Abstract
This communication reports a new mathematical and analog computation of in vivo or extracellular fluid (ECF) base excess (BEe) of man derived from blood pH and PCO 2 . BEe is defined here as BE of blood diluted fourfold with extracellular fluid, as estimated by reading Siggaard-Andersen's alignment nomogram at 3 gm hemoglobin (Hb). An equation for his nomogram, which can be solved analogically but not analytically, is: BEe = 0.61 × 10π - 24.4 - 3.8 (1.2 - π)+ where π = log PCO2 f(pH - 7.4), and = Δ log PCO2/ΔpH, a function of Hb and BE. At Hb = 3, = 11.5/(BEe 37.5) 0.95. + indicates that negative values of the final term are counted zero. The multiplier f is generated in a FET in which source-drain resistance is a hyperbolic function of gate voltage, controlled by feedback from the computed BEe. The π summing amplifier drives both an antilog circuit to obtain 10π and, through a diode, a linear subtraction of the final term, which applies only when -30 <BE <-15. The analog solution tracks the nomogram within ±0.5 mEq/l. An intermediate solution of plasma HCO3 - is obtained by setting = 1.044 and dropping the two final terms.
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