Sample cells for respired gas sampling and methods of manufacturing same

A sample cell (10) for a respired gas sensor has a single-piece injection molded main body (40) defining a gas flow path including an optical sampling bore (42), a gas inlet lumen (50) connected with the inlet end (44) of the optical sampling bore, and a gas outlet lumen (52) connected with the outlet end (46) of the optical sampling bore. The gas flow path includes at least two curved walls (100, 102, 104, 106). The sample cell may be manufactured by assembling mold pins (120, 122, 124, 126, 128) for defining the gas flow path wherein at least two mold pins (122, 124) have curved surfaces for defining the at least two curved walls of the gas flow path, and injection molding the single piece injection molded main body including removing the mold pins after defining the gas flow path including the at least two curved walls.

FIELD

The following relates generally to the capnography arts, respired gas sampling arts, and to sample cells for use in such devices and to manufacturing methods for such sample cells, and to related arts.

BACKGROUND

Capnography is the monitoring of the concentration or partial pressure of carbon dioxide (CO2) in respiratory gases. A known capnograph device is the Respironics® LoFlo® Sidestream CO2sensor available from Koninklijke Philips N.V., Eindhoven, the Netherlands, which uses a non-dispersive infrared (NDIR) single beam optical measurement technique to measure CO2in respiratory gas samples via a nasal cannula or other patient accessory. The LoFlo® CO2sensor includes a pump for drawing respiratory gas into a sample cell. A feature of the LoFlo® CO2sensor is the use of a disposable sample cell that is preferably replaced for each patient. This has advantages including avoiding contamination of the optical windows and flow path over time when the sample cell is re-used. In other capnograph devices, the sample cell is a non-disposable component which hence is prone to accumulating contamination on the optical windows and/or respiratory gas flow path.

The following discloses a new and improved systems and methods that address the above referenced issues, and others.

SUMMARY

In one disclosed aspect, a sample cell for a respired gas sensor is disclosed. The sample cell comprises: a single-piece injection molded main body defining a gas flow path including (i) an optical sampling bore with opposite inlet and outlet ends, (ii) a gas inlet lumen connected with the inlet end of the optical sampling bore, and (iii) a gas outlet lumen connected with the outlet end of the optical sampling bore; an inlet optical window attached to the single-piece injection molded main body and covering the inlet end of the optical sampling bore; and an outlet optical window attached to the single-piece injection molded main body and covering the outlet end of the optical sampling bore.

In another disclosed aspect, a sample cell for a respired gas sensor is disclosed. The sample cell comprises: a main body defining a gas flow path including (i) an optical sampling bore with opposite inlet and outlet ends, (ii) a gas inlet lumen connected with the inlet end of the optical sampling bore, and (iii) a gas outlet lumen connected with the outlet end of the optical sampling bore; an inlet optical window attached to the main body and covering the inlet end of the optical sampling bore; and an outlet optical window attached to the main body and covering the outlet end of the optical sampling bore; wherein the connection of the gas inlet lumen and the inlet end of the optical sampling bore includes at least one curved wall. In some embodiments, the connection of the gas outlet lumen and the outlet end of the optical sampling bore also includes at least one curved wall.

In another disclosed aspect, a method is disclosed of manufacturing a sample cell for a respired gas sensor having a single piece injection molded main body defining a gas flow path including (i) an optical sampling bore with opposite inlet and outlet ends, (ii) a gas inlet lumen connected with the inlet end of the optical sampling bore, and (iii) a gas outlet lumen connected with the outlet end of the optical sampling bore, wherein the gas flow path includes at least two curved walls. The method comprises: assembling mold pins for defining the gas flow path wherein at least two mold pins have curved surfaces for defining the at least two curved walls of the gas flow path; and injection molding the single piece injection molded main body including removing the mold pins after the mold pins have defined the gas flow path including the at least two curved walls.

One advantage resides in providing more accurate CO2measurements by improved respiratory gas flow through the sample cell.

Another advantage resides in providing CO2measurements with reduced time latencies and/or memory effects by improved respiratory gas flow through the sample cell.

Another advantage resides in providing a disposable or non-disposable respiratory gas sample cell with reduced manufacturing cost and simplified assembly.

Another advantage resides in providing a disposable respiratory gas sample cell with improved handling characteristics.

DETAILED DESCRIPTION

Disclosed herein are improved sample cells for a capnography device or other respiratory gas sampling device.

With reference toFIGS. 1 and 2, a capnography device is shown. The capnography device is a device for sampling carbon dioxide (CO2) concentration or partial pressure in respired gas, and may alternatively be referred to as a CO2sensor device. As diagrammatically shown inFIG. 2, the capnography device includes a sampling bench8and a detachable sample cell10that inserts into a receptacle12of the sampling bench8.FIG. 1shows the disposable sample cell10before insertion into the receptacle12of the sampling bench8, whileFIG. 2shows the assembly after the sample cell10is inserted into the sampling bench8. The sample cell10is connected with an inlet air hose14via an intermediary water trap filter16. The end of the inlet air hose14distal from its connection to the sample cell10is suitably connected to a patient accessory such as a nasal cannula or an in-line patient accessory coupling into a respirator line (patient accessory not shown) from which respired gas is drawn for sampling in the sidestream arrangement. The illustrative sample cell10is advantageously detachable and is preferably replaced at least between successive patients, so as to reduce buildup of contamination. While the illustrative sample cell10is detachable, in other embodiments it is contemplated for the sample cell to be a permanently installed component of the sampling bench.

With particular reference toFIG. 2, an inset18shows a cross-sectional view of the sample cell10from just downstream of the water trap filter16, along with selected internal components of the sampling bench8. As shown in inset18, the sampling bench8houses an optical CO2sensing assembly comprising a laser or other light source20and a light detector22. The illustrative sampling bench8is a sidestream sampling bench that draws (i.e. “samples”) respired gas flow from the inlet air hose14through the sample cell10using a pump24that connects with an outlet end of the sample cell10via internal air tubing26. The air flow system may also include an illustrative air pressure sensor28, an air flow sensor (not shown), or other diagnostic sensor(s).

The illustrative sampling bench8further includes an on-board electronic data processing component30, for example a microprocessor or microcontroller. The processing component30may be programmed to perform one or more self-diagnostic algorithms, for example, to detect if the unit is not connected with a patient based on the pressure reading output by the pressure sensor28and/or an air flow reading measured by an air flow sensor. The processing component30may additionally or alternatively be programmed to output respired air component information, for example CO2partial pressure or concentration as appropriate for the illustrative capnography device. This processing may include converting measured optical transmission from the infrared emitting device20to the sensor22into [CO2] concentration, optionally with compensation such as for the barometric pressure, known FiO2level (for a patient receiving supplemental oxygen), or so forth. The respired carbon dioxide data may be output as a waveform, e.g. [CO2] samples acquired at a sampling rate, and/or may be output in post-acquisition processed form, for example performing an end-tidal CO2(etCO2) calculation algorithm comprising (1) detecting breath cycles from air pressure and/or flow versus time data acquired by the sensor(s)28and/or from the [CO2] waveform, (2) detecting the peak CO2level for each breath which usually occurs in the end-tidal phase, and (3) optional filtering or other processing of the per-breath etCO2values for example averaging over N breaths to suppress noise. It will be appreciated that in various embodiments the processing performed on-board (that is, by the electronic processor30of the sampling bench8) versus off-board can be varied. For example, in some embodiments the on-board electronic processor30outputs only the [CO2] waveform and a bedside patient monitor (not shown) receives this waveform and computes the etCO2. It is also contemplated to omit the electronic processor30entirely, e.g. outputting optical transmission measurement samples acquired by the optical detector22which are then converted to a [CO2] waveform by a bedside monitor or other external device.

The respired gas flow output from the pump24may be vented directly to the ambient atmosphere. Alternatively, if the patient or other monitored subject is receiving an inhaled medication that should not be vented into the ambient atmosphere, then the gas flow output from the pump24may be output to a discharge air hose (not shown) via a suitable outlet air hose coupling32. The illustrative sidestream sampling bench8further includes an electrical cable34which may, for example, carry: electrical power for driving components such as the light source20and the electronic processor30; and one or more data lines carrying information such as the CO2data, self-diagnostic data, or so forth. In some embodiments, it is contemplated for the CO2data and/or self-diagnostic data to be output wirelessly, e.g. via a Bluetooth® or Zigbee® wireless communication link (not shown).

By way of non-limiting illustrative example, in some embodiments it is contemplated for the sampling bench8to be the sampling bench component of the Respironics® LoFlo® Sidestream CO2sensor (available from Koninklijke Philips N.V., Eindhoven, the Netherlands). This sampling bench uses a non-dispersive infrared (NDIR) single beam optical measurement technique to measure CO2, and includes a pump for drawing respiratory gas into a sample cell. The Respironics® LoFlo® Sidestream CO2sensor includes a receptacle for receiving a detachable sample cell, and various embodiments of the illustrative detachable sample cell10disclosed herein may be employed in conjunction with this commercially available sampling bench.

It will be further appreciated that the disclosed sample cell embodiments may be employed in conjunction with other types of respiratory gas sensors that are designed to sense other respired gas components such as oxygen partial pressure or concentration, and may advantageously employ the disposable (as illustrated) or non-disposable sample cell10.

With reference toFIGS. 3(a)-(g)and4-6, the illustrative sample cell10comprises a single-piece injection molded main body40, for example made of an injection molded plastic. This single-piece injection molded main body40is shown in multiple views inFIGS. 3(a)-(g).FIG. 4shows a side view of the sample cell10including the main body40and optical windows70,72, with a Section S-S line indicated.FIG. 5shows the Section S-S along the line indicated inFIG. 4.FIG. 6shows an enlarged view of Section S-S.

As seen in the sectional views ofFIGS. 5 and 6, the single-piece injection molded main body40defines a gas flow path including (i) an optical sampling bore42with an inlet end44and an outlet end46, (ii) a gas inlet lumen50connected with the inlet end44of the optical sampling bore42, and (iii) a gas outlet lumen52connected with the outlet end46of the optical sampling bore42. The optical sampling bore42defines an optical axis54along which the light source20(seeFIG. 2) directs infrared probe light. In the illustrative main body40, the gas inlet lumen50and the gas outlet lumen52are parallel, the gas inlet lumen50is orthogonal to the optical axis54, and the gas outlet lumen52is also orthogonal to the optical axis54. More particularly, in the illustrative embodiment the gas inlet lumen50and the gas outlet lumen52are coaxial as they share a common axis55as indicated inFIG. 5. Such a coaxial arrangement is advantageous in achieving compactness and can also reduce off-balance forces applied to the sample cell10when connecting components. To facilitate the illustrative arrangement, an inlet plenum60is disposed between the gas inlet lumen50and the inlet end44of the optical sampling bore42, and similarly an outlet plenum62is disposed between the gas outlet lumen52and the outlet end46of the optical sampling bore42.

As further seen inFIGS. 5 and 6, an inlet optical window70is attached to the single-piece injection molded main body40and covers the inlet end44of the optical sampling bore42. Likewise, an outlet optical window72is attached to the single-piece injection molded main body40and covers the outlet end46of the optical sampling bore42. In some embodiments, these optical windows70,72seal the respective ends44,46of the optical sampling bore42. The optical windows70,72may, for example, be biaxially oriented polypropylene films, although any window material may be used that is optically transparent for light output by the light source20and (if used to seal the optical sampling bore42) provides sufficient sealing capacity. The optical windows70,72may be secured to the main body40at the respective ends44,46of the optical sampling bore42by any suitable adhering mechanism, such as ultrasonic welding, heat staking, laser welding, or so forth. In the illustrative sample cell10, the inlet optical window70is oriented transverse to the optical axis54, and the outlet optical window72is oriented transverse to the optical axis54.

With particular reference toFIGS. 3(a)-(g), the single-piece injection molded main body40is shown in six orthogonal views inFIGS. 3(a)-(f)and in a perspective view inFIG. 3(g). The illustrative main body40includes a rectangular frame78that supports a tubular gas inlet80defining the gas inlet lumen50and a tubular gas outlet82defining the gas inlet lumen52. A bore section84between the tubular gas inlet and outlet sections80,82defines the optical sampling bore42and the plenums60,62. A cylindrical water filter hood86coaxially surrounds the tubular gas inlet80and provides additional support for the water trap filter16. Optionally (or if required by applicable regulations), this filter hood86is illustrated with a standard ISO symbol for a gas inlet, as seen inFIGS. 3(a), (d), and (g). In the illustrative embodiment, the tubular gas inlet80has a nib88, and the water trap filter16attaches to tubular gas inlet80via the nib88, preferably with no adhesive being used to secure the water trap filter16on the tubular gas inlet80. The tubular gas outlet82may, for example, be sized and shaped (e.g. with an illustrative conical tip) to mate into the internal air tubing26of the sampling bench8when the sample cell10is inserted into the mating receptacle12of the sampling bench8(seeFIGS. 1 and 2). The illustrative main body40further includes finger grips90,92on opposite sides of the single-piece injection molded main body40to facilitate the attachment and detachment, and a clasp, clip, or detent94on one clip90(as illustrated, or alternatively on both clips) to secure the sample cell10in the receptacle12. It will be appreciated that if the sample cell is a permanent component of the sampling bench, rather than being detachable as illustrated, then the finger grips90,92are suitably omitted and the clip90replaced by a permanent affixation mechanism.

With particular reference toFIG. 6, the illustrative sample cell10includes features which improve respired gas flow through the gas flow path50,60,42,62,52. The improvements reduce flow turbulence and circulation at transitions that can lead to high background carbon dioxide readings, time latencies and/or memory effects. For example, if the respired gas tends to form a circular flow pattern at a relatively abrupt directional change, this circular flow pattern can hold carbon dioxide. Such an effect is of most significance when it traps or delays respired gas prior to entering the optical sampling bore42. To suppress such effects, it is disclosed herein to incorporate at least one curved wall into the connection of the gas inlet lumen50and the inlet end44of the optical sampling bore42. As best seen inFIG. 6, a concave curved wall100is arranged to re-direct gas flow exiting the gas inlet lumen50into the inlet plenum60disposed between the gas inlet lumen50and the inlet end44of the optical sampling bore42. The concave curved wall100improves flow at the ˜90° flow directional change. A convex curved wall102is arranged between the inlet plenum60and the inlet end44of the optical sampling bore42to suppress recirculation at this ˜180° flow directional change.

Smooth flow out of the optical sampling bore42is also expected to reduce carbon dioxide background, memory effects or the like. To this end, a convex curved wall104is arranged between the outlet end46of the optical sampling bore42and the outlet plenum62to suppress recirculation at this ˜180° flow directional change. A concave curved wall106is arranged to redirect flow from the outlet plenum62into the gas outlet lumen52, which improves flow at this ˜90° flow directional change.

A further improvement that is predicted to improve flow uniformity is to construct the optical sampling bore42as a tapered cylinder with the taper oriented such that the outlet end46of the optical sampling bore has a larger diameter than the inlet end44of the optical sampling bore42. In some embodiments the taper is about 3°. A similar widening of the gas outlet lumen52, as seen inFIG. 6, further improves flow by reducing likelihood of flow resistance at the gas outlet lumen52during high respired gas flow rates.

With reference toFIG. 7, flow through the gas flow path50,60,42,62,52with the described turbulence-suppressing curved walls100,102,104,106and flow resistance-reducing tapers of the optical sampling bore42and gas outlet lumen52was simulated, and the simulation results are shown inFIG. 7. It was found that the curved walls100,102resulted in no observable turbulence for respired gas inflow into the optical sampling bore42, and only minimal recirculation. Similarly, the curved walls104,106resulted in no turbulence and only a small unswept corner110for the gas outflow, as seen at the outlet end46of the optical sampling bore42. In transient simulations it was found that the carbon dioxide signal rise time was improved by 20% compared with an earlier design that did not include the curved walls100,102,104,106and flow resistance-reducing tapers.

The disclosed sample cell10provides a synergistic combination of advantages. Construction as a single-piece injection molded main body40with only the optical windows70,72and water trap filter16being separate components substantially reduces assembly complexity and cost when compared with existing approaches that require assembling multiple parts to form the main body, and also eliminates joints which are potential respired gas leakage paths. Use of the nib88to attach the water trap filter16further simplifies assembly as compared with existing approaches that employ glue to attach the water filter. The disclosed flow turbulence reducing features100,102,104,106further improve performance of the disclosed sample cell10.

With reference now toFIG. 8, manufacturing of the single-piece injection molded main body40is challenging, because the gas flow path50,60,42,62,52includes numerous sharp angles on the order of 90° or even 180°, and further includes the curved walls100,102,104,106and flow resistance-reducing tapers.FIG. 8illustrates a suitable combination of mold pins for use in the injection molding. The illustrative combination of mold pins includes an inlet lumen-defining mold pin120which is a straight cylindrical pin that defines the gas inlet lumen50. A first complex mold pin122has two prongs and defines the inlet plenum60and the inlet end44of the optical sampling bore42. The first complex mold pin122includes curve surfaces for defining the concave curved wall100and the convex curved wall102of the gas flow path. A second complex mold pin124has two prongs and defines the outlet plenum62and a small portion of the outlet end46of the optical sampling bore42. The second complex mold pin124includes curved surfaces for defining the convex curved wall104and the concave curved wall106. A bore-defining pin126defines most of the tapered optical sampling bore42including most of its outlet end46. Finally, an outlet lumen-defining pin128defines the tapered gas outlet lumen52.

The combination of mold pins120,122,124,126,128is designed to allow the mold pins to be pulled out, either during curing or after curing, in order to leave the defined lumens. The inlet lumen-defining mold pin120is withdrawn in the direction indicated by arrow130to remove it during or after the curing. The first complex mold pin122is withdrawn in the direction indicated by the arrow132to remove it during or after the curing. The second complex mold pin124is withdrawn in the direction indicated by the arrow134to remove it during or after the curing. The bore-defining pin126is then withdrawn in the same direction as indicated by the arrow136. Since the second complex mold pin124“overlaps” the bore-defining pin126, the order for pulling these mold pins is constrained: the second complex mold pin124is pulled first in direction134and then the bore-defining pin126is pulled in the same direction136. Moreover, the bore-defining pin126can only be pulled in the direction136(and not, for example, in the opposite direction132) due to the tapering of the bore-defining pin126. The outlet lumen-defining pin128is pulled in the direction indicated by arrow138, which again comports with the tapering of this mold pin.

The mold pins120,122,124,126,128are suitably made of steel, although other materials that can withstand the injection molding temperature and chemistry are also contemplated. Although not shown inFIG. 8, it will be appreciated that the junctions between the various mold pins may include mating features to minimize the potential for mold flashing at these junctions. It is also contemplated to secure some mold pins, such as the complex mold pins122,124, as part of the injection mold so that they are removed upon opening the injection mold.

With reference toFIG. 9, a suitable process for manufacturing the sample cell10is described. In an operation150the single-piece injection molded main body40is formed by injection molding, e.g. using the mold pins described with reference toFIG. 8. Advantageously, this single step produces the main body40including the tubular gas inlet80with the nib88for attaching water trap filter16, the tubular gas outlet82, the optical sampling bore42and inlet and outlet gas paths50,52,60,62preferably including the turbulence-reducing curved walls100,102,104,106and tapers, and the handling extensions90,92with serrations or other grip assists. In an operation152, the inlet optical window70and the outlet optical window72are attached to the main body10using ultrasonic welding, heat staking, laser welding, or another suitable attachment method. In an operation154the water trap filter16is attached to the tubular gas inlet80using the nib88to retain the filter on the gas inlet. Preferably, the operation154does not include the use of glue or any other adhesive in securing the water trap filter16. In an operation156, the air hose14of a nasal cannula (or more generally, the air hose of a patient accessory) is attached to the water filter trap16. (The order of the operations154,156may be swapped). The result is the finished sidestream sampling consumable including the patient accessory, air hose14, water trap filter16, and disposable sampling accessory10.

In the illustrative embodiments the single-piece injection molded main body40is employed. The skilled artisan readily appreciates that this component is structurally identifiable at least because it does not include seams or junctions due to its being injection molded as a single piece, and because it is made of a single material throughout, and because the gas flow path comprises segments that can be defined by mold pins, for example as described with reference toFIG. 8. These structural characteristics of the single-piece injection molded main body40have practical consequences such as elimination of potential gas leaks at seams or junctions between parts, and reduced manufacturing cost/complexity.

As previously noted, while the illustrative respired gas sensor is a carbon dioxide (CO2) sensor, i.e. a capnography sensor, the disclosed sample cell10is readily employed in the context of other types of respired gas sensors, such as a respired oxygen sensor, where the improved manufacturability and/or reduced flow turbulence of the disclosed embodiments is/are readily seen as advantageous. It should be noted that while in the illustrative embodiments light propagation from the light source20to the light detector22is parallel with gas flow through the optical sampling bore42from the inlet end44to the outlet end46, in other contemplated embodiments the gas flow may be in the opposite direction from the light propagation. Moreover, a non-parallel angle between the light propagation and the optical sampling bore axis54is contemplated. It is further noted that the inlet and outlet plenums60,62can have shapes other than those of the illustrative embodiment. For example, the relatively sharp 90° turns at the concave curved walls100,106and/or the relatively sharp 180° turns at the convex curved walls102,104can be reduced by sloping these plenums to distribute the curvature over a longer gas flow distance, albeit at the cost of a sample cell with greater overall length and possibly more mold pins and/or more complex mold pin withdrawal configurations being needed to define such plenums. In another contemplated variant (not shown), if it is acceptable for gas inlet lumen50and the gas outlet lumen52to be non-coaxial, then the gas inlet lumen could directly connect with the inlet end44of the optical sampling bore42and likewise for the gas outlet lumen, so that the two plenums60,62could be omitted entirely and a single ˜90° convex wall placed at each connection to reduce turbulence.