Positive airway pressure therapy with adaptive servoventilation: part 1: operational algorithms.

The beginning of the 21st century witnessed the advent of new positive airway pressure (PAP) technologies for the treatment of central and complex (mixtures of obstructive and central) sleep apnea syndromes. Adaptive servoventilation (ASV) devices applied noninvasively via mask that act to maintain a stable level of ventilation regardless of mechanism are now widely available. These PAP devices function by continually measuring either minute ventilation or airflow to calculate a target ventilation to be applied as needed. The apparatus changes inspiratory PAP on an ongoing basis to maintain the chosen parameter near the target level, effectively controlling hypopneas of any mechanism. In addition, by applying pressure support levels anticyclic to the patient's own respiratory pattern and a backup rate, this technology is able to suppress central sleep apnea, including that of Hunter-Cheyne-Stokes breathing. Moreover, ASV units have become available that incorporate autotitration of expiratory PAP to fully automate the treatment of all varieties of sleep-disordered breathing. Although extremely effective in many patients when used properly, these are complex devices that demand from the clinician a high degree of expertise in understanding how they work and how to determine the proper settings for any given patient. In part one of this series we detail the underlying technology, whereas in part two we will describe the application of ASV in the clinical setting.