Disposable speculum for tympanic thermometer
United States Patent 1 1 Twentier [451 Apr. 22, 1975 1 DISPOSABLE SPECULUM FOR TYMPANIC THERMOMETER [75] lnventor: Max E. Twentier, Phoenix, Ariz.  
 173] Assignee: Products International Marketing,  
 Phoenix, Ariz.  
 [22] Filed: Aug. 23, 1973 [21] Appl. No: 390,687  
 Primary Examiner-Richard A. Gaudet Assistant E.\&#39;uminerl-lenry S. Layton Attorney. Agent, or FirmChristie, Parker &amp; Hale [57] ABSTRACT A disposable plastic speculum is used on an infrared sensing thermometer used by placing it in the patient&#39;s ear for sensing body temperature through the tympanic membrane. The speculum has the general shape of a funnel with relatively shallow and relatively steep tapered frustoconical sections. The speculum is placed on a speculum retainer on the thermometer for use. The exterior of the speculum retainer has the general shape of interior of the speculum and includes 21 peripheral enlargement near its smaller end. When the speculum is placed on the retainer it is stretched by the enlargement and thereby retained in place. The speculum is made of a plastic having limited resistance to stress cracking so that the stretched portion over the enlargement cracks during retention on the speculum retainer. Since the speculum thus inherently destroys itself, it is assured that the speculum will be discarded and a new one used for each patient.  
 8 Claims, 6 Drawing Figures DISPOSABLE SPECL&#39;LL&#39; FOR TYNIPANIC THERMOXIETER BACKGROUND it has been proposed to measure temperature of the human body by way of the car rather than the mouth or rectum as is most commonly done. Oral thermometers have several noticeable hazards of significant concern to hospital and clinic personnel. lf the thermometer is broken in the patient&#39;s mouth. as can readily happen with children or elderly persons. the patient may ingest mercury or glass fragments. Further. if thermometers are not thoroughly sterilized between uses communicable diseases may be transmitted from one pa tient to another. ()ral thermometers ha\ e the additional disadvantage that they only apprmimate deep body temperature since the patient may ha\e ingested cooling or warming materials which mask the true temperature.  
  Oral thermometers are of limited usefulness with infants and rectal thermometers are commonly used. Many serious accidents have occurred due to breakage of the thermometer during such use. in addition. both oral and rectal thermometers are subject to high breakage rates during normal handling. Both oral and rectal thermometers take a substantial time interval to come to temperature equilibrium and the time of valuable health personnel is often wasted during the wait for equilibrium. If the personnel are rushed. inadequate time may be allotted and the thermometer may not ha\e reached equilibrium when the reading is made.  
  To overcome these difficulties. measurement ofbody temperature through the car has been proposedv One such instrument places a thermistor in intimate thermal contact with the interior of the car. A preferred instrument employs an infrared sensor which detects radiation from within the ear. the infrared sensors are opti cal instruments requiring an unobstructed &#34;light path between the sensor and the region where temperature sensing is desired. Such a technique is advantageous since the tympanic membrane is substantially transparcat to infrared radiation and the temperature measured is effectively that of the carotid artery which passes in close proximity to the tympanic membrane. Such an infrared sensor is very rapid and comes to equilibrium within seconds. A suitable technique is disclosed in [&#39;S. Pat. No. liillilb.  
  When such a tympanic thermometer employing an infrared sensor is used. it is desirable to insert an end portion into the ear canal so that temperature of the surroundings does not influence the reading obtained. Such a tympanic thermometer is used for many patients much as an otoscope or other car examining instrumeat. It has often been the practice to simply wipe the tip ofthe speculum that enters the patient&#39;s ear with alcohol between patients to effect limited sterilization and remove any was that may have been deposited. Al though the likelihood of cross contamination from one patient to another through the ear is very low. it is preferable that a clean speculum be used for each patient.  
  It is therefore desirable to provide a speculum that is sufficiently inexpensive that it can be disposed of between usages. Preferably. the speculum should have a limited lifetime so that medical personnel do not continue to use the same speculum. and in effect are forced to dispose of it between successive patients. Such a speculum cover should be inexpensive. non- Fill contaminating. nondrritating. and maintain a fived optical path for the infrared radiation to the sensor.  
 BRIEF SLMMARY OF THE INVENTION There is. therefore. pro\ ided in practice of this inv ention according to a presently preferred embodiment. a disposable speculum for use with a speculum retainer having a generally conical tip with a peripheral enlargement thereon. The speculum is a generally conical sheath of elastically stretchable plastic having a relatively larger open end and relatively smaller open end with an elastically stretchable portion adjacent the rela tively smaller open end with sufficient strength to be installed on a speculum retainer at least once and sufficiently susceptible to stress cracking to rupture during retention on the speculum retainer due to stretching by the enlargement.  
 DRAWlNGS These and other features and ad\ ant-ages of the present invention will be appreciated as the same becomes better understood by reference to the following de tailed description of a presently preferred embodiment when considered in connection with the accompanying drawings wherein:  
  FlG. 1 illustrates in e\ploded \ie\\ a tympanic ther moeter and speculum constructed according to principles of this imention&#39;.  
 FIG. 2 is a longitudinal crosssection ofthe speculum;  
 FIG. 3 is an end \iew of the speculum:  
  FIG. 4 is a longitudinal cross-section ofthe speculum on a speculum retainer:  
  FIG. 5 is a longitudinal cross-scctioit of another embodiment of the speculum retainer; and  
  FIG. 6 is a longitudinal cross-section of another embodiment of speculum constructed according to principles of this invention.  
 DESCRlP&#39;l&#39;lON FIG. 1 illustrates in phantom a representative tympanic thermometer I0 and. exploded therefrom. a speculum ll constructed according to principles of this invention. The thermometer has an instrument housing l2 for mounting a conventional infrared sensor. power supplies. electronic circuits and the like. none of which need by separately illustrated herein. A dial. electroluminescent or other suitable indicator [3 is mounted on the housing for showing the temperature sensed. A hand grip handle [4 is used for holding the instrument and a trigger 16 is used for actuating it. A speculum retainer 17 on the housing receives the speculum ll when the instrument is used.  
  When it is desired to use the thermometer. the specu him is placed on the retainer and inserted in the pa tient&#39;s car. The trigger is depressed. thereby actuating the infrared sensor and electronic circuitry associatct therewith. and within no more than a few seconds lht patient&#39;s temperature is shown on the indicator. Prefer ably. this is shown as a digital display for minimizing reading errors by the operator. The speculum is thei discarded and a new speculum installed for the next pa tient.  
  The speculum ll has the general shape of a funne with a first hollow. generally frustoconieal base sectio 18 having a relatively shallow taper. An enlarged bea [9 is formed around the relatively larger open end c the base section. The base section 18 blends graduall into a second hollow generally frustoconical nose or tip section 2| having a relati ely steep taper. As best seen in FIG. 2, the base section 18 has a relatiiely greater wall thickness and the wall thickness of the nose section 2| gradually decreases towards its smaller open end. A small turned-in lip 22 is present at the smaller tip end ofthe speculum to shield the end ofthe retainer from deposits of ear wa\. Any way deposits are discarded with the disposable speculum.  
  The speculum retainer 17 has an e\terior profile suh stantially complementary to the interior profile of the speculum with one e\ccption. The retainer has a base section 23 flaring outwardly and approyimately complementary to the interior of the base section 18 of the speculum. The retainer also has a more nearly cylindrical frustoconical nose section 24 complementary in general to the interior of the nose section 21 of the speculum. The eyterior of the retainer differs from the interior ofthe speculum by ha\ ing a peripheral enlargement 26 adjacent its smaller open end. The speculum retainer is hollow as seen in FIG. 4. to proi&#39;ide an optical path for infrared radiation. As seen in FIG. 4. when the speculum is pressed onto the speculum retainer into a position wherein its base portion [8 is in engagement with the base portion 23 of the retainer. the wall of the speculum near its tip is stretched to fit oi er the enlargement 26. This stretching of the speculum makes the properties of the plastic of which the speculum is formed of importance.  
  the speculum retainer has a reduced diameter portion 27 between the enlargement Z6 and its base portion. Stretching of the plastic speculum over the cnlargement occurs as it is installed on the retainer. The stretching is well within the elastic range of the plastic and the portion inwardly from the tip (that is. nearer the base of the speculum) contracts after passage in er the enlargement. thereby lightly gripping the retainer. l&#39;he taper of the nose portion ofthe retainer is not sufficient for causing the speculum to creep off 0\ er the enlargement since this would entail stretching ofthe plastic that has contracted into the reduced diameter portion 27. It is also desirable that the interior of the spec ulum he \cry slightly roughened for inhibiting such creeping. Thus. once the speculum is installed on the retainer. it remains in place until manually dislodged. In order to remme the speculum. all one needs do is press forwardly on the head 19 and the speculum pops off readily.  
  The plastic of which the speculum is formed must be sufficiently elastically stretchable that the stretching of the wall as it passes oyer the enlargement of the retainer does not cyceed the fast tensile strength of the plastic. This keeps the speculum from cracking when it is installed on the retainer.  
  Many plastics are susceptible to what is known as stress cracking. Stress carcking occurs when the plastic is sub ected to tensile stress fora period of time. Thus. a stressrelieiing crack may occur in the plastic when it is maintained under a stress appreciably below its fast tensile strength. The susceptibility of a plastic to stress cracking can be measured by ASTM Test Method D- 2561. It is desirable that the plastic of which the speculum i formed ha\e an appreciable susceptibility to stress cracking so that after it has remained in a stretched condition on the enlargement for a period of time. a crack spontaneously de elops&#39;. This spontaneous&#34; cracking provides a self-destruct feature for the Ill (ill  
 speculum so that the medical personnel using it are in duced to discard the speculum rather than re using it for more than one patient. Such stress cracking should occur in no more than a few minutes on the retainer so that it will not he reused several times before discarding.  
  Preferably. the speculum is formed of polyethylene with a relatively low melt index (ASTM Test Method D4138). [n polyethylene and many related thermoplastic materials. the susceptibility to stress cracking is related to the melt index so that the higher the melt index the greater the resistance to stress cracking.  
  lt is found that to form a suitable speculum. the plas tic should have a resistance to stress cracking not greater than that of polyethylene having a melt index of less than about 30 gm/li) min. It is found with such resistance to stress cracking that a crack ordinarily appears in the speculum adjacent the peripheral enlargement on the retainer within one or two minutes. This is ample time for taking and even rcchecking a patients temperature. If a plastic having a greater resistance to stress cracking is employed. the naturally occurring self-destruction of the speculum may be unduly prolonged so that the speculum is used for multiple pa tients. The crack that forms is ordinarily only in the region of stretching and does not propagate to both ends of the speculum.  
  The time until stress cracking occurs is also dependent upon the wall thickness of the speculum adjacent the peripheral enlargement. If the wall is made too thick. cracking may occur as soon as the speculum is installed. It is therefore important that the wall be sufficiently thin that it can tolerate a peripheral enlargement of about 20 percent without exceeding the fast tensile strength of the plastic. This permits it to be safely installed without cracking over a peripheral enlargement that causes a 20 percent elongation. It will be noted that plastics ofthese properties often ha e an elongation at rupture in a fast tensile test IASTM Test Method D4138) of as much as llll) percent.  
  A particularly suitable plastic for forming the speculum is equivalent to a polyethylene a ailable from Rexenc Polymers Company. a division of Dart Industries. lnc.. under their trade designation Rescue PE 207C. This is a polyethylene having a melt index of about 22 gmflt) min and a density of about 0.925. A speculum made of such a material (with small addition of a corn yentional slip additive for mold release) can be rapidly and economically formed by injection molding. Such a speculum can be installed on a retainer with 20 percent peripheral elongation without immediate cracking. Cracking does occur. however. within no more than a few minutes after installation. thereby inducing disposal of the speculum. It will also be noted that if a speculum is placed on the retainer. removed. then reinstalled. cracking seems to occur sooner. thereby inhibiting re-use of specula that may ha e been ejected before actual cracking occurred.  
  FIG. 5 illustrates in longitudinal cross-section a slightly different embodiment ofspeculum retainer. As hereinabo e described. this speculum retainer also has a base portion 3| and nose portion 32 with a hollow interior for passage of infrared radiation. A peripheral enlargement 33 is provided adjacent the smaller open end and differs to the extent that the maximum diameter of the enlargement is set back from the tip slightly further than in the abo e-descrihed embodiment. Thus.  
 at the tip of the speculum retainer. there is a conical section 34 with an included angle of about 60. In addition. a shallow locking groo e 36 is pro ided on the outside of the retainer between the point of maximum diameter of the enlargement and the reduced diameter portion 37 spaced inwardly from the tip.  
  FIG. 6 illustrates in longitudinal cross-section an embodiment of speculum connectable to the slightly modified retainer of H6. 5. This embodiment of speculum also has a generally funnel shape with most element substantially the same as hereinabme described. lhe speculum has a frustoconical base portion 4| with peripheral bead 42 at its open larger end. The smaller end of the base portion blends into a tapered nose portion 43. The wall thickness of the nose portion 43 decreases gradually from the base portion to a point where a small internal rdige 44 is formed. Forwardly from the ridge 44 there is a short section 46 wherein the wall thickness is substantially uniform and is typically about 15 to It) mils thick. Thereafter. extending forwardly. there is a section 47 wherein the wall thickness gradually increases to provide greater stiffness.  
  W hen the speculum of Fl(i. 6 is installed on the re tainer of FIG. 5. it fits much in the manner herein-above described and the end of the retainer reaches approximately to a line 48 illustrated in phantom in FIG. 6. lhis brings the ridge 44 within the speculum into engagement with the groove 36 on the outside of the retainer. The portion of the speculum w here the ridge occurs is somewhat stretched. as seen in phantom in H6. 6. and the cooperation between it and grooye further inhibit inad crtent ejection of the speculum from the retainer. lt will also he noted from the phantom lines in Fl(i. 6 that the section 46 ha ing uniform wall thickness is stretched oyer the enlargement on the retainer. lhis stretching of the speculum induces stress cracking in the manner hercinahoye described for selfdestruction of thc speculum.  
  The somewhat stiffened extension 47 on the speculum beyond the end of the retainer scrtes as a guide as the instrument is inserted in the ear of the patient. The enlargement is such that. on most patients. intrusion of the speculum into the ear is limitcd by contact with the bony structure The end portion 47 of the speculum may extend somewhat further into the ear for shielding the retainer from contamination by waxes or the like. Any wax that may be picked up on the end ofthe speculum is thus discarded with the disposable speculum. The extending tip 47 also pro\ides a somewhat longer optical path within the instrument and apparently rctards heat transfer for assuring accurate temperature measurement. &#39;l&#39;he end portion beyond the stretchable section 46 is preferably somewhat thicker to enhance stiffness in this region and pre cnt collapse ofthe speculum in case it is somewhat twisted within the car. If the speculum were to collapse. portions of it could enter the optical path of the infrared radiation and interfere with temperature measurement.  
  Although limited embodiments of speculum and retainer for a tympanic thermometer ha e been described and illustrated herein. many modifications and \ariations will be apparent to one skilled in the art. Thus. for example. although the speculum is particularly useful in an instrument for measuring temperature in the ear of a patient. it is also quite suitable for use on an otoscope or other ear examining instrument.  
 Similar arrangements of speculum for entering other body orifices will be apparent.  
  If desired for enhanced self-destruction. a peripher ally extending notch may be proyided in the speculum for propagation of the stress crack. Due to the direction of stressing as the speculum is stretched over the enlargement. it is found that the stress crack occurs in a longitudinal direction. A peripherally extending notch may cause propagation of the crack in a peripheral direction further inducing medical personnel to discard the speculum after each patient. Many other modifications and \ariations will be apparent to one skilled in the art and it is therefore to be understood that within the scope ofthe appended claims the in\ention may be practiced otherwise than as specifically described.  
 What is claimed is:  
  l. A disposable speculum for use with a speculum retainer haying a generally conical tip with a peripheral enlargement thereon comprising:  
 a generally conical sheath of elastically stretchable plastic ha ing a relati cly larger open end and a rel ati ely smaller open end:  
 an elastically stretchable portion adjacent the rela&#39; ti ely smaller open end ha ing sufficient strength and elasticity to be installed on a speculum retainer at least once and sufficiently susceptible to stress cracking to spontaneously rupture during no more than a few minutes retention on the speculum re tainer with the stretchable portion on the enlarge ment.  
  2. A disposable speculum for use with a speculum retainer ha ing a generally conical tip with a peripheral enlargement thereon comprising:  
 a generally conical sheath of elastically stretchable plastic ha ing a relatiyely larger open end and a relati cly smaller open end. and  
 an elastically stretchable portion adjacent the rela ti ely smaller open end having sufficient strength and elasticity to be installed on a speculum retainer at least once. the plastic haying a resistance to stress cracking not greater than polyethylene hay ing a melt index of less than about 30 for being sufficiently susceptible to stress cracking to spontaneously rupture during retention on the speculum retainer with the stretchable portion on the enlargement.  
  3. A disposable speculum as defined in claim 2 wherein the elastically stretchable portion has a periph eral elongation of about 20 percent without exceeding the fast tensile strength of the plastic.  
  4. A disposable speculum as defined in claim I including a portion between the elastically stretchable portion and the smaller open end for extending beyond the tip of a speculum retainer and shielding it from ear wax.  
  5. A disposable speculum as defined in claim -I wherein the portion extending beyond the tip comprises an inwardly directed lip for co ering the end of the retainer.  
 6. A disposable speculum comprising:  
 a first hollow. generally frustoconical base section ha ing a relati &#39;ely shallow taper;  
 a second hollow generally frustoconical nose section having a relatively steep taper. the base of the nose section being essentially a continuation of the smaller end of the base section;  
 (ill  
 Ill  
 riotl of timc.  
  7. A disposable speculum as defined in claim 6 lur- Ihcr comprising an inwardlt directcd lip adjaccnt the smallcr open end of the second section.  
  8. A disposable speculum as dcfincd in claim 7 furthcr comprising a pcriphcral heat] for manual ejection of thc speculum,