Biomedical subjects

J R Levick

Publications and source records attributed to J R Levick.

At least 37 records · Page 2Linked to original sources

PubMed2003

Impairment of lymph drainage in subfascial compartment of forearm in breast cancer-related lymphedema.

BACKGROUND: In arm lymphedema secondary to axillary surgery and radiotherapy (breast cancer-related lymphedema), the swelling is largely epifascial and lymph flow per unit epifascial volume is impaired. The subfascial muscle compartment is not measurably swollen despite the iatrogenic damage to its axillary drainage pathway, but this could be due to its low compliance. Our aim was to test the hypothesis that subfascial lymph drainage too is impaired. METHODS AND RESULTS: Quantitative lymphoscintigraphy was used to measure the removal rate constant (local lymph flow per unit distribution volume) for technetium-99m-human immunoglobulin G injected intramuscularly in the forearms of nine women with unilateral lymphedema. The removal rate constant was on average 31% lower in the ipsilateral swollen forearm than in the contralateral forearm (swollen arm: -0.096+/-0.041% min(-1), contralateral arm: -0.138+/-0.037% min(-1); mean+/-SD, p = 0.037). The decrease in subfascial rate constant correlated strongly with increase in arm volume (r = -0.88, p = 0.002), even though the swelling is mainly epifascial. There was no convincing evidence of dermal backflow. CONCLUSIONS: Lymph flow in the subfascial muscle compartment is decreased in breast cancer-related lymphedema. The correlation between impairment of subfascial drainage and epifascial arm swelling could be because both depend on the severity of axillary damage, or because loss of function in subfascial lymphatics impairs drainage from the epifascial to the subfascial system.

Aged↗

PubMed2002

Interactive effect of chondroitin sulphate C and hyaluronan on fluid movement across rabbit synovium.

The polysaccharide hyaluronan (HA) conserves synovial fluid by keeping outflow low and almost constant over a wide pressure range ('buffering'), but only at concentrations associated with polymer domain overlap. We therefore tested whether polymer interactions can cause buffering, using HA-chondroitin sulphate C (CSC) mixtures. Also, since it has been found that capillary filtration is insensitive to the Starling force interstitial osmotic pressure in frog mesenteries, this was assessed in synovium. Hyaluronan at non-buffering concentrations (0.50-0.75 mg ml(-1)) and/or 25 mg ml(-1) CSC (osmotic pressure 68 cmH(2)O) was infused into knees of anaesthetised rabbits in vivo. Viscometry and chromatography confirmed that HA interacts with CSC. Pressure (P(j)) versus trans-synovial flow (;Q(s)) relations were measured.;Q(s) was outwards for HA alone (1.2 +/- 0.9 microl min(-1) at 3 cmH(2)O, mean +/- S.E.M.; n = 6). CSC diffused into synovium and changed;Q(s) to filtration at low P(j) (-4.1 microl min(-1), 3 cmH(2)O, n = 5, P < 0.02, t test). Filtration ceased upon circulatory arrest (n = 3). At higher P(j), 0.75 mg ml(-1) HA plus CSC buffered;Q(s) to approximately 3 microl min(-1) over a wide range of P(j), with an outflow increase of only 0.04 +/- 0.02 microl min(-1) cmH(2)O(-1) (n = 4). With HA or CSC alone, buffering was absent (slopes 0.57 +/- 0.04 microl min(-1) cmH(2)O(-1) (n = 4) and 0.86 +/- 0.05 microl min(-1) cmH(2)O(-1) (n = 5), respectively). Therefore, polymer interactions can cause outflow buffering in joints. Also, interstitial osmotic pressure promoted filtration in fenestrated synovial capillaries, so the results for frog mesentery capillaries cannot be generalised. The difference is attributed to differences in pore ultrastructure.

Adjuvants, Immunologic↗

PubMed2002

Inside-out cannulation of fine lymphatic trunks used to quantify coupling between transsynovial flow and lymphatic drainage from rabbit knees.

The coupling of periarticular lymph flow to transsynovial flow from a joint cavity, i.e., fluid load, is essential to avoid periarticular edema, which is associated with arthritic morning stiffness. To study coupling in swollen joints, a new method, "inside-out" cannulation, which eliminates dead space, resistance and cutout, was used to collect lymph from fine femoral lymph trunks in anesthetised rabbits while the knee joint cavity was infused with Evans blue albumin (EVA) at controlled intraarticular pressure and transsynovial drainage rates. The amount of joint lymph in femoral lymph (volume fraction V(v)) was calculated by EVA analysis. Joint lymph flow and EVA clearance was 1.5 +/- 0.4 microl min(-1) (mean +/- SEM, n = 62) at mean trans-synovial flow, 23 microl min(-1), and increased with pressure. Volume fraction increased from 16% at 10 cmH(2)O to 43% at 41 cmH(2)O. The increase in lymph flow with pressure, 0.052 +/- 0.025 microl min(-1) cmH(2)O(-1) (n = 61) was much smaller than the increase in transsynovial flow (periarticular fluid load) with pressure, 0.71 +/- 0.14 microl min(-1) cmH(2)O(-1) (P < 0.001). Their ratio, the coupling coefficient, was only 0.06-0.11. Thus, although up to 43% of femoral lymph could stem from a single swollen joint, this drained away only a small fraction of the transsynovial filtrate. The study showed that joint lymphatic drainage is coupled to joint pressure and transsynovial flow; but the coupling is insufficient to prevent periarticular fluid accumulation under conditions of joint volume expansion and limb immobility. This may contribute to the periarticular edema of arthritis.

Albumins↗

PubMed2002

Evidence for dermal angiogenesis in breast cancer related lymphedema demonstrated using dual-site fluorescence angiography.

OBJECTIVE: To determine whether the skin expansion associated with breast cancer related lymphedema (BCRL) reduces microvessel density or causes a compensatory angiogenesis. METHODS: Dermal microvessel density was measured by simultaneous fluorescence video angiography in the ipsilateral and contralateral forearms of 25 patients treated for breast cancer, 12 with BCRL (excess volume 30 +/- 20%) and 13 without. RESULTS: Microvessel density was as high in the swollen arm (27.2 +/- 7.2 mm(-2)) as in the contralateral arm (24.2 +/- 6.2 mm(-2)) despite a 16 +/- 12% increase in local circumference. Total microvessels in a 1-mm annulus of skin was 30% greater in the swollen arm (752 +/- 211) than the contralateral arm (578 +/- 157; p = 0.005, t-test). Microvessel density was similar in each arm in control patients (ipsilateral 24.1 +/- 6.2 mm(-2), contralateral 26.1 +/- 8.8 mm(-2)). CONCLUSIONS: The number of microvessels increased in the expanded skin to maintain microvessel density at a normal level. Therefore, angiogenesis occurs during chronic limb swelling. The control group results indicate that angiogenesis is not caused by the cancer treatment.

Aged↗

PubMed2002

Contribution of F-actin to barrier properties of the blood-joint pathway.

OBJECTIVES: Because fibroblast filamentous actin (F-actin) influences cutaneous interstitial matrix swelling pressure (5), we investigated whether F-actin in fibroblast-derived synoviocytes influences the hydraulic permeability of the trans-synovial interstitial pathway. The study also tested whether F-actin in fenestrated synovial endothelium contributes to the blood-joint barrier in vivo. METHODS: The clearance of Evans blue-albumin (EVA) from plasma into the knee joint cavity was determined in joint infused with F-actin disrupting cytochalasin D (1-200 microM), latrunculin B (100 microM) or vehicle in anesthetized rabbits. The hydraulic permeability of the lining was determined as the slope relating net trans-synovial flow Q(s) to intra-articular pressure P(j). Synovium was examined histologically after i.v. Monastral blue to assess endothelial leakiness. RESULTS: EVA permeation in vivo was increased up to 25-fold by cytochalasin (p = 0.0002, ANOVA), with an EC(50) of 23 microM (95% confidence limits 13-43 microM). Washout quickly reversed the increase. Latrunculin had a similar effect. F-actin disruption switched Q(s) from drainage (control) to filtration into the cavity at low P(j) in vivo and raised the conductance Q(s)/dP(j) by 2.13 (p = 0.001, ANOVA). Circulatory arrest abolished these effects. Monastral blue revealed numerous endothelial leaks. CONCLUSIONS: F-actin is crucial to the barrier function of fenestrated endothelium in situ. No significant effect of synoviocyte F-actin on matrix permeability was detected.

Actins↗

PubMed2001

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.

Actins↗

PubMed2001

Immunohistochemical evaluation of psoriatic plaques following selective photothermolysis of the superficial capillaries.

BACKGROUND: Elongated and tortuous capillary loops are distinctive features of psoriasis. The significance of these microvascular changes in the pathogenesis of plaques, however, remains unclear. OBJECTIVES: To determine what part the expanded superficial capillary bed plays in the pathogenesis of clinical lesions by selectively thermolysing psoriatic capillaries with a pulsed dye laser (PDL). METHODS: Cutaneous lesions were biopsied before and after treatment and sections assessed by standard immunohistochemical techniques for changes in known indicators of angiogenesis, including endothelial surface area, endothelial cell proliferation and endothelial cell expression of adhesion molecules. We also measured lymphocytic infiltration and epidermal thickness, and quantified the presence of a marker of keratinocyte proliferation before and after treatment. RESULTS: The effect of the PDL was limited to the superficial capillary bed, with no changes in the microvessels (including venules and arterioles) of the upper reticular dermis. Although there was significant clinical improvement in plaques after treatment (P = 0.02), complete clearance of lesions was not achieved. Thermolysis of psoriatic capillaries caused a reduction in both endothelial surface area (P < 0.01) and endothelial cell proliferation in the superficial dermis (P = 0.04). Endothelial expression of surface adhesion molecules (integrins and E-selectin) important in angiogenesis was not, however, altered by treatment. The CD4+ and CD8+ T-cell infiltrate was significantly reduced in the superficial papillary dermis (P = 0.02 and P = 0.04, respectively), but not in the epidermis or upper reticular dermis. Laser treatment significantly reduced epidermal thickness (P = 0.001), but did not alter epidermal keratinocyte proliferation (P = 0.2). CONCLUSIONS: The results demonstrate that dermal capillary changes alone are unlikely to be causal in psoriasis. They indicate that the expanded psoriatic capillaries may be important in facilitating the access of activated T cells to the skin and in maintaining the psoriatic plaque. These results do not refute the consensus view that plaque formation may be mediated by the release of growth factors/cytokines from activated epidermal T cells/keratinocytes.

Adult↗

PubMed2001

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.

Animals↗

PubMed2001

Differences in lymph drainage between swollen and non-swollen regions in arms with breast-cancer-related lymphoedema.

Recent research indicates that the pathophysiology of breast-cancer-related lymphoedema (BCRL) is more complex than simple axillary lymphatic obstruction as a result of the cancer treatment. Uneven distribution of swelling (involvement of the mid-arm region is common, but the hand is often spared) is puzzling. Our aim was to test the hypothesis that local differences in lymphatic drainage contribute to the regionality of the oedema. Using lymphoscintigraphy, we measured the removal rate constant, k (representing local lymph flow per unit distribution volume, VD), for 99mTc-labelled human immunoglobulin G in the oedematous proximal forearm, and in the hand (finger web) in women in whom the hand was unaffected. Tracer was injected subcutaneously, and the depot plus the rest of the arm was monitored with a gamma-radiation camera for up to 6 h. VD was assessed from image width. Contralateral arms served as controls. k was 25% lower in oedematous forearm tissue than in the control arm (BCRL, -0.070+/-0.026% x min(-1); control, -0.093+/-0.028% x min(-1); mean+/-S.D.; P=0.012) and VD was greater. In the non-oedematous hand of the BCRL arm, k was 18% higher than in the control hand (BCRL, -0.110+/-0.027% x min(-1); control, -0.095+/-0.028% x min(-1); P=0.057) and 59% higher than forearm k on the BCRL side (P=0.0014). VD did not differ between the hands. Images of the BCRL arm following hand injection showed diffuse activity in the superficial tissues, sometimes extending almost to the shoulder. A possible interpretation is that the hand is spared in some patients because local lymph flow is increased and diverted along collateral dermal routes. The results support the hypothesis that regional differences in surviving lymphatic function contribute to the distribution of swelling.

Aged↗

PubMed2000

Action of polysaccharides of similar average mass but differing molecular volume and charge on fluid drainage through synovial interstitium in rabbit knees.

Hyaluronan (HA), an anionic polysaccharide of synovial fluid, attenuates fluid loss from joints as joint pressure is raised ('outflow buffering'). The buffering is thought to depend on the expanded molecular domain of the polymer, which causes reflection by synovial extracellular matrix, leading to flow-dependent concentration polarization. We therefore assessed the effects of polysaccharides of differing average molecular volume and charge. Trans-synovial fluid drainage( 8d s) was measured at controlled joint fluid pressure (Pj) in knees of anaesthetized rabbits. The joints were infused with polydisperse HA of weight-average mass 2100 kDa (4 mg x ml(-1), n = 17), with polydisperse neutral dextran of similar average mass (2000 kDa; n = 7) or with Ringer solution vehicle (n = 2). The role of polymer charge was assessed by infusions of neutral or sulphated dextran of average molecular mass 500 kDa (n = 6). When HA was present, 8d s increased little with pressure, forming a virtual plateau of approximately 4 microl x min(-1) from 10 to 25 cmH2O. Neutral dextran 2000 failed to replicate this effect. Instead, 8d s increased steeply with Pj, reaching eight times the HA value by 20 cmH2O (P = 0.0001, ANOVA). Dextran 2000 reduced flows in comparison with Ringer solution. Analysis of the aspirated joint fluid showed that 31 +/- 0.07 % (s.e.m.) of dextran 2000 in the filtrand was reflected by synovium, compared with > or = 79 % for HA. The viscometric molecular radius of the dextran, approximately 31 nm, was smaller than that of HA (101-181 nm), as was its osmotic pressure. Anionic dextran 500 failed to buffer fluid drainage, but it reduced fluid escape and synovial conductance d 8d s/dPj more than neutral dextran 500 (P < 0.0001, ANOVA). The anionic charge increased the molecular volume and viscosity of dextran 500. The results support the hypothesis that polymer molecular volume influences its reflection by interstitial matrix and outflow buffering. Polymer charge influences flow through an effect on viscosity and possibly electrostatic interactions with negatively charged interstitial matrix.

Animals↗

PubMed2000

Role of hyaluronan chain length in buffering interstitial flow across synovium in rabbits.

1. Synovial fluid drains out of joints through an interstitial pathway. Hyaluronan, the major polysaccharide of synovial fluid, attenuates this fluid drainage; it creates a graded opposition to outflow that increases with pressure (outflow 'buffering'). This has been attributed to size-related molecular reflection at the interstitium-fluid interface. Chain length is reduced in inflammatory arthritis. We therefore investigated the dependence of outflow buffering on hyaluronan chain length. 2. Hyaluronan molecules of mean molecular mass approximately 2200, 530, 300 and 90 kDa and concentration 3.6 mg ml-1 were infused into the knees of anaesthetized rabbits, with Ringer solution as control in the contralateral joint. Trans-synovial drainage rate was recorded at known joint pressures. Pressure was raised in steps every 30-60 min (range 2-24 cmH2O). 3. With hyaluronan-90 and hyaluronan-300 the fluid drainage rate was reduced relative to Ringer solution (P < 0.001, ANOVA) but increased steeply with pressure. The opposition to outflow, defined as the pressure required to drive unit outflow, did not increase with pressure, i.e. there was no outflow buffering. 4. With hyaluronan-530 and hyaluronan-2000 the fluid drainage rate became relatively insensitive to pressure, causing a near plateau of flow. Opposition to outflow increased markedly with pressure, by up to 3.3 times over the explored pressures. 5. Hyaluronan concentration in the joint cavity increased over the drainage period, indicating partial reflection of hyaluronan by synovial interstitium. Reflected fractions were 0.12, 0.33, 0.25 and 0.79 for hyaluronan-90, -300, -530 and -2200, respectively. 6. Thus the flow-buffering effect of hyaluronan depended on chain length, and shortening the chains reduced the degree of molecular reflection. The latter should reduce the concentration polarization at the tissue interface, and hence the local osmotic pressure opposing fluid drainage. In rheumatoid arthritis the reduced chain length will facilitate the escape of hyaluronan and fluid.

Animals↗

PubMed2000

Interaction of intraarticular hyaluronan and albumin in the attenuation of fluid drainage from joints.

OBJECTIVE: How is fluid volume regulated in joints? Fluid drainage rate is an important factor, both in normal joints and those with effusions. Hyaluronan and albumin, separately, are known to attenuate drainage, conserving synovial fluid volume in the presence of raised joint pressure. Hyaluronan and albumin normally coexist, however, in joint fluid. The objective was to determine their interactive effect on drainage. METHODS: The fluid escape rate from the joint cavity through synovium was measured at controlled intraarticular pressures using a rabbit knee model in vivo. One joint contained 4 mg/ml hyaluronan and the other contained 4 mg/ml hyaluronan plus 20 mg/ml albumin, as in normal synovial fluid. Hyaluronan-albumin interactions were assessed in vitro by viscometry and osmometry. RESULTS: Hyaluronan alone greatly attenuated fluid escape. Drainage rates plateaued at 4-5 microl/minute as pressure was raised, because the opposition to drainage increased with pressure. Addition of albumin to hyaluronan shifted the opposition-versus-pressure relation upward and further attenuated drainage by 22.5%, despite a small fall in the viscosity of the mixture. Osmometry showed a small synergistic interaction. Analysis of aspirates showed that < or =8% of albumin molecules in the draining fluid were reflected by the synovial lining (compared with 79% of hyaluronan molecules). CONCLUSION: Hyaluronan and albumin act together at normal concentrations to conserve synovial fluid in the presence of raised drainage pressures. Hyaluronan has the greater effect, acting osmotically by way of a concentration polarization boundary layer. Attenuation of this effect in arthritic effusions with low hyaluronan concentrations is one of several factors limiting fluid accumulation and, hence, the size of the effusion.

Albumins↗

PubMed2000

Concentration dependence of interstitial flow buffering by hyaluronan in synovial joints.

Hyaluronan concentration in synovial fluid spans a 20-fold range, from as low as 0.2 mg ml(-1) in synovitis to as high as 4 mg ml(-1) in healthy joints. The aim was to determine the effect of this on fluid drainage from the joint cavity. The study extends the finding of P. J. Coleman, D. Scott, R. M. Mason, and J. R. Levick (1999, J. Physiol. 514, 265-282) that dissolved hyaluronan at 3.6-4.0 mg ml(-1) (the concentration in young human and rabbit joints) causes the opposition to interstitial fluid drainage to increase with pressure. Hyaluronan was infused into rabbit knees at 0, 0.2, 2.0, and 4.0 mg ml(-1) over a range of intraarticular pressures. Hyaluronan at 2 mg ml(-1) (as in healthy elderly joints and some osteoarthritis) greatly reduced drainage rates and generated a flattening (convex) pressure-flow relation, as observed previously with 4 mg ml(-1). Drainage rates were greater at 2 mg ml(-1) than at 4 mg ml(-1) hyaluronan (P < 0.0001, ANOVA, n = 7). The opposition to outflow (pressure required to drive unit outflow) increased with pressure, but less markedly than with 4 mg ml(-1) hyaluronan. Hyaluronan at 0.2 mg ml(-1) reduced outflow by approximately 50% relative to Ringer solution (P < 0.0001, ANOVA, n = 7) but the pressure-flow relation no longer flattened out with increasing pressure, because there was no significant increase in opposition to outflow with pressure. At 0 mg ml(-1) hyaluronan, outflow opposition decreased with pressure. Viscometry showed a marked transition in the hyaluronan state at >/=1.35 mg ml(-1), indicating that this is the critical concentration for molecular domain overlap and intermolecular coupling. The results broadly supported the concentration-polarization hypothesis, which predicts significant osmotic buffering of drainage at >/=1 mg ml(-1) hyaluronan; at 0.2 mg ml(-1) other factors may predominate. It is inferred that hyaluronan at physiological concentrations can conserve synovial fluid when pressures are raised (e.g., flexion): whereas dilution of hyaluronan, as in severe effusions, can effectively abolish buffering and thus facilitate fluid drainage.

Aged↗

PubMed1999

Characterization of the effect of high molecular weight hyaluronan on trans-synovial flow in rabbit knees.

1. The effect of a rooster comb hyaluronan (3.6-4.0 g l-1) of similar chain length to rabbit synovial fluid hyaluronan, on the trans-synovial escape of fluid from the joint cavity in the steady state ( 8d s) was studied in 29 rabbit knees at controlled intra-articular pressures (Pj). 2. Rooster hyaluronan caused the pressure-flow relation to flatten out as pressure was raised. At 10-20 cmH2O the slope of the quasi-plateau, 0.05 +/- 0.01 microliter min-1 cmH2O-1 (mean +/- s.e.m.), was 1/39th that for Ringer solution (1.94 +/- 0.01 microliter 2O-1 ). 3. Bovine synovial fluid had a similar effect to hyaluronan in Ringer solution. 4. The quasi-plateau was caused by increasing opposition to outflow; the pressure required to drive unit outflow increased 4.4-fold between 5 and 20 cmH2O. The increased opposition to outflow at 20 cmH2O was equivalent to an effective osmotic pressure of 13-17 cmH2O at the interface. Since the infusate's osmotic pressure was only 0.9 cmH2O, this implied concentration polarization to 15-18 g l-1 hyaluronan at the interface. 5. Mechanical perforation of the lining, or enzymatic degradation of the interstitial matrix by chymopapain, abolished the quasi-plateau. Hydrational expansion of the matrix by approximately 2-fold did not. The increased opposition to outflow was reversible by washing out the hyaluronan, or by reducing Pj. It was unaffected by interruption of tissue blood flow or synoviocyte oxidative metabolism. These properties are compatible with a concentration polarization mechanism, i.e. flow-induced concentration of hyaluronan at the synovial interface due to molecular reflection. 6. A concentration polarization theory was developed for a partially reflected solute. Numerical solutions supported the feasibility of this osmotic explanation of the quasi-plateau. Additional mechanisms may also be involved. 7. It is concluded that native-size hyaluronan helps to retain synovial fluid in the joint cavity when pressure is raised and acts, at least in part, by exerting osmotic pressure at the interface between synovial matrix and a concentration polarization layer.

Animals↗

PubMed1999

Increased dermal lymphatic density in the human leg compared with the forearm.

During orthostasis, capillary filtration pressure is higher in the leg than in the arm due to the effect of gravity. We investigated the possibility that the lymphatic network in leg skin might be adapted to cope with a greater fluid load. The dermal lymphatics of the forearm and lower leg were studied in white-skinned and brown-skinned men using fluorescence video microscopy. From video print lymphangiograms the following were determined: lymphatic length density at a series of radii from the centre of the lymphangiogram (LDr); maximum lymphatic density (LDmax); total length of lymphatic vessel (LL); maximum spread of lymphatic vessel; number and size of lymphatic rings (continuous circuits of vessel); and vessel diameter. There were no differences between the two racial types, but clear differences between the arm and leg. In the leg, mean (+/- SD) peak LDr (25.13 +/- 5.65 cm-1), LDmax (32.95 +/- 6.89 cm-1), LL (40.17 +/- 27.42 cm), and spread (1.39 +/- 0.08 cm) were all significantly higher than in the arm (18.03 +/- 5.48 cm-1, 23.91 +/- 7.21 cm-1, 11.76 +/- 5.47 cm, and 1.00 +/- 0.05 cm respectively, P </= 0.001). In the region of maximum lymphatic density there were 2.4 times more rings in the leg than in the arm, ring size being similar. Vessel image diameters were 89.6 +/- 26.3 micron (leg) and 94.8 +/- 10.9 micron (arm). Leg skin thus has a denser and more extensive lymphatic network than arm skin. This supports the hypothesis that lymph transport capacity in the leg is enhanced to compensate for a greater gravitational fluid loading.

Adult↗

PubMed1999

Control of cutaneous blood vessels in psoriatic plaques.

The aim of this study was to compare local blood flow in psoriatic plaques before and after provocations known to alter cutaneous vascular resistance, in order to determine whether plaque hyperemia is caused by a failure of normal vascular control mechanisms. Cutaneous blood flow was recorded using a laser Doppler flowmeter over plaque skin (plaque site) and clinically normal skin (nonplaque site) on the opposite arm, at least 5 cm away from the nearest plaque. It is important to note that most of the laser Doppler signal comes from the subpapillary plexus of the skin and only a small portion (2%-10%) is produced by capillary blood flow. In the psoriatic plaques the basal flux was between nine and 13 times greater than nonplaque skin. The biologic zero (a signal independent of perfusion, which also persists after complete proximal arterial occlusion) was also significantly greater at plaque sites compared with nonplaque sites. Sympathetic and local vasoconstriction in psoriatic skin was shown to be intact and responses to vasodilator tests were likewise intact, i.e., there was no failure of response to normal vascular control mechanisms, albeit some quantitative differences. Tests of vasodilatation indicated that, although basal flux is high in plaque compared with nonplaque skin, arterioles supplying plaque skin can dilate further, i.e., lesional arterioles are not normally maximally dilated but have a basal constrictor tone. Interestingly, the red cell flux at maximum dilatation in nonplaque skin is less than even the basal flux in plaque skin. This means that in plaque skin either there are more arterioles than in nonplaque skin, or there is chronic, structural widening of the existing arterioles in plaque skin.

Adult↗

PubMed1999

Comparison of microvascular filtration in human arms with and without postmastectomy oedema.

Oedema is caused by impaired lymphatic drainage and/or increased microvascular filtration. To assess a postulated role for the latter in postmastectomy oedema, filtration was studied in the forearms of 14 healthy subjects and 22 patients with chronic, unilateral arm oedema caused by surgical and radiological treatment for breast cancer. A new non-contact optical device (the Perometer) and a conventional mercury strain gauge were used simultaneously to record forearm swelling rates caused by microvascular filtration during applied venous congestion. Filtration rate (FR) per 100 ml tissue was measured over 10-15 min at a venous pressure of 30 cmH2O, a pressure reached in the dependent forearm (FR30), and then at 60 cmH2O (FR60). Apparent filtration capacity of 100 ml soft tissue (CFCa) was calculated from FR60 - FR30/30, after adjustment for bone volume. The Perometer and strain gauge gave similar results in normal and oedematous arms. Mean CFCa in healthy subjects was (3.8+/-0.4) x 10(-3) ml (100 ml)-1 cmH2O-1 min-1, close to literature values. In the patients, FR30 was 47 % lower in the oedematous forearm than in the opposite, unaffected forearm (P = 0.04). FR60 showed a similar trend but did not reach significance (P = 0.15). The values of CFCa of (2.2+/-0.5) x 10(-3) ml (100 ml)-1 cmH2O-1 min-1 in the oedematous arm and (2.8+/-0.5) x 10(-3) ml (100 ml)-1 cmH2O-1 min-1 in the unaffected arm were not significantly different (P = 0.47). When differences in arm volume on the two sides were taken into account, the total fluid load on the lymphatic system of the oedematous forearm was (411.0+/-82.2) x 10(-3) ml min-1 at 30 cmH2O and (1168+/-235.6) x 10(-3) ml min-1 at 60 cmH2O, similar to the normal side, namely (503.7+/-109.3) 10(-3) ml min-1 and (1063+/-152.0) x 10(-3) ml min-1, respectively (P >/= 0.50). The filtration capacity of the entire oedematous forearm (CFCa scaled up by total soft tissue volume), (25.4+/-6.2) x 10(-3) ml cmH2O-1 min-1, was not significantly greater than that of the normal forearm, (18.3+/-2.6) x 10(-3) ml cmH2O-1 min-1 (P = 0.40). The results indicate that no major change occurs in the microvascular hydraulic permeability-area product of the forearm, or in the total filtration load on the lymph drainage system during dependency, in the arm with postmastectomy oedema compared with the normal arm. This argues against a significant haemodynamic contribution to postmastectomy oedema.

Aged↗

PubMed1998

Effect of depletion of glycosaminoglycans and non-collagenous proteins on interstitial hydraulic permeability in rabbit synovium.

1. The hydraulic resistance of synovial interstitium helps to retain a lubricating fluid within the joint cavity. The contributions of sulphated glycosaminoglycans to resistance were assessed by selective depletion by chondroitinase ABC, keratanase and heparinases I, II and III in vivo. Also, since glycosaminoglycans do not account fully for the resistance, the contribution of non-collagenous, structural proteins in interstitium was assessed by treatment with chymopapain, a collagen-sparing protease. 2. Ringer solution containing enzyme was injected into the synovial cavity of the knee in anaesthetized rabbits. After >= 30 min the intra-articular pressure was raised and the relation between pressure (Pj) and trans-synovial outflow (Qs) determined. The slope dQs/dPj at low pressures, i.e. below yield pressure, represents the hydraulic conductance of the lining, i.e. 1/resistance. The contralateral joint received Ringer solution without enzyme as a control. Action of enzymes on the tissue was confirmed by histochemical and immunohistochemical studies. 3. Treatment with chondroitinase ABC (5 joints) increased the hydraulic conductance of the lining by 2.3 times (control, 1.34 +/- 0.22 microliter l min-1 cmH2O-1; post-enzyme, 3.11 +/- 0.45 microliter l min-1 cmH2O-1). This was significantly less than the effects of leech, Streptomyces and testicular hyaluronidases, which caused an average 4.7 times increase (P < 0.001, ANOVA). Analogous findings were made above yield pressure. 4. Treatment with keratanase (3 joints) or heparinases I, II and III (3 joints) caused no significant increase in trans-synovial flows or conductance, even though the concentration of heparan sulphate in synovium is higher than that of chondroitin sulphates or hyaluronan. 5. Treatment with chymopapain (7 joints) caused the greatest increases in trans-synovial flow, which exceeded control flow by an order of magnitude in one case. After 0.1 U chymopapain the average conductance was 6.6 times the control conductance below yield pressure. Immunohistochemical studies confirmed that chymopapain treatment removed the synovial proteoglycans. 6. It is concluded that, despite their similar resistivities in vitro, the different glycosaminoglycans do not contribute equally, weight for weight, to interstitial resistance in vivo. Hyaluronan is the dominant glycosaminoglycan governing synovial interstitial resistance. In addition, non-collagenous structural proteins contribute significantly to interstitial resistance.

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