Effects of impulse noise stimulation on electrocorticogram and heart rate

It is now recognized that high-level impulse noises penetrate the uterus of pregnant sheep, elevate thresholds of fetal auditory-evoked potential and produce damage to fetal inner ear hair cells. However, little is known abou t functional effects of airborne impulse noise on the late-term fetus. In t he present study, the effects of a series of 20 impulses on the behavioral state of 6 fetal sheep were tested, Noise impulses produced 169.3 peak soun d pressure level (pSPL) in air. Peak levels recorded near the fetal head av eraged 161.1 dB. Impulses delivered to the fetus during periods of NREM sle ep resulted in a decrease in average fetal heart rate (FHR) from 185 +/- 22 beats/min (bpm) before stimulation to 174 +/- 23 bpm 2-5 s after stimulati on (p < 0.05). During REM sleep, an FHR acceleration occurred (before stimu lation: 177 <plus/minus> 24 bpm, after stimulation: 189 +/- 31 bpm; p < 0.0 5). Impulse exposure during NREM sleep resulted in reductions in delta-, th eta- and alpha-band powers. As a consequence, total power decreased from 10 0 to 72 <plus/minus> 16% (p < 0.05). During REM sleep, stimulation provoked a short decrease in total band power from 100 to 73 <plus/minus> 20% and a similar decrease in the theta- and beta-band powers. The results indicated that impulse noise evoked short-term alterations in FHR and cortical activ ity. These changes were mediated by auditory brain stem activation that led to cortical desynchronization during both NREM and REM sleep in late-term fetal sheep. Copyright (C) 2001 S. Karger AG, Basel.