I think the problem doesn't lie in those sites, it probably lies in me. There were some rather technical terms here, and I think I didn't understand half of it, and I wasn't able to competently visualize how the ECG works in the 1940s.
In the piece I'm currently working on, there's a scene set in the 1940s, soviet Russia. It's also an urban fantasy, so there's an alternate history that ties in with our own version. Basically, the protagonist is a Fox-shifter, immortal, and he's being tortured at the cruel mercy of a fellow Fox. Right now, they're trying to break his will, trying to get him to co-operate, and in my mind he's hooked onto an ECG that monitors his heart rate, so that they can tell if he's lying, or if he's feeling any particularly strong emotion. So that they can use whatever he feels strongly about against him.
In my mind, the ECG works like the version we have today, with the electronic graph and the little beeps. I belatedly realized that the version back then should be different from what we have now. I've read up that there used to be the soaking of limbs into saline solution, but was it still so in the 1940s?
A huge thank you in advance for help rendered!