Chronaxie calculated from current–duration and voltage–duration data

• Published in: Journal of neuroscience methods Vol. 97; no. 1; pp. 45 - 50
• Main Authors: Holsheimer, Jan, Dijkstra, Emiel A, Demeulemeester, Hilde, Nuttin, Bart
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.04.2000; Elsevier Science
• Subjects: Biological and medical sciences; Brain - cytology; Brain - physiology; Chronaxie; Chronaxy; Current–duration measurements; Deep brain stimulation; Electric Impedance; Electric Stimulation - instrumentation; Electric Stimulation - methods; Electric Stimulation Therapy - methods; Electrodes, Implanted; Fundamental and applied biological sciences. Psychology; Humans; Methodology. Experimentation; Neurons - physiology; Parkinson Disease - complications; Parkinson Disease - therapy; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Psychometrics. Statistics. Methodology; Rheobase; Time Factors; Tremor - etiology; Tremor - therapy; Voltage–duration measurements; Chronaxie; Current–duration measurements; Deep brain stimulation; Rheobase; Voltage–duration measurements; Human; Instrumental stimulation; Methodology; Central nervous system; Electrophysiology; Measurement method; Experimental study; Impedance; Current clamp method; Brain (vertebrata)
• ISSN: 0165-0270; 1872-678X
• DOI: 10.1016/S0165-0270(00)00163-1

To determine the rheobase and the chronaxie of excitable cells from strength–duration curves both constant-current pulses and constant-voltage pulses are applied. Since the complex impedance of the electrode-tissue interface varies with both the pulsewidth and the stimulation voltage, chronaxie values estimated from voltage–duration measurements will differ from the proper values as determined from current–duration measurements. To allow a comparison of chronaxie values obtained by the two stimulation methods, voltage–duration curves were measured in human subjects with a deep brain stimulation electrode implanted, while the current and the load impedance of the stimulation circuit were determined in vitro as a function of both stimulation voltage and pulsewidth. Chronaxie values calculated from voltage–duration data were shown to be 30–40% below those estimated from current–duration data. It was also shown that in the normal range of stimulation amplitudes (up to 7 V) the load impedance increases almost linearly with the pulsewidth. This result led us to present a simple method to convert voltage–duration data into current–duration data, thereby reducing the error in the calculated chronaxie values to ≈6%. For this purpose voltage–duration data have to be measured for pulses up to 10–20 times the expected chronaxie.