Noise Immune Stethoscope
In combat casualty and civilian emergency medical environments, an unmet need existed for a stethoscope that would enable the user to hear heart and especially breathing sounds in the presence of high ambient noise. The noise can be from helicopter and fixed wing aircraft as well as ambulances where the prevailing sound levels preclude auscultation with standard stethoscopes. Without this capability, patients can potentially expire from undetected collapsed lungs or loss of intubation integrity.
In cooperation with the U.S. Army’s Aeromedical Research Laboratory (USAARL) in Ft. Rucker, AL, Active Signal Technologies developed a noise immune stethoscope that has been tested in simulated Blackhawk helicopter environments up to 110 dBA, the limit of USAARL’s acoustic reverberation chamber. The device uses a combination of highly sophisticated sensors, signal conditioning and Doppler technology to accomplish this goal. It has been judged by the USAARL staff to be the only device in existence that enables the caregiver to hear heart and lung sounds in these environments. US Patent Application Publication No. US 2007/0165872.
This Stethoscope has been tested in several environments, military and civilian. Its first tests were at Ft. Rucker’s USAARL’s reverberation chamber (see "A Dual-Mode Noise-Immune Stethoscope For Use In Noisy Vehicles", Houtsma, et. al, 4th ASA/ASJ Joint Meeting, Honolulu, HI, Dec. 2006) followed by successful airworthiness testing at the same facility. Further military field testing has been conducted by a special ops unit stationed at Ft. Campbell, Ky. with follow-up testing by a Army Rangers unit.
Civilian testing has been conducted on various medevac units, and a formal study has just begun in England using a passive only version of the stethoscope in their upgraded medevac fleet with the McDonald Douglas MD902 Explorer.
In all cases, except for the highest background noise environments, the passive option allows perfectly adequate auscultation with the active Doppler feature available for higher noise environments.
The device is shown below in its current configuration as modified in response to several rounds of Army user testing.
Dual-mode noise immune stethoscope
In addition to its external noise rejecting capability, the stethoscope provides greater sensitivity and fidelity than existing air-coupled bell and diaphragm stethoscope heads through its solid state direct contact sensor. The device detects and amplifies sounds over a much greater bandwidth than a conventional mechanical stethoscope, the response of which typically rolls off sharply above 1kHz.
Active Signal and the Army are currently pursuing FDA clearance in parallel with productization / manufacture of the device. The Air Force is also considering a modification to the stethoscope that will provide a visual display that can be incorporated into the monitoring suite used by the Critical Care Air Transport Teams (CCATT).
The ability to hear subtle and low amplitude sounds, particularly in the presence of competing ambient noise, has wide-ranging applications beyond medical diagnosis. These applications are also enhanced by the increased sensitivity and bandwidth noted above. For example, an Army Special Operations group that was testing the device for its medical potential also remarked on its capability as a contact sensor for eavesdropping through walls. In the maintenance arena the device may have application in both diagnosing faults in machinery / pipes and potentially preempting failure by listening for tell-tale frequencies that reflect wear, increased clearances or rubbing, for example.
On the medical side, potential exists for applications beyond simple auscultation in loud environments. For example, observations at the University of Maryland Shock Trauma Center have revealed high pitched sounds associated with pneumothorax that are inaudible with a conventional stethoscope and have never before been reported in the literature. Similarly, in environments remote from the hospital setting cardiovascular findings may be enabled that would otherwise only be possible in the ultrasound lab. For example it may be possible to interrogate the condition of artificial heart valves and characterize bruits accompanying stenosis in major arteries. The Army is also initiating internal studies to evaluate the potential diagnostic capability of the Doppler mode for characterizing respiratory disfunction.
Future embodiments of the device may incorporate a display, record, and capture system for data viewing and archiving for later comparison or more precise diagnosis using algorithms that Active Signal has developed for brain injury diagnostics.