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Concept
Sleep and breathing
Résumé
When we sleep, our breathing changes due to normal biological processes that affect both our respiratory and muscular systems.
Breathing changes as we transition from wakefulness to sleep. These changes arise due to biological changes in the processes that regulate our breathing. When we fall asleep, minute ventilation (the amount of air that we breathe per minute) reduces due to decreased metabolism.
During NREM sleep, we move through three sleep stages, with each progressively deeper than the last. As our sleep deepens, our minute ventilation continues to decrease, reducing by 13% in the second NREM stage and by 15% in the third. For example, a study of 19 healthy adults revealed that the minute ventilation in NREM sleep was 7.18 liters/minute compared to 7.66 liters/minute when awake.
Rib cage contribution to ventilation increases during NREM sleep, mostly by lateral movement, and is detected by an increase in EMG amplitude during breathing. Diaphragm activity is little increased or unchanged and abdominal muscle activity is slightly increased during these sleep stages.
Airway resistance increases by about 230% during NREM sleep. Elastic and flow resistive properties of the lung do not change during NREM sleep. The increase in resistance comes primarily from the upper airway in the retro-epiglottic region. Tonic activity of the pharyngeal dilator muscles of the upper airway decreases during the NREM sleep, contributing to the increased resistance, which is reflected in increased esophageal pressure swings during sleep. The other ventilatory muscles compensate for the increased resistance, and so the airflow decreases much less than the increase in resistance.
The Arterial blood gasses pCO2 increases by 3-7mmHg, pO2 drops by 3-9mmHg and SaO2 drops by 2% or less. These changes occur despite a reduced metabolic rate, reflected by a 10-20% decrease in O2 consumption, suggesting overall hypoventilation instead of decreased production/metabolism.
Periodic oscillations of the pulmonary arterial pressure occur with respiration.
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