Diminished Cerebral Circulatory Autoregulation
in Obstructive Sleep Apnea Investigated
by Near-infrared Spectroscopy

Larisa P. Safonova, Antonios Michalos, Ursula Wolf, Jee Hyun Choi,
Martin Wolf, William W. Mantulin, Dennis M. Hueber, and Enrico Gratton

We applied near-infrared spectroscopy (NIRS) to assess cerebral tissue oxygenation and hemodynamics in obstructive sleep apnea (OSA) sufferers and control volunteers. We designed NIRS sensors and applied measurement schemes that included certain polysomnography parameters, such as arterial hemoglobin oxygen saturation (SaO2), heart rate (HR), and respiratory signal (RS), together with NIRS parameters, such as oxy- ([O2Hb]), deoxy- ([HHb]), total hemoglobin ([tHb]) concentrations, and tissue hemoglobin oxygen saturation (SO2). Twenty-one volunteers (8 females, 13 males, age 22-74 years) participated in the study. Eight were OSA sufferers, while 13 constituted the control group. Measurements were conducted during breath holding exercises and 30-45 minute daytime naps. In comparing OSA subjects with controls during breath holding, a smaller increase or even a decrease in SO2, [O2Hb], and [tHb] and a simultaneous larger increase in [HHb], confirmed insufficiency of the circulatory compensatory mechanism that prevents brain tissue hypoxia. Changes in cerebral oxygenation and hemodynamics due to hypoxia during breath holding showed statistically significant differences (p<0.05) between control and OSA subjects and between non-snorers and OSA subjects (p<0.03 for Δ[O2Hb], Δ[HHb], Δ[tHb], and ΔSO2). NIRS provides the clinician with important, direct insight on the cerebral tissue oxygenation and hemodynamics related to the chronic intermittent hypoxia in OSA for potential identification of individuals at risk for cerebrovascular morbidity.

 

The Dynamic Topography of Individual Sleep Spindles
Scott M. Doran

Healthy adult non-REM sleep was recorded using 64-channel electroencephalogram (EEG) to image millisecond changes in the scalp topography of individual sleep spindles. Matched frequency filtering isolated fast (13-15 Hz) and slow (11-13 Hz) ends of the spindle spectrum. Sequential voltage maps of filtered data across time produced topographically precise movies of individual spindles. Slow spindles (centered around 12 Hz) show a more dynamic topography, primarily over the frontal cortex and with bilateral variability between and within spindles. Fast spindles (centered at 14 Hz) are topographically and dynamically limited to the superior central and parietal cortex. Peak activity patterns suggest that slow spindles result from cortical-cortical activation following spindle initiation, while fast spindles in the EEG reflect only cortico-thalamic activation.

 

Intentional Versus Reactive Cosleeping
Kathleen D. Ramos

Parent-child cosleeping is typically considered by researchers and parenting advisors to be a unitary construct. However, existing evidence suggests that parents who purposefully sleep with their young children at night (intentional cosleepers) may be very different than those who co-sleep in reaction to existing sleep problems (reactive cosleepers). The object of the current study is to compare these two groups along three dimensions: demographics, sleep behaviors, and maternal attitudes toward sleep. Participants recruitment occurred through two parenting e-mail listservs; one considered mainstream and one devoted to attachment parenting. The survey was completed online and submitted electronically. Participants included 450 mothers in the United States (mostly White and well-educated) with a target child between the ages of 6 and 59 months who cosleeps at least occasionally. Reactive cosleepers and intentional cosleepers reported many differences in their children's sleep behaviors and their own attitudes about family sleep, but few demographic differences. Frequent all-night cosleeping and parental ideological endorsement of cosleeping characterize intentional cosleeping. Reactive cosleeping is characterized by reduced parental satisfaction. Reactive and intentional cosleepers both report shared beliefs with their partners and a select group of friends, but a definite lack of shared beliefs with other elements of their social support systems. The distinction between intentional and reactive cosleeping appears to be a valid and useful one. Researchers should be aware of the differences when studying sleep in families with young children.

 

Perfusion of a 5-HT1A Antagonist in the Cat DRN
Increases Wakefulness and Extracellular 5-HT Level in DRN

Alvhild A. Bjørkum, Robert E. Strecker, Chiara M. Portas,
Tarja Porkka-Heiskanen, Mahesh Thakkar

The serotonergic system is involved in modulation of sleep and waking and shows a state dependent activity: waking (W) > slow wave sleep (SWS) > rapid eye movement sleep (REM). Our laboratory has recently shown that microdialysis perfusion of a 5-HT1A receptor agonist 8-OH-DPAT in the DRN decreases serotonin (5-HT) release and increases REM sleep in the freely moving cat. We now demonstrate that DRN perfusion of a 5-HT1A antagonist (p-MPPI) produces an increase in the extracellular 5-HT levels in the DRN paralleled by an increase in waking as measured by polygraphic techniques. These results are compatible with the blockade of the inhibitory 5-HT1A somatodendritic autoreceptors on 5-HT neurons leading to increased serotonergic activity and a corresponding increase in wakefulness.

 

Nocturnal Elevation of Extracellular Adenosine in the Rat Basal Forebrain
James T. McKenna, Lynda J. Dauphin, Kara J. Mulkern,
Aaron M. Stronge, Robert W. McCarley and Robert E. Strecker

The purine nucleoside adenosine may facilitate sleepiness by inhibiting neurons of the magnocellular basal forebrain that are known to enhance cortical activation during wakefulness. In vivo microdialysis sample collection in rats coupled to microbore high performance liquid chromatography analysis determined extracellular basal forebrain adenosine levels across the 24 hours of the day (lights on/off 07:00/19:00). During the dark period, when rats are predominantly active and awake, adenosine levels were elevated two-fold. Also, basal forebrain adenosine increased during 6 hrs of sleep deprivation and declined slowly thereafter. The data support the hypothesis that basal forebrain adenosine levels may reflect the homeostatic sleep drive that occurs daily in animals exhibiting a diurnal pattern of sleep and wakefulness.

 

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