IEEE transactions on bio-medical engineering
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The strength-duration curve is a plot of the threshold current (I) versus pulse duration (d) required to stimulate excitable tissue. On this curve are two points: 1) rheobase (b) and 2) chronaxie (c). Rheobase is the threshold current for an infinitely long-duration stimulus. ⋯ The mathematical expression for the strength-duration curve is I = b(1 + c/d). Although there are many published values for chronaxie for various excitable tissues, the range of variability for a given tissue type is quite large. This paper identifies five factors that can affect the accuracy of chronaxie measurement and shows that the most reliable values can be obtained with a rectangular pulse delivered from a constant-current source.