Note: Descriptions are shown in the official language in which they were submitted.
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DIS;POSABLE SPECULUM FOR TYMPANIC THERMOMETER
Background
It has been proposed to measure temperature of the
human body by way of the ear 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. If the thermometer is broken in the patient'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 patient to
another. Oral thermometers have the additional disadvantage
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that they only approximate deep body temperature since the
patient may have 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 breakagé of the thermometer
during such use. In addition,, both oral and rectal thermo-
meters 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 andthe~ thermometer may not have reach equili-
brium when the reading is made.
To overcome these difficulties, measurement of body
temperature through the ear has been proposed. One such instru- ~,
ment places a thermistor in intimate thermal contact with the
interior of the ear. A preferred instrument employs an infra-
red sensor which detects radiation from within the ear. The
infrared sensors are optical instruments requiring an unob-
; structed-"light" path between the sensor and the region where
temperature sensing is desired. Such a tehcnique is advantage-
ous since the tympanic membrane is substantially transparent
to infrared radiation and the temperature measured is effectively
that of the carotid artery which passes i~ 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 U.S. Patent No. 3,282,106.
When such a tympanic thermometer employing an infrared
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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 ear
examining instrument. It has often been the practice to
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simply wipe the tip of the speculum that enters the patient's
ear with alcohol between patients to effect limited steriliza-
tion and remove any wax that may have been deposited~ Although
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 life-
time so that medical personnel do not continue to use the samespeculum, and in ef~ect are forced to dispose of it between
successive patients. Such a speculum cover should be inexpen-
sive, non-contaminating, non-irritating, and maintain a fixed
optical path for the infrared radiation to the sensor.
~0 Brief~Summary of the Invention
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There is, therefore, provided in practice of this inven-
tion according to a presently preferred embodiment, a dispos- ;
able 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 relatively smaller open end with sufficient
strength to be installed on a speculum retainer at least onae
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and sufficientl~ susceptible to stre$s cracking to ruptu~e
during retention on the speculum retainer due to stretching by ,
. . .
the enlargement. : '
Thus according to the present invention there is ~:
provided a speculum in combination with a speculum retainer,
said speculum retainer comprising: a rigid member having an
axial interior passage and a generally frustoconical exterior
with a peripheral enlargement nearer its smaller end and a
reduced cross-section portion between the enlarged portion and
. the wider portion of the exterior; and said speculum comprising: ;:
a generally frustoconical plastic member having a principal
portion interiorly complementary to the exterior of the retainer
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: and a minor portion elastically stretchable to conform to the
enlargement of the retainer without exceeding the fast tensile ~ ' '
,~ 15, strength of the plastic in the stretched portion of the speculum.
Also in accordance with the present invention there ,:
is provided a disposable speculum comprising: a first hollow, , ~ :.
~: generally frustoconical base section having a relatively shallow
~ taper; a second hollow generally frustoconical nose section
:: 20~ : having a relatively steep taper, the base of the nose section :.
,being essentially a continuation of the smaller end of the base
sec~tion; said nose section being sufficiently thin relatively ~,
nearer its small end~to have a peripheral elongati~n of about '
20~ without exceeding the fast tensile strength of the plastic :::~:
:~ 25 ,for temporary retention on a speculum retainer without''cracking
and for spontaneous cracking when retained on a speculum ~ :
':~' retainer for a period of time; in:combination with: a speculum: i:
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retainer in the form of a rigid member having an axial interior
~; ~ passage and a generally frustoconical exterior with a peripheral
enlargement nearer its small end and a reduced cross section
portion botween the enlarged portion and the~wider portlon of the
:
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exterior, the exterior of the rigld member being complementary :
to the interior of the disposable speculum except for the
peripheral enlargement which has a larger diameter than the
speculum for elastic stretching thereof. ~ :
Drawings .
These and other features and advantages of the present
invention will be appreciated as the same becomes better under- .... .~
stood by reference to the following detailed description of a
presently preferred embodiment when considered in connection
10 with the accomp.anying drawings wherein~
FIG. 1 illustrates in exploded view a tympanic ~:
thermometer and speculum constructed according to principles
of this invention,
FIG. 2 is a longitudinal cross-section of the
~15 speculum; ;
FIG. 3 is an end view of the speculum;
" , .
FIG. 4 is a longitudinal cross-section of.the ; r '~
: speculum on a speculum retainer;
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FIG. 5 is a lonyitudinal cross-seetion of another
embodiment of the speculum retainer; and
FIG. 6 is a longitudinal cross-section of another
embodiment of speeulum constructed aceording to principles
of this invention.
Description
FIG. 1 illustrates in phantom a xepresentative
tympanic thermometer 10 and, exploded therefrom, a speculum 11
constructed~according to principles of this invention. The
thermometer has an instrument housing 12 for mounting a con-
ventional infrared sensor, power supplies, electronic circuits
and the like, none of which need be separately illustrated herein~
A dial, electroluminescent or other suitable indicator 13 is
mounted on the housing for showing the temperature sensed. A
hand grip handle 14 is used for holding the instrument and a
trigger 16 is used for aetuating it. A speculum retainer 17
on the housing reeeives the speculum 11 when the instrument
is used.
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When it is desired to use the thermometer, the speculum
is placed on the retainer and inserted in the patient's ear.
The trigger is depressed, thereby actuating the infrared
sensor and electronic circuitry associated therewith, and
within no more than a few seconds the patient's temperature
is shown on the indicator. Preferably, this is shown as a
digital display for minimizing reading errors by the operator.
The speculum is then discarded and a new speculum installed
for the next patient.
The speculum 11 has the general shape of a funnel with
a first hollow, generally frustoconical base section 18 having
a relatively shallow taper. An enlarged bead 19 is formed around
the relatively larger open end of the base section. The base
section 18 blends gradually into a second hollow generally
frustoconical nose or tip section 21 having a relatively steep
taper. As best seen in FIG. 2, the base section 18 has a
relatively greater wall thickness and the wall thickness of
the nose section 21 gradually decreases towards its smaller
open end. A small turned-in lip 22 is present at the
smaller tip end of the speculum to shield the end of the
retainer from deposists of ear wax. Any wax deposits are
discarded with the disposable speculum.
The speculum retainer 17 has an exterior profile sub-
stantially complementary to the interior profile of the
speculum with one exception. The retainer has a base section 23
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flaring outwardly and approximately complementary to the inter-
ior 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 exterior of the retainer differs from the
interior of the speculum by having a peripheral enlargement 26
adjacent its smaller open end. The speculum retainer is hollow
as seen in FIG. 4, to provide 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 18 is in engagement with the base portion 23 of the
retainer, the wall of the speculum near its tip is stretched
to fit over 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 26 and its base portion. Stretching
of the plastic speculum over the enlargement 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 over the enlargement, thereby lightly gripping the
retainer. The taper of the nose portion of the retainer is
not sufficient for causing the speculum to creep off over the
enlargement since this would ential stretching of the plastic
that has contracted into the reduced diameter portion 27. It
is also desirable that the interior of the speculum be very
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 remove the
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speculum, all one needs do is press forwardly on the bead 19
and the speculum pops off reàdily.
The plastic of which the speculum is formed must be
sufficiently elastically stretchable that the stretching of
the wall as it passes over the enlargement of the retainer
does not exceed 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 cracking occurs when the plastic is subjected
to tensile stress for a period of time. Thus, a stress-relieving
crack may occur in the plastic when it is maintained under a
stress appreciably below its fast tensile strength. The sus- ;
ceptibility 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 is formed have 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 develops. This spontaneous cracking provides a
20 self-destruct feature for the speculum so that the medical per-
sonnel using it are induced 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 be reused several times before discarding.
Preferably, the speculum is formed of polyethylene with a
relatiyely low melt index (ASTM Test Method D-1238). In poly-
ethylene and many related thermoplastic materials, the suscepti-
bility to stress cracking is related to the melt index so that
the higher the melt index the greater the resistance to stress
cracking.
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It is found that to form a suitable speculum, the
plastic should have a resistance to stress crac~ing not greater
than that of polyethylene having a melt index of less than about
30 gm/10 min~ It is found with-such resistance to stress cxack-
ing that a crack ordinarily appears in the speculum adjacentthe peripheral enlargement on the retainer within one or
two minutes. This is ample time for taking and even rechecking
a patient's temperature. If a plastic having a greater resis-
tance 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 patients. 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 sufficieintly thln that it can tolerate a peri-
pheral enlargement of about 20%~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% elonyation. It will be noted that plastics of
these properties often have an elongation at rupture in a fast
- tensile test (ASTM Test Method D-638) of as much as 100%.
A particularly suitable plastic for forming the speculum
is equivalent to a polyethylene available from Rexene Polymers
Company, a diuision of Dart Industriesj Inc., under their trade
designation Rexene PE 207C. This is a polyethylene having a
melt index of about 22 gm/10 min and a density of about 0.925. ;~
A speculum made of such a material (with small addition of a
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conventional 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% 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 rein- ~ ;
stalled, cracking seems to occur sooner, thereby inhibiting
re-use of specula that may have been ejected before actual
cracking occurred.
FIG. 5 illustrates in longitudinal cross-section a slightly
different embodiment of speculum retainer. As hereinabove des-
cribed, this speculum retainer also has a base portion 31 and
nose portion 32 with a hollow interior for passage of infrared
radiation. A peripheral enlargement 33 is provided adjacent
the small 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 above-described 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 groove 36 is provided 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 embodi-
ment of speculum connectable to the slightly modified retainer
; of FIG. 5. This embodiment of speculum also has a generally
funnel shape with most elements substantially the same as
hereinabove described. The speculum has a frustoconical base
portion 41 with peripheral bead 42 at its open larger end.
The smaller end of the base portion blends into a tapered nose
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portion 43. The wall thickness of the nose portion 43 decreasesgradually from the base portion to a point where a small inter-
nal ridge 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 20 mils thick. Thereafter,
extending forwardly, there is a section 44 wherein the wall
thickness gradually increases to provide greater stiffness.
When the speculum of FIG. 6 is installed on the retainer
of FIG. 5, it fits much in the manner hereinabove described and
the end of the retainer reaches approximately to a line 48
illustrated in phantom in FIG. 6. This brings the ridge 44
within the speculum into engagement with the groove 36 on the
outside of the retainer. The portion of the speculum where the
ridge occurs is somewhat stretched, as seen in phantom in FIG.
6, and the cooperation between it and groove further inhibit
inadvertant ejection of the speculum from the retainer. It
will also be noted from the phantom lines in FIG. 6 that the ~ -
section 46 having uniform wall thickness is stretched over the
enlargement on the retainer. This stretching of the speculum
induces stress cracking in the manner hereinabove described for
self-destruction of the speculum. ;
The somewhat stiffened extension 47 on the speculum beyond
the end of the retainer serves 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 limited 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 of the specull]m is
thus discarded with the disposable speculum. The extending
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tip 47 also provides a somewhat longer optical path within the
instrument and apparently retards heat transfer for assuriny
accurate temperature measurement. The end portion beyond the
stretchable section 46 is preferably somewhat thicker to enhance
stiffness in this region and prevent collapse of the speculum
in case it is somewhat twisted within the ear. 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 have been described and illustrated
herein, many modifications and variations 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 peripherally
extending notch may be provided in the speculum for propayation
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 peri-
pherally 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 variations will be apparent to one skilled in the art and
it is therefore to be understood that within the scope of the
appended claims the invention may be practiced otherwise than
as specifically described.
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