 60 min in vivo implantation period and the first 30 min post-mortem, when again starting to rise. COP in fluid isolated from dry wicks implanted in muscle post-mortem approached or even exceeded that of plasma, suggesting leakage of intracellular proteins to wick fluid. Electrophoresis of dry wick fluid from subcutis showed a pattern similar to that of plasma, while protein fractions not present in plasma were observed in muscle wick fluid. For measurement of COPi we recommend the use of dry wicks implanted post mortem for subcutis and saline-soaked or dry wicks implanted in vivo for 90-120 min for skeletal muscle.

Colloid osmotic pressure of subcutaneous wick fluid in rats

Colloid osmotic pressure of subcutaneous wick fluid in rats