Sleep deprivation enlarges the blood vessels and reduces vascular compliance, according to research published in Sleep.
The findings could have important implications for the results of neural imaging methods that rely on measuring cerebral blood flow (CBF) or volume (CBV), such as functional magnetic resonance imaging and positron emission tomography.
“Chronic sleep restriction or sleep deprivation could push the vasculature to critical levels, limiting blood delivery,” note Derrick Phillips (Washington State University, Pullman, USA) and co-workers. This could lead to “metabolic deficits with the potential for neural trauma,” they add. The team found, however, that lower basal neural activity during recovery sleep might allow blood vessel compliance to recover.
In a study involving seven adult female rats, Phillips and colleagues used surgically implanted cortical electrodes to measure evoked auditory responses over a 72-hour period. The auditory responses were instigated by a series of periodic 65 decibel clicks. Hemodynamic responses were measured simultaneously using near infrared spectrophotometry at three different wavelengths to determine changes in oxygenated and deoxygenated hemoglobin during varying sleep deprivation conditions.
The researchers report significant reduction in evoked hemodynamic amplitudes in the rats after 8 or 10 hours of sleep deprivation compared with no sleep deprivation. In addition, there was an increase in steady state oxyhemogobin levels during deprivation and this was maintained for up to 9 hours before returning to baseline.
The study “revealed that vasodilation is larger for extended waking periods and can lead to blunted hemodynamic responses during initial recovery sleep,” comment Steffen Krieger (Monash University, Melbourne, Victoria, Australia) and Gary Egan (Max-Planck Institute for Human Cognitive and Brain Science, Leipzig, Germany) in an editorial. They note that it is unsurprising, perhaps, that sleep deprivation results in diminished or slowed cognitive and motor responses.
“This has important consequences for the conduct of functional neuroimaging studies,” Krieger and Egan write. “The level of sleep deficit at the time an experiment is performed may have a significant influence on the functional activation results.”
The editorialists conclude: “Future studies are needed to quantify the effects of sleep deprivation in humans on hemodynamic responses and individual physiological parameters, such as CBF or CBV.” They suggest that researchers should also look at the effects of sleep deprivation on circadian rhythms.
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