clinical applications of spectral analysis winni hofman, phd university of amsterdam medcare...
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Clinical Applications ofSpectral Analysis
Winni Hofman, PhD
University of Amsterdam
Medcare Amsterdam
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• Introduction of spectrum calculations
• Spectra and sleep staging• Spectral analysis for differentiating various
night patterns• Spectral analysis and arousals• Frequency analysis of snoring
Outline
4 Examples of applications of Spectral Analysis
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Spectral Analysis is a tool to:• Quantify the frequency content of
signals, like EEG or snore signal, for further calculations
• Help you with your manual sleep stage scoring
• Detect problems in the recording, e.g. 60 Hz noise
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Frequency content of a signal
EEG frequency bands:Beta - > 12 Hz
Sigma - 12 – 14 Hz
Alpha - 8 – 12 Hz
Theta - 4 – 7 Hz
Delta - 0.5 – 4 Hz
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Frequency content of a signalR&K definition of sleep EEG:
• Stage 1: Relatively low voltage, mixed frequency EEG in 2 – 7 cps range without rapid eye movements
• Stage 2: 12-14 cps sleep spindles and K complexes on a background of relatively low voltage, mixed frequency EEG
• Stage 3: 20%-50% of high amplitude, slow wave activity
• Etc…….
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Complex signals
• Signals like the EEG are complex signals, existing of many superimposed waveforms with:– Various frequencies– Various amplitudes– Various phase relationships
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Describing frequency content of a signal
Sine waves are used for description because they can be defined exactly by their:
– Frequency– Amplitude– Phase
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Sine wave
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Cosine wave
1 cycle
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Spectral Analysis describes a signal:
• By calculating the contributions of the various superimposed frequency components
• Shows these contributions in a Power Spectrum plot
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Spectral analysis and Sleep Stages
• Differences in frequencies between sleep stages are visible in a Power Spectrum
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R&K definition of stage Wake:
• Wake: alpha activity and/or low voltage, mixed frequency activity
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WakeAlpha peak
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R&K definition of stage 2:
• Stage 2: 12-14 cps sleep spindles and K complexes on a background of relatively low voltage, mixed frequency EEG
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Stage 2
Theta peak
Alpha peak
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R&K definition of stage 4:
• Stage 4: > 50% of high amplitude, slow wave activity
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Stage 4
Delta peak
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R&K definition of stage REM:
• Stage REM: a relatively low voltage, mixed frequency EEG (in conjunction with episodic REMs and low amplitude EMG)
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Stage REM
Theta peak
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Delta waves with superimposed alpha
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Power spectrum S4 with alpha
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Spectral colour plot
• Shows changes in frequency content of a signal over longer time period (for example a whole night)
– Colour: power– Y-axis: frequency– X-axis: time
• Each point in time in the Spectral colour plot represents a power spectrum of a 30 sec epoch
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Spectral analysis and various sleep patterns
• Changes over time in the distribution of the various frequencies follows changes in sleep pattern:– Rhythmicity in delta sleep– REM sleep periodicity– Periods of wakefullness
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Delta activity
Low voltage mixed frequency in REM sleep 50 Hz notch
filter
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Transition to stage Wake
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Delta
Alpha
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Normal sleep pattern
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Insomnia sleep pattern
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CPAP titration
Sleep pattern during CPAP titration
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Heinzer et al., Chest 2002
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Spectral analysis and arousal(Black et al., Am.J.Respir.Crit.CareMed., 2000)
• Apnea can be followed by arousal
• Micro-arousals are often not visually recognized as arousals according to ASDA criteria
• Spectral analysis can give more insight into EEG alterations occurring after an apnea
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Arousal and Eso
Black et al., 20.., Chest
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Arousal and Eso
Black et al., 2000, Am.J.Respir.Crit.CareMed.
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Arousal and Eso
Black et al., 2000, Am.J.Respir.Crit.CareMed.
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Arousal and Eso
Black et al., 2000, Am.J.Respir.Crit.CareMed.
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Spectral analysis of snore sounds
• Differences in frequency content of snoring sounds might be clinically important (high versus low frequency)
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Snores with high frequency sound vibrations
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Snores with low frequency sound vibrations
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High frequency snore sound vibrations
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Low frequency snore sound vibrations