IMPROVED MEASUREMENT OF PEAK FLOW
REFERENCE TO RELATED REQUESTS
This application is a continuation in part of the pending application Series No. 0 &/ 3l + l +, 530 filed on November 23, 199H, entitled "Peak Flow Meter" which is a continuation of the application Series No. 06 / 153,091, filed on November 17, 1993, now abandoned. The applications identified above, in their entirety, are incorporated herein by reference.
BACKGROUND OF THE INVENTION
This invention relates to an improved peak flow meter. Peak flow meters are used to measure the peak flow of air from a patient's exhalation. Peak flow meters allow doctors to track changes in the patient's respiratory status and potential diagnosis of existing breathing problems. Patients also use peak flow meters at home to monitor their own condition on a regular basis. Existing peak flow meters provide several ways to measure peak air flow. For example, the patent of E.U.A. I, l + 21, i20 describes a peak respiratory flow monitor with multiple openings and a rod that generates a sound when the air flow reaches a minimum adjustable value. Although the device described in the '120 patent is relatively simple to use and indicates a minimum peak flow value, it does not provide detailed measurement readings to a patient. An example of a peak flow meter that provides more detailed information to a user is the US patent. No. 5,246,010. As is common with mechanical peak flow meters, the '010 patent describes a peak flow meter with an indicator that responds to internal pressure as generated by the peak air flow. Three adjustable markers are adjacent to the scale along which the indicator moves. A personal area calculator is provided to determine where to place the adjustable markers. Although the '010 patent provides patients with more detailed information, it is relatively complicated to fix and use. Therefore, there is a need for a peak flow meter that provides accurate, detailed information that is easy to set and use.
BRIEF DESCRIPTION OF THE INVENTION
The present invention provides an improved peak flow meter for use by doctors and patients. One embodiment of the present invention includes a peak flow meter having a hollow body to accommodate an exhaled air flow. An indicator is associated with the body and can be moved to a position along a scale on the body. The position along the scale is related to the peak air flow that passes through the hollow body of the peak flow meter. The hollow body has at least one vent, and preferably a plurality of vents, designed in such a way that the position of the indicator in response to the peak flow of exhaled air conforms to the logarithmic scale on the body. In accordance with another aspect of this invention, a peak flow meter is provided that is adaptable for use in the measurement of low flow rates, such as peak flow of exhalation in a small child. The adaptive peak flow meter includes a bypass vent to alter the flow measurement capability. In one embodiment, the peak flow meter has an adjustment window by means of a removable hop designed to fit in a window slot in the body of the peak flow meter. An evaluation tape addable to the peak flow meter is described for use in determining respiratory performance. In one embodiment, the tape has a plurality of colored zones that represent fixed percentage deviations below any point along a logarithmic scale in the peak flow meter, thus eliminating the need for a calculator as shown in the art. previous
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side view of a peak flow meter in accordance with a preferred embodiment of the present invention. Figure 2 is a top view of the peak flow meter of Figure 1; Figure 3 is a bottom view of the peak flow meter of Figure 1; Figure 4 is a fragmentary end view of the peak flow meter of Figure 1, Figure 5 is an enlarged cross-sectional view taken along Figure 5-5 of Figure 2; Figure 6 is a cross-sectional view taken along line 6-6 of Figure 3; Figure 7 is a side view of a second embodiment of a peak flow meter in accordance with the present invention. The figure & is an anterior view of the peak flow meter in Figure 7. Figure 9 is a fragmentary rear view of the peak flow meter of Figure 7. Figure 10 is a fragmentary cross-sectional view taken along line 10. -10 of Figure 9. Figure 11 is a side view of a third embodiment of a peak flow meter in accordance with the present invention. Figure 12 is a fragmentary rear view of the peak flow meter of Figure 11. Figure 13 is a cross-sectional view taken along line 13-13 of Figure 12. Figure 14 is a fragmentary front view taken along line 14-14 of Figure 11. Figure 15 is a fragmentary cross-sectional view taken along Figure 15-15 of Figure 13. Figure 16 is a view taken along of line 16-16 of Figure 11. Figure 17 is a top view of an evaluation tape for use with a peak flow meter. The ifi figure is a bottom view of the peak flow meter of figure 3, adapted for high and low flow measurement. Figure 19 is a left side view of a fourth embodiment of a peak flow meter in accordance with the present invention. Fig. 20 is a rear view of the peak flow meter of Fig. 19. Fig. 21 is a right side view of the peak flow meter of Fig. 19. Fig. 22 is a front view of the peak flow meter of Fig. 20. Figure 19. Figure 23 is a fragmentary exploded view of the peak flow meter of Figure 19.
DETAILED DESCRIPTION OF CURRENTLY PREFERRED MODALITIES
Figures 1-6 illustrate a preferred embodiment of a peak flow meter 10. Figure 1 shows a peak flow meter 10 with a body 16 having an inlet 12 and an outlet 14. The peak flow meter 10 also has a 1 & for a patient using the device. As seen in more detail in Figure 2, the peak flow meter 10 has a window slot 22 in the body 16 covered by a clear window 20. The window slot 22 and the window allow the display of a mounted indicator 26 Within the body 16 which can be moved with respect to the body longitudinally between the inlet 12 and the outlet 14. Adjacent to the window slot 22 is a logarithmic scale 24 against which the position of the indicator 26 can be measured. In a preferred embodiment , the logarithmic scale 24 can be printed or integrally molded on the body 16. In another preferred embodiment, the logarithmic scale 24 can be printed or integrally molded onto the window 20. The body 16 and the window 20 are preferably made of a plastic material . A logarithmic scale, as inherent in its defined mathematical nature, provides greater intervals between measurement marks at the lower end of the scale and progressively smaller intervals at the higher end. A logarithmic scale 24 is preferable in a peak flow meter because the scale is compressed to the high end where small variations in peak flow are less critical and expanded at the low end where small variations are more important. As well, young children produce a lower peak flow than adults so that the expanded lower extreme scale provides younger users with an even easier scale to read. One advantage of the logarithmic scale used in the currently preferred modalities is that simple evaluation tapes can be used to help evaluate an individual patient condition. Figure 2 illustrates a preferred embodiment of an evaluation tape 15. The evaluation tape 15 comprises a single colored strip having a plurality of colored translucent areas. The tape can be mounted directly on the window 20. Preferred fixing means are an adhesive coating on one side of the tape. Preferably, the evaluation tape has three color zones in colors such as green, yellow and red. Each colored area indicates a fixed percentage scale below a better reference value as established by a physician. Window 20, in another preferred embodiment, can be an opening window by means of a removable jump. The window 20 may be wide enough to cover the slot 22 of &;
window and body portions 16 that surround the window slot or can simply be fixed within the window slot. A jump-opening window allows a patient to mount an evaluation tape 15 below the window 20 to further ensure that the evaluation tape is not inadvertently detached. Figure 3 shows better the plurality of 2 & in the bottom 30 of the peak flow meter 10. The peak flow meter 10 can have one, and preferably more than one vent. The vents 2fl extend longitudinally along the bottom 30 of the peak flow meter 10 and increase in size from the inlet 12 to the outlet 14. Preferably, the vents 2fi are circular. The 2 & They are circular, they can also be of any shape or combinations of shapes in another preferred embodiment. Alternatively, the 2 & they can comprise one or more slots that increase the size from the entrance 12 to the exit 14. Regardless of the type of ventilation 2 & employed, a plurality of 2 & they are empirically designed to conform to the response of the peak flow meter 10 to the patient's forcible exhalation in such a way that the movement of the indicator 26 conforms to the logarithmic scale 24. Figures 4 and 6 best illustrate a preferred multiple channel design of a currently preferred mode. The peak flow meter 10 preferably includes a channel showing 34 and at least one bypass channel 32 parallel to the sample channel 34. The air exhaled to the inlet 12 is divided between the sample and bypass channels 34, 32. The Sample channel 34 is configured to accept a predetermined percentage of the air and the remaining air passes through the bypass channels 32. Figure 6 illustrates the position of the vents 26 with respect to the channels. The vents 26 preferably connect the sample channel 34 to the ambient air directly outside the body 16. In another preferred embodiment, the vents 26 are located in the walls 33 between the channels 32, 34 within the body 16. The internal vents 26 provide the additional advantage of avoiding accidental blocking in addition to the logarithmic measurement response. Figures 4-6 show a hollow grooved tube 36 extending longitudinally through the sample chamber 34 within the peak flow meter. The hollow slotted tube 36 is fixed to a central support 36 at each end of the peak flow meter 10. The indicator 26 is preferably slidably mounted in a slot 40 in the tube 36. A piston 44 for releasably engaging the indicator 26 is also slidably mounted on the tube 36 between the inlet 12 and the indicator 26. The ircunrency of the piston 44 is less than the internal circumference of the body 16. A spring 37 fixes the piston 44 to the inlet end of the hollow tube 36 and retracts the piston 44 after the patient exhales inside the peak flow meter 10. A patient using the peak flow meter exhales forcefully into the inlet. The force of the exhaled air pushes against the piston which in turn pushes the indicator. The indicator stops at a point along the hollow tube where the force exerted on the piston 44 by the spring 37 is substantially equal to the force of the exhaled air remaining in the body. To obtain the preferred logarithmic response, the plurality of vents allow empirically exhaled amounts of exhaled air to escape to the hollow body 16 so that the position of the indicator conforms to the logarithmic scale 24. A position spring 39 holds the indicator in place when the piston retracts. After reading the position of the indicator along the logarithmic scale, the patient returns the indicator to its initial position holding the output end and shaking the peak flow meter. A return mass 41, preferably a pair of ball bearings, mounted on the hollow slotted tube between the indicator and the outlet end helps return the indicator to its reset position. The return mass does not restrict the movement of the indicator because the exhaled air also pushes the mass separately along the tube. In an alternative embodiment, the walls of the sample channel can be empirically designed to a non-linear curve outwardly from the entrance to the exit. The outward curve of the walls causes an increasing space to develop between the piston edge and the walls as the exhaled air forces the piston along the sample chamber. The increasing space increases the amount of exhaled air needed to move the indicator and is designed empirically so that the movement of the indicator conforms to the logarithmic scale. The non-linear expansion walls and a plurality of vents can also be used in combination to achieve the desired indicator response. Figures 7-10 disclose an improved peak flow meter 50 in accordance with a second preferred embodiment of the present invention. The peak flow meter 50 includes a vertical section 52 fixed to a horizontal section 54. The horizontal section has an inlet 56 and an outlet 60 for passing exhaled air through a bypass channel 76. The bypass channel is connected to a sample channel 72 within the vertical section 52. As shown in Figure 6, the peak flow meter 50 has a window slot 64 in the vertical section 52. The window slot 64 is covered by a window 62. Preferably, the window 62 is constructed of clear plastic. Adjacent to the window slot 64 is a logarithmic scale 66. Within the vertical section 52 and visible through the window 62 is an indicator 66 slidably mounted on a hollow tube 74 extending longitudinally along the sample channel 72. Figure 9 illustrates the plurality of windows 70 located on the vertical section 52 of the peak flow meter. The vents 70 are designed in such a way that the indicator 76 moves to a position corresponding to a logarithmic measurement of a peak exhaled air flow to the inlet 56. The vents 70 preferably increase in size from the portion of the vertical section 52 connected to the horizontal section of the vertical section outlet 56. Figures 6-10 show the hollow tube 74 within the sample channel 72. Preferably, the indicator 66 is slidably mounted in a slot 75 in the tube 74. When a patient exhales towards the inlet 56 of the peak flow meter 50, the exhaled air passes through the bypass channel 76 and a portion flows through the sample channel 72. The vents 70 in the sample channel 72 increase the force necessary to move the indicator allowing progressively more air to exit the mass channel 72 as the indicator moves along the tube 74. The increase in force required to move r the indicator is empirically designed so that the final position of the indicator corresponds to a logarithmic scale that measures the peak air flow. The logarithmic relationship allows a logarithmic scale 66 that has the above advantages to be used. When a patient exhales within the peak flow meter, the exhaled air received in the sample channel 72 pushes a piston 76 against the indicator 66. The piston pushes the indicator 66 along the tube 74 until the return force of the spring 76 exceeds the force of the exhaled air remaining in the sample channel. An alternative embodiment of an evaluation tape for use with the peak flow meter is shown in Figure 17. The tape 120 is preferably a single piece having a pair of colored strips 124 parallel to a clear central strip 122. The colored strips 124 preferably include at least two zones of color. As shown in figure 6, an evaluation tape 120 is preferably adhesively fixed on the window in a logarithmic scale 66. Typically, a physician will measure the peak flow of a patient and the physician or the patient will then apply the tape 120 to the peak flow meter 50. color zones on the scale represent fixed percentages of peak flow measured. Because the plurality of vents in the peak flow meter 50 are designed in such a way that a logarithmic scale 66 can be used, the tape 120 can be manufactured in such a way that each color zone not only represents a fixed percentage of a peak value in particular, but also represent the same fixed percentage of any peak value anywhere on the scale. A single tape that can be fixed anywhere on the scale without adjustment allows any patient to use it. In addition, a single adhesive tape having multiple zones can be fixed in a simple manner and is less likely to be accidentally moved by a user. A third preferred embodiment of an improved peak flow meter 90 is shown in Figures 11-16. Figure 11 shows a peak flow meter 90 having an inlet area 94 and an outlet area 96 on a hollow body 92. The body 92 also contains vents 97 along the side of the body 92 which increase the size from the entrance side to the exit side. Figure 12 illustrates the outlet portion 96 of the peak flow meter 90 and the logarithmic scale 101, the window slot 106 and the window 106. Below the window 106, an indicator 102 is slidably mounted on a hollow tube 100. The interior of the hollow body 92 is best seen in Figure 13. The inlet 94 receives exhaled air from a patient. The exhaled air pushes a folding paddle 104 against the indicator 102 slidably mounted in the hollow tube 100. As shown in Fig. 14, the inlet 94 contains air passages 95 and a holder 96 for the hollow tube 100. The hollow tube is fixed to the outlet portion 96 by means of an external fastener 99. Figure 15 shows the folding paddle 104 behind the indicator 102 inside the body 92 of the peak flow meter 90. The hollow tube 100 passes through the folding paddle 104 in such a way that the paddle 104 can push the indicator 102 along the tube 100 under the force of exhaled air. Directly above the tube 100 is a window slot 106 and a window 106. As seen in FIG. 16, the window 106 covers the window slot 106 in such a way that a finger that is deflected can not interfere with the movement of the window. indicator 102. As with the modalities shown in Figs. 1-10, the embodiment in Figs. 11-16 also employs a logarithmic scale 101 as a result of the vents 97 providing predetermined logarithmic response. Figure 16 illustrates an improved peak flow meter 130 in accordance with another alternative embodiment of the invention. The mode can be adjusted to measure high or low flow rates. The peak flow meter 130 shown in FIG. 16 is a modification of the peak flow meter of FIGS. 1-6. A bypass vent 140 is located on the body 130 of the peak flow meter 130. Preferably, the bypass vent 140 is a slot 144 with a slidable door 142. When the door 142 is closed, the slot 144 is sealed and can be sealed. Measure a low flow rate. When the door 142 is opened, more exhaled air escapes, which requires a greater effort to move the indicator in the body. In another embodiment, the door 142 may have more than two positions corresponding to different flow rates desired. The peak flow meter 130 preferably has interchangeable windows that fit by jumping in the window slot on the body. One window preferably includes a logarithmic scale with an expanded scale for speeds of low flow speed. The low flow rate scale can be used with the peak flow meter 130 set such that the gate 142 of the bypass vent 140 is closed. A higher flow rate window can replace the low flow rate window when the peak flow meter is adjusted so that the gate 142 opens. The upper flow rate window preferably includes a less compressed logarithmic scale. Interchangeable windows and bypass vent 140 are advantageous to make peak flow meter 130 more adaptable for use by adults and children. Figure 19 illustrates a fourth preferred embodiment of a peak flow meter 140. Figure 19 shows a peak flow meter having a serrated area 152 and an exit area 153 on a curved hollow body 154. An advantage 156 covers one side of the body 154. The window 156 is preferably a clear plastic material affixed to the body 154 with a pair of fasteners 156, such as screws or bolts. Figure 20 shows a rear view of the peak flow meter 150. The exit area 153 preferably comprises at least one opening in the rear part of the body 154. Figure 21 provides another side view of the peak flow meter. As best seen in Figure 21, fasteners 156 are secured by a pair of anchors 162, such as a threaded portion in the body or bolts. As shown in Figure 22, the inlet 152 is preferably a hollow tube integral with the body 154. Referring again to Figure 19, the window 156 preferably includes a plurality of vents 160 that increase in size from the inlet 152 to the output 153. Also on the window 156 is a logarithmic scale 164. The logarithmic scale 164 can be printed or molded on the inside or outside of the window. A rigid paddle 166 and an indicator 166 are mounted within the hollow body 154 and the window. Both the paddle 166 and the indicator 166 are frictionally coupled to the body and window at the base of the peak flow meter 150. The paddle releasably engages the indicator when the patient exhales to the inlet of the peak flow meter 150. This mode of the meter peak flow preferably operates using a torsion spring 170 which is best shown in Figure 23. The spring 170 is removably connected with a slot 172 in a tongue 174 engaging with the paddle that is fixed to the interior of the body 154. When the open end 175 of the hollow cylinder 176 at the base of the paddle 166 passes over the mating tab 174 of the paddle, the spring 170 also removably connects to a slot within the cylinder 176. An indicator 166 fits slidably around a ring of projection 160 on the inside of the window 156. The cylindrical plug 160 on the paddle 166 fits slidably within the center of the ring or projection 160. Assembled, pallet 166 is located between the indicator and the inlet 152. The inlet receives exhaled air from a patient. The exhaled air pushes the rigid paddle against the indicator. Both the vane and the indicator rotate in the plane of the advantage around the joint created by the assembly of the tongue 174 engaging with the vane, the projection ring 160, the cylinder 176 and the cylindrical plug 176. The spring 170, which is removably attached to the body 154 and the paddle, provides resistance to the exhaled air towards the inlet against the rigid paddle. The plurality of vents 160 in the window are empirically designed to cooperate with the spring resistance force such that the indicator response conforms to a logarithmic scale 164 on the body. In an alternative embodiment, the plurality of vents can be eliminated by, or used in combination with, changing the shape of the body and window. The shape can be changed to non-linearly increase the space between the pallet and the body or window thereby increasing the force needed to move the indicator as it is pushed along the 164. scale. As with the plurality of Ventilated, the increased space is designed empirically in such a way that the position of the indicator is conformed to a logarithmic scale on the window. In another embodiment of the peak flow meter 150, the torsion spring 170 can be used with a flexible vane to achieve the desired movement of the indicator. After a peak flow of air has caused the paddle to push the indicator, paddle 166 returns to its rest position under the force of spring 170. Indicator 166 remains in the position at which it was moved by the paddle and is held in place by friction against the projection ring 160. The friction is maintained by a splitting wire spiral 169 surrounding the base of the indicator 166. The indicator 166 can be returned to the rest position by rotating the exposed portion. of the indicator 166 on the bottom of the peak flow meter 150. As with the modalities described above, an advantage of using the logarithmic scale is that it can be used in combination with an evaluation tape that indicates the same percentage of derivation below any given peak flow measurement regardless of the location along the scale. The evaluation tape can be manufactured to conform to any constant scale curvature on the peak flow meter. Other preferred alternative techniques for obtaining a response to peak air flow that conforms to the logarithmic scale are included in the present invention. A variable response spring, whether torsional or expansion, is a technique. The diameter of the spring coil can be increased gradually so that the force varies non-linearly. Another technique is the pulse of a flexible piston that is flexed to allow larger amounts of air to pass as the force of the air against it increases. Additionally, the slotted hollow tube bearing the indicator can be constructed in such a way that the flexure between the indicator and the tube increases as the indicator is pushed further down the tube. These techniques can be used individually or in combination with each other so that the response of the indicator to the peak flow of exhaled air conforms to a chosen logarithmic scale. From the foregoing, an improved peak flow meter has been described. The peak flow meter includes at least one vent, and alternatively a plurality of vents, to obtain a logarithmic response to the exhaled air. An evaluation tape cooperates with a logarithmic scale for simple, accurate and informative peak flow measurements of a patient. Additionally, an adaptive peak flow meter has been described which is useful for low flow and high flow applications. It is intended that the above detailed description be considered as illustrative and not as limiting, and that it be understood that the following claims, including all equivalents, define the scope of this invention.