I appreciate this may seem a little off-topic, but it is in fact
relevant (as I will indicate later), especially in that it may be
useful in conjunction with optimising the physical state of our brains
and bodies, as in the case of held-breath underwater swimming.
Essentially, there's some controversy over whether plants in the
bedroom are advisable or not. For one thing, certain kinds of plant
are supposed to help purify the air and remove toxins (which
presumably can only be a beneficial thing): see for example
http://answers.google.com/answers/threadview?id=437186 . What is of
more concern, however, is that they produce oxygen during the daytime
when photosynthesis occurs, and produce trace amounts of carbon
dioxide during the night.
Now...
Some people advise against keeping plants in the bedroom on account of
the CO2 production
(http://health.yahoo.com/experts/drmao/218/improve-your-sleepwith-a-bedroom-makeover,
http://fengshui.about.com/od/faq/f/plantsinbedroom.htm).
Some people argue that the amount of CO2 produced is negligible unless
the room is sealed / airtight:
(http://au.answers.yahoo.com/question/index.php?qid=20070612124148AAZHiWZ)
And yet, on the other hand, some athletes invest huge amounts of money
in "high-altitude simulators" which reduce oxygen levels and so
increase the efficiency of air-usage in the body: (see, for example,
http://www.mensjournal.com/healthFitness/0701/performance_tents.html).
The controversy reminds me somewhat of Win's criticisms of hyperbaric
oxygen treatment alongside his advocacy of held-breath underwater
swimming: (http://www.winwenger.com/ebooks/guaran3.htm). Indeed: I'm
left wondering whether more highly oxygenated air is preferential to
our well-being or in fact damaging to it. So, I thought it would be
advisable to get some perspectives from people who have perhaps
already done some research on this topic, or perhaps even from people
with pertinent background knowledge (appropriate academics,
biologists, scientists, doctors, etc.).
So, anyone have any pertinent knowledge they'd like to share? All
contributions gratefully received - and it would be hugely appreciated
if you could source your information, considering the confusion! 
Many thanks in advance,
.
