An isotropic restraint was a medical device used to prevent any movement from a patient.
When Neelix's lungs were removed by a Vidiian in 2371, The Doctor used an isotropic restraint to implement holographic lungs in Neelix's body. The restraint prevented him from moving, so that the lungs could stay aligned in his body. (VOY: "Phage")
In 2372, a mutated Tom Paris was placed under an isotropic restraint while his DNA was restructured with bursts of antiproton radiation. This procedure involved the restraint to be connected to the warp engines in order to receive the radiation. However, Paris was able to break the restraint and escape. (VOY: "Threshold")