Automatic detection of delta sleep: with correlation with nocturnal release

The cose temporal relationship between nocturnal GH release and delta sleep is well known. In order to overcome the practical difficulties in nocturnal hormonal study for clinical routine, an automatic processing system has been developed to detect on-line delta sleep. Eight adult volunteers were involved: GH samples were drawn during sleep, and sleep was evaluated by usual polygraphic recording and simultaneously analyzed by the automatic system. Fp1-Fp2 electrodes were connected to an eight bit microcomputer through an Analog/Digital interface provided with a zerotross detector and a Z80 CTC. Time domain EEG analysis was based on the comparison of the II Hjorth parameter with a threshold value, computed as alpha-band's percentage. We assumed that when zerocross was below this threshold value, the corresponding sleep stage was delta sleep. The microcomputer warned about the delta sleep recognition only if it was sufficiently steady. Delta sleep epochs detected by the automatic system were in good agreement with those obtained by visual evaluation. GH levels in samples drawn according to the warning signal were higher than those drawn in other stages of sleep. We conclude that the proposed system is able to efficiently detect sleep on-line and, for its simplicity, to be used by nursing staff.