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Biomedical subjects

J R Levick

Publications and source records attributed to J R Levick.

At least 109 records · Page 6Linked to original sources
PubMed1983

Time-dependence of the pressure-volume relationship in the synovial cavity of the rabbit knee.

The pressure-volume curve of the synovial cavity of the rabbit knee has been determined by the infusion of a non-absorbable oil into the joint space. Pressure (greater than 3 cm H2O) at a given volume decayed as a curvilinear function of time. In consequence, a plot of volume against pressure immediately after a volume increment (the immediate compliance curve) was steeper than a plot of volume against pressure after 5-20 min (the delayed compliance curve) above atmospheric pressure. Similarly, the compliance curve for a rapidly expanded joint was steeper than the compliance curve for the opposite, slowly expanded joint. Observations 2 and 3 indicated that the joint investment was visco-elastic. Pressure at a given volume during aspiration of the expanded joint was always less than pressure at the same volume during infusion. This hysteresis was substantial, the mean energy dissipation being about 37%. Pressure at a given volume increased as a function of time during aspiration, but the pressure recovery was less pronounced than pressure decay during infusion. When the cycle of infusion and aspiration was repeated, the pressure-volume hysteresis loop was displaced progressively towards the volume axis. Observations 5 and 6 were attributed to plasticity of the joint investment. It is concluded that intra-articular pressure at a given volume depends on the rate of change of volume, the direction of change, and the previous history of the joint. The relevance of these properties to fluid dynamics in other interstitial compartments, in arthritic human joints, and to the neurophysiology of mechanoreceptors in the joint investment is discussed.

Animals↗
PubMed1982

Pressure-volume relationships above and below atmospheric pressure in the synovial cavity of the rabbit knee.

1. The pressure-volume relationship in the synovial cavity of the rabbit knee was investigated by the infusion of a non-absorbable oil into the cavity. 2. The pressure (P)-volume (V) curve was sigmoid. Its slope dP/dV (elastance) was steep at subatmospheric, physiological pressures, least steep at 5 cm H2O, and steepened progressively at higher, pathological pressures. 3. Elastance dP/dV was a good approximation to linear functions of P below atmospheric pressure and above 5 cm H2O. Each part of the pressure-volume relationship could therefore be described by an exponential expression. 4. Flexion of the joint increased pressure at a given volume. This was mainly due to steepening of the pressure-volume curve, and also partly due to a shift towards the pressure axis. 5. Pressure-volume curves determined by the infusion of normal saline or Krebs solution were grossly distorted, because these fluids were absorbed across the permeable synovium. 6. The physiological significance of the synovial pressure-volume curve is discussed, and mechanical explanations of the curve are suggested.

Animals↗
PubMed1982

Physiological compartmentation of fluid within the synovial cavity of the rabbit knee.

1. The relationship between pressure in the suprapatellar region (Psp) of the synovial cavity of the rabbit knee, and volume of fluid (oil or saline) infused into that region displayed a pressure plateau (15 . 5 cm H2O) between 1 . 2 and 2 . 0 ml. 2. No pressure plateau occurred when fluid was infused simultaneously into the suprapatellar and posteromedial regions of the synovial space. 3. Pressure in the posteromedial region (Ppm) did not respond to suprapatellar fluid infusions until onset of the suprapatellar pressure plateau. During the plateau phase, Ppm rose steadily towards Psp. At the end of the plateau phase the two pressures were almost equal and rose in parallel. 4. The plateau phenomen also occurred during aspiration of volume-expanded joints; and was present at all joint angles. 5. It was concluded that the joint space, although anatomically continuous, is divided into two hydraulically separate compartments at physiological pressures. 6. The sites of communication between the two compartments at pathological pressures were explored by casts of the synovial cavity.

Animals↗
PubMed1981

Permeability of rheumatoid and normal human synovium to specific plasma proteins.

A method is described for the determination of the permeability of the blood-joint barrier to specific plasma proteins, using the ratio of protein concentration in synovial fluid to that in plasma. The inadequacy of the ratio per se as a direct index of permeability is discussed. Permeabilities are evaluated for the normal and rheumatoid human knee. Permeability increases in the rhematoid knee by approximately 6 times for the rheumatoid knee by approximately 6 times for albumin and over 40 times for macroglobulins. The effect of protein molecular dimensions upon permeability is analyzed. Permeability shows less dependence upon solute dimensions in the rheumatoid knee than in the normal knee, i.e., molecular selectivity is reduced. From these data and synovial morphology, a two-membrane model of the blood-joint barrier is developed. The relative contribution of the component intimal and endothelial layers to the total barrier is found to depend upon solute dimensions.

Arthritis, Rheumatoid↗
PubMed1980

Contributions of the lymphatic and microvascular systems to fluid absorption from the synovial cavity of the rabbit knee.

1. The trans-synovial flow (Qs) of Ringer solution from the cavity of immobile knee (stifle) joints was determined in anaesthetized rabbits when intra-articular hydrostatic pressure (PJ) was elevated in steps from 2 to 25 cm H2O. 2. It has been demonstrated previously (Levick, 1978) that slope DQs/dPJ shows an abrupt sixfold increase at a 'breaking point' (PB) around 9 . 5 cm H2O, rising from a mean of 0 . 49 microliter.min-1 cm H2O-1 (PJ less than PB) to 2 . 81 microliter.min-1 cm H2O-1 (PJ greater than PB). 3. Perforation of the synovial intima by an intra-articular cannula increased dQs/dPJ below breaking pressure and thus largely abolished the breaking point phenomenon, indicating that the phenomenon might be simulated by a break-down in synovial resistance to flow. 4. Ligation of the femoral lymph trunks draining the joint did not significantly alter the relationship between Qs and PJ. The slope dQs/dPJ was 0 . 60 +/- 0 . 17 microliter.min-1 cm H2O-1 (mean +/- S.E.) below a breaking pressure of 8 . 8--10.5 cm H2O, and 2 . 90 +/- 0 . 64 microliter.min-1 cm H2O-1 above breaking pressure. Thus changes in synovial lymph flow did not explain the breaking point phenomenon. 5. Interruption of synovial blood flow by vascular clamps or by killing the animal reduced, but did not abolish fluid absorption; nor was the breaking point phenomenon abolished. Slope dQs/dPJ increased from 0 . 37 +/- 0 . 06 microliter.min-1 cm H2O-1 below breaking point (10 . 5 +/- 1 . 0 cm H2O) to between 1 . 82 and 0 . 96 +/- 0 . 15 microliter.min-1 cm H2O-1 above breaking pressure. Fluid accumulated in extra-synovial interstitial spaces. 6. When the synovial intima was divested of its surrounding tissues, lymphatic and vascular supplies by extensive dissection, the denuded synovium still showed a marked increase in hydraulic conductivity at normal breaking pressures. The breaking point phenomenon was therefore not caused by changes in extra-synovial interstitial pressure or compliance. 7. It is concluded that fluid absorption from the joint cavity occurs by two parallel pathways viz. the synovial capillary bed and the extra-synovial interstitial spaces. A simple analysis of the system indicates that the breaking point phenomenon cannot be explained by an abrupt increase in synovial conductivity (cf. Edlund, 1949) but is explicable if synovial conductivity (and possibly interstitial conductivity) becomes a continuous function of PJ above breaking pressure. This hypothesis reconciles the non-linear pressure-flow relationship with Starling's hypothesis for fluid absorption from connective tissue spaces (1896).

Absorption↗
PubMed1979

An investigation into the validity of subatmospheric pressure recordings from synovial fluid and their dependence on joint angle.

1. Synovial fluid hydrostatic pressures were measured in normal knee (stifle) joints of anaesthetized rabbits using perforated cannulae. Pressures were subatmospheric in seventy out of seventy-two joints, with a mean value of -4.6 cm H2O (range 0 to -12 cm H2O) at joint angles of 120--150 degrees. 2. Similar values were obtained by a wick-in-needle technique (mean -4.0 cm H2O), which along with several other tests indicated that the subatmospheric values were not artifactual. 3. A slow rise in pressure of 1--2 cm H2O per hour in the motionless joint was attributed to a net filtration of fluid into the joint space. 4. Pressure increased as a curvilinear function of joint angle when the joint was flexed passively, the slope of the relationship depending on synovial fluid volume. Pressure also increased on active flexion of the joint, or on passively increasing the tension of soft peri-articular tissues. 5. Positive (above atmospheric) pressures in acutely flexed joints declined with time. Pressures declined less rapidly when synovial fluid was replaced by nonabsorbable paraffin oil. It was concluded that joint fluid can be absorbed by the synovium during acute flexion. 6. Processes which might generate subatmospheric pressures are discussed. The hypothesis is advanced that the flexion-dependent 'trans-synovial pump', possibly in series with a lymphatic pump, may account for the maintenance of a small synovial fluid volume and subatmospheric pressure in the face of a net filtration of fluid from synovial capillaries into the joint space.

Animals↗
PubMed1979

The influence of hydrostatic pressure on trans-synovial fluid movement and on capsular expansion in the rabbit knee.

1. The flow of Ringer solution or paraffin oil from an infusion reservoir into the cavity of the knee (stifle) joint was measured in anesthetized rabbits, as intraarticular pressure was progressively elevated from its intrinsic slightly subatmospheric value to +25 cm H2O. 2. Paraffin oil did not penetrate the tissues lining the joint cavity, yet a continuous flow of oil occurred into the joint at pressures over +2 cm H2O. It was concluded that the joint investment behaved as a visco-elastic tissue. 3. Trans-synovial flow of Ringer solution was calculated by correcting the observed inflow for visco-elastic expansion of the joint capsule. At intra-articular pressures +2 to +9 cm H2O, trans-synovial flow increased at an average rate of 0.49 microliter min-1.cm H2O-1. The hydraulic conductivity of the synovium was therefore similar to that of subcutaneous connective tissue. At around +9 cm H2O, the 'breaking pressure', the slope of the pressure-flow relationship increased by almost sixfold to 2.81 microliter min-1.cm H2O-1. 4. Changes in joint visco-elasticity, synovial surface area, blood pressure, colloid osmotic pressure of plasma and of joint fluid, and inflammation were excluded as explanations of the marked increase in rate of fluid absorption, which is tentatively attributed to increases in synovial hydraulic conductivity. Some physiological and clinical implications of the data are discussed.

Absorption↗
PubMed1978

The effects of position and skin temperature on the capillary pressures in the fingers and toes.

1. Direct measurements of the capillary pressure (P(c)) were made in capillaries at the base of the nails of the fingers and toes of two subjects (the authors of this paper).2. With the hand or foot at heart level, P(c) varied over the range of 7-70 cm H(2)O with mean values of 43 cm H(2)O in both the fingers and the toes. P(c) was higher in the arterial limb (mean 49 cm H(2)O) than in the venous limb (mean 34 cm H(2)O) of the capillary loops. The plasma colloid osmotic pressures for the two subjects were 33 and 34 cm H(2)O.3. For capillaries at heart level there was a strong positive correlation between P(c) and skin temperature when the latter was varied over the range 23-36 degrees C.4. When the hand or foot was lowered, P(c) increased less than the local arterial (P(a)) and venous pressures (P(v)). Furthermore the variation in P(c) was reduced. In fourteen measurements of P(c) made on capillaries in the toes of standing subjects, P(c) was no more than 10 cm H(2)O greater than P(v). It is argued that the increase in the ratio (P(a) - P(c))/(P(c) - P(v)) with hydrostatic load represents an increase in the ratio of pre- to post-capillary resistance.5. When P(v) was increased by inflating a sphygmomanometer cuff around the upper arm, (P(a) - P(c))/(P(c) - P(v)) increased in the hand held at heart level. These changes were similar to those seen with changes in position.6. The implications of the results are discussed with respect to fluid balance between the blood and tissues. It is argued that since P(c) in the warm hand was never less than the plasma colloid osmotic pressure, fluid is not reabsorbed from the tissues into the capillaries of the warm skin of the hand even at heart level. Compensatory changes in the circulation appear to minimise the filtration of fluid into the feet of the standing subject but the mechanism of these changes remains obscure.

Blood Pressure↗
PubMed1977

Variations in permeability along individually perfused capillaries of the frog mesentery.

When single capillaries in the exposed transilluminated frog mesentery were perfused with solutions containing patent blue V (molecular radius 0-7 nm), unbound T1824 (molecular radius 1-3 nm) and T1824-albumin (molecular radius 3-6 nm), the coloured molecules initially appeared to enter the extracapillary tissues more easily at some places than at others along the length of the vessels. Three patterns of extravascular distribution were observed: (1) High frequency unevenness: patent blue V and unbound T1824 first appeared outside the capillary as spots, bars or bands set at intervals 30-80 mum apart along the length of the vessel. (2) Low frequency unevenness: at later times, the extravascular dye was seen to be unevenly distributed on a much larger scale, with lengths of vessel of up to 400 mum surrounded by little extravascular dye separating similar lengths around which much dye had accummulated. This pattern of distribution was seen for all three solutes. (3) Arteriovenous gradient: perfusions with all three solutes resulted in more extracapillary colouration accumulating around the venous ends of the capillaries. Reasons are given for believing that the distribution of extracapillary solute reflected the distribution of permeability along the length of the capillary. The variations in permeability were attributed to an uneven distribution of small pores along the capillary rather than to presences of large pores.

Animals↗