Sleep stage determination apparatus

1. A sleep stage determination apparatus comprising:

respiratory-signal detection means for detecting a variation in a respiratory signal from the body of a human subject; and

sleep-stage determination means for determining a plurality of sleep stages with respect to each of a plurality of unit zones defined by segmenting said respiratory-signal variation on a given time period basis, said sleep-stage determination means including:

in-bed/out-of-bed determination means for determining between an in-bed state and an out-of bed state, based on said respiratory-signal variation;

body-movement determination means for determining the presence and level of a body movement, based on said respiratory-signal variation;

wake determination means and intervening-wake determination means for determining between a wake state and a sleep state, based on a determination result of said body-movement determination means;

sleep-initiation determination means for determining a sleep-initiation state having a transition from the wake state to the sleep state, based on said respiratory-signal variation, and the respective determination results of said in-bed/out-of-bed and wake determination means;

sleep determination means for determining a depth of sleep based on said respiratory-signal variation, and respective determination results of said in-bed/out-of-bed, body-movement, sleep-initiation and wake determination means; and

wake-up determination means for determining a wake-up state based on said respiratory-signal variation, and respective determination results of said in-bed/out-of-bed, body-movement, sleep-initiation, wake and sleep determination means;

wherein said in-bed/out-of-bed determination means is operable, when said respiratory signal continues for a given time period or more at an amplitude equal to or greater than a given threshold value, to discriminate said in-bed state;

wherein said body-movement determination means is operable to discriminate one of a gross body movement state, a fine body movement state and a no body movement state, based on a plurality of threshold values assigned, respectively, to an amplitude fluctuation and amplitude level of said respiratory signal and a cycle of said respiratory signal; and

wherein said threshold value assigned to the amplitude fluctuation of said respiratory signal is compared to a standard deviation of amplitudes of three consecutive respiratory signals.

2. The sleep stage determination apparatus as defined in claim 1 , wherein said wake determination means is operable to discriminate one of a wake state, an unsteady state and a steady state, based on a variation of the body movement state within a given time period.

3. The sleep stage determination apparatus as defined in claim 1 , wherein said intervening-wake determination means is operable, when the body movement continues for a given time period or more at a given level or more, to discriminate said given time period of wake state.

4. The sleep stage determination apparatus as defined in claim 1 , wherein said sleep-initiation determination means is operable to discriminate the wake state based on a transition pattern of an initial wake state and a variation pattern of the respiratory signal in a region around sleep initiation of the subject, to determine said sleep initiation state.

5. The sleep stage determination apparatus as defined in claim 1 , wherein said sleep-initiation determination means includes deep-sleep determination means for determining a deep sleep state, and REM-sleep/light-sleep determination means for determining a REM-sleep state and a light-sleep state.

6. The sleep stage determination apparatus as defined in claim 5 , wherein said deep-sleep determination means is operable, when each of a respiratory rate within a given time period, a fluctuation of the respiratory rate and a fluctuation of a respiratory cycle is equal to or less than a given threshold, and there is no body movement within a given time period, to discriminate said deep sleep state.

7. The sleep stage determination apparatus as defined in claim 5 , wherein said REM-sleep/light-sleep determination means is operable to make a determination based on comparing between a respiratory rate within a given time period and an average respiratory rate of the entire sleep states and counting a successive number of said given time periods, and a determination based on whether an apneic state is present or absent within said given time period, so as to discriminate said REM-sleep state and said light-sleep state in accordance with said determination results.

8. The sleep stage determination apparatus as defined in claim 1 , wherein said wake-up determination means is operable, when no wake state appears before a given time period elapses from a time of the last determination of the wake state, to discriminate that said wake-up state occurs at said time of the last determination of the wake state.

9. The sleep stage determination apparatus as defined in claim 1 , which further includes:

heartbeat signal detection means for detecting a heartbeat-related parameter; and

correction means for correcting said sleep stages using said detected heartbeat-related parameter.