Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
  • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
  • G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
  • G01F23/284—Electromagnetic waves
  • G01F23/292—Light, e.g. infrared or ultraviolet
  • G01F23/2921—Light, e.g. infrared or ultraviolet for discrete levels
  • G01F23/2922—Light, e.g. infrared or ultraviolet for discrete levels with light-conducting sensing elements, e.g. prisms

Definitions

• This invention generally relates to maintaining the surface tension of instruments, operational with aqueous liquids, greater than the surface tension of the aqueous liquids they are used with. This is accomplished by altering the surface tension characteristics of the instrument, the aqueous liquid or both. Surfaces of instruments operational with aqueous liquids can be made more hydrophilic. This limits adherence of submerged gas bubbles to the surfaces and reduces the likelihood of impaired operation. Also, the invention generally relates to making more hydrophilic, optical surfaces whose operation is impaired by the adherence of liquid droplets to unsubmerged surfaces. Similar results can be achieved by decreasing the surface tension of the aqueous liquids below the surface tension of the instruments or devices. Adherence of . gas bubbles to submerged surfaces or liquid droplets to unsubmerged surfaces is impaired.
• the invention particularly relates to ventilator, humidifier devices useful in humidifying inhalation gas being administered to patients under respiratory therapy.
• Liquid level sensing devices that automatically replenish liquid, to provide generally optimum humidification conditions, specifically benefit from this invention.
• This invention relates to improvements in the automatic liquid level sensing device. The improvements impair the adherence of gas bub ⁇ bles, submerged in aqueous liquids, to the liquid level sensing means of the device by using surfactants in the aqueous liquids, treating the device, or both. Adherence of gas bubbles to the liquid level sensing means can result in erroneous indications of liquid level.
• containers enclosing the basic elements of the ventilator, humidifier device and containing the aqueous liquid can be treated using surfactants. Treating interiors of the con ⁇ tainers with a surfactant impairs adherence of gas bubbles to elements submerged in the aqueous liquids and contained in the container. Use of a surfactant treated container also impairs adherence of liquid droplets to elements within the container.
• liquid is maintained typically at a relatively low level within the cannister so that the circulating gas is humidified primarily from the tubular wick.
• More liquid may be added to the cannister, for example, from a solution bag of sterile water, through a tube into the cannister.
• the tube generally passes through a solenoid switch which pinches the tubing shut to stop flow and intermittently opens the tube when a low liquid level is sensed.
• a light probe is positioned in the cannister so that visible light, or typically light from the infrared portion of the spectrum, passes down the probe and is reflected from a conical-shaped end of the probe in the event that the liquid level is low.
• a sensor detects the reflected light and actuates the solenoid to open the switch. Liquid then flows into the cannister until reflected light is no longer detected.
• U.S. Patent 4,354,984, Liquid Level Controller for a Humidi ⁇ fier, to Richardson, et al. discloses a tube clamp assembly for an oxygen gas humidifier used in respiratory therapy.
• the clamp assembly is part of a control system for controlling the flow of replacement liquid to the humidifier cannister.
• a light probe and sensor are a part of the liquid level control system.
• the light probe, or light pipe, used to detect liquid level is made from a hydrophobic, the ⁇ noplastic material.
• the liquid level sensing probe has an end which may be defined by a conical surface if desired, or any other surface which pro ⁇ vides angled surfaces positioned to permit light passing into the highly transparent probe and toward the end surface to be reflected back up the probe in a returning beam of light after striking at reflection points.
• the refractive conditions at the end surface are changed because of the relatively slight difference in the index of refraction of liquid with respect to the light probe so that the light beam is not reflected. Instead, the light passes through the surface, continuing its downward path so that there is no significant reflective light beam. Accordingly, the presence or absence of contacting liquid at the end surface can be indicated by the presence or absence of a reflected light beam.
• a light sensor in the Grimm patent, communicating with the other end of the light probe detects the reflected light.
• the light sensor actuates a solenoid to open a valve permitting liquid flow through tubing to the cannister.
• the liquid level rises until the end surface of the probe is covered.
• the reflected beam terminates, thus deactivating the light sensor and causing the solenoid to de ⁇ activate. This, in turn * closes the valve, shutting off liquid flow.
• Gas bubble formation or nucleation generally is caused by air or another gas fixing to a site and adhering to microscopic fissures, cavities, scratches and other surface irregularities.
• gas bubble formation occurs when the surface tension of the aqueous liquid is greater than the surface tension of the light probe.
• the present invention provides for maintaining the surface tension of an optical surface, such as a light probe used in humidifier devices or the like, greater than the . surface tension of aqueous liquids used therewith.
• Aqueous liquids generally are contained in cannisters of the humidifier devices. Maintaining this relationship between optical surfaces of the humidifier devices and aqueous liquids is accomplished by altering the sur- " face tension characteristics of the light probe, the aqueous liquid or both so that the surface tension of the light probe is greater than that of the aqueous liquid with which it is used.
• a surface active agent also referred to as a surfactant
• a surface active agent is applied to the surface of the light probe or light pipe used in the humidifier container.
• a quantity of surface active agent can be added to the aqueous liquid used in the humidifier, a surface active agent can be applied to por ⁇ tions of the interior surface of the humidifier container, or the surface of the light probe can be subjected to plasma surface treating processes such as corona discharge. Plasma surface treating processes can be used alone or in combination with treat ⁇ ments involving use of a surfactant.
• Submerged gas bubbles do not adhere to the surface of the light probe in a humidifier treated accordingly; hence, desired operation of the light probe is not impaired.
• aqueous liquid When the end of the light probe is in contact with aqueous liquid * light is not internally reflected at the probe end but instead passes through the surface, continuing its path into the liquid.
• Beads and droplets of liquid do not adhere to unsubmerged portions of the light probe in a humidifier treated accordingly, hence, desired operation of the light probe is not impaired.
• desired operation of the light probe is not impaired.
• an amount of surface active agent may be added to the liquid in the container.
• the formation of air bubbles in the liquid and on the submerged surfaces of instruments operating with the liquid would be reduced or eliminated. Formation of beads and droplets of liquid on unsubmerged surfaces of instru- ments operating with the liquid would be reduced or eliminated.
• Surface tension characteristics of the aqueous liquid also can be altered by coating portions of the interior surfaces of the humidifier container.
• a surface active agent to the surface of a light probe or light pipe made of a transparent hydrophobic plastic such as LEXAN ® thermoplastic.
• LEXAN ® is a registered trademark of the General Electric Company for polycarbonate thermoplastic
• polyacrylate thermoplastic or another thermoplastic.
• Application of a surface active agent to the light probe makes the surface more hydrophilic. It is known in the art which surface active agents make more hydrophilic the particular surface materials involved.
• the surface active agent may consist essentially of a non-ionic ester of a carbohy- drate moiety and an organic monoacid of 8 to 30 carbon atoms. It has been found that this particular family of surface active agents is physiologically compatible, easily metabolized and is subject to a low degree of toxic reaction.
• the surface active agent of this invention which is preferred is a mixture of monoesters of sorbitan with capric, 1auric, myristic, palmitic or oleic acids or all of them.
• the mixture may include the follow ⁇ ing typical weight percentages of monoesters, sold as SPAN ® 20
• _-_V ⁇ __ surfactant by ICI Americas, Inc. (SPAN ® is a registered trademark of ICI Americas, Inc.): sorbitan caprate 1.1%; sorbitan laurate 43.5%; sorbitan myristate 27.8%; sorbitan palmitate 19.2%; and sorbitan oleate 8.4%.
• other analogous esters can be used, pure or mixed, preferably monoesters of carbohydrate such as sorbitan, glucose, fructose, or other etabolizable carbohy ⁇ drates of preferably 5 to 6 carbon atoms.
• the organic monoacids used of 8 to 30, and preferably 10 to 20, carbon atoms may be any appropriate monoacid which reacts with the carbohydrate moiety to preferably form a monoester, "that is, 1 carbohydrate molecule reacted with 1 monoacid molecule.
• the acids which may be used in ⁇ clude those described above or others such as tridecanoic acid, or mixed acids such as linseed oil acids, to provide an appropriate hydrophobic portion, combined with the hydrophilic carbohydrate moiety to form the desired surface active agent.
• a light pipe or other instrument whose operation with water may be impaired by the adherence of air bubbles thereto can be coated with the surface active agent of this invention.
• an amount of these surface active agents may be added to the aqueous liquid or used to coat portions of the interior of the humidifier cannister thereby inhibiting the forma ⁇ tion of gas bubbles in the liquid which would adhere to submerged surfaces and minimizing or greatly reducing liquid droplet forma ⁇ tion on unsubmerged surfaces.
• Preferred surface active agents ' for direct addition to an aqueous liquid contained in a humidifier or for coating surfaces are SPAN ® 20 surfactant, ethoxylated sorbitan onoiaurates, for example, polyoxyethylene (20) sorbitan monolaurate, sold by ICI Americas, Inc. as TWEEN ® 20 surfactant, and polyoxyethylene (4) sorbitan monolaurate sold as TWEEN ® 21 surfactant by ICI Americas, Inc.
• Surface tension on the light probe can be maintained greater than surface tension of the aqueous liquids they are used with by treating the light probe using conventional plasma generators such as corona discharge devices. Corona discharge or plasma gen ⁇ erator treating processes deliver results essentially similar to coating the light pipe with SPAN ® 20 surfactant. With these treatments, the light probes are exposed to an ionized gas such as oxygen that alters the surface of the light probe, thereby increasing surface energy. The surface of the light probe becomes more hydrophilic.
• Figure 1 is an exploded perspective view of a humidifier portion of a ventilator humidifier device showing the light probe element therein.
• Figure 2 is an enlarged, fragmentary elevational view of the remote end of the light-transmitting probe unsubmerged, show ⁇ ing light being reflected.
• Figure 3 is an enlarged, fragmentary elevational view of the remote end of the light-transmitting probe submerged in liquid, showing light passing into the water.
• Figure 4 is an enlarged, fragmentary elevational view of the remote end of the light-transmitting probe submerged in liquid, showing light being reflected due to the presence of gas bubbles.
• Figure " 5 is an enlarged, fragmentary elevational view of the remote end of the light-transm tting probe unsubmerged, with liquid condensate droplets thereon, showing light being refracted away from the probe.
• Figure ⁇ is an enlarged, fragmentary elevational view of the remote end of the light- ransmitting probe unsubmerged, with a monolayer of condensate thereon showing light being internally reflected.
• FIG. 1 is an exploded per ⁇ spective view of a humidifier cannister illustrating the basic elements contained therein.
• Humidifier element 10 is adapted for insertion into the well of a heater assembly.
• Humidifier element 10 comprises a seamless, open mouthed.metal cannister 14 defining cylindrical walls and a closed bottom end 16.
• Can ⁇ nister 14 simply may be a commercial beverage can purchased from a can manufacturer at low cost.
• Wick means 18 may be made from a sheet of material rolled up into a structure which preferably is generally cylindrical, wick means 18 being made of a porous paper material or the like. Accordingly, wick means 18 absorbs water in the bottom of can ⁇ nister 14 and presents it in dispersed, high surface area form to gases flowing through cannister 14.
• Closure 20 may be made of a single piece of molded plastic. It is adapted to fit in tight, sealing manner about mouth 22 of cannister 14. Closure 20 defines a gas inlet port 24. Baffle 26 is provided to prevent shunting of non-humidified gas out of outlet aperture port 28, which is defined as shown by closure 20. Both inlet port 24 and outlet 28 are adapted for attachment to flexible gas flow tubing of conventional design for a patient breathing ci cui or the like.
• Closure 20 also defines light access port 30 through which may extend translucent probe means 32.
• Probe means 32 may be made of highly transparent polycarbonate plastic, polyacrylate plastic, polysulfanone plastic, or the like. Probe means 32 ex ⁇ tends through cannister 14 preferably to at least the remotest third of the cannister interior from closure 20 to serve as a liquid level measuring means as described below. It is preferred that liquid level 34 be maintained in the lower third of cannister 14. This exposes a large surface area of wick means 18, which is preferably of essentially the same height as that of cannister 14, to take up the liquid and to expose a large surface area of wet wick means 18 to dry gases entering through inlet port 24, for improved humidification due to the large surface . area.
• flexible tubing 44 is connected to port 45 in closure 20 to supply liquid to humidifier element 10.
• a standard drip chamber 46 is provided adjacent the free end of tubing 44, which terminates in a standard hollow piercing spike 48, for penetration into a conventional liquid supply container, for example, a bottle or bag of sterile water sold by Travenol Laboratories, Inc., of Deerfield, Illinois.
• Liquid level light probe means 32 defines end 33 which may be defined by a conical surface if desired, or any other surface which provides angled surfaces. Referring to Figure 2, light beam 36a passing in the transparent probe means 32 toward end surface 33 is reflected in a returning beam of light 36b after striking at two reflection points 38, 40, causing the light beam to make two 90° angle reflective turns. Conical surface 42 preferably defines an angle of 45° to the axis of probe 32 and particularly incoming light beam 36a.
• a light sensor at light access port 30 detects the reflected light beam 36b.
• the light sensor activates a solenoid to open a valve permitting liquid flow through tubing into cannister 14.
• the solenoid is deactivated, thereby closing the valve, when liquid level 34 is above end 33 of light probe 32 as is illustrated in Figure 3.
• Light beam reflection takes place when gas bubbles 43 adhere to end 33 of probe 32.
• reflection points 38, 40 are points having effected indices of refraction caused by the difference in the index of refraction of the liquid with respect to the gas of bubbles 39 and 41.
• Light beam 36b is reflected back to the light sensor at light access port 30 even though there is a sufficient liquid level 34.
• the solenoid is activated to open the valve ⁇ permitting liquid to flow into cannister 14. In this instance, addition of liquid would not cause deactivation of the solenoid.
• Liquid would continue to flow into cannister 14 until a local disturbance dislodged gas bubbles 39, 41, until the liquid source was de ⁇ pleted, or until a specified time period elapsed.
• Plasma treatment such as corona discharge treatment of the surface of probe 32, addition of a surface active agent to the surface of probe 32, addition of a surface active agent to the liquid, addition of a surface active agent to portions of the interior surface of cannister 14, or combinations of these alter- natives inhibit the adherence of gas bubbles to the surface of submerged light probe 32.
• Such treatments, or combinations thereof additionally inhibit liquid droplet formation on unsubmerged por ⁇ tions of light probe 32.
• Figure 3 is illustrative of the effect which surface active agents or surface treatments have on the submerged portion of light probe 32.
• the surface of light probe 32 can be coated with SPAN ® 20 surfactant earlier described.
• SPAN ® 20 surfactant can be used to coat portions of the interior surface of cannister 14 or it can be added to the liquid in cannister 14.
• Amounts of TWEEN ® 20 or TWEEN ® 21 surfactants can be used to coat surfaces or added to the liquid in cannister 14 to provide similar results. Also, it is believed that quaternary ammonium compounds will have similar surface effects.
• the surface of light probe 32 can be subjected to a plasma treat ⁇ ment such as corona discharge.
• a plasma treat ⁇ ment such as corona discharge.
• Corona discharge and other plasma treatments of light probe 32 alter the surface and increase the surface energy. It is also believed that these treatments assist in removing hydrophobic contaminates and also slightly oxidize the surface.
• the surface tension on a polycarbonate light probe can be changed from 30-40 dynes per centimeter to greater than 72 dynes per centimeter. The surface of the polymer, thereby, becomes more hydrophilic.
• FIG. 5 illustrates light probe 32 above liquid level 34.
• Liquid droplets 50 are shown adhering to the surface of light probe 32.
• Light beam 36a travels down light probe 32 and upon encountering liquid droplets 50 is refracted out of light probe 32 instead of being reflected back upward.
• a false indication of sufficient liquid level would be perceived.
• Liquid in cannister 14 would continue to be depleted until liquid droplets 50 were evaporated or shaken loose. Risk inheres that a patient would receive insufficiently humidified oxygen or in- halation gas.
• Light probe 32 Treatment of the surface of light probe 32 will inhibit liquid droplet formation. Light probe 32 can be subjected to the corona
• light probe 32 can be coated with SPAN ® 20 surfactant. Similar results of inhibiting liquid droplet formation on light probe 32 can be accomplished by the addition of TWEEN ® 20 or TWEEN ® 21 surfactants to the liquid in cannister 14 or by coating portions of the in ⁇ terior surface of cannister 14 with surfactants. Thereafter, liquid beads do not form but generally "sheet” or form a thin layer of liquid parallel to the probe surface. Internally re ⁇ flected light is not refracted away from light probe 32. False indications of sufficient liquid level are avoided.
• Figure 6 illustrates, in exaggerated detail, thin liquid layer 52 on light probe 32. Light beam 36a is reflected at reflection points 38, 40 and light beam 36b progresses to the light detector/solenoid combination. The solenoid thereafter will open the valve allowing liquid to flow into cannister 14 until sufficient liquid level is established.
• a LEXAN ® polycarbonate material light probe of known confi ⁇ guration as disclosed in the Grimm patent was subjected to a plasma treatment.
• a plasma generator manufactured by Sorenson Research, Inc. * was used to provide the surface plasma treatment. This equipment is operated on an inductive coupled principle. Several light probes were inserted into the evacuated cylinder of this device. Operating pressures of this device were between 0.1 to 10 mm Hg. The cylinder of the device is surrounded by an aluminum coil which generated a radio frequency field at 13,5 megahertz for 1 to 3 minutes. Air was the plasma medium and is
• OMPI the preferred plasma medium; however, it is believed that other gases will deliver similar results.
• a treated light probe and an untreated light probe were observed in a humid atmosphere, that is, suspended in vapor from boiling water and thereafter submerged. No beads or droplets of aqueous liquid appeared on the unsubmerged surfaces of the treated light probe. Liquid sheeted as opposed to beaded on the unsubmerged surfaces of the treated probe. Beads of liquid appeared on the unsubmerged sur ⁇ faces of the untreated light probe. Little or no entrapment of gas bubbles was observed on submerged surfaces of the treated light probe when suspended in boiling water. Relatively sub ⁇ stantial entrapment of gas bubbles was observed on submerged surfaces of the untreated light probe suspended in boiling water.
• Corona discharge treatment was performed by using a portable, hand-held, high frequency electrode to create an ionized air at ⁇ mosphere over the surface of LEXAN ® polycarbonate material light probes.
• the electrode was brushed over the surface of individual light probes to within 1/8 inch to 1 inch allowing the spark and corona to cover the entire tip and shaft of light probe for a period ranging from 5 to 60 seconds.
• the corona discharge treatment was performed at ambient pressures, and it was performed in air; however, it is believed that other gases will deliver similar results. A treated light probe and an untreated light probe were observed in a humid
• OMPI atmosphere that is, suspended in vapor from boiling water and thereafter submerged.
• Relatively substan ⁇ tial entrapment of gas bubbles was observed on submerged surfaces of the untreated light probe suspended in boiling water.
• a LEXAN ® polycarbonate material light probe was dipped in a mixture of the following volume percentages: 10% SPAN ® 20 sur ⁇ factant and 90% isopropyl alcohol.
• the isop ⁇ opyl alcohol solvent was allowed to evaporate,
• a treated light probe and an untreated light probe separately were observed in a humid atmosphere, that is, suspended in vapor from boiling water and thereafter submerged. No beads or droplets of aqueous liquid appeared on the unsubmerged surfaces of the treated light probe. Liquid sheeted as opposed to beaded on the unsubmerged surfaces of the treated light probe. Beads of liquid appeared on the unsubmerged surfaces of the un ⁇ treated light probe. Little or no entrapment of gas bubbles was observed on submerged surfaces of the treated light probe when separately suspended in boiling water. Relatively substantial entrapment of gas bubbles was observed on submerged surfaces of the untreated light probe separately suspended in boiling water.
• a LEXAN ® polycarbonate material light probe was dipped in a mixture of the following volume percentages: 5% TWEEN ® 20 surfactant and 95% isopropyl alcohol. The isopropyl alcohol solvent was allowed to evaporate.
• a treated light probe and an untreated light probe separately were observed in a humid atmosphere, that is, suspended in vapor from boiling water and thereafter submerged. No beads or droplets of aqueous liquid appeared on the unsubmerged surfaces of the treated light probe. Liquid sheeted as opposed to beaded on the unsubmerged surfaces of the treated light probe. Beads of liquid appeared on the unsubmerged surfaces of the un ⁇ treated light probe. Little or no entrapment of gas bubbles was observed on submerged surfaces of the treated light probe when separately suspended in boiling water. Relatively substantial entrapment of gas bubbles was observed on submerged surfaces of the untreated light probe separately suspended in boiling water.
• a LEXAN ® polycarbonate material light probe was dipped in a mixture of the following volume percentages:. 5% TWEEN ® 21 sur ⁇ factant and 95% isopropyl alcohol. The isopropyl alcohol solvent was allowed to evaporate..
• a treated light probe and an untreated light probe separately were observed in a humid atmosphere, that is, suspended in vapor from boiling water and thereafter submerged. No beads or droplets of aqueous liquid appeared on the unsubmerged surfaces of the treated light probe. Liquid sheeted as opposed to beaded on the unsubmerged surfaces of the treated light probe. Beads of liquid appeared on the unsubmerged surfaces of the un- treated light probe.
• a cannister for the humidifier Into a cannister for the humidifier was dropped 0.5 cc of SPAN ® 20 surfactant. The cannister was filled with water to approximately the half full level. A cannister similarly filled with water but without surfactant therein was observed alongside the treated cannister. Little or no entrapment of gas bubbles was observed on surfaces of the light probe submerged in boiling water in the treated cannister. Relatively substantial entrapment of gas bubbles was observed on surfaces of the light probe sub- merged in boiling water in the untreated cannister.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Thermal Sciences (AREA)
• Fluid Mechanics (AREA)
• General Physics & Mathematics (AREA)
• Physical Or Chemical Processes And Apparatus (AREA)
• Apparatus For Disinfection Or Sterilisation (AREA)
• Treatments Of Macromolecular Shaped Articles (AREA)

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• 1984
  • 1984-02-24 JP JP84501210A patent/JPS60501772A/ja active Pending
  • 1984-02-24 WO PCT/US1984/000265 patent/WO1985000301A1/en not_active Application Discontinuation
  • 1984-02-24 EP EP19840901266 patent/EP0148188A4/de not_active Withdrawn
  • 1984-06-12 CA CA000456403A patent/CA1252541A/en not_active Expired

Patent Citations (5)

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