Pulse wave amplitude drops during sleep are reliable surrogate markers of changes in cortical activity.
BACKGROUND
During sleep, sudden drops in pulse wave amplitude (PWA) measured by pulse oximetry are commonly associated with simultaneous arousals and are thought to result from autonomic vasoconstriction. In the present study, we determine whether PWA drops were associated with changes in cortical activity as determined by EEG spectral analysis.


METHODS
A 20% decrease in PWA was chosen as a minimum for a drop. A total of 1085 PWA drops from 10 consecutive sleep recordings were analyzed. EEG spectral analysis was performed over 5 consecutive epochs of 5 seconds: 2 before, 1 during, and 2 after the PWA drop. EEG spectral analysis was performed over delta, theta, alpha, sigma, and beta frequency bands. Within each frequency band, power density was compared across the five 5-sec epochs. Presence or absence of visually scored EEG arousals were adjudicated by an investigator blinded to the PWA signal and considered associated with PWA drop if concomitant.


RESULTS
A significant increase in EEG power density in all EEG frequency bands was found during PWA drops (P<0.001) compared to before and after drop. Even in the absence of visually scored arousals, PWA drops were associated with a significant increase in EEG power density (P<0.001) in most frequency bands.


CONCLUSIONS
Drops in PWA are associated with a significant increase in EEG power density, suggesting that these events can be used as a surrogate for changes in cortical activity during sleep. This approach may prove of value in scoring respiratory events on limited-channel (type III) portable monitors.
Centre d'Investigation et de Recherche sur le Sommeil, Département de Médecine interne, Service de Neurologie, CHUV and Université de Lausanne, Lausanne, Switzerland.
Alexandre
A
Delessert
Fabrice
F
Espa
Andrea
A
Rossetti
Gilles
G
Lavigne
Mehdi
M
Tafti
Raphael
R
Heinzer
D000328:Adult; D001143:Arousal / Q000502:physiology*; D002540:Cerebral Cortex / Q000503:physiopathology*; D015331:Cohort Studies; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D017286:Polysomnography; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012307:Risk Factors; D012890:Sleep / Q000502:physiology*; D012891:Sleep Apnea Syndromes / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology*; D055815:Young Adult