I am almost 100% certain the pulsed DC will present no problem. The static DC will cause blood to clump together. In the many capillaries in the body, the capillaries are often so narrow at the ends that a single blood cell will fit through. I forgot where I read that, but that was the basic explanation why static Dc will cause a problem. The 4 hertz setting may actually be a better setting than 3.9 hertz. John Crane listed both 3.9 hertz and 4 hertz as regeneration and healing. Although John Crane was not up to the caliber of Royal Rife, he still know a great deal. 4 hertz is also listed for Malaria and I heard of several people curing malaria with a Beck zapper. It makes sense also because Malaria is primarily a disease of the blood. It would be good to know exactly what each zapper can do, so people know ahead of time. Additionally 4 hertz at 50% duty cycle will hit 12 hertz and 20 hertz. 20 hertz is one of the few frequencies almost all "pad-type Rife" sessions use. The short list of very solid frequencies would be 20, 464-465, 727-728, 787, 800 (or sometimes 802) and 880. Frequency lists in the 1,000's of frequency sets get a little ridiculous in complexity, but that short list is solid and cleans many microbes.