An Analogue Program for Standing-Gradient Osmotic Flow

Diamond and Bossert (1) proposed a model of standing-gradient osmotic flow as a mechanism to explain the coupling of water and solute transport in epithelia. In their computations they used a digital program in F O R T R A N on an IBM 7094 to solve for the two dependent variables, C and v, where C was the osmolar concentration at any point, x along the channel and v was the linear velocity at this same point. In the following communication, their equations (4-6) have been solved with a simple analogue program, provided with proper scaling. Test parameters may be set readily and the concentration profile from C,= = 0 to C,, = L may be generated and read out on any convenient laboratory recorder or X-Y plotter. The analogue program is simple and will generate a continuous function. Furthermore, a proper choice for Cx=0 may be made readily with a minimum expenditure in machine time and expense. Fig. 1 describes the unsealed program in its simplest form. Table I lists the scaled parameters for curves 1, 2, 3, and 4 in Fig. 3 of their paper (1). Fig. 2 is the output recorded on an X-Y plotter. One may refine the program so as to generate Cem~gent according to the equation.