I have been told by doctors, as well as read in a variety of books about ADD, that in order to increase dopamine levels etc and improve brain functioning that exorcise is key. I’m rather skeptical about inversion tables, sounds like something a crafty inventor came up with as a get rich quick scheme. Pesonally, I would think excercise is the better choice since it’s required for general health not just ADD.
I just googled a bit more on this and found the following.
A small study published in a Russian medical journal in 1985 concluded that while inversion raises cerebral blood supply, the brain’s use of oxygen during inversion actually decreases.
source: http://www.livestrong.com/article/338934-what-are-the-benefits-of-gravity-inversion-tables/
In an about.com article about the benefits of exercise for ADD I found the following quote from famous Dr. Ratey:
There are many reasons for exercise in ADHD. Exercise almost immediately elevates dopamine and norepinephrine and keeps them up for a period of time so that it acts like a little bit of Ritalin or Adderall. It also helps to still the impulsivity and still the cravings for immediate gratification as it works to wake up the executive function of the frontal cortex, which in turn allows for delay, better choices, a bit more time to evaluate consequences.
source: http://add.about.com/od/treatmentoptions/a/ratey.htm for the complete article
Anyway, Just sayin’, but if you wanna hang like a bat go for it 
…..