Abstrict A peak flow meter is provided comprising an elongated body having
a longitudinal direction and a predetermined cross sectional shape
and a growing area. The body has an open entering end and an open
exit end. The body is circumferentially continuous substantially
from end to end. A piston and an indicator are mounted in said body
for movement longitudinally thereof upon exhalation into the open
entering end. The indicator is pushed along said body for movement
by the piston longitudinally of said body. The indicator is of low
mass so as not to overshoot, and is returned to rest by shaking
a weight against it. A logarithmic scale is provided along said
body against which the position of said indicator can be read.
Claims The invention is claimed as follows:
1. A peak flow meter comprising an elongated body having a longitudinal
direction and a predetermined cross sectional shape, said body having
an open entering end and an open exit end, a piston and an indicator,
means for mounting said piston in said body for longitudinal movement
thereof upon exhalation into said open entering end, means for mounting
said indicator in said body for engagement by said piston for movement
by said piston longitudinally of said body, said indicator staying
in the position to which it has been moved by said piston, means
for retracting said piston independently of said indicator, a mass
longitudinally movable in said body for returning said indicator
independently of said piston, and means along said body against
which the position of said indicator can be read.
2. A peak flow meter as set forth in claim 1 and further including
a spring operatively connected to said piston for limiting advance
of said piston and for retracting said piston.
3. A peak flow meter as set forth in claim 2 wherein said spring
comprises a tension spring.
4. A peak flow meter as set forth in claim 1 wherein said piston
mounting means and said indicator means comprise an elongated member
extending substantially longitudinally of said body and along which
said piston and said indicator are movable.
5. A peak flow meter as set forth in claim 4 wherein said elongated
member is cylindrical, and wherein said elongated cylindrical member
comprises a hollow tube having a longitudinal slot therein substantially
from end to end and a means for carrying said indicator slidably
mounted in said slot.
6. A peak flow meter as set forth in claim 5 wherein said indicator
and carrying means therefore are substantially T-shaped having a
stem extending through said slot, an enlargement on said stem interiorally
of said tube, and a spring compressed between said indicator and
said tube.
7. A peak flow meter as set forth in claim 5 wherein said indicator
and said carrying means for said indicator have low mass, and a
mass longitudinally movable in said body for returning said carrying
means and said indicator toward the entering end of said body.
8. A peak flow meter as set forth in claim 7 wherein said mass
is slidably mounted within said tube.
9. A peak flow meter as set forth in claim 8 wherein the mass comprises
a cylinder.
10. A peak flow meter as set forth in claim 8 wherein the mass
comprises spherical means.
11. A peak flow meter as set forth in claim 1 wherein said piston
has a predetermined fixed cross sectional area, and wherein said
body has an increasing internal area from said entering end toward
said exit end and of greater area than said predetermined area of
said piston.
12. A peak flow meter as set forth in claim 11 wherein both said
body and said piston have a circular cross section.
13. A peak flow meter as set forth in claim 11 and further including
a logarithmic scale on said body for reading the position of said
indicator.
14. A peak flow meter as set forth in claim 13 wherein both said
body and said piston have a circular cross section.
15. A peak flow meter comprising an elongated body having a longitudinal
direction and a predetermined cross sectional shape, said body having
an open entering end and an open exit end, a piston with a predetermined
cross sectional area, means for mounting said piston in said body
for longitudinal movement thereof upon exhalation into said open
entering end, an indicator mounted internally of said body and independently
of said piston for movement by said piston longitudinally of said
body, said piston having a fixed predetermined cross sectional area,
said body having a cross sectional area varying logarithmic along
said longitudinal direction, and means along said body against which
the position of said indicator can be read.
16. A peak flow meter as set forth in claim 15 wherein said body
cross sectional area is greater at the exit end than at the entering
end.
17. The peak flow meter as set forth in claim 16 wherein said means
along said body for reading the position of said indicator comprises
a logarithmic scale.
18. A peak flow meter for determining peak air flow of an exhaling
patient, comprising:
a hollow body for accommodating a flow of exhaled air therethrough;
an indicator adjacent to said body and movable relative to said
body to a position along a scale on said body, said position related
to a peak of the flow of exhaled air through said body;
said body having an internal area related to said scale such that
said scale represents a logarithmic scale of the peak of the exhaled
flow of air through said body; and
at least one zone adjacent said logarithmic scale said zone indicating
a predetermined range of a patient's air flow independent of placement
along said logarithmic scale.
19. The peak flow meter of claim 18 said flow meter further comprising:
a mouthpiece connected to said body and into which the patient
blows air.
20. The peak flow meter of claim 18 wherein said at least one zone
is positioned on an approval tape affixable adjacent said scale.
21. The peak flow meter of claim 20 wherein said approval tape
includes a plurality of zones.
22. The peak flow meter of claim 21 wherein the zones on the tape
are related logarithmically to the scale.
23. The peak flow meter of claim 20 wherein said approval tape
is affixable to said scale at various locations.
24. The peak flow meter of claim 20 wherein said approval tape
includes a plurality of zones representing fixed percentage ranges.
25. The peak flow meter of claim 20 wherein said approval tape
includes a green zone representing a clinically determined reasonable
range for the patient's peak air flow.
26. The peak flow meter of claim 20 wherein said approval tape
includes a yellow zone representing a range indicating that a patient
should be wary of the potential need of medical attention.
27. The peak flow meter of claim 20 wherein said approval tape
includes a red zone representing a range indicating a need for obtaining
medical attention.
28. The peak flow meter of claim 18 said flow meter further comprising:
a plurality of approval tapes to be positioned on said body adjacent
said scale.
29. The peak flow meter of claim 18 wherein said scale includes
markings.
30. The peak flow meter of claim 29 wherein said markings represent
the peak air flow through the body.
31. A peak flow meter comprising:
a hollow elongated body;
an entering end on the hollow elongated body for receiving a flow
of air;
an exit end opposite the entering end;
an indicator adjacent to said body and movable relative to said
body to a position along a scale on said body, said position related
to a peak of the flow of air through said body;
said scale being a logarithmic scale extending longitudinally along
the body; and
said hollow elongated body having a non-linearly expanding diameter
designed to cooperate with the logarithmic scale.
32. The peak flow meter of claim 31 wherein the diameter of the
hollow elongated body enlarges non-linearly from the entering end
to a maximum diameter at the exit end.
33. The peak flow meter of claim 31 wherein the logarithmic scale
is expanded in an area representing lower exhalation.
34. The peak flow meter of claim 31 wherein the logarithmic scale
is compressed in an area representing higher exhalation.
35. The peak flow meter of claim 31 wherein the peak flow meter
further comprises:
a transparent tape having a plurality of contiguous bands for marking
a reasonable range of exhalation.
36. The peak flow meter of claim 35 wherein the plurality of bands
are different colors.
37. The peak flow meter of claim 35 wherein the tape is adhesively
securable to the peak flow meter.
38. The peak flow meter of claim 35 wherein the tape has a clear
longitudinal section and two parallel sections of colored bands
extending longitudinally on either side of the clear longitudinal
section.
39. A peak flow meter comprising:
a hollow elongated body;
an entering end on the hollow elongated body for receiving a flow
of air;
an exit end opposite the entering end;
a longitudinal tube inside the hollow elongated body extending
substantially from the entering end to the exit end;
a piston slidably mounted on the longitudinal tube;
an indicator slidably mounted on the longitudinal tube, said indicator
separate from the piston and positioned between the piston and the
exit end;
an indicator return mass for returning the indicator to a rest
position separately from the piston;
a logarithmic scale on the hollow elongated body, said logarithmic
scale extending longitudinally along the body; and
said hollow elongated body having a non-linearly expanding diameter
designed to cooperate with the logarithmic scale.
40. The peak flow meter of claim 39 wherein the hollow elongated
body has an interior surface, said interior surface having a frosted
portion and a clear portion.
41. The peak flow meter of claim 40 wherein the clear portion is
a rectangular portion extending longitudinally along the body whereby
the clear portion is aligned so that the indicator is viewed through
the clear portion.
42. The peak flow meter of claim 39 wherein the hollow elongated
body is tubular and completely closed circumferentially.
Description BACKGROUND OF THE INVENTION
Many patients have respiratory problems, and it often is advantageous
for a doctor to be able to ascertain the maximum peak rate of flow
of a single forced expiration. It is further desirable to have a
small instrument readily used by the patient himself to measure
the peak flow. With a peak flow meter it is possible for the patient
to ascertain if his peak flow rate remains at a more or less constant
level, or if it deteriorates over time, or if it improves.
Instruments for such use, especially by patients, have been developed
and are available commercially. However, the instruments now on
the market are not fully satisfactory. They often have a member
extending through a slot in a cylindrical body and blown along the
body by a patient's exhalation into the cylindrical body. Such type
of construction allows for entry of contaminants into the body,
some of which leave residue that impairs movement of the indicator
member along the slot. Most such meters have compressed scales which
are difficult to read.
It is desirable that upon initial testing by the doctor a marker
be applied to the meter indicating desirable range for the particular
patient, as well as an improved range and a poor or deteriorating
range. Such markers as known today are generally not satisfactory
in that they are not capable of representing a percentage above
or below the desirable range, since the desirable range for a given
patient might be quite different from that of another patient. All
that can be indicated is a fixed number above or below the desirable
range, but there will be a different percentage of the desirable
range depending upon where the desirable range is located on the
meter.
In accordance with known meters, as indicated above, having a slot
in the body through which the indicator moves, an opportunity is
presented for a patient accidentally to block movement of the indicator
with a misplaced finger. In the usual case the indicator is moved
by a piston within the body, and as the piston travels along the
body a progressively greater amount of air is expelled through the
slot as the piston moves from rest position. Accordingly, the piston
travels to a point at which the venting of air from the body balances
a spring restraining the piston. Upon the cessation of blowing,
the piston is returned to rest position by the spring, with the
indicator remaining in the position reached until manually returned
to rest position. The indicator must be of a relatively lightweight
construction. If it is heavy, it will have inertia, and even though
the piston stops, the indicator will continue to move according
to its inertia, and thus introduce false readings. However, if the
indicator is of extremely light weight and is exposed exteriorly
of the body through the slot in which it moves, then it must be
relatively fragile and susceptible to damage.
OBJECTS AND SUMMARY OF THE PRESENT INVENTION
It is an object of the present invention to provide an improved
peak flow meter which is inexpensive to produce, long lived, and
overcome the deficiencies of the prior art.
More particularly, it is an object of the present invention to
provide a peak flow meter in which the moving indicator is disposed
entirely within the confines of the elongated body, and wherein
there is no longitudinal slot in the body as in the prior art.
Yet another object of the present invention is to provide a peak
flow meter operating on a logarithmic scale, and which has a body
expanding non-linearly to match such scale whereby progressively
to bypass greater amounts of exhaled air as the piston moves away
from rest position.
A further object of the present invention is to provide a peak
flow meter in which an indicator or marker is moved along by a piston,
wherein the indicator is of extremely low mass, and does not overshoot.
It includes the provision o a weight or mass which is not attached
to the indicator, but is used for returning the indicator to rest
position.
In obtaining the foregoing and other objects I provide a peak flow
meter having an elongated tube which expands in diameter from rest
position to permit reading against a logarithmic scale. An axial
tube is provided within the housing, and has a longitudinal slit
therein. An indicator is retained on the tubing by means of an enlargement
within the tubing, with a thinner portion extending through the
slit. A piston of fixed diameter is spring urged toward the inlet
end of the housing, and moves along the tube upon exhalation by
a user. The indicator thus is moved along by the piston. However,
the indicator is pushed by, but is not connected to the piston,
and has a Spring therein bearing against the tube to hold the indicator
in the position reached under the impetus of the piston. A weight
or mass is contained within the tube, and moves ahead of the indicator.
The indicator itself is of very low mass so that it does not overshoot.
The weight is used to return the indicator to rest position for
a subsequent use of the meter.
Since the indicator moves on a slot or slit in the central tube
there is no need for a slot in the housing, whereby the housing
is sealed except at the entering and exit ends. In keeping with
the non-linear expansion of the housing the peak flow meter is provided
with a longitudinal logarithmic scale against which the indicator
is read.
THE DRAWINGS
The present invention best will be understood with reference the
following specification when taken in connection with the accompanying
drawings, wherein:
FIG. 1 is a side view of the peak flow meter of the present invention
as used by patient;
FIG. 2 is a more detailed view similar to FIG. 1 on an enlarged
scale;
FIG. 3 is a top view of the peak flow meter as shown in FIG. 2.
FIG. 4 is a left end view of the flow meter of FIGS. 2 and 3;
FIG. 5 is a right end view of the flow meter;
FIG. 6 is a fragmentary exploded perspective view of the central
slitted tube of the flow meter and the parts associated therewith;
FIG. 7 is a fragmentary longitudinal sectional view of a portion
of the flow meter;
FIG. 7A is a partial cross-sectional view as taken substantially
along the line 7A--7A in FIG. 7;
FIG. 8 is a fragmentary longitudinal sectional view similar to
FIG. 7 showing the parts in a different position of operation;
FIG. 9 is an enlarged cross-sectional view taken substantially
along the line 9--9 in FIG. 2;
FIG. 10 is a cross-sectional view as taken substantially along
the line 10--10 in FIG. 2;
FIG. 11 is a fragmentary top view of the present peak flow meter
on a substantially enlarged scale showing the logarithmic longitudinal
scale of the flow meter;
FIG. 12 is a side view generally similar to FIG. 2 of an improved
form of the invention;
FIG. 13 is a top view generally similar to FIG. 3 and corresponding
to the improved form of the invention in FIG. 12;
FIG. 14 is a left end view of the invention as shown in FIG. 12;
FIG. 15 is a right end view of the form of the invention shown
in FIG. 12;
FIG. 16 is a sectional view as taken along the line 16--16 in FIG.
15;
FIG. 17 is an exploded perspective view of the right or exit end
of the invention as shown in FIGS. 12-15 but inverted in order
best to show certain features of the invention;
FIG. 18 is a fragmentary side view partially in section showing
details of the marker and returning mass; and
FIG. 19 is a fragmentary top view corresponding to FIG. 18.
DETAILED DISCLOSURE OF THE ILLUSTRATED EMBODIMENT
Turning now in greater particularity to the drawings, and first
to FIGS. 1-3 a peak flow meter 20 constructed in accordance with
the principles of the present invention comprises an elongated body
22 of hollow, tubular construction. The body is smallest at its
left or entering end 24 and expands to a maximum diameter at its
right or exit end 26. The diameter and cross-sectional area do not
expand on a linear basis, but rather to match a logarithmic scale.
Hence, a longitudinal element of the body is not a straight line,
but is concave outwardly. Looking at this from a mathematical standpoint,
it is the generatrix that is outwardly curved. The body 22 is circumferencially
completely closed, but is open at both ends. The body 22 preferably
is made of plastic material which is transparent at least above
the indicator shortly to be disclosed.
A plastic cylinder 28 is inserted in the left or entering end of
the body. The cylinder 28 preferably is secured within the end of
the body 22 such as by sonic or chemical welding. The major portion
of the cylinder is of increasing inside diameter, but has a short
portion at the extreme left end of reduced inside diameter. as indicated
at 30 (see also FIGS. 4 and 10), A diametrical bar 32 extends across
the portion of reduced diameter at 30 and the length of this portion.
The bar is provided with a central longitudinally extending projection
or pip 34 the purpose of which will be apparent shortly.
As will be seen in FIG. 2 the left or entering end of the body
22 comprises a mouthpiece, and is designed to be placed within a
patient's mouth for exhalation. Considering the direction of air
flow through the peak flow meter 20 the left end may also be considered
as the upstream end, whereas the right or exit end may be considered
as the downstream end. In any event, the right end is provided with
a spider 36 (see FIGS. 5 and 9) having a central hub 38 and a plurality
of radial arms or spokes 40 extending to a circular rim 42 having
an outer diameter fitting snugly within the inner diameter of the
right end of the body 22. Outwardly of the rim there is an integral
cap 44 of greater diameter at its maximum equaling the outer diameter
of the end 26 and preferably tapering inwardly therefrom. The spider
36 fits snugly and frictionally within the right end 26 of the body.
In this embodiment of the invention it is not permanently secured
to the body. Similarly, the cylinder 28 at the left or entering
end could be held in place simply by a friction fit rather than
being permanently secured in place. The central hub 38 is provided
with an axial projection or pip 46 which is aligned with the pip
34.
All of the parts herefore referred to are constructed of a resinous
plastic material (commonly referred to as plastic) which is molded
to the desired shape by known molding methods. Axially of the body
there is a metallic tube 48 extending nearly the entire length of
the body and having its opposite ends centered on and supported
by the pips 34 and 46. The inside diameter of the tube is related
to the outside diameter of the pips so as to form a snug fit. A
narrow straight slit 50 extends longitudinally of the tube 48 from
end to end thereof. Attention should be paid to FIGS. 6-8 along
with FIGS. 1-3 at this point. A piston 52 is slidable on the tube
48 longitudinally of the tube. The piston comprises a transverse
disk 54 of fixed outside diameter less than the internal diameter
of the body 22 of the peak flow meter 20. An integral cylinder 56
extends axially from the disk 54 in the direction of the entering
end 24 of the body. The disk 54 and cylinder 56 have a common bore
of very slightly greater diameter than the outside diameter of the
tube 48 to allow sliding thereon. The disk and cylinder are preferably
molded of a suitable plastic.
The cylinder 56 immediately adjacent the disk 54 is provided with
a reduced diameter circumferential notch 58. A helical spring 60
tensionally urges the piston back toward the entering end 24. The
inside diameter of the spring 60 is substantially greater than the
outside diameter of the tube 48 so as to fit loosely there-about,
and is of substantially the same diameter as the outside diameter
of the cylinder 56. However, the last two turns of the spring 60
as indicated at 62 are of reduced diameter so as to grip within
the notch 58 and thereby attach the spring to the piston. The opposite
end of the spring is provided with an elongated portion 64 having
a re-entrant end 66 which loops over the end of the tube and is
firmly held in place thereon by an interference fit with the pip
34.
Also slidable along the tube 48 and specifically in the slit or
slot 50 therein, is a marker 68. The marker has a generally T-shaped
cross section having at the top thereof a diamond shaped indicator
70 with the major axis of the diamond arranged transversely of
the slit 50. The marker also includes a stem 72 depending from the
indicator 70. The upper portion of the stem is semi-cylindrical
74 while a lower portion comprises a flat plate 76 slidably fitting
within the tube slot 50. At the bottom of the stem is an enlargement
78 somewhat less than a semi-cylinder and fitting inside the tube.
A coil spring 80 encircles the stem 72 and is fairly lightly compressed
between the tube 48 and the underside of the indicator 70. The spring
80 holds the marker frictionally at whatever point it happens to
be along the tube 48.
The marker is of very low mass, and moves along ahead of the disk
54 of the piston 52 as the latter advances against the tension of
the spring 60 as the entering end of the peak flow meter is blown
into as indicated in FIG. 1. When the piston reaches a balance point
between blowing force and the spring, it stops. The marker 68 also
stops at the same time as the piston due to its low mass, and does
not overshoot as has often been a problem in the prior art.
The piston 52 retracts to rest position as determined by the turns
of the coil spring 60 engaging one another when a patient stops
blowing. The marker stays at the position reached until returned
for another exhalation test. The marker, being of very low mass,
is not satisfactorily returned to its rest position gravitationally,
or by shaking. In order to return the marker, I provide a cylindrical
slug 82 of a appreciable mass downstream of the marker. This mass
is of no great significance as the piston and marker advance, and
when the piston stops any inertia build up in the slug simply causes
it to move further along the tube with no influence on the position
of the marker. However, the flow meter may be held in the hand,
and shaken down, much in the manner of shaking down a fever thermometer.
The mass presses or pounds against the marker and returns it to
rest position against the piston as shown in FIGS. 1-3.
The logarithmic scale 83 referred to is shown rather generally
in FIGS. 2 and 3 and specifically in FIG. 11. The markings and
numerals, best seen in FIG. 11 are on a logarithmic scale. It readily
will be appreciated that the scale is progressively compressed as
one moves upscale, as are the associated numbers. The scale preferably
is molded in or printed directly on the plastic material of the
body 22. In addition to this, a transparent tape is supplied with
the meter, and is adhesively secured to the surface of the body
22 above and aligned with the slot 50 in the tube 48. As a practical
matter, there may be two parallel strips of adhesive tape 81 and
84 leaving a clear channel 86 between them. Alternatively, the two
strips can be made as one, with a clear section in the middle to
permit viewing of the tube and of the slider indicator 70. The tape
or tapes are provided with a longitudinally central area 88 of a
chosen color, light yellow being exemplary. A downstream band 90
therefrom preferably is green, and an upstream band 92 is red. It
will be observed that the bands are progressively narrower from
input to output end of the meter. The doctor by test determines
what is a reasonable range for a given patient's peak exhalation,
and the green portion 90 is applied in that area. If the patient
is always successful at home in producing movement of the indicator
70 into that area, then there is no need for the patient to see
his doctor immediately. However, if the indicator falls in the red
zone 92 he should call his doctor immediately. If the indicator
stops in the yellow area he should be wary. If he can re-enter the
green area all is well, but if he falls into the red area he should
contact his doctor promptly.
A logarithmic scale is excellent for reading, since it is expanded
in the low area where a patient's exhalation is critical. As the
exhalation moves upscale, the markings are compressed, but this
is of less importance since the patient is doing well if he can
get into this higher area. Due to the logarithmic nature of the
scale the bands comprise fixed percentages, no matter where the
tape or tapes are placed along the scale.
The cross sectional area of the body is not itself directly on
a logarithmic scale, but is empirically related to the logarithmic
reading scale so that proper readings are obtained. Empirical results
provide the final determination of diameter and cross sectional
area.
It will now be apparent that the parts of the meter are housed
entirely within the body of the meter. A stray finger cannot stop
the indicator, and the indicator cannot be manually advanced beyond
its stopping place from a breath exhalation. As has been noted heretofore,
the marker is of very low mass, and does not overshoot the position
to which it is moved by the piston. The low mass of the marker makes
it impossible to return it directly by a shaking or stamping motion,
but the metallic pellet within the tube relatively easily returns
the marker to rest position.
It will be appreciated that some contaminants do enter the body
of the meter along with the patient's breath. This can result in
reading inaccuracies, but the period of time before any inaccuracy
might appear is much greater than in prior art peak flow meters
in which the marker or indicator rides in a slot and partially extends
from the body of the meter. From time to time the meter may be flushed
out by running water or other mild cleaning fluid through the peak
flow meter from end to end.
Various improvements have been made in the present peak flow meter
in readying the device for production and sale. Such improvements
are illustrated in FIGS. 12-19. Most of the parts are the same or
similar to those previously described, and similar numerals are
utilized with the addition of the suffix a to identify similar parts.
Thus, the peak flow meter 20a comprises a body of hollow, tubular
construction which enlarges non-linearly from the left or entering
end to the right or exit end. Most of the body is frosted on the
interior surface thereof as a part of the manufacturing process.
This presents a more attractive appearance than a totally clear
body, and concentrates vision on the important internal parts, and
minimizes distractions that might be caused by internal condensation.
A rectangular, elongated portion 94 aligned with the tube 48a remains
clear, and the indicator 70a is visible through this area. Another
area 96 180.degree. from the clear area 94 also is clear for display
of the manufacturer's trademark, etc.
The entering end 24a of the body 22a is of unitary construction,
and the current portion of the body immediately adjacent to the
entering end comprises an inwardly stepped cylinder 98 molded as
an integral portion of the remainder of the body 22a. The diametrical
bar 32a is also integral with the inwardly stepped cylinder 98 and
the remainder of the body 22a. A mouthpiece 100 fits over the entering
end and is removable therefrom and is removable for cleaning.
The right end 26a of the body 22a is best seen in FIGS. 16 and
17. It is shown in upright position in FIG. 16 but the entire assembly
has been inverted or rotated 180.degree. in FIG. 17 in order to
show certain parts to best advantage. The end 26a is provided with
a peripheral ridge 102 and with a rectangular notch 104 leading
into the end of the body. An end cap 44a is provided with a flange
106 which abuts the right end 26a of the body. An annular flange
108 extends to the left from the flange 106 and grips the outer
wall of the body 22a. The interior annular recess 110 in this annular
flange 108 receives the annular ridge 102 at the end 26a of the
body 22a, and partially serves to retain the cap 44a on the end
of the body.
The cap 44a further is provided with a projection or enlargement
112 which provides a flat, tangent surface 114 which prevents rolling
of the peak flow meter when placed on a table or other horizontal
supporting surface. A radially inwardly projecting member or tang
116 extends from the enlargement 112 and annular flange 108 and
is received in the notch or recess 104 at the end of the body to
ensure proper rotational alignment of the body and of the end cap
44a.
A cup 118 extends axially of the body inwardly from the hub 38a
of the end cap 44a, being provided with a central well or opening
120. A key 122 extends radially in from the sidewall of the cup,
and is received in the slot 50a of the tube 48a to ensure proper
rotational alignment of the tube 48a with the end cap 44a. It will
be observed that the key 122 is displaced 180.degree., whereby the
open portion of the tube, and the indicator 70a will be properly
aligned with the clear viewing area 94 of the body, and will be
upwardly directed if the peak flow meter is placed on a table or
the like due to the positioning by the tangent surface 114.
The end wall or flange 106 of the end cap 44a is provided with
six through-holes 124 respectively aligned with the arms or spokes
40a of the spider 36a. Axial projections or studs 126 are spaced
about the end 26a of the body and project through the holes 124.
The studs are permanently secured in the holes by a sonic welding
process.
The cylindrical mass 82 initially used for return of the marker
68 sometimes does not move as freely within the tube 48 as is desired.
This is particularly true with aging of the peak flow meter and
accumulation of oxides, dirt, etc. Such possible sticking has been
overcome by providing two spherical balls 128 downstream of the
base 78a of the marker 68a. Considerably less mass is provided by
the two balls 128 as contrasted with the cylinder 82 thus minimizing
any resistance to movement of the marker when blown downstream by
a patient and the piston 52a. The contacting surfaces of the balls
with the inner surface of the slotted tube are much less in area
than the contacting surfaces of the previous cylindrical mass with
the inner wall of the tube. Thus, there is substantially no sticking
or binding of the balls 128 within the tube, and the marker is readily
returned to rest position by shaking of the peak flow meter in the
manner of a fever thermometer, notwithstanding the lesser mass of
the balls.
Initially the low mass of the marker 68 precluded overshoot thereof
when tested on a standard square wave flow machine. However, I discovered
experimentally that some people with normal lung capacity could
initially exert a spike of high pressure that caused the marker
to overshoot. This s believed to be true of many or perhaps all
commercial peak flow meters now known, but I considered any overshoot
to be unacceptable.
I discovered experimentally that the length of the entering end
portion 24a is of little consequence, but that the diameter (and
hence area) is important in limiting the initial spike of increased
air pressure entering the peak flow meter. I have further found
that with the inside diameter of the entering end portion limited
to not more than about 0.545 inch the mariner cannot be made to
overshoot either by a test machine or by a normally healthy person
with strong exhalation. The length of the entering end portion 24a
is 0.400 inch.
It has been mentioned earlier, but is worthy of repetition that
no matter where the tape is placed by the doctor axially of the
flow meter the three colored bans 8890 and 92 respectively comprise
a fixed percentage off logarithmic scale. Three colored bands have
been illustrated, but greater or lesser numbers could be used, and
the bands could be discerned other than by color.
The specific embodiments of the invention as herein shown and described
are for illustrative purposes. Various changes in structure will
no doubt occur to those skilled in the art, and will be understood
as forming a part of the present invention insofar as they fall
within the spirit and scope of the appended claims. |