Ultrasound and infrasound a must read. In talking with my dad, a cardio vascular tech, he explained to me the difference in dopplers; the lower the ultrasound frequency, the deeper the image penetration. It's why fetal dopplers are 2 & 3mhz while vascular dopplers are 4, 5, & 6mhz. My daughter’s BJU press textbook talked about ultrasonic waves and infrasonic waves. It did say ultrasonic can be dangerous over a long period of time. [I’ll be blogging this info at some point] A cat’s purr, which is infrasonic, is healing. Your cat may
not just be purring in contentment though. I find the information interesting because when I'm pregnant one of my cats is extremely attracted to my pheromones and often nuggles up to my round belly and just sits and purrs. Purring is not always contentment, but also for healing. Infrasound can travel through mountains, buildings, etc; while ultrasound is made to travel short distances.
When chickens were exposed to infrasound they grew denser bones. It's also why
cats heal better and have fewer injuries than dogs. I've heard pregnant women
can't swim with dolphins because they can see she's pregnant and they become
overly nurturing and can bump her to hard, accidentally, and she hogs the entire
dolphin’s attention in the dolphin encounters. http://paulapeterson.com/CatsPurr.html