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J R Levick

Publications and source records attributed to J R Levick.

115 records · Page 7Linked to original sources
PubMedDate not supplied

The mechanism of synovial fluid retention in pressurized joint cavities.

OBJECTIVE: Hyaluronan (HA) in synovial fluid is vital to fluid retention in joint cavities. This study aims to evaluate a HA concentration polarization hypothesis and to examine, quantitatively, the agreement between theoretical predictions and experimental results. METHODS: A non-steady-state model was developed for HA ultrafiltration and concentration polarization on the synovial surface. The Kedem-Katchalsky equation was used to calculate the trans-synovial filtration rate Q as the HA concentration polarization layer built up. Model parameters were based on data from experiments. Effects of parameters on fluid filtration were investigated. RESULTS: The HA osmotic pressure at the synovial surface was found to approach the intra-articular pressure, P, during fluid infusion. The model simulated the experimentally observed decay in Q with the time at constant P, and predicted nonlinear P-Q relations in good agreement with experimental results over a range of bulk HA concentrations, from pathological (0.2 g L(- 1)) to physiological (4.0 g L(-1)). It gave quantitative insights into the development of the osmotic pressure and the significance of the HA reflection coefficient. CONCLUSIONS: The osmotic pressure of a HA concentration polarization layer on the synovial surface leads to outflow buffering. This provides the mechanism by which the vital lubricating synovial fluid is retained in a joint cavity under pressure.

Animals↗
PubMedDate not supplied

Enhanced cutaneous lymphatic network in the forearms of women with postmastectomy oedema.

Postmastectomy oedema (PMO) of the arm is a common aftermath of axillary lymphatic damage during treatment for breast cancer. The aim of the present study was to quantify the forearm dermal lymphatic capillaries in order to determine whether they exhibit adaptive responses to PMO. Both forearms were examined by fluorescence microlymphography in 16 patients with oedema following treatment for breast cancer (mean swelling 25 +/- 4%) and 19 patients treated for breast cancer but without oedema. Delineated lymphatic networks were analysed stereologically. The main findings were: (1) lymphatic density at any specified distance from the injection site was greater in the swollen arm than the control arm (p < 0.01, t test); (2) taking into account the increased skin area, the total length of lymphatic capillaries in a 1-cm annulus of skin was 676 +/- 56 cm (swollen), compared with 385 +/- 30 cm (control) (p < 0.001, t test); (3) fluorescent marker was transported over a greater distance before draining deep in the swollen arm (2.74 +/- 0.33 cm) than in the control arm (1.59 +/- 0.24 cm) (p = 0.02); (4) there was no evidence of lymphatic dilatation in the swollen arm, and (5) in breast cancer patients without swelling, the arm on the side of radiotherapy/surgery (otherwise referred to as the unswollen arm) showed none of the above changes, indicating that the changes are linked to the oedema rather than being universal responses to breast cancer or its treatment. It is concluded that microlymphatic changes occur in the swollen arm, namely a local superficial rerouting of lymph drainage and either lymphangiogenesis and/or increased recruitment of dormant lymphatic vessels. Since blood capillary angiogenesis occurs in the swollen arms, and lymphangiogenesis occurs in experimental lymphoedema, there is a precedent for proposing lymphangiogenesis in PMO. An increased number of functional vessels would help to maintain the ratio of local tissue drainage capacity to filtration capacity.

Adult↗
PubMedDate not supplied

Skin microvascular architecture and perfusion studied in human postmastectomy oedema by intravital video-capillaroscopy.

Breast cancer treatment often causes chronic arm oedema. Oedema depends on the balance between microvascular filtration and lymph drainage, but little is known about the microvessels in postmastectomy oedema (PMO). We investigated cutaneous capillary density in PMO, since capillary density is one of the factors influencing fluid load on the lymphatic system. Video-capillaroscopy allows the skin microcirculation to be examined in vivo and recorded for later analysis. Patient arm volumes, measured optoelectronically, increased by 30 +/- 13%. The forearm skin of each arm was examined in 7 normal subjects (mean age 22 years) and 15 PMO patients (mean age 61 years). Native capillaroscopy was found to underestimate capillary density. Venous congestion increased the number of capillaries detected by native capillaroscopy by 26-28%. Fluorescein detected 19-27% more capillaries than native capillaroscopy. Using fluorescein, no significant difference in mean capillary density was found between the right (50 mm-2) and left (48 mm-2) arms of normal subjects (p = 0.53). Surprisingly, cutaneous capillary density in the swollen arm (33 mm-2) was not significantly less than in nonswollen arms (35 mm-2) of patients, despite a mean 14% increase in skin area. Capillary density decreased significantly with age. Relative to the volume and area changes, the density results indicated that cutaneous neovascularization had occurred in the swollen arm.

Adult↗
PubMedDate not supplied

Normal cutaneous microcirculation in gaiter zone (ulcer-susceptible skin) versus nearby regions in healthy young adults.

Skin just proximal to the medial malleolus ('gaiter' zone) is the usual site for venous ulceration in later life, whereas shin and dorsum of the foot are generally unaffected. We studied the microcirculation of these regions in 6 healthy young adults to see whether any premorbid, constitutional differences in microvascular physiology or anatomy exist between local leg sites even in normal subjects. Capillary density was assessed by capillaroscopy (native and fluorescein) and local flow by laser Doppler fluxmetry, in supine and upright positions and during reactive hyperaemia. Supine capillary densities in supramedial malleolar skin (SMMS) averaged 31038 mm(-2) (fluorescein and native count means, respectively) and was not statistically significantly different from those in the dorsum of the foot (36.0-36.2 mm(-2) or shin 30-51 mm(-2)). Dependency did not alter the counts significantly, but the fluorescein transport time from antecubital vein to capillary increased by 16-69% (SMMS 40%). In the supine position, red cell flux in SMMS was only 42-43% of the flux in skin over the shin and dorsum of the foot (p<0.04, 2-way analysis of variance) and cumulative reactive hyperaemia in SMMS was also less marked. Basal flux and reactive hyperaemia at all sites fell to closely similar levels in dependency (veni-arteriolar response). In relative terms, however, the posturally induced vasoconstriction was weaker in SMMS (flux reduction by 29% of supine value) than at other sites (reductions 61-61% of supine value). The results showed that even in young healthy legs the cutaneous microcirculation is not physiologically homogeneous, raising the possibility that constitutional factors might influence the siting of overt pathology if chronic venous insufficiency develops in later life.

Adult↗