Effect of lung resection on pleuro-pulmonary mechanics and fluid balance.

The aim of the study was to determine in human patients the effect of lung resection on lung compliance and on pleuro-pulmonary fluid balance. Pre and post-operative values of compliance were measured in anesthetized patients undergoing resection for lung cancer (N=11) through double-lumen bronchial intubation. Lung compliance was measured for 10-12 cm H2O increase in alveolar pressure from 5 cm H2O PEEP in control and repeated after resection. No air leak was assessed and pleural fluid was collected during hospital stay. A significant negative correlation (r(2)=0.68) was found between compliance at 10 min and resected mass. Based on the pre-operative estimated lung weight, the decrease in compliance following lung resection exceeded by 10-15% that expected from resected mass. Significant negative relationships were found by relating pleural fluid drainage flow to the remaining lung mass and to post-operative lung compliance. Following lung re-expansion, data suggest a causative relationship between the decrease in compliance and the perturbation in pleuro-pulmonary fluid balance.

Clinical and neuropsychological correlates of major depression following post-traumatic brain injury, a prospective study.

OBJECTIVES: Major depression disorder (MDD) is the most frequent psychiatric complication after traumatic brain injury (TBI), with a prevalence of 14-77%. The aim of this study was to analyse the psychiatric sequelae of TBI, and to identify the neuropsychological and psychopathological correlates of post-TBI MDD in order to highlight their differences from those of primary MDD. METHODS: This was a longitudinal, prospective, case-control study. Sixteen patients with closed brain injury, and a lesion revealed by computed tomography (CT), were recruited and were evaluated one (T1), three (T3) and six (T6) months after discharge from Neurosurgery Department; the controls were six patients with MDD. The psychiatric symptoms were evaluated using brief psychiatric rating scale (BPRS), Hamilton depression rating scale (HRSD), Beck depression inventory scale (BDI), Hamilton anxiety rating scale (HRSA), global assessment of functioning (GAF) and instrumental activity of daily living (IADL). Neuropsychological profiles were assessed by using neuropsychological tests, focused on memory and frontal-executive functioning. RESULTS: At T1, MDD was observed in 10 cases (62.5%), a manic episode in 12.5%, and post-traumatic stress disorder in 6.5%. At T3 and T6, MDD was diagnosed in, respectively, eight (50%) and six cases (37.5%). Post TBI MDD had less severe depressive symptoms, showed greater social isolation and hostility and more cognitive deficits in comparison with the control group. CONCLUSIONS: MDD is a frequent TBI complication. Patients with post-TBI MDD have a specific psychopathological profile characterised by a less severe depressive symptomatology and a neuropsychological pattern that is significantly associated with greater deficits in cognitive functions than those with primary MDD.

Cellular uptake of coumarin-6 as a model drug loaded in solid lipid nanoparticles.

The aim of present work was to elucidate the interaction of solid lipid nanoparticles (SLNs) with cellular plasma-membrane to gain insight of intracellular drug delivery. To this aim we followed the uptake of coumarin-6 (a drug model) either free in the extracellular medium or loaded on SLN (c-SLN). Alveolar epithelial cells were exposed to a biocompatible concentration of c-SLN (0.01 mg/ml of tripalmitin) prepared by warm microemulsion whose lipid matrix was constituted by low melting point molecules (fatty acids, triglycerides). Intracellular fluorescence and preferential accumulation in the perinuclear region were increased by 54.8% on comparing c-SLN to the same amount of free coumarin-6 in the medium. Lowering temperature from 37 ° to 4 °C decreased the intracellular signal intensity by about 48% equally for the free as well as for loaded drug, thus suggesting the inhibition of a similar non-endocytotic entrance pathway. No specific co-localization of the fluorescence with intracellular organelles was found. The c-SLN calorimetric profile obtained with differential scanning calorimetry (DSC), revealing transition within the range 58-62 °C, altered remarkably upon incubation with cells, suggesting a change in SLN structure after association with cells membranes. We propose that the uptake of the model drug loaded on SLN is only partly related to the endocytotic pathway; it occurs despite the loss of integrity of the original SLN structure and it appears to be more efficient when the drug is vehicled rather than being free in the culture medium.

Respiratory and leg muscles perceived exertion during exercise at altitude.

We compared the rate of perceived exertion for respiratory (RPE,resp) and leg (RPE,legs) muscles, using a 10-point Borg scale, to their specific power outputs in 10 healthy male subjects during incremental cycle exercise at sea level (SL) and high altitude (HA, 4559 m). Respiratory power output was calculated from breath-by-breath esophageal pressure and chest wall volume changes. At HA ventilation was increased at any leg power output by ∼ 54%. However, for any given ventilation, breathing pattern was unchanged in terms of tidal volume, respiratory rate and operational volumes of the different chest wall compartments. RPE,resp scaled uniquely with total respiratory power output, irrespectively of SL or HA, while RPE,legs for any leg power output was exacerbated at HA. With increasing respective power outputs, the rate of change of RPE,resp exponentially decreased, while that of RPE,legs increased. We conclude that RPE,resp uniquely relates to respiratory power output, while RPE,legs varies depending on muscle metabolic conditions.

Interstitial pressure and lung oedema in chronic hypoxia.

We evaluated how the increase in lung interstitial pressure correlates with the pulmonary vascular response to chronic hypoxia. In control and hypoxic (30 days; 10% O2) Wistar male rats, we measured: pulmonary interstitial pressure (P(ip)), cardiac and haemodynamic parameters by echocardiography, and performed lung morphometry on tissue specimens fixed in situ. In control animals, mean ± sd P(ip), air/tissue volume ratio and capillary vascularity index in the air-blood barrier were -12 ± 2.03 cmH2O, 3.9 and 0.43, respectively. After hypoxia exposure, the corresponding values of these indices in apparently normal lung regions were 2.6 ± 1.7 cmH2O, 3.6, and 0.5, respectively. In oedematous regions, the corresponding values were 12 ± 4 cmH2O, 0.4 and 0.3, respectively. Furthermore, in normal regions, the density of pre-capillary vessels (diameter ~50-200 µm) increased and their thickness/internal diameter ratio decreased, while opposite results were found in oedematous regions. Pulmonary artery pressure increased in chronic hypoxia relative to the control (39.8 ± 5.9 versus 26.2 ± 2.2 mmHg). Heterogeneity in local lung vascular response contributes to developing pulmonary hypertension in chronic hypoxia. In oedematous regions, the decrease in capillary vascularity correlated with the remarkable increase in interstitial pressure and morphometry of the pre-capillary vessels suggested an increase in vascular resistance; the opposite was true in apparently normal regions.

Mechanisms controlling the volume of pleural fluid and extravascular lung water.

Pleural and interstitial lung fluid volumes are strictly controlled and maintained at the minimum thanks to the ability of lymphatics to match the increase in filtration rate. In the pleural cavity, fluid accumulation is easily accommodated by retraction of lung and chest wall (high compliance of the pleural space); the increase of lymph flow per unit increase in pleural fluid volume is high due to the great extension of the parietal lymphatic. However, for the lung interstitium, the increase in lymph flow to match increased filtration does not need to be so great. In fact, increased filtration only causes a minor increase in extravascular water volume (<10%) due to a marked increase in interstitial pulmonary pressure (low compliance of the extracellular matrix) which, in turn, buffers further filtration. Accordingly, a less extended lymphatic network is needed. The efficiency of lymphatic control is achieved through a high lymphatic conductance in the pleural fluid and through a low interstitial compliance for the lung interstitium. Fluid volume in both compartments is so strictly controlled that it is difficult to detect initial deviations from the physiological state; thus, a great physiological advantage turns to be a disadvantage on a clinical basis as it prevents an early diagnosis of developing disease.

Translocation pathways for inhaled asbestos fibers.

We discuss the translocation of inhaled asbestos fibers based on pulmonary and pleuro-pulmonary interstitial fluid dynamics. Fibers can pass the alveolar barrier and reach the lung interstitium via the paracellular route down a mass water flow due to combined osmotic (active Na+ absorption) and hydraulic (interstitial pressure is subatmospheric) pressure gradient. Fibers can be dragged from the lung interstitium by pulmonary lymph flow (primary translocation) wherefrom they can reach the blood stream and subsequently distribute to the whole body (secondary translocation). Primary translocation across the visceral pleura and towards pulmonary capillaries may also occur if the asbestos-induced lung inflammation increases pulmonary interstitial pressure so as to reverse the trans-mesothelial and trans-endothelial pressure gradients. Secondary translocation to the pleural space may occur via the physiological route of pleural fluid formation across the parietal pleura; fibers accumulation in parietal pleura stomata (black spots) reflects the role of parietal lymphatics in draining pleural fluid. Asbestos fibers are found in all organs of subjects either occupationally exposed or not exposed to asbestos. Fibers concentration correlates with specific conditions of interstitial fluid dynamics, in line with the notion that in all organs microvascular filtration occurs from capillaries to the extravascular spaces. Concentration is high in the kidney (reflecting high perfusion pressure and flow) and in the liver (reflecting high microvascular permeability) while it is relatively low in the brain (due to low permeability of blood-brain barrier). Ultrafine fibers (length < 5 mum, diameter < 0.25 mum) can travel larger distances due to low steric hindrance (in mesothelioma about 90% of fibers are ultrafine). Fibers translocation is a slow process developing over decades of life: it is aided by high biopersistence, by inflammation-induced increase in permeability, by low steric hindrance and by fibers motion pattern at low Reynolds numbers; it is hindered by fibrosis that increases interstitial flow resistances.

Mechanisms behind inter-individual differences in lung diffusing capacity.

We measured diffusing capacity (DLCO), alveolar membrane properties (D (m)), capillary lung volume (V (c)), and alveolar volume (V (A) ) in 20 healthy subjects (12 males; age 32.4 +/- 13 (SD); BMI 21.7 +/- 3; non smokers) at total lung capacity (TLC) and at approximately 80, 60, and 40% TLC. In all subjects, D (m) increased with lung volume, the increase being significantly greater for higher values of D (m)(TLC): the inter-individual differences can be interpreted by a greater number of alveolar units coupled to a lower thickness of the air-blood barrier (thus a higher alveolar surface to thickness ratio S (A)/tau). On the average, the volume-dependent increase of D (m) from approximately 40 to 100% TLC is less than expected based on geometrical increase of S (A) /tau. In fact, up to approximately 80% TLC, the increase in D (m) closely reflects only the increase of S (A), suggesting "unfolding" of the septa with no appreciable decrease in tau. Conversely, above 80% TLC, the decrease in tau due to parenchymal stretching becomes the main factor affecting D (m). In all subjects, V (c) decreased with increasing lung volume, in line with an increase in parenchymal stretching; the decrease was significantly larger for higher values of V (c) (40% TLC). Possibly reflecting differences in alveolar capillary density. No correlation was found between D (m)(TLC) and V (c)(40%TLC). The individual specificity in the lung volume dependence of V (c) and D (m) can be reasonably described by evaluating the V (c)/D (m) ratio at TLC and at approximately 40%TLC.

Organic extract of tire debris causes localized damage in the plasma membrane of human lung epithelial cells.

The potential toxicity of tire debris organic extracts on human alveolar epithelial cells (A549) was investigated. We analysed time- and dose dependent modifications produced on plasma membrane molecular composition and on lipid microdomains expression (caveolae and lipid rafts) that represent specific signalling platforms. Cells were exposed to increasing organic extract concentrations (10, 60 and 75mug/ml) for 24, 48 and 72h. An up to three fold dose and time dependent increase in specific protein markers of lipid microdomains was found, suggesting a corresponding increase in signalling platforms. Since the total pool of these plasma membrane markers was unchanged, we supposed that these proteins were translocated within the plasma membrane as to assemble the newly formed lipid microdomains. Despite no major modifications in lipid bilayer composition, a time- and dose dependent toxic effect was documented at 48h of exposure by an increase of cells positive to Trypan Blue assay. After 48h a dose dependent increase in the cell medium of the cytosolic enzyme lactate dehydrogenase was also observed, indicating greater damage of the plasma membrane as prenecrotic sign. The overall ultrastructural morphology of the plasma membrane of treated cells was not greatly modified, suggesting that organic extracts from tire debris cause focalized discontinuities on cell surfaces.

Effect of changing the gravity vector on respiratory output and control.

We studied the respiratory output in five subjects exposed to parabolic flights [gravity vector 1, 1.8 and 0 gravity vector in the craniocaudal direction (Gz)] and when switching from sitting to supine (legs bent at the knees). Despite differences in total respiratory compliance (highest at 0 Gz and in supine and minimum at 1.8 Gz), no significant changes in elastic inspiratory work were observed in the various conditions, except when comparing 1.8 Gz with 1 Gz (subjects were in the seated position in all circumstances), although the elastic work had an inverse relationship with total respiratory compliance that was highest at 0 Gz and in supine posture and minimum at 1.8 Gz. Relative to 1 Gz, lung resistance (airways plus lung tissue) increased significantly by 52% in the supine but slightly decreased at 0 Gz. We calculated, for each condition, the tidal volume changes based on the energy available in the preceding phase and concluded that an increase in inspiratory muscle output occurs when respiratory load increases (e.g., going from 0 to 1.8 Gz), whereas a decrease occurs in the opposite case (e.g., from 1.8 to 0 Gz). Despite these immediate changes, ventilation increased, going to 1.8 and 0 Gz (up to approximately 23%), reflecting an increase in mean inspiratory flow rate, tidal volume, and respiratory frequency, while ventilation decreased (approximately -14%), shifting to supine posture (transition time approximately 15 s). These data suggest a remarkable feature in the mechanical arrangement of the respiratory system such that it can maintain the ventilatory output with small changes in inspiratory muscle work in face of considerable changes in configuration and mechanical properties.

Non-linear dependence of interstitial fluid pressure on joint cavity pressure and implications for interstitial resistance in rabbit knee.

AIMS: Synovium retains lubricating fluid in the joint cavity. Synovial outflow resistance estimated as dPj/dQs (Pj, joint fluid pressure and Qs trans-synovial flow) is greater, however, than expected from interstitial glycosaminoglycan concentration. This study investigates whether subsynovial fluid pressure increases with intra-articular pressure, as this would reduce the estimated resistance estimate. METHODS: Interstitial fluid pressure (Pif) was measured as a function of distance from the joint cavity in knees of anaesthetized rabbits, using servo-null pressure-measuring micropipettes and using an external 'window'. Joint fluid pressure Pj was either endogenous (-2.4 +/- 0.4 cmH2O, mean +/- SEM) or held at approximately 4, 8 or 15.0 cmH2O by a continuous intra-articular saline infusion that matched the trans-synovial interstitial drainage rate. RESULTS: At endogenous Pj the peri-articular Pif was subatmospheric (-1.9 +/- 0.3 cmH2O, n = 19). At raised Pj the Pif values became positive. Gradient dPif /dx was approximately 20 times steeper across synovium than subsynovium. Pif close to the synovium-subsynovium border (Pif*) increased as a non-linear function of Pj to 1.4 +/- 0.2 cmH2O (n = 23) at Pj = 4.3 +/- 0.1 cmH2O : 2.3 +/- 0.2 cmH2O (n = 17) at Pj = 7.6 +/- 0.2 cmH2O: and 3.0 +/- 0.4 cmH2O (n = 26) at Pj = 15 +/- 0.2 cmH2O (P = 0.03, anova). CONCLUSIONS: Synovial resistivity is approximately 20x subsynovial resistivity. The increase in Pif*with Pj means that true synovial resistance d(Pj-Pif*)/dQs is overestimated 1.5x by dPj/dQs. This narrows but does not eliminate the gap between analysed glycosaminoglycan concentration, 4 mg ml(-1), and the net interstitial biopolymer concentration of 11.5 mg ml(-1) needed to generate the resistance.

Effect of gravity and posture on lung mechanics.

The volume-pressure relationship of the lung was studied in six subjects on changing the gravity vector during parabolic flights and body posture. Lung recoil pressure decreased by approximately 2.7 cmH(2)O going from 1 to 0 vertical acceleration (G(z)), whereas it increased by approximately 3.5 cmH(2)O in 30 degrees tilted head-up and supine postures. No substantial change was found going from 1 to 1.8 G(z). Matching the changes in volume-pressure relationships of the lung and chest wall (previous data), results in a decrease in functional respiratory capacity of approximately 580 ml at 0 G(z) relative to 1 G(z) and of approximately 1,200 ml going to supine posture. Microgravity causes a decrease in lung and chest wall recoil pressures as it removes most of the distortion of lung parenchyma and thorax induced by changing gravity field and/or posture. Hypergravity does not greatly affect respiratory mechanics, suggesting that mechanical distortion is close to maximum already at 1 G(z). The end-expiratory volume during quiet breathing corresponds to the mechanical functional residual capacity in each condition.

Effect of low intensity electrical stimulation on quadriceps muscle voluntary maximal strength.

BACKGROUND: Evaluate the effect of low intensity electrical stimulation (ES) training on strength. We purposefully used a low ES stimulation intensity to have it well accepted by middle aged and low performing people. Relate strength to metabolic parameters. METHODS: Experimental design. Protocol 1: effects of 11 day low intensity ES training on quadriceps muscle maximal voluntary contraction (MVC). Protocol 2: effects of 3 day training at low intensity ES + voluntary contraction at 60% of MVC (co-contraction). VARIABLES MEASURED: maximal voluntary strength (FMAX), strength during ES (FES), strength developed during co-contraction (FES-C), oxygen consumption, heart rate. Experimental design included a basal session, a training program and controls of measured variables during and at the end of the training program. PARTICIPANTS: protocol 1: experiments were done on 13 healthy and sedentary subjects (6 males and 7 women, mean age 50.6 years). Protocol 2: experiments done on 6 healthy sedentary men (mean age 31.5 years). RESULTS: Protocol 1: FMAX increased significantly (p<0.05) to 14 and 19% at day 6 and 11, respectively. During ES, oxygen consumption increased by 20%, but no change in heart rate was observed. Protocol 2: FMAX significantly increased (about 5%) in subjects who trained with co-contraction; conversely, FMAX did not significantly increase in a control group matched for age who trained only with voluntary contractions. CONCLUSIONS: Low intensity ES in sedentary and poorly performing people increases significantly FMAX during MVC possibly via facilitatory neurogenic mechanism.

Effect of gravity on chest wall mechanics.

Chest wall mechanics was studied in four subjects on changing gravity in the craniocaudal direction (G(z)) during parabolic flights. The thorax appears very compliant at 0 G(z): its recoil changes only from -2 to 2 cmH(2)O in the volume range of 30-70% vital capacity (VC). Increasing G(z) from 0 to 1 and 1.8 G(z) progressively shifted the volume-pressure curve of the chest wall to the left and also caused a fivefold exponential decrease in compliance. For lung volume <30% VC, gravity has an inspiratory effect, but this effect is much larger going from 0 to 1 G(z) than from 1 to 1.8 G(z). For a volume from 30 to 70% VC, the effect is inspiratory going from 0 to 1 G(z) but expiratory from 1 to 1.8 G(z). For a volume greater than approximately 70% VC, gravity always has an expiratory effect. The data suggest that the chest wall does not behave as a linear system when exposed to changing gravity, as the effect depends on both chest wall volume and magnitude of G(z).

Pulmonary microvascular and perivascular interstitial geometry during development of mild hydraulic edema.

To study pulmonary arteriolar vasomotion in control conditions and in the transition to hydraulic edema, changes in subpleural pulmonary arteriolar diameter and perivascular interstitial volume were evaluated in anesthetized spontaneously breathing rabbits. Images of subpleural pulmonary microvessels were recorded in control conditions and for up to 180 min during a 0.5 ml x kg(-1) x min(-1) intravenous saline infusion through an intact parietal pleural window. Images were digitized and analyzed with a semiautomatic procedure to determine vessel diameter and perivascular interstitial thickness from which interstitial fluid volume was derived. In control vessels, the diameter of approximately 30-, approximately 50-, and approximately 80-microm arterioles and the perivascular interstitial thickness were fairly stable. During infusion, the diameter increased maximally by 20% in approximately 30 microm vessels, was unchanged in approximately 50 microm vessels, and decreased by 25% in approximately 80-microm arterioles; the perivascular interstitial volume increased by 54% only around 30-microm microvessels. In papaverine-treated rabbits, all arterioles dilated and a larger increase in perivascular interstitial thickness was observed. The data suggest that the opposite vasomotor behavior of 30- and 80-microm arterioles during development of mild edema may represent a local specific response of the pulmonary microcirculation to reduce capillary pressure in the face of an increased transendothelial fluid filtration, thus counteracting progression toward severe edema.

Interstitial pressure gradients around joints; location of chief resistance to fluid drainage from the rabbit knee.

The hypothesis has been advanced that synovium offers the main resistance to fluid escape from joints, even though it is under 20 microm thick. To test this, fluid was infused into the knee joint cavity of anaesthetised rabbits to set up a pressure gradient, then the profile of periarticular interstitial fluid pressure (P(if)) was measured by advancing a micropipette, connected to a servo-null pressure recorder, in steps through a periarticular tissue 'window' until the joint cavity was entered. With intra-articular pressure (P(j)) raised to 15 cmH(2)O (the pressure of an acute joint effusion) the pressure gradient dP(if) /dx (where x is distance) across the synovial lining was 0.47 +/- 0.04 cmH(2)O microm(-1) (n = 10 joints). This was 23.5-fold greater than the gradient in the subsynovium (0.02 +/- 0.01 cmH(2)O microm(-1); P < 0.0001, Student's t test), indicating that the hydraulic resistivity of the subsynovium is 4 % of that of the synovium. The pressure profile was not altered by circulatory arrest. To test the hypothesis further, the effect of a stab perforation of the synovial lining on fluid drainage rate ((.Q(s)) was studied. Perforation raised both.Q(s) and the conductance term d.Q(s)/dP(j) more than 10-fold (n = 6 joints; P < 0.0001, ANOVA). The results thus support the view that, despite its thinness, the synovial lining offers the main hydraulic resistance to fluid drainage from a synovial joint.

Steady-state pleural fluid flow and pressure and the effects of lung buoyancy.

Both theoretical and experimental studies of pleural fluid dynamics and lung buoyancy during steady-state, apneic conditions are presented. The theory shows that steady-state, top-to-bottom pleural-liquid flow creates a pressure distribution that opposes lung buoyancy. These two forces may balance, permitting dynamic lung floating, but when they do not, pleural-pleural contact is required. The animal experiments examine pleural-liquid pressure distributions in response to simulated reduced gravity, achieved by lung inflation with perfluorocarbon liquid as compared to air. The resulting decrease in lung buoyancy modifies the force balance in the pleural fluid, which is reflected in its vertical pressure gradient. The data and model show that the decrease in buoyancy with perfluorocarbon inflation causes the vertical pressure gradient to approach hydrostatic. In the microgravity analogue, the pleural pressures would be toward a more uniform distribution, consistent with ventilation studies during space flight. The pleural liquid turnover predicted by the model is computed and found to be comparable to experimental values from the literature. The model provides the flow field, which can be used to develop a full transport theory for molecular and cellular constituents that are found in pleural fluid.

Influence of actin cytoskeleton on intra-articular and interstitial fluid pressures in synovial joints.

Fibroblast microfilamentous actin (F-actin) influences interstitial fluid pressure via linkages to collagen in rat skin (Berg et al., 2001). The present aims were to determine whether the actin cytoskeleton of synovial endothelium, fibroblasts, and synoviocytes influences in vivo (i) fluid exchange between a joint cavity and synovial microcirculation and (ii) extracellular fluid pressures in joints. Rabbit knee joints were treated intra-articularly with the F-actin disrupting drugs cytochalasin D and latrunculin B while joint fluid pressure P(j) was recorded. In joints injected with small volumes of control solution, P(j) fell with time (-0.05 +/- 0.01 cm H2O x min(-1), mean +/- SEM, n = 9, equivalent drainage rate 3.9 microl x min(-1)). Cytochalasin or latrunculin reversed this in approximately 4 min in vivo; P(j) increased with time, e.g., +0.12 +/- 0.04 cm H2O x min(-1) at 200 microM cytochalasin (equivalent filtration rate into joint 6.6-12.5 microl x min(-1), n = 4), with a cytochalasin EC50 of 45 microM. Plasma gamma-globulin clearance into the joint cavity was also increased. Post mortem, cytochalasin did not reverse dP(j)/dt and had no more effect on P(j) than did control solution. Also, when synovial interstitial fluid pressures were measured by servonull micropipette post mortem (control -0.95 +/- 0.37 cmH2O, n = 18) cytochalasin had no significant effect on interstitial pressure over 60 min, even at 1 mM. It was concluded that synovial endothelial F-actin has an important role in the normal synovial microvascular resistance to fluid filtration and plasma gamma-globulin permeation and is thus a potential link between pro-inflammatory mediators and arthritic joint effusions. The results provided no support for the hypothesis that synoviocyte F-actin influences the swelling tendency of synovial matrix and hence extracellular fluid pressures, in contrast to the findings of Berg et al. (2001) in rat dermis.