F-waves in neonates: increased spinal anterior horn motor neuron excitability.

We analyzed characteristics of F-waves in neonates to establish normal parameters for this age. F-waves recorded from the median nerve in 26 normal neonates were analyzed and compared to those in 10 adults. F-wave parameters measured included occurrence rate (Fpersistence), latency (Flatency), latency corrected for subject height (normalized Flatency), duration (Fduration), amplitude (Famplitude) and its ratio to M-wave amplitude (F/M ratio), F-wave conduction velocity (FCV), and Fchronodispersion. Mean Fpersistence in neonates was 100%. Famplitude and the F/M ratio were higher in neonates than in adults. Similar F-wave waveforms were observed repeatedly in neonates, while waveforms varied in adults. These results in neonates suggest increased excitability of motor neurons in the spinal anterior horn reflecting immaturity of inhibition by the central nervous system.