F‐wave acquisition using low‐current stimulation

Abstract

The purpose of this study was to assess the feasibility of utilizing low-current stimulation for F-wave generation, thereby avoiding the discomfort of repetitive supramaximal stimulation. We employed the same technique as is used for generating F waves in the conventional way, except for using a stimulating current that was just strong enough to evoke a motor response on the oscilloscope. This usually required a stimulus of about 10-15 mA at 0.2-ms duration. Both median nerves of 30 subjects were evaluated with this technique and with F waves generated by the conventional technique in the same subjects. Amplitudes were larger when using supramaximal current stimulation. However, there was no statistical difference between F-wave latencies, chronodispersion, and persistence (penetrance) elicited with maximal and low-current stimulation. This procedure should represent a significant improvement for patient comfort during electrodiagnostic procedures involving F-wave studies.

F-wave records with submaximal stimulation: sustainability of the data and subject discomfort levels

“…Mean values obtained by supramaximal stimulation for all the F wave parameters conform to the similar studies in the past. [16][17][18][19] Stimulus magnitude for submaximal stimulation in the present study (for median nerve F-wave study) was 10.52±3.58 (mA±SD) (Table 1) which is in accordance with the similar study by DiBenedetto et al 12 This study reported no statistically significant difference between F-wave latencies, chronodispersion, and persistence elicited with maximal and low-current stimulation. Only amplitudes were found to be larger when using supramaximal current stimulation.…”

“…9 Low-intensity stimulation hence could lessen patient discomfort without affecting F-wave latency or duration. [10][11][12] All normative F-wave data are usually based on supramaximal stimulation. If submaximal stimulation can produce reliable and reproducible information for all Fwave parameters, and the number of stimuli required for such values has been determined then it could serve to minimize the discomfort or pain during the recording.…”

Investigation of anodal stimulation and its implications for F‐wave examinations

“…Considering that the supposed threshold for anodal stimulation of motor fibers is 1.4 times the MNAP threshold described in Table , a 15–20‐mA current may begin to evoke anodal stimulation, and a 30–40‐mA current may stimulate around half of nerve fibers by anodal stimulation in many subjects. The current values described in the literature for F‐wave examinations are often much higher than these values, 50 mA or more, which raises suspicion that anodal stimulation may occur commonly in actual practice. Cathode proximal stimulation in F‐wave examinations may be thought of as a simple method to avoid anodal stimulation, although this method is not preferred by some researchers, including us, due to a number of other drawbacks or complexities …”

“…In F-wave examinations, a supramaximal stimulus intensity may often be employed, although it is not actually necessary. 10 Considering that the supposed threshold for anodal stimulation of motor fibers is 1.4 times the MNAP threshold described in Table 2, a 15-20-mA current may begin to evoke anodal stimulation, and a 30-40-mA current may stimulate around half of nerve fibers by anodal stimulation in many subjects. The current values described in the literature for F-wave examinations are often much higher than these values, 50 mA or more, 2,10 which raises suspicion that anodal stimulation may occur commonly in actual practice.…”

“…In F‐wave examinations, a supramaximal stimulus intensity may often be employed, although it is not actually necessary . Considering that the supposed threshold for anodal stimulation of motor fibers is 1.4 times the MNAP threshold described in Table , a 15–20‐mA current may begin to evoke anodal stimulation, and a 30–40‐mA current may stimulate around half of nerve fibers by anodal stimulation in many subjects.…”