The sound of air being sucked through partially collapsed airways and the vibration of the soft palate is evidence of obstructed airflow. As snoring becomes more severe, there may be further limitation of airflow with the possibility of complete airway collapse and no movement of air whatsoever. A situation where there is no effective movement of air to ventilate the lungs is termed apnoea and it follows that those who experience collapse of the upper airway with a subsequent loss of ventilation through either the nose or mouth during sleep, despite normal or increased efforts to breathe, are suffering from obstructive sleep apnoea (OSA). It is not uncommon for complete obstruction to occur several hundred times a night in advanced OSA.
Another form of apnoea occurs when no effort is made to breathe; a pause of 10 seconds or longer between breaths is commonly accepted as a significant apnoeic event. The rate at which we breathe and the volume of air taken in during inspiration is driven by the need to maintain a sufficient blood oxygen level. This is coordinated by a part of the brain called the respiratory control centre which, under normal circumstances, receives messages relating to the amount of oxygen in the blood and sends appropriate messages to the lungs to maintain that level. Sometimes there is a breakdown in either the message going to or being sent from the respiratory control centre so that there is no effective attempt to breathe. The pause in respiration resulting from an absent or inadequate message from the brain is called central apnoea. It is possible for snorers to suffer both obstructive and central apnoeas during sleep but we will be dealing mostly with the obstructive component.
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