Elaborate and powerful feedback mechanisms ensure adequate delivery. It is true that carbon dioxide retention, in this case achieved through breathing techniques, does increase blood flow to the brain. There is absolutely no reason to believe, however, that such increased flow is at all helpful to the developing brain. Despite the fact that patterning is theoretically bankrupt, if empirical evidence existed which demonstrated that patterning improves neurological development, it would be accepted and used. There are many mainstream interventions which are employed in modern medicine that lack a fully understood theoretical basis.
Physicians are, at their heart, practical individuals, and if something works, it works.
They require proof, however, that an intervention does indeed work and is safe. On this score, patterning has just not delivered. Over a period of approximately ten years in the late 60's and early 70's there were dozens of clinical trials comparing improvement in groups of developmentally delayed children given patterning treatment compared to controls who were given no treatment but similar amounts of attention. Although most of the studies had significant methodological flaws, some were fairly well designed. None were perfect.