A-Flex is a Philips-Respironics brand-specific term for CPAP Exhalation pressure relief.
According to the Philips-Respironics website: "A-Flex is designed to work with our clinically proven auto CPAP algorithm to improve comfort even more by matching pressure delivery to the patient’s entire breathing cycle. Like C-Flex, A-Flex provides flow-based pressure relief at the beginning of exhalation. Like Bi-Flex, A-Flex softens the pressure transition from inhalation to exhalation to provide additional comfort in an auto-CPAP mode. The pressure profile mirrors the patient’s breathing, and with the auto algorithm intelligence, it will respond to the patient’s therapeutic need throughout the sleep session."