Techniques and devices for extending a piston and/or compression unit, for example connected to a medical device such as a mechanical CPR device, to accommodate different sized patients, are described herein. In some cases, a piston of a mechanical CPR device may include an inner piston at least partially slidable into an external piston sleeve. In one aspect, some aspects, the piston includes sleeves which can move relative to each other to extend the piston. In additional aspects, the compression mechanism may also extend downward toward the patient. In all aspects, the change in length of the piston may be detected and used to modify movement of the piston, for example to more safely perform mechanical CPR.

Examples of the disclosure are directed to mechanical compression devices that can adjust a location of a compression position relative to a patient. One or more of the mechanical compression devices can adjust the compression position in an adjustment plane that is generally perpendicular to a patient. Some of the mechanical compression include support columns that have actuators that can be set asymmetrically to adjust the compression position and/or can be tilted relative to the backboard to adjust the compression position. Other examples includes mechanical compression devices that have multiple actuators that can be used to adjust the compression position as well as provide compressions.

Among other things, in one aspect, we describe a system for assisting with cardiopulmonary resuscitation (CPR). The system includes at least one sensor; and one or more processors configured for calculating a chest compliance relationship based on data received from the at least one sensor, and determining a neutral position of chest compression based at least in part on a feature of the chest compliance relationship. The system can take the form of an active compression-decompression device.

A device for applying compressions to a chest of a patient has a suction cup configured to contact the chest of the patient. The device also has a valve configured to allow air to exit or to enter a cavity through a boundary of the suction cup, the cavity being between the suction cup and the chest of the patient, and the device has a pump configured to evacuate the cavity through the valve.

A mechanical cardiopulmonary resuscitation (CPR) device that includes a central housing, a telescoping piston, and a driving component. The telescoping piston includes an outer piston sleeve structured to move toward and away from the patient's torso and toward and away from the central housing. The proximal end of the outer piston sleeve is configured to remain within the central housing when the telescoping piston extends from the central housing. The telescoping piston includes an inner piston sleeve within the outer piston sleeve that is structured to move relative to the outer piston sleeve toward and away from the patient's torso. The proximal end of the inner piston sleeve is configured extend beyond the central housing when the telescoping piston extends from the central housing. The driving component is configured to drive the telescoping piston to extend toward the patient's torso and retract the telescoping piston from the patient's torso.