Figure 4.

The amplitude ratios of paired APS were used to assess the changes of refractory period during 200 Hz A-HFS trains. (A) Top: typical recording of 1 min long 0.3 mA 200 Hz A-HFS with prolonged IPI gaps inserted every 2 s. The red bar above the signal denotes the HFS durations. The red dots below the signal denote the evoked APSs subsequent to the gaps. Middle: expanded insets show the evoked APS waveforms at the onset of HFS (A₂ ≈ A₁) and around 3 examples of the total 29 gaps (A₂ < A₁). The APS waveforms subsequent to the prolonged IPI gaps (i.e., A₁) are drawn by red color. The dashed lines with arrow heads in the expanded plots denote the location of the removed stimulation artifacts. Bottom: the scatter diagram of APS amplitude evoked by every stimulation pulse. The APS subsequent to the gaps (i.e., A₁) are denoted by red dots. (B) Amplitudes of the preceding APS (A₀) and subsequent APS (A₁) to the gaps, normalized by the amplitude of the very first APS at the onset of HFS, indicate sufficient recovery of A₁ while A₀ was suppressed. (C) Ratios of A₂/A₁ and A₃/A₁ during HFS indicate that the refractory period extended to longer than 5 ms. Note: the regular interval of 200 Hz is 5 ms.