Plasma protein osmotic pressure equations for humans

Pump-Free Microfluidic Hemofiltration Device

Hemofiltration removes water and small molecules from the blood via nanoporous filtering membranes. This paper discusses a pump-free hemofiltration device driven by the pressure difference between the artery and the vein. In the design of the filtering device, oncotic pressure needs to be taken into consideration. Transmembrane pressure (TMP) determines the amount and direction of hemofiltration, which is calculated by subtracting the oncotic pressure from the blood pressure. Blood pressure decreases as the channels progress from the inlet to the outlet, while oncotic pressure increases slightly since no protein is removed from the blood to the filtrate in hemofiltration. When TMP is negative, the filtrate returns to the blood, i.e., backfiltration takes place. A small region of the device with negative TMP would thus result in a small amount of or even zero filtrates. First, we investigated this phenomenon using in vitro experiments. We then designed a hemofiltration system taking backfiltration into consideration. We divided the device into two parts. In the first part, the device has channels for the blood and filtrate with a nanoporous membrane. In the second part, the device does not have channels for filtration. This design ensures TMP is always positive in the first part and prevents backfiltration. The concept was verified using in vitro experiments and ex vivo experiments in beagle dogs. Given the simplicity of the device without pumps or electrical components, the proposed pump-free hemofiltration device may prove useful for either implantable or wearable hemofiltration.

Whole body acid-base and fluid-electrolyte balance: a mathematical model

A cellular compartment was added to our previous mathematical model of steady-state acid-base and fluid-electrolyte chemistry to gain further understanding and aid diagnosis of complex disorders involving cellular involvement in critically ill patients. An important hypothesis to be validated was that the thermodynamic, standard free-energy of cellular H(+) and Na(+) pumps remained constant under all conditions. In addition, a hydrostatic-osmotic pressure balance was assumed to describe fluid exchange between plasma and interstitial fluid, including incorporation of compliance curves of vascular and interstitial spaces. The description of the cellular compartment was validated by close comparison of measured and model-predicted cellular pH and electrolyte changes in vitro and in vivo. The new description of plasma-interstitial fluid exchange was validated using measured changes in fluid volumes after isoosmotic and hyperosmotic fluid infusions of NaCl and NaHCO3. The validated model was used to explain the role of cells in the mechanism of saline or dilutional acidosis and acid-base effects of acidic or basic fluid infusions and the acid-base disorder due to potassium depletion. A module was created that would allow users, who do not possess the software, to determine, for free, the results of fluid infusions and urinary losses of water and solutes to the whole body.

Equation for osmotic pressure of serum protein (fractions)

The colloid or protein osmotic pressure (Pi) is a function of protein molarity (linear) and of Donnan and other effects. Albumin is the major osmotic protein, but also globulins influence Pi. Equations based on concentrations of albumin and nonalbumin (globulin concentration + fibrinogen concentration) protein approximate Pi better than albumin alone. Globulins have a wide range of molecular weights, and a 1956 diagram indicated that Pi of globulin fractions decreased in the order alpha1-, alpha2-, beta-, and gamma-globulin. The molecular weight of the serum protein fractions had been extrapolated, so van't Hoff's law and nonlinear regression analysis of the curves permitted expression of the diagram as an equation: product Pi(s,Ott,2 degrees C,cmH2O)=x(alb)(0.338C(tot)+0.00339C(tot)(2))+x(alpha1)(0.518C(tot)+0.0107C(tot)(2))+x(alpha2)(0.203C(tot)+0.00155C(tot)(2))+x(beta)(0.187C(tot)+0.000577C(tot)(2))+x(gamma)(0.161C(tot)+0.000223C(tot)(2)), where Pi(s,Ott,2 degrees C,cmH2O) is Pi of serum at 2 degrees C (in cmH2O) computed from the 1956 diagram, C(tot) is the concentration (g/l) of total protein in serum, and x(alb), x(alpha1), x(alpha2), x(beta), and x(gamma) are the fractions of albumin, alpha1-, alpha2-, beta-, and gamma-globulin, respectively. At one and the same concentration of fractions, Pi("Ott") decreases in the order alpha1-globulin, albumin, alpha2-globulin, beta-globulin, and gamma-globulin.