A clinical meaning of CAP is that a number of sleep disorders can be qualified as relat-ing either to the A-phase or to the B-phase [16]. CAP is an index to determine the quality of sleeping and as a marker of arousal instability. CAP can appear spontaneously in non-REM sleep, but it can occur also in association with identifiable sleep pathophysiologies
and neurovegetative activities
Increased amounts of arousals and of CAP rate both reflect a condition of disturbed sleep
(Figure source:Origin and Significance of the Cyclic Alternating Pattern (CAP), Sleep Medicine Reviews,Mario Giovanni Terzano and Liborio Parrino, 2000.)
(e.g. sleep-disordered breathing and periodic leg movement activity) [1]. CAP occurs not only at drowsiness and light sleep, but in all NREM stages. The CAP sequence, originally conceptualized as an arousal phenomenon, has evolved theoretically to encompass both the process of sleep maintenance and sleep instability. When falling into sleep, information is exchanged among many parts of brain during consciousness, and the frequency of in-formation exchanging reduces, while the exchanges won’t disappear. During sleep, EEG would show the waves with higher frequency and amplitude, which calls ”micro-arousal”.
This kind of micro-arousal is to detect whether our body has problem or not. That is why we say CAP likes the sentinel. CAP time and CAP rate can be used to evaluate the sleep efficiency. CAP time can be calculated throughout total NREM sleep and within the single NREM stages. CAP rate is defined by the ratio of CAP time to sleep time. By detecting the rate of CAP which can be measured in NREM sleep (the ratio of CAP time to NREM stage time) and in the single NREM stages (the ratio of CAP time to a given NREM stage to the total duration), the higher the CAP rate the poorer sleep quality. Many factors may affect the CAP rate. For example, CAP rate is increased by perturbing conditions and de-creased by hypnotic medication. But the strongest factor is age. Some previous researches show that CAP rate shows a u-shape evolution along the life span (teenagers: mean 43.4%;
Figure 1.2: CAP sequence and EEG signal C3-A2
young adults: 31.9%; middle aged: 37.5%; elderly: 55.3% [17]) in human sleep. We can observe micro cyclical alternation of sleep by a diagram which is called sleep capsnogram.
As shown in Figure 1.2, it appears different CAP phases following with different time in sleep process.
The CAP subtype classification extends the current American Sleep Disorders Asso-ciation (ASDA) definitions to include a periodicity dimension and a possible marker of pre-arousal activation regarding CAP to be an arousal process [15] [2]. These typically transient events such as EEG bursts with high-amplitude, delta-like wave or K-complex sequence are considered to reflect a possible arousal process. According some sleep phe-nomena with sleep instability, CAP A-phase can classify as the type of slow wave activity (subtypes A1 of CAP) marks the brains attempt to preserve sleep and subtypes A2 and A3 of CAP with the high-amplitude, slow activity to perform that sleep becomes too unstable or the preservation attempt fails.
CAP analysis is not a method to replace sleep staging or arousal scoring. But CAP analysis is a quantitative sleep analysis and provides a tool to use in our quest to look at human sleep.
Figure 1.3: Delta burst. Top 4 channels is Bioplolar parasagittal EEG derivation of the right side : FP2F4 , F4C4 , C4P4 , P4O2; C4A1: C4 connects to left ear (A1); EOG: Elec-trooculogram; EMG: Electromyogram; EKG: Electrocardiogram. (Figure source: Sleep Medicine 3, Consensus Report, Mario Giovanni Terzano et al.: Atlas, rules, and recording techniques for the scoring of cyclic alternating pattern (CAP) in human sleep, p 187-199, 2002)
1.3.1 CAP A-phase EEG events
In this section, we introduce CAP A-phase EEG events. A-phase can be composed of rhythms with slower and higher-voltage, rhythms with faster and lower-voltage, or by mixed patterns including both. They may include: delta bursts, vertex sharp transients, K-complex sequences with or without spindles, polyphasic bursts, K-alpha, intermittent alpha, and EEG arousals [15].
Delta bursts
The EEG delta burst is a wave with frequency range from 0.5 to 4 Hz and with at least 1/3 higher average amplitude than the background signal activity.
Vertex sharp transients
Vertex sharp transients are EEG potentials which has variable amplitude (up to 250 mV) and length of time between 50 ms to 200 ms. Sequences of vertex sharp transients are composed at least two repetitive potentials lasting at least 2 s.
Figure 1.4: Sequence of vertex sharp transients. Top 4 channels: Bipolar parasagittal EEG derivation on the left side : P3O1 , F7T3 , T3T5 , FzCz; C3A2: C3 connected to right ear (A2). (Figure source: Sleep Medicine 3, Consensus Report, Mario Giovanni Terzano et al.:
Atlas, rules, and recording techniques for the scoring of cyclic alternating pattern (CAP) in human sleep, p 187-199, 2002)
K-complex sequences with or without spindles
complex sequences is composed at least two consecutive complexes. Each K-complex presents a biphasic pattern or triphasic pattern consisting of a rapid negative com-ponent and a slower positive wave. The K-complex may be mixed with or followed by a sleep spindle. The length of time of a single K-complex is between 0.5 to 2 s; therefore, K-complex sequence duration is more than 2 s.
Polyphasic bursts
Polyphasic bursts consist of high-voltage delta waves and intermixed with theta, alpha, or beta waves. Polyphasic bursts can include at least two delta peaks.
K-alpha
K-alpha is composed of a K-complex and the following as an alpha (8-13 Hz) burst.
The overall duration of K-alpha is at least 2 s.
Figure 1.5: K-complexes sequences associated with spindles. Top 5 channels: EEG deriva-tion as in Figure 1.3 (Figure source: Sleep Medicine 3, Consensus Report, Mario Giovanni Terzano et al.: Atlas, rules, and recording techniques for the scoring of cyclic alternating pattern (CAP) in human sleep, p 187-199, 2002).
Intermittent alpha
At sleep onset, the alpha rhythm field tends to spread forward, then it fragments into intermittent sequences in sleep stage 1. When sleep progresses, it disappears. Before it vanishes, the EEG activity of Alpha may also increase in amplitude and decrease in frequency.
EEG arousals
EEG arousals could interrupt sleep continuity shortly and the duration of EEG arousals is more than 3 s. It is a phenomenon that are sudden frequency shifts to faster rhythms such as theta, alpha, beta, but not spindles.
1.3.2 Scoring Rules for CAP or non-CAP
From previous researches, we can list systematically with CAP scoring rules [15].
Requirements for scoring a CAP sequence
1. A CAP cycle consists of an A-phase and followed by a B-phase.
Figure 1.6: Polyphasic burst in stage 2 sleep. Top 5 channels: EEG derivation as in Fig-ure 1.3 (FigFig-ure source: Sleep Medicine 3, Consensus Report, Mario Giovanni Terzano et al.: Atlas, rules, and recording techniques for the scoring of cyclic alternating pattern (CAP) in human sleep, p 187-199, 2002).
2. Each CAP sequence is composed of at least two CAP cycles.
Onset and termination of a CAP sequence
3. All CAP sequences start with a A-phase and end with a B-phase.
Non-CAP
4. If the CAP sequence disappear more than 60 s, This period of time is scored non-CAP.
5. An isolated A-phase means that is preceded or followed by another A-phase but the duration between them is more than 60 s. An isolated A-phase is scored non-CAP.
6. The A-phase in the end of the CAP sequence is scored as non-CAP.
7. B-phase with duration between 2 s and 60 s is the signal between two A-phases.
Minimal criteria for the detection of a CAP sequence
8. CAP sequences have no upper limits on overall duration and on the number of CAP cycles.
Figure 1.7: K-alpha complex in stage 2 sleep. Top 5 channels: EEG derivation as in Figure 1.4 (Figure source: Sleep Medicine 3, Consensus Report, Mario Giovanni Terzano et al.: Atlas, rules, and recording techniques for the scoring of cyclic alternating pattern (CAP) in human sleep, p 187-199, 2002).
Stage shifts
9. CAP sequence is scored in non-REM sleep and CAP sequence scoring can extend across adjacent sleep stages so it is not interrupted by a sleep stage shift.
Temporal limits
10. Each phase of CAP is between 2 s and 60 s in duration.
11. If the B-phase between two A-phases less than 2 s, the two A-phases are scored an A-phase.
12. If the B-phase between two A-phases longer than 60 s, the two A-phases is scored two different CAP sequences.
Amplitude limits
13. phase is the repetitive element represented by the recurring EEG feature. The A-phases phasic activities is at least 1/3 higher average amplitude than the background signal activity.
Figure 1.8: Intermittent alpha rhythm in stage 1 sleep. Top 5 channels: EEG derivation as in Figure 1.3 (Figure source: Sleep Medicine 3, Consensus Report, Mario Giovanni Terzano et al.: Atlas, rules, and recording techniques for the scoring of cyclic alternating pattern (CAP) in human sleep, p 187-199, 2002).
14. B-phase is a background signal. Phase B is used to separate the A-phase.