Does holding in marijuana smoke get you higher than blowing it out immediately?

In a 1989 study, subjects were asked to hold their breath in three different intervals ranging from zero to 20 seconds. There was no measurable difference between those who held the smoke and those that immediately exhaled. For those of you who swear that you get higher, you may be getting a stronger head rush from oxygen deprivation and an increased heart rate — not from the smoke.