Inserting a needle into subcutaneous spaces should allow a subatmospheric pressure to be measured if interstitial fluid pressure is truly negative as measured by the capsule and wick techniques. Previous needle measurements of interstitial fluid pressure have produced a positive value, but in most instances fluid has been injected into the tissues prior to recording of pressure. Therefore, we measured subcutaneous needle pressure in anesthetized dogs without fluid injection into the tissues. Approximately 30 min are required for an equilibrium pressure after insertion of the needle. The mean 30-min pressure was 4.6 +/- 0.5 (SE) mmHg (n equals 41). With observable edema, interstitial fluid pressures as measured with the needle were always positive. However, the needle method for continuous recording of pressure lacks rapid sensitivity to changes in tissue fluid pressures. In order to develop a needle method that would follow changes in interstitial fluid pressure, 0.5-1 mul of saline was injected into or withdrawn from the tissue. With this method, pressure plateaued in 10-20 min. This plateau pressure increased with tissue hydration and decreased with dehydration.
Our purpose was to explore the effects of variations in pH, particularly in the physiological range, on the colloid osmotic pressure (COP) of the body's fluids. Theoretically, changing pH would alter the electrical charge density on plasma proteins and the interstitial ground substance, thereby altering plasma and interstitial protein osmotic pressure as well as interstitial fluid pressure. We found that the COP of human plasma, human albumin, bovine albumin, and Wharton's jelly from human umbilical cords increased linearly as pH increased over the range of 6.0-8.0. COP of plasma and the albumins all displayed essentially the same sensitivity to pH. At equal concentrations, hyaluronate in umbilical cords was approximately 16 times more sensitive to pH than was plasma. Dextran 70 displayed no COP dependency on pH. For plasma, the albumins, and hyaluronate the pH dependence of COP on pH also decreased linearly with concentration (C in g/dl). For plasma and the albumins over the physiological range of pH, COP = COPpH 7.4 [1.00 + 0.01C (pH -7.40)] at 37 degrees C. The data suggest that, relative to the normal net transcapillary pressure gradient, physiological variations in pH affect plasma COP as well as interstitial fluid pressure and thus may play a significant role in regulating the body's fluid distribution.
Three of the four Starling forces were measured in the intact dog forelimb after anesthetization and all four of the Starling forces were measured in the same forelimb which was surgically isolated yet innervated. In the isolated forelimb, isogravimetric capillary pressure (Pci) averaged 15.6 mmHg; colloid osmotic pressure of the plasma proteins (IIp) averaged 19.9 mmHg; mean interstitial fluid pressure (Pif) was +0.4 mmHg, and the average value of interstitial colloid osmotic pressure (IIif) was 4.9 mmHg. Thus the net imbalance in the Starling forces, i.e., (Pci - Pif) - (IIp - IIif), averaged 0.3 mmHg. Furthermore, the value of IIif was consistently decreased after isolation (average decrease of 1.2 mmHg) while Pif was always increased following isolation (average increase of 4.3 mmHg). In addition, it was found that if the forelimb was denervated during isolation, then Pif was increased by an average of 2 mmHg above Pif in the innervated, isolated forelimb. In summary, these studies show that the differences between the intact and isolated forelimb are that Pci averages 10-11 mmHg in the intact forelimb and 15-16 mmHg in the isolated innervated forelimb while interstitial fluid pressure is negative in the intact limb and positive in the isolated limb.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.