WO2013046098A2

WO2013046098A2 - Pressure sensing tube with in-line contaminant blocking

Info

Publication number: WO2013046098A2
Application number: PCT/IB2012/054989
Authority: WO
Inventors: Michael Brian Jaffe
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-09-29
Filing date: 2012-09-20
Publication date: 2013-04-04
Also published as: WO2013046098A3

Abstract

An apparatus includes a flexible tube having a first end and a second end and an inner wall extending from the first end to the second end defining an inner channel; and a contaminant blocking device disposed within the inner channel of the flexible tube. The contaminant blocking device is configured to communicate a gas pressure there through from the first end to the second end, and to prevent contaminants from passing from the first end to the second end. The apparatus may be a pressure sensing tube connecting a differential pressure sensor and a flow meter in a ventilation arrangement.

Description

PRESSURE SENSING TUBE WITH IN-LINE CONTAMINANT BLOCKING

TECHNICAL FIELD

This invention pertains to patient circuits for connecting ventilators with patients, and in particular, an in-line filter for a pressure sensing tube which passes transmitted pressure, but blocks the passage of contaminants, for example body fluids.

BACKGROUND AND SUMMARY

Ventilators are used in a variety of settings. For example, in a hospital a patient may be ventilated as part of their medical care. In particular, ventilators are commonly provided in hospital intensive care units (ICUs).

It is necessary to measure airway flow for mechanically ventilated patients.

Various technologies have been used to measure airway flow, including pressure sensors that sense the air pressure in-line from the ventilator to the patient.

The advent of latest edition of the critical care ventilator standard (60601-2-12) provides that:

Gas pathways through the VENTILATOR and its ACCESSORIES that can become contaminated with body fluids or expired gases during NORMAL

CONDITION or SINGLE FAULT CONDITION shall be designed to allow dismantling for cleaning and disinfection or cleaning and sterilization.

Dismantling and sterilization procedures are time consuming and inconvenient in an operational setting. Mechanical ventilation often includes in-line pressure sensing with pressure sensing tubing connected to a pressure flowmeter. Therefore, it is desired to prevent cross-contamination between patients when using in-line pressure sensing in the event of a single fault condition so that the need for such dismantling and sterilization of a pressure flowmeter can be reduced or eliminated.

Accordingly, it would be desirable to provide a device or system which can address these requirements. In one aspect of the invention, a system comprises: a patient circuit configured to be connected between a ventilator and a patient; a differential pressure sensor disposed in line with the patient circuit and the patient, and being configured to sense a respiratory gas flow of the patient, the differential pressure sensor including first and second pressure sensing ports; a flowmeter including first and second input ports, wherein the first and second input ports are in communication with the first and second pressure sensing ports of the differential pressure sensor, wherein the flowmeter is configured to measure a differential pressure between the first and second input ports and to output an electrical signal responsive to the differential pressure; and first and second pressure sensing tubes connected between the first and second pressure sensing ports of the differential pressure sensor and the first and second input ports of the flowmeter. Each pressure sensing tube has an inner wall defining an inner channel and includes a corresponding contaminant blocking device disposed within the inner channel. Each of the contaminant blocking devices is configured to communicate a gas pressure therethrough from the differential pressure sensor to the flowmeter for measurement of the differential pressure by the flowmeter, and to prevent contaminants from passing therethrough to the flowmeter.

In some embodiments, the patient circuit comprises a dual-limb patient circuit including a wye element having first and second ports connected to the dual limbs and having a third port connected to the differential pressure sensor.

In some embodiments, each of the contaminant blocking devices is disposed proximal to the flowmeter within the inner channel of the corresponding pressure sensing tube.

In some embodiments, each of the contaminant blocking devices comprises a hydrophobic hollow fiber filter element.

In some embodiments, the hollow fibers of the hydrophobic hollow fiber filter element are folded over to form a closed end portion disposed at a side of the contaminant blocking device disposed closest to the differential pressure sensor.

In some embodiments, each contaminant blocking device further comprises flow blocking means for preventing unfiltered fluid from reaching the flowmeter.

In some embodiments, the flow blocking means comprises a blocking material inserted in between the hollow fibers and the inner wall of the corresponding pressure sensing tube.

In some embodiments, each of the contaminant blocking devices has an inlet disposed closest to the differential pressure sensor and an outlet disposed closest to the flowmeter, and comprises: a hydrophobic member disposed across the channel at a location proximate to the outlet; and a hydrophilic member disposed proximate to the hydrophobic member at a side closest to the inlet, such that contaminants passing through the channel over at least a portion of the hydrophilic member before reaching at least a portion of the hydrophobic member.

In some embodiments, the hydrophilic member has a first edge that contacts a surface of the hydrophobic member.

In some embodiments, the hydrophobic member has an outer surface that is coupled to the inner wall of the pressure sensing tube in a gas-tight and fluid-tight arrangement.

In some embodiments, the hydrophilic member has an outer surface that is coupled to the inner wall of the pressure sensing tube in a gas-tight and fluid-tight arrangement.

In another aspect of the invention, an apparatus comprises: a flexible tube having a first end and a second end and an inner wall extending from the first end to the second end defining an inner channel; and a contaminant blocking device disposed within the inner channel of the flexible tube. The contaminant blocking device is configured to

communicate a gas pressure therethrough from the first end to the second end, and to prevent contaminants from passing from the first end to the second end. The apparatus may be a pressure sensing tube connecting a differential pressure sensor and a flowmeter in a ventilation arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a functional block diagram of a ventilation arrangement that includes an in-line proximal differential pressure based flow sensor with pressure sensing tubing.

FIG. 2 is a detailed illustration of a portion of an example embodiment of the arrangement illustrated in FIG. 1.

FIGs. 3A-B illustrate one embodiment of an in-line proximal differential pressure sensor.

FIG. 4 is a functional block diagram of a ventilation arrangement that includes an in-line proximal differential pressure based flow sensors with pressure sensing tubing with contamination blocking. FIG. 5 is a detailed illustration of a portion of an example embodiment of the arrangement illustrated in FIG. 4.

FIG. 6 illustrates one example embodiment of a pressure sensing tube having a contaminant blocking device which may be employed in the arrangement of FIG. 4.

FIG. 7 illustrates another example embodiment of a pressure sensing tube having a contaminant blocking device which may be employed in the arrangement of FIG. 4.

DETAILED DESCRIPTION The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided as teaching examples of the invention.

FIG. 1 is a functional block diagram of a ventilation arrangement 100 that includes an in-line proximal differential pressure based flow sensor with pressure sensing tubing. The arrangement 100 includes a ventilator 110, a humidifier 120, and a patient circuit 130, including a wye 132, a pressure sensor 134, a flowmeter 136, and first and second pressure sensing tubes 138a and 138b.

In the illustrated embodiment, patient circuit 130 is a dual limb circuit having a first limb connected to ventilator 110 and a second limb connected to ventilator 110 via humidifier 120. Beneficially, pressure sensor 134 is a differential pressure sensor.

Beneficially, flowmeter 136 is a pressure flowmeter. It should be noted that although for illustration of a concrete example FIG. 1 shows an arrangement 100 having a dual- limb patient circuit, in other embodiments a ventilation system may have a single limb patient circuit.

As shown in FIG. 1, pressure sensor 134 is connected proximal to a patient between the patient and wye 132.

In practice, a facility (e.g., an intensive care unit) may have an installed ventilator 110 and humidifier 120, and when a patient is to be ventilated, patient circuit 130, including wye 132, pressure sensor 134 and flowmeter 136 may be separately provided.

FIG. 2 is a detailed illustration of a portion of an example embodiment of the arrangement illustrated in FIG. 1. In particular, FIG. 2 illustrates an example where the pressure sensor 134 is connected to an endotracheal tube 210 inserted into the interior 52 of a patient's trachea 55.

Operationally, ventilator 110 supplies gas from the ventilator inspiratory port to the humidifier 120. Typically, the gas may consist of room air or an elevated level of oxygen. The gas is typically dry and at room temperature which is nominally 25°C. Gas exiting humidifier 120 is typically at 100% relative humidity (RH) (i.e. saturated) and at a temperature greater than room temperature and less than or equal to body temperature of

37°C. This gas is supplied to the patient via the "lower limb" ("inspired limb") of patient circuit 130, including wye 132 and pressure sensor 134. Gas returning from the patient is less than 100% RH due to condensation and at a lower temperature (such as 33°C) and returns to ventilator 110 via the "upper limb" ("expired limb") of patient circuit 130, including wye 132 and pressure sensor 134.

Pressure sensor 134 operates with flowmeter 136 to measure a respiratory gas flow for the patient. Beneficially, pressure sensor 134 senses gas pressure differentially, and first and second pressure sensing tubes 138a and 138b communicate the sensed gas pressure to pressure flowmeter 136 which measures the differential pressure and in response thereto may generate one or more electrical signals.

FIGs. 3A-B illustrate one embodiment of an in-line proximal differential pressure sensor 300 which is one embodiment of pressure sensor 134. Further details of example embodiments of an in-line proximal differential pressure sensor and a pressure flowmeter which may be incorporated in arrangement 100 may be found in U.S. Patent 5,535,633, which is incorporated by reference herein.

During normal operations, where there is no leak or fault in the arrangement 100, each of the first and second pressure sensing tubes 138a and 138b is filled with a gas volume or column whose pressure changes in response to respiratory action by ventilator

110 and the patient. The changes in pressure are measured by flowmeter 136. In other words, gas does not normally flow through first and second pressure sensing tubes 138a and 138b from pressure sensor 134 to flowmeter 136.

However, in the event of a single fault condition, it is possible for pressure sensing tubes 138a and/or 138b to become contaminated, for example with body fluids (e.g., liquid matter) from a patient via patient circuit 130, and this contamination could be

communicated through pressure sensing tubes 138a and/or 138b to flowmeter 136. In that case, as discussed above, it may be required to dismantle, clean, and disinfect and/or sterilize flowmeter 136, which is undesirable.

One device which can be used for protecting pressure sensors from contaminants is a BRO Gas Line Filter, such as the Model BR012, from the Pall Corporation.

However, such a filter is large and obtrusive, and it is particularly undesirable to have two such filters arranged side-by-side in series with two relatively small (exemplary inner diameter 3/32") pressure sensing tubes 138a and 138b that extend from pressure sensor 134 to flowmeter 136 in the arrangement 100 of FIG. 1.

Accordingly, to address this problem, the inventors have conceived of a pressure sensing tube that has a contaminant blocking device disposed within its inner channel that can filter out and prevent body fluids and other contaminants, for example gas-borne particles, from reaching a flowmeter to which it is attached. Beneficially, the contaminant blocking device possesses certain characteristics, including: communicates gas pressure or gas pressure changes without significant attenuation; provides an effective barrier with high gas-borne bacterial removal efficiency; it may be used with all medical gases such as C02, N2 and 02; and it has a relatively small form factor that is consistent with the relatively small diameter of the pressure sensing tube. For example, as noted above, in one example embodiment the pressure sensing tube may have an inner diameter of 3/32" compared to an inner diameter of tubing in the patient circuit which may typically be on the order of 15 mm. Beneficially, the contaminant blocking device has a relatively large surface area within the relatively small space within the inner wall of the pressure sensing tube.

FIG. 4 is a functional block diagram of a ventilation arrangement 400 that includes an in-line proximal differential pressure based flow sensor with pressure sensing tubing and in-line contaminant blocking. Like elements in arrangement 400 and arrangement 100 have the same reference numerals, and a description thereof will not be repeated.

Arrangement 400 is the same as arrangement 100 described above, except for first and second pressure sensing tubes 438a and 438b including corresponding contaminant blocking devices 410a and 410b. Again, it should be noted that although for illustration of a concrete example FIG. 4 shows an arrangement 400 having a dual-limb patient circuit, in other embodiments a ventilation system may have a single limb patient circuit.

FIG. 5 is a detailed illustration of a portion of an example embodiment of the arrangement illustrated in FIG. 4.

As better seen in FIG. 5, differential pressure sensor 134 includes first and second pressure sensing ports 134a and 134b having associated first and second connectors, and flowmeter 136 includes first and second input ports 136a and 136b having associated first and second connectors.

Each of the pressure sensing tubes 438a/438b is connected between a

corresponding one of the pressure sensing ports 134a/134b of differential pressure sensor 134 and a corresponding one of the first and second input ports 136a and 136b of flowmeter 136. Pressure sensing tubes 438a/438b each have a first end (e.g., connected to differential pressure sensor 134) and a second end (e.g., connected to flowmeter 136), and an inner wall defining an inner channel extending therethrough from the first end to the second end.

First and second contaminant blocking devices 410a/410b are each disposed in the inner channel of a corresponding one of the first and second pressure sensing tubes 438a/438b. Each of the contaminant blocking devices 410a/410b has an inlet disposed at a side of the corresponding pressure sensing tube 438a/438b connected to differential pressure sensor 134, and an outlet disposed at a side of the corresponding pressure sensing tube 438a/438b connected to flowmeter 136. Each of the contaminant blocking devices 410a/410b is configured to communicate a gas pressure or gas pressure change therethrough from differential pressure sensor 134 to flowmeter 136 for pressure measurement, and to prevent contaminants, including for example liquid and airborne particles, from flowing therethrough from differential pressure sensor 134 to flowmeter

136. Beneficially, contaminant blocking devices 410a/410b prevents substantially all such contaminants from reaching flowmeter 136, thus eliminating the need for dismantling and cleaning or sterilization of flowmeter 136 when it is deployed for a new patient.

Beneficially, pressure sensing tubes 438a/438b are flexible tubes and with the exception of contaminant blocking devices 410a/410b may be the same as any standard tubing, particularly pressure sensing tubes 138a/138b of the arrangement 100. Similarly to arrangement 100 discussed above, in normal operation, pressure sensing tubes 438a/438b may be filled with a gas volume or column whose pressure changes in response to respiratory action by ventilator 110 and the patient. These changes in pressure are measured by flowmeter 136. In other words, gas does not normally flow through first and second pressure sensing tubes 138a and 138b from pressure sensor 134 to fiowmeter 136. Beneficially, contaminant blocking devices 410a/410b block contaminants, but do not significantly attenuate gas pressure or gas pressure changes from being communicated to flowmeter 136.

FIG. 6 illustrates one example embodiment of a pressure sensing tube 600 having a contaminant blocking device which may be employed in the arrangement 400 of FIG. 4. As described above, the contaminant blocking device is configured to transmit a gas pressure or gas pressure change therethrough and to prevent contaminants such as a liquid from flowing therethrough.

Pressure sensing tube 600 comprises a substantially flexible tube 2 having a relatively small diameter, defining a space 4 therein and having an inlet end portion 6 and an outlet end portion 8 defining therein fluid flow passages 10 and 12, respectively. As seen in FIG. 6, in some embodiments the inlet and outlet end portions 6 and 8 are configured to provide smooth and gradual transition sections 14 and 16 between the relatively larger internal space 4 of flexible tube 2 and the internal fluid flow passageways 10 and 12 of end portions 6 and 8, respectively.

Flexible tube 2 has an inner wall defining an inner channel, and disposed within the inner channel is a contaminant blocking element 18, composed of a hydrophobic hollow fiber filter. Contaminant blocking element 18 is preferably formed by folding over the fibers, thus providing a first closed end portion 19 and a second open end portion 20.

Contaminant blocking element 18 is shaped and located inside flexible tube 2 such that first closed end portion 19 reaches the space delimited by transition section 14 and second open end portion 20 reaches the space delimited by transition section 16. Advantageously the internal diameters of flexible tube 2 and end portions 6 and 8 are calculated so that the cross-sectional area of the free space inside flexible tube, i.e., the space unoccupied by contaminant blocking element 18 and passageways 10 or 12 are substantially the same. The hollow fibers of contaminant blocking element 18, in conjunction with the small diameter of flexible tube 2, form a contaminant blocking device having at least four times smaller volume per square centimeter of filter material, or of effective filter area, than the dead space obtained utilizing a filter element of the flat membrane type. In order to assure that non-filtered contaminants such as a fluid will not reach outlet end portion 8, a blocking material 22 may be inserted in between the hollow fibers and the inner wall of flexible tube 2 at second end portion 20. The contaminant blocking device may further include means 24 for further reducing the dead space within fiexible tube 2. Such means may be embodied by non-permeable material, e.g., glass particles or beads, as illustrated in FIG. 6.

Closed end portion 19 of contaminant blocking element 18, as well as the walls along the entire fibers, provide thin walls through which gas pressure changes traverse with minimal disturbance. Hence, in the overall effort to provide an efficient contaminant blocking device through which gas pressure changes can be communicated from inlet end portion 6 to outlet end portion 8 with minimal disturbance, there is provided a combination of elements cooperating in achieving same.

FIG. 7 illustrates another example embodiment of a pressure sensing tube 700 having a contaminant blocking device which may be employed in the arrangement 400 of FIG. 4. As described above, the contaminant blocking device is configured to communicate a gas pressure or gas pressure change therethrough and to prevent contaminants, for example a liquid, from flowing therethrough.

Pressure sending tube 700 includes a flexible tube 101, which may be formed of a suitable polymer and have a cylindrical shape. Flexible tube 101 has axially opposed first and second ends 103 and 105, and an inner channel defined by an inner wall 107.

A hydrophilic member 102 is disposed in flexible tube 101 and is coupled to inner wall 107 of flexible tube 101 by any technique known to those skilled in the art including, but not limited to, a mechanical press fit. Hydrophilic member 102 may be formed of a porous material suitable for accomplishing a wicking function, such as a fibrous material, having a pore volume ranging from approximately 40% to approximately 90%, where the pore volume is the ratio of a porous material's air volume to a porous material's total volume. Exemplary fibrous materials include single component fibers as well as fiber blends, such as bi-component, multi-component and functional fibers. An example of a fibrous material suitable for hydrophilic member 102 is disclosed in U.S. patent application Ser. No. 10/464,443 (publication no. 2003/0211799). Such fibers may possess absorbent properties that, in effect, create reservoirs with substantial liquid holding capacity. The illustrated hydrophilic member 102 is cylindrical and constructed of thermally bonded fibers. In an exemplary embodiment, the fibers consist of a polyester core with a polyester sheath and are sintered to form the cylindrical structure. Other shaped structures are contemplated that may enhance the water holding capacity.

In an exemplary embodiment, hydrophilic member 102 has a diameter that is slightly greater than the diameter of inner wall 107 of flexible tube 101 to assure a tight fit of hydrophilic member 102 in the inner channel of flexible tube 101 without significant compression.

In the illustrated exemplary embodiment, hydrophilic member 102 is a disc or cylinder with a diameter that is greater than the diameter of the channel defined by inner wall 107 of flexible tube 101 so that a sufficiently tight seal is made. Beneficially, hydrophilic member 102 forms a gas-tight and fluid-tight arrangement with inner wall 107. Hydrophilic member 102, in one embodiment, is constructed of a porous plastic, such as polyethylene, with an additive coating that self seals upon wetting. Materials known in the art, such as cellulose gum, can serve this function. Additionally, a sufficiently large pore volume of hydrophilic member 102 permits not only moisture to be efficiently absorbed.

As illustrated in FIG. 7, hydrophilic member 102 lines inner wall 107 of flexible tube 101 from a first end 103 to a point where a hydrophobic member 109 is located, which is proximate to second end 105. It is to be understood, however, that hydrophilic member 102 in general does not extend along the entire length of flexible tube 101, need not fill the channel, and need not be formed from a single, unitary material. Rather, hydrophilic member 102 can be formed from multiple pieces of material, and each portion or piece of the hydrophilic member need not be formed from the same material. For example, the portions of hydrophilic member 102 can be formed such that the absorbency of the material changes along the length of the housing, in the radial direction or is maximized where it is more likely that condensation will gather.

A hydrophobic member 109 is positioned proximate second end 105 of the contaminant blocking element. Hydrophobic member 109 has an outer diameter, defined by an outer surface 111 thereof that may approximate or exceed the diameter of inner wall 107 of flexible tube 101 such that outer surface 111 is closely coupled with inner wall 107 of flexible tube 101 in a gas-tight and fluid-tight arrangement, as known to those of ordinary skill in the art. In this manner, only gases passing through hydrophobic member 109 are permitted to reach flowmeter 136.

In the illustrated embodiment, an upstream surface 113 of hydrophobic member

109 is in contact with a downstream edge 104 of hydrophilic member 102.

However, in some embodiments there need not be direct contact between these members. Instead, a gap can be provided between hydrophobic member 109 and hydrophilic member 102. This can gap can be used as a reservoir for materials that may accumulate in the contaminant blocking device. It is generally, understood that the larger the gap, the more likely the gas pressure waveform for the monitored gas will be adversely impacted. To address this concern, some embodiments include an inert filler material between the hydrophobic and hydrophilic members. As illustrated in FIG. 7, positioned downstream of hydrophobic member 109 is a connector 115 (e.g., a connector of a first or second input port 136a/136b of flowmeter 136) for communicating the filtered gases to flowmeter 136. Coupled with first end 103 of flexible tube 101 is a connector 117 (e.g., a connector of a first or second pressure sensing port 134a/134b of differential pressure sensor 134). An outer surface 119 of connector 117 is coupled in a gas-tight and fluid-tight manner to inner wall 107 of flexible tube 101.

In operation, gas pressure and pressure changes are communicated through the inner channel of flexible tube 101 and moisture and contaminants are removed from the gas column present in flexible tube 101 by hydrophilic member 102. While hydrophilic member 102 is capable of absorbing a substantial portion of the moisture from the gas stream, some moisture may remain in the stream. Thus, hydrophobic member 109 is provided as a second line of defense against moisture reaching flowmeter 136. Because hydrophobic member 109 is formed of a hydrophobic material, gas pressure and gas pressure changes are able to be communicated therethrough but liquids will be

substantially prevented from passing through hydrophobic member 109. Instead, any liquid remaining in the gas will remain within the spaces within hydrophilic member 102 and may be absorbed by the downstream-most portions of hydrophilic member 102 or wicked away from hydrophobic member 109 using the hydrophilic member or a separate wicking material.

As flexible tube 101 is coupled in a gas-tight and fluid-tight arrangement with connector 115, any material that may exit flexible tube 101 is passed through hydrophobic member 109 first. Further, because of the sufficient pore volume and fibrous nature of hydrophilic member 102, the gas pressure waveform of the gas sample is permitted to proceed substantially undisturbed from the point at which the sample is collected at differential pressure sensor 134 to flowmeter 136.

While preferred embodiments are disclosed herein, many variations are possible which remain within the concept and scope of the invention. Such variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the scope of the appended claims.

Claims

CLAIMS What is claimed is:

1. A system, comprising:

a patient circuit configured to be connected between a ventilator and a patient; a differential pressure sensor disposed in line with the patient circuit and the patient, and being configured to sense a respiratory gas flow of the patient, the differential pressure sensor including first and second pressure sensing ports;

a flowmeter including first and second input ports, wherein the first and second input ports are in communication with the first and second pressure sensing ports of the differential pressure sensor, wherein the flowmeter is configured to measure a differential pressure between the first and second input ports and to output an electrical signal responsive to the differential pressure; and

first and second pressure sensing tubes connected between the first and second pressure sensing ports of the differential pressure sensor and the first and second input ports of the flowmeter, wherein each pressure sensing tube has an inner wall defining an inner channel and includes a corresponding contaminant blocking device disposed within the inner channel, and wherein each of the contaminant blocking devices is configured to communicate a gas pressure therethrough from the differential pressure sensor to the flowmeter for measurement of the differential pressure by the flowmeter, and to prevent contaminants from passing therethrough to the flowmeter.

2. The system of claim 1, wherein the patient circuit comprises a dual- limb patient circuit including a wye element having first and second ports connected to the dual limbs and having a third port connected to the differential pressure sensor.

3. The system of claim 1, wherein each of the contaminant blocking devices is disposed proximal to the flowmeter within the inner channel of the corresponding pressure sensing tube.

4. The system of claim 1, wherein each of the contaminant blocking devices comprises a hydrophobic hollow fiber filter element.

5. The system of claim 4, wherein the hollow fibers of the hydrophobic hollow fiber filter element are folded over to form a closed end portion disposed at a side of the contaminant blocking device disposed closest to the differential pressure sensor.

6. The system of claim 4, wherein each contaminant blocking device further comprises flow blocking means for preventing unfiltered fluid from reaching the flowmeter.

7. The system of claim 6, wherein the flow blocking means comprises a blocking material inserted in between the hollow fibers and the inner wall of the corresponding pressure sensing tube.

8. The system of claim 1, wherein each of the contaminant blocking devices has an inlet disposed closest to the differential pressure sensor and an outlet disposed closest to the flowmeter, and comprises:

a hydrophobic member disposed across the channel at a location proximate to the outlet; and

a hydrophilic member disposed proximate to the hydrophobic member at a side closest to the inlet, such that fluid passing through the channel passes over at least a portion of the hydrophilic member before reaching at least a portion of the hydrophobic member.

9. The system of claim 8, wherein the hydrophilic member has a first edge that contacts a surface of the hydrophobic member.

10. The system of claim 8, wherein the hydrophobic member has an outer surface that is coupled to the inner wall of the pressure sensing tube in a gas-tight and fluid-tight arrangement.

11. An apparatus, comprising:

a flexible tube having a first end and a second end and an inner wall extending from the first end to the second end defining an inner channel; and

a contaminant blocking device disposed within the inner channel of the flexible tube, wherein the contaminant blocking device is configured to communicate a gas pressure therethrough from the first end to the second end, and to prevent contaminants from passing from the first end to the second end.

12. The apparatus of claim 11, wherein the first end of the flexible tube is connected to a differential pressure sensor, and the second end of the flexible tube is connected to a flowmeter.

13. The apparatus of claim 11, wherein the contaminant blocking device comprises a hydrophobic hollow fiber filter element.

14. The apparatus of claim 13, wherein the first end comprises an inlet and the second end comprises an outlet, and wherein the hollow fibers of the hydrophobic hollow fiber filter element are folded over to form a closed end portion disposed at a side of the contaminant blocking device disposed closest to the inlet.

15. The system of claim 13, wherein the contaminant blocking device further comprises a blocking material inserted in between the hollow fibers and the inner wall of the flexible tube.

16. The apparatus of claim 13, wherein the contaminant blocking device has an inlet and an outlet, and comprises:

a hydrophilic member disposed proximate to the hydrophobic member at a side closest to the inlet, such that contaminants passing through the channel passes over at least a portion of the hydrophilic member before reaching at least a portion of the hydrophobic member.

17. The apparatus of claim 16, wherein the hydrophilic member has a first edge that contacts a surface of the hydrophobic member.

18. The apparatus of claim 16, wherein the hydrophobic member has an outer surface that is coupled to the inner wall of the flexible tube in a gas-tight and fluid-tight arrangement.

19. The apparatus of claim 18, wherein the hydrophilic member has an outer surface that is coupled to the inner wall of the flexible tube in a gas-tight and fluid-tight arrangement.