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Cerebral circulation in REM sleep: is oxygen a main regulating factor?
P Lenzi1, G Zoccoli, A M Walker
1Department of Human and General Physiology, University of Bologna, Bologna, Italy.
Sleep Research Online : SRO
|May 31, 2001
Summary
Brain activation during sleep increases blood flow and glucose uptake, but oxygen (O2) uptake is limited. This study suggests O2 diffusion limitations cause localized hypoxia, impacting brain function and REM sleep.
Area of Science:
- Neuroscience
- Sleep Science
- Physiology
Background:
- Brain activation, particularly during the transition from NREM to REM sleep, involves increased cerebral blood flow, glucose uptake, and O2 uptake.
- Increased capillary PO2 and lactate production accompany brain activation, leading to hypotheses like oxidative machinery saturation.
- Existing data, such as hypoxic spots in the brain and altered tissue [H+] with varying arterial PO2, challenge the saturation hypothesis.
Purpose of the Study:
- To investigate the underlying mechanisms of anaerobic glycolysis and lactate production during brain activation, especially during REM sleep.
- To propose and provide evidence for an alternative hypothesis explaining observed physiological changes during brain activation.
Main Methods:
- Analysis of existing data on cerebral blood flow, glucose and O2 uptake, capillary PO2, and lactate production during brain activation.
- Evaluation of the impact of arterial hypoxia and hyperoxia on brain tissue and REM sleep duration.
- Formulation of the O2 diffusion limitation hypothesis based on physiological observations.
Main Results:
- Hypoxic microregions exist in the brain, particularly at mid-distances between capillaries, which increase during arterial hypoxia and decrease in hyperoxia.
- Tissue acidity ([H+]) decreases as arterial PO2 increases beyond 100 mmHg, suggesting a complex O2-tissue interaction.
- REM sleep duration is significantly reduced by hypoxic atmospheres and increased by hyperoxic atmospheres, supporting the O2 diffusion limitation theory.
Conclusions:
- Oxygen diffusion limitation in the brain, where microregions become hypoxic and rely on anaerobic glycolysis, is proposed as a key mechanism.
- These hypoxic microregions can influence local blood flow regulation through vasodilatatory signals.
- Pathological decreases in arterial PO2 or O2 delivery pose a specific risk during REM sleep due to these diffusion limitations.