Measurement of interstitial fluid pressure in dogs: evaluation of methods

Interstitial fluid pressure (IFP) was measured with two acute (micropipettes and wick-in-needle) and two chronic methods (perforated and porous capsules) in dog skin/subcutis. In control conditions all techniques gave similar mean pressures, approximately -2 mmHg. Overhydration induced by intravenous Ringer infusion, 10% of body wt, caused two to three times greater increase in pressure recorded with chronic than with acute methods but 2 h after the end of the infusion all methods gave similar pressures. An almost opposite pattern was observed during dehydration induced by peritoneal dialysis with hypertonic glucose. The fall in pressure recorded with the perforated capsule exceeded that of the porous capsule, both exceeding the pressure reduction measured with the acute methods by a factor of 2-5. The difference between pressures measured with both acute methods and the perforated capsule increased in the 90 min following dialysis. Acute overhydration or dehydration as well as aspiration from or infusion into perforated capsules caused a pressure gradient between lumen, capsule wall, and surrounding skin. We propose that the transient pressure differences recorded by acute vs. chronic methods during changes in hydration result from different physical properties of the capsule lining compared with that of the surrounding skin, in addition to a possible osmometer effect of the capsule lining.

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Transcapillary Starling forces using membrane osmometry

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1980.238.6.h886 ◽

1980 ◽

Vol 238 (6) ◽

pp. H886-H888

Author(s):

J. L. Christian ◽

R. A. Brace

Keyword(s):

Osmotic Pressure ◽

Interstitial Fluid ◽

Subcutaneous Tissue ◽

Fluid Pressure ◽

Colloid Osmotic Pressure ◽

Interstitial Fluid Pressure ◽

Tissue Samples ◽

Small Pore ◽

The Difference ◽

Good Agreement

Membrane osmometry was used to estimate the four transcapillary Starling pressures in subcutaneous tissue of rats, guinea pigs, and dogs. Isolated subcutaneous tissue samples were either placed on a large-pore or small-pore osmometer that measured the interstitial fluid pressure (Pif) and the difference between the interstitial fluid pressure and the interstitial protein osmotic pressure (Pif-pi if), respectively. The colloid osmotic pressure of the interstitial fluid (pi if) was obtained from the difference in these two pressures. A plasma sample placed on the small-pore osmometer yielded the colloid osmotic pressure of the plasma proteins (pi c). Finally the capillary pressure (Pc) was calculated from the three other Starling forces. In the rat, guinea pig, and dog, respectively, the estimated Starling forces were as follows: Pif -2.2, -2.1, and -4.8 mmHg; pi if, 7.3, 4.8, and 4.4 mmHg; pi c, 21.3, 19.5, and 19.2 mmHg; and Pc, 11.8, 12.6, and 10.0 mmHg. A comparison with data obtained in other studies using different methods shows good agreement and strongly supports membrane osmometry as a method for measuring the Starling pressures in subcutaneous tissue.

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Interstitial fluid pressure, composition of interstitium, and interstitial exclusion of albumin in hypothyroid rats

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.2000.278.5.h1627 ◽

2000 ◽

Vol 278 (5) ◽

pp. H1627-H1639 ◽

Cited By ~ 39

Author(s):

Helge Wiig ◽

Rolf K. Reed ◽

Olav Tenstad

Keyword(s):

Thyroid Hormones ◽

Interstitial Fluid ◽

Fluid Pressure ◽

Interstitial Fluid Pressure ◽

Albumin Concentration ◽

Rat Serum ◽

Interstitial Fluid Volume ◽

Hindlimb Muscle ◽

The Difference ◽

And Control

Lack of thyroid hormones may affect the composition and structure of the interstitium. Hypothyrosis was induced in rats by thyroidectomy 4–12 wk before the experiments. In hypothyroid rats ( n = 16), interstitial fluid pressure measured with micropipettes in hindlimb skin and muscle averaged +0.1 ± 0.2 and +0.5 ± 0.2 mmHg, respectively, with corresponding pressures in control rats ( n = 16) of −1.5 ± 0.1 ( P < 0.001) and −0.8 ± 0.1 mmHg ( P < 0.001). Interstitial fluid volume, measured as the difference between the distribution volumes of 51Cr-EDTA and125I-labeled BSA, was similar or lower in skin and higher in hypothyroid muscle. Total protein and albumin concentration in plasma and interstitial fluid (isolated from implanted wicks) was lower in hypothyroid compared with control rats. Hyaluronan content ( n = 9) in rat hindlimb skin was 2.05 ± 0.15 and 1.92 ± 0.09 mg/g dry wt ( P > 0.05) in hypothyroid and control rats, respectively, with corresponding content in hindlimb skeletal muscle of 0.35 ± 0.07 and 0.23 ± 0.01 mg/g dry wt ( P < 0.01). Interstitial exclusion of albumin in skin and muscle was measured after 125I-labeled rat serum albumin infusion for 120–168 h with an implanted osmotic pump. Relative excluded volume for albumin (Ve/Vi) was calculated as 1 − Va/Vi, and averaged 28 and 28% in hindlimb muscle ( P > 0.05), 44 and 45% in hindlimb skin ( P > 0.05), and 19 and 32% in back skin ( P < 0.05) in hypothyroid and control rats, respectively. Albumin mass was higher in back skin in spite of a lower interstitial fluid albumin concentration, a finding explained by a reduced Ve/Vi in back skin in hypothyroid rats. These experiments suggest that lack of thyroid hormones in rats changes the interstitial matrix again leading to reduced interstitial compliance and changes in the transcapillary fluid balance.

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Control of interstitial fluid pressure: Role of [beta ]-integrins

Seminars in Nephrology ◽

10.1053/snep.2001.21646 ◽

2001 ◽

Vol 21 (3) ◽

pp. 222-230 ◽

Cited By ~ 42

Author(s):

Rolf K. Reed ◽

Ansgar Berg ◽

Eli-Anne B. Gjerde ◽

Kristofer Rubin

Keyword(s):

Interstitial Fluid ◽

Fluid Pressure ◽

Interstitial Fluid Pressure

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Dynamics of Interstitial Fluid Pressure in Extracellular Matrix Hydrogels in Microfluidic Devices

Journal of Biomechanical Engineering ◽

10.1115/1.4031020 ◽

2015 ◽

Vol 137 (9) ◽

Cited By ~ 5

Author(s):

Joe Tien ◽

Le Li ◽

Ozgur Ozsun ◽

Kamil L. Ekinci

Keyword(s):

Extracellular Matrix ◽

Pressure Distribution ◽

Interstitial Fluid ◽

Scaling Laws ◽

Fluid Pressure ◽

Interstitial Fluid Pressure ◽

External Loading ◽

Interstitial Pressure ◽

Time Resolved ◽

Long Time

In order to understand how interstitial fluid pressure and flow affect cell behavior, many studies use microfluidic approaches to apply externally controlled pressures to the boundary of a cell-containing gel. It is generally assumed that the resulting interstitial pressure distribution quickly reaches a steady-state, but this assumption has not been rigorously tested. Here, we demonstrate experimentally and computationally that the interstitial fluid pressure within an extracellular matrix gel in a microfluidic device can, in some cases, react with a long time delay to external loading. Remarkably, the source of this delay is the slight (∼100 nm in the cases examined here) distension of the walls of the device under pressure. Finite-element models show that the dynamics of interstitial pressure can be described as an instantaneous jump, followed by axial and transverse diffusion, until the steady pressure distribution is reached. The dynamics follow scaling laws that enable estimation of a gel's poroelastic constants from time-resolved measurements of interstitial fluid pressure.

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