Abstract:
An apparatus for causing air flow to vibrate a selected tissue includes a tube and a deflector. The tube defines a passage for guiding air flow from an inlet to an outlet thereof. The deflector is disposed to receive the air flow from the outlet of the tube. The configuration of the deflector is such as to channel air flow from the outlet past the selected tissue. This causes vibration of the selected tissue.

Description:
TECHNICAL FIELD 
     This invention relates to devices for assessment of tissue pliability and in particular, to the assessment of vocal fold and skin pliability. 
     BACKGROUND 
     The vocal folds, because of their position in the airway, play a vital role in speech, swallowing, and breathing. In order to perform these functions normally, the laryngeal muscles must be able to open and close the folds. In addition, the folds must have the proper biomechanical properties to efficiently and effectively control the air stream when used for voice production. 
     Each vocal fold is composed of a muscle covered by a ligament running the length of the vocal fold and a more superficial, free mucosal edge that vibrates during voice production. The tissues lying above the muscular body of the vocal fold, called the lamina propria, can be separated into discrete layers based on the concentration of elastin and collagen fibers and fiber orientation. The delicate arrangement of the extracellular matrix proteins within the lamina propria permits passive movement of a vocal cover over the body, resulting in the formation of a mucosal wave as air is passed through the glottis. Mobility of these tissue layers influences the fundamental vibration frequency of the vocal folds and directly impacts the voice. 
     Scar tissue may form in the vocal fold. This scar tissue can cause adhesion of the vocal fold epithelium to the vocal ligament or deeper tissues, effectively eliminating the gelatinous material of the superficial lamina propria at the scar location. Without the gelatinous layer of the lamina propria, a vocal fold is unable to generate a normal mucosal wave during phonation. Such a vocal fold is referred to as “dysphonic.” 
     Patients with dysphonia caused by vocal fold scarring are typically evaluated by indirect laryngoscopy and video stroboscopy, with particular attention paid to vocal fold mobility, glottic closure, and the presence, amplitude, and symmetry of the mucosal wave. 
     During speech, the mucosal wave is best observed by illuminating the vocal folds with evenly-spaced light pulses from a strobe light in a technique know as stroboscopy. If the pulsation frequency matches the fundamental vibration frequency of the vocal folds, then the folds will appear stationary even though they are vibrating. If, however, the strobe&#39;s pulsation frequency is slightly offset from that of the vocal folds, then the folds will appear to move in slow-motion. The visual appearance of the vocal fold mucosal wave when thus illuminated is a diagnostically important aspect of vocal fold assessment. 
     Injection of gelatinous material into the superficial lamina propria to treat vocal fold scarring is best performed when the patient is under general anesthesia. The targeted layers of vocal fold are thin and delicate, and must be stationary to ensure accurate injection without tissue trauma. The accuracy of the injection is increased when the surgeon has a direct, magnified view of the injection site through a glottiscope. 
     Surgeons who inject material into scarred vocal folds to restore pliability would benefit from feedback about how each injection made during the procedure affects vocal fold biomechanical properties. Unfortunately, glottiscope placement is invasive and requires general anesthesia. Under these circumstances, it is impractical to remove the glottiscope and awaken the patient between each intraoperative manipulation in order to ask the patient to phonate. 
     SUMMARY 
     In one aspect, the invention includes an apparatus for causing air flow to vibrate a selected tissue, the apparatus includes a tube defining a passage for guiding air flow from an inlet to an outlet thereof. A deflector is disposed to receive the air flow from the outlet. The configuration of the deflector causes channeling of the air flow from the outlet past the selected tissue. This causes the selected tissue to vibrate. 
     In one embodiment, the deflector includes a cup portion having a rim shaped to conform to tissue proximate to the selected tissue. The cup portion and the tissue proximate to the selected tissue define a chamber for receiving air from the outlet. The cup portion can be made of a variety of materials, such as gold, silver, or surgical steel. In some embodiments, the geometry of the cup portion seals a volume adjacent to a vocal fold. In other embodiments, the geometry of the cup portion seals a volume adjacent to a region of skin surface. 
     Embodiments of the invention include those in which the cup portion has One geometry of the cup portion a back edge and a front edge, the back edge having a radius-of-curvature greater than a radius-of-curvature of the front edge. Other embodiments include those in which the cup portion has a rim shaped to seal a volume adjacent to a vocal fold. 
     The deflector can include a flat portion disposed for placement across from the selected tissue and separated therefrom by a gap through which air escapes from the chamber. The deflector can be welded to the tube or it can be integral with the tube. 
     The apparatus can also include a camera disposed to view the vibrating tissue, and a computer in data communication with the camera, the computer being configured for video stroboscopy. Or, the apparatus can include a microphone disposed to receive an acoustic signal from the vibrating tissue. 
     In other embodiments, the apparatus also includes a measurement port in fluid communication with the lumen of the tube, the measurement port providing an opening for measurement of a property of air in the tube. 
     In another aspect, the invention includes a method for assessing mechanical properties of a selected tissue by defining an expansion chamber adjacent to the selected tissue, passing pressurized air into the expansion chamber, and providing an opening through which the pressurized air can escape the expansion chamber, the opening being disposed such that, while escaping from the expansion chamber, air passes by the selected tissue, thereby causing the selected tissue to vibrate. 
     The tissue whose mechanical properties are to be assessed can be any tissue, including in particular vocal fold tissue and skin. 
     In one practice, the method includes measuring acoustic waves generated by the vibrating tissue. Other practices include illuminating the vibrating tissue with a stroboscope, determining a fundamental vibration frequency of the selected tissue, and/or determining a phonation threshold pressure of the selected tissue. 
     These and other embodiments may have one or more of the following advantages. An aerodynamic tissue driver enables intraoperative stroboscopy of vocal fold vibration in the anesthetized patient. The aerodynamic tissue driver enables experimental control of subglottic pressure during phonation. The aerodynamic tissue driver also enables simultaneous stroboscopy and measurement of acoustic and aerodynamic variables. The aerodynamic tissue driver enables independent assessment of right and left vocal fold vibration. Since the patient is anesthetized during usage of the aerodynamic tissue driver, the aerodynamic tissue driver enables assessment of vocal fold vibration that is independent of patient behavior such as conscious voice modification. In other applications, the aerodynamic tissue driver can be applied to enable measurement of pliability of other tissues such as skin. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a cross-sectional view of an aerodynamic tissue driver. 
         FIG. 1B  is a cut-away view of the aerodynamic tissue driver of  FIG. 1A . 
         FIGS. 2A and 2B  are views of aerodynamic tissue drivers for driving the left and right vocal folds, respectively. 
         FIG. 3  is a view of an aerodynamic tissue driver being inserted between vocal folds of a patient. 
         FIGS. 4 and 5  are cut-away views of an aerodynamic tissue driver in position for driving left and right vocal folds respectively. 
         FIG. 6  is a view of an aerodynamic tissue driver for driving skin tissue. 
         FIG. 7  is a view of the aerodynamic tissue driver of  FIG. 6  driving skin on a forearm. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1A , a system  10  for assessing vocal fold vibration includes a tissue driving subsystem for driving a vocal fold  14  and a diagnostic subsystem for collecting data indicative of the response of the vocal fold  14  to the driving subsystem. 
     The driving subsystem includes an air supply  11  having a compressor  24 , for supplying pressurized air, and a humidifier  25 , for adding moisture to the compressed air. A suitable air supply  11  is based on the design of Jiang &amp; Titze “A methodological study of hemilaryngeal phonation,” Laryngoscope 1993; 10:872-82, the contents of which are herein incorporated by reference. 
     The driving subsystem further includes an aerodynamic tissue driver  18  having a tube  20 . A proximal end of the tube  20  is connected to the air supply  11 . A distal end of the tube  20  is attached a deflector  22 , which will be described in more detail below with reference to  FIG. 2A . A handle  30 , shown schematically in  FIG. 1A , is attached near the proximal end of the tube  20  to allow a surgeon to manipulate the position of the deflector  22 . 
     A sensor  19  placed in fluid communication with the interior of the tube  20  allows measurement of characteristics of the air in the tube  20 . Exemplary characteristics can include pressure, velocity, temperature, and humidity. Information concerning air pressure is particularly useful for recording how much air pressure is required to initiate vocal fold vibration (phonation threshold pressure). A suitable sensor is available as MPX2010GP from Motorola® of Schaumburg, Ill. 
     The diagnostic subsystem includes a microphone  23 , a strobe light  26 , and a video camera  29 , all of which are in communication with a computer  28 . 
     The microphone  23  is positioned near the patient&#39;s mouth, preferably about fifteen centimeters therefrom. The microphone  23  records sound from the vocal fold  14  as an analog signal. This analog signal is digitized by an A/D converter (not shown). The resulting digitized signal is provided to the computer  28 . The computer  28  applies a fast Fourier transform (FFT) to the digitized signal to generate its frequency spectrum, from which a fundamental frequency of the vocal fold  14  is determined. 
     A first optical relay  31  directs periodic light pulses from the strobe light  26  toward the vocal fold  14 . This periodic illumination enables the surgeon to see the mucosal waves. A second optical relay  33  directs light from the vocal fold  14  to the video camera  29 , which then provides video information to the computer  28 . In addition, the camera  29  sends information about the phase of recorded video frames to the strobe light  26 , thereby enabling the strobe flashes to be coordinated with video recording for optimal video quality. 
     The strobe light  26 , computer  28 , optical relays  31 ,  32 , and video camera  29  are typically packaged as part of a video stroboscopy unit for measuring the frequency of vocal fold vibrations. An example of a video stroboscopy unit is the Digital Video Stroboscopy System Model 9295 from Kay Elemetrics Corp. of Lincoln Park, N.J. 
     A high speed video recording system (not shown) can also be used to record motion of the vocal fold  14 . Examples of a suitable video system include those that can record digitized images at 2000 frames/second. An example of such a video system is the High-Speed Video System, Model 9700 from Kay Elemetrics® Corp. of Lincoln Park, N.J. 
     The aerodynamic tissue driver  18  enables real-time assessment of pliability and function of a single vocal fold  14  of an anesthetized patient. This assessment can be performed during phono-microsurgery to evaluate a vocal fold  14  after initial surgical treatment. 
       FIG. 2A  shows the deflector  22  of the aerodynamic tissue driver  18  in more detail. The deflector  22  includes a flat portion  66  and a cup portion  64  distal to the flat portion  66 . A tapered bottom portion  68  of the deflector  22  permits the aerodynamic tissue driver  18  to slide into the anterior commissure between the anterior intersection of the left and right vocal folds. The overall shape of the cup portion  64  is selected to form a tight seal against the tracheal wall just below the vocal fold  14 . 
     When properly inserted, the flat portion  66  of the deflector  22  opposes the larynx wall at the level of the vocal fold  14 . Meanwhile, the cup portion  64 , when seated against the larynx wall below the vocal fold  14 , forms a seal. The tracheal wall and the cup portion  64  of the deflector  22  define an expansion chamber having a single narrow opening. The opening is the gap between the flat portion  66  and the vocal fold  14 . 
     The deflector  22  can be cast using metals such as silver, gold, and surgical steel. Other metals or materials can also be used to form the deflector  22 . The mold for casting can be made from a wax version of the deflector  22  shaped with reference to an actual vocal fold  14  and trachea wall. 
     The tube  20  can be a metal tube that is attached to the deflector  22 . In other examples, the deflector  22  and the tube  20  can be formed simultaneously using a single mold. This is followed by boring an air passageway through the tube  20 . 
     In operation, pressurized air exits the tube  20  and enters the chamber formed by the cup portion  64  and the tracheal wall. Having no place else to go, this air rushes past the vocal fold  14  as it exits through the gap between the vocal fold  14  and the flat portion  66 . This phonates the vocal fold  14 . 
     A particular advantage of the configuration is that only a single vocal fold  14  is driven. As a result, coupling of vibration between vocal folds is avoided. 
     As noted above, the cup portion  64  has a geometry designed to follow the contour of the subglottal airway below the vocal fold. The trachea walls below the right and left vocal folds become more recessed relative to the medial upper edge of each vocal fold towards the back of the patient. This results in a non-symmetrical cup portion  64 . Therefore, there are separate, asymmetrical models of the aerodynamic tissue driver  18 : one for driving the right vocal fold and another for driving the left vocal fold. Furthermore, the deflector  22  can be sized to conform to different sizes of vocal folds. 
     The phonation threshold pressure for phonation of single vocal folds by the aerodynamic tissue driver  18  is consistently higher than the phonation threshold pressure for whole larynx phonation, but shows a similar relative difference for onset versus offset phonation threshold pressure. Experimental alterations of vocal fold properties to simulate pathological conditions result in predictable and reproducible changes in aerodynamic tissue driver phonation measures. The aerodynamic tissue driver  18  can thus characterize altered vocal fold biomechanics following experimental injuries, even if those injuries are not apparent from whole larynx phonation. 
     Referring to  FIG. 1B , a surgeon inserts the tube  20  down an anesthetized patient&#39;s throat through a surgical glottiscope  70 . Following insertion of the tube  20 , the surgeon uses the handle  30  to guide the deflector  22  to the correct position against the lateral airway and adjacent to the driven vocal fold  14 . 
       FIG. 2B  shows an aerodynamic tissue driver  80  used to drive a right vocal fold. The right aerodynamic tissue driver  80  is a mirror image of the left aerodynamic tissue driver  50  shown in  FIG. 2A . 
       FIG. 3  shows the aerodynamic tissue driver  80  inserted between the left and right vocal folds  120 ,  104  to contact the lateral tracheal wall below the right vocal fold  104 . 
       FIG. 4  shows the left aerodynamic tissue driver  50  placed to phonate the left vocal fold  120 . Below the left vocal fold  120  is a tapered front trachea wall section  122  and a more recessed back trachea wall section  124 . 
     Referring to  FIG. 5 , the back portion  92  of the right aerodynamic tissue driver  80  is shaped with a deep curvature to conform to the deep curvature of the trachea wall area  102  below the right vocal fold  104 . 
     The general principle of phonating tissue to measure its pliability can be applied to tissues other than the vocal folds. For example, pliability of skin is often of concern to individuals. A quantitative measurement of skin pliability can be useful for determining the effectiveness of skin care products, such as creams. The measurement of skin pliability can also be used to assess a need for plastic surgery, as well as for comparing the differences in pliability before and after the surgery or other treatment. 
     Referring to  FIG. 6 , an aerodynamic tissue driver  300  can vibrate or phonate skin of a patient to measure pliability of the patient&#39;s skin. The aerodynamic tissue driver  300  vibrates or phonates skin by passing air through a tube  302  and into a deflector  304  placed against the skin below a driven portion thereof. The deflector  304  and the skin form an expansion chamber having a narrow opening. Air flows through the tube  302  and into this chamber. The air then escapes from the chamber and flows through a gap between a flat portion  305  and the driven skin. This causes the skin to vibrate. 
     The aerodynamic tissue driver  300  can be made from different materials. For instance, the deflector  304  can be cast from various metals such as silver, gold, or surgical steel. The tube  302  can be a metal tube connected to an air supply as described previously with respect to  FIG. 1A . Similarly, a fundamental frequency of vibration of the skin fold can be measured using a microphone or using video stroboscopy as described previously with respect to  FIG. 1A . The fundamental frequency can be related to the pliability of the patient&#39;s skin, as can the threshold air pressure required to drive the skin into vibration. 
     Referring to  FIG. 7 , the aerodynamic tissue driver  300  is used to phonate a skin fold  310  by firmly pressing the cupped surface  304  against skin below the skin fold  310  to form a seal. The tube  302  is then pressurized. A microphone  312  held close to the exposed skin fold  310  provides a signal representing the resulting vibratory sound. This vibratory signal is then digitized. A computer (not shown) applies a FFT to the digitized signal to generate its frequency spectrum, from which a fundamental frequency of the skin fold  310  is determined. As described previously, a video stroboscopy system  314  can also be used to measure the fundamental frequency of the skin fold  310 . In other examples, the aerodynamic tissue driver  300  can be used to phonate a skin fold of a breast, under an arm, and elsewhere on a body. Embodiments of the aerodynamic tissue driver  300  can be sized differently according to sizes of these skin folds. 
     Only selected embodiments of the invention have been described. Nevertheless, the invention includes embodiments other than those described herein. For example, modifications to the embodiments described herein can be made without exceeding the scope of the invention.