mary j. morrell, donald w. mcrobbie, rebecca a. quest, andrew r.c. cummin, ramesh ghiassi, douglas...
TRANSCRIPT
Mary J. Morrell, Donald W. McRobbie, Rebecca A. Quest, Andrew R.C. Cummin, Ramesh Ghiassi, Douglas R. Corfield
2003
Kathy Liu
IntroductionWhat is obstructive sleep apnea (OSA)?-periodic breathing-episodic hypoxemia-repeated arousals from sleep-1-4% of middle-aged adults-24-30% of elders(Bixler EO, Vgontzas AN, Lin T, et al.)
Introduction-Both hypoxia and sleep fragmentation
independently result in cognitive deficits.-In rats, chronic exposure to intermittent hypoxia
during sleep results in cellular damage within the CA1
region of the hippocampus (Gozal D, Daniel JM, Dohaich
GP.)-Hippocampal cortex is sensitive to hypoxic damage-Hippocampus is closely associated with the neural
processing of memory (Maguire EA, Gadian DG,
Johnsrude IS, et al.)
Hypothesis OSA is associated with changes in brain
morphology; in particular, a focal loss of gray matter within the hippocampus and other cortical areas linked with cognitive function
MethodParticipants-7 right handed, male patients with newly
diagnosed OSA (median, range: age 50, 28-65)-7 healthy, non-apneic male -all patients and controls had normal lung
function-no patients had started continuous positive
airway pressure treatment -body weight >130kg or girth measurement
>152cm were excluded
MethodProcedure-recruited from sleep clinic -an overnight home study during which breathing,
O2 saturation , heart rate and body position were monitored
-an apnea was defined as a >50% reduction in airflow for more than 10s
-hypopnea : between 50%-75% reduction in airflow for more than 10s
-median range of apnea hypopnea index (AHI)=28 events/h
Method -MR brain scan -Voxel-based morphormetry (VBM) -Normalisation: To account for normal differences
in brain size and shape and in positions of the gyri, each brain image is resized and reshaped to fit a standardised brain template
-Segmentation: each brain image is segmented into three compartments (cerebrospinal fluid, gray and white matter), based on the signal intensity of the MR image
-Smoothing: To account for small scale differences in brain morphology
Result-significantly lower gray matter concentration
in the OSA patients within the left hippocampus
-No further significant focal gray matter differences were seen in the right hippocampus and in other brain regions
-No difference in total gray matter volume between apneics and controls
(mean ± SEM : 0.914 ± 0.012 vs. 0.913 ± 0.0131)
Discussion-acute hypoxia produces both molecular and cellular
neuronal damage-hippocampal neurons show increased sensitivity to
low-O2 conditions and repetitive intermittent hypoxia reduces neuronal excitability in the CA1 region (Gozal D, Daniel JM, Dohaich GP)
-gray matter loss in patients results from the hypoxic insult
-role of frequent arousals and the associated sleep fragmentation on any structural changes is less clear
-cortical excitability is reduced following sleep deprivation (Manganotti P, Palermo A, Patuzzo S, et al.)
Strength and limitation-moderate OSA is associated with focal gray
matter loss in areas required for cognitive function
-relatively small study size and relatively moderate AHI and hypoxaemia present in patient group
-not able to relate the disease severity to the amount of gray matter loss
-not correlated gray matter loss with indices of cognitive function
Further research
-correlation of gray matter loss with cognitive
function
-whether treatment of the OSA could prevent
the neuronal damage
-loss of gray matter is the result of treatment?
Reference-Bixler EO, Vgontzas AN, Lin T, et al. Effects of age on sleep apnea in men: I.
Prevanlence and severity. Am J Pespir Crit Care Med 1998; 157: 144-8
-Gozal D, Daniel JM, Dohaich GP. Behavioural and anatomical correlates of chronic
episodic hypoxia during sleep in the rat. J Neurosci 2001; 21: 2442-50
-Maguire EA, Gadian DG, Johnsrude IS, et al. A voxel-based morphometric study
ofagein gin 465 normal adult human brains. Neuroimage 2001; 97: 4398-403
-Manganotti P, Palermo A, Patuzzo S, et al. Decrease in motor cortical excitability in
human subjects after sleep deprivation. Neurosci Lett 2001; 304: 153-6
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