Brain oxygenation is determined by the product of CaO2 and the cerebral blood flow (CBF), the modification of one or the other can affect the neuronal O2 availability.

Besides the effect of the PaO2, the CBF is also regulated by the PaCO2. During effort in state of hypoxia, the drop of the PaO2 associated to a potential decrease of the PaCO2 and therefore of the CBF, can create an important dizziness between the demand and the supply of cerebral O2.

It seems that hypoxia can trouble in a significant way the response of central neurons, just as the production of a motor cortex generated motor command.

Studies suggest that exercise in severe hypoxia condition can constitute a necessary threat for brain oxygenation and the motor command, with the consequence a decrease of the exercise performance.

This projects aim to study effects of hypoxia on the brain function for patients suffering from chronic respiratory disease. Neurophysiologic responses of the brain while resting or exercising, including drip and cerebral oxygenation, cortical excitation and motor command resulting for hypoxic subjects before and after a treatment to correct abnormalities of gaz in blood.

The study will use a multidisciplinary and supplementary methodological approach : the near-infrared spectroscopy (NIRS) to appreciate the drip and cerebral oxygenation, CBF, neurostimulation procedures and electromyography (EMG) to appreciate the cortical excitability, measure the level of central activation and motor command.

The goals of this study will be :

• Measure the drip and cerebral oxygenation, the cortical excitability, mechanisms of voluntary activation and central fatigue to the effort for the chronic hypoxemic patient compared to healthy control subjects.
• Analyse disruptions of locomotion parameters and posturographyc, in simple and double task, involving different levels of cerebral task.
• Analyse acute effects of an improvement of arterial oxygenation for patients suffering from chronic obstructive pulmonary disease (COPD) on drip and cerebral oxygenation, cortical excitability, mechanisms of voluntary activation and central fatigue.
• Evaluate effects of a treatment by continuous positive airway pressure (CPAP) for patients suffering from obstructive sleep apnea (OSA) with the same parameters.

Inclusion Criteria:

COPD patients

• stages GOLD III - IV, FEV1/FVC ratio < 0,7 and maximum voluntary ventilation (MVV) < 50% of predicted values
• BMI < 30 kg/m²
• Age between 18 and 80 years
• Non-smoking or ex-smoker (stop since more than 3 months)
• Stable condition since more than 3 months
• PaCO2 < 45 mmHg resting with ambiant air
• No OSA diagnostic

OSA patients

• Severe OSA recently dignosed (apnoea-Hypopnoea Index (AHI) > 30)
• Score on Epworth Sleepiness Scale (ESS) > 10
• Age between 18 and 80 years
• BMI < 30 kg/m²

Control subjects

• Age between 18 and 80 years
• BMI < 30 kg/m²
• Non-smoker
• Without any chronic respiratory pathology, cardiovascular, metabolic, renal or neuromuscular, vestibular and/or visual disorder

Exclusion Criteria:

OSA and COPD patients

• Pathologies cardiovascular, neuromuscular, métabolic, renal
• Alcoholism
• BMI > 30 kg/m²
• Psychiatric disorders or history of behavioural disorders, vision disorders, vestibular disorders, neurologic disease sensitive to disrupt the postural control and the walking, cognitive disorders
• Instability since less than 3 months
• Counter argument to the application of an external magnetic field

Control subjects

• Respiratory pathologies, cardiovascular, neuromuscular, metabolic, renal
• Alcoholism
• BMI > 30 kg/m²
• Psychiatric disorders or history of behavioural disorders
• Counter argument to the application of an external magnetic field