The Doom novel 'Infernal Sky' goes into greater detail about the blue spheres. They're called "Soul Spheres" and are semi-sentient creatures (capable of replicating a blurry human face). Their primary use is evidently medical.
Medbot found us!
Its voice had always been pleasant. Now it was
music to my ears: "Sears and Roebuck sent a message.
Part of your unit has been damaged."
I slowed down, caught my breath, tried to be
coherent. "We need your help. We need one of those,
oh, you know--the blue spheres that help sick
"They are called soul spheres."
"How . . . appropriate," whispered Albert, hanging
on the edge of consciousness.
"Yes," Fly got into the act. "Like the one you used
The medbot's voice was unemotional but not a
monotone. It could have been my imagination, but I
thought it sounded sorry when it said, "That was the
Beyond that, the only mention of the "Soul Spheres" in any detail occurs in the Doom Manual