Accuracy limitations of chronaxie values.
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. Chronaxie, the excitability constant, is the duration of a pulse of current of twice rheobasic strength. 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.
Geddes
Leslie A
LA
Department of Biomedical Engineering, Purdue University, West Lafayette, IN 47907-1296, USA. geddes@ecn.purdue.edu
D000200:Action Potentials / Q000502:physiology*; D002462:Cell Membrane / Q000502:physiology*; D002907:Chronaxy / Q000502:physiology*; D004056:Differential Threshold / Q000502:physiology; D017097:Electric Impedance; D004558:Electric Stimulation / Q000295:instrumentation* / Q000379:methods*; D004566:Electrodes; D004735:Energy Transfer / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity