My father got 3 stents inserted during an angiogram. The reason was most likey that he was suffering from sleep apnea (his breathing stopped around 60 times an hour and his o2 saturation dropped to 50/60) without knowing it. In his case it was central sleep apnea but after he got a CPAP machine his o2 saturation went back up to > 90%. One easy way to check this is to wear a pusle oximater overnight and check the o2 saturation.