Naval Submarine Medical Research Laboratory 

 NSMRL Report 1214 25 JULY 2000 

NOISE REDUCTION STETHOSCOPE 

FOR UNITED STATES NAVY 

APPLICATION 

by 

Joseph S. Russotti, Robert P. Jackman, 

Thomas P. Santoro, and Deborah D. White 

Released by 

M.D. Curley, CAPT, MSC, USN 

Commanding Officer 

Naval Submarine Medical Research Laboratory 

Approved for public release; distribution unlimited 
Correspondence and reprint requests: 

Joseph S. Russotti 

Naval Submarine Medical Research Laboratory 

 PO Box 900 

 Naval Submarine Base 

Groton, CT 06349-5900 

 

Acknowledgment and Disclaimer 

This project was conducted under Naval Medical Research Development Command Research 

Work Unit 64771N-M00933.002-5624. The opinions and assertions expressed in this report are 

those of the authors and are not to be construed as official or reflecting the views of the 

Department of the Navy, the Uniformed Services University of the Health Sciences, the 

Department of Defense, or the US Government. This research has been conducted in compliance 

with all applicable federal regulations governing the protection of human subjects in research. 

The authors wish to acknowledge Derek Schwaller, our biomedical engineer, for his tireless, 

conscientious achievements in instrumentation, data gathering, digital editing and signal analysis. 

Special acknowledgment is due to Surgeon Commander Steven Ryder, Royal Navy for 

invaluable guidance during the design of this research and clinical evaluation of our selected 

"patients". We greatly appreciate the voluntary efforts of LT Michael Waltz, MC, who took over 

as medical monitor for LT Jackman MC, and who, was not only able to enlist our highly trained 

medical listeners on short notice, but also endured at least five hours as a subject himself. We 

appreciate the efforts of all our participants for their conscientious performance, patience and 

endurance in such a demanding task. We are intensely grateful to Lynne Marshall for her 

extensive editorial efforts as a reviewer to help make this report more clearly convey our 

findings. 

This research is dedicated to Thomas E. Hanna, a Braveheart who led by example. Thanks for 

your confidence and support from the onset. 

Joseph S Russotti, is Principal Investigator, and Thomas P. Santoro, LT Robert Jackman, MC, 

LT Deborah White, MSC, are all Associate Investigators on this project at the Naval Submarine 

Medical Research Laboratory. The co-authors are listed in alphabetical order since each 

contributed equally to this research project. 
ii

TABLE OF CONTENTS

TABLE OF CONTENTS ..................................................................................................................... II

SUMMARY PAGE ...................................................................................................................... III

ABSTRACT .................................................................................................................................IV

INTRODUCTION................................................................................................................................1 

Currently available technology...........................................................................................2 

OBJECTIVE ..................................................................................................................................3 

RESEARCH PLAN .........................................................................................................................3 

The modular approach ........................................................................................................4 

Product evaluation requirements ........................................................................................5 

Product selection.................................................................................................................6 

PHASE 1: LABORATORY EVALUATION............................................................................................7 

METHOD..................................................................................................................................7 

Subjects...............................................................................................................................7 

Experimental Design ..........................................................................................................7 

Environmental Simulation..................................................................................................7 

Environmental Sounds........................................................................................................7 

Vital-Sounds Signals ..........................................................................................................8

Recording of Vital-Sounds Stimuli ....................................................................................8 

Source Stimuli ....................................................................................................................9 

Stimulus Generation ...........................................................................................................9

Stimulus Presentation .........................................................................................................9

Test Procedure ....................................................................................................................9 

RESULTS AND DISCUSSION ...................................................................................................10 

CONCLUSIONS .......................................................................................................................22 

PHASE 2: FIELD EVALUATION.......................................................................................................23 

Method......................................................................................................................................23 

Subjects.............................................................................................................................23 

Experimental Design ........................................................................................................23 

Evaluation Questionnaire .................................................................................................23 

RESULTS....................................................................................................................................24 

Analysis ............................................................................................................................24 

CONCLUSIONS ...........................................................................................................................27 

SUMMARY & CONCLUSIONS.................................................................................................30 

REFERENCES .............................................................................................................................34 

APPENDIX A:.............................................................................................................................37 

APPENDIX B:.............................................................................................................................39 

APPENDIX C:.............................................................................................................................41 

APPENDIX D..............................................................................................................................51 

APPENDIX E: .............................................................................................................................57 

APPENDIX F: .............................................................................................................................60 
iii

SUMMARY PAGE 

The Problem: Conventional stethoscopes cannot function effectively unless ambient noise is 

maintained at approximate examination-room levels. This serious limitation inhibits diagnosis 

and monitoring of patients in a variety of common military medical situations: in field hospitals, 

in high ambient noise environments such as engine rooms, in vehicles such as ambulances, fixed 

and rotary wing aircraft, or in hyperbaric chamber treatment facilities. Trying to measure blood 

pressure, determining if a faint heart-beat is present in a casualty, or listening to respiratory 

events can be nearly impossible under field conditions. 

The Approach: The objective of this project was to evaluate commercial off-the-shelf 

(COTS) products and recommend one or several compact noise-reducing/canceling stethoscopes 

for field, medical-transport, and shipboard use, in moderately noisy environments (up to 90 dB 

SPL). At the onset of this project a working group was convened to assess Navy need and 

requirements for a noise-reducing stethoscope for casualty care and general medical use. In 

general terms, given present and projected COTS state-of-the-art technology, a modular

approach using a simpler device tailored to the application, will be more cost-effective, for 

general-issue, than a single device. We selected three such simpler devices for laboratory testing 

using both the listening-headsets provided, and a highly accurate active noise cancellation (ANC) 

headset. 

The Findings: Laboratory data show exceptional performance of noise reduction 

stethoscopes in detection of heart/lung sounds, especially in noisy environments up to around 95 

dB SPL. Of greater relevance, a conventional device is unable to detect abnormal breath sounds 

when the noise field exceeds about 76 dB SPL; abnormal heart sounds can only be detected at 

levels below 81 dB SPL. For one of the two best COTS devices, the detection advantage over a 

conventional stethoscope for these abnormal sounds is 17 dB for breath and 12 dB for heart. 

Evaluation of the results from field data on normal heart/breath sounds confirmed their utility 

and provided user-suggestions on possible improvements in design. Contracted pre-production 

prototypes address several field-test recommendations. 

The Application: Based upon the results of this laboratory study and field analyses, we 

recommend two COTS devices for immediate military field use in environments below 95 dB 

SPL, and suggest a prototypic device as a candidate for Small Business Research Initiative 

(SBIR). We also recommend that these devices be used for their ability to provide the best 

possible electrical signal for telemetry and also as a signal source for COTS software programs 

that allow acoustic records of patient pathology. Recommended models are the SmartMedTM

Stethoscope by C.F. Electronics and Sonar Sound TM model 160 by Flow Scan. 

ADMINISTRATIVE INFORMATION 

This report was conducted under Naval Medical Research and Development Command 

Research Work Unit 64771N M00933.002-5624. The views expressed in this report are those of 

the authors and do not reflect the official policy or position of the Department of the Navy, 

Department of Defense, or the U.S. government. This report was approved for publication on 25 

July 00 and designated Naval Submarine Medical Research Laboratory Report 1214.
iv

ABSTRACT 

Conventional stethoscopes cannot function effectively unless ambient noise is maintained at 

approximate clinical levels (approximately 70 dB SPL). This serious limitation inhibits 

diagnosis and monitoring of patients in a variety of common military medical situations: in field 

hospitals, in high ambient noise environments such as engine rooms, in vehicles such as 

ambulances, fixed and rotary wing aircraft, or in hyperbaric chamber treatment facilities. Trying 

to measure blood pressure, determining if a faint heartbeat is present in a casualty, or listening to 

respiratory events can be nearly impossible under field conditions. Technology is immediately 

available to dramatically reduce this shortfall. The objective of this research was to evaluate 

several compact noise-reducing/canceling stethoscopes for field, moderately-loud medicaltransport, and shipboard use in noisy environments. Three commercial off the shelf (COTS) 

noise reducing stethoscopes, having electronic outputs, were evaluated quantitatively in a 

controlled laboratory study. Laboratory data on detection of vital sounds in operationallyrelevant sound-fields showed the devicesí ability to adequately present abnormal heart and 

breath sounds in 90 to 95 dB SPL. By their design these devices could tolerate higher levels of 

environmental noise that normally would interfere with such detection. This is a significant 

improvement in the tolerable ambient sound-field over an average 76 dB SPL upper limit for 

detecting abnormal breath sounds, and an average 81 dB SPL upper limit for detecting abnormal

heart sounds, when using a conventional device. After laboratory and operational evaluation, we 

are able to recommend two available COTS devices for military use, and to suggest a prototypic 

device, (a vastly miniaturized version of one of the two devices we recommend) as a candidate 

for Small Business Research Initiative (SBIR). It is also our recommendation that these devices 

be used for their ability to provide the best possible electrical signal for telemetry and also to any 

of the various software programs that allow acoustic records of patient pathology. 

KEY WORDS 

Stethoscope, Noise Reduction, Noise Reducing Stethoscope 
1

NOISE REDUCTION STETHOSCOPE 

FOR UNITED STATES NAVY APPLICATION 

INTRODUCTION

Since its initial development by Laennec in 1819 (1), the stethoscope has provided 

physicians with an invaluable diagnostic tool. This simple sound-powered device acoustically 

couples the small movements collected over a large area into relatively larger movements on the 

surface of the eardrum. By virtue of the differences in surface area between eardrum (55-90 mm2

) 

(2) and the pickup, (1300 mm2

) an acoustic gain is achieved. This elegant device continues to be 

a mainstay diagnostic tool to the present day and is a readily recognizable icon of the medical 

profession. It was originally designed for listening to sounds in the chest, heart and abdomen but 

other uses have been developed since its invention. In 1905 Korotkoff (3) published a report on a 

procedure that used the stethoscope to provide a measurement of blood pressure, both systolic and 

diastolic. Sekhar and Wasserman (4) developed a novel stethoscope that couples to the human 

eyeball to detect intracranial vascular lesions. More recently, Gallo et al. (5) used the stethoscope 

in reverse to measure sounds in the ear canal to detect tempero-mandibular joint abnormalities. 

The original stethoscope developed by Rene Laennec, approximately 180 years ago, was a 

monaural (one ear) mechanical instrument. Demonstrating the elegance of the original concept, 

only minor design changes have been subsequently incorporated. George Camman developed the 

binaural stethoscope approximately 30 years later, which increased the audibility of body sounds 

by feeding the signal to both ears. Blocking the ambient airborne sound to the occluded ear 

canals effectively decreased interfering external noise. The U.S. Air Force introduced the analog 

electronic amplifier stethoscope in 1955 to improve auscultation by the amplification of low-level 

body sounds. Unfortunately, this model also amplified surrounding noise as well as body sounds. 

In 1991, Ljungvall and Thulin (6) reported on their work to modify the stethoscope head into a 

smooth surfaced thin wedge shape for "hands-free" operation under the edge of a blood-pressure 

cuff. This research identified a major weakness in the conventional stethoscope: its sensitivity to 

the movements of the patient, hand tremor of the examiner, finger and nail movements, and self 

noise of the stethoscope's pickup-head moving against skin and against the pressure cuff during 

blood pressure measurement. Other limitations include the severe attenuation of sound 

transmission as a function of frequency, and the maxima and minima at very specific frequencies 

due to tubular resonance effects and differences in transmission properties observed between 

different stethoscopes (7). 

Interfering noise 

Emergency medical situations often occur in noise environments that preclude the use of the 

conventional stethoscope. Brogan et al. (8) reported that The Military Aircraft Command in 1966 

recommended that an electronic stethoscope be developed for use "...aboard aero-medical 

evacuation aircraft, since listening procedures were extremely difficult, if not impossible with 

regular stethoscopes." They reported their efforts to improve the signal-to-noise ratio by devising 

both an acoustically shielded pickup transducer and headphones, and by band-limiting the 

amplified signal. The belt mounted electronics package was quite large and clumsy at 6.75" x 6" 

and approximately 2" thick. While they reported improved performance, no mention is made of 

actual noise attenuation characteristics in their report. In 1969 Allred et al. (9) reported 

development and evaluation of two electronic stethoscopes of novel design which they later 

incorporated into a single device of conventional size and shape. The first design shifted the 

frequency of Korotkoff sounds and eliminated acoustic coupling between pickup and earpieces. 

The second stethoscope eliminated all acoustic coupling but avoided frequency shifting. 
2

Pasic and Poulton (10) reported on the increasing use of aero-medical transportation and 

concomitant increased intense noise exposure of helicopter pilots, aircrew and transported 

patients. They warn, "Noise makes impossible the use of the standard stethoscope to auscultate 

breath sounds, heart sounds or Korotkoff's sounds." In 1990 Bishop (11) reported on the inability 

to detect arterial sounds using a conventional stethoscope during a domestic commercial flight. 

This was confirmed by Cottrell and Kohn (12), who reported similar findings derived from their 

earlier 1989 published study of emergency treatments during commercial flight. A study by Hunt 

et al. (13) attempted to assess the capabilities of a traditional and an amplified stethoscope during 

air medical transport. They concluded "...flight nurses using a traditional or amplified 

stethoscope are unable to hear normal breath sounds during flight in an MBB BO-105 helicopter". 

Conventional stethoscopes (mechanical or electronic) cannot function effectively unless 

ambient noise is maintained at normally encountered clinical levels (which are approximately 70 

dB SPL1

). This serious limitation inhibits diagnosis and monitoring of patients in a variety of 

common medical situations: in hospital emergency rooms and trauma facilities (65 dB SPL to 80 

dB SPL); in emergency service vehicles such as ambulances, fixed and rotary wing aircraft (85 to 

140 dB SPL); or in areas where patients are attached to pulmonary ventilators, in neonatal 

incubators, or in hyperbaric chamber treatment facilities (75 to 95 dB SPL) (9, 10, 12, 14, 18). 

As a result of these reports and technological advances in modern computer and digital 

technology, electronic stethoscopes of varied types and capabilities are currently at various stages 

of development. The digital electronic stethoscope was introduced about 6 years ago. It is a 

microphone-transducer-amplifier concept with a digital signal processing capability built into the 

system. Unfortunately, it too has the same inability to function in noisy environments as the 

analog stethoscope. The search for a more effective stethoscope for use in high noise conditions 

persists (13). 

Currently available technology 

Currently, cumbersome prototype electronic devices exist for ascultation in noisy 

environments. Depending on how they reduce the noise, the devices are commonly referred to as: 

active noise cancellation (ANC), active noise reduction (ANR), and noise reduction (NR) 

stethoscopes. Within the group of acoustic devices that reduce noise using active means 

(electronic signal modification), ANC devices use an inverted real-time analog signal from 

another microphone directly to remove noise by cancellation (15). In ANR devices a transfer 

function is digitally applied to the real-time sensor microphone to mimic the response 

characteristics (bandwidth and spectral shape) of a conventional stethoscope-head to actively 

reduce noise. The transfer function may be a fixed equation or it can be derived from a control 

microphone that monitors signal and noise in real time. More elaborate procedures such as those 

reported by Zacharias et al. (16), Suzuki et al. (17), and most recently by Patel et al. (18), use 

adaptive filter techniques to modify the transfer function to compensate for differences in the 

noise transmission path through different points on the body. Other simpler NR electronic 

devices utilize pickup transducers immune to airborne noise for example, by translation of skin 

torsional forces (via a piezoelectric thin-film sensor) to an acoustic signal, or utilize noise 

attenuating materials around the sensor to reduce the interfering airborne sound on the sensor. 

Applying acoustic signals generated outside the range of human hearing, Kopczynski et al. (19) 

reported on an ultrasonic blood pressure monitoring device developed by USAF School of 

Aerospace Medicine that employs the "Doppler shift principle to detect blood flow and arterial 

 

1

 Decibels in Sound Pressure Level where 0 dB SPL is relative to 20 micro (μ) Pascal. This SPL reference 

will be used throughout the report. 
3

wall motion... rather than detecting Korotkoff sounds." The device detects the Doppler shift in 

the ultra-sonic signal and converts it into an audible sound indicating arterial wall motion. The 

audible signals appear and disappear in equivalent manner to Korotkoff cues. They concluded the 

device proved to be effective in eliminating the effects of in-flight noise and vibration on blood 

pressure measurements. 

As one might expect, the most sophisticated devices are costly and, by incorporating 

additional processing hardware, are usually physically larger (far too large for field-pack 

applications). The assessed devices all have specific advantages and drawbacks related to cost, 

size, and complexity of transducer placement. Presently, no one device is ideal for universal use. 

The majority of devices are either proof-of-concept prototypes using rack mount hardware, or in 

Phase II (initial hardware development). They are not at a production stage. It should be noted 

that all of the developers of the most elaborate multiple-sensor stethoscope devices have 

abandoned their efforts at further development while the simpler devices have evolved into 

marketed products. 

OBJECTIVE

In an effort to address Navy medical needs, Naval Submarine Medical Research Laboratory 

(NSMRL) has undertaken the identification of ascultation requirements identified by the 

operating forces and an assessment of currently available commercial off the shelf (COTS) 

devices to best meet those requirements. 

Along with the objective of providing the best commercially available technology, was the 

crucial need to understand and define exactly the present and future needs of our end-users. To 

achieve that end, a Noise Reducing Stethoscope Working Group Meeting was convened in 

Washington, D.C. in September of 1996. Participants were a mix of personnel from operational 

theaters as well as operating forces and manufacturers. The plan involved identifying our 

customers, and having them identify their needs, but with knowledge of what was commercially 

available and what was potentially feasible. Representatives came from the Naval Surface Force 

U.S. Pacific Fleet, Naval Special Warfare Command (NAVSPECWARCOM), United States 

Uniformed Health Services (USUHS), Joint Medical Readiness Training Command (JMRTC), 

U.S. Special Operations Command (USSOCOM), Naval Aerospace Medical Institute (NAMI), 

Bureau of Medicine and Surgery (BUMED) Codes 21, 22, and 23. Additional members were 

acoustic, operational-medicine and auditory researchers from Penn State Applied Research 

Laboratory and from NSMRL. Based upon the presentations, a consensus of operational needs 

and requirements evolved. A synopsis of that information is described in Appendix A. 

RESEARCH PLAN

Given the opportunity at the Noise Reducing Stethoscope Working Group, the operating 

forces identified their needs for a device far beyond what was commercially feasible within the 

time-frame of this project. After attending manufacturers demonstrated their existing technology, 

it was clear that no current or immediately imminent device would fill all the anticipated needs of 

operational medicine. However, the device specifications, which were circulated back to the 

manufacturers, were of value in identifying the direction toward which manufacturers needed to 

advance. Appendix B details the physical and other specifications that the ideal instrument of the 

future will have to meet. 

Clearly, the primary (and most restrictive) criterion was that the device not be much larger 

than a conventional stethoscope. The operating forces made clear that they were willing to 
4

sacrifice universality of application (i.e., to encompass intense airborne and structurally 

transmitted interference as encountered in helicopters) for a smaller far less expensive device that 

would have a far greater chance of being issued to all medical personnel. Situations of intense 

noise were far less prevalent than moderate noise, and in many intense noise situations (e.g. 

rotary-wing aircraft) the requirement for a tiny portable field device was less critical. Other 

methods (larger, specialized, more costly, non-acoustic etc.) could be used to monitor vital-signs 

in these environments. The group unanimously agreed that a less, not more, complex device was 

desirable for general issue. It was decided that this general-issue device should function well in 

environments up to 90 dB SPL. 

So, given that the Working Groupís ideal stethoscope was a highly sophisticated dataprocessing device that was technologically possible but, because of size constraints, far into the 

future, what could be provided in the interim? 

The modular approach 

The near term COTS noise-reducing electronic stethoscope must have the advantages of the 

acoustic stethoscopes, without the limitations. Of primary importance, it must be small, 

dependable, and simple to operate. There should be accurate and adjustable amplification, little 

ambient artifact noise, and minimal instrument manipulation artifact noise. The earpieces or 

sound transducers should be comfortable, adjustable, and provide excellent acoustic isolation 

from ambient sounds. There could be a bell and a diaphragm-filtering mode or some equivalent. 

It must also have an ergonomic design and, most important, it must be operationally acceptable. 

Near-equally important, it must also be inexpensive enough for general-issue. More to the point, 

it must be a compromise of general utility and dependability over high technology. One of the 

best ways to that goal is a modular approach. We need a small dependable device that wastes 

none of its power consumption or valuable component volume or cost on unnecessary processing. 

For modular application, it must have an electrical signal output, but given modern analog to 

digital processing, a clean analog output is all that is needed. Additional processing can be done 

outboard to conserve battery power in our primary device. We need a primary device that 

everyone can be issued and can not only operate more effectively with, but one that serves as the 

noise-immune front-end for the rapidly evolving world of miniaturized signal-processing 

hardware. As a modular interfaced component, miniature hand-held CPU devices and software 

can instantly upgrade without obsolescence. If a manufacturer can optimize such a sensor device, 

and price it competitively it can become general-issue. Clearly it cannot work miracles. It 

sacrifices intense noise situations and the ability to cancel structurally transmitted internal- body 

noise for size, general-issue and dependability. 

The decision herein to seek a less complex device to be applied in a modular-configuration

is predicated on the fact that much of the noise that interferes with ascultation enters into the 

process at the sensor-head and also at the coupling to the ear. In 1993 Zacharias et al. (16) 

described a model for the noises ìimpinging on the medic/stethoscope/patientî at three separate 

points. Noise N1 acts on the medics auditory system bypassing the stethoscope. Noise Ns

2 acts on 

the stethoscope itself, from the contact point with the patient, to the medicís earpieces. This noise 

spectrum is modified by the transfer-function of the stethoscope. Finally, noise Np

2 is the noise 

that has entered into the patientís body and is modified by the acoustic transfer characteristics of 

the trunk or torso. Given this background, with a modular approach the operator could tailor the 

noise-reduction potential (and cost) of the product to the application. In fact for moderate levels, 

noise-reduction solely at the pick-up sensor might suffice. The manufacturer's inclusion of an 

ANC headset in the original COTS would likely have resulted in added noise-reduction benefits 

essential for some users, but would require an additional cost. Inclusion of state of the art 

(SOTA) ANC headsets could price the product well out of the commercial stethoscope market. 

Similarly, there is not a major commercial market for a specialized stethoscope with an insert-
5

earphone (earpiece) that can function under a chemical warfare body suit. With a modular 

approach, specific military needs can be addressed. 

Within our solution was the requirement to tailor the COTS device to the application. We 

evaluated the deviceís intrinsic ability to extract information in operationally relevant situations. 

We parsed out pick-up and signal extracting capability from both headset or earpiece fidelity and 

headset or earpiece noise reduction capability. To accomplish this, we tested the product as 

supplied, and also with other noise-attenuating headphone combinations that would adapt the 

device to a broader operational use. COTS products were modified by changing their signal 

output characteristics in ways that would most likely significantly enhance their ability to function 

in noise. There were no modifications to their electrical output, only the fidelity and/or noisereduction capability of the listening headphone. It must be noted that any noise-reduction 

achieved by the device is done before the signal is fed to the earpiece. To maintain that noise 

reduction, the appropriate transmission to the ear is also critical but independent of the methods 

used to reduce noise at the pick-up. Most important, we already knew that ANC headsets were an 

optimal method of reducing noise when we present an acoustic signal to the ear. 

In terms of optimal bandwidth2

 of acoustic stethoscopes, perhaps the most extensive 

evaluation of their transmission characteristics was conducted by Ertel et al. (20), using a 

Zwislocki ear simulator to match the acoustic impedance of the ear. Twenty-eight unaltered 

commercial stethoscopes were tested and showed a 20 Hz to 3 kHz bandwidth was achievable 

(21). Ertel et al. concludes, that ìÖit is yet to be proven that there are significant cardiovascular 

sound components above 3 kHzî but strongly recommends that devices with better high frequency 

response be selected. 

Product evaluation requirements 

With the objective of ranking and rating different products for their ability to extract vital 

sounds with immunity from airborne environmental noise, we need to meet several criteria: 

1) Ability to accurately re-create airborne sound

The ability to spectrally re-create several operationally representative noise sources in the 

laboratory over a range of discrete steps in level provides a metric for comparative product 

performance. We can step the level of the environmental-noise signal from below, to well 

above, the true environmental-level to determine detection threshold of various visceral 

sounds for medically trained listeners using a specific device. This provides a relative 

measure of intrinsic product effectiveness in reducing interfering airborne noise in a generic 

operational environment. 

2) Ability to measure detection of the relevant sound

By using adaptive tracking tasks to determine the maximum airborne sound-level at which 

the sound of interest is detectable, we have a metric that is extremely sensitive and highly 

reliable (22). The task uses a time-window to validate subject responses. The adaptive 

aspect forces the subject response to a specific level of performance accuracy (23). 

3) Ability to present the same body sound to each listener 

Perceptual research of this nature requires that each listener be presented with exactly the 

same stimuli. In this case, device placement is also a critical parameter that can vary. As a 

result, all listeners need to hear the same placement on the same subject located exactly in 

the same sound -field environment. 

 

2

 The difference between the upper and lower cutoff frequencies. The range of frequencies that can contain 

or describe the signal. 
6

Using digital storage devices, recursive recording provides a methodology to faithfully 

recreate the stimulus (in this case, the vital-sign embedded in interfering environmental 

noise). In this application, we stored the electrical output of each device under each 

condition: visceral-sound type x device x environmental-noise type x level of noise. This 

allowed replay of the signal over the manufacturer's supplied earpiece with no change 

imparted to the intended signal. This significantly maintained low variability across listening 

conditions. 

These laboratory procedures gave us a reliable quantitative method of ranking device 

performance based on detection of sounds. Field use provided insight on how well the COTS 

device functions in a field environment with noise. 

Human subjects were used as vital-sounds sources because of the novel nature of the pick-up 

sensors. Vital-signs training-devices are available that generate both normal and abnormal 

visceral sounds. However, such devices use artificial skin with a loudspeaker beneath, which 

could likely confound the performance of a manufacturerís noise-immune non-acoustic pick-up. 

Product selection 

Finally, after identifying available COTS items, we selected three devices. The three COTS 

devices can be seen in Appendix E. Each device met our requirements of being small enough to 

be carried on the body, with a pickup head not much larger than a conventional stethoscope. Of 

utmost importance, each device had an electronic output separate from its own headset output. In 

our preliminary listening tests, each device seemed to perform better than a conventional 

stethoscope in reducing moderately-loud levels of outside noise. As we gathered our 

environmental recordings, several of the devices tested were still under development. We were 

fortunate to incorporate the final improved models into our vital-signs data gathering tests. The 

devices chosen were: the SmartMedTM Stethoscope by C.F. Electronics (Device 1), the Sonar 

Sound TM model 160 by Flow Scan (Device 2), and the E-Scope TM Electronic Stethoscope by 

Cardionics (Device 3). 

The SmartMed uses a special sound-dampened acoustic transducer connected to a 3.75 x 

1.75 x 6.75 inch case which has a .25 inch stereo phone jack into which a Sony closedcircumaural (around the ear) headset is connected. The Sonar Sound uses a unique polyvinyl 

sheet-material, which generates an electrical signal when torsionally flexed, as the sensor. A 1.5 

square-inch pad of this material is housed beneath a sensor-head, designed to be clasped between 

two extended fingers. A short cable connects the head to a 2.5 x 0.93x 4.38 inch case, which 

controls the signal cabled to a headset with stethoscope-like earpieces. The E-Scope uses a 

conventional looking diaphragm coupled to an attached microphone-element which is cabled to a 

1.0 x 2.38 x 3.75 control box. Conventional stethoscope earpieces are acoustically connected to a 

transducer within the box. 

These devices were evaluated in the laboratory as manufactured, and also with the device 

output properly interfaced to a Bose Aviation Series I Commercial ANC headset. In that 

configuration the letter A was appended to the device number. Given the three devices as 

manufactured and paired with the ANC headset, the seven test device designations were 1/1A 

(SmartMedTM Stethoscope), 2/2A (Sonar SoundTM Stethoscope), 3/3A (E-ScopeTM Stethoscope), 

and standard (Littmanô Classic II stethoscope). 
7

PHASE 1: LABORATORY EVALUATION

METHOD

Subjects 

Fourteen highly experienced medical personnel were used as listeners. The sample 

population consisted of two medical doctors (U. S. Navy, and Royal Navy), with the remaining 

twelve U. S. Navy Hospital Corpsmen with hospital-ward experience using stethoscopes. Two 

were emergency medical technicians (EMTs) during their off-duty. Several were Independent 

Duty Corpsmen (IDCs). All had normal hearing in at least one ear as measured by routine 

audiometry. Normal limits were defined as having no losses greater than 25 dB HL over the 

range of audiometric test frequencies: 125, 250, 500, 750, 1k, 1.5k, 2k, 3k, 4k, and 6k Hz 

. 

Experimental Design 

Auditory detection of normal and abnormal heart and breath sounds were compared under 

three operationally-relevant intense-noise conditions using one standard, and six experimental, 

stethoscope-listening conditions. The three relevant environmental airborne-noise conditions 

recreated were: A) a field-hospital 100 kilowatt generator (KWG); B) the patient area inside a 

moving HumVee soft-top field-ambulance (HUV); and C) the interior of an airborne C-130 

Transport (C130). During each of four randomly-assigned listening sessions, one session per day, 

subjects heard a different vital-sound (normal or abnormal heart, or normal or abnormal breath) 

presented within a random serial order of the three noise environments. Each daily listening 

session used a random order of seven stethoscope conditions repeated across the three 

environmental conditions. These stethoscope conditions consisted of a standard stethoscope and 

three COTS stethoscopes tested as supplied, and also tested with a COTS active noise 

cancellation (ANC) headset substituted for the supplied listening earpiece (headset). What was 

measured was the maximum level of airborne noise at which each device could enable detection 

of the four visceral sounds. All subjects heard all conditions. The repeated-measures design 

ensured that each medically-trained listener served as his/her own control across the various testlistening conditions. 

Environmental Simulation 

A high-intensity sound system was instrumented to operate within a 30 x 16.5 x 11 foot high 

cement-block-walled reverberant room. The system consisted of four speaker arrays, each 

containing two 18 inch drivers, a 15 inch driver, and one 4 inch diameter titanium horn-driver. 

Each transducer was independently powered, by a configuration of Crown amplifiers capable of 

producing 1,310 watts RMS in each of 4 channels with THD at less than .02% at rated power. 

Each channel of the system was fed by a separate channel of a Digidesign Pro Tools III digital 

hard disk recorder/editor. Four analog output channels of a Digidesign 888 interface were 

distributed to the amplifiers of each array through a pair of Rane AC-23 active crossovers. Just 

ahead of the AC-23 inputs, each of the channels was digitally controlled by a separate Wilsonics 

model PATT attenuator. 

Environmental Sounds: 

Field recordings were made at various operationally relevant sites using precision recording 

equipment. Airborne-noise, received by a Bruel and Kjaer (B&K) type 4191 free-field 1⁄2 inch 

diameter condenser microphone with type 2619 preamplifier and 227 battery-power supply, was 

recorded on either a Tascam DA-P1 or a Panasonic SV-250 portable DAT recorder for postanalysis. The microphone-preamplifier assembly was attached to a vibration-isolated extension 

handle to remove and decouple the data-gatherer from the measured sound-field. Microphone 

placement was at a region representative of the position of a listenerís head. 
8

At the start of each recording, a B&K sound level calibrator type 4230 was coupled to the 

microphone to produce a 1 kHz tone at 93.8 dB SPL re 20 micro (μ) Pascal. By setting the DAT 

recorder input-level once for the calibration tone, all subsequent recordings can be referenced to 

that sound pressure level. 

DAT recordings were spectrally analyzed using either a Data Physics ACE or DP-430 FFT 

signal analyzer. Root mean square (RMS) averages of the energy measured in 1/3-octave bands 

were calculated. The resultant overall RMS, A-weighted, and 1/3-octave band data were used to 

recreate these recorded signals at operationally relevant levels in the reverberant field test facility. 

Relevant environmental signals were transferred to the Digidesign system and edited to form a 

continuous loop. Once a seamless edit was achieved, three additional copies were generated, each 

randomly shifted in time from the original. These four sound files were separately and 

simultaneously fed to the speaker arrays to create a homogeneous non-directional (diffuse) sound 

field. 

Vital-Sounds Signals 

In this first phase, ìpatientsî were used solely as a source of normal and abnormal body 

sounds. Volunteer ìpatientsî were placed in the specially designed sound room, which 

reproduces operationally relevant noise environments, while visceral sounds were recorded using 

each stethoscope as the sensor. Normal heart and breath sounds were both taken from the same 

healthy male. Abnormal heart sounds were recorded from a male diagnosed as having aortic 

stenosis secondary to rheumatic fever as a child. Abnormal breath sounds were gathered from a 

female exhibiting acute asthma recorded just prior to medication. The visceral-sounds were 

chosen by two medical doctors to be representative of vital sounds important for ascultation. 

Both abnormal sounds were chosen for their relevance and difficulty. 

Recording of Vital-Sounds Stimuli 

Prior to data collection, ìpatientsî wearing appropriate hearing protection were placed on a 

stretcher in the diffuse-field test chamber and the pick-up sensor of the stethoscope device to be 

tested was carefully moved in location on their body until maximum signal levels of internal body 

sounds were obtained. The calibrated sound field in the room was on at some predetermined low 

starting level. A medical doctor or independent duty corpsman (IDC) adjusted the pick-up-head 

position as they listened to the output of the device over ANC headphones. Once adjusted, the 

ìpatientî was signaled and the sound field was raised in 2 dB steps, starting at 66 dBA3

 every 10 

seconds to maximum level, while device electronic output was digitally recorded. The electronic 

output recorded was the same signal that was fed to the headphone. Ambient sound in the room 

was raised to no more than 94 dBA. Total data collection time for one sound-field was less than 3 

minutes (15, 2dB steps X 10 seconds per step = 150 seconds). Data collection was resumed using 

another sound-field following this same procedure until vital-signs recordings for all three 

environmental sources were recorded using that same stethoscope device. 

Since the environmental-sounds generated in the test chamber were recordings, no 

unexpected sounds or intensities could occur. All signals were accurately monitored during data 

collection. Because of the brief duration and hearing protection, noise exposure was well within 

the Hearing Conservation Guidelines put forth in DOD instruction 6055.12 (24) 

 

3

 During all noise exposure conditions, sound levels were monitored in dBA, where the A-weighting scale is 

applied to better assess the effect of the airborne sound on the human listener's hearing. However, for 

assessing the actual levels of the environmental sounds, we were interested in the unweighted dB SPL values 

since this better described the energy in which the sensors were required to extract the signal. 
9

The electronic outputs of three COTS stethoscopes were used in data collection. In addition, 

as a comparison, the acoustic output of a Littmann Classic II Stethoscope with soft-sealing eartips 

was recorded through ears of a specially treated acoustic test manikin. The earpieces of the 

Littmann were carefully fitted into the ear canals of a KemarÆ manikin. This device, equipped 

with Zwislocki ear simulators that model the acoustic impedance of the ear, has been used 

extensively in our headphone research (25, 26). Pliant bags of lead shot placed within the 

manikin were used to block sound transmission to the calibrated microphone ìeardrumî from 

pathways other than the ear canals. Electroacoustic test results confirmed our ability to attenuate 

such transmission at 40 dB or greater from 160 Hz to 500 Hz, 50 dB or better from 500 Hz to 2 

kHz, and 60 dB or more from 2 to 15 kHz. A specially designed bridged-T filter, proposed by 

Killion (27), was employed to properly remove the filtering effects of the ear-simulators for 

accurate reproduction at the listeners ear. Levels presented at the eardrum were identical to those 

normally available using the stethoscope. Recordings from the three experimental devices and 

those recorded from the Littman stethoscope were all made using live patients as our source of 

visceral sound. 

Source Stimuli 

To recap, stimuli were digital sound files of vital-signs signals collected on human patients in 

three operationally relevant noise-fields (at 15 different levels of the environmental noise-field) 

using a standard stethoscope and three experimental models. A 3x15matrix of sound files for 

each vital-sign signal was stored on hard disk for rapid access. The vital-sign signals were normal 

breath and heart sounds and abnormal breath and heart sounds. The normal sounds were taken 

during different sessions from the same patient. The two abnormal sounds were gathered from 

two different patients. 

Stimulus Generation 

A 16 bit digital-to-analog converter (DAC) with a 48-kHz sample-rate was used to generate a 

repetition of the previously digitized stethoscope sound sample (sound file) from the matrix. 

These parameters meet or exceed those recommended for professional audio applications (28). 

Analog to digital (AD) and digital to analog (DA) processes were implemented using a Data 

Translation DT2823 digital converter board resident in a PC. During both digitization and 

playback, a Rockland model 2783 140 dB/octave low-pass filter, with cut-off at 22 kHz, was used 

as an anti-aliasing device. 

Stimulus Presentation 

As described above stimulus generation was accomplished using a PC based DAC. For 

automated testing and data collection, a second PC was used to control the presentation of those 

signals and also control the level of environmental sound generated in the room. Algorithms to 

implement the test procedure and control stimulus selection and level, target4

 onset and duration 

and assess listener response were executed to implement the test procedure described below. 

Adjustment of the environmental sound-field in 2 dB steps was digitally controlled through 

the four Wilsonics model PATT programmable attenuators to reproduce the appropriate room 

intensities prior to and during each stethoscope listening trial. Simultaneously, a TDT electronic 

switch, under PC control, gated the appropriate level vital-sounds signal, accessed from the stored 

matrix, for the stethoscope being tested. 

Test Procedure 

Subjects listened to visceral sounds recorded through the stethoscope devices in the various 

 

4

 The embedded signal to be detected. In this case visceral sounds embedded in environmental and internal

body-noise. 
10

noise environments using the headset provided by the manufacturer as well as an ANC headset. 

Target detection threshold was estimated by rule using an adaptive tracking technique that was 

developed from the modified International Standards Organization threshold-tracking procedures 

described by Harris (22). 

The adaptive tracking technique used in threshold estimation required the subject to respond 

by pressing and releasing a button within specified time limits to indicate target onset and 

termination. Target onset was random, in a gaussian distribution with a mean of 2.8 seconds and 

a standard deviation of +0.8 seconds. Target-on time was slightly greater than 4 seconds. This 

duration provided listeners with at least one complete period of vital-signs signal. At the start of 

the trial, the level of the environmental sound in the room was automatically set to -16 dB from 

full-scale output5

. The subject then heard the visceral sound, that was recorded through a specific 

stethoscope, when the environmental sound in the room was at that same sound intensity for a 

ìfamiliarizationî or pre-test listening period. Then adaptive tracking testing began, and the same 

visceral-sound was presented at that same level for a response in the appropriate recreated level of 

airborne environmental-noise. If undetected, the airborne level in the room was lowered 2 dB; if 

detected, it was raised an additional 2 dB and the appropriate stimulus presented from the matrix. 

As trials were presented, a change in performance from detection to failed detection, or its 

converse, was counted as a reversal in response. In all cases the vital-sounds signal presented at 

each trial was from the matrix previously recorded for that combination of device, and operational 

environment. 

The dB value half-way between successive reversals during a trial was recorded as threshold. 

From this, the absolute value of that threshold's deviation from the trial accumulated mean

threshold was derived. The sum of these absolute values was used to determine the average 

deviation (AD) which had to be 2 dB or less. At the end of 6 thresholds, if the value of the 

average deviation exceeded 2, additional thresholds were measured until 6 successive thresholds 

yielded an AD of 2 dB or less. Once this criterion was met, the averaged threshold and AD were 

recorded for the completed trial. If, after an additional 2 thresholds, the criterion was not met, 

testing was suspended and the subject re-instructed. A trial was also terminated and the subject 

re-instructed if the distance between successive reversals was greater than 10 dB. 

LABORATORY EVALUATION

RESULTS AND DISCUSSION

Data were subjected to a 3-way analysis of variance for repeated measures (29). As in any 

non-mixed repeated-measures design, all subjects were presented all conditions. As seen in Table 

1, results showed a significant difference in the airborne levels at which the different stethoscopes 

could effectively present detectable vital-sounds (F = 72.5, df 6, 78). As expected the four 

different visceral sounds were significantly different in detectability (F =24.8, df 3, 39) as were 

the three environments (F =218.6, df 2, 26). All F values on these 3 main factors (device, vital 

sound, and environment) were significant beyond the .001 level. 

Not surprising was a significant interaction between the various devices and the vital-sound 

to be detected (F = 13.1, df 18, 234), which was caused almost exclusively by the performance of 

the standard stethoscope. This interaction can be seen in Figure 1, which plots the detectability of 

 

5

 Full scale output level in dB SPL was different for each of the environmental sounds. Calibration of the 

airborne level for each sound was done with the attenuator set to minimum attenuation (full gain). The 

starting point for testing was 16 dB below that level. 
11

visceral sounds (as a function of the maximum level of device-tolerable6 airborne noise ), 

averaged across heart/lung sounds and noise environments, with the various stethoscopes. It is 

most important to note that with a conventional stethoscope detection of abnormal heart/breath is 

severely degraded by the noise environment. It is this difference in performance that is 

responsible for the significant interaction. 

Table 1. Results of 3-way repeated measures analysis of variance 

Source of Variation df SS MS F 

Subjects 13 12519.000 

Vital-sound 3 7324.000 2441.333 24.840* 

Error 39 3833.000 98.282 

 

Environment 2 14359.000 7179.500 218.580* 

Error 26 854.000 32.846 

Device 6 13305.000 2217.500 72.492* 

Error 78 2386.000 30.589 

Vital-sound x Environment 6 4217.000 702.833 21.085* 

Error 78 2600.000 33.333 

Vital-sound x. Device 18 5680.000 315.555 13.183* 

Error 234 5601.000 23.9359 

Environment x Device 12 1015.000 84.583 6.578* 

Error 156 2006.000 12.859 

3-way Interaction 36 2197.000 61.027 4.652* 

 468 6139.000 13.1175 

 * significant - [p <.001] 

There was a significant interaction between environment and the type of visceral-sound to be 

detected (F = 21.0, df 6,78). However, when the standard stethoscope is removed from the 

comparison, the only interaction remaining causes abnormal heart sounds to become slightly less 

detectable in the HumVee ambulance environment, than in the hospital field-generator 

environment. This can be seen in Figure 2, which depicts the mean detection and standard error 

for the various visceral sounds in different environments collapsed across only the six 

experimental-stethoscope conditions. This interaction, graphically seen as crossing plots between 

the Hum Vee and KW Generator is caused by the poor performance of the E-Scope stethoscope 

(3/3A) on abnormal heart sounds in the HumVee environment. Figure 5 depicts the poorer 

performance of the E-Scope stethoscope averaged across all of the tested visceral sounds. 

Though not shown as a figure, re-plotting Figure 2 with the E-Scope stethoscope (3/3A) removed, 

eliminates the plot-crossing in the heart-abnormal condition. A significant interaction between 

device and the environment in which the device was used is expected (F = 6.5, df 12, 156). The 

interaction between these three variables was also significant (F = 4.6, df 36, 468). All F values 

on these four interactions were significant beyond the .001 level. 

Table 2, which lists the differences in detection performance in the three operational 

environments, shows that our selection of environments was well chosen. As seen by the 95% 

confidence intervals, the highest dB SPL values in which listeners could still detect the relevant 

 

6

 Maximum airborne noise level at which the visceral sound could be detected using the device. 
12

75

80

85

90

95

100

1 1A 2 2A 3 3A Standard

Stethoscopes

dB SPL

Heart-Normal

Heart-Abnormal

Breath-Normal

Breath-Abnormal

Smart Med Sonar Sound E-Scope Littmann Classic

Figure 1. Detectability of visceral sounds with the 7 various stethoscopes 

sounds were quite different. Detection of heart/lung sounds was hardest in the C-130 (84 to 88 

dB SPL, ambient airborne noise), somewhat easier at the recommended distance from a fieldhospital generator (88 to 92 dB SPL), and easier in a HumVee field-ambulance (92 to 96 dB 

SPL). Of course those values are averages for all vital-sounds tested and across all stethoscopes, 

including the standard device, to show the overall effect of environmental differences on 

detection7

. 

Table 2. Maximum detectability of heart/lung sounds in three different environments. 

Environment Mean Std. Error 95% Confidence Interval [dB SPL] 

 [dB SPL] [dB SPL] Lower Bound Upper Bound 

KW Generator 90.2 .992 88.1 92.4 

C-130 85.8 .929 83.7 87.8 

HumVee 94.3 .882 92.4 96.2 

Table 3 lists device performance averaged over all conditions. A Neuman Keuls test shows 

that for these 7 devices (n = 7, df 78), a critical value of greater than 5.51 is necessary for 

significance at the .05 level. Clearly, all 3 devices both as supplied, and with the added 

attenuation of the ANC headset, have averaged performance that is significantly better than the 

standard stethoscope. We cautiously limited the upper levels of noise exposure to safe limits 

based on duration and intensity. As a result, with some devices many listeners were still able to 

detect the visceral sounds at our highest levels. Unfortunately, we were only able to report their 

performance to that safe level. Our averaged results are therefore most likely conservative 

 

7

 Figure 2 plots these same conditions, averaged with the standard stethoscope removed. 
13

8 0

8 5

9 0

9 5

100

105

H e a rt-N O R H e a rt-A B N B re a th -N O R B re a th -A B N

V isc era l so u n d s

dB SPL

Hum Vee

K W G e n e ra to r

C -130

Figure 2. Detection of heart/lung sounds averaged across environments for six experimental 

stethoscope combinations. 

(reduced) estimates of device performance. As far as the performance of the standard 

stethoscope, we positively biased its performance since, for a few subjects, an occasional inability 

to detect the vital-sound at the lowest level of presentation was estimated as a detection that 

would have occurred at the next lower level. Consequently, the difference estimates between our 

test devices and the normal stethoscope are most likely conservative. Also, note the tight 5 dB 

range of performance and operating-noise levels capable with the Smart Med and Sonar Sound 

devices. It compares favorably with the range of performance obtained using the standard 

stethoscope users were quite accustomed to. 

Table 3. Maximum detectability of heart/lung sounds across three environmental conditions. 

Stethoscope Mean Std. Error 95% Confidence Interval [dB SPL] 

 [dB SPL] [dB SPL] Lower Bound Upper Bound 

1 Smart Med 92.8 .935 90.8 94.9 

1A [1 with ANC] 93.8 1.087 91.5 96.2 

2 Sonar Sound 90.7 .863 88.8 92.6 

2A [2 with ANC] 92.3 .696 90.8 93.8 

3 E scope 88.7 1.310 85.9 91.6 

3A [3 with ANC] 89.4 1.049 87.1 91.6 

Standard 83.0 .849 81.2 84.8 

Figures 3, 4, and 5 depict individual device performance in detecting heart/lung sounds 

within the three operational environments of field-hospital generator (KWG), C-130 transport 

(C130) and field-ambulance (HUV) respectively. In these three figures the maximum airborne 

levels in which the heart/lung sounds could still be detected is shown. Note that in each of the 

three conditions the Smart Med would be the best overall choice and the E-Scope the poorest 

choice. 
14

76 78 80 82 84 86 88 90 92 94 96 98

dB SPL

1

Stethoscopes

KW Generator

Standard

Device 3A

Device 3

Device 2A

Device 2

Device 1A

Device 1

S

76 78 80 82 84 86 88 90 92 94 96 98

dB SPL

1

Stethoscopes

C 130

Standard

Device 3A

Device 3

Device 2A

Device 2

Device 1A

Device 1

Figure 3. Individual device performance in the vicinity of a 100 KW generator for normal and 

abnormal heart/lung sounds. For comparison, actual field-measured levels were 90 dB SPL.

Figure 4. Individual device performance inside a C-130 transport for normal and abnormal 

heart/lung sounds. For comparison, actual field-measured levels were 104 dB SPL

* 

Actual level @ 25 feet 

Actual level:104 dB SPL 
15

Figure 5. Individual device performance in a HumVee field-ambulance for normal and abnormal 

heart/lung sounds. For comparison, actual field-measured levels (97 dB SPL) are indicated.

Table 4. Device performance in each environment. 

Environment Stethoscope Mean Std. Error 95% Confidence Interval [dB SPL] 

 [dB SPL] [dB SPL] Lower Bound Upper Bound 

KW Generator 1 Smart Med 92.2 1.082 89.9 94.5 

 1A [1+ANC] 94.6 1.075 92.3 96.9 

 2 Sonar 

Sound 

90.1 1.143 87.6 92.6 

 2A [2+ANC] 92.1 .954 90.0 94.1 

 3 E Scope 89.2 1.311 86.3 92.0 

 3A [3+ANC] 89.8 1.349 86.9 92.7 

Standard 83.7 .856 81.8 85.5 

C-130 1 Smart Med 89.2 1.064 86.9 91.5 

 1A [1+ANC] 89.9 1.350 87.0 92.8 

 2 Sonar 

Sound 

85.0 .838 83.2 86.8 

 2A [2+ANC] 86.6 .682 85.1 88.1 

 3 E Scope 84.6 1.356 81.7 87.5 

 3A [3+ANC] 85.8 1.056 83.6 88.1 

Standard 79.1 .946 77.0 81.1 

HumVee 1 Smart Med 97.1 .909 95.1 99.1 

 1A [1+ANC] 96.9 1.289 94.1 99.7 

 2 Sonar 

Sound 

97.0 .870 95.1 98.9 

 2A [2+ANC] 98.1 .676 96.7 99.6 

 3 E Scope 92.4 1.441 89.3 95.5 

 3A [3+ANC] 92.4 .990 90.3 94.6 

Standard 86.2 .924 84.2 88.2 

76 78 80 82 84 86 88 90 92 94 96 98

dB SPL

1

Stethoscopes

HUM VEE 

Standard

Device 3A

Device 3

Device 2A

Device 2

Device 1A

Device 1

* 

Actual level inside patient area 
16

Table 4 presents for each environment, the maximum dB SPL values, averaged across 

heart/lung sounds, at which listeners could detect the various vital-sounds. A critical value of 

3.52 (Neuman Keuls n = 7, df 156) between devices is significant at the .05 level. These results 

show that, in the Hum Vee environment, though the E-Scope was able to function significantly 

better than the standard stethoscope, both the Smart Med and Sonar Sound devices were 

significantly better than the E-Scope in their tolerance to external noise. For the C-130 

environment all three devices were significantly better than the standard. The E-scope and Sonar 

Sound were not significantly different from each other and the Smart Med was significantly better 

than all the rest. For the KW generator, the three non standard devices though not significantly 

different from one another were all significantly better than the standard stethoscope in their 

tolerance to airborne environmental noise. 

Figures 6 and 7 depict, respectively, the detection advantage (or delta value) of Device 1, the 

Smart Med stethoscope, as supplied and when equipped with an ANC headphone, against a 

standard stethoscope. Both figures depict the average difference in intensity of operational-noise 

at which the tested devices allowed detection of the various vital-sounds. All 14 subjects heard 

all conditions using all seven possible listening conditions. The critical value necessary for a 

significant difference at the .05 level is 3.49 (Neuman Keuls n = 7, df 468). Non-significant 

differences are plotted in gray 

Figures 8 and 9 depict, respectively, the detection advantage of Device 2, the Sonar Sound 

stethoscope, as supplied and when equipped with an ANC headphone, against a standard 

stethoscope. Both figures depict the average difference in intensity of operational noise at which 

the tested devices allowed detection of the various vital-sounds. The critical value necessary for a 

significant difference at the .05 level is 3.49 (Neuman Keuls n = 7, df 468). 

Figures 10 and 11 depict, respectively, the detection advantage of Device 3, the E-Scope 

stethoscope, as supplied and when equipped with an ANC headphone, against a standard 

stethoscope. Both figures depict the average difference in intensity of operational noise at which 

Figure 6. Device 1 (Smart Med) detection advantage over a standard stethoscope

B-A H-A

B-N

H-N

KW C-130

HV

0

2

4

6

8

10

12

14

16

18

20

22

Detection Gain dB SPL

Visceral Sounds

ENVIRONMENTS

Device 1 Detection Advantage
17

the tested devices allowed detection of the various vital-sounds. Again, the critical value 

necessary for a significant difference at the .05 level is 3.49 (Neuman Keuls n = 7, df 468). 

B-A H-A B-N H-N

KW C-130 HV

0

2

4

6

8

10

12

14

16

18

20

22

Detection Gain dB SPL

Visceral Sounds

Environments

Device 1 A Detection Advantage

B-A

H-A

B-N

H-N

KW

C-130

HV

-2

0

2

4

6

8

10

12

14

16

18

20

22

Detection Gain dB SPL

Visceral 

Sounds

Environments

Device 2 Detection Advantage

Figure 8. Device 2 (Sonar Sound) detection-advantage over a standard stethoscope. 

Figure 7. Device 1A (Smart Med/ANC) detection advantage over a standard stethoscope. 
18

B-A

H-A

B-N

H-N

KW

C-130

HV

0

2

4

6

8

10

12

14

16

18

20

22

Detection Gain dB SPL

Visceral 

Sounds

Environments

Device 2 A Detection Advantage 

Figure 9. Device 2A (Sonar Sound/ANC) detection-advantage over a standard stethoscope. 

Figure 10. Device 3 (E-Scope) detection-advantage over a standard stethoscope. 

B-A

H-A

B-N

H-N

KW

C-130

HV

-2

0

2

4

6

8

10

12

14

16

18

20

22

dB SPL

Visceral 

Sounds

Environments

Device 3 Detection Advantage
19

To recap, in all four of the 3-dimensional representations depicted in Figures 6 through 11, 

those comparisons relative to a standard stethoscope that did not reach significance are shown in 

light gray. These comparisons are based on the averaged performance of all subjects. In no case 

did any of the devices perform significantly poorer than a standard stethoscope. Clearly, the 

greatest gains in audibility over a standard stethoscope are seen with abnormal breath (B-A) and 

abnormal heart (H-A) sounds, and those gains (8 dB to 22 dB) seen in Figures 6 through 9, are 

quite impressive for both the Smart Med and Sonar Sound devices even as supplied (8 dB to 19 

dB). In fact, averaged across the three environmental conditions the detection gains achieved by 

the Smart Med stethoscope, when listening to non-normal sounds are 17.0 dB for breath and 12.4 

dB for heart respectively. Under those same conditions, the Sonar Sound stethoscope exhibits a 

15.8 dB gain for abnormal-breath and a 9.7 dB improvement for detection of abnormal-heart 

sounds, over the standard stethoscope. 

Table 5 provides an operationally useful comparison among the various stethoscope 

configurations collapsed across conditions. Would the added audibility afforded from an ANC 

headset be worthwhile? As seen in Table 5, the 0.9 dB improvement gained with ANC for Smart 

Med stethoscope (1 /1A) is not significant. However, the 1.5 dB improvement obtained with 

ANC for the Sonar Sound stethoscope (2/2A) is a significant one. The gain might not be cost 

effective for general-issue, but it is available for specific applications where ANC headsets are 

already provided. For example, flight crew personnel commonly wear BOSE military ANC 

communications-headsets within their helmets, which are compatible with the outputs on these 

devices. In any decision, size is a most critical factor, and one that might exclude the use of 

Smart Med stethoscope over its 2dB less-noise-immune rival, the Sonar Sound stethoscope, which 

is significantly smaller. In comparison against the standard stethoscope Table 5 also shows that 

averaged across all conditions, Smart Med stethoscope produces an average 9.8 dB improvement 

over the standard stethoscope. Under those same conditions, Sonar Sound stethoscope produces a 

7.7 dB improvement while E-Scope stethoscope produces a 5.7 dB improvement. 

B-A

H-A

B-N

H-N

KW

C-130

HV

-3

-1

1

3

5

7

9

11

13

15

17

19

21

dB SPL

Visceral 

Environments

Device 3A Detection Advantage

Figure 11. Device 3A (E-Scope/ANC) detection-advantage over a standard stethoscope.
20

Table 5. Pairwise comparisons of devices averaged across environments and heart/lung sounds. 

(I) Stethoscope (J) Stethoscope Mean Difference 

(I-J) 

Std. 

Error 

Significance 

level. 

95% Confidence Interval 

for Difference [dB SPL] 

 Lower Bound Upper Bound 

1 Smart Med 1A [1+ANC] -.9 .552 .097 -2.1 .2 

 2 Sonar Sound 2.1 .516 .001 1.0 3.2 

 2A [2+ANC] .5 .551 .318 -.6 1.7 

 E Scope 4.1 .643 .000 2.7 5.4 

 3A [3+ANC] 3.4 .604 .000 2.1 4.7 

 Standard 9.8 .778 .000 8.1 11.5 

1A [1+ANC] 1Smart Med .9 .552 .097 -.2 2.1 

 2 Sonar Sound 3.1 .552 .000 1.9 4.3 

 2A [2+ANC] 1.5 .509 .009 .4 2.6 

 3 E-Scope 5.0 .690 .000 3.6 6.5 

 3A [3+ANC] 4.4 .274 .000 3.8 5.0 

 Standard 10.8 .693 .000 9.3 12.3 

2 Sonar Sound 1Smart Med -2.1 .516 .001 -3.2 -1.0 

 1A [1+ANC] -3.1 .552 .000 -4.3 -1.9 

 2A [2+ANC] -1.5 .335 .000 -2.2 -.8 

 3 E-Scope 1.9 .585 .005 .7 3.2 

 3A [3+ANC] 1.3 .437 .009 .3 2.2 

 Standard 7.7 .631 .000 6.3 9.0 

2A [2+ANC] 1Smart Med -.5 .551 .318 -1.7 .6 

 1A [1+ANC] -1.5 .509 .009 -2.6 -.4 

 2 Sonar Sound 1.5 .335 .000 .8 2.2 

 3 E-Scope 3.5 .804 .001 1.8 5.2 

 3A [3+ANC] 2.8 .425 .000 1.9 3.8 

 Standard 9.2 .589 .000 7.9 10.5 

3 E-Scope 1Smart Med -4.1 .643 .000 -5.4 -2.7 

 1A [1 +ANC] -5.0 .690 .000 -6.5 -3.6 

 2 Sonar Sound -1.9 .585 .005 -3.2 -.7 

 2A [2+ANC] -3.5 .804 .001 -5.2 -1.8 

 3A [3+ANC] -.6 .653 .347 -2.0 .7 

 Standard 5.7 .847 .000 3.8 7.5 

3A [3+ANC] 1Smart Med -3.4 .604 .000 -4.7 -2.1 

 1A [1 +ANC] -4.4 .274 .000 -5.0 -3.8 

 2 Sonar Sound -1.3 .437 .009 -2.2 -.39 

 2A [2+ANC] -2.8 .425 .000 -3.8 -1.9 

 3 E-Scope .6 .653 .347 -.7 2.0 

 Standard 6.3 .659 .000 4.9 7.7 

Standard 1Smart Med -9.8 .778 .000 -11.5 -8.1 

 1A [1 +ANC] -10.8 .693 .000 -12.3 -9.3 

 2 Sonar Sound -7.7 .631 .000 -9.0 -6.3 

 2A [2+ANC] -9.2 .589 .000 -10.5 -7.9 

 3 E-Scope -5.7 .847 .000 -7.5 -3.8 

 3A [3+ANC] -6.36 .659 .000 -7.7 -4.9 

Discussion 

What is there about abnormal breath and heart sounds that makes them less detectable in 

noise using a standard stethoscope than any of the electronic versions? Clearly it is because they 

are fainter and therefore present a lower level at the ear. The abnormal breath sounds are shorter 

in duration and are more likely to have high-frequency energy that is attenuated by the transfer 

function of a standard acoustic stethoscope. Data on frequency response of conventional 

stethoscopes that show a 35 dB drop in output from 300 Hz to 3kHz (20, 21) would corroborate 

this. Apparently the electronic stethoscopes do not mimic the high-frequency attenuation 

characteristics of standard acoustic devices. 
21

In Figure 1, the stellar performance of the Smart Med stethoscope (device 1) on normal heart 

sounds, which even exceeds that measured with the ANC headphones (device 1A), is primarily 

due to the exaggerated low-frequency response-characteristic of the Sony headset selected by the 

stethoscope manufacturer. Even at the highest levels of interfering noise, many reported ìfeelingî 

the heart-beat at the ear-drum. Despite noise-reduction advantages and a measured more accurate 

frequency response, the ANC headset did not elicit the same sensation. However a simple change 

in equalization in the active ANC headset electronics could duplicate the measured response of 

the Sony headset. 

From Figure 5 we could see that the E-Scope stethoscope (3/3A) was not able to perform as 

well as the Smart Med stethoscope (1/1A) and the Sonar Sound stethoscope (2/2A ) in the fieldambulance environment (about 5 dB poorer). The HumVee ambulance had a great deal of low 

frequency energy. Actual values recorded inside the patient area of a canvas-topped version 

transiting on flat terrain were 97 dB SPL. For the HumVee environment, the dBA weighting, 

which attenuates these lower frequency components, was 16 dB lower than the dB SPL values. 

Because the inclusion of an ANC headset with excellent low-frequency noise attenuation had no 

effect, we can safely conclude that, the E-Scope stethoscope does not attenuate lower frequencies 

of airborne sound as well as the other devices. That could account for the interaction it was found 

to cause, that was seen in Figure 2. Smart Med stethoscope and Sonar Sound stethoscope 

effectively extract the signal from the noise. The sensor-head on the Sonar Sound is apparently 

best at this, since with the added benefit of ANC, it improved further. 

For the hospital field-generator, seen in Figure 3, it is apparent that each electronic device 

performs better with ANC, implying that the supplied headsets did not block the noise as well as 

the sensor-head made the signal available. Sound levels measured 25 feet from the 100 KW fieldhospital power source were 90 dB SPL. 

The C-130 environment was indeed the harshest, with a measured level of 104 dB SPL at the 

stretcher. In addition to a large noise component at lower frequencies, there is a large amount of 

energy in the 6 kHz region. As seen in Figure 4, each experimental device performs better, 

averaged across the visceral sounds, with the added noise reduction provided by the ANC headset. 

This implies, that in that noise environment, the supplied headset was unable to supply the 

information detected by the sensor. 

The data make a strong point for the cost-effectiveness and simplicity of reducing only the 

airborne-noise that impinges on the stethoscope and on the listenerís ears. During our laboratory 

data-collection we found that even slight re-location of the sensor-head had a major audible effect 

on the spectral characteristics of the noise picked up from within the torso. That is to say, using 

nomenclature from Zacharias et al. (16), noise Np

2, the noise that has entered into the patientís 

body, is modified by the acoustic transfer characteristics of the torso, even with small changes in 

sensor position. When attempting techniques that use a separate skin mounted microphone, as a 

signal comparator, the requisite task of trying to model that location-specific transfer would seem 

a costly challenge. For whatever reason, all of the device manufacturers that exhibited proof of 

concept devices that attempted to reduce Np

2 as well as those that attempted ANC technology at 

the sensor-head were unable to market a product during the course of our device testing. 

Perhaps the strongest point to be made for the application of these noise reducing devices can 

be seen best in Figure 1 and in Figures 6-11. The fact that the abnormal visceral sounds were far 

more detectable using the noise-reducing devices makes a strong argument for using their 

listening advantage in health-emergency conditions. 
22

LABORATORY EVALUATION

CONCLUSIONS

Under the well-controlled procedures of a repeated-measures test design, each stethoscope 

device was tested in a controlled noise environment as supplied, as well as with maximum 

attenuation of environmental noise at the ear using an ANC headset. Comparison allowed an 

evaluation of the intrinsic ability of the sensor and electronics to reduce environmental noise 

divested from any potential deficiencies caused by manufacturersí choice of listening device. 

Using digital storage techniques, listeners all heard the same visceral sound recorded earlier on a 

real patient using the device under test in a specific level of interfering environmental noise, with 

that same level accurately recreated around them. Performance biases potentially caused by the 

physical characteristics of the device were minimized, since only the device headset was provided 

to the listener during testing. 

Laboratory results, best depicted in Figure 1, clearly indicate the numeric advantage of Smart 

Med and Sonar Sound devices over the standard stethoscope. But more important, they show that 

they really excel where it counts. They are exceptional in the detection of abnormal or faint 

visceral sounds more likely encountered in a real emergency environment. Figures 6 and 8 

graphically show their detection advantage in detecting abnormal breath and abnormal heart 

sounds, compared to the standard stethoscope, in real-world interfering noise. Averaged across 

all conditions, Table 5 shows an overall detection advantage of 9.8 dB for Smart Med , and 7.7 

dB for Sonar Sound over the standard stethoscope. However, for Smart Med , these gains 

dramatically improve to 17 dB for abnormal breath and 12.4 dB for abnormal heart sounds over 

the standard stethoscope. For Sonar Sound stethoscope, the gains are 15.8 dB for abnormal

breath and 9.7 dB for detection of abnormal heart sounds. 
23

PHASE 2: FIELD EVALUATION

METHOD

Subjects 

All participants were informed volunteers. A total of 33 medical personnel were recruited, 

13 members from the 156 Air Medical Squadron (C-130), 8 members from the USS John C. 

Stennis (CVN), and 12 members from the 1st Battalion 10th Marines supporting a Desert 

Combined Arms Exercise (CAX). No subjects withdrew from the study. Eighteen of the 

participants were enlisted personnel and 15 were officers. 

Experimental Design 

The data were collected from all three groups over a three-week period. Participants were 

asked to evaluate 4 types of stethoscopes: a Littmann conventional stethoscope and 3 noise 

reducing (NR) stethoscopes (SmartMed (device 1); SonarSound(device 2); and Escope(device 3). Prior to the evaluation period, participants were given instructions on how to 

use the stethoscopes and requested to perform auscultation tasks (heart sounds, lung sounds, and 

blood pressure) with each stethoscope during the evaluation period. Because of potential risks to 

real patients during field exercises, device-effectiveness in detection of abnormal heart and 

breath sounds could not be field-tested. Each participant had the opportunity to use the various 

stethoscopes on healthy war-fighters in noisy environments that were indicative of their normal 

working conditions (Table 6). 

Table 6. Environmental Areas used during the Stethoscope Field Evaluations

GROUP TESTING AREAS

C-130 

156 Air Medical Squadron 

North Carolina Air National Guard 

Morris Field, Charlotte, NC 

• On the flight line tarmac, while a C-130 engine was turning. 

• In the cargo hold area of the C-130 during flight. 

CVN 74 

USS John C. Stennis 

Naval Air Station North Island 

San Diego, CA 

• On the flight deck (Vultureís Row and LSO platform) and 

in the Hanger Bay during flight operations. 

• In the primary Medical Spaces (Flight Deck Battle Dressing 

Station and Main Medical). 

• Engineering/Reactor spaces. 

• Berthing area passageway. 

• In a helicopter. 

CAX 

1st Battalion 10th Marines 

Camp Lejeune 

Jacksonville, NC 

On temporary assignment to the Combined Arms 

Exercise held at Twenty Nine Palms, CA 

• On the M-16 Rifle Range. 

• In and near a field ambulance. 

• Near a running field generator. 

• Near a tank while the engines were running. 

• On the flight line tarmac, while helicopter engines were 

turning. 

Evaluation Questionnaire 

Upon completion of the field assessments, participants were asked to complete an evaluation 

questionnaire. The questionnaire was comprised of questions which fell into four primary 

categories: (a) duration of use, (b) design acceptance, (c) performance abilities, and (d) overall 

comments. As a result of comments made by the C-130 group, the first group to participate in the 

field trials, the questionnaire was modified to include blood pressure performance questions. A 

complete copy of the survey is included as Appendix C.
24

For questions regarding design and performance aspects of the stethoscopes (questions 2 ñ 

16), the participants rated how closely they agreed with each item by selecting one of five 

possible responses: ì1î Strongly Agree; ì2î Agree; ì3î Undecided; ì4î Disagree; or ì5î Strongly 

Disagree. Participants were also asked to rank the stethoscopes according to the stethoscopeís 

ability to perform certain functions (question 18.a ñ e) by selecting one of four possible 

responses: ì1î representing the Best to ì4î representing the Worst. Participants were given the 

opportunity to provide specific and general comments on each of the stethoscopes. Data from the 

questionnaires were entered into STATISTICA for Windows, (StatSoft, Inc.) and analyzed. 

Comments by the subjects are given in Appendix D. 

FIELD EVALUATION 

RESULTS

Analysis 

Descriptive analyses were performed for all questions. Results are presented as means +

S.D.8

. The criteria for significance were determined a priori at p <0.05. Each question was 

analyzed using a split-plot repeated measures analysis of variance (29) (ìgroupsî as the 

independent variable and ìstethoscopesî as the dependent variable), followed by a Tukeyís HSD 

post hoc test. Differences between group and ultimate choice were analyzed using Chi-square. 

Questions that requested a written response were reviewed and the frequency recorded by the 

primary field-investigator. 

Results

(1) Usage and Design: As shown in Table 7, the stethoscopes each received a usage

response of 2 indicating that all were used 1-5 times by each participant. The overall head/sensor 

design on each of the stethoscopes was found to be acceptable by all the groups in terms of ease 

of placement on the patient. However, the C-130 group agreed significantly more (p<.01) than 

the CVN group regarding placement ease. Compared to the conventional (p<.01) or E-Scope 

(p<.01) design, the head/sensor on the Sonar Sound was slightly harder to place on the patient. 

The conventional head style was easier to stabilize compared to the Sonar Sound (p<.05) and 

SmartMed (p<.01) design. The CAX group found the head/sensors on the Sonar Sound (p<.02) 

and conventional (p<.02) stethoscopes were slightly more comfortable than on the SmartMed. 

Comments from the participants indicated that the SmartMed head/sensor was big and bulky and 

that Sonar Sound produced excessive background noise when the head/sensor was moved from 

area to area on the chest. 

The participants agreed that the cable lengths and the earpiece/headsets were adequate for 

all the models. The location of the control box relative to the listener was also found to be 

acceptable, however there was a slight variation in the strength of this agreement relative to the 

stethoscopes, which was not further defined after performing a post hoc test. The size of the 

SmartMed control box9

 was unacceptable compared to the others (p<.01) and was found to be 

slightly harder to operate than the E-Scope (p<.04) model. The control buttons on the SmartMed 

were also slightly harder to reach than on the Sonar Sound model (p<.05). Compared to the EScope model, the control buttons on the Sonar Sound (p<.03) were slightly easier to see. 

Although the overall layout of the stethoscope models were adequate, the conventional 

stethoscope was considered more adequate than the SmartMed (p<.02) or Sonar Sound (p<.05) 

designs. 

 

8

 Standard Deviation 

9

 Box size has been reduced to 46% of original size in newest production model. 
25

Table 7. Usage and Design: Evaluation Questionnaire

 Significant Difference Mean S.D. 

I. USAGE: 

1. Indicate the number of times you used each stethoscope (i.e. number of patients) (1: None 2: 1-5 times): 

 [1] Smart Med: 2.00 0.25 

 [2] Sonar Sound: 2.00 0.26 

 [3] E-Scope: 2.03 0.17 

 

II. DESIGN: (1: Strongly Agree 2: Agree 3: Undecided 4: Disagree 5: Strongly Disagree)

 2. Head/Sensor is easy to place on the patient: ** 

 [1] Smart Med: 1.81 0.69 

 [2] Sonar Sound: 2.03 0.94 

 [3] E-Scope 1.69 0.64 

 Conventional: 1.47 0.51 

 

 3. Head/sensor is easy to stabilize (keep from moving): ** 

 [1] Smart Med: 2.09 0.93 

 [2] Sonar Sound: 1.86 0.79 

 [3] E-Scope: 1.72 0.63 

 Conventional: 1.40 0.50 

 

 4. Head/sensor fits comfortably in the hand: ** 

 [1] Smart Med: 2.13 1.06 

 [2] Sonar Sound: 1.63 0.89 

 [3] E-Scope 1.69 0.59 

 Conventional: 1.47 0.51 

 

 5. Cable/hose length from the head/sensor to the control box is adequate: 

 [1] Smart Med: 2.03 0.82 

 [2] Sonar Sound: 1.97 0.73 

 [3] E-Scope: 2.06 1.01 

 

 6.Control Box is easy to operate: ** 

 [1] Smart Med: 2.56 1.16 

 [2] Sonar Sound 2.17 0.87 

 [3] E-Scope: 2.06 0.80 

 

 7. The size of the control box is acceptable: ** 

 [1] Smart Med: 4.00 0.88 

 [2] Sonar Sound: 2.53 1.22 

 [3] E-Scope: 2.25 1.02 

 

 8. Control buttons are easy to reach: ** 

 [1] Smart Med: 2.47 1.05 

 [2] Sonar Sound: 2.13 0.73 

 [3] E-Scope: 2.16 0.68 

 

 9. Control box is conveniently located on the listener: ** 

 [1] Smart Med: 2.94 1.19 

 [2] Sonar Sound: 2.37 0.89 

 [3] E-Scope: 2.44 0.91 

 

 10. Control buttons are easy to see: ** 

 [1] Smart Med: 2.19 0.86 

 [2] Sonar Sound: 2.10 0.61 

 [3] E-Scope: 2.56 0.95 

 

 11. Ear piece/headset is comfortable: 

 [1] Smart Med: 1.94 1.01 

 [2] Sonar Sound: 2.23 0.90 

 [3] E-Scope: 2.23 0.92 

 Conventional 1.95 0.78 

 

 12. Cable length from the ear piece/headset to the control box is acceptable: 

 [1] Smart Med: 2.23 0.80 

 [2] Sonar Sound: 2.17 0.66 

 [3] E-Scope: 2.19 0.83 

 13. The overall layout (control box, head, earphones) of the stethoscope is adequate: ** 

 [1] Smart Med: 2.81 1.03 

 [2] Sonar Sound: 2.33 0.84 

 [3] E-Scope: 2.31 0.90 

 Conventional 1.85 0.75 

 **p<0.05 for stethoscope effect 
26

N/A - Not applicable; these questions were not addressed to these subject groups. 

(2) Performance: As shown in Table 8, the CAX group agreed that the electronic 

stethoscope models improved their ability to determine blood pressure and hear heart and lung 

sounds in a noisy environment. The C-130 group were given an earlier questionnaire that posed 

this question slightly differently asking them to compare NR stethoscope performance against a 

conventional stethoscope. For that reason their response to that question is not included in Table 

8. In response to that question, compared to a conventional stethoscope, the C-130 group agreed 

the Sonar Sound (2.91 + 1.22; p<.01) model improved their ability to hear normal heart and lung 

sounds, while the E-Scope (4.45 + 0.69) and SmartMed (4.18 + 0.98) models did not improve 

their ability. Overall, the participants were undecided on whether the stethoscopes would improve 

the quality of patient care in a noisy environment, with the C-130 group responding a little more 

strongly that the models may not improve patient care (p<.01) than the CAX group. 

With regard to specific performance factors, the participants ranked the conventional 

stethoscope (p<.01) as being the easiest model to use compared to the SmartMed model. For the 

ability to reduce noise, the C-130 (p<.04) and CAX (p<.02) groups ranked the conventional 

stethoscope much worse than the CVN group. When compared to the C-130 group, the CVN and 

CAX groups tended to rate the NR stethoscopes as being slightly better in their ability to hear 

heart and lung sounds. Compared to the conventional Stethoscope, the SmartMed model was 

III.

Mean S.D. Mean S.D. Mean S.D. Mean S.D.

14. Stethoscope improves ability to hear heart and 

lung sounds in a noisy environment: N/A N/A

[1] SmartMed: 2.37 1.12 3.00 1.41 1.91 0.54

[2] Sonar Sound: 3.00 1.37 3.88 1.55 2.30 0.67

[3] E-Scope: 2.68 1.42 3.13 1.55 2.36 1.29

Conventional: 2.94 1.21 2.43 0.79 3.27 1.35

15. Stethoscope improves ability to determine blood 

pressure in a noisy environment: N/A N/A

[1] SmartMed: 2.25 0.97 2.75 1.04 1.92 0.79

[2] Sonar Sound: 2.39 1.04 2.38 1.06 2.40 1.07

[3] E-Scope: 2.60 1.10 2.75 1.04 2.50 1.17

Conventional: 2.65 1.09 2.63 0.74 2.67 1.30

16. Stethoscope would improve the quality of 

patient care in a noisy environment: * *

[1] SmartMed: 2.94 1.32 3.58 1.38 2.88 0.99 2.33 1.23

[2] Sonar Sound: 2.60 1.13 2.83 1.40 2.75 1.16 2.20 0.63

[3] E-Scope: 3.13 1.34 3.92 1.16 2.63 1.19 2.67 1.30

Conventional: 2.85 0.99 2.50 0.53 3.08 1.16

17. In a noisy environment, I would choose to use 

this stethoscope (group percentage): N/A N/A

[1] SmartMed: 15% 0% 25%

[2] Sonar Sound: 20% 25% 17%

[3] E-Scope: 35% 25% 42%

Conventional: 30% 50% 17%

17a. Compared to the Conventional, it improves my 

ability to hear heart and lung sounds in noise: N/A N/A

[1] SmartMed: 3.91 0.83

[2] Sonar Sound: 2.82** 1.08

[3] E-Scope: 4.09 0.83

(1: Strongly Agree 2: Agree 3: Undecided 4: Disagree 5: Strongly Disagree)

CVN

PERFORMANCE: 

Table 8. Performance: Evaluation Questionnaire

Total C-130 CAX

 * p < 0.05 for group effect

** p < 0.05 for stethoscope effect
27

considered to be better for hearing heart sounds (p<.02) and the E-Scope model was better for 

hearing lung sounds (p<.03). 

For the CVN and CAX participants, when asked which stethoscope they would choose to use 

in a noisy environment, the choice frequency was: 15% for SmartMed, 20% for Sonar Sound, 

30% for the conventional and 35% for E-Scope. The C-130 group indicated they would prefer to 

use the Sonar Sound model instead of the conventional stethoscope.

FIELD-TEST

CONCLUSIONS

The primary purpose in conducting the field trial study was to assess some of the operational 

capabilities and limitations associated with the various noise-reducing (NR) stethoscopes. Thus, 

the primary focus of the questionnaire was on factors related to design, performance, and 

operational acceptability. The data from the operational testing needs to be interpreted in a 

conservative fashion. While many of the comparisons between the various subject groups and 

stethoscope models were statistically significant, it should be noted that this study was limited by: 

1) The inability to evaluate abnormal heart and breath sounds in field-operation conditions, 

because of potential human risks to real patients during the operational exercise. This is 

most relevant since, analysis of the laboratory data makes it clear that it is exactly in these 

more-critical listening tasks that these products dramatically outperform the standard 

stethoscope. 

2) The novelty of the devices compared to the use-experience of a standard stethoscope 

3) The inability to control and limit the sound-levels on which subjects based their 

evaluations. Our subjects insisted on trying the devices in noise levels beyond their 

design limit. 

4) The incapability to standardize the types of sound environments and levels of the visceral 

sounds experienced by each of the subjects as they evaluated the stethoscopes during 

actual field operations. 

5) A small sample size within each group 

Within those limitations, the field preference-data appropriately do not support the 

assumption that a single NR stethoscope model could accommodate the medical needs of all the 

groups in all military field-environments where some noise levels can easily exceed 120 dB SPL. 

Keep in mind that the design goal was for a small, simple, general-issue device that would 

function at levels under 90 dB SPL over a device, yet to be built, that can remove structural 

vibration transmitted into the torso. With regard to the overall design of the stethoscopes, the 

groups were in agreement that the conventional stethoscope was the most adequate design. 

However, they preferred the small compact size of the E-Scope stethoscope with its integral 

control box, and the push-button style membrane switch associated with the Sonar Sound 

stethoscope. Other factors will be addressed separately for each group. 

 

C-130 Group: During the evaluation period, the C-130 group was almost constantly exposed 

to an extremely high noise environment (greater than 100 dBA), especially during the flight 

operations. Within this environment, the participants were unable to detect even normal heart or 

lung sounds with any of the stethoscopes since it was well out of the intended operating range of 

these compact devices. Several participants mentioned they were able to detect blood pressure 
28

with the Sonar Sound stethoscope while in flight, which could be considered an operational 

benefit. The participants currently rely on the palpation method for patient evaluation during 

flight and would prefer a more accurate way of monitoring the patient. Although automatic blood 

pressure devices are available that do not rely on acoustic input for measurements, several devices 

would be needed to accommodate the large number of patients that can be transported aboard the 

C-130, thus making the purchase of those machines cost prohibitive. Some participants 

mentioned that it would be a benefit if the headset/earpiece could be incorporated into their flight 

communication headsets to prevent any unprotected exposure to the C-130 noise level. In fact all

of the tested devices can easily be patched into their flight helmet ANC headsets. 

The participants also evaluated the stethoscopes at a staging-area located directly behind the 

C-130. This is an area where final patient evaluation may occur before the aircraft takes off. The 

sound level in this area is approximately around 70 ñ 80 dBA. The participants found that the 

Sonar Sound stethoscope performed better than the other stethoscopes for detecting blood 

pressure and for hearing normal heart and lung sounds. Overall, the C-130 group indicated that 

the Sonar Sound stethoscope could potentially improve their patient care abilities. 

CVN Group: In the general comment section of the questionnaire, a corpsman aboard the 

USS John C. Stennis reported: 

ìIn most cases a patient on the flight deck who is thought to have an injury which 

must be further assessed with a stethoscope will be taken to Main Medical within minutes. 

The environment is too loud and hazardous to keep a patient there, for long. Generally we 

assess airway, c-spine, breathing, and circulation, put the patient on a stretcher and have 

them in Main Medical in about 2-8 minutes post the time of injury.î 

As demonstrated by this statement, the medical personnel aboard an aircraft carrier rarely 

perform medical procedures in extremely high noise environments (greater than 100 dBA), such 

as the Flight Deck, Hanger Bay, or Engineering Spaces. These areas are considered unsafe for 

both the patient and medical personnel, so procedures have been developed to move the patient 

safely away from the noisy environment to a safer area. The noise around the safer areas would 

probably be around 80-84 dBA. Within these areas, the participants found that, for normal

healthy patients, the NR stethoscopes performed only slightly better than the conventional 

stethoscope. Since the conventional stethoscope performed adequately in the slightly noisy areas, 

50% of the participants indicated that they would choose the conventional stethoscope over the 

NR stethoscope models. Again, keep in mind they were never given the opportunity to evaluate a 

faint or abnormal visceral sound in their evaluation. Participants also indicated that often times 

they use their own personal conventional stethoscope (i.e. Littmann Cardio II), which is slightly 

better than the government issued item. In fact this is the model we used as the conventional 

device in our laboratory tests, to afford our listeners the best possible acoustic stethoscope for 

their comparisons. The laboratory results for the Littman seen in Figure 1 corroborate their field 

findings on detection of normal healthy heart and breath sounds. 

The Navy is currently researching the possibility of incorporating telemedicine technology as 

part of the shipboard medical capabilities. The ability to interface a stethoscope with the 

telemedicine system would be an operational asset to the medical facility. The conventional 

stethoscope does not have Telemedicine capability, however the NR stethoscopes are able to link 

with computer systems and provide the advantage of noise reduction as well. 
29

CAX Group: Similar to the CVN group, the participants within this group were exposed to a 

wide range of noise levels and they had also developed procedures to remove patients from the 

high noise environments when possible. For the field trials, most of the participants evaluated the 

stethoscopes in high and moderately-high noise environments (between 85 to 100 dBA), such as 

those found near field generators, truck engines, and artillery fire. 

General comments indicate that size, simplicity, and durability were the main factors that 

influenced a number of their responses. Forty-two percent of the participants said they would 

choose the E-Scope stethoscope over the others, though laboratory data show this device to be the 

least effective of the three. This apparent selection bias was likely due to E-Scope stethoscope's 

small, compact, and easy to use, design. From their operational point of view, the stethoscope 

needs to be small enough to fit within their medical packs. Although it is similar in size to EScope stethoscope, only 17% said they would choose Sonar Sound stethoscope. Concern was 

expressed that the removable cable connection between the head and the control box may be a 

durability and safety concern. Subsequent to their evaluation the Sonar Sound stethoscope has 

been modified as prototype 2 seen in Appendix E. The head is no longer removable from the 

cable. 

With regard to performance capabilities with healthy patients, the participants ranked the EScope stethoscope better than the conventional stethoscope for ability to reduce noise, detect 

blood pressure, and improve the ability to hear normal healthy heart and lung sounds. Similar to 

E-Scope stethoscope, Smart Med stethoscope was also considered the best for hearing heart 

sounds; however only 25% of the participants would choose Smart Med stethoscope, mainly 

because of the large control box size. Participants mentioned in their comments that they would 

have considered Smart Med stethoscope if it were smaller and more compact. Subsequent to their 

evaluation, Smart Med stethoscope has been reduced in size by 46% (prototype1, Appendix E). 

Since Smart Med stethoscope has a headset design as opposed to an earpiece design, concern was 

raised that the corpsmen would need to remove their flak helmets in order to assess patients, 

which in a combat situation could be an operational hazard. 

As mentioned in the CVN group, Smart Med stethoscope costs more than E-Scope 

stethoscope and significantly more than the conventional stethoscope, which makes this option a 

strong cost consideration for this group (and needlessly biases their selection if the item were 

general issue). However, the potential for telemedicine is also an important factor. As discussed 

earlier, the NR stethoscopes evaluated were selected for their ability to connect with various 

telemedicine systems, including systems located on laptop and mini-laptop computers. This 

capability would provide a greater communication link between the field corpsmen, the Battle Aid 

Stations, the Field Hospitals, and the main medical facilities. 

Final Recommendations Based on Field Trials With Normal Heart And Breath Sounds: In 

general, the evaluation survey revealed advantages and limitations for the three NR stethoscopes, 

which were dependent upon the type and level of noise environment used during the evaluation. 

Based on factors related to design, performance, cost, and operational acceptability, the following 

recommendations can be made as to preference for or against the standard stethoscope: 

C-130 Group: Sonar Sound stethoscope, because of its ability to detect blood-pressure while 

in flight and improve ability to hear heart and lung sounds while on the flight line. 
30

CVN Group: Sonar Sound stethoscope or E-Scope stethoscope, because these smaller 

models will allow for telemedicine capabilities and will improve ability to hear heart and lung 

sounds in moderately noisy shipboard areas. 

CAX Group: E-Scope stethoscope, because itís small, compact, and is easy to use. It also 

has the ability to reduce noise, detect blood pressure, and improve the ability to hear heart and 

lung sounds. However, Smart Med stethoscope may be a better choice if design modifications 

could be made to reduce the size of the box and the head/sensor and replace the headset with an 

earpiece design. [Subsequent to the field tests the newest production model of this device has 

been reduced in size by nearly 46% which is a major reduction in size. See Appendix E: 

production-prototype 1.] This significant improvement in functionality would also be relevant to 

the sized related selection criteria manifest by the CVN group. 

SUMMARY & CONCLUSIONS 

LABORATORY & FIELD-TESTING

The present study has provided an evaluation of several small COTS noise-reduction 

stethoscopes capable of exceptional performance in moderately-intense noise, which can be used 

stand-alone by medics in the battlefield, but also can function as a key component in electronic 

data gathering. These products allowed trained medical personnel to detect heart/breath sounds in 

noise environments significantly louder than possible when using a conventional stethoscope. 

Because each is relatively inexpensive, (less than $500 in single quantities), mass distribution is 

possible. Once a general-issue item, familiarity with its use and placement should enhance 

performance beyond our limited-experience comparisons made against a highly familiar 

stethoscope device. Since each was selected to have an electrical output, with available software 

it can serve as the ideal front-end acoustic sensor for medical diagnostics within the rapidly 

developing field of ultra-miniaturized COTS Pentium devices. As a modular, rather than totally 

integrated component, it is less likely to obsolescence in such a rapid evolution in processor 

hardware and software. It is in this modular application that the easily-operated general-issue

(therefore familiar) noise-reducing stethoscope device becomes essential. 

Each stethoscope device was laboratory-tested in a controlled-noise environment both as 

supplied, and with maximum attenuation of environmental noise at the ear. Comparison allowed 

an evaluation of the intrinsic ability of the sensor and electronics to reduce environmental noise 

divested from any potential deficiencies caused by manufacturersí choice of listening device. 

Using digital storage techniques, listeners all heard the same visceral sound recorded earlier on a 

real patient using each device in a range of levels of interfering environmental noise, with that 

same level accurately recreated around them. 

Laboratory Findings 

Laboratory data show that for the SmartMedÆ stethoscope, performance improvement, 

averaged over the three environments, is 17 dB for abnormal breath sound and 12.4 dB for 

abnormal heart sound. For the Sonar Soundô stethoscope, performance improvement for these 

same abnormal sounds is 15.8 and 9.7 dB respectively. These performance improvements are, of 

course, gains in detectability over a standard stethoscope. Of far more relevance, they allow 

trained medical personnel the ability to hear medically relevant abnormal visceral sounds in the 

region from 85 to 95 dB SPL, a region well out of the listening range afforded by even the best 
31

conventional stethoscope. Laboratory data also show that while normal healthy heart sounds can 

be heard with a conventional stethoscope in a fairly loud environment, abnormal or weak visceral 

sounds cannot. 

Field Test Caveats: 

 The field-testing must be viewed in perspective. We field-evaluated the three COTS devices 

over a range of simulated combat situations that in most cases far exceeded our operating criterion 

of 90 dB SPL10; environments where little design effort was taken to reduce the structurally 

transmitted components of energy that entered the torso. Basically our test volunteers wanted to 

see exactly what these devices could do across the full range of combat environments without

regard to their design operating limits. While it was useful to check their potential in this 

environment, inclusion of these excessive conditions did bias these field-test listeners by trying to 

use the devices in airborne and structurally transmitted noise environments beyond their intended 

operating range. Sound pressure levels in the C-130 were 14 dB higher than the intended designoperating range of the miniature field-device. However, the field tests were able to demonstrate 

that the Sonar Sound device was extremely useful in detecting blood pressure in the 104 dB SPL 

environment of a C-130. Most relevant to interpreting the field-reports is the fact that, because of 

our concern for the safety of patients with abnormal vital signs, detection of abnormal heart and 

lung sounds were not evaluated in field-exercise testing. Analysis of the laboratory data makes it 

clear that it is exactly in these more-critical listening tasks that these products dramatically 

outperform the standard stethoscope. For that reason the field data are most appropriately used to 

assess users' comments on questions 1-13 (Appendix C). The field-users had no way of assessing 

how much better these devices worked on abnormal visceral sounds, and during their volunteer 

field-test efforts they used them in environments well beyond their intended operating level. As a 

result their responses to questions 14 through 17a (Appendix C) are not an accurate assessment of 

the improved capability of the device within its intended sound-level design limits in true medical 

trauma. The laboratory-data seen in Figure 1 clearly confirm this. Based on the ability to detect 

normal heart sounds from a healthy young adult male, the added cost of these stethoscopes would 

not be warranted. However in emergency situations, abnormal or faint heart and breath sounds 

are quite relevant, and here the performance of these devices is exceptional. 

Field Findings 

Perhaps the most important fact that the field data show is that users will sacrifice 

performance for size and familiarity. No matter how well they perform over the conventional, 

novel devices of any type require more than a few hours use to become second nature. They 

require different handling and methods of stowage that need to become "routine." For that 

familiarity to occur rapidly, they need to be intuitively simple for the user to deploy and operate. 

Our Recommendation 

It is our recommendation that the two noise- reduction stethoscopes mentioned below, and 

specified in Appendix F, be issued into the federal stock system for immediate use in the far-more 

commonly encountered moderately-loud (70-90 dB SPL) noise environments. With those 

specifications the devices can be competed under bid. While these are currently COTS devices, 

with large purchases ruggedization for specific extreme application is always possible. For use 

under extreme battlefield conditions we recommend further ruggedization of any COTS device. 

 

10 Actual measured levels of the environments: 100 KW Generator @ recommended 25 feet 90 dB SPL 

 Hum Vee (patient area during soft-sand transit) 97 dB SPL 

 C-130 (patient area during level flight) 104 dB SPL 
32

Along with that general-issue recommendation is the recommendation that users be given 

training in their significant capability in noisy environments and training to understand those 

limitations based on size and cost that specifically limits use to exclude intense noise levels (above 

90 dB SPL). Usually such environments, as in military helicopters, are contaminated by 

structurally-transmitted noise that these small field-pack devices are not designed to handle. 

Users must also be instructed to understand that, in noise areas above 90 dB SPL, with continuous 

exposure without the additional protection of ANC headsets (such as in aviation flight-helmets), 

they are exposing themselves to risk. The standard noise exposure instructions outlined in 

OPNAVINST 5100.23E (see their Appendix 18-C) apply (30). 

It is also our recommendation that these small devices be used for their ability to provide the 

best possible electrical signal for telemetry and also to any of the various software programs that 

allow acoustic records of patient pathology11. 

Once a general-issue item, by virtue of their broad use and familiarity, proper placement for 

maximum information will be second nature to the user. As a result, placing the sensor to use its 

output in more elaborate configurations will be intuitive. 

Follow-on 

Subsequent to our laboratory-data analysis, we contracted the developers of devices 1 and 2, 

as best performers, to reduce the size of their product without changing any of its electronics or 

sensor technology. Results to miniaturize the physical device have been extremely successful. 

Prototype 1 from Smart MedÆ (Appendix E) is now a production model. This upgrade 

significantly reduces the device's size by 46% thereby eliminating its field-identified major 

drawback. The device-case will now fit in a shirt pocket. Prototype 2, the NORE Scope from 

Medicoustics (upgrade of Sonar Soundô) is a major design breakthrough. Although it appears 

bulky in its cost-constrained machined-case prototype, it proves that all of the electronic 

components of the Sonar Soundô Stethoscope can be incorporated into the sensor-head. Fieldidentified comments on the Sonar Soundô regarding noise, as the device is relocated on the 

patient, are eliminated with the pressure-sensitive on switch. The manufacturer claims surfacemount technology can reduce the electronics to completely fit within a package smaller than the 

sensor on the original Sonar Sound (Appendix E, Figure 2) at a weight of approximately 3 ounces, 

and a battery-life of 200 hours on-time. This manufacturer would be ideal candidate for SBIR 

development. 

Based upon our quantitative laboratory data, the two recommended COTS stethoscopes are 

the SmartMedÆ Stethoscope (in its upgraded smaller control-box version as specified in Appendix 

F), and the SonarSoundô Stethoscope, or its miniaturized prototype version the Medicoustics 

NORE-Scope, (also specified in Appendix F). Other than the fact that the Sonar Soundô (or its 

upgrade) is probably more appropriate for measuring blood-pressure in noise-environments well 

beyond the intended noise-level operating-range, decisions as to which is appropriate for a 

specific application below 90 dB SPL can be up to the style preferences of the end-user. 

Laboratory data (Table 5) show that, averaged across environments and across visceral sounds, 

the SmartMedÆ is 2.1 dB better in performance than the Sonar Sound device. However as seen in 

 

11 One specific medical-software product is AMORE from Medivisio Products Helsinki Finland. With this 

software, visceral sounds can be recorded, identified by sensor location and graphically displayed and 

played-back within a patient record database. 
33

Table 4, in the HumVee-ambulance noise-environment, both perform equally. Further, the Sonar 

Soundô is smaller and uses a more conventional stethoscope headset, which would fit under a 

field helmet. The prototype upgrade of the Sonar Soundô (Medicoustics NORE-Scope) is still 

smaller. The decision on which of these excellent devices is ideal should be based upon the 

operational needs of the end user. For their abilities to detect the most critical visceral sounds, 

any of the recommended devices will dramatically outperform the conventional stethoscope. 

Not surprisingly, these effective devices have been integrated with outboard, miniaturized, 

digital processing hardware for visual presentation and telemetry. Using the COTS product ìas 

isî or with further miniaturization, the possibilities for passive acoustic diagnosis in the battlefield 

are open. 
34

REFERENCES 

(1) Laennec, R.T., (1819) De Lauscultation Mediate, ou Traite du Diagnostic des 

Maladies des Poumons et du Coeur, Fonde Principlement sur ce Nouveau 

Moyen d'Exploratin. Paris: J.A. Brosson & J.S. Chaude. 

(2) Yost, W.A. (1994) Fundamentals of Hearing: An Introduction. San Diego: 

Academic Press. 

(3) Korotkoff, N.S. (1905) A Contribution to the Problem of Methods for the Determination of 

Blood Pressure: II. St. Petersburg: Bulletin of the Imperial Military Medical Academy: 

365-67. 

(4) Sekhar, L.N., and Wasserman, J.F. (1984) Noninvasive Detection of Intercranial Vascular 

Lesions Using an Electronic Stethoscope. Journal of Neurosurgery, 60(3), 559-72. 

(5) Gallo, L.M., Airoldi, R., and Palla, S. (1993) Power Spectral Analysis of 

Tempromandibular Joint Sounds in Asymptomatic Subjects. Journal of Dental 

Research, 72(5), 871-75. 

(6) Ljungvall, P., and Thulin, T. (1991) Hand-free Stethoscope- Method and Instrument for 

More Reliable Blood Pressure Measurements. Journal of Internal Medicine, 230(3), 

213-17. 

(7) Grenier, M., Gagnon, K., Genest, J., Durand, J., Durand, L. (1998) Clinical Comparison 

of Acoustic and Electronic Stethoscopes and Design of a New Electronic Stethoscope. 

The American Journal of Cardiology, 81, 653-656. 

(8) Brogan, F.A., Collins, F.G., and Wing, M.E. (1967) An Experimental Electronic 

Stethoscope for Aircraft Use. A Preliminary Report. SAM Technical Report 67-39, 

Brooks Air Force Base, TX: USAF School of Aerospace Medicine. 

(9) Allred, J.E., Brammell, H.L., Hunt, M.A. (1969) Two Electronic Stethoscopes for Use in 

High Noise Environments. SAM Technical Report 69-61, Brooks Air Force Base, TX: 

USAF School of Aerospace Medicine. 

(10) Pasic, T.B., and Poulton, T.J. (1985) The Hospital-Based Helicopter.Archives of 

Otolaryngology Head and Neck Surgery, 1985, 111, 705-08. 

(11) Bishop, L.C. (1990) Aviation Auscultation. Journal of the American Medical Association, 

263(2) , 233. 

(12) Cottrell, J.J., and Kohn G.M. (1990) Aviation Ausculation (In Reply). Journal of the 

American Medical Association, 263(2), 233. 

(13) Hunt, R.C., Bryan, D.M., Brinkley, V.S., Whitley, T.W., and Benson, N.H. (1991) 

Inability to assess breath sounds during air medical transport by helicopter. Journal of 

the American Medical Association, 265(15), 1982-84. 
35

(14) University Research Engineers and Associates, INC (1996) Digital Active Noise 

Attenuation Vital Signs Monitor DANA-VSM Interim Status Report, 30Jun96. 

(15) Callahan, M., Kokar, M., Wodicka, G., and Callahan, T. (1994) An Auscultation Sensor 

and Telemetry Device for Use in High Noise Environments. (Phase I SBIR Program 

with University Research Engineers and Associates, Acton MA), Armstrong 

Laboratory Report AL/AO-TR-1994-0185, Brooks Air Force Base, TX: Air Force 

Materiel Command. 

(16) Zacharias, G.L., Miao, A.X., Moore, J.A., Collier, R.D., Asdigha, M. and Remington, P.J. 

(1993) Active Noise Cancellation Stethoscope (Phase I Final Report) Report R92241 

AD No. B176951 Cambridge MA: Charles River Analytics Incorporated. 

(17) Suzuki, A., Sumi, C., Nakayama, K., and Mori, M. (1995) Real Time Adaptive Canceling 

of Ambient Noise in Lung Sound Measurement. Medical and Biological Engineering 

and Computing, 335(5), 704-708. 

(18) Patel, S.P., Wodicka, G.R., and Callahan, M.G. (1996) Active Noise Reduction 

Stethoscopy for Lung-sounds Measurement in Loud Environments. 131st Meeting of 

Acoustical Society of America, . (Abstract: Journal of the Acoustical Society of 

America 99, Suppl. 2p BV4, 2477). 

(19) Kopczynski, H.D., Stoner, D.L., and Rex, G.A. (1975) Inflight Patient Monitoring/Blood 

Pressure Measurement-Device. SAM Technical Report 75-9, Brooks Air Force 

Base,TX: USAF School of Aerospace Medicine. 

(20) Ertel, P.Y., Lawrence, M., Brown, R.K., and Stern, A.M. (1966) Stethoscope Acoustics: I. 

The doctor and his stethoscopeî, Circulation, 34, 889-898. 

(21) Ertel, P.Y., Lawrence, M., Brown, R.K., and Stern, A.M. (1966) Stethoscope Acoustics: II. 

Transmission and filtration patternsî, Circulation, 34, 899-908. 

(22) Harris, J.D. (1980) A comparison of computerized audiometry by ANSI, Bekesy fixed 

frequency, and modified ISC procedures in an industrial hearing conservation program. 

Naval Submarine Medical Research Laboratory Report, No. 930. 

(23) Russotti, J.S., Santoro, T.P., Hanna, T.E. and Wojtowicz, J. (1993) (U) Effects of digital 

sampling rate and bit quantization on passive sonar target detection performance. Naval 

Submarine Medical Research Laboratory Report No. 1184. 

(24) DoD Instruction 6055.12 of April 22 1996, DOD Hearing Conservation Instruction. 

(25) Russotti, J.S., Santoro, T.P., and Haskell, G.B. (1988). Proposed technique for earphone 

calibration. Audio Engineering Society Journal, 36, 643-650. 

(26) Russotti, J.S. (1995) Sonar headphone selection for optimum performance: an overview. 

Naval Submarine Medical Research Laboratory Report, No 1197. 
36

(27) Killion, M. C. (1979) Equalization Filter for Eardrum-Pressure Recording Using a 

KEMAR Manikin. Journal of the Audio Engineering Society, 27, 13-16. 

(28) Audio Engineering Society (1984) AES recommended practice for professional audio 

applications-preferred sampling frequencies. Journal of the Audio Engineering Society, 

32(10), 781-785.

(29) Winer, B. J. (1962). Statistical Principles in Experimental Design. New York: McGrawHill. 

(30) OPNAV Instruction 5100.23E of 15 January1999, Navy Occupational Safety and Health 

(NAVOSH) Program Manual for Forces Afloat (NOTAL). 
APPENDICES

37

APPENDIX A: 

NRS WORKING GROUP CONCLUSIONS

NR Stethoscope and Military Need 

 In broad long-range terms, the ideal noise-reducing stethoscope should meet criteria in four 

areas: 1) have the ability to convey reproducible sounds of interest in a noisy environment, 2) have 

environmental durability, 3) be easily used by medical and non-medical (emergency-rescue) personnel 

and, 4) have the potential to transmit, monitor, and store information. Furthermore, there are needs that 

are specific for the military, in particular the United States Navy (USN), that the stethoscope must meet, 

such as use in harsh environments, ease of use by Independent Duty Corpsmen (IDCs), and field pack 

portability and low maintenance. The following is an in depth discussion of the above points. 

Fidelity of Extracted Sounds 

 Primarily, the ideal noise reducing stethoscope needs to be a fully functioning stethoscope, 

which reproduces visceral sounds (heart, lung, bowel) within a noisy environment, either by audible 

transmission of the sound via headphones, or by a visual translation of the sound to an easy to interpret 

display - preferably both. Examining current technology, it is judged that two stethoscope models need 

to be differentiated, since size, complexity, and ultimately cost are related to universality of application. 

The first device would function in noise from 75 to 90 dB SPL. This model would have a very wide 

application since most general noise falls within this range. Practical situations include: loud 

conversation, traffic, ICU settings, ambulance transportation with sirens, and military medical settings 

such as near generators or equipment, hyperbaric medical pressure chambers, on board submarines and 

surface ships, and in the battlefield. The second more elaborate device would be required to function in 

noise up to 130-140 dB SPL. This model would be applicable to extremely noisy environments such as 

helicopter air-evacuations, and on board vessels with continuous loud impact noise. This model would 

sacrifice size and low cost for specialized use in limited environments. 

 

The ideal stethoscope should be able to detect and accurately reproduce different medical sounds 

within an organ - especially the heart and lungs. The instrument should be able to detect presence and 

absence of abnormal heart-rate, important murmurs, and the amplitude of the heart-beat. Also, the 

presence and absence of various lung sounds should be auscultatable; i.e., breath sounds, wheezes 

(whistling high frequency sounds found in asthma) as a minimum, and additionally, rales (popping 

sounds found with fluid/pus/blood in lungs), and rhonchi (lower frequency sounds found in bronchitis). 

Environmental Durability 

 In the military environment, stethoscopes will be required to function under harsh conditions and 

environments. Extreme temperature conditions should be tolerated, with heat greater than 100 degrees F 

(desert warfare, boiler rooms aboard surface vessels and submarines, and summer field exercises), and 

cold less than 0 degrees F (winter warfare, winter field exercises, high-altitude exercises, and cold 

weather operations). High or low pressure situations should also be tolerated, for example, treatment in 

hyperbaric medical chambers (used by the USN diving community for diving related injuries), locking 

in/out of submarines (SEALS/Special Warfare) or general diving operations (marines, combat swimmers, 

SEALS/Special Warfare), treatment at high altitude during mountain exercises, and medical care 

delivered on board helicopters and fixed-wing craft during flight. Appendix B details the physical and 

other specifications that the ideal instrument of the future will have to meet. 
APPENDICES

38

Utility 

 Because this medical instrument will often be used in a field environment, it is most important 

that it be simple to operate. It should be easy to carry and no more cumbersome or outwardly complex 

than the traditional instrument. It should need infrequent battery or component replacement, be easy to 

maintain, require minimal quality assurance checks or calibration, and need little additional training prior 

to use. In military operations the majority of personnel who will be using the stethoscope will be nonphysicians. These will include emergency medical technicians (EMTs) and Independent Duty Corpsmen 

(IDCs). Given the operational requirements, the instrument should be designed for immediate ease of 

use. 

 

Data Transmission 

 Telemedicine, the ability to electronically transmit large volumes of medical information, is of 

increasing importance to the military. This would enable complex data, e.g., lab results, radiographs and 

even video of physical signs, to be transmitted between remote operational units, where local medical 

support is minimal, to centers of medical expertise. In order to participate in this process, it is desirable 

that the ideal stethoscope have the ability to store and output its received data in a form that could be 

electronically transmitted. 

 

Operational Requirements 

 Below is a summary of the needs of the Navy and of the medical community in regard to the 

minimum criteria for a feasible noise-reducing stethoscope of the future without regard to current 

technological capability. These criteria are a summary of the consensus determined by the working group 

held in Washington, D. C. 

NEEDS OF THE NAVY: 

1. Readily portable in the medical field-pack, with minimal supplies. 

2. Environmentally hardy to: temperature and pressure extreme, shock, sand, sea, EMI, and 

corrosion. 

3. Easy to use. 

4. Require minimal training. 

5. Require minimal maintenance and calibration. 

6. Capable of storing data in a form for electronic transmission. 

7. Capable of being an effective diagnostic instrument within 75 to 90 dB SPL background noise 

for one model and 90-140 dB SPL for another (which would sacrifice size, complexity, and cost 

for operation in high noise). 

8. Low cost. 

9. Capable of being used in a wide range of military settings e.g. SPECWAR, surface/aviation, 

undersea etc. 
APPENDICES

39

APPENDIX B: 

SAMPLE FUTURE END-GOAL NR STETHOSCOPE

SPECIFICATIONS

Ideal Noise Reduction Stethoscope of the Future: base model 

SPECIFICATIONS 

Case: 

Size: (phase 1) 3.25 x 3.25 x 1.25 max. 

(Ideal) 3.6 x 2.2 x 1.0" + 1% 

 Shape: all edges with radius of 0.125 in min. 

 Maximum Volume (phase 1) 13.2 cu inches 

(Ideal) 8.0 cu inches 

Integral stainless steel belt clip (either u shaped wire or flat leaf-spring) 

Output: 

Visual: LCD monochromatic, water-resistant mount, integral with case. 

Acoustic: Mini stereo headphone jack wired mono (tip & ring +, sleeve -) Jack housed in 

water-resistant cavity in case, to protect internal components. Output circuitry 

load-resistor protected 

 

Digital: Water-resistant connector with enough pins to support an RS-232 compatible output 

format. 10ft cable with mating water-resistant connector, one end, and RS 232 connector 

on other end, for computer interface. 

Functional: 

A water-resistant three-button operating system is desirable: The device is activated by 

simultaneously depressing buttons 1and 2, and memory can be reset by simultaneously 

depressing all three buttons. Once activated: a single button-press of Button 1, initiates 45-60 

sec data-gathering, analysis, alpha numeric display of results, and time-marked storage of both 

ANR signal and visually displayed data. Entry serially indexed for retrieval. Each additional 

manual button press results in a similar 45-60 sec data gathering, analysis, display of results, and 

storage, again sequentially indexed by order of entry. Device holds 10 such data files. Button 2 

serially displays stored data files by increasing index number and time of recording. Holding 

down button 2 rapidly sequences through index of available stored files. Releasing button 2 

stops the sequence at the displayed file. Button 3 is used to initiate playback of the currently 

displayed file. Cycle repeatable. An 1lth entry on button one will remove the earliest entry (1) 

and renumber all later entries (2 becomes 1 etc.). Device shut-off requires simultaneously 

depressing buttons 1 and 2. To conserve battery power system shuts down automatically after 10 

min. with all data saved. 
APPENDICES

40

Environmental: 

 Operating mechanical shock tolerance: 5G 

Operating temperature range - 10 to 110 degrees Fahrenheit 

 Immunity to salt-water spray 

 Immunity to EMI 

 Case water resistant to 10 feet 

Operational: 

Battery life: 6 months min. under daily 8hr. use 1460 hrs. 

 MTBF 3,000 hrs. 

Noise reduction effective enough to allow full operation in 90 dB broadband pink noise and also 

in Military and Civilian Ambulances at speeds of 50 MPH 

Full operation: 

Visually displayed numeric data on Blood Pressure, pulse, respiration, valve sounds and 

murmurs. 

Aurally presented information audible enough for evaluation of pulse, respiration, valve sounds 

and presence of murmurs. 

Suggestions: 

Removable Neoprene boot with flap to cover LCD display for added shock protection and covert 

use. 

 

Adjunct development of add-on piggyback or tethered (belt mounted) infrared transmitter for use 

with cordless earphone receiver. 

 

Data format and or software to interface with a standard A/D PC sound board during Hyper and 

Hypo-baric operation 

 

Operation in temperature extremes 
APPENDICES

41

APPENDIX C: 

ID#:ÖÖÖÖÖ. 

Noise Reducing Stethoscope

Questionnaire (C-130) 

 This questionnaire evaluates the performance of noise reducing stethoscopes in various military 

environments. Your expertise and experience with day-to-day use of stethoscopes makes your answers and comments 

of extreme importance to this survey. Your comments, positive or negative, will be highly regarded and will be used 

to make recommendations regarding potential military use. 

 All the information you provide will be confidential and names will not be associated with the data or 

reports. Names will only be used as an index for data collection and recovery.

Name:_________________________ Rank/Rate:___________ Date:__________ 

Command:__________________________ Occupation:______________________ 

1. Indicate the number of times you used each stethoscope (i.e. number of patients): 

 None 1-5 6-10 11-15 16-20 21(+)

 SmartMed:      

 Sonar Sound:      

 E-Scope:      

Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

 Strongly Strongly 

 Agree Agree Undecided Disagree Disagree

2. Head/sensor is easy to place and move on the patient: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

3. Head/sensor is easy to stabilize (keep from moving): 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 
APPENDICES

42

 Strongly Strongly 

 Agree Agree Undecided Disagree Disagree

4. Head/sensor fits comfortably in the hand: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

5. Cable/hose length from the head/sensor to the control box is adequate: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

6. Compared to a conventional stethoscope, the outside noise is minimized: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

7. Control box is easy to operate: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

8. The size of the control box is acceptable: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 
APPENDICES

43

 Strongly Strongly 

 Agree Agree Undecided Disagree Disagree

9. Control buttons are easy to reach: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

10. Control box is conveniently located on the listener: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

11. Control buttons are easy to see: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

12. Earpiece/headset is comfortable: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

13. Cable length from the earpiece/headset is acceptable: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 
APPENDICES

44

 Strongly Strongly 

 Agree Agree Undecided Disagree Disagree

14. The overall layout (control box, head, earphones) of the stethoscope is adequate: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

15. Compared to the conventional stethoscope, this stethoscope improves my ability to hear heart and 

lung sounds in a noisy environment: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

15. Stethoscope would improve quality of patient care in a noisy environment: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

16. In a noisy environment, I prefer to use this stethoscope instead of the conventional stethoscope: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

17. Rank the stethoscopes for their effectiveness on the following factors (1=best to 4=worst): 

 SmartMed Sonar Sound E-Scope Conventional

Ease of use ___ ___ ___ ___ 

Ability to reduce noise ___ ___ ___ ___ 

Ability to hear heart sound ___ ___ ___ ___ 

Ability to hear lung sound ___ ___ ___ ___ 
APPENDICES

45

18. Further comments: 

 

SmartMed:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

Sonar 

Sound:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ...ÖÖÖÖÖ

Ö 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

E-Scope:ÖÖÖÖÖÖÖÖÖÖ.ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ. 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

General:ÖÖÖÖÖÖÖÖÖÖ.ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ. 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

Thank you for your time and participation in this study. 
APPENDICES

46

ID#:ÖÖÖÖÖ. 

Noise Reducing Stethoscope 

Questionnaire (CVN and CAX) 

 This questionnaire evaluates the performance of noise reducing stethoscopes in various military 

environments. Your expertise and experience with day-to-day use of stethoscopes makes your answers 

and comments of extreme importance to this survey. Your comments, positive or negative, will be highly 

regarded and will be used to make recommendations regarding potential military use. 

 All the information you provide will be confidential and names will not be associated with the 

data or reports. Names will only be used as an index for data collection and recovery.

Name:_________________________ Rank/Rate:___________ Date:__________ 

Command:__________________________ Occupation:______________________ 

1. Indicate the number of times you used each stethoscope (i.e. number of patients): 

 None 1-5 6-10 11-15 16-20 21(+) 

 SmartMed:      

 Sonar Sound:      

 E-Scope:      

Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

 Strongly Strongly 

 Agree Agree Undecided Disagree Disagree

2. Head/sensor is easy to place and move on the patient: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Conventional:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

3. Head/sensor is easy to stabilize (keep from moving): 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Conventional:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 
APPENDICES

47

 Strongly Strongly 

 Agree Agree Undecided Disagree Disagree

4. Head/sensor fits comfortably in the hand: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Conventional:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

5. Cable/hose length from the head/sensor to the control box is adequate: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

6. Control box is easy to operate: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

7. The size of the control box is acceptable: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

8. Control buttons are easy to reach: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 
APPENDICES

48

 Strongly Strongly 

 Agree Agree Undecided Disagree Disagree

9. Control box is conveniently located on the listener: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

10. Control buttons are easy to see: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

11. Earpiece/headset is comfortable: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Conventional:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

12. Cable length from the earpiece/headset to the control box is acceptable: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

13. The overall layout (control box, head, earphones) of the stethoscope is adequate: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Conventional:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 
APPENDICES

49

 Strongly Strongly 

 Agree Agree Undecided Disagree Disagree

14. Stethoscope improves my ability to hear heart and lung sounds in a noisy environment: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Conventional:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

15. Stethoscope improves my ability to determine blood pressure in a noisy environment: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Conventional:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

16. Stethoscope would improve the quality of patient care in a noisy environment: 

 SmartMed:     

 Sonar Sound:     

 E-Scope:     

 Conventional:     

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

17. In a noisy environment, I would choose to use this stethoscope (circle one): 

 SmartMed Sonar Sound E-Scope Conventional 

 Comments:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

18. For the following factors, rank the stethoscopes (1=best to 4=worst) according to their effectiveness 

in a noisy environment: 

 SmartMed Sonar Sound E-Scope Conventional

Ease of use ___ ___ ___ ___ 

Ability to reduce noise ___ ___ ___ ___ 

Ability to hear heart sound ___ ___ ___ ___ 

Ability to hear lung sound ___ ___ ___ ___ 

Ability to detect blood pressure ___ ___ ___ ___ 
APPENDICES

50

19. Further comments: 

 

SmartMed:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

Sonar 

Sound:ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ...ÖÖÖÖÖÖ.Ö

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

E-Scope:ÖÖÖÖÖÖÖÖÖÖ.ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

General:ÖÖÖÖÖÖÖÖÖÖ.ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ. 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ

ÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖÖ 

Thank you for your time and participation in this study. 
APPENDICES

51

APPENDIX D 

I. C-130 Group: (*) 

II. CVN-74: (&) 

III. CAX 10: (+)

Q1: Too much background noise - roaring type. (*) 

 Sonar Sound best - could hear BP great, others just heard static. Could never hear heart 

sounds at all with any of them. (*) 

 Patient variation limited to time/occupational restraints. (+)

Q2: They move very easy. (*) 

 Movement with the Sonar Sound causes excessive amounts of noise. (&) 

 Sonar Sound bulky. (+) 

 Head/Sensor of SmartMed is big. (+)

Q3: SmartMed too small for large handed people. (*) 

 The Sonar Sound amplifies sound all over the headpiece making it difficult to hold 

without making additional noise where as the others can be held without worry of hand 

placement. (&)

 Seemed to be very awkward and bulky for SmartMed. (+) 

 Sonar Sound headpiece not optimal. (+) 

Q4: SmartMed head/sensor is too big. (*) 

 Sonar Sound head is too bulky. (&) 

 The head/sensor of SmartMed is a discomfort. The head/sensor of Sonar Sound fits very 

well between the finger, which makes it more stable. (+) 

Q5: E-Scope a little short. (+) 

 Maybe reduce on SmartMed from control box to sensor. (+) 

Q6: Control knobs on SmartMed would be better if there were buttons to push. (*) 

 With SmartMed, dials for volume/filter and size made operation complicated. (+) 

 SmartMed's control box is big and the switches are knobs instead of push buttons. (+) 

Q7: SmartMed control box is too big. (*) 

 SmartMed too big. (*) 

 SmartMed too large for handling. (*) 

SmartMed's box is a little too large. E-Scope box is great in its location, weight, and 

size. (&) 

 SmartMed box is too big! (+) 

 SmartMed too big. Both SmartMed and Sonar Sound should be configured into one unit 

like E-Scope. (+) 

 SmartMed size would not hurt if properly cased with strap. (+) 

 SmartMed control box too big. (+) 

 Smaller box for SmartMed. (+) 

 SmartMed box is way too big. It would definitely be hard to find a spot for it in any 

medical bag. (+) 
APPENDICES

52

Q9: SmartMed control box has too many cords. (*) 

 SmartMed/Sonar Sound have too much cord length which hinders rapid utilization. (+) 

Q10: E-Scope's buttons are small and on the side instead of being in the front. (+)

Q11: Earpiece can be painful when too tight. (*) 

 Headset was too big on my ears - not snug enough, so it might have made a difference in 

sound if more snug to ears. (*) 

SmartMed's earphones are nice but donít provide enough of a seal around ears. That 

minor adjustment could make a big difference. (&) 

 SmartMed is comfortable but bulky. (+) 

 Sony headset probably too bulky for field use, unless offering an acoustic benefit such as 

noise canceling. (+) 

 Headset on SmartMed maybe a little to big and loose, even when reduced to the smallest. 

Maybe need another inch for it on the smaller side. (+) 

Q12: SmartMed and Sonar Sound too long, tangles easily. (+) 

 SmartMed and Sonar Sound too long. (+) 

Q13: SmartMed has too many cords. (*) 

 SmartMed a little clumsy. (*) 

 SmartMed box is a little cumbersome (too bulky). (*) 

 SmartMed too big. Both SmartMed and Sonar Sound should be configured into one unit 

like E-Scope. (+) 

 Thought control box on SmartMed could have some casing. (+) 

Q14: Sonar Sound picks up too much additional noise. (&) 

 Only in low vibration background noise. (+) 

 When environment gets too loud there is not much stethoscope could do. (+) 

 E-Scope picks up too much outside sound. (+) 

Q15: No better than AMAL equivalent. (&) 

 Had difficulty getting very audible Karotkoff sounds with Sonar Sound. (+) 

 The SmartMed is more adequate than others are, but all of them would be hard to hear a 

B/P in a helicopter. (+) 

Q16: Could not hear heart or breath sounds - only air craft noise. (*) 

 Couldn't hear any of them , only finger taps. (*) 

 I'm not sure that there would be a case where this equipment would be essential. 

Automated BP machine would be another option. In the case of real combat injuries, 

accurate BP is irrelevant because IV fluids will be given regardless prior to evac. (+) 

Could help with stomach and chest palpitations. (+) 

Q17: (Sonar Sound) is more helpful for BPs - but could not hear any heart or breath sounds. 

 Palpation used. (*) 

 No model that much better than Littmann Cardiology II used. Slightly better than 

Conventional Littmann. BP and heart-sounds OK, breath-sounds impossible with all 

methods. (&) 
APPENDICES

53

 E-Scope provides ease of use and good sound amplification but all of these are worthless 

a majority of the time on the flight deck. (&) 

 Very Noisy E-Scope. Moderately noisy Sonar Sound. (&) 

Or Littmann Cardio II. (&) 

 I would use conventional unless I really couldn't hear it, then I'd rather have the more 

compact, one piece E-Scope. (+) 

 SmartMed if had a casing that would sit in field bag. (+) 

 If you could make the SmartMed smaller and easier to stow away it would be the most 

ideal of all. (+)

Q18b: None actually reduced noise - 3 models actually made it worse for listing to breath 

sounds. (&) 

Q18e: Little difference among all in ability to detect blood pressure. (&)

Q6a: Too much static with SmartMed/(all 3). (*) 

 Sonar Sound really works well with the BP noise but again unable to hear heart sounds 

due to static. (*) 

Q15a: Could only hear a BP using the Sonar Sound - could not hear HR or SB on any of the 

products. (*) 

 Unable to hear heart/lungs with any. (*)

E-Scope: 

• Too much plane vibration. (*) 

• Again too much outside noise. (*) 

• Keep working at it - this is definitely not the answer to noise reduction/hearing ability on 

stethoscopes. (*) 

• Overall the worst. Too noisy. Could not hear heart or lung sounds. (*) 

• See Sonar Sound. (&) 

• This device was the best for capturing heart and breath sounds. These sounds were at least 

detectable. In trauma situations this device would be useful. It can detect both heart and a 

breath sounds and does BP. (&) 

• Practical for size but again amplified all noise so sounds are hard to hear. (&) 

• This is the consolidated design, which is necessary for ease of use and durability in field. 

Dial is easy to use. Overall, I felt this was the best although the other models had some 

advantages under some conditions. (+) 

• While testing this unit, I found it to be the most reliable and easiest to handle. It did have 

limitations when it came to taking BP at close proximity to noise source, but overall a very 

compact and useful tool. The only drawback would be on durability. The cord connecting 

the bell/diaphragm to the "box" seems as if it could be damaged easily. (+) 

• Best design, maybe improved if noise cancellation tech could be added. (+) 

• Overall layout is good. The size is good. Still needs improvement in filtering the noise. (+) 

• Would be more comfortable with a headset rather than earpiece. (+)

• As far as compact, this one is the better of the new devices. It does however pick-up too 

much outside noise. If in a noise enhanced environment and had to choose between regular 

stethoscope and this unit, I would choose this one. It takes a keen ear to distinguish when 

hearing for breath sounds. (+) 
APPENDICES

54

• If static was reduced in unit, this could be useful unit. (+) 

SmartMed

• Good on ground, only fair on plane. (*) 

• Too much outside noise to be effective. (*) 

• Has good potential with better sound proof headphones. Would be neat if it had the ability to 

hear heart and lung sounds through earplugs. (*) 

• The earphones were too large for my head, so don't know if they were fitted if that would 

have made a difference. The box I though was too big but length of stethoscope was 

adequate. (*) 

• Headphones helped but were bulky-best of 3 at reducing ambient noise. (&) 

• I think it would be a good asset with improvements made on the headset and if the box was 

reduced a bit. (&) 

• This device picks up too much ambient noise and amplifies it. In both low frequency and 

high frequency environments. Transmittance of ambient sound was intolerable. The 

headphones do not provide adequate protection against ambient sound either. Blood pressure 

was accomplished by sheer sound output causing an impulse vibration. (&) 

• Awkward to use - would be better if headset was Mickey mouse style - seal off outside noise 

better. (&) 

• Too bulky - both control box and headphones. Lines too easily tangled on self and with other 

instruments. Filter dial makes little or no difference when I tried it. Heart sounds could be 

heard and felt in headphones. (+) 

• In field testing this device, I did not experience any improvement in quality using the filter 

aspect. Regardless of the filter setting, a great deal of ambient noise still filtered through. 

However, I did feel the external headphones provided some benefit. (+) 

• Too many parts, good sound but needs streamlining. (+)

• Stethoscope could have been improved with a field case or place in field med bag. Headsets 

were effective during B/P. This model however was not tested during actual flight. (+) 

• The control box should be cut in half. He configuration of the control box should be cut in 

half. The configuration of the control box should be changed. The switches should be 

changed to buttons not turn knobs. The headset is good, but not ideal for the field. Good for 

taking blood pressure. The head/sensor should be changed. (+) 

• Control box could be downsized for easier use. (+) 

• If the unit was smaller and the length of the hose were smaller it maybe easier to use. The 

headset was too big and the earphones may need to be a little smaller. The unit was the best 

at reducing noise unless you move or the patient is moving, such as a bumpy road. It cuts out 

and becomes static. I believe that in a flight environment it would be useless. I have used a 

"Propak" in the flight environment and that compared to these is a more efficient and 

effective tool. (+) 

• With a reduction in size of audio cord, earphones and unit size, this is one of the better 

devices. (+) 

• With shortening of the box and reduction in earpiece, the SmartMed would be ideal for a 

field setting. (+)
APPENDICES

55

Sonar Sound 

• Seemed best of three. (*) 

• This unit was the only one I could hear a heart beat with. This was only by placing a blood 

pressure cuff on the patientís arm and listening. (*) 

• Outside noise but able to hear sound the best. (*) 

• Could be of good use in a noisy environment if further design is done. Great Scope! (*) 

• I heard a great BP - loud and clear but had a lot of difficulty hearing heart sounds. I would 

encourage to further work on getting better with heart sounds and lung sounds. Perfect it if it 

can be. This was best of all three. (*) 

• Increase volume also increased background noise. Filter of no appreciable help. (&) 

• Work needs to be done to make the head less sensitive and a place should be made where the 

examiner could hold the headpiece without fear of hand movement. (&) 

• This device picks way too much ambient noise. Ambient sound was deafening and absolutely 

intolerable. Sounds were indiscernible with all of the noise. I would never use this item in 

the field. (&) 

• Tend to break too soon with bad noise levels but better than others in vibration environment - 

together with Mickey mouse ears - would probably be good combo. (&) 

• Push button controls - not easy to discern status (i.e. need light to indicate on/off or switch so 

you can easily determine by looking). Also, need lights or digital number to discern volume 

level, which cannot be determined by looking at buttons on unit. Lines easy to tangle. Head 

comes off easily - would be lost in field (was lost during testing)! Sound canceling aspect 

leads to cutting out frequently which makes BP and other measurements difficult with 

background noise or movement. (+) 

• Headpiece unusual, does not look durable and tends to get lost. Needs streamlining. 

• The head/sensor is excellent. Has excellent stabilization. Hard to take BP in field. Could 

hear heart only if patient breathes deeply. (+) 

• Would be more comfortable with a headset rather than earpiece. (+) 

• Device is very simple to use. If this device could filter out background noise a little better, it 

would be the one I would use. Device is just the right size for easy carrying. (+) 

General 

• I will say in fairness to all, I do have a high frequency loss of hearing from being on a C-130 

too long but - with a BP cuff I could hear a faint beat with the Sonar Sound. (*) 

• While on the ground with outside noises of other C-130s running engines, I could hear heart 

and breaths sounds. But when we were in the air - could not hear any breath or heart sounds. 

Was able to hear BP with the sonar sound. SmartMed and E-Scope were unable to pickup 

any heart or breath sounds. Was thrilled to have the opportunity to test the various 

stethoscopes. Unfortunately the C-130 has more power. (*) 

• None of them drowned out C-130 engine noises! Heard very little with engines! (*) 

• It seems that all three could have safety violations because of the noise without our earplugs. 

A better seal in the ear would be beneficial. (*) 

• None of the 3 models improved my ability to hear breath sounds in the areas we tested 

(Reactor Room and Hanger Bay). Heart sounds were slightly clearer than the Littmann 

Cardiology II I used. However, neither BP nor BS are significantly improved. (&) 

• In most cases a patient on the flight deck who is thought to have an injury which must be 
APPENDICES

56

further assessed with a stethoscope will be taken to Main Medical within minutes. The 

environment is too loud and hazardous to keep a patient there for long. Generally we assess 

airway, c-spine, breathing, and circulation, put the patient on a stretcher and have them in 

Main Medical in about 2-8 minutes post the time of injury. (&) 

• These devices are good stepping stones. The E-Scope would be very useful and helpful in 

our environment until better models are developed - especially in our line of work. (&) 

• Overall - they did not reduce noise but amplified all noise (body and outside). Good idea but 

helpful in noisy environment only at certain levels. (&) 

• Units must be durable, easy to hold, and hard to tangle or break in field. None of the units 

worked in high-noise/high-vibration environment of helicopter. Doppler sensors would be 

superior for heart sounds and possibly BP in high background noise/vibration, but would not 

work for breath sounds. Visual readout meters would eliminate need for using earphones 

and may be advantageous in some environments. Small automatic BP units may be 

necessary in high noise/vibration. (+) 

• Again, I suspect only limited benefit would be realized by adoption of any of these models 

for military use. Regular stethoscopes are fine in most environments, are cheap, durable, and 

do not require batteries. (+) 

• There was no B/P, lung sounds, or heart sounds taken during actual flight. However 

stethoscopes were effective and helpful while on flight line during turn up prior to flight. (+) 

• Can't hear through the Noise. (+) 

• Overall I think that all three would help in a noisy environment, but I believe that with a 

headset the E-Scope would work better. (+) 

• Easy to use, hard to hear. (+) 
APPENDICES

57

APPENDIX E: 

PHOTOS OF DEVICES

Device 1: SmartMed Æ 

Device 2: Sonar Soundô 
APPENDICES

58

Device 3: E-Scopeô 
APPENDICES

59

MINIATURIZED VERSIONS OF TESTED MODELS

PROTOTYPE 1: SMARTMED Æ PRODUCTION-READY MODEL-UPGRADE. 

PROTOTYPE 2: NORE-SCOPE PROOF-OF-CONCEPT PROTOTYPE 

(UPDATE OF SONARSOUNDô ) 
APPENDICES

60

APPENDIX F: 

Updated Device Specifications for Devices 1 and 2 Tested in this Study 

Noise Reduction Stethoscope: Upgrade of SmartMedÆ

SPECIFICATIONS 

Operational Description: 

Aurally presented visceral information audible enough for evaluation of pulse, respiration, 

and presence of murmurs in 90 dB SPL pink noise. Sensor-head approximately similar in 

diameter and shape to a conventional stethoscope. Must have an electronic IC amp-buffered 

output. Must have noise reducing capabilities and signal fidelity equal to or better than the C. 

F. Electronics Smart Med Stethoscope in a smaller package. 

Physical Characteristics, Case: 

Size: approximately 11.3 x 7x 4.5 cm +2%, 380 cubic cm maximum. 

Shape: all edges radiused. 

 Integral stainless steel belt clip (either U shaped wire or flat leaf-spring) 

PHYSICAL CHARACTERISTICS, STETHOSCOPE HEAD: 

 Size: diameter, 5 cm or less 

 thickness 2.2 cm or less 

 Moldex (NAMRL) or equal noise-attenuating coating on back of head. 

PHYSICAL CHARACTERISTICS, CABLING - HEAD TO CASE

 Coiled cord (retracted) 70 cm max., (extended) 55 cm min. 

PHYSICAL CHARACTERISTICS, OUTPUT: 

Acoustic: Mini stereo headphone jack wired mono (tip & ring +, sleeve -). 

Output circuitry load-resistor protected, IC amplified. 

Closed circumaural headset provided. 

ELECTRICAL CHARACTERISTICS, OUTPUT: 

 .5v RMS 

 capable of driving any headset of 10 to 200 ohms 

FUNCTIONAL CHARACTERISTICS: 

 On/off switch, volume control, variable filter, battery operated, automatic shut-off 

OPERATIONAL CHARACTERISTICS: 

Noise reduction effective enough to allow full operation in up to 90 dB SPL noise field. 

Suggestions: 

Acoustic output to be presented over a pair of closed circumaural headphones (supplied) or 

insert earphones embedded in noise-attenuating-foam earplugs. Additional attenuation is 

available with circumaural passive hearing protectors worn over the insert earphones. 

Alternate use of self-powered active-noise-cancellation (ANC) headsets/flight-helmets is 

possible if needed. 
APPENDICES

61

Updated Device Specifications for Devices 1 and 2 Tested in this Study 

Noise Reduction Stethoscope: Upgrade of Sonar Sound ô

SPECIFICATIONS 

Operational Description: 

Aurally presented visceral information audible enough for evaluation of pulse, respiration, 

and presence of murmurs in 90 dB SPL pink noise. Sensor-head integral with electronics. 

Must use thin sheet PVDF (Polyvinylidene Fluoride) piezoelectric polymer sensor material to 

gain immunity from airborne noise. Electronic IC amp-buffered output required. Noisereducing capabilities and signal fidelity will be equal to or better than Sonar Sound 

Stethoscope in a smaller package. 

Physical Characteristics, Case, including sensor head: 

Size: approximately 6.5 x 5.0 x 3.75 cm +2%, 124.5 cubic cm max. 

Shape: all edges radiused. 

Physical Characteristics, Output: 

Acoustic: Mini stereo headphone jack, wired mono. 

Output circuitry load-resistor protected, IC amplified. 

Earpiece-headset provided. 

Battery compartment inline on headphone cord. 

Electrical Characteristics, Output: 

 Bandwidth: 100 to 1000 Hz 

 Level: approx. .4v RMS @ 1kHz 

 Capable of driving any headset of 125 ohms or greater. 

Functional Characteristics: 

 Hold-down on/off switch, volume control, battery operated 

 

Operational Characteristics: 

Noise-reduction effective enough to allow full operation in up to 90 dB SPL noise field. 

SUGGESTIONS: 

Acoustic output shall be presented over a pair of stethoscope earphones (supplied) or insert 

earphones embedded in noise-attenuating-foam earplugs (user supplied). Additional 

attenuation is available with circumaural passive hearing protectors worn over the insert 

earphones. Alternate use of self-powered active-noise-cancellation (ANC) headsets/flighthelmets is possible if needed.