this got my brain working, so I looked up the effect THC has on bronchodilation. My thinking here is what happens when someone smokes Cannabis in the first place in regards to its assistance or restriction of O2's ability to reach your red blood cells in the first place. As DukeJH seems throws out there, what is the damage of the chemicals in the smoke, also, does the smoke itself cause the bronchial tubes to close which would also constrict oxygen.
Obviously without more time and access to the full journal articles to difficult to throw out too many conclusions, but the research I saw (Brittish Medical Association '97) (IACM-Bulletin of 12 November 2000; Calignano A, et al)(Del Bono N, Sconosciuto F, Del Bono L. '81) indicated that Marijuana assists with Bronchodilation, but it seems that the have been a couple of studies, including the above referenced article that talk about the counterproductive effects caused by the smoke. One other really interesting snippet I found from an article I just read seems to conclude that while THC does produce Bronchodilation, in doses over 200 micrograms, it actually has the opposite effect and has a constricting effect. In other words, in small doses it helps, but at a certain point, it has the opposite effect:
"Doses of A1-THC which are large enough to cause bronchodilatation when taken orally are invariably associated with psychological effects, and direct
bronchial administration of a smaller dose is, therefore, more appropriate. Smoking marijuana can cause bronchodilatation in asthmatic patients (Tashkin et al., 1974) and prevent experimentally- induced bronchospasm (Tashkin, Shapiro, Lee &
Harper, 1975) but the dose is difficult to control, the smoke irritates the airways and long-term use can impair lung function (Henderson, Tennant & Guerry,
1972). More recently, therefore, aerosolized A'-THC has been investigated. The smallest dose which has previously been shown to cause bronchodilatation
when given by aerosol to asthmatic patients is 200 micrograms
(Williams et al., 1976). Other workers have found larger doses given in this way to be effective, but not without psychological or local irritant effects (Tashkin, Reiss, Shapiro, Calvarese, Olsen & Lodge, 1977; Vachon, Robins & Gaensler, 1976)." Br. J. clin. Pharmac. (1978), 5, 523-525
it goes on to say:
"The optimal dose would appear to be 100 micrograms. The differences between 100 and 200 micrograms were small. We have found that doses higher than this commonly cause coughing and restrosternal discomfort, even in normal subjects, and this is more pronounced in asthmatics, in whom a transient increase in airways
obstruction may be found. It is possible that the local irritant effect of Al-THC even at 200 jig caused bronchoconstriction in all but the largest airways,
which opposed the direct bronchodilator activity of the drug, and this may have been responsible for the inversion of the dose response effect with respect to
FEV1." (Br. J. clin. Pharmac. (1978), 5, 523-525)
So I guess what that would infer is that if you took in too much THC (even as a tasty treat like a brownie so that you dont get any of the nasty stuff that comes with the smoke) that it could have the effect of constricting your bronchial tubes, thereby restricting the bodies ability to get O2 into the lungs in the first place.
Obviously this is very limited, and tons of research has been done that this doesn't even scratch the surface of, but I would wonder if the Cerebralvascular benefits citied in the OP's post would really do all that much good unless the dose was controlled enough to make sure that
a) the THC maintains its effects as a Bronchiodialator, thus allowing more o2 to reach the alveoli, thus giving it the opportunity to bond with the red blood cells and;
b) is not so high that it has the reverse effect, which would reduce the available o2 in your lungs.