Six months later, this patient was again referred to the sleep lab.  At this point his LVEF had improved to 47%, but he still had CSA, AHI 46 with 70% central respiratory events and still had a low PaCO₂.  Looking at his ventilatory response to CO₂, he had a very low ventilatory threshold, which was probably a partial explanation for why this patient still had CSA.  What this Figure also shows is how important it is to have sleep stability.  With sleep stability the patient experienced maximum saturation oscillation, which is related to the sleep apnea events.  In the early part of the night, where the sleep is quite stable, there should probably be fewer respiratory events.