Abstract:
A humidifier for producing humidified air, particularly for use with a continuous positive air pressure device. The humidifier has an air inlet and outlet. An elongate passageway extending between the air inlet and the air outlet. The passageway is adapted to be partially filled with water so that air passing along the passageway becomes humidified as it passes over the water from the air inlet to the air outlet.

Description:
This is a continuation of application Ser. No. 08/918,004, filed on Aug. 25, 1997, now U.S. Pat. No. 6,135,432, which is a File Wrapper Continuation of U.S. Ser. No. 08/633,413 filed Jun. 10, 1996, now abandoned, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The invention relates to a humidifier for producing humidified air, and particularly, although not exclusively, to a humidifier for use with a Continuous Positive Airway Pressure (CPAP) device. 
     A CPAP device is used in the treatment of obstructive sleep apnea syndrome, which is a disorder characterised by cycles of snoring, obstruction of the upper airway, and partial awakening during the night. In order to treat obstructive sleep apnea, a CPAP device can be used to deliver air under continuous positive pressure to the nasal passages of the patient during sleep. The positive air pressure prevents obstruction of the upper airway so that the patient is not troubled by frequent awakenings during sleep. 
     In order to prevent drying of the patient&#39;s airway during use of a CPAP device, it is known to pass the air through a humidifier before supplying the air to the patient. Humidification can be achieved by simply passing the air over an area of water within a humidifier so that the air absorbs moisture from the water before being delivered to the patient. 
     When a humidifier is used with a CPAP device, it is convenient to be able to place the CPAP device on top of the humidifier. In this case, it is desirable that the humidifier is designed so as to form a low, generally flat base for supporting the CPAP device. Such a humidifier is known as a low-profile humidifier. Because a low-profile humidifier is of low height, it is more likely to suffer from the problem of entrainment of water droplets in the output air flow to the patient. This problem arises because as the air passes through the humidifier it induces waves on the surface of the water, and water droplets are stripped from the waves by the air flow, and carried by the air flow to the outlet of the humidifier. It is also important when designing a low-profile humidifier to ensure that maximum use is made of the available water surface area. For example, there is no point in providing a large surface area of water within the humidifier if the air flow passes over only a small portion of this area. 
     The present invention has arisen from attempts to overcome the above difficulties, but is not limited to low-profile humidifiers, or to humidifiers for use with CPAP devices. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided a humidifier for producing humidified air, comprising an air inlet for receiving air to be humidified, an air outlet for discharging humidified air, and an elongate passageway, extending between the air inlet and air outlet, for directing air from the air inlet to the air outlet, the passageway being adapted to be partially filled with water so that air passing along the passageway becomes humidified as it passes over the water from the air inlet to the air outlet. 
     The use of an elongate passageway between the air inlet and outlet ensures that the airflow passes over substantially the whole of the surface area of the water, so that the whole of the surface area of the water contributes towards humidifying the air flow. 
     Preferably, the passageway is arranged so as to direct the air from the air inlet to the air outlet along a single path. 
     This feature ensures that each portion of the surface area of the water contributes equally to the humidifying of the air flow. In an arrangement where the air flow can take a number of different paths between the air inlet and the air outlet, there is a danger that certain paths will contribute more greatly to the humidifying process than others, for example because the air is flowing at different speeds along different paths. Such an arrangement does not make maximum use of the available water surface area. 
     In a preferred embodiment of the invention, the passageway is divided into a plurality of elongate subpassageways and corner portions, each subpassageway being substantially straight, and the subpassageways being connected end to end along the length of the passageway by the corner portions. 
     The subpassageways can be integrally formed with the corner portions, so that the passageway as a whole is integrally formed. 
     This feature avoids the possibility of leaks which might otherwise occur at the connections between the subpassageways and corner portions. 
     One or more of the corner portions can be generally U-shaped, so that the two subpassageways adjacent the or each generally U-shaped corner portion lie side by side, and substantially parallel with each other. 
     For example, if the passageway is divided into two, three or four subpassageways, the subpassageways can be arranged to form U-, S- or W-shaped serpentine passageways respectively. 
     It will be appreciated that the use of generally U-shaped corner portions enables the humidifier to be of compact construction, since the subpassageways lie side by side. This allows a greater number of subpassageways to be accommodated within a humidifier of a given size. 
     Preferably, the passageway is provided with at least one generally U-shaped corner portion which bulges outwardly at the inside side of the corner defined by the corner portion so as to force air passing through the corner portion outwardly towards the outside side of the corner defined by the corner portion. 
     This feature ensures that substantially the whole of the surface area of the water in the corner portion is used for humidifying the air flow. 
     The last corner portion through which air passes before reaching the air outlet will be referred to below simply as “the last corner portion”. 
     Desirably, the last corner portion, whether or not generally U-shaped, increases in width as it passes from the penultimate subpassageway to the last passageway. 
     It should be understood that the word “width” used above is intended to refer to the dimension of the passageway which lies generally in the plane defined by the surface of the water, and perpendicular to the direction of the air flow along the passageway. Furthermore, the “last” subpassageway is the last passageway through which air in the humidifier passes before reaching the air outlet. The advantage of increasing the width of the passageway at the last corner portion is that it reduces the amount of turbulence in the air flow at the corner portion. It should be noted that most of the air turbulence within the passageway is created at the corner portions, and this turbulence is particularly acute in the case of U-shaped corner portions. The air turbulence creates waves on the water surface which can result in entrainment of water droplets in the air flow at the air outlet, or, if the waves are large enough, indirect spillage of water into the air outlet. By reducing the air turbulence at the last corner portion, the chances of water spillage, or entrainment of water droplets, at the air outlet are greatly reduced. 
     Preferably, the width of the last corner portion increases gradually as the last corner portion passes from the penultimate subpassageway to the last subpassageway. 
     Such a gradual increase causes a greater reduction in air turbulence at the corner portion. 
     In one embodiment of the invention, the ratio of the width of the last corner portion at its inlet side to its width at its outlet side is 9:10. 
     Preferably, the upper wall, or roof, of the last subpassageway rises gradually along the length of the last subpassageway, towards the air outlet, so as to allow the air outlet to be positioned at a greater height above the water within the last subpassageway. 
     The gradual increase in height of the roof of the last subpassageway results in a smooth air flow and less air turbulence. 
     Ideally, the roof of the last subpassageway rises gradually along substantially the whole length of the last subpassageway,. 
     Similarly, the roof of the first subpassageway may rise gradually along the length of the first subpassageway, towards the air inlet, in the same manner as the roof of the last subpassageway. 
     In a preferred embodiment of the invention, the passageway terminates at an end wall adjacent the air outlet, and the air outlet is arranged so that it communicates with the interior of the passageway at a location which is spaced away from said end wall. 
     When the air flow within the passageway creates waves on the surface of the water, it has been found that the water has a tendency to splash against the end wall of the passageway, resulting in a danger of water spilling into the air outlet. It has been found that by spacing the air outlet aperture away from the end wall, the danger of water spilling into the air outlet is greatly reduced. 
     In a second aspect of the invention there is provided a humidifier for producing humidified air, comprising a chamber adapted to be partially filled with water, the chamber being provided with an air inlet for receiving air to be humidified, and an air outlet for discharging humidified air from the chamber after the air has passed over said water, wherein the air outlet is arranged so that it communicates with the interior of the chamber at a location which is spaced away from all of the chamber walls. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention will now be described, by a way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a W-shaped humidifier formed from a transparent material; and 
     FIG. 2 is a side view showing the outlet attachment of the humidifier in greater detail. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, the humidifier  1  comprises a W-shaped elongate passageway  2 , an air inlet  4  and an air outlet  6 . The humidifier is integrally formed by an extrusion blow-moulding process from translucent, polycarbonate material. During use, the humidifier is partially filled with water, and a use of the translucent material enables the operator to see the water level within the passageway  2  at all times. Furthermore, the integral construction of the humidifier avoids the possibility of leaks of air and water from within the humidifier. 
     The humidifier is a low-profile humidifier, and is of generally flat, rectangular, box-like construction. The upper and lower walls  8  and  10  of the humidifier are pinched together along a central strip  12  and two outer strips  14  so as to define the shape of the passageway  2 . The central strip  12  extends to the rear wall  16  of the humidifier, and the outer strips  14  extend to the front wall  18  of the humidifier, so as to define a generally W-shaped passageway  2  which comprises four subpassageways  20 ,  22 ,  24 , and  26 . The central strip  12  and the two outer strips  14  also provide the humidifier with increased structural rigidity. 
     The four subpassageways  20 ,  22 ,  24 , and  26  are each of generally straight, elongate construction. The first subpassageway  20  is connected to the second subpassageway  22  by a first corner portion  28 ; the second subpassageway  22  is connected to the third (or penultimate) subpassageway  24  by a central corner portion  30 ; and the third subpassageway  24  is connected to the fourth (or last) subpassageway  26  by a last corner portion  32 . All of the corner portions are generally U-shaped, so that the four subpassageways  20 ,  22 ,  24 , and  26  lie side by side and generally parallel with each other. 
     The central strip  12  bulges gradually as the central strip  12  passes towards the front wall  18  of the humidifier, to form an enlarged end portion  34  which defines the shape of the inside side of the central corner portion  30 . The shape of the enlarged portion  34  ensures that air passing through the central corner portion  30  is forced outwardly towards the corner regions  36  of the central corner portion  30 , so that maximum use is made of the available water surface area within the central corner portion  30 . 
     The width of the last corner portion  32  increases gradually from the third subpassageway  24  to the fourth subpassageway  26 . For example, the dimensions labelled a, b and c in the drawing can be 40 mm, 45 mm, and 50 mm respectively. The increase in width of the last corner portion  32  reduces air turbulence within the last corner portion  32 , and hence reduces the entrainment of water droplets in the air flow, and reduces spillage of water into the air outlet  6 . 
     The roofs  38  and  40  of the first and fourth subpassageways  20  and  26  respectively, rise gradually from the first and last corner portions  28  and  32  to the air inlet  4  and the air outlet  6  respectively. This allows the air inlet  4  and the air outlet  6  to be raised in position with respect to the second and third subpassageways  22  and  24 , so that spillage of water into the air inlet  4  or air outlet  6  is less likely to occur. A further advantage of raising the roofs  38  and  40  with respect of the second and third subpassageways  22  and  24  is that a natural hollow or recess  41  is formed between the first and fourth subpassageways  20  and  26 . The recess  41  is shaped so as to be of complementary shape to the underside of a CPAP device so that the CPAP device (not shown) fits snuggly on top of the humidifier. It should also be noted that the humidifier is of symmetrical construction, so as to reduce the risk of malfunction, or injury to a patient, if the user should accidentally mistake the air inlet for the air outlet and vice versa. 
     As shown in FIG. 2, the air outlet  6  is formed as an outlet attachment  42  which is attached to a circular tube  44  which projects outwardly from the end wall  46  of the fourth subpassageway  26 . The outlet attachment  42  is provided with a tube  48  which projects through the circular tube  44  and into the fourth subpassageway  26 , the tube  44  being gripped between the outer surface of the tube  48  and the inner surface of an outer skirt portion  49 . The tube  48  extends along a portion of the length of the fourth subpassageway  26 . This ensures that air can only leave the fourth subpassageway  26  via the circular aperture  50  at the end of the tube  48 , which aperture  50  is spaced away from the end wall  46 . 
     When water waves are formed within the fourth subpassageway  26 , the waves have a particular tendency to splash against the end wall  46 , resulting in the danger of water spilling into the air outlet  6 . It has been found that spacing the aperture  50  of the air outlet  6  away from the end wall  46  overcomes this problem since the water is less turbulent away from the end wall  46 . The aperture  50  should preferably be spaced at least 2 cm away from the end wall  46 . 
     It should be appreciated that the idea of spacing the outlet aperture, in this case the aperture  50  of the tube  48 , away from the walls of the humidifier is of general applicability, and may be used in other humidifiers, regardless of whether the humidifiers are formed with elongate passageways.