Sleep classification according to AASM and Rechtschaffen & Kales: effects on sleep scoring parameters

Abstract

Study objective: To investigate differences between visual sleep scoring according to the classification developed by Rechtschaffen and Kales (R&K, 1968) and scoring based on the new guidelines of the American Academy of Sleep Medicine (AASM, 2007).

Design: All-night polysomnographic recordings were scored visually according to the R&K and AASM rules by experienced sleep scorers. Descriptive data analysis was used to compare the resulting sleep parameters.

Participants: Healthy subjects and patients (38 females and 34 males) aged between 21 and 86 years.

Interventions: N/A.

Measurement and results: While sleep latency and REM latency, total sleep time, and sleep efficiency were not affected by the classification standard, the time (in minutes and in percent of total sleep time) spent in sleep stage 1 (S1/N1), stage 2 (S2/N2) and slow wave sleep (S3+S4/N3) differed significantly between the R&K and the AASM classification. While light and deep sleep increased (S1 vs. N1 [+10.6 min, (+2.8%)]: P<0.01; S3+S4 vs. N3 [+9.1 min (+2.4%)]: P<0.01), stage 2 sleep decreased significantly according to AASM rules (S2 vs. N2 [-20.5 min, (-4.9%)]: P<0.01). Moreover, wake after sleep onset was significantly prolonged by approximately 4 minutes (P<0.01) according to the AASM standard. Interestingly, the effects on stage REM were age-dependent (intercept at 20 years: -7.5 min; slope: 1.6 min for 10-year age increase). No effects of sex and diagnosis were observed.

Conclusion: The study shows significant and age-dependent differences between sleep parameters derived from conventional visual sleep scorings on the basis of R&K rules and those based on the new AASM rules. Thus, new normative data have to be established for the AASM standard.

Figure 1

Single case 1: 24-year-old man (healthy subject) who shows “no changes” in the sleep scoring parameters. In addition to the R&K and AASM hypnograms (first and second traces, respectively), arousals, delta and spindle intensity as revealed by the Somnolyzer 24×7 adapted for the AASM standard are shown in the upper part of the figure. The lower part shows a typical 30-s epoch in sleep stage N3 with 2 EOG derivations (Pos8-M1 and Pos18-M1), a mental EMG derivation, and 6 EEG derivations (F4-M1, F3-M2, C4-M1, C3-M2, O2-M1, O1-M2), as well as a channel indicating automatically detected arousals. To facilitate comparisons, all scales are the same for Figures 1 to 3. Note that the high-amplitude slow waves surpass the 75 μV criteria by far already at central leads.

Figure 2

Single case 2: 32-year-old woman (healthy subject) who shows an “increase in N3/SWS” in the sleep scoring parameters. For details see Fig. 1. Note that the amplitudes of the slow waves at central leads are sometimes just below 75 μV, while the amplitude criterion of 75 μV is reached at frontal leads.

Figure 3

Single case 3: 80-year-old-man (healthy subject) who shows an “increase in N1/S1” in the sleep scoring parameters. For details see Fig. 1. Note the relatively high number of arousals and the low delta and spindle intensity. As seen specifically in the second sleep cycle, many sleep stages scored as S2 according to R&K were scored as N1 according to AASM because of cortical arousals. For an example see the lower part of the figure.

Figure 4

Single case 4: 22-year-old woman (healthy subject) who shows a “decrease in REM/R.” For details see Figure 1. Note the longr NREM intrusions in the first and second REM phase in the AASM hypnogram. The relatively low-amplitude K-complex in the central leads at the beginning of the 30-s example is confirmed by its typical topographic distribution with a fronto-central maximum (see lower part of the Figure).