Changes In Interstitial Fluid Pressure Research Articles

Pneumatic piston hydrostatic bioreactor for cartilage tissue engineering

During exercise, mechanical loads from the body are transduced into interstitial fluid pressure changes which are sensed as dynamic hydrostatic forces by cells in cartilage. The effects of these loading forces in health and disease are of interest to biologists, but the availability of affordable equipment for in vitro experimentation is an obstacle to research progress. Here, we report the development of a cost-effective hydropneumatic bioreactor system for research in mechanobiology. The bioreactor was assembled from readily available components (a closed-loop stepped motor and pneumatic actuator) and a minimal number of easily-machined crankshaft parts, whilst the cell culture chambers were custom designed by the biologists using CAD and entirely 3 D printed in PLA. The bioreactor system was shown to be capable of providing cyclic pulsed pressure waves at a user-defined amplitude and frequency ranging from 0 to 400 kPa and up to 3.5 Hz, which are physiologically relevant for cartilage. Tissue engineered cartilage was created from primary human chondrocytes and cultured in the bioreactor for five days with three hours/day cyclic pressure (300 kPa at 1 Hz), simulating moderate physical exercise. Bioreactor-stimulated chondrocytes significantly increased their metabolic activity (by 21%) and glycosaminoglycan synthesis (by 24%), demonstrating effective cellular transduction of mechanosensing. Our Open Design approach focused on using ‘off-the-shelf’ pneumatic hardware and connectors, open source software and in-house 3 D printing of bespoke cell culture containers to resolve long-standing problems in the availability of affordable bioreactors for laboratory research.

The Hippo pathway drives the cellular response to hydrostatic pressure.

Cells need to rapidly and precisely react to multiple mechanical and chemical stimuli in order to ensure precise context‐dependent responses. This requires dynamic cellular signalling events that ensure homeostasis and plasticity when needed. A less well‐understood process is cellular response to elevated interstitial fluid pressure, where the cell senses and responds to changes in extracellular hydrostatic pressure. Here, using quantitative label‐free digital holographic imaging, combined with genome editing, biochemical assays and confocal imaging, we analyse the temporal cellular response to hydrostatic pressure. Upon elevated cyclic hydrostatic pressure, the cell responds by rapid, dramatic and reversible changes in cellular volume. We show that YAP and TAZ, the co‐transcriptional regulators of the Hippo signalling pathway, control cell volume and that cells without YAP and TAZ have lower plasma membrane tension. We present direct evidence that YAP/TAZ drive the cellular response to hydrostatic pressure, a process that is at least partly mediated via clathrin‐dependent endocytosis. Additionally, upon elevated oscillating hydrostatic pressure, YAP/TAZ are activated and induce TEAD‐mediated transcription and expression of cellular components involved in dynamic regulation of cell volume and extracellular matrix. This cellular response confers a feedback loop that allows the cell to robustly respond to changes in interstitial fluid pressure.

Computational Modeling of Interstitial Fluid Pressure and Velocity in Non-small Cell Lung Cancer Brain Metastases Treated With Stereotactic Radiosurgery.

Background: Early imaging-based treatment response assessment of brain metastases following stereotactic radiosurgery (SRS) remains challenging. The aim of this study is to determine whether early (within 12 weeks) intratumoral changes in interstitial fluid pressure (IFP) and velocity (IFV) estimated from computational fluid modeling (CFM) using dynamic contrast-enhanced (DCE) MRI can predict long-term outcomes of lung cancer brain metastases (LCBMs) treated with SRS.Methods: Pre- and post-treatment T1-weighted DCE-MRI data were obtained in 41 patients treated with SRS for intact LCBMs. The imaging response was assessed using RANO-BM criteria. For each lesion, extravasation of contrast agent measured from Extended Tofts pharmacokinetic Model (volume transfer constant, Ktrans) was incorporated into a computational fluid model to estimate tumor IFP and IFV. Estimates of mean IFP and IFV and heterogeneity (skewness and kurtosis) were calculated for each lesion from pre- and post-SRS imaging. The Wilcoxon rank-sum test was utilized to assess for significant differences in IFP, IFV, and IFP/IFV change (Δ) between response groups.Results: Fifty-three lesions from 41 patients were included. Median follow-up time after SRS was 11 months. The objective response (OR) rate (partial or complete response) was 79%, with 21% demonstrating stable disease (SD) or progressive disease (PD). There were significant response group differences for multiple posttreatment and Δ CFM parameters: post-SRS IFP skewness (mean −0.405 vs. −0.691, p = 0.022), IFP kurtosis (mean 2.88 vs. 3.51, p = 0.024), and IFV mean (5.75e-09 vs. 4.19e-09 m/s, p = 0.027); and Δ IFP kurtosis (mean −2.26 vs. −0.0156, p = 0.017) and IFV mean (1.91e-09 vs. 2.38e-10 m/s, p = 0.013). Posttreatment and Δ thresholds predicted non-OR with high sensitivity (sens): post-SRS IFP skewness (−0.432, sens 84%), kurtosis (2.89, sens 84%), and IFV mean (4.93e-09 m/s, sens 79%); and Δ IFP kurtosis (−0.469, sens 74%) and IFV mean (9.90e-10 m/s, sens 74%).Conclusions: Objective response was associated with lower post-treatment tumor heterogeneity, as represented by reductions in IFP skewness and kurtosis. These results suggest that early post-treatment assessment of IFP and IFV can be used to predict long-term response of lung cancer brain metastases to SRS, allowing a timelier treatment modification.

Antisecretory Factor-Mediated Inhibition of Cell Volume Dynamics Produces Antitumor Activity in Glioblastoma.

Interstitial fluid pressure (IFP) presents a barrier to drug uptake in solid tumors, including the aggressive primary brain tumor glioblastoma (GBM). It remains unclear how fluid dynamics impacts tumor progression and can be targeted therapeutically. To address this issue, a novel telemetry-based approach was developed to measure changes in IFP during progression of GBM xenografts. Antisecretory factor (AF) is an endogenous protein that displays antisecretory effects in animals and patients. Here, endogenous induction of AF protein or exogenous administration of AF peptide reduced IFP and increased drug uptake in GBM xenografts. AF inhibited cell volume regulation of GBM cells, an effect that was phenocopied in vitro by the sodium-potassium-chloride cotransporter 1 (SLC12A2/NKCC1) inhibitor bumetanide. As a result, AF induced apoptosis and increased survival in GBM models. In vitro, the ability of AF to reduce GBM cell proliferation was phenocopied by bumetanide and NKCC1 knockdown. Next, AF's ability to sensitize GBM cells to the alkylating agent temozolomide, standard of care in GBM patients, was evaluated. Importantly, combination of AF induction and temozolomide treatment blocked regrowth in GBM xenografts. Thus, AF-mediated inhibition of cell volume regulation represents a novel strategy to increase drug uptake and improve outcome in GBM. Mol Cancer Res; 16(5); 777-90. ©2018 AACR.

Subharmonic-Aided Pressure Estimation for Monitoring Interstitial Fluid Pressure in Tumors: Calibration and Treatment with Paclitaxel in Breast Cancer Xenografts

Interstitial fluid pressure (IFP) in rats with breast cancer xenografts was non-invasively estimated using subharmonic-aided pressure estimation (SHAPE) versus an invasive pressure monitor. Moreover, monitoring of IFP changes after chemotherapy was assessed. Eighty-nine rats (calibration n = 25, treatment n = 64) were injected with 5 × 106 breast cancer cells (MDA-MB-231). Radiofrequency signals were acquired (39 rats successfully imaged) with a Sonix RP scanner (BK Ultrasound, Richmond, BC, Canada) using a linear array (L9-4, transmit/receive: 8/4 MHz) after administration of Definity (Lantheus Medical Imaging, North Billerica, MA, USA; 180 μL/kg) and compared with readings from an invasive pressure monitor (Stryker, Berkshire, UK). An inverse linear relationship was established between tumor IFP and SHAPE (y = −1.06x + 28.27, r = −0.69, p = 0.01) in the calibration group. Use of this relationship in the treatment group resulted in r = 0.74 (p < 0.05) between measured (pressure monitor) and SHAPE-estimated IFP (average error: 6.24 mmHg). No significant before/after differences were observed with respect to paclitaxel treatment (5 mg/kg, Mayne Pharma, Paramus, NJ, USA) with either method (p ≥ 0.15).

Thermal dose fractionation affects tumour physiological response

Purpose: It is unknown whether a thermal dose should be administered using a few large fractions with higher temperatures or a larger number of fractions with lower temperatures. To evaluate this we assessed the effect of administering the same total thermal dose, approximately 30 CEM43T90, in one versus three to four fractions per week, over 5 weeks.Materials and methods: Canine sarcomas were randomised to receive one of the hyperthermia fractionation schemes along with fractionated radiotherapy. Tumour response was based on changes in tumour volume, oxygenation, water diffusion quantified using MRI, and a panel of histological and immunohistochemical end points.Results: There was a greater reduction in tumour volume and water diffusion at the end of therapy in tumours receiving one hyperthermia fraction per week. There was a weak but significant association between improved tumour oxygenation 24 h after the first hyperthermia treatment and extent of volume reduction at the end of therapy. Finally, the direction of change of HIF-1α and CA-IX immunoreactivity after the first hyperthermia fraction was similar and there was an inverse relationship between temperature and the direction of change of CA-IX. There were no significant changes in interstitial fluid pressure, VEGF, vWF, apoptosis or necrosis as a function of treatment group or temperature.Conclusions: We did not identify an advantage to a three to four per week hyperthermia prescription, and response data pointed to a one per week prescription being superior.

Mild elevation of body temperature reduces tumor interstitial fluid pressure and hypoxia and enhances efficacy of radiotherapy in murine tumor models.

Human and rodent solid tumors often exhibit elevated interstitial fluid pressure (IFP). This condition is recognized as a prognostic indicator for reduced responses to therapy and decreased disease-free survival rate. In the present study, we tested whether induction of a thermoregulatory-mediated increase in tissue blood flow, induced by exposure of mice to mild environmental heat stress, could influence IFP and other vascular parameters within tumors. Using several murine tumor models, we found that heating results in a sustained reduction in tumor IFP correlating with increased tumor vascular perfusion (measured by fluorescent imaging of perfused vessels, laser Doppler flowmetry, and MRI) as well as a sustained reduction in tumor hypoxia. Furthermore, when radiation therapy was administered 24 hours postheating, we observed a significant improvement in efficacy that may be a result of the sustained reduction in tumor hypoxia. These data suggest, for the first time, that environmental manipulation of normal vasomotor function is capable of achieving therapeutically beneficial changes in IFP and microvascular function in the tumor microenvironment.

A phase I/II study of cisplatin and radiation in combination with sorafenib in cervical cancer: Evaluation of biomarkers.

5037 Background: This is a single-arm, open-label, phase I/II trial in patients with early stage carcinoma of the cervix investigating the addition of sorafenib (S), a dual kinase inhibitor with anti-VEGF properties which may increase the affect of chemotherapy and radiation on tumor cells. Methods: All patients received conventional treatment with radiation and chemotherapy (RTCT) but a low risk/para-aortic group received S alone in escalating doses for 1 week prior to the start of (RTCT), while high risk patients received S alone in escalating doses for 1 week prior to the start of RTCT, plus concurrently with RTCT. Biomarkers of response to S were measured at baseline, after 7 days of S alone (400 or 800 mg daily) and after 1 week of RTCT. Three Magnetic Resonance (MR) biomarkers of perfusion and vascular permeability were evaluated: 1. Enhancement fraction at 25s (EF25) - indicative of early phase enhancement; 2. Relative signal intensity (RSI) - indicative of late phase enhancement; and 3. iAUC60. In addition, tumor median pO2 (mpO2), hypoxic proportion (HP) and interstitial fluid pressure (IFP) were measured using needle-based techniques. The paired Wilcoxin signed ranks test was used to evaluate differences in the biomarkers relative to baseline. Results: Thirteen patients have been enrolled onto the study and the low risk cohort is complete. Most common toxicities of any grade include diarrhea (82%), lymphopenia (82%), and nausea (82%). Tumor volume increased with 7 days of S alone (86 vs 78 cm3, p<0.01), and EF (73 vs 86%, p=0.02) were decreased and RSI (1.7 vs 1.9, p=0.07) was unchanged. The tumors also became more hypoxic (mpO2 3 vs 14 mm Hg, p=0.01; and HP 67 vs 51%, p=0.06) but there was no change in IFP (21 vs 24 mm Hg). MR biomarkers were also obtained in week 2 (after the start of RTCT) for 12/13 patients, IFP in 10 and mpO2/HP in 7. Tumor volume decreased (57 vs 81 cm3, p=0.01) and there was a significant reduction in IFP (16 vs 24 mm Hg, p=0.04). However, EF, RSI, mpO2 and HP were not significantly different from baseline. Conclusions: Thus study demonstrates that the combination of RTCT and S is tolerable and that biomarkers show increasing hypoxia, and indications of reductions in markers of vasculature with S.

Hyperoxia increases the uptake of 5-fluorouracil in mammary tumors independently of changes in interstitial fluid pressure and tumor stroma

BackgroundHypoxia is associated with increased resistance to chemo- and radiation-therapy. Hyperoxic treatment (hyperbaric oxygen) has previously been shown to potentiate the effect of some forms of chemotherapy, and this has been ascribed to enhanced cytotoxicity or neovascularisation. The aim of this study was to elucidate whether hyperoxia also enhances any actual uptake of 5FU (5-fluorouracil) into the tumor tissue and if this can be explained by changes in the interstitium and extracellular matrix.MethodsOne group of tumor bearing rats was exposed to repeated hyperbaric oxygen (HBO) treatment (2 bar, pO2 = 2 bar, 4 exposures à 90 min), whereas one group was exposed to one single identical HBO treatment. Animals housed under normal atmosphere (1 bar, pO2 = 0.2 bar) served as controls. Three doses of 5FU were tested for dose response. Uptake of [3H]-5FU in the tumor was assessed, with special reference to factors that might have contributed, such as interstitial fluid pressure (Pif), collagen content, oxygen stress (measured as malondialdehyd levels), lymphatics and transcapillary transport in the tumors.ResultsThe uptake of the cytostatic agent increases immediately after a single HBO treatment (more than 50%), but not 24 hours after the last repeated HBO treatment. Thus, the uptake is most likely related to the transient increase in oxygenation in the tumor tissue. Factors like tumor Pif and collagen content, which decreased significantly in the tumor interstitium after repeated HBO treatment, was without effect on the drug uptake.ConclusionWe showed that hyperoxia increases the uptake of [3H]-5FU in DMBA-induced mammary tumors per se, independently of changes in Pif, oxygen stress, collagen fibril density, or transendothelial transport alone. The mechanism by which such an uptake occur is still not elucidated, but it is clearly stimulated by elevated pO2.

Mechanistic evaluation of the combination effect of paclitaxel (Pac) and bevacizumab (Bev) in breast cancer xenografts

11007 Background: Chemosensitization is the ability to augment the effects of standard chemotherapy. One of the possible mechanisms for chemosensitization is improving intratumoral chemotherapy concentrations by increasing total or regional delivery of chemotherapy to the tumor. This mechanism potentially leads to a decreased tumor interstitial fluid pressure (IFP). This study evaluates the interaction between tumor IFP, intra-tumor drug accumulation and blood vessel perfusion. Methods: GILM2 human breast cancer (triple negative phenotype) cells were injected into the mammary fat pad of female nude mice. Mice were randomized to 4 arms: Control, Pac 24 mg/Kg, Bev 10 mg/Kg, and the same dose for the combination Pac + Bev, twice a week for 3 weeks. Tumor IFP was assessed using an ultraminiature catheter-tip technique (Ozerdem 2005). Concentration of Pac in tumor tissue was measured using liquid chromatography mass spectrometry (LC/MS) and blood vessel perfusion was assessed by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Ultrastructural morphology changes were assessed by electron microscopy (EM). Results: Treatment started 35 days after implantation; tumor tissue concentration of Pac was significantly increased when combined with Bev (P = 0.03). In mice treated with the combination of Pac + Bev, IFP values decreased more gradually, with sustained and significant reduction at the end of the treatment (P = 0.0068; mean SEM day 0: 28,44 ± 6,1; mean SEM day 21: 7,41 ± 2,0). The IFP changes in the other 3 experimental arms did not reach statistical significance. The combination of Pac and Bev produced substantial changes to the proportions of endothelial cell/pericytes and increased apoptosis in tumor cells by 75% (detected by immunostaining for cleaved-caspase 3). Conclusions: The combination of Pac and Bev produces significant tumor reduction and increases three-fold the concentration of Pac in the tumor. This intra-tumor augmentation of Pac was correlated with the decrease of tumor IFP, which was independent of the action of Bev alone. Results of DCE-MRI and EM analyses of the treated tumors will also be presented. No significant financial relationships to disclose.

Interstitial Fluid Pressure in Free Vascularized Skin Flaps of the Rat Epigastrium

The purpose of this study was to observe the magnitude and time course of changes in tissue edema in experimental free flaps. Thirty female Sprague Dawley rats underwent elevation and orthoptic transplantation of free epigastric skin flaps. Using a modified "wick in needle" technique, interstitial fluid pressure (IFP) was measured in the flaps at various times up to 2 weeks postoperatively. Increases in IFP to positive values were seen by 12 hours. IFP remained elevated for 3 to 5 days, after which they gradually returned to control values by 2 weeks. This is the first study to follow the time course and magnitude of changes in IFP and edema in free flaps. It is a useful animal model by which the hemodynamic effects of physical and pharmacological manipulation of flaps can be studied.

Patupilone Induced Vascular Disruption in Orthotopic Rodent Tumor Models Detected by Magnetic Resonance Imaging and Interstitial Fluid Pressure

Evaluation of vascular disruptive activity in orthotopic models as potential surrogate biomarkers of tumor response to the microtubule-stabilizing agent patupilone. Mice bearing metastatic B16/BL6 melanoma and rats bearing mammary BN472 tumors received vehicle or efficacious patupilone doses (4 and 0.8-1.5 mg/kg i.v., respectively). Tumor vascularity assessment by dynamic contrast-enhanced or dynamic susceptibility contrast magnetic resonance imaging and interstitial fluid pressure (IFP) occurred at baseline, 2 days (mice and rats), and 6 days (rats) after treatment and were compared with histologic measurements and correlated with tumor response. In B16/BL6 metastases, patupilone (4 mg/kg) induced a 21 +/- 5% decrease (P < 0.001) in tumor blood volume and a 32 +/- 15% decrease (P = 0.02) in IFP after 2 days and reduced tumor growth and vessel density (>42%) after 2 weeks (P < or = 0.014). Patupilone dose-dependently inhibited BN472 tumor growth (day 6) and reduced IFP on days 2 and 6 (-21% to -70%), and the percentage change in IFP correlated (P < 0.01) with the change in tumor volume. In both models, histology and vascular casts confirmed decreases in tumor blood volume. One patupilone (0.8 mg/kg) administration decreased (P < 0.01) tumor IFP (54 +/- 4%), tumor blood volume (50 +/- 6%), and vessel diameter (40 +/- 11%) by day 6 but not the apparent diffusion coefficient, whereas histology showed that apoptosis was increased 2.4-fold and necrosis was unchanged. Apoptosis correlated negatively (P < 0.001) with IFP, tumor blood volume, and tumor volume, whereas tumor blood volume and IFP were correlated positively (P = 0.0005). Vascular disruptive effects of patupilone were detected in situ using dynamic contrast-enhanced or dynamic susceptibility contrast magnetic resonance imaging and IFP. Changes in IFP preceded and correlated with tumor response, suggesting that IFP may be a surrogate biomarker for patupilone efficacy.

Enhancement of fluid filtration across tumor vessels: implication for delivery of macromolecules.

Cancer therapies using genes and other macromolecules might realize their full clinical potential if they could be delivered to tumor tissue in optimal quantities. Unfortunately, the compromised circulation within tumors poses a formidable resistance to adequate and uniform penetration of these agents. Previously, we have proposed elevated interstitial fluid pressure (IFP) as a major physiological barrier to delivery of macromolecules. Here we postulate that modulation of tumor microvascular pressure (MVP) and associated changes in IFP would enhance macromolecular delivery into a solid tumor. To test our hypothesis, we altered tumor MVP by either periodic injection or continuous infusion of angiotensin II (AII) and measured the resulting changes in IFP and uptake of macromolecules. We used the nicotinyl hydrazine derivative of human polyclonal IgG (HYNIC-IgG) as a nonspecific macromolecule and CC49 antibody as a specific macromolecule. We found that both chronic and periodic modulation of tumor MVP enhances transvascular fluid filtration, leading to a 40% increase in total uptake of the specific antibody within 4 hr of its administration. Conversely, neither continuous nor periodic infusion of AII induced any increase in uptake of nonspecific antibodies. Strategies to improve delivery of macromolecules and limitations of this approach are identified.

Corticotropin-releasing hormone inhibits lowering of interstitial pressure in rat trachea after neurogenic inflammation

Increased negativity of interstitial fluid pressure ( P if) is a key determinant of edema formation after tissue injury. In this study, we addressed the question of whether the anti-inflammatory effects of corticotropin-releasing hormone (CRH) shown by others are mediated by changes in interstitial fluid pressure. CRH, 25 to 50, but not 5 and 11 μg/kg s.c., administered 45 min before antidromic stimulation of the vagal nerve inhibited the lowering of interstitial fluid pressure in rat trachea produced by nerve stimulation. This inhibitory effect of CRH was blocked by pretreatment with the CRH receptor antagonist, α-helical CRH-(9–41), 0.15 mg/kg i.v., administered 5 min before CRH. These results suggest that CRH receptors modulate the structural integrity of the extracellular matrix in rat trachea for its response to inflammatory stimuli.

The Effect of Acute Inflammatory Episodes (Cellulitis) on the Treatment of Lymphoedema

Lymphoedema is a chronic, progressive condition which affects a significant number of patients following treatment for cancer. AcutelnflammatoryEpisodes(AIE),commonlyknown as cellulitis, may be a complication, or causative factor, in the development of lymphoedema, and has a detrimental effect on the management of lymphoedema. This paper reviews the literature regarding the pathophysiology oflymphoedema and its treatment using conservative treatment measures. The prevention and treatment of AlE is addressed, highlighting the importance of identifying those patients at risk of developing lymphoedema, and consequently AlE. The role of the nurse in patient education is discussed. INTRODUCTION The literature cites several factors which play a role in the developmentoflymphoedema. Of particular interest is the role of cellulitis, both in the development, and as a complication, of secondary lymphoedema related to cancer and its treatment This paper focuses on the physical effects of lymphoedema, and reviews the pathophysiology of lymphoedema. The development of AlE and its effect on current conservative lymphoedema treatments will be discussed with reference to the treatment and prophylaxis of AlE. The role of the nurse in the education of the patient will be outlined, with suggestions for future development Prior to commencing this review, two objectives were identified: 1) To achieve greater personal understanding of the patho-physiology of lymphoedema, its treatment and the role of AlE. 2) To provide a theoretical background (through this literature review) for the development of a controlled clinical study into the prophylaxis of AlE related to lymphoedema. For the purpose of this paper, the term 'nurse' will be used to describe those members of the multi-disciplinary team (whether they be nurse, physiotherapist, occupational therapist or surgical appliance officer) who are involved in the provision of care to patients with lymphoedema. PATHOPHYSIOLOGY OF LYMPHOEDEMA Lymphoedema is commonly referred to as a chronic swelling resulting from a failure of the lymph drainage system, with the consequent accumulation of protein-rich interstitial fluid 1•2•3•• 5 • 6 • 7 • 8 • One or more limbs may be affected, and sometimes the adjacent quadrant of the trunk • To achieve an understanding of the problems that may occur whenthelymphaticsystemfails,itisfirstnecessarytounderstand the basic pathophysiology of the lymphatic system. The lymphatic system The lymphatics serve two major purposes: the regulation of tissue homeostasis, and an immunological function • 9•• It comprises a complex network of vessels which provide an accessory one-way drainage route by which fluid can flow from the interstitial spaces, carrying macromolecules (including protein and bacteria) back into the bloodstream. It has also been likened to the route taken by a river from its source (tissues) to the sea (bloodstream) • The blood and lymph systems complement each other, providing a fine balance between filtration and reabsorption 11 • Fluid leaves the capillaries and enters the tissues under the compulsion of hydrostatic pressure, which is greater at the arterial end of the capillary. Proteins act as the vehicles in the blood transport system, carrying oxygen and nutrients to the cells of the tissues. At the venous end of the capillary, osmotic pressure (exerted by the plasma proteins remaining in the bloodstream) draws the fluid back into the capillaries. However, macromolecules such as protein and bacteria are unable to return directly to the bloodstream, and must exit via the lymphatic route • Approximately 90% of the tissue fluid returns via the venous system, and the other 10% enters the lymphatic capillaries to combine with plasma proteins, cell debris, organic matter, foreign bodies and fat (from the intestine) to form lymph. The rate of lymph flow is influenced by three major factors: changes in interstitial fluid pressure; muscular activity; and the continual rhythmic contraction of the lymphatic vessels • •• The development of lymphoedema Lymphoedema can be classified into two types: primary and secondary. Primary lymphoedema arises from a congenital abnormality of the lymphatics (which will not be specifically discussed), whereas secondary lymphoedema results from obstruction or damage to the lymphatic vessels 2•5• The literature describes several factors which reduce the transport capacity of the system (Fig 1), and precipitate the presentation of lymphoedema. Currently there has been no work to suggest the degree of risk attached to each factor. The literature describes several factors which reduce the transport capacity of the system: Axillary or groin dissection .s·••• Axillary radiotherapy 1.s·8•15 Tumour Post-operative wound infection•••.ZO Venous complications Radiodermatitis•

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.

Interstitial fluid pressure of ileum measured from chronically implanted polyethylene capsules

Steady-state fluid pressure measurements were obtained from polyethylene capsules chronically implanted in the walls of cat ileum. Measurements were performed while ileal venous outflow pressure was maintained at 0, 10, 20, or 30 mmHg. The resulting mean steady-state capsule pressure ranged from -0.56 to 7.3 mmHg over the range of imposed venous outflow pressures. The data provide evidence that at an ileal venous outflow pressure in the range of 10 mmHg, comparable to a normal portal pressure, interstitial fluid pressure is positive, increasing as tissue hydration increases, and is a significant contributing force opposing increases in the transcapillary filtration force. Additionally, the qualitative response of implanted capsules to close intra-arterial infusion of normal saline (transcapillary filtration), Dextran 40 (transcapillary absorption), and histamine (transcapillary filtration-permeability changes), and during and after an arterial occlusion of 60-s duration (transcapillary absorption-filtration) were obtained. The results demonstrate that the implanted capsules appropriately track changes in interstitial fluid pressure when the state of tissue hydration is altered by an induced net transcapillary fluid filtration or absorption. Finally, total protein concentration of capsule fluid was not significantly different from lymph fluid derived from a lymphatic vessel draining the ileal segment.

Tissue pressure in rat oral mucosa measured by micropuncture technique

Tissue pressure or interstitial fluid pressure (IFP) was measured in 68 rats in different areas of the oral mucosa (free gingiva, attached gingiva in front and molars, alveolar mucosa, hard palate, cheek) by glass pipettes (diameter 2‐4 μm) connected to a servocontrolled counterpressure system. All the measurements of IFP were considerably above ambient pressure. The highest IFP was measured in the hard palate (14.8 mm Hg) and in attached gingiva (8.6, 9.2 mm Hg), while free gingiva, alveolar mucosa and cheek showed lower values (2.3, 3.6, 1.5 mm Hg respectively). Venous stasis resulted in an immediate rise in IFP in the attached gingiva. Repeated measurements of IFP at the same location gave the same results 3 h after induction of anesthesia, and there was no change in IFP in continuous recordings for up to 30 min. Administration of indomethacin did not change IFP. The results show that IFP in oral mucosa is high and that there is a marked regional variation in IFP, which may reflect regional differences in aspects of anatomy and function. The great difference between IFP in attached and free gingiva shows that there is a pressure gradient between these tissues, possibly maintained by the anatomical structure and the drainage of gingival fluid into the gingival sulcus.

Interstitial fluid pressure in the isolated perfused rabbit lung.

Interstitial fluid pressure was measured in nine isolated perfused rabbit lungs with the servonull micropipette method. Bevelled glass micropipettes, with tip diameter 2-6 micrometers (o.d.) were inserted 2-6 mm into the left lung. At alveolar pressures of 3 to 5 cm H2O we found mean interstitial fluid pressures of 1.0 (SD 1.0) and 1.6 (SD 1.0) cm H2O relative to pleural pressure in the upper (n = 19) and lower (n = 21) lobes respectively. The vertical distance between the measuring sites in the upper and lower lobes was about 3 cm. Net filtration caused by elevated left atrial pressure caused practically no change in interstitial fluid pressure. Increased alveolar pressure either increased or decreased interstitial fluid pressure. The measured pressures probably represent interstitial fluid pressure in alveolar junctions or in the interstitium around small pulmonary arteries or veins. We conclude that interstitial fluid pressure in these sites is between alveolar and pleural pressure, and that it is only moderately affected by changes in alveolar pressure. The interstitial compliance appears to be high and there seem to be little or no vertical gradients in interstitial fluid pressure within the lung.

High-Frequency Ventilation

The effects of high-frequency oscillatory (HFV) ventilation on lung fluid balance and microvascular permeability to macromolecules were measured in open-chest dog lungs. Prenodal lung lymph flow, concentration of total plasma proteins in lymph and plasma, pulmonary arterial and left atrial pressure,cardiac output, and blood-free lung wet-to-dry weight ratios were measured for conventional mechanical ventilation (CMV, 12/min, 200–300 ml tidal volume) and HFV of 15 Hz and a stroke volume of 40–50 ml for normal and elevated left atrial pressures. HFV increased both lymph flow and lung water (68 and 20%, respectively), and lymph-to-plasma ratios of total plasma proteins remained unchanged. When left atrial pressure was increased, an analysis of lymph protein flux indicates that the lung microvascular permeability was not altered by HFV. The increase in lymph flow and lung water associated with HFV may reflect an increased microvascular exchange surface area or a change in interstitial fluid pressure.