GB2192136A

GB2192136A - Humidifiers for inhalers

Info

Publication number: GB2192136A
Application number: GB08715417A
Authority: GB
Inventors: Allan Beacham
Original assignee: VIROTHERM LAB Ltd
Current assignee: VIROTHERM LAB Ltd
Priority date: 1986-07-04
Filing date: 1987-07-01
Publication date: 1988-01-06
Anticipated expiration: 2007-07-01
Also published as: DK114988D0; EP0274493A1; JPH01500088A; WO1988000068A1; DK114988A; GB2192136B; AU7647487A; GB8715417D0; AU601756B2

Abstract

The apparatus incorporates a temperature control arrangement by which air drawn through the apparatus is supplied in a heated, moist condition at or close to a critical temperature of 43 DEG C. The apparatus comprises a water chamber (6), heating means (11) for the water, means (preferably a fan 4) for drawing air over the water to an outlet (8), a face mask (15) for the outlet, and a temperature sensor (13) within the outlet adapted to control either the heating means and hence the water temperature, or the speed at which the air is drawn over the water, or both, to maintain the air at or close to a required elevated temperature. Preferably, the apparatus is designed to deliver air to the face mask (15) in a volume substantially greater than that required for breathing, and the face mask covers the nose and mouth of the user and is formed with vents (23) through which excess air together with air exhaled by the user can pass to atmosphere.

Description

SPECIFICATION Medical breathing apparatus This invention relates to breathing apparatus for medical purposes.

It has been found that humid air at around 90% relative humidity and a critical temperature of 43 C, when breathed by a patient for periods up to around 20 minutes, is effective in rendering groups ofviruses in the upper respiratory tract inactive, which re sults in the body being able to counteract colds, aller- gies, etc efficiently, and thereby reduce dramatically the patient's recovery time.

Although breathing apparatus has been proposed for such treatment, the arrangement of the apparatus, particularlythetemperature control, has not been well designed. Hence, the temperature of the heated, moist air has varied widely from the critical temperature, thereby reducing the effectiveness of the apparatus.

An object of the invention is to provide breathing apparatus incorporating an efficient temperature control arrangement by which air drawn through the apparatus is supplied to the user- in a heated, moist condition at or close to the critical temperature.

According to this invention such breathing apparatus is characterised by a water chamber, heating means for the water, means for drawing airoverthe waterto an outlet, a face maskforthe outlet, and temperature sensor means located atoradjacent said outlet adapted to control either the heating means and hence the water temperature, orthe speed at which the air is drawn over the water, or both, to maintain the air at or close to a required el- evated temperature.

Prnferably, the apparatus is designed to deliver air to the face mask in a volume substantially greater than that required for breathing, and the face mask is formed with vents through which excess airtogether with air exhaled by the user can pass to atmosphere.

Preferably the means for drawing air is a fan driven by an electric motor, which may be powered by the mains or a battery.

Conveniently, the heating means is either an electrical resistance, or positive temperature co-efficient (PTC) elements and is controlled bythetemperature sensor, and temperature adjustment is effected via an electrical control circuit, e.g. a solid state circuit, designed to regulate the power supplied to said heating means and/orto the fan motor.

In orderthatthe invention may be readily understood, four embodiments of breathing apparatus in accordance therewith will now be described, with reference to the accompanying drawings in which: - Figures land 2 are half-sectional views of the first and second embodiments, respectively, Figure 3 is an exploded perspective view ofthe third embodiment, Figure 4 is a part sectional rear view showing the interior of the third embodiment, Figure 5 is a part sectional side view ofthethird embodiment, and Figure Sis a part sectional side view ofthefourth embodiment.

Referring to Figure 1, in this embodimentthe apparatus isfree-standing and comprises a re ctangularhousing 1 which may be moulded from plastics material, eg ABS. The housing has an air inlet opening 2 leading to an inletchamber3inwhich a fan 4 driven by a motor 5 is located, a water chamber 6 in the lower part of the housing, and a mixing chamber7 leading to an outlet8which is preferably a flexible pipe to which a face mask 15 can be removablytitted.

The water chamber 6 is filled with water via a filler 9 and has an associated sight glass 10 to indicate the level of water therein. An electric resistance heating element 11 is located within the water chamber 6 and power is fed thereto from the mains or a battery, in a regulated manner, via an electric control circuit, e.g.

a solid-state printed circuit 12, in response to a temperature sensor probe 13 located in the outlet 8. The mixing chamber7 is insulated, in this embodiment by a surrounding sealed cavity wall 14which provides an air pocket, so that the temperature in the mixing chamber is substantially unaffected by external changes in temperature.

In use, ambient air is drawn into the inlet chamber via the fan 4 and isguideddownwardlytowardsthe water surface, where it passes along said surfaceto abstract heat and water droplets therefrom, thereby to heatand humidify the air. The heated, humid air then flows upwardly to collect in the mixing chamber 7 from where it is supplied, in use, to the face mask 15.

The temperature and, if required, the humidity of the air passing through the outlet 8 is sensed by an appropriate device, such as the temperature probe 13, and if the air is found to be outside a required range, e.g. a temperature range between 40 - 45 C, it initiates the control circuit 1 2to regulate the power supplied to the heating element 11 and, if desired, to the fan motor 5 so as to adjust appropriately the temperature of the water and possibly the air flow speed.

For electrical safety, and prevention of corrosion, the fan motor 5 is preferably encapsulated and operates at a low DC voltage. The circuit board 12 is also encapsulated for safety and reliability of operation in humid conditions. For additional safety, the apparatus can be powered from an external A.C. or D.C.

voltage supply using a double isolation transformer.

As mentioned hereinbefore, it is preferable to limit use of the apparatus to periods up to approximately 20 mins,forwhich an appropriate timing/alarm mechanism could conveniently be built into the apparatus.

Referring to Figure 2, the second embodiment shown therein is also free standing and like parts have been given the same reference numerals.

In this embodiment, the housing 1 is in three parts, preferably moulded from a plastics material such as ABS, and comprises a one part base 16, which incorporates the water chamber 6, and a two part cover 17, 18. The lower cover part 17 has a shaped wall 19 which carries most of the associated equipment, in cluding the fan 4 and motor5,the heating element 11,and circuit board 12.

The motor 5 is mounted on a sloping part ofthe wall 19 immediately beneath the inlet opening 2, which isformed in thetop cover part 18. The fan 4 is coupled to the motor beneath the wall 19 and draws air through openings in said wall and directs it across the surface of the water in cham ber 6 towa rds the outlet 8, which is formed in the lower cover part 17.

The heating element 11 in this embodiment is of the electric resistance type and has an aluminium shell which is encased with in a coating of PTFE to prevent oxidation of the casing and to facilitate cleaning. The element is located vertically beneath the wall 19 and is mounted at its upper end within a boss 20 formed in said wall with its terminal above the latter.

The circuit board 12, which is preferably encapsulated for safety and reliability of operation, is mounted directly above the heating element 20 and is appropriately connected to the associated equipment, including the temperature sensor 13 located within the outlet8. The apparatus can be conveni entlysited on a worktop, or floor, and the height of the face mask 15, which is designed to fit over the nose and mouth of the user, can be adjusted by one, or more, or even a telescopic extension tube 21, which is connected to the face mask via a ball joint 22 sothatthe mask can be pivoted and/or rotated to a comfortable position for the user.

It will be noted that the arrangement of the equip- ment, and in particularthe heating element, is such that all electrical connections are well above the fill level ofthe chamber6, and indeed are separated therefrom bythewall 19, thereby enhancing safety.

A pair of supports are provided in the base part 16, one (not shown) in frontof, and one 23 to the rear of, the heating element 11 as seen in the drawing. These supports ensure that the lower part ofthe heating element 11 is not damaged when the cover part 17 is removed and laid upon a work surface for cleaning orservice. Conveniently, at leastone ofthe supports incorporates a water probe over its height which, by means of an electrical connection via the circuit board 12, indicates the level of water in the chamber 6.

twill be notedthatthetwo partcover 17,18can be lifted clear of the base part 16 to provide ready access to the chamber6forfilling,whilst access to the associated equipment for repair of servicing is obtained by removing the top cover part 18.

The apparatus is designed to produce an airspeed of approximately 5 metres/sec across the water sur- face, and to retain the critical temperature of the air, the water is maintained substantially constant atan appropriate temperature depending upon the fill volume and ambient conditions, eg between 65 to 75 C. Thus, moist air is produced at or close to the critical temperature of 43 C, which is delivered at a pressure above atmospheric to the face mask (15), in a volume of approximately40 litres/min. This volume is, of course, far in excess of that required by the user and, hence, vents 22 are provided in the mask so that the excess air, together with the air ex haied by the user, can vent to atmosphere.This is important since, when air at43 C is inhaled it is cooled substantially, perhaps to around 37 C, due to vascular cooling in the bronchii. This reduced tem perature, when exhaled, could otherwise affect the constancyofthetemperatureofthe heated, moist air being produced by the apparatus. It will be appreciated that, by providing a mask 15 which covers the nose and mouth,the heated, moist air not inhaled and venting to atmosphere nevertheless acts to warm the outside of the nose and mouth and,therefore, ensures the minimum of heat dissipation aroundthis area.

Referring to Figures 3 to 5 thethird embodiment is portable and like parts are again given the same reference numerals.

In this embodiment the housing is in two parts comprising a base 24 and a cover 25.

The base 24 incorporates the water chamber 6, and most of the associated equipment including the fan 4 which isinclinedtodirectairtowardsthechamber6, motor 5, heating element 11, and circuit board 12.

The cover 25 incorporates a baffle wall 26 to guide air from the fan towards and over the water surface in the chamber 6 into the mixing area 7 and outlet 8 to the face mask 15.

As shown in Figures 3 to 5, the apparatus is prov- ided with a wedge shaped front wall to provide stability when placed upright on a worktop. In this position, the user would tend to press his mouth and nose down into the face mask 15 as shown in dashed outline "x" in Figure 5. However, in most cases,the user would probably press the face mask manually against his nose and mouth and perhaps strap it in place. For this, it would be more comfortable forthe userto adopt the position shown in dotted outline "y". To caterforthesedifferent user positions, the face mask 15 is pivotally mounted to the top ofthe cover 25so that it can rotate from the position shown in solid lines in FigureS to the position shown chain dotted.

Referring again to Figure 4, in more detail, the heating element 11 comprises a number of positive temperature co-efficient (PTC) elements 27 spaced across the bottom wall of the chamber 6 which are regulated to operate at a working temperature which will maintain the water at an appropriate temperature, eg approximately 80 C, depending upon the normal fill volume of water used inthechamber6 and ambient conditions. Thefill level line "z" forthe apparatus is controlled by an overflow pipe 28which can drain into the sealed air space provided around the chamber 6 for insulation.This water can be subsequently removed via a drain plug 28a.Because of the relatively high temperature required for the heating element, safety is extremely important, and PTC elements are especially advantageous since they are inherently safe against overheating. However, if a conventional electrical resistance element such as described for the first and second embodiments is used, athermal cut-out would be included in the heating element to prevent overheating. In either case a thermal cut-out could be used in the circuit board 12 for additional safety.

The circuit board 12 is solid state and preferably encapsulated for reliability of operation. It would be designed to include the following control features: a) a water level sensing circuit including water sensing probes 29, b) a temperature control sub-circuit, for con- trolling the temperature of the heating element 11, and hence the water temperature, in dependence upon the water level sensed, and/or for adjusting the fan speed, and hence the airflow over the water sur- face. This control circuit is preferably in the form of a proportional band, zero voltage switch for providing pulsed or continuous voltage to the heating element so asto provide accurate control and to reducethe possibility of electrical interference in use.

c) a comparator sub-circuit for com paring the output resistance from the sensor 13, which is preferably a thermistor with a basic pre-set value, this subcircuit being connected to the temperature control sub-circuitfor providing a correcting signal forfinely adjusting the watertemperature, or fan speed.

d) a mercury tilt switch connected so as to cut-off powerto the heating element 11 if the apparatus moves beyond a predetermined angle from its upright position so as to ensure electrical safety.

To reduce to a minimum the possibility of scalding the user shou Id the apparatus fall over, an anti-spill cover 30 (see Figure3) is provided for the water chamber 6 having sloping front and rear side walls 31,32 to act as adam to retain the water.

Referring to Figure 6, this embodiment is also of a convenientdesignto be portable. It comprises an elongatetubular housing 1 which, in use, is orientated to be generally upright. The housing comprises an upper end portion 33 and a lower end portion 34 of smaller dimensions, enabling it to be conveniently held by the hands of the user. The motor 5 is supported centrally within the portion 34, to leave an air passage around it (as shown), above the air inlet opening 2, which is defined bythe bottom of the casing 1. The fan 4 is mounted abovethe motor nearthe junction between the portions 33 and 34. The water chamber 6 is supported centrally within the portion 33to leave an air passage around it (as shown), the water chamber having a suitable heating element 11 associated therewith.Aface mask 15 is mounted on the top of the portion 33, which would be generally as described above with reference to the third embodiment, and the temperature sensor 13 isapp- ropriately located therein. The circuit board 17 is mounted in a convenient position, e.g. as shown.

In use, as shown by the arrows, air is drawn up wardlythrough the opening 2 and through the air passages around the motor Sand tank 6, whereafter it is deflected by sloping walls 34 defining the face mask 15 across the water in thetank 6 and then upwardlythrough an outlet8to pass into and through the face mask. As described in respect oftheforego- ing embodiments, the heated, moist, air delivered to thefacemasklSisin avolumefargreaterthanbody requirements and the excess airwould be vented to atmosphere.

Claims

1. Breathing apparatus incorporating a temperature control arrangement by which air drawn through the apparatus is Supplied in a heated moist condition, characterised by a water chamber, heating means for the water, means for drawing air over thewaterto an outlet, a face maskforthe outlet, and temperature sensor means located at or adjacent said outlet adapted to control either the heating means and hence the watertemperature, orthe speed at which the air is drawn over the water, or both, to maintain the air at orcloseto a required elevated temperature.

2. Breathing apparatus according to Claim 1, characterised in that said apparatus is designed to deliver air to the face mask in a volume substantially greater than that required for breathing, and in that the face mask is formed with vents through which excessairtogetherwith air exhaled by the user can pass to atmosphere.

3. Breathing apparatus according to Claim 1 or 2, characterised in that the means for drawing air over the water delivers said airto the outlet at a pressure above atmospheric.

4. Breathing apparatus according to any one of Claims 1 to 3, characterised in that the face mask is designed to coverthe nose and mouth of the user.

5. Breathing apparatus according to any one of Claims 1 to 4, characterised in that the means for drawing air is a fan driven by an electric motor.

6. Breathing apparatus according to any one of Claims 1 to 5, characterised in that the heating means is either an electrical resistance, or positive temperature co-efficient (PTC) elements, in that the heating element is controlled by the temperature sensor, and in thattemperature adjustment is effected via an electrical control circuit, designed to regulate the power supplied to said heating means and orto the fan motor.

7. Breathing apparatus according to Claim 6, characterised in that the electrical control circuit includes a temperature control sub-circuit for con trolling the temperature of the heating element in de pendence upon the water level sensed, and/or for adjusting the fan speed, and a comparatorsub circuitfor comparing the output from thetemperature sensor with a pre-setvalve and providing a correcting signal to the temperature control sub circuitforfinely adjusting the watertemperature, of fan speed.

8. Breathing apparatus according to any one of Claims 1 to 7, and which is designed to be portable, characterised in that the face mask is pivotally moun ted to the outlet to enable the user to tilt the mask in relation to the body of the apparatus into a comfortable position.

9. Breathing apparatus according to any one of Claims 1 or8, and which is designed to be portable, characterised in that the water chamber is provided with an anti-spill cover having sloping walls which act as a dam to prevent egress of water should the apparatus fall over.

10. Breathing apparatus according to Claim 9 characterised in that the electrical circuit includes a tilt switch connected to cut-off power to said heating element if the apparatus moves beyond a predetermined angle from its upright position.

11. Breathing apparatus according to any one of Claims 1 to 5, characterised in that the housing is of elongatetubularform and is intended to be used in a generally upright condition with the air inlet opening at the bottom and the face mask at the top of the housing, in thatthe motor, fan and watertankare located at spaced positions within the housing to leave air passages through the housing, and in that air is drawn through the length of the housing and deflected over the water in the water tank before passing through an outlet into the face mask.

12. Breathing apparatus constructed, arranged and adapted for use substantially as hereinbefore described with reference to, and as shown in, Figure 1,2, to 5 or 6 of the accompanying drawings.