Tone bursts of 1000 Hz with linear on and off ramps and plateaus of various durations were used to evoke cortical (vertex) potentials in five adult subjects. With 30 msec rise time, the amplitude, from N1 peak to P2 trough, and the latency to either the N1 peak or P2 trough were all independent of duration of the plateau from 0 to 300 msec. With 3 msec rise time, the amplitudes were progressively reduced when the plateau was shortened from 30 msec to 10, 3, or 0 msec. With a long plateau, the amplitudes were nearly constant for rise times of 50 msec or less. The latency of the V potential was prolonged at intensities of 45 dB (ISO) or less and also in relation to the slope of the onset ramp. With very gradual slope [300 msec to reach 45 dB (ISO)], mean latency to N1 was 169 msec while with very steep slope [3 msec to reach 85 dB (ISO)], it was 109 msec. OFF responses showed similar relations but with smaller amplitudes and shorter (by 16 msec) latencies. For evoked-response audiometry, the rise time of the test signal will not be critical if it is 30 msec or less and the plateau is at least 30 msec long, and any plateau of 30 msec or longer will be acceptable.

The purpose of this study was to assess the adaptive effects of endurance training on autonomic function in athletes with spectral analysis of cardiovascular variability signals. Continuous ECG, arterial blood pressure (ABP), and respiratory signals were recorded from 15 athletes (VO2max > 55 mL.min-1.kg-1) and 15 nonathletes (VO2max < 45 mL.min-1.kg-1) during 10 min at sitting position. Autonomic function was assessed by low frequency power (LF power: 0.06-0.14 Hz) and high frequency power (HF power: the region of the respiratory frequency based on respiratory spectrum) obtained from the autospectra of RR interval, systolic arterial pressure (SAP), and diastolic arterial pressure (DAP) variability signals. The spontaneous baroreflex sensitivity was evaluated by the moduli, BRSLF and BRSHF, of the transfer function between RR interval and SAP variability in LF and HF bands. The resting HR in athletes was significantly lower than that in nonathletes. The HF power, an index of parasympathetic activity, in RR interval spectra were significantly higher in athletes than in nonathletes. Meanwhile, the LF power (an indicator of sympathetic activities contributing to RR interval and of ABP variabilities) showed no significant difference between both groups, although that of athletes was slightly less than that of nonathletes. Also, BRSLF and BRSHF were not significantly different between athletes and nonathletes. These results indicate that endurance training results in the enhanced vagal activities in athletes, which may contribute in part to the resting bradycardia.

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