Respiratory control and instability in the breathing pattern during sleep. Unstable breathing during sleep plays an important role in the development of sleep related breathing disorders (SRBD). Periodic breathing, as a hallmark of this instability, is a common initiator of these disorders. In addition, structure and function of the upper airway are prone to intrinsic and extrinsic, congenital and acquired abnormalities which are as well responsible for the pathogenesis of SRBD.