Publication of the Association of Polysomnographic Technologists • Spring, 2003 • www.aptweb.org
Cyclic Alternating Pattern —
A New Way to Look At Sleep
BY WILLIAM W. ECKHARDT BS RPSGT CRT
yclic alternating pattern (CAP) is a phenomenon where the EEG
activity is periodic within non-REM sleep. CAP is characterized by
sequences of transient electro cortical events that are distinct from
background EEG activity and recur at up to 1-minute intervals. This peri odic activity originally thought to be arousals is now theorized to be the
process of sleep maintenance and sleep fragmentation. CAP in sleep
has been shown to reflect disturbed sleep and may give a more accurate picture of sleep quality. This theory extends the AASM arousal classification with periodicity and possibly a pre-arousal phenomenon. Some
investigators believe that CAP can help determine when to treat and
what to treat with, in sleep disordered breathing (SDB).
C
CAP scoring is not meant to replace how we score today but rather
enhances our understanding of sleep and perhaps therapy. CAP introduces a periodicity element to scoring and may give us incite into the
physiological sleep mechanisms and processes.
The electro cortical events occur in cycles or periods comprised of
phase A + phase B and one determines the rate that these periods
occur. Phase A is a repetitive EEG feature of the period. Phase B is the
interval between the repetitive phase A. CAP can occur spontaneously
in NREM sleep. Subtypes have been identified. Subtype A1 may occur
when the brain is trying to maintain sleep. The other two subtypes A2
and A3 may occur due to central nervous system arousal.
CAP can be seen on most standard montages we use in clinical
sleep laboratories. Most referential montages use (C4-A1, C3-A2, O2A1, and O1-A2). Bipolar montages used in seizure montages also
work well for scoring CAP. Standard filter settings lend themselves to
reflect the appropriate EEG waveforms. Auxiliary channels for clinical
studies remain the same i.e. SaO2, respiratory effort, ECG, Leg EMG,
and intercostals.
A CAP sequence consists of two or more CAP cycles each having
an A and B phase lasting between 2 and 60 seconds (see Fig. 1).
These sequences begin with an A phase and end with a B phase.
Phase A is identified by activating complexes of R&K sleep stages.
Phases may cross over different stages of sleep in NREM sleep and
will therefore have different patterns within the same CAP sequence.
Conventional staging should be done prior to identifying CAP. When an
EEG pattern is identified as having the characteristics of phase A it is
initially considered a phase A candidate. In order to be scored in a
CAP cycle it must be preceded or followed by a phase B. Non-CAP is
scored when there is a period of >60 seconds between two A phases. Phase As that end a CAP sequence are counted as non-CAP. Or
because CAP is scored by the succession of CAP cycles, a phase A
plus phase B, if there are three consecutive A phases followed by a
non-CAP state, the CAP sequence is interrupted at the end of the
second B phase. The period will be scored as non-CAP starting from
the third A phase. The phases should have balance of duration
between phases A and B (see Fig. 2). Changes are often joined by
changes in airflow, HR, and SaO2. Phase A and B are differentiated
by phase A increases and phase B decreases in HR, muscle tone and
respiratory activity.
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Fig. 1: Definitions:
Delta bursts, Vertex sharp transients, K-complex
sequences (spindles possible), Polyphasic bursts,
K-alpha, intermittent alpha, EEG arousals.
Phase A — recurring EEG
feature (repetitive part of
periodic activities). A’s are
slower higher voltage, faster
lower voltage rhyuthms or a
mix of both.
Phase B — background,
separates Phase A episodes.
+
Period or Cycle
The sum of Phase A & B
duration. Give us the
recurrence rate.
Each phase is 2-60s.
Delta Burst: ≥ 2 waves freq. Of 0.5 to < 4 Hz with amp. ≥ 1/3
higher than background activity.
Verrtex Sharp Transients: EEG potentials of 50-200 ms duration
& up to 250 uV.
K-complex Sequences: ≥ 2 consecutive Ks 0.5 to 2 s duration,
appear in stages 2, 3, 4.
Polyphasic Bursts: Groups of high-volt. delta waves mixed with
alpha or beta rhythums, appear in stages 2, 3, 4 but mostly in
stage 2 prior to REM onset.
K-Alpha: K-complex followed by an alpha burst, ≥ 2s duration.
Intermittent Alpha: 8-13 Hz wake, sleep onset then disappears,
may be seen during stage shifts and in REM.
EEG Arousals: Spontaneous freq. shifts to a faster rhythum ≥ 3s
Arousals of different levels are grouped into three categories, different subtypes may be seen in the same CAP sequence. In REM sleep
A phases are made up of only arousals.
Subtype A1 consists of periods of K complexes and delta bursts,
polyphasic bursts, vertex sharp transients, with < 20% of EEG desynchrony. Intermittent alpha is included in this subtype or may be scored
independently.
Subtypes A2 fast and low amplitude EEG patterns proceeded by or
mixed with slow waves of high voltage. Some increase in both muscle
tone and respiratory rate is seen. EEG desynchrony of 20-50%.
Subtypes A3 an EEG pattern, lasting ≥ 2/3 of phase A’s length and,
composed of fast low voltage activity, of which > 50% is composed of
EEG desynchrony. A movement artifact will fall into this category.
Parrino et al has shown a remarkable correlation between subtypes
A2 and A3 with AASM arousals.
➟
Publication of the Association of Polysomnographic Technologists • Spring, 2003 • www.aptweb.org
Fig. 2: Scoring CAP
Stage shifts in non-REM do not effect whether it is Phase A or
Phase B, stage shifts do not interrupt sequence.
1. Score study according to R&K-AASM guidelines.
2. CAP sequence — has repetitive CAP cycles.
CAP cycle — phase A + phase B beginning with A ending with B.
Each phase is of 2-60s duration.
3. Non-CAP — Continuous non-REM EEG pattern for > 60s when there
is no CAP for > 60s. This includes a Phase A preceded or followed
by another Phase A but with > 60s of non-CAP. A Phase A that ends
a CAP sequence is counted as non-CAP (this is the Transition).
4. CAP Scoring Requirements — Amplitude of Phase A must be
1/3 higher than the Background voltage. This is determined by EEG
activity 2s prior and 2s after the Phase A.
In 1997 Scharf states that “While much needs to be done to verify
the relationship between CAP rates and sleep quality, the potential of
this parameter in identifying sleep quality is exciting.” Clinical studies
have demonstrated a relationship between poor sleep and elevated CAP
rates. Changes in CAP are not seen in Rechtschaffen and Kales scoring
method however in 2001 Terzano et al wrote the Atlas, rules, and
recording techniques for the scoring of cyclic alternating pattern in
human sleep.
Scharf et al have found that non-apneic snorers had higher CAP
rates in sleep than did non-snores and that the CAP rate in snores
decreases when wearing an external nasal dilator. CAP rates also have
been shown to increase in insomniacs, people with dysthymia, peri- and
postmenopausal women and decrease in elderly insomniacs receiving
temazepam. Postmenopausal women taking estrogen replacement
therapy have improvement in objective and subjective evaluation of
sleep. These improvements correlate with reduced CAP rates. CAP
Body movements can trigger or interrupt CAP sequences.
You must have at least 2 CAP cycles to have a sequence. CAP sequence
must contain complete CAP cycles of A + B. Phase A is scored only if
preceded/followed by another A within the 2-60s time limits.
CAP sequence must be preceded by non-CAP unless:
1. No time limit before the 1st CAP sequence arising from non-REM sleep.
2. No time limit after wake/sleep transition.
3. No time limit after REM/non-REM transition.
Normally CAP does not occur in REM but some pathologies do
cause CAP sequences in REM. CAP often precedes the transition
from non-REM to REM ending prior to REM onset.
Body movements may be included in a CAP sequence if linked to one
or more Phase As within the 2-60s time limit so long as other scoring requirements are met.
Some examples of CAP:
A
B
A
Fig. 3: A CAP cycle phase A + phase B, followed by another phase A.
continued on page 32
APT Flashcards — Study Material
for the Registry Exam!
Fig. 4: All night histogram of CAP patient. Note the lack of events in REM
(being studied). Also see the architecture and how events relate.
See APT Merchandise order form on page 45.
31
Publication of the Association of Polysomnographic Technologists • Spring, 2003 • www.aptweb.org
Cyclic Alternating Pattern — A
New Way to Look At Sleep
continued from page 31
rates appear to be sensitive to the “first night effect.” And therefore
Scharf also states that this may be an important parameter that could
aid in the evaluation of hypnotic drugs and other treatments for transient insomnia.
Fig. 6: Two CAP cycles followed by a phase A. Meets minimal requirements
for a CAP sequence being at least three phase As in succession.
I find it interesting to watch these patterns during acquisition and
scoring. For years I have seen parts of this phenomenon going across
my screen/paper. I had never linked the epochs into a phenomenon. I
have seen a patient with their best breathing in REM and total chaos in
stage 2 some of the time. Beware when titrating these people with high
CAP rates. Some researchers say that it is very hard if not impossible
to treat CAP with CPAP and at best possible to treat with Bilevel. ★
References
Scharf MB, Stover R, McDannold M, Herbert K, Berkowitz D, Comparative Effects of Sleep
on a Standard Mattress to an Experimental Foam Surface on Sleep Architecture and CAP
rates Sleep, Vol. 20, No. 12, 1997
phase A
phase B
Fig. 7: Subtype A1 - EEG complexes composed of K-complexes and delta bursts.
Terzano MG, Parrino L, Sherieri A, Chervin R, Chokroverty S, Guilleminault C, Hirshkowitz M,
Mahowald M, Moldofsky H, Rosa A, Thomas R, Walters A, Atlas, rules, and recording techniques for the scoring of cyclic alternating pattern (CAP) in human sleep Sleep Medicine Vol.
2 No. 6 Nov. 2001
Scharf MB, McDannold M, Zaretsky N, Spinner O, Stover R, Berkowitz D, Conrad C,
Evaluation of Sleep Architecture and Cyclic Alternating Pattern Rates in Depressed Insomniac
Patients Treated with Nefazodone Hydrochloride American Journal of Therapeutics 1999
6(2)
Parrino L, Smerieri A, Rossi M, Terzano MG, Relationship of Slow and Rapid EEG
Components of CAP to ASDA Arousals in Normal Sleep Sleep, Vol. 24 No. 8, 2001
About the Author
Mr. Eckhardt is the Director of Education at Sleep HealthCenters in Newton Mass. He is available for lectures and can be reached at e-mail [email protected].
Subtype A1 phase A
phase B
Subtype A2
Fig. 8: Subtype A2 - EEG desynchrony 20-50% of phase A with a mixture of
fast and slow waves. Note polyphasic bursts.
Subtype A3
phase A
phase B
Fig. 9: Subtype A3 - Note K-alpha
A
B
A
Fig. 5: Phase A & B and their correspondence to respiratory events.
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Fig. 10: Subtype A3 - EEG is mostly fast low-voltage waves with >50% of
phase A comprised of EEG desynchrony.