02130nas a2200265   4500000000100000008004100001260001300042653002200055653001500077653001000092653002100102653001100123653001100134653000900145653001700154653001600171653002200187100002200209700001700231245004000248300001100288490000700299520154400306022001401850       1997                            d  c1997 Dec10aAction Potentials10aAdolescent10aAdult10aElectromyography10aFemale10aHumans10aMale10aMedian Nerve10aMiddle Aged10aNeural Conduction1 aMarques Júnior W1 aBarreira A A00aNormal median near nerve potential.  a1431-50 v303 a<p>In routine studies of sensory nerve conduction, only fibers > or = 7 microns in diameter are analyzed. The late components which originate from thinner fibers are not detected. This explains why a normal sensory action potential (SAP) may be recorded in patients with peripheral neuropathies and sensory loss. In the present study we investigated the late component of the median SAP with a near nerve needle electrode technique in 14 normal volunteers (7 men and 7 women), aged 34.5 +/- 14.8 years. The stimulus consisted of rectangular pulses of 0.2-ms duration at a frequency of 1 Hz with an intensity at least 6 times greater than the threshold value for the main component. Five hundred to 2000 sweep averagings were performed. The duration of analysis was 40 or 50 ms and the wave analysis frequency was 200 (-6 dB/oct) to 3000 Hz (-12 dB/oct). We used an apparatus with a two-channel amplifier system, 200 M omega or more of entry impedance and a noise level of 0.7 microVrms or less. The main component mean amplitude, conduction velocity and latency and the late component mean amplitude, conduction velocity and latency were respectively (mean +/- SD): 26.5 +/- 5.42 microV, 56.8 +/- 5.42 m/s, 3.01 +/- 0.31 ms, 0.12 +/- 0.04 microV, 16.4 +/- 2.95 m/s and 10.6 +/- 2.48 ms. More sophisticated equipment has an internal noise of 0.6 microVrms. These data demonstrate that the technique can now be employed to study thin fiber neuropathies, like in leprosy, using commercial electromyographs, even in non-academic practices.</p>  a0100-879X