THE PRESSURE AND INTERSTITIAL RESISTANCE PREVAILING IN THE NORMAL AND EDEMATOUS SKIN OF ANIMALS AND MAN

Mounting Pressure in the Microenvironment: Fluids, Solids, and Cells in Pancreatic Ductal Adenocarcinoma

The microenvironment influences the pathogenesis of solid tumors and plays an outsized role in some. Our understanding of the stromal response to cancers, particularly pancreatic ductal adenocarcinoma, has evolved from that of host defense to tumor offense. We know that most, although not all, of the factors and processes in the microenvironment support tumor epithelial cells. This reappraisal of the roles of stromal elements has also revealed potential vulnerabilities and therapeutic opportunities to exploit. The high concentration in the stroma of the glycosaminoglycan hyaluronan, together with the large gel-fluid phase and pressures it generates, were recently identified as primary sources of treatment resistance in pancreas cancer. Whereas the relatively minor role of free interstitial fluid in the fluid mechanics and perfusion of tumors has been long appreciated, the less mobile, gel-fluid phase has been largely ignored for historical and technical reasons. The inability of classic methods of fluid pressure measurement to capture the gel-fluid phase, together with a dependence on xenograft and allograft systems that inaccurately model tumor vascular biology, has led to an undue emphasis on the role of free fluid in impeding perfusion and drug delivery and an almost complete oversight of the predominant role of the gel-fluid phase. We propose that a hyaluronan-rich, relatively immobile gel-fluid phase induces vascular collapse and hypoperfusion as a primary mechanism of treatment resistance in pancreas cancers. Similar properties may be operant in other solid tumors as well, so revisiting and characterizing fluid mechanics with modern techniques in other autochthonous cancers may be warranted.

THE EFFECTS OF VENOUS OBSTRUCTION UPON INTERSTITIAL PRESSURE IN ANIMAL AND HUMAN SKIN

The changes of intracutaneous pressure in the limbs of mice and human beings have been followed during and after periods of venous obstruction with almost unhindered arterial flow. During the first 30 minutes of obstruction the interstitial pressure in the tense skin of the lower legs of mice, a pressure which is slightly higher than that in the loose skin of the ears, backs, and thighs (21), rose from 2.6 to 4.6 cm. of water to about 32 cm., thereafter remaining constant. It would appear that the escape of fluid from the capillaries is checked at this pressure. In the skin of the arm and leg of man the interstitial pressure rose from 2.5–3.7 cm. of water to 15.0–23.0, within 15 to 27 minutes after venous obstruction had been produced, mounting no higher during the period of observation. When venous obstruction had existed for about 20 minutes or more the subjects sometimes experienced sensations of relief from congestion as if some tissue adjustment or the opening of some venous by-pass in the marrow had occurred, preventing a further rise of pressure. However this may be, the pressures still appeared to be great enough to prevent further escape of fluid from the capillaries, at least for the time being.

Biology of platelet-derived growth factor and its involvement in disease

Platelet-derived growth factor (PDGF) is mainly believed to be an important mitogen for connective tissue, especially for fibroblasts that serve in wound healing. However, PDGF also has important roles during embryonal development, and its overexpression has been linked to different types of fibrotic disorders and malignancies. Platelet-derived growth factor is synthesized by many different cell types, and its expression is broad. Its synthesis is in response to external stimuli, such as exposure to low oxygen tension, thrombin, or stimulation by other cytokines and growth factors. In addition, PDGF may function in autocrine stimulation of tumor cells, regulation of interstitial fluid pressure, and angiogenesis. Recently, several drugs were developed that are potent inhibitors of the tyrosine kinase activity of PDGF receptors. Thus, it is important to understand the physiology of PDGF and its receptors and the role of PDGF in different diseases. This review summarizes the physiologic activity of PDGF, the expression of PDGF during embryonal development, and the roles of PDGF expression in nonmalignant disease and in different tumors.

The intrarenal pressure; its relation to age, weight, blood pressure, and sex

1. The intrarenal pressure of dogs anesthetized with pentobarbital averages 26 mm. Hg, and ranges from 10 to 58 mm.; that of decerebrate dogs is 25 mm., and that of unanesthetized dogs with explanted kidneys is 25 mm. Tests of a few cats and rabbits indicate that their intrarenal pressure has about the same magnitude. 2. There is a slight positive correlation between intrarenal pressure and both body weight and kidney weight, but intrarenal pressure is not related to sex, blood pressure, or age.

Pressure measurements during injection of corticosteroids: in vivo studies

Intralesional injection of corticosteroids is an effective treatment for capillary hemangiomas. Complications include embolisation of corticosteroid particles into the ocular circulation resulting in permanent loss of vision. This research is aimed at developing an injection cannula and monitoring system to prevent such inadvertent embolisation. A cannula has been designed to simultaneously estimate the pressure at its tip and the flow rate during injection. The estimation technique has previously been validated using an in vitro model. In this study, the cannula was tested in vivo with canine liver at injection flow rates of 2.5 to 21 ml min-1. The pressure generated in the tissue during injection was calculated using the technique developed. This was compared with direct in situ pressure measurements made with a coaxial outer cannula. The mean calculated pressure was seen to be linearly related to the mean measured pressure with a slope of 0.97, correlation coefficient of 0.99 and standard error of 2.74 mmHg. Similar trends were observed between the maximum calculated and maximum measured injection pressure: slope = 1.0, r = 0.99 and standard error = 5.54 mmHg. The estimation of the mean and maximum pressure from the cannula and monitoring system was accurate in canine liver. High pressures close to 250 mmHg were generated in tissues during injection.

Pressure measurements during injection of corticosteroids

Corticosteroid injection into the orbit, eyelid and larynx is a common treatment for inflammation and neoplasm. Complications include embolisation into the ocular circulation resulting in permanent loss of vision. The overall aim of the reported research is to develop an injection cannula and monitoring system which can prevent inadvertent embolisation into the ocular circulation during injection of corticosteroids. To that end, a special cannula was designed that allows simultaneous estimation of pressure at the tip of the cannula and flow rate during injection. The cannula was tested with backpressures corresponding to physiological ranges of 0 to 125 mmHg and injection flow rates of 3 to 11 cm3 min-1. The estimated pressure at the tip of the cannula during injection of corticosteroids was compared with direct pressure measurements. The results show that the mean estimated pressure is linearly related to the mean measured pressure with a slope of 0.99 and correlation coefficient of 0.99. Statistical analyses show that with standard error of estimate (SEE) of 2.14 mmHg, the estimated pressure is well within the 95% prediction interval limits of the measured values. The estimation of pressure from the cannula and monitoring system was accurate and warrants further testing in animal models.

Interstitial fluid pressure as a circulatory monitor in skin flaps

Intradermal interstitial fluid pressure (IFP) in the rat epigastric flap has been measured under varying conditions of blood flow. Pressure changes were not as expected. An attempt has been made to explain these anomalous results using radiolabelled isotopes.

Interstitial fluid pressure changes during cardiopulmonary bypass

The effects of cardiopulmonary bypass using hemodilution on interstitial fluid pressure were measured using the Scholander wick technique. In 10 mongrel dogs, interstitial fluid pressure was measured in subcutaneous tissue, skeletal muscle, stomach, and left ventricle before and during 2 hours of cardiopulmonary bypass. Changes in interstitial fluid pressure were correlated with plasma colloidal osmotic pressure and duration of bypass. In subcutaneous tissue and skeletal muscle, interstitial fluid pressure increased during bypass; it did not change in the stomach. End-diastolic interstitial fluid pressure in the left ventricle increased significantly. These increases in pressure were presumably due to an increase in interstitial water. The rise in interstitial fluid pressure acts to partially neutralize the fall in plasma colloidal osmotic pressure.

Venous occlusion pressure plethysmography in the human upper limb

Two techniques of venous occlusion pressure plethysmography were examined experimentally in the human upper limb. The first was the classical method, in which external pressure is applied to the limb solely by way of the plethysmograph. In the second, the entire upper limb including the plethysmograph and venous occlusion cuff was enclosed in a box within which the air pressure could be raised. For each method the predictability of perfusion pressure was estimated by measuring local tissue pressure, venous pressure and arterial pressure. Artifacts in the recording of blood flow were also sought. In the first method there was a nonuniform increase in tissue pressure, venous pressure and probably arterial pressure. The changes were uniform and predictable in the second. Flow cessation pressure was 19 to 36 mm Hg in the warm hand and 13 to 30 mm Hg in the forearm using the first method. It was less than 10 mm Hg with the other method. It is suggested that the second technique offers a method for reexamining pressure-flow relations in the human upper limb under more precisely controlled conditions than hitherto.

Distribution of blood in the functional kidney

An attempt to measure the distribution of blood in the functional kidney of dogs was made. The method involved the injection of liquid latex rubber into the vascular system at physiologic pressures, fixation of the rubber in situ, and then, after corroding away all tissue, measurement of the volume of the rubber casts. The kidney contains, in its functionally distended state, 14 per cent blood. Of this, 4.5 per cent is apparently in the arteries and some 7 per cent in the veins. The functional engorgement of the cortical interlobular veins (about 4 per cent) is particularly striking, for they form a dense palisade of 40 to 300 micro vessels. These are not seen at the usual autopsy since they have drained out and collapsed. It is pointed out that attempts to describe the blood distribution in the kidney after it has been drained of blood are of dubious value. In the light of these data, also, the nature of the measurement of "intrarenal pressure," accomplished by inserting a needle into the renal parenchyma, may be better understood: it is suggested to be primarily a measure of interlobular venous pressure.