Acoustic sensor pad for physiological monitoring

The Army Research Laboratory has developed an acoustic sensor pad technology that is useful for combat casualty care and soldier performance monitoring. Heartbeats, breaths, motion, and other physiological sounds relating to injured and uninjured soldiers can be detected, transmitted, and analyzed for diagnostic purposes. The acoustic sensor pad is a fluid-filled bladder with a hydrophone that couples well to the soldier's torso. Since the human body is mostly water, the pad acts as a fluid extension of the body to form an acoustical conduit to a sensitive hydrophone within the pad that detects body sounds. The sensing pad can be a hand-held version for the field medic or doctor, or a torso-sized pad incorporated into casualty transport hardware such as litters or gurneys. Acoustic analysis of the sensor-pad output can provide amplitude, phase, frequency, duration, rate, and correlative information that may be useful for medical diagnosis, patient care, and research. Data collected with prototype devices show excellent signal-to-noise ratios for heart and breath sounds; such devices could be used in the field to detect conditions such as irregular heartbeats, cardiac distress, obstructed airways, sucking chest wounds, fluid in the lungs, or other respiratory and circulatory emergencies. Joint time-frequency Fourier analysis of sensor output shows that human cardiopulmonary function contains infrasonic (sounds below 20 Hz) signals, which cannot be beard with human ears, but may be useful for medical diagnostics. If soldiers were equipped with small monitoring sensor pads with transmit capability to carry in contact with the torso, squad performance level could be assessed, or those missing in action could be medically interrogated from a remote location for heart and breathing sounds. The technology can also be used to monitor operators of vehicles or aircraft, and initiate appropriate safety actions in the event of sudden incapacitation resulting from weapons fire, heart attack, or blackout.