A wearable cardioverter defibrillator system, comprising: a support structure configured to be worn by a patient; a power source connected to a first circuit ground; an energy storage module connected to the first circuit ground and configured to be coupled to the support structure, to be charged from the power source and to store an electrical charge; a discharge circuit coupled to the energy storage module; a patient parameter sense port (219; 319; 419) configured to be coupled to the patient; a measurement circuit (220; 320; 420) configured to render a physiological input from the patient parameter sense port (219; 319; 419), the measurement circuit including an isolating circuit configured to electrically isolate the patient parameter sense port from the first circuit ground; and a processor (230; 330; 430) connected to a first circuit ground (224; 324; 424; 524; 524), operatively coupled to the measurement circuit (220; 320; 420), and configured to: determine from the physiological input whether or not a shock criterion is met, and control the discharge circuit to discharge the electrical charge through the patient if the shock criterion is met,. characterized in that the power source and the energy storage module are connected to a first circuit ground (224; 324; 424; 524; 624) and that the measurement circuit (220; 320; 420) includes an isolating circuit (222, 322; 422; 522; 622) configured to electrically isolate the patient parameter sense port (219; 319; 419) from the first circuit ground (224; 324; 424; 524; 624), wherein the isolating circuit (522; 622) includes an isolated circuit portion connected to a second circuit ground (526; 626) isolated from the first circuit ground (524; 626) and a non-isolated circuit portion connected to the first circuit ground (524; 624), and the isolating circuit (522; 622) further includes a voltage-difference reducing circuit between the first and second circuit grounds (524, 626). a support structure configured to be worn by a patient; a power source connected to a first circuit ground; an energy storage module connected to the first circuit ground and configured to be coupled to the support structure, to be charged from the power source and to store an electrical charge; a discharge circuit coupled to the energy storage module; a patient parameter sense port (219; 319; 419) configured to be coupled to the patient; a measurement circuit (220; 320; 420) configured to render a physiological input from the patient parameter sense port (219; 319; 419), the measurement circuit including an isolating circuit configured to electrically isolate the patient parameter sense port from the first circuit ground; and a processor (230; 330; 430) connected to a first circuit ground (224; 324; 424; 524; 524), operatively coupled to the measurement circuit (220; 320; 420), and configured to: determine from the physiological input whether or not a shock criterion is met, and control the discharge circuit to discharge the electrical charge through the patient if the shock criterion is met,. characterized in that the power source and the energy storage module are connected to a first circuit ground (224; 324; 424; 524; 624) and that the measurement circuit (220; 320; 420) includes an isolating circuit (222, 322; 422; 522; 622) configured to electrically isolate the patient parameter sense port (219; 319; 419) from the first circuit ground (224; 324; 424; 524; 624), wherein the isolating circuit (522; 622) includes an isolated circuit portion connected to a second circuit ground (526; 626) isolated from the first circuit ground (524; 626) and a non-isolated circuit portion connected to the first circuit ground (524; 624), and the isolating circuit (522; 622) further includes a voltage-difference reducing circuit between the first and second circuit grounds (524, 626). determine from the physiological input whether or not a shock criterion is met, and control the discharge circuit to discharge the electrical charge through the patient if the shock criterion is met,. characterized in that the power source and the energy storage module are connected to a first circuit ground (224; 324; 424; 524; 624) and that the measurement circuit (220; 320; 420) includes an isolating circuit (222, 322; 422; 522; 622) configured to electrically isolate the patient parameter sense port (219; 319; 419) from the first circuit ground (224; 324; 424; 524; 624), wherein the isolating circuit (522; 622) includes an isolated circuit portion connected to a second circuit ground (526; 626) isolated from the first circuit ground (524; 626) and a non-isolated circuit portion connected to the first circuit ground (524; 624), and the isolating circuit (522; 622) further includes a voltage-difference reducing circuit between the first and second circuit grounds (524, 626).