WO2013055394A1

WO2013055394A1 - Laser stethoscope

Info

Publication number: WO2013055394A1
Application number: PCT/US2012/000500
Authority: WO
Inventors: James J. SCIRE, Jr.; James R. Markham; Joseph E. Cosgrove
Original assignee: Advanced Fuel Research, Inc.
Priority date: 2011-10-14
Filing date: 2012-10-05
Publication date: 2013-04-18

Abstract

A laser stethoscope employs a laser Doppler vibrometry technique in which the beam from a laser diode is focused upon the reflective inner surface of a first diaphragm, which is spaced from a second diaphragm positioned for contact against a patient's skin. Self-mixing of laser light reflected from the first diaphragm with light from the laser produces interference fringes, which are monitored for generating signals representative of internal bodily pressure change.

Description

LASER STETHOSCOPE

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of United States Provisional Patent Application

No. 61/627,611 , filed October 14, 2011, the entire specification of which is incorporated hereinto by reference.

STATEMENT REGARDING GOVERNMENT INTEREST

The United States Government has rights in this invention under National Aeronautics and Space Administration contract Number NNX11CD42P.

BACKGROUND OF THE INVENTION

Auscultation, or listening to internal sounds made by the body of a patient, is an important tool in medical diagnostics. Heart, lung, circulatory, and bowel function can be assessed by auscultation with a stethoscope. There are numerous situations, however, where the faint sounds collected using an ordinary stethoscope are overwhelmed by ambient noise. For example, the United States National Aeronautics and Space Administration will benefit from an auscultation device/stethoscope that outperforms conventional and currently available stethoscopes, which are of limited usefulness in noisy environments. In like fashion, the military services will benefit during patient transport in noisy environments (land, sea, and air transports), as will emergency first-responders and medical personnel at accident scenes, large public events, industrial accident sites, during patient transport, and in noisy hospital settings.

Representative of prior art pertinent to the present invention are the following United States patents:

No. 5,515,865 No. 7,668,589

No. 5,853,005 No. 7,735,598

No. 5,945,640 No. 7,806,226 No. 6,726,635 No. 8,092,396

No. 7,128,714

SUMMARY OF THE INVENTION

It is the broad object of the present invention to provide a novel sensor, or stethoscope head, and a novel stethoscope system, wherein and whereby internal body sounds can be detected, which head and system perform well and highly advantageously despite being used in environments subject to high levels of ambient noise.

In all instances displacement of the patient's skin is measured using laser Doppler vibrometry (LDV), whereby movements of a diaphragm placed against or near the patient's skin is converted into encoded electrical signals. The diaphragm is isolated from outside noise by the chest piece (or more generally, head structure), while its displacement is measured optically. This approach avoids the coupling of noise into a long acoustic signal path like that which exists in conventional stethoscopes.

In preferred embodiments the measured displacement may be corrected for external acoustic coupling to the body by subtracting filtered measurements from an ambient-noise microphone mounted in the stethoscope chest piece. In such instances an adaptive filter maintains the noise-cancellation capability for changing conditions and different auscultation sites. This approach dramatically reduces the effects of external noise while still providing the familiar auscultation sounds associated with measurements at the skin surface; simple filtering may yield conventional stethoscope sounds.

The laser Doppler vibrometry measurements employ a low-power diode laser used in a self- mixing configuration. The chest piece directs light from a low-power diode laser to the stethoscope diaphragm. Some of the laser light is reflected from the diaphragm, and a portion of that reflected light makes its way back into the laser cavity. In the cavity the reflected light can interfere with the light from the laser (i.e., by self-mixing), and the interference fringes can be monitored using the integrated monitor photodiode in the laser (in more typical applications, this diode is used to control the laser power output). After analog signal processing, the LDV signal is digitized, along with the signal from an integrated microphone, and adaptive filtering (if employed) and additional signal processing are performed in the digital domain; the resultant audio output is sent to a digital-to-analog converter and amplifier system, which normally drives headphones worn by the clinician.

The optical configuration of the system is straightforward. A fixed lens focuses the laser on the diaphragm. An optical attenuator may be incorporated for reduction of the power of the out-going and returning signals; the attenuator controls the self-mixing feedback level, and may be tilted to prevent Fresnel reflections at its surfaces from returning to the laser (the surfaces will usually also be coated to impart anti-reflection properties). The described optical configuration leads to a very compact and efficient system, which is especially suitable for outer space applications.

An additional complication addressed by the present stethoscope headpiece and system has to do with how LDV is used to measure skin displacement. In principle, skin displacement itself could be measured directly, without any interposed diaphragm, by monitoring laser light reflected by the skin. Variation in the optical properties and surface texture of skin, however, makes the use of a diaphragm having fixed optical properties much more effective and advantageous. In accordance with the present invention, an innovative diaphragm design not only maintains the optical properties at the measurement point but also reduces the low-frequency variation in the position and orientation of this point. This approach ensures that the LDV signal strength and integrity are maintained throughout the use of the stethoscope.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Figure 1 is a perspective view illustrating a system embodying the present invention;

Figure 2 is a cross-sectional view, taken along an axial plane, of a chest piece embodying the present invention and employed in the system of Figure 1 ;

Figure 3 is a view of the laser diode package utilized in the chest piece of Figure 2, drawn to an enlarged scale and shown in partial section;

Figure 4 is a diagrammatic representation of an alternative arrangement for monitoring the self- mixing signal produced during operation of the stethoscope; and

Figure 5 is a schematic representation of signal processing components employed in the system of Figure 1.

DETAILED DESCRIPTION OF THE PREFERRED AND ILLUSTRATED EMBODIMENTS OF THE INVENTION

During auscultation, an ordinary stethoscope diaphragm moves a great deal at very low frequencies. The low-frequency movements inevitably include some tilt, and it can be demonstrated that this tilt can enhance multiple reflections from the diaphragm which, in turn, leads to distortions in the LDV signal. These distortions in the signal lead to acoustic artifacts where the large-scale, low- frequency movements are translated into sounds at audio frequencies, which can be distracting during auscultation. The construction of the hereinafter-illustrated chest piece decouples the DC portion of the deflection and tilt from the surface measured by LDV. An outer diaphragm presses against the skin surface. Skin movement causes fluid movement in front of the inner diaphragm, which causes it to deflect as well. One or more leak paths around the edge of the inner diaphragm isolate DC deflections and tilt in the outer diaphragm so as to substantially avoid effects upon the inner diaphragm (desirably, there are also slow-leak paths preventing pressure buildup inside the cell). Large deflections initially move the inner diaphragm, but it settles back to its equilibrium position if such deflections hold.

Behind the inner diaphragm the system is enclosed with a rigid outer container and a window, which prevent ambient noise from reaching the inner diaphragm through the back of the stethoscope.

More particularly, certain objects of the invention are attained by the provision of a head for use in a laser stethoscope system, comprised of a body having an inwardly extending outer cavity, at one side, and an inner cavity in axial alignment, and optical communication, with the outer cavity; a laser diode and a monitor photodiode, desirably comprising a diode package contained in the inner cavity; at least one planar diaphragm that is deflectable in response to bodily pressures, the at least one diaphragm having a laser beam-reflective inner surface and being disposed in the outer cavity to define therewithin an inner chamber and an outer chamber, and the outer chamber having an entrance at the one side of the body; structure surrounding the entrance to the outer chamber and lying in a plane axially spaced from and substantially parallel to the plane of the at least one diaphragm; passage- defining means for establishing fluid-flow communication between the inner chamber and the outer chamber, the inner chamber being otherwise closed and both of the chambers normally containing a fluid; and means for transmitting and focusing a beam generated by the laser diode to and upon the reflective surface of the at least one diaphragm, whereby light reflected by the at least one diaphragm can self-mix with light generated by the laser diode to produce interference signals, representative of movement of the at least one diaphragm, for detection by the monitor diode.

In preferred embodiments the stethoscope head will additionally include a second planar diaphragm that is deflectable in response to bodily pressures, the second diaphragm being supported by the structure that surrounds the entrance, to overlie and close the outer chamber. In most instances the head will comprise a stethoscope chest piece.

The head will normally include a laser beam-transmissive window, having parallel surfaces, sealingly interposed between the inner and outer cavities substantially on the axis of alignment thereof. The window may have light-attenuation properties, or a separate optical attenuator may be included, and an integrated microphone, for detecting ambient sound, will usually be provided in the head as well. The head will usually also include an electronic circuit for driving the laser diode and for processing signals received by the photodiode, the electronic circuit normally being disposed within the inner cavity, desirably at a location inwardly spaced from the laser diode (or laser diode package), and including means for operative connection thereto and to external electronic data processing means. The head may additionally desirably include an adjustable stage, mounted within the inner cavity, means for adjusting the tilt of the stage, and a lens comprising the means for transmitting and focusing a beam generated by the laser diode, at least the lens being mounted on the adjustable stage.

Certain objects of the invention are attained by the provision of a stethoscope system that includes the head described, in operative connection with data-acquisition means, amplification means, electronic data processing means, and means for generating a signal that is representative of monitored bodily pressures and is perceptible by at least one human sense.

A laser stethoscope system embodying the present invention was tested by volunteers, and its performance was compared to that of a conventional, passive stethoscope and to that of a commercially available electronic stethoscope; comparisons were carried out both in quiet environments and also in environments with added background noise. The inventive system was judged to be more sensitive than the conventional stethoscope in quiet environments. In noisy environments, the present system was found to perform well at noise levels at which the conventional stethoscope and the electronic stethoscope were no longer effective. Testing showed that the instant stethoscope retained its effectiveness at ambient sound levels up to and beyond 80 dBA.

Turning now to Figure 1 of the drawings, therein illustrated is a complete stethoscope system embodying the present invention. The system includes a stethoscope chest piece, generally designated by the number 34, which connects via the cable 33 to a small in-line module 32. The in-line module contains a power source, such as a battery (not shown), which powers the components of the chest piece, along with electronics (also not shown) that process the signals sent via the cable 33 to generate auscultation audio, which is output to noise-canceling headphones 30 via the cable 31. The noise- canceling headphones reduce ambient noise that might couple into a clinician's ears and thereby corrupt the audio generated by the electronics in the stethoscope head 34 and in-line module 32. It is to be noted that this noise-coupling path is entirely separate from paths in which unwanted sounds enter through the body or stethoscope head, and thus the operation of the noise-canceling headphones is entirely separate from adaptive filtering that takes place in the stethoscope itself, as will be described presently.

As seen in Figure 2, the main body 1 of the chest piece 34 mounts, in an outer cavity, both an outer diaphragm 2 and an inner diaphragm 3. The outer diaphragm 2 serves to make contact with the patient's skin, as in an ordinary stethoscope. The inner diaphragm 3 is spaced axially from the outer diaphragm 2 so as to define an outer chamber 4 and an inner chamber 5, the inner chamber 5 being defined on the opposite side by a window 6. The chambers may contain air or, alternatively, another fluid such as water to better match the acoustic impedance of the patient's body. Small passages 7 connect the two chambers, allowing fluid to flow back and forth between the chambers. These passages may be located symmetrically around the main body 1 of the chest piece, as depicted, or they may be provided as a continuous or discontinuous gap formed around the periphery of the inner diaphragm by making the circumferential groove 8, which mounts diaphragm 3, wider (in an axial sense) and of larger diameter than the diaphragm so as to allow fluid to flow around the edge of the diaphragm. It is noted that the wall surrounding the outer chamber 4 is of an inwardly tapered conical configuration, which enhances impedance matching.

An upper portion of the main body 1 of the chest piece 34 defines a cavity 35, which houses a laser diode 9, lens 10, and a tilt stage 11, and has an optical attenuator 22 spanning an aperture 24 at its lower side. Light from the laser diode 9 is condensed by the lens 10 to form a beam that travels essentially axially (i.e., in a vertically downward direction, in the orientation shown), and passes through the attenuator 22; it then passes through the window 6 which spans an aperture 36 provided in a lower wall portion 37, and is focused on the upper surface of the inner diaphragm 3. Some of this light is reflected back, making its way back through the window 6, attenuator 22, and lens 10 to reenter the laser diode 9.

It will be appreciated that the tilt stage 11 allows the orientation of the laser 9 and lens 10 to be adjusted relative to the inner diaphragm 3, through adjustment of fine-pitch adjustment screws 12 (of which three or four, at equidistantly spaced peripheral positions, would normally be provided) Springs 14 hold the tilt stage 11 to the stage base plate 15, which is mounted to the top of the main body 1. The attenuator 22 reduces the intensity of the light with each pass, and serves to limit the return signal from the diaphragm and to prevent multiple reflections at the diaphragm and laser from affecting the signal.

With additional reference now to Figure 3, light reflected from the inner diaphragm 3 that makes its way back into the laser diode 40 interferes with the light inside the laser diode cavity (not seen, but conventionally provided by a small region, having parallel planar ends, cleaved into the semiconductor material), producing variations in the laser output. These variations can be monitored using the photodiode 41 integrated into the laser diode package 9. Drive current for the laser and the signal from the monitor photodiode pass through wires 16 connecting these components to the printed circuit board 17, mounted (by means not shown) above the tilt-stage base plate 15. The printed circuit board is comprised of circuits that drive the laser diode and process the photodiode signals, which thereafter leave the stethoscope chest piece 34 through the cable 18 that passes through a grommet 19 in the upper housing 20. The upper housing 20 covers the printed circuit board 17 and completes the stethoscope chest piece enclosure. The cable 18 provides electrical power to the chest piece and brings the photodiode signal out of the chest piece for further processing or for auscultation audio (and/or indeed video or tactile) output.

As can be seen, the upper housing 20 also contains a microphone 23 for monitoring ambient sounds. Such sounds may pass through the patient's body and overwhelm the normal auscultation sounds. Adaptive filtering of the diaphragm displacement signal to remove the ambient sounds is therefore desirably employed, using the signal from the microphone as a reference.

In the embodiment shown, the outer diaphragm 2 is mounted to the main body 1 with a retaining ring 21, but alternatively the outer diaphragm 2 may be designed to stretch over the edge of the main body and retain itself there through elastic tension. In embodiments that use a fluid other than air to fill the chambers 4 and 5, the outer diaphragm 2 is sealed to the main body to prevent fluid leakage. The diaphragms 2 and 3 will usually be substantially parallel to one another but, in any event, the inner diaphragm will be oriented so that the beam generated by the laser diode 9 will be

substantially normal to its reflective upper surface.

In an alternative (albeit less preferred) embodiment, the outer diaphragm 2 may be omitted, with the edge surrounding the outer cavity (or mouth) of the main body being pressed directly against the patient's skin. In such cases the patient's skin effectively becomes the outer diaphragm and, of course, both chambers 4 and 5 will be filled with air.

As seen in Figure 2, the surfaces of the window 6 and the attenuator 22 are oriented normal to the direction of the laser beam, tending to cause specular reflections off of their respective surfaces to contribute to the light returning to the laser. To eliminate such reflections these two optical elements may desirably be tilted so as to redirect specular reflections away from the laser. It will also be appreciated by those skilled in the art that, rather than employing a separate light attenuator, the incorporated window 6 may itself have inherent light-attenuation properties, either by virtue of its composition or through the application of a suitable coating material.

The system operates as follows: Internal sounds from the patient's body result in skin vibrations that are transferred to the outer diaphragm 2 (if present) through direct surface contact. These vibrations create pressure waves in chamber 4, which travel through the chamber and cause the inner diaphragm 3 to move responsively. Movement of the diaphragm 3 is then detected through laser Doppler vibrometry by monitoring the self-mixing signal from the laser diode 9, which is thus representative of movement of both diaphragms 2 and 3. Figure 4 shows an alternative, or supplemental, arrangement for monitoring the self-mixing signal. Instead of using an integrated monitor photodiode 41 in the laser diode package 9, which might not be present for certain laser diode packages or might not be optimal for certain laser diode packages (due, for example, to high dark current), an external monitor photodiode 60 may be employed. In such a case, a laser beam 62, formed by the laser diode 40 and focused by the lens 10, is sampled with beam sampling means 61, and the sampled beam 63 is sent to the external monitor photodiode 60. The remainder of the beam 64 remains in optical communication with the remaining components of the system, and the light returning along the beam 64 generates self-mixing at the laser diode that can be monitored by the external monitor photodiode 60.

The double-diaphragm construction described optimally provides two important advantages for optical measurement of the motion. Firstly, non-symmetrical deflections of the outer diaphragm 2, conforming largely to the patient's body at the auscultation site, become more symmetrical in character as they are transferred through the fluid in chamber 4 to the inner diaphragm 3. Bones or other hard structures inside the patient's body, which are present at most auscultation sites, generally produce nonsymmetrical deflections of the outer diaphragm. If a diaphragm disposed in direct contact with the patient's skin were itself monitored optically, the system would need to be tolerant of such nonsymmetrical deflections, which might include tilt relative to the laser beam where the beam contacts this diaphragm, even if the beam were aimed at the center of the diaphragm. In the illustrated arrangement, pressure waves emanating from different points on the outer diaphragm 2 combine to produce a largely symmetric movement of the inner diaphragm 3.

A second advantage of the double-diaphragm construction is that it provides high-pass filtering of the movements that occur at the outer diaphragm 2. When it is pressed against the patient's skin, the outer diaphragm experiences a displacement due to this pressing that is large relative to the displacements associated with the auscultation sounds. The magnitude of this displacement depends on how the stethoscope chest piece is held against the patient's body, and tends to vary, with time, at frequencies from zero to less that about 10 Hz. The magnitude of these low- frequency displacements may be on the order of one millimeter, which would be enough to move the outer diaphragm out of focus, if it were monitored directly. The narrow passages 7, that provide fluid-flow connection between chamber 4 and chamber 5 in the double-diaphragm construction, prevent low-frequency motions from being coupled to the inner diaphragm 3. Low-frequency pressure variations between chambers 4 and 5 lead to flow through the passages 7 that equalize the pressure, thereby preventing them from deflecting the inner diaphragm 3. Higher frequency variations, such as those associated with auscultation sounds, do not traverse the narrow passages 7 but instead cause the inner diaphragm 3 to deflect. So, despite any variations in the mean deflection of the outer diaphragm 2, the inner diaphragm 3 maintains zero mean deflection and remains in the focus of the beam for optimal optical monitoring of those frequencies important for auscultation, between 10 Hz and 1000 Hz.

Similar advantages are afforded by the alternative embodiment of the headpiece described, in which only an inner diaphragm 3 is provided, with the patient's skin, circumscribed by the lip or edge of the mouth to the outer cavity, functioning in a manner analogous to an outer diaphragm. Thus, nonsymmetrical skin movements would become more symmetrical in character as they are transferred through air trapped within the outer chamber 4, and pressure-equalizing passages, connecting the open- mouth outer chamber to the inner chamber 5 would help to maintain zero mean diaphragm deflection and beam focus.

As shown in the signal -processing schematic representation of Figure 5, in operation of the present system the signal 51 from the photodiode 41 is amplified by an amplifier. The amplified photodiode signal 55 undergoes further analog signal processing in analog signal processing electronics, which may include, for example, filtering or demodulation elements. Similarly, the signal 52 from the microphone 23 is amplified by a second amplifier. The amplified microphone signal 56 then undergoes further analog signal processing in analog signal processing electronics. The processed photodiode signal 59 and the processed microphone signal 61 are then digitized by a data acquisition system. The digital signals 53 undergo further signal processing in a digital signal-processing module. The processing desirably includes adaptive filtering of external noise using the microphone signal as a reference. Finally, the processed signal 65 is sent to the output device, which generates a signal representative of the monitored bodily pressures, for perception by the clinician or other personnel. That signal may, for example, consist of auscultation sounds or the visual display of skin-displacement information.

The body of the headpiece will typically be constructed of aluminum or stainless steel. For illustrative purposes only it is noted that, again in the embodiment of the chest piece shown, the mouth was about 45 mm in diameter (as was the approximate diameter of the outer diaphragm 2). The height of the outer chamber 4 was about 10 mm, the inner diaphragm 3 was about 30 mm in diameter, and the height of the inner chamber 5 was about 10 mm. The laser diode was typically mounted about 30 to 50 mm from the inner diaphragm, and the overall height of the entire stethoscope head was between 50 and 80 mm.

The diaphragms will typically be constructed of a polyester film (e.g., the material sold under the MYLAR trademark, which is often metallized), acrylic, acetal (e.g., the material sold under the DELRIN trademark), or silicone resins, or stainless steel. Typically, the diaphragms will be 5 to 20 mils thick.

The laser diode "package" will normally comprise an outside case that contains a very small laser diode, with a monitor photodiode coupled to its back end. The semiconductor material contains a small region that acts as the gain medium, and is typically cleaved to make a laser cavity with planar, parallel ends.

While it is not necessary that the fluid in the defined chamber or chambers match the acoustic impedance of the patient's body, doing so is advantageous. An impedance-matching fluid makes it more difficult for outside noise to couple to the inner diaphragm because internal (body) sounds reach it more easily than do external sounds from outside the stethoscope head. As mentioned above, however, even when the fluid is air some impedance matching is obtained due to the tapered shape of the "mouth" of the outer chamber.

Perhaps it should be emphasized that the motion of the inner diaphragm is not coupled to that of an outer one at zero frequency. If one depresses an outer diaphragm, and holds it there (so that the displacement "input" to the outer diaphragm is a step function), the inner diaphragm initially deflects, but settles back to its equilibrium position over time (i.e., it does not "hold"). If one moves the outer diaphragm in and out sinusoidally, for example, the response of the inner diaphragm will also be sinusoidal (at least, to the first order); its relative magnitude and phase will depend however upon the frequency of the input sinusoid.

Thus, it can be seen that the present invention provides a novel stethoscope headpiece and stethoscope system that are especially useful for auscultation in noisy environments. Astronauts frequently fly without a trained medical professional as a part of the crew, and therefore must be able to perform examinations on one another within the noisy confines of the spacecraft. Meanwhile, the medical personnel in charge of the astronauts' health, who are monitoring them from the ground, are in the best position to fully evaluate the auscultation sounds; means for recording and transferring the audio (or other signals) to them is therefore important under such circumstances. The innovation of the present invention affords all of the features necessary to fulfill, in particular, the needs of NASA, but it will, in addition, be of benefit in maintaining the health of the general population. In the normal environment the present laser stethoscope has been found to be more sensitive than the traditional stethoscope to internal body sounds, and it is believed that such increased sensitivity will enable the detection of additional abnormal sounds by a practitioner, to the significant benefit of any patient.

Claims

THE CLAIMS Having thus described the invention, what is CLAIMED is:

1. A head for use in a laser stethoscope system, comprised of a body having an inwardly extending outer cavity, at one side, and an inner cavity in axial alignment, and optical communication, with said outer cavity; a laser diode contained in said inner cavity and at least one photodiode contained in said body; at least one planar diaphragm that is deflectable in response to bodily pressures, said at least one diaphragm having a laser beam-reflective inner surface and being disposed in said outer cavity to define therewithin an inner chamber and an outer chamber, said outer chamber having an entrance at said one side of said body; structure surrounding said entrance to said outer chamber and lying in a plane substantially parallel to and spaced axially from the plane of said at least one diaphragm; passage-defining means for establishing fluid-flow communication between said inner chamber and said outer chamber, said inner chamber being otherwise closed and both of said chambers normally containing a fluid; and means for transmitting and focusing a beam generated by said laser diode to and upon said reflective surface of said at least one diaphragm, whereby light reflected by said at least one diaphragm can self-mix with light generated by said laser diode to produce interference signals, representative of movement of said at least one diaphragm, for detection by said monitor photodiode.

2. The head of Claim 1 wherein said head includes a laser diode package comprised of said laser diode and said at least one monitor photodiode.

3. The head of Claim 1 wherein said fluid normally contained in said chamber is air.

4. The head of Claim 1 additionally including a second planar diaphragm that is deflectable in response to bodily pressures, said second diaphragm being supported by said structure surrounding said entrance to overlie and close said outer chamber.

5. The head of Claim 1 additionally including a laser beam-transmissive window sealingly interposed between said inner and outer cavities substantially on the axis of alignment thereof.

6. The head of Claim 5 wherein said window has parallel surfaces.

7. The head of Claim 1 additionally including an optical attenuator, said attenuator being interposed between said laser diode and said at least one diaphragm so that light passing between said laser diode and said diaphragm passes through said attenuator.

8. The head of Claim 5 wherein said beam-transmissive window is so constructed as to attenuate light passing therethrough.

9. The head of Claim 2 additionally including an electronic circuit for driving said laser diode and for processing signals received by said at least one monitor photodiode, said electronic circuit including means for operative connection of said laser diode and said at least one monitor photodiode to external electronic-data processing means.

10. The head of Claim 1 additionally including an adjustable stage mounted within said inner cavity, means for adjusting the tilt of said stage, and a lens comprising said means for transmitting and focusing a beam generated by said laser diode, at least said lens being mounted on said adjustable stage.

11. The head of Claim 9 additionally including a microphone, for detecting ambient sound, operatively connected to said electronic circuit.

12. The head of Claim 1 comprising a stethoscope chest piece.

13. A head for use in a laser stethoscope system, comprised of a body having an inwardly extending outer cavity, at one side, and an inner cavity in axial alignment, and optical communication, with said outer cavity; a laser diode contained in said inner cavity, and at least one photodiode contained in said body; a first planar diaphragm that is deflectable in response to bodily pressures, said first diaphragm having a laser beam-reflective inner surface and being disposed in said outer cavity to define therewith an inner chamber and an outer chamber, said outer chamber having an entrance at said one side of said body; structure surrounding said entrance to said outer chamber and lying in a plane substantially parallel to and spaced axially from the plane of said first diaphragm; a second diaphragm that is deflectable in response to bodily pressures, said second diaphragm being supported by said structure surrounding said entrance, to overlie and close said outer chamber; passage-defining means for establishing fluid-flow communication between said inner chamber and said outer chamber, said inner chamber being otherwise closed and both of said chambers normally containing a fluid; and means for transmitting and focusing a beam generated by said laser diode to and upon said reflective surface of said first diaphragm, whereby light reflected by said first diaphragm can self-mix with light generated by said laser diode to produce interference signals, representative of movement of said first and second diaphragms, for detection by said at least one monitor photodiode.

14. A stethoscope system, comprising, in operative interconnection:

a head comprised of a body having an inwardly extending outer cavity, at one side, and an inner cavity in axial alignment, and optical communication, with said outer cavity; a laser diode contained in said inner cavity, and at least one monitor photodiode contained in said body; at least one planar diaphragm that is deflectable in response to bodily pressures, said at least one diaphragm having a laser beam-reflective inner surface, and being disposed in said outer cavity to define therewith an inner chamber and an outer chamber, said outer chamber having an entrance at said one side of said body; structure surrounding said entrance to said outer chamber and lying in a plane substantially parallel to and spaced axially from the plane of said at least one diaphragm; passage-defining means for establishing fluid-flow communication between said inner chamber and said outer chamber, said inner chamber being otherwise closed and both of said chambers normally containing a fluid; and means for transmitting and focusing a beam generated by said laser diode to and upon said reflective surface of said at least one diaphragm, whereby light reflected by said at least one diaphragm can self-mix with light generated by said laser diode to produce interference signals, representative of movement of said at least one diaphragm, for detection by said at least one monitor photodiode; data-acquisition means; amplification means;

electronic data processing means; and

means for generating a signal that is representative of monitored bodily pressures and is perceptible by at least one human sense.

15. The system of Claim 14 wherein said head additionally includes a second planar diaphragm that is deflectable in response to bodily pressures, said second diaphragm being supported by said structure surrounding said entrance, to overlie and close said outer chamber.

16. The system of Claim 14 wherein said head additionally includes a laser beam-trans- missive window sealingly interposed between said inner and outer cavities substantially on the axis of alignment thereof.

17. The system of Claim 14 wherein said head additionally includes an optical attenuator, said attenuator being interposed between said laser diode and said at least one diaphragm so that light passing between said laser diode and said diaphragm passes through said attenuator.

18. The system of Claim 14 wherein said head additionally includes an electronic circuit for driving said laser diode and for processing signals received by said at least one monitor photodiode, said electronic circuit including means for operative connection of said laser diode and said at least one monitor photodiode to external electronic data processing means.

19. The system of Claim 14 wherein said head additionally includes an adjustable stage mounted within said inner cavity, means for adjusting the tilt of said stage, and a lens comprising said means for transmitting and focusing a beam generated by said laser diode, at least said lens being mounted on said adjustable stage.

20. The system of Claim 18 wherein said head additionally includes a microphone, for detecting ambient sound, operatively connected to said electronic circuit.