Interrogation of most current PAP devices can provide an estimated apnea-hypopnea index (AHI), and careful attention to these estimates may be helpful if an oronasal or oral interface is substituted for a nasal appliance. Furthermore, autotitration settings may be advantageous over fixed pressures in patients who switch between different interfaces. Clearly, given the difficulty in establishing stable breathing in some of Andrade et al's subjects using pressures up to 20 cm H2O, this is a strategy that warrants careful investigation in future research. Finally, patients who remain or become symptomatic after an interface change, even if estimated AHI is normal, may require retitration in the sleep laboratory. The AHI reported by a PAP device is an estimate only, based on indirect measurement of airflow. This AHI may differ significantly from polysomnographic AHI, particularly with respect to hypopnea.,, Moreover, there is no consistent method by which these devices estimate AHI, and it has been recommended that these values be interpreted with caution. Finally, interface changes may yield other unintended consequences, such as the development of central sleep apnea.