Clinical course of apnea and HV attacks on fifth day after admission: Patient 1. The patient presented a 3.5-minute episode of apnea after an HV attack with a minimum SpO2 of 60% and cyanosis of the lips and nail beds. The patient did not exhibit hypoxemia during the HV attack or during normal respiration. X1 and X3 represent the apneic starting time. X2 and X4 represent the time of the assisted ventilation by bag-mask. X1X2 and X3X4 are the lengths of the apneic times, which were 3.5 and 2 minutes, respectively. X1X2 and X3X4 were recorded, but times X1,X2, X3, and X4 were not recorded correctly. HV: hyperventilation.