Abstract:
A device is provided for increasing humidity for respirating patients, especially for a respiration humidifier or an anesthesia reflector. The device includes a gas channel for passing through breathing air, a control and/or regulating device, a temperature sensor and a dew sensor for measuring the humidity present in the breathing air by electromagnetic radiation with a generating device and with a detection device for electromagnetic radiation. The humidity of the breathing air is determined at a low cost and in a reliable manner and condensation is avoided in the respiration system without any additional effort for sterilization. Humidity in the breathing air is determined by the a dew sensor by the change in the reflection of the electromagnetic radiation as a function of dew formation at a condensation-fogged and condensation-free boundary surface between breathing air and a medium having an optical density higher than that of breathing air.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2008 001 022.7 filed Apr. 7, 2008, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention pertains to a device for respirating (also known as ventilating) patients, especially a respiration humidifier or anesthesia reflector. The present invention pertains, furthermore, to a process for controlling and/or regulating the humidity of breathing air in a device for respirating patients. 
     BACKGROUND OF THE INVENTION 
     Respiration humidifiers are necessary during the artificial respiration of patients, in whom the function of the nose is bridged over by a tube. The inspired air must therefore be humidified and optionally heated to physiological values during artificial respiration to preserve the lung function. 
     Inhalative sedation or anesthesia of patients is necessary for various medical applications, e.g., during surgery. Anesthesia reflectors are used to transfer the anesthetic from the expiration gas breathed out by the patient to the inspiration gas to be breathed in by the patient (reflection) and thus to make multiple utilization possible and not to increase the concentration of anesthetic in the room in which the patient is located. Furthermore, the anesthesia reflector shall humidify and optionally heat the inspired air to physiological values. 
     Humidity sensors are used in respiration humidifiers and anesthesia reflectors in order to determine the humidity in the breathing air, i.e., the inspired gas and/or the expired gas. The data measured by the humidity sensors are used to control and regulate the humidity of the breathing air. 
     The use of humidity sensors with inexpensive measurement methods, e.g., a capacitive humidity measurement, is too inaccurate. The use of the dew point-mirror principle of measurement is too expensive for application in respiration humidifiers. Such sensors are, moreover, arranged in the breathing air, i.e., in a gas channel or a humidifying chamber, so that there are bacteriological problems. 
     U.S. Pat. No. 5,468,961 shows a humidity sensor for a device for respirating patients. Breathing air, whose humidity is to be determined, is sent through a sample cell. An infrared light source generates infrared light, which is sent through the sample cell and is subsequently detected by a detector. The humidity contained in the breathing air absorbs the infrared light, so that the quantity of infrared light detected by the detector decreases with increasing humidity in the breathing air and vice versa. The manufacture of the infrared light source, detector as well as sample cell is expensive. Furthermore, complicated means are needed to avoid the condensation of water on the inner surface of the sample cell. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is therefore to make available a device for respirating (ventilating) patients and a process for controlling and/or regulating the humidity of breathing air in a device for respirating patients, in which the humidity of the breathing air can be determined at a low cost and in a reliable manner. Furthermore, the device for respirating patients shall not cause any additional effort for sterilization. 
     This object is accomplished with a device for respirating patients, especially with a respiration humidifier or with an anesthesia reflector, comprising means for increasing the humidity and/or the anesthetic concentration in breathing air, at least one gas channel for passing through breathing air, a control and/or regulating means, at least one temperature sensor and at least one dew sensor for measuring the humidity contained in the breathing air with a generating means and with a detection means for electromagnetic radiation, wherein the at least one dew sensor determines a change in the reflection of the electromagnetic radiation at a boundary surface between breathing air and a medium having an optical density higher than that of air as an indicator of a change in dew formation at said boundary surface. 
     The degree of reflection of the electromagnetic radiation is affected as a function of dew formation. The boundary surface may be fogged with water of condensation or free from water of condensation. 
     In another embodiment, the denser medium is a solid. Solids can be easily installed in tubes and housings. In addition, humidity can lead to water vapor readily condensing on solids. 
     In an additional embodiment, the denser medium is glass or a plastic transparent to electromagnetic radiation, e.g., Plexiglas. The electromagnetic radiation can thus be introduced into the medium having a higher optical density on a first side. The boundary surface, on which humidity can be deposited, is located on a second side of the medium having a higher optical density. The first and second sides are preferably located opposite each other. The medium having the higher density can thus be easily installed in tubes and/or housings. Furthermore, a transmitting and receiving diode can be detachably fastened to the medium having the higher density, e.g., glass or Plexiglas, on the first side. 
     The electromagnetic radiation is preferably light. 
     In another embodiment, the boundary surface is arranged at the means for increasing the concentration of humidity and/or anesthetic in the breathing air. 
     In another variant, the boundary surface is an inner side of the at least one gas channel for passing through breathing air. 
     The solid is advantageously heatable by means of a heater preferably integrated in the solid. The water condensed on the solid because of a high humidity in the breathing air causes the electromagnetic radiation to be always reflected only partially at the boundary surface and to also be refracted, so that the dew sensor always measures a high humidity, even though the humidity in the breathing air may already have dropped again. The water of condensation is briefly evaporated with the heater. The solid preferably has a low mass, so that the solid cools rapidly after heating, and, in particular, the breathing air contributes to rapid cooling of the solid. The electromagnetic radiation is again reflected totally and is not refracted at the boundary surface after evaporation of the water of condensation on the solid and after cooling of the solid. High humidity can again be measured in the breathing air because condensation of water on the solid brings about a change in the degree of reflection of the electromagnetic radiation. 
     Additional sensors for other parameters, e.g., temperature, CO 2  or breathing gas volume, are arranged at the at least one dew sensor in an additional embodiment. 
     The additional sensors and the at least one dew sensor are preferably integrated in a sensor block. As a result, the sensors can be attached in a compact form, e.g., to a tube or housing. 
     In another embodiment, the solid of the medium having the higher density is designed as a sample holder and/or a wall of at least one gas channel or of a housing of the means for increasing the humidity and/or the anesthetic concentration in breathing air. The solid thus forms part of the wall of the gas channel or of the housing, so that no additional body has to be arranged in the area through which the breathing air flows. 
     A process according to the present invention for controlling and/or regulating the humidity of breathing air in a device for respirating patients has the following steps: Measurement of the humidity contained in the breathing air by means of at least one dew sensor, analysis of the data determined by the at least one dew sensor and control and/or regulation of the humidity in the breathing air on the basis of the data measured by the at least one dew sensor, wherein the detection of the humidity in the breathing air is carried out with the steps of generating an electromagnetic radiation, especially light; sending the electromagnetic radiation to a boundary surface between breathing air and a medium having an optical density higher than that of breathing air; at least partial reflection of the electromagnetic radiation at the boundary surface; detection of the electromagnetic radiation reflected at the boundary surface only; and analysis of the quantity of reflected electromagnetic radiation to determine the humidity in the breathing air. 
     In another embodiment, the medium having a higher density is a solid, especially glass or a plastic more transparent to electromagnetic radiation, e.g., Plexiglas. 
     In another variant, the humidity is increased in the breathing air until the humidity reaches a limit value. The limit value is, in general, a relative humidity of 100% or nearly 100%. The breathing air as an inspiration gas is said to have normally a relative humidity of about 100%. 
     In particular, the humidity in the breathing air is increased until a reduction in the reflection of the electromagnetic radiation occurs because of the formation of water of condensation on the surface of the solid. 
     In an additional embodiment, the solid is heated during the formation of water of condensation on the surface of the solid in order to evaporate the water of condensation. 
     The humidity in the breathing air is preferably reduced when a limit value of the humidity in the breathing air is reached. 
     In another variant, the humidity in the breathing air is reduced when the reflection of the electromagnetic radiation decreases because of the formation of water of condensation on the surface of the solid. A reduction in humidity is normally necessary when water of condensation forms on the medium having a higher density, especially glass or Plexiglas. The raising or lowering of the humidity makes it possible to regulate the humidity in the breathing air in the range of 100% relative humidity. 
     The raising or reduction of humidity in the breathing air is advantageously achieved by increasing or reducing the temperature in a humidifying chamber of a respiration humidifier or the heating power supplied. 
     Six exemplary embodiments of the present invention will be described in greater detail below with reference to the drawings attached. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a schematic section of a dew sensor arranged in a gas channel; 
         FIG. 2  is a schematic section of a humidifying chamber of a respiration humidifier with a dew sensor arranged at an outlet pipe; 
         FIG. 3  is a schematic section of the humidifying chamber of the respiration humidifier with a sensor block with the dew sensor arranged at the outlet pipe; 
         FIG. 4  is a schematic section of the respiration humidifier with a dew sensor arranged at an inspiration tube and with a liquid dispensing unit; 
         FIG. 5  is a schematic section of an anesthesia reflector with a dew sensor arranged at the inspiration tube; and 
         FIG. 6  is a schematic section of the respiration humidifier with a dew sensor arranged at an inspiration tube. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in particular,  FIG. 1  shows a section of an optical dew sensor  7 , which is arranged at a gas channel  4  designed as an inspiration or expiration tube  16 ,  17 . A sample holder and/or a wall  11  made of glass  10 , i.e., a solid  9 , is formed at the gas channel  4 . A generating means for electromagnetic radiation  18 , designed as a transmitting diode  19 , generates a light beam  22 , which is sent to and through the wall  11 . The light beam  22  is reflected at a boundary surface  12  between the wall  11  as the medium  8  with a higher optical density and the breathing air flowing in the gas channel  4  as the medium with the lower optical density and subsequently detected by a detection means for electromagnetic radiation  20 , which is designed as a receiving diode  21 . 
     The light beam  22  is reflected at the boundary surface  12  according to the law of reflection with an angle of incidence equal to the reflection angle. The angle of incidence is preferably selected to be such that the light beam  22  is totally reflected and the angle of incidence thus corresponds to the critical angle of the total reflection. According to the Snellius law of refraction, the light beam  22  can also be refracted at the boundary surface  12 , and the refracted light beam  22  (not shown) is not detected by the receiving diode  21 . 
     Humidity is contained in the breathing air being sent through the gas channel  4 . The humidity present in the air condenses at high relative humidity of the air in the breathing air, especially in the range of 100%, and precipitates on the wall  11  and hence at the optical boundary surface  12  in the form of water drops or a water film. The condensed water present at the boundary surface  12  changes the refractive index, so that the light beam  22  is no longer reflected totally at the boundary surface  12  but is partially refracted as well. Thus, only the partially reflected light beam  22  is detected by the receiving diode  21 . The optical change in the reflection of the light beam  22  is thus detected by the receiving diode  21  and transmitted to a control and/or regulating unit  5 . The change in the reflection of the light beam at the boundary surface  12  is an indicator of a change in dew formation at this boundary surface  12  and hence of the humidity in the breathing air in the gas channel  4 . The control and/or regulating unit  5  analyzes the data of the receiving diode  21  and thus determines the humidity in the breathing air or a limit value of the humidity in the breathing air. The dew sensor  7  is thus an optical dew sensor. The transmitting and receiving diodes  19 ,  21  are arranged in a sensor housing  23 . The sensor housing  23  can be easily attached to and removed from the gas channel  4  when the inspiration or expiration tube  16 ,  17  is replaced. Only the wall  11  remains as a window in the tube  16 ,  17  in order to prevent cross contamination between different patients. 
       FIGS. 2 and 3  show two different possibilities of arrangement of the dew sensor  7  at the humidifying chamber  24  with water  27  of a respiration humidifier  2 . An inlet pipe  25  and an outlet pipe  26  are formed at the humidifying chamber  24 . The outlet pipe  26  is manufactured with a wall  11 , in which a window  29  is formed for coupling with the dew sensor  7 . The sensor housing  23  with the transmitting and receiving diodes  19 ,  21  is detachably fastened to the wall  11  ( FIG. 2 ). In addition, a sensor  13  for the concentration of CO 2  and a sensor  14  for the breathing gas volume flowing in as well as a temperature sensor  6  can be integrated in the sensor housing  23 , so that a sensor block  15  is present ( FIG. 3 ). Furthermore, the dew sensor  7  may also be installed analogously in the inspiration or expiration tube  16 ,  17  ( FIG. 4 ). 
       FIG. 4  shows a schematic section of the respiration humidifier  2  with a dew sensor  7  arranged at the inspiration tube  16  and with a liquid dispensing unit  31 . The liquid dispensing unit  31  is controlled and/or regulated by a control and regulating unit  5 , which dispenses a defined quantity of liquid necessary for humidifying the breathing air. The breathing air to be humidified flows for this through an inlet pipe  25  into the humidifying chamber  24  and leaves same through an outlet pipe  26 . A sensor  14  for measuring the breathing gas volume flow (breathing gas volume per unit of time) (not shown) may be optionally provided at the inlet pipe  25 . Water  27  can be fed into the humidifying chamber  24  from a container  30  by means of the liquid dispensing unit  31 , and the water  27  evaporates from a heater  28  arranged in the humidifying chamber  24 . The temperature of the heater  28  is adjusted to a constant value. A temperature sensor  6  each is arranged at the outlet pipe  26  and at the end of the inspiration tube  16 . Furthermore, the dew sensor  7  is positioned at the end of the inspiration tube  16 . The two temperature sensors  6 , the dew sensor  7 , heater  28  for the water  27 , the tube heater  32  and the dispensing unit  31  are connected to a control and regulating unit  5 , so that the data detected by the sensors  6  and  7  can be transmitted for analysis to the control and regulating unit  5 . The dispensing unit  31 , the heater  28  and the tube heater  32  can be controlled and/or regulated by the control and regulating unit  5 , corresponding to the values determined for dew formation at the boundary surface  12  of the dew sensor  7 , the water  27  is dispensed by the liquid dispensing unit  31 . The humidity of the breathing gas is thus regulated by regulating the quantity of water  27  that is fed to the heater  28  via the liquid dispensing unit  31 . 
       FIG. 5  shows an anesthesia reflector  3 . The inspiration gas as the breathing air to be breathed in is sent through the inspiration tube  16  and through a Y-piece  34  to a patient. The breathing air breathed out by the patient is sent as expiration gas through the expiration tube  17  to a reflector unit  33  for anesthetic. The anesthetic is reflected onto the inspiration gas in the reflector unit  33  and the inspiration gas is humidified. The inspiration gas is sent through the reflector unit  33  before it flows through the inspiration tube  16 . A temperature sensor  6  each and a dew sensor  7  each are arranged in the reflector unit  33  and at the end of the inspiration tube  16  in the area of the Y-piece  34 . The inspiration tube  16  can be heated by means of a tube heater  32 . A heater  28  for the reflector unit  33  makes it possible to heat the reflector unit  33  as well. 
     The two temperature and dew sensors  6 ,  7 , heater  28  for the reflector unit  33  and the tube heater  32  are connected to a control and regulating device  5  for analysis. The heater  28  and the tube heater  32  can be controlled and/or regulated by the control and regulating unit  5 . Condensation is to be avoided in the anesthesia reflector  2  in the inspiration tube  16  and in the reflector unit  33 . 
     When the anesthesia reflector  3  is switched on, the inspiration gas is at first heated with heater  28  until the temperature sensor  6  arranged in the reflector unit  33  detects a preset temperature. At the same time, the actual value of the inspiration temperature is detected at the end of the inspiration tube  16  by the temperature sensor  6  arranged there and the set point of the inspiration temperature is controlled and/or regulated by means of the tube heater  32 . As soon as dew formation is detected at one of the two dew sensors  7 , the set point of the preset temperature of the breathing air is reduced at the temperature sensor  6  of the reflector unit  33  by the heating output of the tube heater  32  being reduced. This is carried out until dew formation declines or no dew formation occurs any longer. If no dew formation is detected any longer, the preset temperature of the breathing air is slightly raised at the temperature sensor  6  of the reflector unit  33 . This operation is carried out in a control loop, so that the heating output of heater  28  and/or of the tube heater  32  is regulated around the dew point at the two dew sensors  7 . The heating output of the heater  28  and/or of the tube heater  32  is thus controlled and/or regulated by means of the control and/or regulating unit  5  such that dew formation is avoided or maintained at a low level in the inspiration tube  16  as well as preferably also in the expiration tube  17  and in the reflector unit  33 . 
       FIG. 6  shows a respiration humidifier  2  with the humidifying chamber  24  and with a heater  28  for the humidifying chamber  24 . The breathing air to be humidified flows through an inlet pipe  25  into the humidifying chamber  24  containing water  27  and leaves same through an outlet pipe  26 . The water can be heated with the heater  28  and the relative and absolute humidity in the inspiration gas flowing through the outlet pipe  26 , which inspiration gas is sent to the patient through an inspiration tube, can thus be controlled and/or regulated. A temperature sensor  6  each is arranged at the outlet pipe  26  and at the end of the inspiration tube  16 . Furthermore, the dew sensor  7  is positioned at the end of the inspiration tube  16 . The inspiration tube  16  can be heated by a tube heater  32 . The two temperature sensors  6 , dew sensor  7 , heater  28  for the water  27  and the tube heater  32  are connected to a control and regulating unit  5 , so that the data detected by the sensors  6 ,  7  can be transmitted to the control and regulating unit  5  for analysis. The heater  28  and the tube heater  32  can be controlled and/or regulated by the control and regulating unit  5 . The heater  28  and hence the evaporation of the water  27  are regulated corresponding to the values determined for the dew formation at the boundary surface  12  of the dew sensor  7 . The heating output of the heater  28  and/or of the tube heater  32  is thus controlled and/or regulated by means of the control and/or regulating unit  5  such that dew formation is avoided or maintained at a low level in the inspiration tube  16  as well as preferably also in the expiration tube  17  and in the reflector unit  33 . 
     On the whole, considerable advantages are associated with the device  1  for respirating patients. The dew sensor  7  can measure dew formation with certainty and reliably and it can be manufactured at a low cost. Cross infection is not possible, because the wall  11  remains at the tubes  16 ,  17  when a tube  16 ,  17  is replaced and the sensor housing  23  with the transmitting and receiving diodes  19 ,  21  can be easily attached to another tube  16 ,  17  with a corresponding wall  11 . 
     The optical measurement method has the advantage that no cables need to be used inside the tube  16 ,  17 . Furthermore, condensation can be avoided in the respiration system. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. 
     APPENDIX 
     List of Reference Numbers 
     
         
           1  Device for respirating patients 
           2  Respiration humidifier 
           3  Anesthesia reflector 
           4  Gas channel 
           5  Control and/or regulating unit 
           6  Temperature sensor 
           7  Dew sensor 
           8  Medium with the higher optical density 
           9  Solid 
           10  Glass 
           11  Wall 
           12  Boundary surface 
           13  Sensor for CO 2  measurement 
           15  Sensor block 
           16  Inspiration tube 
           17  Expiration tube 
           18  Generating means for electromagnetic radiation 
           19  Transmitting diode 
           20  Detection means for electromagnetic radiation 
           21  Receiving diode 
           22  Light beam 
           23  Sensor housing of the dew sensor 
           24  Humidifying chamber 
           25  Inlet pipe 
           26  Outlet pipe 
           27  Water 
           28  Heater 
           29  Window 
           30  Tank 
           31  Liquid dispensing unit 
           32  Tube heater 
           33  Reflector unit for anesthetic 
         Y-piece