This is why you should strengthen your lungs and respiratory system using the powerlung or powerbreathe(google search. They are worth the money) and doing wind sprints which is running than doing a fast 30-40 second sprint and than returning to normal running speed.
Eating a lot of nuts and seeds which are high in fat helps also.
These methods will train your lungs to utilize oxygen which in turn will increase your thc absorption but the thing is you will be able to hold in the vapor long without any feel of unease and because this is not smoke but clean vapor you will get blasted and utilize all of the vapor which means your vapor will go a long way.
BTW, the difference between powerlung and powerbreathe is that the powerbreathe only works out your inhale strength while powerlung works both your inhale and exhale strength. These two are considered the best, at least in their price range, for strengthen the respiratory system.
If you are really serious about getting high having a strong immune system(eating whole foods nuts, seeds, leafy vegetables(juicing for high affect), fruit, beans, grains), nervous system(resistance training) and cardiovascular system(aerobics) will get you BLASTED especially when vaporizing or eating herb off of very little.
Here's an article on wind sprints:
http://www.healthcentral.com/diet-exercise/fitness-survival-guides-81076-137.html
How Do I Do Wind Sprints?
During the middle of your aerobic exercise, add several short bursts of intensity by going faster or increasing the resistance. Don't try to go as fast or as hard as you can. Just go fast enough so that after 20-40 seconds you are breathing harder.
The real secret to increasing fitness with wind sprints is what you do AFTER the sprint.
To get the maximum benefit from your sprint, you've got to return to the speed you were going prior to the sprint. Do not stop or go slower than pre-sprint speed. After you have recovered from the sprint, repeat this sprint/recover cycle. You can eventually add up to 5-10 sprints per workout. Here's a bonus: when you add sprints to your workout you can shorten the total exercise time.