Principles of operation of adaptive servo-ventilation

Principles of operation of servo-ventilation are depicted.
The airflow tracing (top) depicts a classical crescendo (orange arrow) and decrescendo (red arrow) pattern of Cheyne-Stokes breathing, followed by an ensuing central apnea. The servo-controlled automatic adjustment of the inspiratory positive airway pressure (IPAP) level is inversely related to the changes in peak flow levels over a moving time window (bottom). Specifically, during the crescendo pattern of peak flow rates (orange arrow), the pressure assist (or IPAP) level decreases in order to dampen the rise in inspiratory peak flow rate (or tidal volume). Conversely, during the decrescendo pattern of peak flow rates (red arrow), the pressure assist (or IPAP) level increases in order to dampen the fall in inspiratory peak flow rate (or tidal volume). Therefore, the servo system dampens the inherent oscillatory behavior of the patient's breathing pattern and smooths respiration. During a central apnea, the device's backup rate becomes active and ventilates the patient (bottom).
The IPAP level is depicted in centimeters of H₂O with a maximum IPAP (IPAPmax) set at 17 cm H₂O and a minimum IPAP (IPAPmin) set at 9 cm H₂O (horizontal interrupted blue lines). The expiratory positive airway pressure (EPAP) level was set at 7 cm H₂O. The pressure assist or pressure support level is equal to the IPAP minus EPAP level.