Due to effects on the central nervous system, the cardiovascular system, etc., it is recommended that you start off with a max of four cycles. Eventually, you can work your way up to eight (apparently) but he recommends never more than eight due to the mind/nervous system-altering affects.
Put on the whole armour of God, that ye may be able to stand against the wiles of the devil. For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.
Spiritual Wrestlings 