Is a decrease in plasma oncotic pressure enough to explain the edema of pregnancy?

The balance of fluid across capillaries is given by the Starling equation. Because the plasma protein concentration (one of its components) is decreased in pregnancy, we decided to explore the question as to whether hypoproteinemia with intact protein mass (produced by blood volume expansion) or hypoproteinemia with decreased total protein mass (produced by removal of circulating proteins) alters the oncotic pressure differences across capillaries. We calculated the oncotic pressure difference obtained in seven nonpregnant ewes during periods of normoproteinemia and hypoproteinemia; the influence of fluid infusion under both conditions was also observed. There was an increase in the oncotic pressure difference across the capillary wall during hypoproteinemia produced by a decrease in the total protein mass (p less than 0.01); however, the response to hypoproteinemia produced by fluid infusion was similar (p greater than 0.1). The venous pressure (used as an index of interstitial fluid pressure changes) did not differ in either hypoproteinemia or fluid infusion. Capillary permeability was decreased during hypoproteinemia, as evidenced by a higher lymph/protein ratio of labeled albumin during the control period (p less than 0.05). In conclusion, during a state of decreased plasma protein concentration similar to that of pregnancy, the difference in the oncotic pressure and hydrostatic pressure forces acting to prevent transfer of fluid to the interstitium is increased. Therefore other factors that influence fluid transfer across the capillaries must be investigated to explain the edema of pregnancy.

PEEP increases non-pulmonary microvascular fluid flux in healthy and septic sheep

The potential for significant interaction between PEEP and the peripheral microcirculations is not as well appreciated as are its central circulatory effects. Therefore, we studied the effects of PEEP, 15 mm Hg, on microvascular fluid flux in the hindlimb of ten mature sheep. Changes in prefemoral lymph flow (QL) and in lymph to plasma [L/P] total protein (TP) ratios were measured following the application of PEEP for 2 h, before and during hyperdynamic sepsis. Sepsis was induced by cecal ligation and perforation (CLP). Although the onset of sepsis was not associated with an increase in prefemoral QL, the [L/P] ratio of iodinated 125I human serum albumin (125I-HSA) was significantly greater 72 h after CLP than during the nonseptic baseline study. Histologic examination of gastrocnemius muscle also demonstrated an increase in protein-rich interstitial edema during the septic studies. During the 2 h of PEEP, prefemoral QL increased equally (p less than 0.05) in three study periods: (1) baseline nonseptic, delta QL = +1.2 +/- 1.4 ml/h; (2) septic period 1, 24 to 48 h after CLP, delta QL = +1.3 +/- 1.2 ml/h; and, (3) septic period 2, 72 h after CLP, delta QL = 1.0 +/- 0.6 ml/h. Calculated microvascular hydrostatic pressures also rose significantly during PEEP therapy in all three study periods. We conclude that PEEP, 15 mm Hg, increased hindlimb microvascular fluid flux and may thereby increase interstitial fluid content in tissues drained by the prefemoral lymph node. These effects of PEEP were not aggravated by hyperdynamic sepsis, despite a presumed increase in systemic microvascular permeability at this time.

Pulmonary clearance of 99mTc-DTPA in the diagnosis and evolution of increased permeability pulmonary oedema

We measured pulmonary clearance of aerosolised 99mtechnetium-labelled diethylenetriaminepentacetate (99mTc-DTPA) in thirty-four patients with acute respiratory dysfunction. Results were expressed as a half-time clearance from lung to blood (T1/2). In sixteen non-smoking patients with acute lung injury, clearance was monoexponential, median T1/2 11, range 4-40 min, and in five multi-exponential, median rapid T1/2 3 min, with a slower median T1/2 of 18 min (range 2-4 and 15-31 min respectively). Clearance was significantly (P less than 0.0001) more rapid than normal non-smoking subjects previously studied (median T1/2 70, range 37-182 min). Three smokers with acute lung injury had T1/2S of 5, 18 and 22 min, not significantly (P greater than 0.05) quicker than normal smokers previously studied (median T1/2 20, range 6-73 min). One smoking lung-injured patient had an abnormal multi-exponential 99mTc-DTPA clearance. Four patients with cardiogenic pulmonary oedema had T1/2S within the normal range. Repeated measurements made on nine patients with acute lung injury showed that clearance remained abnormally rapid despite improvements in lung radiographic appearance and gas exchange. We conclude that the 99mTc-DTPA technique provides a virtually non-invasive measure of alveolar-capillary barrier dysfunction in non-smoking patients with acute lung injury.

Blood-tissue transport of substrates in the heart: studies by single circulation tracer dilution

Passive capillary permeability is usually not the rate limiting step to movement of small lipid-insoluble molecules from plasma into the heart. At physiological concentrations the rate of carrier-mediated transport and or receptor binding of blood-borne substrates is often measurable in a single circulation through the coronary bed. Here I review some studies on uptake measured by the single-circulation multiple tracer dilution technique. The method consists of a sudden intra-arterial injection of a mixture of tracers followed by sequential rapid sampling of the venous outflow. Generally the tracers include a molecule confined to the intravascular space (e.g. albumin), another confined to the extracellular space and a third test tracer. The data analysis can give information about: a) capillary permeability-surface product (PS), b) endothelial cell membrane transport, c) the size of the interstitial space, d) transport across the sarcolemma, e) uptake by nerve endings, f) binding to receptors, g) rapid metabolic transformations. Studies were performed in the isolated perfused heart (dog and rabbit). Early observations on rapid tissue uptake of potassium and ouabain have recently been extended. Kinetics of unidirectional trans-sarcolemmal influx of lactate, a metabolic substrate for the myocardium and the neuronal uptake of amines, were investigated as well as the myocardium and the neuronal uptake of amines, were investigated as well as the effects of specific inhibitors for these transport mechanisms. Uptake was also measured for glucose, the amino acids L-phenylalanine, L-alanine and taurine; and for acetate and palmitate. Recent literature which proposes an important role for uptake and metabolism of adenosine by the endothelium is discussed. These studies are of interest for clinical applications such as positron emission tomography (PET) which makes use of short-life isotopes.

[Development of the placenta and utero-placental circulation from the morphologic and functional viewpoint]

All requirements of the conceptus, i.e. the fetus and the placenta are distributed by the maternal blood via the utero-placental vessels. Fetus and placenta need varying amounts of oxygen and nutrients at different stages of pregnancy. In the first half of pregnancy, the placenta, besides growth and development, fulfills the function of an endocrine gland whilst the nutrient supply of the fetus is of minor importance. In the second part of pregnancy, the placenta differentiates into an organ for exchange of gases and nutrients. Placental development may be divided into three stages: Implantation, growth and maturation. In the first half of pregnancy, the placental growth precedes the major fetal growth spurt, whereas, in the second half, the weight ratio placenta: fetus shifts in favour of the fetus and reaches 1:7 to 1:10 at the end of pregnancy. Growth and development of the placenta is the basis for fetal growth and it is not surprising that the weight ratio of the placenta and the newborn is positively correlated at the end of pregnancy. From the morphological point of view the development of the utero-placental circulation is characterized by a loss of the muscular elements in the wall of the peripheral parts of the spiral arteries supplying the endometrium and the intervillous space. These morphological changes functionally correlate with a reduction of resistance in the peripheral vessels. This can be visualized even doppler-sonographically as a reduction of pulsatility in the radial arteries.(ABSTRACT TRUNCATED AT 250 WORDS)

Capillary filtration and lymphatic resorption in diabetes. Application to the pharmacodynamic activity of Daflon 500 mg

Microcirculatory disorders are often a complication of diabetes. They are associated with an increased capillary permeability which can be assessed by the Landis test using 99mTc-labelled albumin. Labelled albumin retention is measured by external detection (residual radioactivity after removal of venous tourniquet). The Fast Fourier Transform of the radioactivity disappearance graph reflects the lymphatic albumin resorption. Thirteen out-patients with diabetes from 1 to 19 years suffering from evident microcirculatory disorders were treated with a micronized flavonoid fraction: Daflon 500 mg (2 tablets per day) during a month. Antihypertensive and/or antidiabetic treatment were continued during the study if they were given before starting. A test was performed before, and at the end of the treatment. In 10 of the 13 patients, the test was carried out a third time 5.5 +/- 1.0 months later, after treatment withdrawal. Results were as follows: 1) labelled albumin retention was abnormal (greater than or equal to 8%) at the start and became normal in the patients and improved in 1 patient. After treatment withdrawal, the results of the third test were again abnormal, in the patients who had been normalized beforehand; 2) the initially abnormal lymphatic resorption became normal in six of the 13 patients at the end of the treatment and became abnormal again in all patients after treatment withdrawal. In a parallel group of 15 patients with abnormal test lymphatic fluctuations and not being treated with a vasculo-protector agent, the initially abnormal test remained abnormal 5 to 48 months later in all patients.(ABSTRACT TRUNCATED AT 250 WORDS)

[Macro- and microcirculatory shifts in the brain of cats during hypoxia and hypercapnia]

The cat hemodynamically isolated brain, when transferred from the air artificial ventilation to the respiration with 10% oxygen or 5-10% carbon dioxide mixtures, developed a decrease in vascular resistance and an increase in the venous outflow. The capillary hydrostatic pressure dropped and the intercellular fluid absorption reduced in both cases. The brain capillary filtration coefficient increased in hypoxia and decreased in hypercapnia. The character of emptying of venous cerebral area was passive in hypoxia and active in hypercapnia. The differences in responses of precapillary sphincters, cerebral capillaries and veins were due to involvement of intracerebral noradrenergic system.

Microvascular permeability, venous stasis and oedema

Microvascular permeability to fluid and hydrophilic solutes is restricted to channels between the endothelial cells and through the fenestrations when these are present. The channels have a molecular filter which appears to be a lattice of fibrous molecules reinforced by plasma proteins. The quantitative description of blood-tissue fluid movements is complicated by plasma protein permeation which leads to a non-linear steady state relation between fluid filtration and microvascular pressure. When fluid filtration is low it can be balanced by lymph flow but at high pressures oedema develops. Microvascular pressure rises less than expected with increments of venous pressure owing to local vasoconstriction of the arterioles. The sluggish flow which results from this vasoconstriction and high venous pressure leads to a haemoconcentration which reduces oedema formation but favours leucocyte and platelet sequestration within the microcirculation.

[The role of changes in vascular permeability, interstitial relaxation and surface tension forces in the alveoli in disordered filtration-absorption equilibrium in pulmonary edema]

Changes of fluid filtration and reabsorption in application and removal of hydrodynamic loads were studied on isolated lungs of dogs. Some models of transcapillary filtration in the lungs were studied on basis of the obtained data. According to the theoretical predictions of these models, the following factors influence the non-linearity of the filtration and reabsorption processes most essentially: interstitial relaxation in the stage of interstitial edema and the appearance of surface tension forces in the alveoli. The hypothesis of the significance of disturbed permeability of the capillary wall is confirmed to a very small measure with such an approach. The described phenomena allow the processes of fluid accumulation in pulmonary edema to be represented on a mathematical model.

Myogenic mechanisms in the control of systemic resistance and transcapillary fluid exchange in man

Myogenic reactions to raised vascular transmural pressure were studied in the forearm of healthy male volunteers. The study was designed to allow adequate comparative analyses of myogenic stimulus-effector response characteristics in the resistance vessels and in the precapillary sphincters, with no or minimal interference with systemic or local venous-arteriolar reflexes or with metabolic vascular control. Both vascular sections proved surprisingly sensitive to transmural pressure as a stimulus, showing graded constrictor responses when transmural pressure was raised 5-20 mmHg. There was a clearcut difference, however, in that the precapillary sphincters reacted very intensely even when transmural pressure was only slightly raised (5 mmHg). This potent myogenic regulation of precapillary sphincter tone may be an important factor in the control of transcapillary fluid exchange, and thereby in the control of plasma and interstitial fluid volumes, for instance in dependent regions on standing.

Lung permeability in adult obliterative bronchiolitis

There is histopathological evidence that, in certain inflammatory disorders involving the smaller airways, extension of the inflammatory process may occur distally into the respiratory bronchioles, alveolar ducts and alveoli (1,2). The objective of this study was to perform a non-invasive evaluation of the possible involvement of gas exchanging regions of the lung in obliterative bronchiolitis presenting with severe airways obstruction. We measured the clearance of technetium 99m-labelled diethylene triamine penta-acetate (99m Tc-DTPA) with time from the lungs to the blood, in 11 normal, non-smoking subjects (mean age 30 years), ten non-smoking patients with cryptogenic fibrosing alveolitis (CFA, mean age 57 years) and ten patients who were non-smokers with obliterative bronchiolitis (mean age 51 years). There was a substantial increase in clearance in patients with CFA, (mean T1/2 19.9 min), compared with either patients with obliterative bronchiolitis (mean T1/2 52.2 min; mean difference 32.3; 95% confidence intervals (CI) 18.40; P less than 0.001) or normal controls (mean T1/2 84.3; mean difference 64.4; 95% CI 55, 74; P less than 0.001). Clearance was also significantly faster in patients with obliterative bronchiolitis than in normal controls (mean difference 32.1; 95% CI 18.48; P less than 0.001). Peripheral deposition of 99m Tc-DTPA was uniform in normal subjects and patients with CFA, but patchy in patients with obliterative bronchiolitis, possibly resulting from altered patterns of ventilation associated with patchy distribution of bronchiolitis within affected lungs. Increased clearance of 99m Tc-DTPA from the lungs in these patients suggests that subtle derangement of the alveolar-capillary membrane occurs in adult obliterative bronchiolitis.

Capillary permeability of 99mTc-DTPA in canine myocardium determined by intracoronary bolus injection and residue detection

Capillary permeability of 99mtechnetium-diethylenetriaminepenta-acetic acid (99mTc-DTPA; MW 485.0) and 51chromium-ethylenediaminetetra-acetate (51Cr-EDTA; MW 340.2) was studied in an in vivo canine heart preparation by the single injection, residue detection (SIRD) method. In experiments on open chest dogs (group A) these indicators were administered separately as bolus injections into a cannulated diagonal branch of the left anterior descending coronary artery (LAD) and the curve of the response function was recorded by external activity registration. In further experiments on closed and open chest dogs (group B) 99mTc-DTPA was injected via a coronary angiography catheter into the ostium of the left coronary artery and the response curve was obtained by external registration. Regional myocardial perfusion coefficients were determined by the local 133xenon washout technique and from kinetic analysis of SIRD experiments. Plasma perfusion coefficients calculated by kinetic analysis of response curves from 99mTc-DTPA SIRD experiments (group A) were on average 98 v 102 ml.min-1.100 g-1 in 51Cr-EDTA experiments, in good agreement with the average plasma flow rate of 92 ml.min-1.100 g-1 determined by local 133Xe washout technique. Mean values of the extraction fractions (E) were 0.463 and 0.475 for 99mTc-DTPA and 51Cr-EDTA, and the permeability-surface area products (PdS) were 52.8 and 57.5 ml.min-1.100 g-1 respectively. At the conventional capillary surface area estimate of 500 cm2.g-1 the permeability coefficient (Pd) for 99mTc-DTPA was 1.76.10(-5) cm.s-1 and for 51Cr-EDTA 1.92.10(-5) cm.s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Transport through deformable matrices

In order to induce and maintain a pressure gradient in a fluid mixture in steady state, the fluid has to pass through a solid-like matrix capable of generating and carrying an extra stress gradient. Frictional interactions between fluid components and the matrix then produce separations. Matrix deformation occurs and the implication of this is discussed. A general solution for multicomponent systems is given and then specialised to the case of three components--a deformable gel matrix component, a solvent and a macromolecular solute. A method is given for solving the system of equations and is applied in the steady state. Applications involving transendothelial flow and self-regulated selectivity are stressed in particular. The calculations are based on the Flory-Huggins equation, on the Flory gel deformation model and on ad hoc, very crude approximations to the concentration dependence of the three, pairwise defined friction coefficients between the three components involved.

Perihemorheology: the bridge between the vessel-blood organ and the organs it penetrates

Perihemorheology concerns the rheology of fluids and structures in the perivascular spaces. Furthermore, the term refers to the exchanges of rheological processes between the vessel-blood organ and its surrounding tissues, as well as in reverse. In 1960, the vessel wall and the circulating blood were considered by the author as an entity which in 1981 he postulated as an organ, named the 'vessel-blood organ', penetrating all other organs. This communication is not a survey but is intended to stimulate biomedical thinking regarding the importance of perihemorheology. The significance of the endoendothelial fibrin(ogenin) lining (EEFL) and fibrin(ogenin) as constituent of the interendothelial cement and the basement membrane in relation to perihemorheology is stressed. The role of albumin in the exchanges between hemorheology and perihemorheology is discussed. The protein content, as found by Witte, in the perivascular spaces as compared to the blood is emphasized regarding the importance of interrelations between the vessel-blood organ and rheological processes in the perivascular spaces. Recent studies, particularly by Laurent and his group, pertaining to hyaluronan in perivascular spaces and the blood demonstrate also the importance of the interrelationship between hemorheology and perihemorheology. The term 'blood-brain barrier', considered no longer to be adequate, is replaced by the term 'basement membrane-brain barrier'. It is proposed that the basement membrane of the vessel-blood organ penetrating the brain may contain certain constituents, unknown thus far, and may have a different structure from the basement membrane of the vessel-blood organ penetrating organs other than the brain.

Histamine effects on pulmonary blood vessels in strangulation

Endothelial cells of asphyxial pulmonary veins possess abundant pores and intracytoplasmic vacuoles. The present radioassay demonstrated an increase in histamine concentrations of the pulmonary tissue in asphyxia. These morphological changes, therefore, appear to represent an enhancement of the endothelial permeability induced by high histamine concentrations in blood plasma. The present immunoelectron microscopy study demonstrated heavy reactions of histamine exclusively on the endothelial surface of the asphyxial pulmonary veins. This may support the endothelial cell-dependent vasodilation mediated by histamine in asphyxial pulmonary veins.

Early effects of abrupt reduction of local pressure on the forearm and its circulation

1. The pressure at the surface of a segment of forearm enclosed in a plethysmograph was abruptly reduced from atmospheric to -20 to -120 mm Hg.2. Forearm circumference (equivalent to the volume of a small segment of forearm (V(f))) was measured with a strain gauge. Pressure was measured in the plethysmograph (P(p)), in veins exposed (P(ve)) and not exposed (P(vne)) to suction, in the brachial artery not exposed to suction (P(bane)) and in forearm tissue (P(t)).3. Reduction of P(p) caused increase of V(f). This was not due to gas evolution, since bubbles would not be liberated at the pressures employed. Nor was increase of V(f) due to venous backflow since P(ve) fell, but P(vne) did not, even with upper arm circulation occluded or when P(vne) was raised by venous occlusion prior to reduction of P(p).4. Reduction of P(p) temporarily arrested venous outflow since P(ve) < P(vne) < P(bane) for 30 sec. With reduction of P(p) 30 sec after occlusion of the upper-arm circulation, P(ve) < P(vne) for > 1 min, indicating that arterial inflow was then minimal.5. Increase of V(f), following reduction of P(p), was therefore due to inflow of arterial blood, of soft tissue or interstitial fluid. Interstitial fluid could flow from regions external to the plethysmograph, or enter as the result of filtration across capillaries. Occlusion of the upper arm circulation was not expected to interfere with motion of forearm soft tissue or the intratissue flow of interstitial fluid. It appears that capillary filtration is small compared with observed blood flow. Therefore subtraction of V(foccl) measured at intervals after reduction of P(p) (upper arm circulation occluded) from V(f) similarly obtained (but upper arm circulation free) appeared to give change of forearm volume due to inflow of arterial blood (DeltaV(b)). V(b), the volume inflow rate of arterial blood during suction, was then obtained.6. Resting forearm flow was 1.8 ml./min/100 ml. in seven normal subjects (average mean arterial blood pressure 86 mm Hg). With P(p) = -90 mm Hg, V(b) was 10.2 ml./min/100 ml. Suction therefore reduced vascular resistance, measured as (P(bane)-P(ve)) /V(b).

The ultrastructural basis of capillary permeability studied with peroxidase as a tracer

The transendothelial passage of horseradish peroxidase, injected intravenously into mice, was studied at the ultrastructural level in capillaries of cardiac and skeletal muscle. Peroxidase appeared to permeate endothelial intercellular clefts and cell junctions. Abnormal peroxidase-induced vascular leakage was excluded. Neutral lanthanum tracer gave similar results. The endothelial cell junctions were considered to be maculae occludentes, with gaps of about 40 A in width between the maculae, rather than zonulae occludentes. Some observations in favor of concurrent vesicular transport of peroxidase were also made. It is concluded that the endothelial cell junctions are most likely to be the morphological equivalent of the small pore system proposed by physiologists for the passage of small, lipid-insoluble molecules across the endothelium.

The pathway between hyaloid blood and retinal neurons in the toad. Structural observations and permeability to tracer substances

The hyaloid vessels form a capillary network on the inner surface of the retina. These capillaries are embedded in the vitreous humor, and they lack a glial investment. The intercellular spaces of the retina communicate with the ocular cavity, as can be evidenced by following the penetration of tracer substances. Hence, there is an extracellular diffusion pathway between hyaloid capillaries and retinal neurons, without interposition of glial cells. Trypan blue and ferrocyanide were not detected within the vitreous humor nor the retina after systemic injection. To this extent, at least, the hyaloid capillaries functionally resemble central nervous system capillaries. Intravascular injections of horseradish peroxidase established the absence of vesicular transfer across the endothelium of the hyaloid capillaries. In addition, quintuple-layered junctions between endothelial cells prevented the intercellular passage of the enzyme. It is likely, therefore, that the only pathway across the endothelium of the hyaloid capillaries is through the plasmalemma of the endothelial cells.