CA1139965A - Pneumotachograph with pitot-like tubes - Google Patents
Pneumotachograph with pitot-like tubesInfo
- Publication number
- CA1139965A CA1139965A CA000352971A CA352971A CA1139965A CA 1139965 A CA1139965 A CA 1139965A CA 000352971 A CA000352971 A CA 000352971A CA 352971 A CA352971 A CA 352971A CA 1139965 A CA1139965 A CA 1139965A
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- Prior art keywords
- tubes
- flow
- baffles
- pitot
- path
- Prior art date
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
- G01F1/05—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects
- G01F1/34—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure
- G01F1/36—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using mechanical effects by measuring pressure or differential pressure the pressure or differential pressure being created by the use of flow constriction
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/08—Measuring devices for evaluating the respiratory organs
- A61B5/087—Measuring breath flow
- A61B5/0876—Measuring breath flow using means deflected by the fluid stream, e.g. flaps
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- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Physics & Mathematics (AREA)
- Medical Informatics (AREA)
- Surgery (AREA)
- Biophysics (AREA)
- Pathology (AREA)
- Engineering & Computer Science (AREA)
- Biomedical Technology (AREA)
- Heart & Thoracic Surgery (AREA)
- Physiology (AREA)
- Molecular Biology (AREA)
- Pulmonology (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Fluid Mechanics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Volume Flow (AREA)
- Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
- Indicating Or Recording The Presence, Absence, Or Direction Of Movement (AREA)
Abstract
Abstract A pneumotachograph including a housing having first and second ports which, during the course of respiration, alternate as input and output ports and which provide a path for generally linear flow of the respiratory bases. A pair of pitot tubes are di posed along the top of said path and are positioned generally at right angles thereto. A pair of baffles or flow deflectors are disposed in the path in alignment with the axes of the pitot tubes. Each of the baffles is positioned at an angle of approximately 45° to the axis of its associated pitot tube and to the path of flow. The baffles serve to reflect the respiratory gases upwardly toward the pitot tubes but since the pitot tubes are arranged above the baffles gravity prevent. the heavier mucus, water and nongaseous materials from entering the pitot tubes. Rather, these heavier particles run up to and over the top of the baffle. The baffles may be held in the flow path by a rigid connection or alternatively, they may be retained there by a resilient connection such that the pitot tube measurement is linearized.
In another embodiment, the baffles may actually be merged into a single baffle thus leaving an annular opening between itself and the housing with the opening of the gap being approximately the same distance as the distance between the pair of tubes. here the mode of operation is a pressure build-up upstream in proximity to the one tube and then a venturi effect downstream for lower pressure in proximity to the other tube.
In another embodiment, the baffles may actually be merged into a single baffle thus leaving an annular opening between itself and the housing with the opening of the gap being approximately the same distance as the distance between the pair of tubes. here the mode of operation is a pressure build-up upstream in proximity to the one tube and then a venturi effect downstream for lower pressure in proximity to the other tube.
Description
~PL 34770-1/TQH/JGW
PNEI~ISOTACHOGRAPH ~ITH PI~OT-LIKE TUBES
Devices for measuring the flow of respiratory gases are well known in the art, and one of such devices is described in applicant's prior issued United States Pa~ent No. ~,083,245, entitled ~Variable Orifice Gas Flow Sensing ~ead. a Other such devices include the well known orifice meter pneumotach-ographs, Although pitot tubes have also been known for many years as a means for measuring flow of gases, pitot tubes have not heen successfully used in the measurement of respiratory gases since, as is well known, pitot tubes operate with an orifice directed into the flow of the ~as to be measured. With such a configuration, the normally present flecks of mucus and drops of moisture found in respiratory gases have a tendency to enter the pitot tube orifice and to bloc~ it. Such blockage, of co~rse, would render the pitot tube inoperativeO In one prior attempt to use pitot tubes, a multiplicity of the tubes were employed on the theory that not all of them would be plugged simul-taneously. This attempt, however, was unsuccessful.
Both orifice meters and classic pitot tubes, when used for flow measurement, operate on the common principle of a constant area and a variable pressure drop. In the case of orifice meters the pressure drop is created by the resistance of an orifice and is measured by a pair of tubes or ~press~re ~3~36~i ~aps." For a respiratory device it is desirable to minimize this resistance. The foregoing patent and an article in Anesthesiology, Vol. 51, No. 2, August 1979, by Jaklad et al. en-titled "Pneumotachography" discusses this technique. Orifice plates are also discussed in the McGraw-Hill Encyclopedia of Science and Technology, 1977~ under the heading "Flow Measurement."
In a classic pitot tube the pressure differential is between an "impact" or "stagnation" pressure and a static pressure.
It is a general object of the present invention to provide a pneumotachograph which utilizes pitot like tubes to provide low resistance with high sensiti-vity and yet avoids the problems of tube blockage from mucus, water or other nongaseous material in the respiratory gases.
According to one aspect of the invention there is provided a bidirectionally operative pneumotachograph comprising: a housing having a pair of :respectively interchangeable input-output ports defining a flow path for respiratory gases, a pair of spaced apart tubes disposed along said flow path, at right angles thereto, and communicating with and penetrating into said flow path by a small, predetermined distance; a fla-t, disc shaped baffle disposed in the center of said flow path and perpendicular thereto to form an annular like opening between said baffle and said housing for said gases, said baffle being positioned between said tubes to produce a high pressure in proximity to the upstream tube and a low pressure in proximity to the downstream tuhe, the pressure differential between said tubes being indica-tive of flow velocity, wherein the spacing of said tubes is approximately the same as the radial dimension of said annular like opening, whereby increased differential pressure between said tubes is promoted regardless of the direc-tion of flow through said path.
`,9 `
~3~
-2a-Re:~erring to the drawing, FIGURF 1 is a cross sectional elevation sho~ing a pneumotachograph in accordance with one emhodiment of the invention;
FIGURE 2 is an end elevation of the pneumotachograph shown i~ FIGURE l;
.-., .
....
, .
.,.
~L i~
FIGURE 3 is a partial cross-sectional elevation similar to FIGURE 1 but showing an alternative embodiment of the invention;
FIG~RE 4 is a cross-sectional elevation æhowing a pneumo-tachograph in accordance with another embodiment of the invention;
FIGURE 5 is a cross-sectional view taken along the line 5-5 of FXGURE 4;
FIGURE 6 is a top view of a component of FIGURE 4; and PIGURE 7 is a set of characteristic curves showing the improvement in sensitivity of the present invention.
The pneumotachograph shown in FIGURES 1 and 2 includes a housing 11 preferably formed of two sections 13 and 15 conne~ted together by means of mating flanges 17 and 19 and connecting screws 21. The housing includes a pair of input-output ports 23 and 25 which may be connected ~o flexible tubes 27 and 29, respectively. The tubes 27 and 29 may be connected to a respiratory apparatus and respiratory mask respectively.
Thus it can be seen that, as the patient breathes, during expiration respiratory gases flow in one direction, and upon inspiration the gases will flow in the opposite direction.
Ports 23 and 25 provide a generally linear path of respira-tory flow shown generally by the arrow 31. A pair of pitot tubes 33 and 35 are included and extend through the ho~sing walls. Pitot tubes 33 and 35 are connected by means of flexible tubing 37 and 39 to a differential pressure gauge which is not shown but which is well known in the art.
Below each of the pitot tubes and in general alignment with ~he axes thereof are disposed a pair of baffles 41 and 43 which are retained upon ~tandards 45 and 47, respectively.
Each of the bafflefi 41 ~nd 43 is disposed at an angle of gas ~low reflection between it~ associated pitot tube and the direction of the flow path from different ones ~f the ports 23 and 25. With a linear flow path as ~hown in FIGURE 1, the baffles are ideally disposed at an angle of from 60~ ~o 70 to the flow path. Thus when the port 23 is serving as the input port and the direction of flow is as shown by the arrow 31, a portion of the gases are reflected by the baffle 41 to the pitot tube 33~ At this time the baffle 43 reflects none or very little of the gases to its associated pitot tube 35. ~hen the direction of flow reverses, the baffle 43 does reflect a portion of the flow to the pi~ot tube 35 and the pitot tube 33 becomes passive since the baffle 41 reflects more or very little of the gases ~o it.
In the embodiment ~hown in FIGURE 1 the 6tandards 45 and 47 are relatively rigid whereby the baffles 41 and 43 are held ~ecurely in the posi`ion shown in FIGURE 1. As can be seen more clearly in FIG~RE 2 the baffles 41 and 43 may ~ake the form of relatively small flat plates and serve essentially as defelctors. In user the upstream baffle directs air into one of the pitot tubes which s,erves as a positive pressure sensor proportional to the flow of gases. The downstream tube would receive none or very little reflected flow and so acts as a passive pressure sensor. During the course of respiration the baffles 41 and 43 alternate as upstr~am and downstream baffles and so t~e pitot tubes alternate as positive pressure sensors and passive pressure sensors.
In operation, as the respiratory ~ases are direc~ed toward the ~affles 41 or 43, the gases themselves are directed up toward tbe pitot tubes 33 or 35 but the heavier flecks of ~ucus, water or o~her nongaseous ~aterial do not rise so easily and ~n reality merely run up to and Dver the top of the baffle falling across the downstream ~ide thereof. Thus the gases which actually reach the pitot tube are relatively clean and do not have any clogging effect.
In the operation of the pneumotachoyraph of ~IG~RE 1 con- -nected to a differential pressure gauge, the vutput is not linear but rather is expQnential such that the measured differential pressure is an exponential function of velocity of flow (see FIGURE 7). Since the relationship between the differential pressure and the velocity of flow is exponential it is a relatively simple matter to linear.i~e with either a micropr~cessor or even by analog techniques both of which are well known to thvse ~killed in the art.
~he pneumotachograph as described above has a substantial advantage over those prior art devices known as orifice meter pneumotachographs in that a higher signal and lower resistance to flow results from the construction. Moreover, the device has no moving parts and is very easy to construct by molding ~uch that mass production of a pneumotachograph for respiratory measurements is economically feasible.
In certain instances it is desirable that the output signal have a linear relationship to the flow without the use of a microprocessor or analog techniques. ~his relationship can be provided by the embodiment shown in FIGURE 3 wherein the baffles 41 and 43 are upported on flexible ~tandards 49 and 51 respectively.
Preferably the standards 49 and 51 are formed of Rapton~
plastic having a thickness of 3 mils. With such a construc-tion the measured differential pressure signal varies linearly with the flow of fluid through ~he pneumotachoqraph regardless of the velocity. Thus as velocity is increased ,~
., . . .
from left to right, as ~hown in FIGURE 3, the standards 49 and 51 flex so th2t they and the baf~les supported thereby move to the position ~hown in dash~dot lines thus decreasing the amount of gases reflected to the pitot tube 33 and permitting some of the bases to be reflected to the pitot tube 35. Thus, the positive signal produced ~y the pitot t~be 33 is decreased whereas, at the ~ame time, the signal at the pitot tube 35 which is essentially zero when in the position shown in ~olid lines in FIGURE 3, shifts toward the positive. The correction provided by the movement of the baffles 41 and 43 is itself exponential and thus cancels out the exponential variation in the differential pressure ~i~nal from the two tubes.
1~ The pneumotachograph shown in PIGURES 4 and 5 includes a housing 61 formed of left and right sections ~2 and 63 connected together by male and female portions a~ 64. ~he housing includes a pair fo inp~t/output ports ~6 and 67 which may be connected to flexible tubes 68 and 69, respec-tively. In the embodiment of E`IG~RE 1, these tubes may be connected to a respiratory apparatus and respiratory mask, respectively. A pair of tubes 68 and 69 are included and extend through the housing walls so that their axes is perpendicular to the nominal flow path of gases indica~ed by the arrow 71. Tubes 68 and 69 are connected to a differen-tial pressure gauge as indicate~.
A disc-shaped baffle 72 is disposed in the center of the flow path 71 and perpendicular to it to form an annular-like opening 73, see especially FIGURE 5, between the cylindrical housing 61 and the disc-shaped baffle ~2. It i6 suspended from the walls of the housing by a fixed rod 77~ Moreover it is positioned substantially below the bottom openings of the tubes 66 snd 69 SD that on the =pstream side, tha~ is, at 74 ~ ~ 3~ ~C3 . .
as~uming the flow in in the direction 71, a hi~h pressure is produced in the proximity to the end ~f tube 69. In addition, a low pressure i~ produced at 75 on this downstream side because ~f a venturi effect.
In accordance with flow measurement theory, the pressure difference between the two tubes in indicative of flow velocity. This is more specifically indicated in FIGURE 7, ~ where the press~re differential, ~P, is the horizontal axis and FLOW the verti~al axis.
The non-linear curve labeled ~NEWa is very similar to that produced by the embodiment of FIGURE 4 and is easily compensated for by the microprocessor techniques. The o~her ~urve labeled ~OLD" indicates prior techniques, especially orifice techni~ues, where at low flow rates, because of the steeper curve, the sensitivity of the gauge is greatly reduced. Thus, ~IGU~E 7 aptly illustrates the improvement of the embodiment of FIGU~E 4 in increased small ignal ~ensitivity compared to an equivalent orifice meter with the same flow resistance.
The present invention also has the advantage of a greater signal to noise ratio. The venturi effect mentioned as a probable cause of a lower pressure at the locality 75 in proximity to tube S9 i5 perhaps not the total cause of the low pressure. In general comparing the embodiments of ~IGURES 1 and 4, ~IGURE 4 might be considered as a scaled-down reflected pitot design where the two reflectors 41 and 43 have been merged into one baffle. It i.s also believed that if the baffles 41 and 43 of FIGURE 1 are made v~rtical, 70% of the ~reflected" effect will be retained. Thusl the tubes 68 and 69 of FIGURE 4 might be called pi~ot-like tubes in one ~ense or pressure ~aps in the sense of s~andard orifice reter or the present invention might be thought of -B-as a hybrid between a ~tandard orifice meter and a standard pitot tube measuring deviceO In any case, it is not intended that the invention be unduly limited ~y the standard defini-tion of a pitot tube whi~h extends directly into the flow of gas to be measured.
In order to insure that the flow of gas is relatively ~table, that is, a misapplied input ~ube 68 might cause an unwanted jet effect where the flow is not uniform over its cross-section, a pair of ~low director horizontal plates 78 and 79 are provided. FIGURE 6 is an elevation view of both of these plates. They are affixed to notches in the side walls of housing halves 62 and 63 with an end notch 81 and B2, respectively, ensuring against slippage out of the ~tructure and into the breathing way of the patient. The flow direct~r plates, o course, are horizontal and co-planar with the flow path 71 and provide stable flow.
An orifice measuring device with a center plate such as 72 has been suggested. For examplet see the Fourth Edition of Perry's Encyclopedia of Chemical Engineering where annular orifice meters are discussed. These apparently are used only in industrial applications and the pressure tap on the downstream side is far enough away from the baffle so as not to be affected by any venturi action. In comparison in the present invention which, of course, must be set up or bi-directional flow, the ~pacing of the tubes with respect to their outer diameters is approximately the same as the annular opening 73. This is believed to cause the pressure 3~ build-up on the upstrea~ side and the lower pressure on the downstream side which provides a significant differential pressure. In fact, there is enough of a pressure difference, which increases sensitivity, that for a readable ~i~nal which is obtained from ~he differential pressure gauge, the ~0~
~ resistance to air flow ls only half ehe ~ of an eq~l-_g._ valen'c orif ice meter. As in 1:he case of FIGURE 1 ? the embodiment o FIGURE 4 avoids the problem of tube blockage by }nucus, watez or other non-gaseous material carried by respiratory gases. In addition ~che construction of FIGURE 4 is smaller and has less dead-space.
PNEI~ISOTACHOGRAPH ~ITH PI~OT-LIKE TUBES
Devices for measuring the flow of respiratory gases are well known in the art, and one of such devices is described in applicant's prior issued United States Pa~ent No. ~,083,245, entitled ~Variable Orifice Gas Flow Sensing ~ead. a Other such devices include the well known orifice meter pneumotach-ographs, Although pitot tubes have also been known for many years as a means for measuring flow of gases, pitot tubes have not heen successfully used in the measurement of respiratory gases since, as is well known, pitot tubes operate with an orifice directed into the flow of the ~as to be measured. With such a configuration, the normally present flecks of mucus and drops of moisture found in respiratory gases have a tendency to enter the pitot tube orifice and to bloc~ it. Such blockage, of co~rse, would render the pitot tube inoperativeO In one prior attempt to use pitot tubes, a multiplicity of the tubes were employed on the theory that not all of them would be plugged simul-taneously. This attempt, however, was unsuccessful.
Both orifice meters and classic pitot tubes, when used for flow measurement, operate on the common principle of a constant area and a variable pressure drop. In the case of orifice meters the pressure drop is created by the resistance of an orifice and is measured by a pair of tubes or ~press~re ~3~36~i ~aps." For a respiratory device it is desirable to minimize this resistance. The foregoing patent and an article in Anesthesiology, Vol. 51, No. 2, August 1979, by Jaklad et al. en-titled "Pneumotachography" discusses this technique. Orifice plates are also discussed in the McGraw-Hill Encyclopedia of Science and Technology, 1977~ under the heading "Flow Measurement."
In a classic pitot tube the pressure differential is between an "impact" or "stagnation" pressure and a static pressure.
It is a general object of the present invention to provide a pneumotachograph which utilizes pitot like tubes to provide low resistance with high sensiti-vity and yet avoids the problems of tube blockage from mucus, water or other nongaseous material in the respiratory gases.
According to one aspect of the invention there is provided a bidirectionally operative pneumotachograph comprising: a housing having a pair of :respectively interchangeable input-output ports defining a flow path for respiratory gases, a pair of spaced apart tubes disposed along said flow path, at right angles thereto, and communicating with and penetrating into said flow path by a small, predetermined distance; a fla-t, disc shaped baffle disposed in the center of said flow path and perpendicular thereto to form an annular like opening between said baffle and said housing for said gases, said baffle being positioned between said tubes to produce a high pressure in proximity to the upstream tube and a low pressure in proximity to the downstream tuhe, the pressure differential between said tubes being indica-tive of flow velocity, wherein the spacing of said tubes is approximately the same as the radial dimension of said annular like opening, whereby increased differential pressure between said tubes is promoted regardless of the direc-tion of flow through said path.
`,9 `
~3~
-2a-Re:~erring to the drawing, FIGURF 1 is a cross sectional elevation sho~ing a pneumotachograph in accordance with one emhodiment of the invention;
FIGURE 2 is an end elevation of the pneumotachograph shown i~ FIGURE l;
.-., .
....
, .
.,.
~L i~
FIGURE 3 is a partial cross-sectional elevation similar to FIGURE 1 but showing an alternative embodiment of the invention;
FIG~RE 4 is a cross-sectional elevation æhowing a pneumo-tachograph in accordance with another embodiment of the invention;
FIGURE 5 is a cross-sectional view taken along the line 5-5 of FXGURE 4;
FIGURE 6 is a top view of a component of FIGURE 4; and PIGURE 7 is a set of characteristic curves showing the improvement in sensitivity of the present invention.
The pneumotachograph shown in FIGURES 1 and 2 includes a housing 11 preferably formed of two sections 13 and 15 conne~ted together by means of mating flanges 17 and 19 and connecting screws 21. The housing includes a pair of input-output ports 23 and 25 which may be connected ~o flexible tubes 27 and 29, respectively. The tubes 27 and 29 may be connected to a respiratory apparatus and respiratory mask respectively.
Thus it can be seen that, as the patient breathes, during expiration respiratory gases flow in one direction, and upon inspiration the gases will flow in the opposite direction.
Ports 23 and 25 provide a generally linear path of respira-tory flow shown generally by the arrow 31. A pair of pitot tubes 33 and 35 are included and extend through the ho~sing walls. Pitot tubes 33 and 35 are connected by means of flexible tubing 37 and 39 to a differential pressure gauge which is not shown but which is well known in the art.
Below each of the pitot tubes and in general alignment with ~he axes thereof are disposed a pair of baffles 41 and 43 which are retained upon ~tandards 45 and 47, respectively.
Each of the bafflefi 41 ~nd 43 is disposed at an angle of gas ~low reflection between it~ associated pitot tube and the direction of the flow path from different ones ~f the ports 23 and 25. With a linear flow path as ~hown in FIGURE 1, the baffles are ideally disposed at an angle of from 60~ ~o 70 to the flow path. Thus when the port 23 is serving as the input port and the direction of flow is as shown by the arrow 31, a portion of the gases are reflected by the baffle 41 to the pitot tube 33~ At this time the baffle 43 reflects none or very little of the gases to its associated pitot tube 35. ~hen the direction of flow reverses, the baffle 43 does reflect a portion of the flow to the pi~ot tube 35 and the pitot tube 33 becomes passive since the baffle 41 reflects more or very little of the gases ~o it.
In the embodiment ~hown in FIGURE 1 the 6tandards 45 and 47 are relatively rigid whereby the baffles 41 and 43 are held ~ecurely in the posi`ion shown in FIGURE 1. As can be seen more clearly in FIG~RE 2 the baffles 41 and 43 may ~ake the form of relatively small flat plates and serve essentially as defelctors. In user the upstream baffle directs air into one of the pitot tubes which s,erves as a positive pressure sensor proportional to the flow of gases. The downstream tube would receive none or very little reflected flow and so acts as a passive pressure sensor. During the course of respiration the baffles 41 and 43 alternate as upstr~am and downstream baffles and so t~e pitot tubes alternate as positive pressure sensors and passive pressure sensors.
In operation, as the respiratory ~ases are direc~ed toward the ~affles 41 or 43, the gases themselves are directed up toward tbe pitot tubes 33 or 35 but the heavier flecks of ~ucus, water or o~her nongaseous ~aterial do not rise so easily and ~n reality merely run up to and Dver the top of the baffle falling across the downstream ~ide thereof. Thus the gases which actually reach the pitot tube are relatively clean and do not have any clogging effect.
In the operation of the pneumotachoyraph of ~IG~RE 1 con- -nected to a differential pressure gauge, the vutput is not linear but rather is expQnential such that the measured differential pressure is an exponential function of velocity of flow (see FIGURE 7). Since the relationship between the differential pressure and the velocity of flow is exponential it is a relatively simple matter to linear.i~e with either a micropr~cessor or even by analog techniques both of which are well known to thvse ~killed in the art.
~he pneumotachograph as described above has a substantial advantage over those prior art devices known as orifice meter pneumotachographs in that a higher signal and lower resistance to flow results from the construction. Moreover, the device has no moving parts and is very easy to construct by molding ~uch that mass production of a pneumotachograph for respiratory measurements is economically feasible.
In certain instances it is desirable that the output signal have a linear relationship to the flow without the use of a microprocessor or analog techniques. ~his relationship can be provided by the embodiment shown in FIGURE 3 wherein the baffles 41 and 43 are upported on flexible ~tandards 49 and 51 respectively.
Preferably the standards 49 and 51 are formed of Rapton~
plastic having a thickness of 3 mils. With such a construc-tion the measured differential pressure signal varies linearly with the flow of fluid through ~he pneumotachoqraph regardless of the velocity. Thus as velocity is increased ,~
., . . .
from left to right, as ~hown in FIGURE 3, the standards 49 and 51 flex so th2t they and the baf~les supported thereby move to the position ~hown in dash~dot lines thus decreasing the amount of gases reflected to the pitot tube 33 and permitting some of the bases to be reflected to the pitot tube 35. Thus, the positive signal produced ~y the pitot t~be 33 is decreased whereas, at the ~ame time, the signal at the pitot tube 35 which is essentially zero when in the position shown in ~olid lines in FIGURE 3, shifts toward the positive. The correction provided by the movement of the baffles 41 and 43 is itself exponential and thus cancels out the exponential variation in the differential pressure ~i~nal from the two tubes.
1~ The pneumotachograph shown in PIGURES 4 and 5 includes a housing 61 formed of left and right sections ~2 and 63 connected together by male and female portions a~ 64. ~he housing includes a pair fo inp~t/output ports ~6 and 67 which may be connected to flexible tubes 68 and 69, respec-tively. In the embodiment of E`IG~RE 1, these tubes may be connected to a respiratory apparatus and respiratory mask, respectively. A pair of tubes 68 and 69 are included and extend through the housing walls so that their axes is perpendicular to the nominal flow path of gases indica~ed by the arrow 71. Tubes 68 and 69 are connected to a differen-tial pressure gauge as indicate~.
A disc-shaped baffle 72 is disposed in the center of the flow path 71 and perpendicular to it to form an annular-like opening 73, see especially FIGURE 5, between the cylindrical housing 61 and the disc-shaped baffle ~2. It i6 suspended from the walls of the housing by a fixed rod 77~ Moreover it is positioned substantially below the bottom openings of the tubes 66 snd 69 SD that on the =pstream side, tha~ is, at 74 ~ ~ 3~ ~C3 . .
as~uming the flow in in the direction 71, a hi~h pressure is produced in the proximity to the end ~f tube 69. In addition, a low pressure i~ produced at 75 on this downstream side because ~f a venturi effect.
In accordance with flow measurement theory, the pressure difference between the two tubes in indicative of flow velocity. This is more specifically indicated in FIGURE 7, ~ where the press~re differential, ~P, is the horizontal axis and FLOW the verti~al axis.
The non-linear curve labeled ~NEWa is very similar to that produced by the embodiment of FIGURE 4 and is easily compensated for by the microprocessor techniques. The o~her ~urve labeled ~OLD" indicates prior techniques, especially orifice techni~ues, where at low flow rates, because of the steeper curve, the sensitivity of the gauge is greatly reduced. Thus, ~IGU~E 7 aptly illustrates the improvement of the embodiment of FIGU~E 4 in increased small ignal ~ensitivity compared to an equivalent orifice meter with the same flow resistance.
The present invention also has the advantage of a greater signal to noise ratio. The venturi effect mentioned as a probable cause of a lower pressure at the locality 75 in proximity to tube S9 i5 perhaps not the total cause of the low pressure. In general comparing the embodiments of ~IGURES 1 and 4, ~IGURE 4 might be considered as a scaled-down reflected pitot design where the two reflectors 41 and 43 have been merged into one baffle. It i.s also believed that if the baffles 41 and 43 of FIGURE 1 are made v~rtical, 70% of the ~reflected" effect will be retained. Thusl the tubes 68 and 69 of FIGURE 4 might be called pi~ot-like tubes in one ~ense or pressure ~aps in the sense of s~andard orifice reter or the present invention might be thought of -B-as a hybrid between a ~tandard orifice meter and a standard pitot tube measuring deviceO In any case, it is not intended that the invention be unduly limited ~y the standard defini-tion of a pitot tube whi~h extends directly into the flow of gas to be measured.
In order to insure that the flow of gas is relatively ~table, that is, a misapplied input ~ube 68 might cause an unwanted jet effect where the flow is not uniform over its cross-section, a pair of ~low director horizontal plates 78 and 79 are provided. FIGURE 6 is an elevation view of both of these plates. They are affixed to notches in the side walls of housing halves 62 and 63 with an end notch 81 and B2, respectively, ensuring against slippage out of the ~tructure and into the breathing way of the patient. The flow direct~r plates, o course, are horizontal and co-planar with the flow path 71 and provide stable flow.
An orifice measuring device with a center plate such as 72 has been suggested. For examplet see the Fourth Edition of Perry's Encyclopedia of Chemical Engineering where annular orifice meters are discussed. These apparently are used only in industrial applications and the pressure tap on the downstream side is far enough away from the baffle so as not to be affected by any venturi action. In comparison in the present invention which, of course, must be set up or bi-directional flow, the ~pacing of the tubes with respect to their outer diameters is approximately the same as the annular opening 73. This is believed to cause the pressure 3~ build-up on the upstrea~ side and the lower pressure on the downstream side which provides a significant differential pressure. In fact, there is enough of a pressure difference, which increases sensitivity, that for a readable ~i~nal which is obtained from ~he differential pressure gauge, the ~0~
~ resistance to air flow ls only half ehe ~ of an eq~l-_g._ valen'c orif ice meter. As in 1:he case of FIGURE 1 ? the embodiment o FIGURE 4 avoids the problem of tube blockage by }nucus, watez or other non-gaseous material carried by respiratory gases. In addition ~che construction of FIGURE 4 is smaller and has less dead-space.
Claims (2)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A bidirectionally operative pneumotachograph comprising:
a housing having a pair of respectively interchangeable input-output ports defining a flow path for respiratory gases, a pair of spaced apart tubes disposed along said flow path, at right angles thereto, and communicating with and penetrating into said flow path by a small, predetermined distance;
a flat, disc shaped baffle disposed in the center of said flow path and perpendicular thereto to form an annular like opening between said baffle and said housing for said gases, said baffle being positioned between said tubes to produce a high pressure in proximity to the upstream tube and a low pressure in proximity to the downstream tube, the pressure differential between said tubes being indicative of flow velocity, wherein the spacing of said tubes is approximately the same as the radial dimension of said annular like opening, whereby increased differential pressure between said tubes is promoted regardless of the direction of flow through said path.
a housing having a pair of respectively interchangeable input-output ports defining a flow path for respiratory gases, a pair of spaced apart tubes disposed along said flow path, at right angles thereto, and communicating with and penetrating into said flow path by a small, predetermined distance;
a flat, disc shaped baffle disposed in the center of said flow path and perpendicular thereto to form an annular like opening between said baffle and said housing for said gases, said baffle being positioned between said tubes to produce a high pressure in proximity to the upstream tube and a low pressure in proximity to the downstream tube, the pressure differential between said tubes being indicative of flow velocity, wherein the spacing of said tubes is approximately the same as the radial dimension of said annular like opening, whereby increased differential pressure between said tubes is promoted regardless of the direction of flow through said path.
2. A pneumotachograph as described in claim 1 and further including a pair of horizontal flow director plates spanning said housing, coplanar with the flow path, adjacent both ports whereby stable flow is provided.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000415239A CA1156494A (en) | 1979-05-29 | 1982-11-09 | Pneumotachograph with pitot-like tubes |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US4326379A | 1979-05-29 | 1979-05-29 | |
| US043,263 | 1979-05-29 | ||
| US15174280A | 1980-05-20 | 1980-05-20 | |
| US151,742 | 1980-05-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1139965A true CA1139965A (en) | 1983-01-25 |
Family
ID=26720201
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000352971A Expired CA1139965A (en) | 1979-05-29 | 1980-05-29 | Pneumotachograph with pitot-like tubes |
Country Status (4)
| Country | Link |
|---|---|
| CA (1) | CA1139965A (en) |
| DE (1) | DE3020265C2 (en) |
| FR (1) | FR2457675A1 (en) |
| GB (1) | GB2052074B (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| IL72446A0 (en) * | 1984-07-19 | 1984-11-30 | Moshe Grinbaum | Spirometer |
| FR2624271B1 (en) * | 1987-12-02 | 1990-03-30 | Aerospatiale | LEAK DETECTOR FOR A FLUID CIRCUIT |
| FI84757C (en) * | 1988-12-12 | 1992-01-10 | Instrumentarium Oy | FOER STROEMNINGSMAETNING AVSETT GASENS STROEMNING BEGRAENSANDE OCH STYRANDE ORGAN. |
| US5038773A (en) * | 1990-06-08 | 1991-08-13 | Medical Graphics Corporation | Flow meter system |
| US5379650A (en) * | 1992-09-23 | 1995-01-10 | Korr Medical Technologies Inc. | Differential pressure sensor for respiratory monitoring |
| US5535633A (en) * | 1992-09-23 | 1996-07-16 | Korr Medical Technologies, Inc. | Differential pressure sensor for respiratory monitoring |
| US5443075A (en) * | 1993-03-01 | 1995-08-22 | Puritan-Bennett Corporation | Flow measuring apparatus |
| US7335164B2 (en) | 1996-07-15 | 2008-02-26 | Ntc Technology, Inc. | Multiple function airway adapter |
| US5789660A (en) | 1996-07-15 | 1998-08-04 | Novametrix Medical Systems, Inc. | Multiple function airway adapter |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2233829A1 (en) * | 1972-07-10 | 1974-03-14 | Westfaelische Metall Industrie | FUEL TANK, IN PARTICULAR FUEL TANK |
| US4083245A (en) * | 1977-03-21 | 1978-04-11 | Research Development Corporation | Variable orifice gas flow sensing head |
| CA1069342A (en) * | 1976-07-29 | 1980-01-08 | Research Development Corporation | Variable orifice gas flow sensing head |
| DE2802830C3 (en) * | 1978-01-23 | 1982-02-11 | Müller, Gerhard, Prof. Dr.-Ing., 7080 Aalen | Fluid flow meter |
| US4197857A (en) * | 1978-04-06 | 1980-04-15 | Research Development Corporation | System for measurement of oxygen uptake and respiratory quotient |
-
1980
- 1980-05-28 FR FR8011821A patent/FR2457675A1/en active Granted
- 1980-05-28 DE DE19803020265 patent/DE3020265C2/en not_active Expired
- 1980-05-29 CA CA000352971A patent/CA1139965A/en not_active Expired
- 1980-05-29 GB GB8017546A patent/GB2052074B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2052074B (en) | 1984-05-10 |
| FR2457675A1 (en) | 1980-12-26 |
| GB2052074A (en) | 1981-01-21 |
| DE3020265A1 (en) | 1981-01-22 |
| DE3020265C2 (en) | 1984-03-15 |
| FR2457675B1 (en) | 1983-11-10 |
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| Date | Code | Title | Description |
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