Respiratory Effort Related Arousals are when a person awakens to instinctively 'effort' to breathe, when the upper airway is narrowed and breathing is difficult. Because they are a transition from sleep to a state of arousal, they do not meet the criteria for an apnea or hypopnea determination.
In other words, a respiratory effort awakening is when the respiratory effort lasts longer than 10 seconds due to upper airway airflow restriction that does not meet the criteria for apnea or hypopnea.
Often associated with snoring, it can be a sign of an underlying sleep disorder, such as upper airway resistance syndrome (UARS) or mild obstructive sleep apnea.