FIG. 33:  The ASV devices monitor recent average minute ventilation or peak flow in a moving time window of 3–4 min.  During this 3–4 min period the device calculates the average minute ventilation or peak flow, and as this time window moves forward through the night, the ASV device can react to recent developments in minute ventilation or peak flow.  By continuously calculating a target ventilation or peak flow throughout the night, the ASV device adjusts pressure support up or down, as needed to achieve the target.  This also means that in the clinical setting it is important when initiating ASV to allow the device a few minutes to adapt to the patient’s ventilation pattern, because the algorithm will probably function optimally after measuring minute ventilation or peak flow within this time window.