Miniature peak flow meter is compact, portable diagnostic device
of beeper size. It consists of two bodies which create a curved
cylinder inside which moves a rotational piston by means of rotation.
The resistance to that movement is achieved by a specially created
torsion spring. The mouthpiece is folded inside the device in unused
position thus contributing to the compactness. By pulling out the
mouthpiece and blowing through it, the patient rotates the piston
by his expiratory flow and moves a pointer secured in a groove on
the top side of the device. The pointer shows the value on a printed
scale, and the patient writes it on a recording chart placed on
the bottom surface of the device.
1. A miniature peak flow meter comprising, in combination:
a hollow body having a top surface;
a curved hollow cylinder disposed within said body, said cylinder
having an opening;
a mouthpiece affixed to said body and adapted to direct a flow
of fluid into said cylinder through said opening;
a piston movably mounted within said cylinder, said piston having
a size and shape such that said piston fits freely inside said cylinder
with enough clearance between said piston and said cylinder to allow
said piston to move substantially frictionlessly along said cylinder;
means for rotationally mounting said piston about an axis extending
through said body, the arrangement being such that said piston rotates
concentrically through said cylinder when impacted by said fluid
a spring mounted between said body and said rotatable mounting
means, said spring biasing said piston in a direction towards said
a pointer mounted within said top surface, said pointer being free
to move along a defined path by rotation of said piston in said
cylinder, whereby upon impact of said fluid flow said piston rotates
from a rest position to a peak flow position causing said pointer
to move along said path until it stops at a point indicating peak
fluid flow, said spring forcing said piston to return to its rest
position while said pointer remains in place along said path indicating
peak fluid flow.
2. A miniature peak flow meter according to claim 1 wherein said
path is defined by a curved groove in said top surface which is
concentric with said curved cylinder, said groove and said cylinder
having a common center located at said axis of rotation and wherein
said pointer is mounted within said groove in contact with said
piston, said piston moving said pointer along said groove upon impact
with said fluid flow.
3. A miniature peak flow meter according to claim 2 wherein a
scale is provided along side said groove for measuring the peak
fluid flow indicated by said pointer, said scale being concentric
with said groove.
4. A miniature peak flow meter according to claim 3 wherein said
hollow body includes side walls a portion of which are open to accommodate
said mouthpiece, said mouthpiece being rotatably mounted within
said open portion so that said mouthpiece can be stored inside said
body when not in use and then rotated outwardly to an operative
position communicating with said cylinder opening for directing
a flow of fluid thereto.
5. A miniature peak flow meter according to claim 4 wherein said
body is provided with means for locking said mouthpiece in both
said stored and operative positions.
6. A miniature peak flow meter according to claim 3 wherein said
body includes a bottom surface and wherein a recording chart is
affixed to said bottom surface for recording measurements of said
peak fluid flow.
7. A miniature peak flow meter according to claim 6 wherein said
recording chart is glued or painted onto said bottom surface.
8. A miniature peak flow meter according to claim 6 wherein said
bottom surface is provided with lips on at least two opposite sides
thereof, said lips creating straight grooves inside of which a semi-disposable
recording chart is removably positioned for recording measurements
of said peak fluid flow.
9. A miniature peak flow meter according to claim 1 wherein said
means for rotationally mounting said piston comprises a central
post mounted for rotation about said axis, an elongated connecting
member affixed at one end to said central post and at the other
end thereof to said rotating piston, said connecting member passing
freely through a slot in said curved cylinder.
10. A miniature peak flow meter according to claim 9 wherein said
spring is a torsion spring having a plurality of cylindrical coils
and including two opposite ends, said coils being mounted about
said axis with one of said opposite ends affixed to said body and
the other of said opposite ends affixed to said central post.
11. A miniature peak flow meter according to claim 10 wherein
said plurality of coils are made from wire having a predetermined
diameter, said coils being separated from each other by gap of about
20 to 50 percent of said wire diameter, thereby providing a substantially
frictionless, uniform response to a load applied thereto.
12. A miniature peak flow meter according to claim 9 wherein said
hollow body includes a top and bottom section, said central post
being formed with integrally molded pins at opposite ends while
said top and bottom sections have inmolded cylindrical holes with
diameters slightly larger than the diameter of said pins and create
bearing surfaces, both said holes and said pins aligning along the
same axis which is perpendicular to said top surface of said body
and parallel to said axis of rotation.
13. A miniature peak flow meter according to claim 9 wherein said
hollow body includes a top and bottom section, said central post
being formed with a cylindrical hole while at least one of said
top and bottom sections are formed with a cylindrical pin that protrudes
through said hole in said central post; said cylindrical hole and
said pin creating bearing surfaces, both said hole and said pin
aligning along the same axis which is perpendicular to said top
surface of said body and parallel to said axis of rotation.
14. A miniature peak flow meter according to claim 1 wherein said
curved cylinder has an exit located within a side wall of said body
and wherein at least one curved secondary passage is provided on
at least one side of said cylinder, said passage having an exit
opening located proximate to said exit of said cylinder.
15. A miniature peak flow meter according to claim 14 wherein
said mouthpiece directs said flow of fluid to both said cylinder
and said secondary passage, the part of said flow of fluid directed
through said secondary passage mixing with ambient air blown ahead
by said piston while moving in said cylinder.
16. A miniature peak flow meter according to claim 15 wherein
said curved cylinder is provided with openings for allowing said
blown air to escape, the size and position of said openings being
such as to ensure accuracy, repeatability and linearity of said
17. A miniature peak flow meter according to claim 16 wherein
said body includes a plurality of openings for communicating with
said openings in said cylinder allowing part of said blown air to
escape while the remainder of said air passes through said exit
of said cylinder.
18. A miniature peak flow meter according to claim 1 wherein said
hollow body includes a top and bottom section which, when assembled,
sandwich together said rotational piston, said spring and said mouthpiece
within the interior of said body in a permanently closed unit.
19. A miniature peak flow meter according to claim 18 wherein
said top and bottom sections have inmolded pins while said mouthpiece
has inmolded holes on opposite sides thereof, said pins and said
holes aligning along the same axis which is perpendicular to said
top surface of said body and parallel to said axis of rotation.
20. A miniature peak flow meter according to claim 18 wherein
said top and bottom sections have inmolded holes while said mouthpiece
has inmolded pins on opposite sides thereof, said pins and said
holes aligning along the same axis which is perpendicular to top
surface of said body and parallel to said axis of rotation.
21. A miniature peak flow meter according to claim 1 wherein the
shape of both said cylinder and said rotatable piston is selected
from the group consisting of rectangular, circular, semi-circular
and rectangular with at least one rounded corner.
22. A miniature peak flow meter according to claim 1 wherein the
surface of said rotatable piston is curved in either the radial
direction or the direction substantially normal to said piston.
BACKGROUND OF THE INVENTION
The present invention deals with a mechanically constructed portable
device commonly known in the pulmonary field as the peak expiratory
flow meter, and, more specifically, with a device that is compact,
portable and can fit into a very small purse or pocket.
In the management of pulmonary diseases, and particularly in the
management of asthma, it is very common to monitor the patients'
peak expiratory flow rate by means of peak flow meters. Most pulmonary
patients are supposed to monitor their peak expiratory flow several
times a day, record it, and present the data to their physicians
on a regular basis. Furthermore, patients may experience a shortness
of breath caused by a certain activity or a change in medication.
In order to avoid a false alarm and panic, the value of peak expiratory
flow is used as one of the first and reliable indicators of lung
performance. In both regular and emergency monitoring the patient
has to have a peak flow meter readily available: in a purse or a
pocket. Often the patient wants a socially acceptable device that
doesn't obviously suggest a medical instrument, as well as a device
that doesn't require multiple actions in for example, preparation
for use or to record the reading.
In accordance with the National Heart, Lung and Blood Institute
guidelines mechanical peak flow meters have to be accurate over
a full range to .+-.10%, the reproducibility being .+-.5% and interdevice
variability being .+-.5%. When we add ease of viewing, size, manufacturing
cost, ease of cleansing, and ease of recording a rather complex
set of problems arises, some of them contradictory. Neither today's
market nor patent art have a single mechanical peak flow meter which
satisfies all of these requirements. This invention is the first
one that addresses and fulfills all of them.
Although many mechanical peak flow meters are labeled as "portable"
and "friendly" to use, they do not in fact satisfactorily
meet these requirements. There is a need for a beeper-size device
with approximate dimensions of 27/8".times.21/4".times.5/8".
The device described in U.S. Pat. No. 5224487 which claims to
be the smallest and is marketed as such, has the dimensions of 63/8".times.2".times.7/8".
Its volume is almost three times the volume of the device according
to this invention; when it is unfolded and ready to use, its volume
is even greater. It also contains one loose piece.
SUMMARY OF THE INVENTION
Although the mechanical peak flow meters seem to be relatively
simple, they need to fulfill multiple requirements, sometimes contradictory
ones. This is why the existing peak flow meters are, from a technical
standpoint, compromise solutions.
One of the first and biggest advantages of the peak flow meter
according to this invention is its true portability because of its
The main portion of the peak flow meter, its body, contains a long,
curved channel inside which a piston moves frictionlessly. This
piston actually rotates around a pivot which is placed outside of
the curved channel. The rotational piston and its pivotal shaft
are connected with the body through a torsion spring or springs
which give resistance to the patient's expiratory flow. The top
of the device has a large groove (for example, more than 180 degrees)
inside of which moves a slidable pointer. When the patient blows
into the device, the spring yields and the piston rotates to a certain
position. The pointer is pushed by the piston inside its groove.
After the blowing action, the piston moves back to initial position
and the pointer stops and indicates the measured volume on the scale
which is printed on the top outside surface. After the reading,
the pointer is also moved to initial position, ready for the new
Although absolute size is very important, the peak flow meter according
to this invention offers other features.
The accuracy, reproducibility and interdevice variability of this
invention far exceed the guidelines set by the National Heart, Lung,
and Blood Institute. This is achieved by the frictionless piston,
and the minimal, predictable, and reproducible friction of the pivot.
The specially engineered frictionless torsion spring contributes
to predictable resistance and once the device is calibrated, the
reproducibility is assured.
Another feature of the peak flow meter according to this invention
is the mouthpiece, pivoted and folded into the device when not in
use. This not only contributes to the compactness of the whole device,
but also protects the mouthpiece from dirt (on fingers, pocket,
bag, etc.) when not in use.
Another advantageous characteristic of this invention is a large
scale for viewing. The length of the pointer groove is about 41/2"
which provides a stretched scale and consequently the comfort of
All existing mechanical peak flow meters are accompanied by a booklet,
fairly large in size, in which a patient records the value of measurements
whenever the device is used and which is presented to the physician
at the next visit. In other words, a patient has to carry both a
peak flow meter, which is fairly unwieldy, and a recording booklet.
This invention offers among other features another very useful one:
while the top surface has a scale and a pointer that serve for visual
monitoring of the patient's performance, the whole bottom surface
of 27/8".times.21/4" is used for a large chart where the
patient can record the measured values. The chart can be sufficient
to record a full week of monitoring activities. A device according
to this invention does not necessarily call for elimination of the
recording booklet, but the patient has the option of transferring
the data into the booklet once a week in the comfort of his or her
The recording feature on the back side of the peak flow meter is
yet another feature. There are two possible variations of this feature.
The recording chart can be permanently glued to the back surface
of the device and its surface will allow writing. After a week of
recording and after the data is transcribed into a booklet, the
data on the chart is erased and ready for a new week of recording.
Another possibility is to use insert charts. They can be written
on on both sides, i.e. used for two weeks, and the patient can bring
the physician the filled-out charts instead of a booklet.
The health care industry is very sensitive to the cost of peak
flow meters. The peak flow meter according to this invention is
basically constructed of five simple and small plastic pieces and
one stainless steel spring, and requires few very simple actions
to assemble them. Since the plastic pieces are injection molded,
this device is very economical to manufacture.
In addition, no maintenance is necessary. Cleaning with cold or
hot water and detergent can be done without compromising the performance
of the device.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawing:
FIG. 1 is a the perspective view of the whole device in storage
position with the mouthpiece folded inside
FIG. 1A is a similar view showing the optional rigid plastic case
FIG. 1B is a the side view of the device with the optional hinged
FIG. 2 A and B, are plan views showing the basic shape of the
FIG. 2C is a perspective view of the bottom of the device with
the optional slide-in disposable chart feature
FIG. 2D is a side view of the the device shown in FIG. 2C.
FIG. 2E is a similar view showing a different embodiment of the
device for attaching the charts.
FIG. 3 is a perspective view of a yet smaller device with rounded
FIG. 4A is a top plan view of the deice showing the pulled-out
mouthpiece ready for use
FIG. 4B is an exploded cross-section view through assembled bodies
FIG. 4C is a perspective view of the mouthpiece before assembly
FIG. 4D is a partial sectional view showing another embodiment
of the device
FIG. 5 is a partial sectional view through the center of the device
and one half of: the device
FIG. 5A is a sectional view of another device with a secondary
FIG. 5B is a partial cross-section view through another embodiment
of the device illustrating the plurality of secondary channels
FIG. 6 is a perspective view of the rotational piston and the spring
FIG. 6A is an enlarged elevational view of the spring.
FIG. 6B is a top view of an alternative shape of the rotational
FIG. 6C is a similar view of another alternative shape of the piston.
FIG. 6D is a sectional view of the device showing another embodiment
of the sandwiched center part of the rotational piston
FIG. 6E is a similar view showing yet another embodiment.
FIG. 7 is a cross-section view that shows a secondary channel and
FIG. 7A is a perspective view of the rear part of the device showing
some air openings.
FIGS. 8 8A and 8B are partial sectional views showing some alternative,
but feasible shapes in case a further reduction in size and weight
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows the basic construction and shape of a peak flow meter
according to the invention. Its shape and size is the so-called
beeper size, with approximate dimensions of 27/8".times.21/4".times.5/8".
The device is made basically out of six pieces, top body 1 bottom
body 2 mouthpiece 3 rotational piston 4 spring 5 (FIG. 5) and
pointer 6. The top surface has the groove 17 inside which is placed
pointer 6 that can slide with very little constant resistance, so
it can stay in any position in the groove, and also be easily moved
by finger to the initial position. On the top surface is also placed
or imprinted the curved scale 18. The scale is shown on the upper
side of the groove 17 but it certainly can be placed on its opposite
side. The bodies 1 and 2 are made out of injection molded plastic
and after insertion or assembly the interior parts 3 4 and 5 are
joined together on surface 1/2 by means of screws, glueing, sonic
welding or snapping.
The whole device can have an optional hard plastic case 81 (FIG.
1A), open on both sides or on one side only. Another option is to
have the cover 82 which is hinged to the top body 1 via hinge 821
On both sides gripping grooves 16/26 are made which not only assure
good gripping by fingers, but also suggest in a no-nonsense way
how to use the device. The surface where 16/26 are placed can be
The bottom body 2 can optionally house the recording chart. The
patient can either enter the value in 1/min for the chosen date
and time (FIG. 2A) or can mark the already scaled chart for the
date and time (FIG. 2B).
FIGS. 2C, 2D and 2E illustrates two proposed shapes of the recording
chart. On the surface 21 of part 2 the chart can be painted or permanently
glued as shown in FIG. 2E. On the exposed surface a person can write.
The trace of ink can be removed or erased only by firm pressing
and wiping with a piece of cloth or cotton, or can be simply washed
with warm water and be ready for the next recording. Another embodiment
(FIGS. 2C and 2D) shows the bottom body 2 having a lip 22 on at
least two opposite sides and a semi-disposable chart can be slid
and temporarily locked on the bottom surface. Its advantage is that
a person can permanently write on both sides, collect the semi-disposable
charts and present them to the physician when visiting.
Although the present peak flow meter in its beeper size is miniature
as far as its absolute dimensions and volume are concerned, another
embodiment of it has an even lesser volume inside the same overall
dimensions, as shown in FIG. 3. Two "dead" corners 123
can be eliminated and a part of the outside shape can be made in
the shape of a curve 124 concentric with the groove 17.
FIG. 4A and 5 show the basic function of the device. The mouthpiece
3 is rotated 90 degrees out from inside the device where it was
in its stored, not-in-use position. The bodies 1 and 2 create a
rectangular channel 19/29 inside which 431 part of which is a rotational
piston 4 (FIG. 6), can freely, frictionlessly move. Pointer 6 is
immediately behind 431 which is in initial position A. The whole
part 4 can rotate around axis Z. Its maximal movement is from point
A to point C which represent, but are not limited to, more than
180 degrees. This also represents the full scale of measurement.
Mechanical peak flow meters are usually made in two ranges: 100-400
1/min and 100-700 1/min. Since in engineering of the present invention
the only variable resistance is solving the force of spring 5 it
is feasible that two above mentioned ranges are achieved by simply
using a spring with the appropriate spring rate, while the rest
of the whole device can be the same. Of course, an appropriate scale
should accompany the chosen spring. This certainly can greatly contribute
to the economy of producing two different products.
When a patient blows air through the mouthpiece 3 the stream of
blown air moves 431 inside 19/29. The resistance to this stream
is the force of the spring 5. The final position B of the piston's
part 431 and consequently the position of the pointer 6 which is
pushed by 431 depends on the "strength" of the patient's
Spring 5 is lightly prestressed in initial position A. In any other
position between A and C the spring stress and consequently accumulated
force is larger than at initial position. When a patient's stream
stops and there is no more energy to move 431 further, the spring
simply moves it to initial position A. But pointer 6 stays in position
B and indicates the patient's effort. After reading it, and recording
the reading in the chart, the patient moves the pointer 6 with a
finger, with minimal effort, to initial position as well and the
device is ready for another measurement.
FIG. 4B and 4C show some construction details of mouthpiece 3 and
appropriate parts of bodies 1 and 2. The entrance of the mouthpiece
is supplied with a lip 31 but does not necessarily have to be that
way. If a larger entrance cross-section is required, lip 31 can
be omitted. Short plastic pins 34 are integrally molded with 3
while two appropriate indentations 14 and 24 are molded in bodies
1 and 2. During assembly, the mouthpiece is sandwiched between bodies
and can rotate from closed to opened position. It is convenient
that the mouthpiece is locked in these two positions. Simple and
inexpensive locking is easy to achieve in such a case. Of numerous
possibilities, one simple way is described, but not limited to,
here. The mouthpiece has integrally molded bumps 35 two on one
side or on both sides. The upper body has a female feature in the
shape of indentation 15. When, by rotating the mouthpiece 3 any
of the bumps 35 meet 15 a sound can be heard and locking is achieved.
As shown in FIG. 4D shows, both features, the molded pins and the
male bumps can be reversed. The pins 141 and bump(s) can be part
of the body (or bodies), while holes 341 and female indentation(s)
351 can be molded in the mouthpiece 3.
Similarly, FIG. 5 shows that the rotational piston is sandwiched
between bodies 1 and 2. As presented in FIG. 5 bodies 1 and 2 have
inmolded cylindrical indentations 111 and 211 where male pins 411
FIG. 6 fit and rotate. Of course, just as mouthpiece 3 piston
4 can be sandwiched in so that inmolded pins protrude from bodies
1 and 2 and that the rotational piston has a hole, FIG. 5B. All
in all, the goal is to secure a minimum predictable and repeatable
friction between swinging elements.
FIG. 6 shows the preferable embodiment of the shape of the rotational
piston 4. It consists of cylindrical body 541 which houses spring
5 piston surface 431 connector 42 and the pin(s) 411. All the
mentioned elements are an integral part of 4; 4 is one, injection
molded, plastic piece.
Although it is possible to use a standard torsion spring, the invention
suggests the use of a special spring 5. The main features of such
a spring would be that the inside diameter of the spring d1 is slightly
larger (5-15%) than the appropriate diameter of pin d. Also, it
is recommended that a small gap Y (0.010"-0.025") be made
between the coils. Both of these measures are aimed at reducing
the friction between the spring and the pin and between coils during
the accepting of the load while the patient blows into the device.
This will greatly contribute to accuracy, reproducibility and reduce
The end 51 of spring 5 fits to a molded groove in body 2 or 1
while the other end 52 is hooked to a molded groove in 4 so that
when 4 is sandwiched between bodies 1 and 2 a slight prestress
of 5 is achieved.
FIG. 5 also shows that groove 17 doesn't necessarily have to be
placed at the geometrical center of 431. It means that "R"
can be different than "r". If a long groove is desired,
R>r, and scale 18 is placed between the axes Z and R, but if
a large scale 18 is desired that fits above 17 like in FIG. 1
then R becomes smaller and possibly even smaller than r.
FIG. 5A illustrates another embodiment of the channel where piston
4 is placed. The channel can be divided and form spaces 191/291
and 110/210. As shown in FIG. 7 the mouthpiece covers both channels.
One part of the stream pushes 431 while the other flows freely
to exit 121 (FIG. 7), and further to exhaust at opening 12. The
volume of space 110/210 is about 0-40% of 191/291 and can contribute
to minimizing the dimensions of the device.
FIG. 5B shows yet another embodiment of the device. For further
minimizing of the device as well as for balancing the air flow,
two secondary channels can be introduced, one from each side of
the channel 19/29 i.e. secondary channels 110/210 and 120/220.
To achieve sensitivity and accuracy of the device, as well as linearity
of the scale 18 openings 11 and 10 are introduced (FIG. 7 and 7A).
For better understanding it is important to be aware of the way
of approaching the problem. The flow dynamic calculation is performed
first which defines the basic geometry of the piston, channel, and
the spring rate. Although the invention calls for construction with
minimum friction, some friction does exist between the moving parts.
Non-linear spring rate of torsion spring is also present. In preproduction
stage all of that has to be compensated for by adding the space
110/210 and openings 11 and consequently 10. The number and the
size of 11 and 10 the size of 110/210 the number of coils 5 the
wire size "s" of 5 and d1 are varied and the device is
FIGS. 6B and 6C shows other embodiments of the rotational piston
4. Basically, the air contact surface can adopt the shape 432 or
FIG. 6D illustrates another embodiment of the device where piston
4 has a hole 412 and bodies 1 and 2 have protruding inmolded pins
112 and 212. When assembled, all pins and a hole fall into the same
axis Z which is the center of rotation. One logical consequence
is that one of the bodies does not have a pin but rather a nest.
For instance, if the assembly starts from the bottom body 2 spring
5 is placed first on pin 213 and engaged with inmolded groove 214
then 4 is put on the pin 213 and engaged with the other end of 5;
1 is placed on top and 113 is engaged with 213. Of course, before
placing 1 the mouthpiece 3 is put in its place.
In FIGS. 8 8A and 8B some other embodiments of shapes of basic
form of 431 are shown. The shapes 434 435 and 436 can be easily
achieved. Of course, the bodies 1 and 2 will consequently follow
the shape of 4 and always leave a gap for frictionless swinging
of piston 4.