CA1070609A

CA1070609A - Tank humidifier

Info

Publication number: CA1070609A
Application number: CA259,736A
Authority: CA
Inventors: Graham C. Grant
Original assignee: Individual
Current assignee: Individual
Priority date: 1975-09-10
Filing date: 1976-08-24
Publication date: 1980-01-29
Also published as: GB1556492A; IT1078758B; FR2323436B1; NZ181807A; FR2323436A1; AU1694876A; SE7609453L; ES451369A1; JPS5235440A; AU503578B2; NL7609519A; DE2639460A1

Abstract

ABSTRACT OF THE DISCLOSURE

A humidifier tank assembly, forming part of a medical humidifier, is arranged to humidify a gas passing through it to a level substantially less than 100% saturation and at a temperature higher than that at which it is to be delivered to a patient. Subsequent cooling of the gas increases the humidification so that when the gas is delivered to the patient it is practically 100% saturated. The tank is so designed that the temperature and degree of the saturation of the gas delivered to the patient is maintained substantially constant over a wide range of gas flows. The tank is devoid of complex vapour-generating surfaces and is easy to clean.

Description

~` ~070609 This invention relates to a medical humidifier and is more specifically concerned with a humidifier tank assembly.
Tank humidifiers arè used to humidify respiratory gas fed from a medical ventilator to a patient so that the gas delivered to the patient is saturated with moisture at the temperature of the patient. The patient can then breathe the gas without his lungs being dehydrated.
As the patient may be in a critical condition it is important that the temperature of the gas supplied from the humidifier should be the same as that of the patient and that risk of the patient drowning through being fed with droplets of condensed water is eliminated.
In my British patent specificationsnumbers 1 448 473 and 1 448 474 is described and claimed a method and apparatus having certain advantages as regards safety, over prior art apparatus in that it is able to supply a patient with gas at the temperature of the patient and without risk of condensate being fed with the gas stream to the patient.
An object of this invention is the provision of a humidifier tank assembly able to maintain a gas flowing there-through at a substantîally constant level of saturation and at a substantially constant temperature, over a wide range of gas flow rates.
In a preferred embodiment of the present invention there is provided a humidifier tank assembly comprising an enclosure containing a float-controlled valve, a humidification chamber surrounding the enclosure and having an upper portion which defines a gas flow path between a gas inlet to the chamber and a gas outlet therefrom, partitioning means de-fining the enclosure and partitioning the enclosure from thechamber, means permitting fluid flow between the enclosure and the chamberl a reservoir located above the enclosure and . -- 1 --~.

~i arranged to supply liquid to a lower portion of the chamber by way of the valve and the enclosure, the valve being operable to maintain a substantially constant level of liquid within the chamber, the gas inlet being arranged to direct gas which enters the chamber downwardly toward a surface of the liquid which, under operating conditions, is within the chamber and spaced a distance below the gas inlet and outlet, and the gas flow path extending between the inlet and the outlet being free of baffles and sharp bends and being disposed about the partitioning means.
Prior art heated hose humidifiers developed by others have usually been based on the principle that the humi-dification tank should produce 100% saturation of the gas flowing through it while raising its temperature to that re-quired at the delivery end of a supply tube which is at least one metre long and is required to deliver the humidified gas to the patient.
It is recognized that medical humidifiers must be capable of being cleaned thoroughly so that they do not supply the patient with gas capable of being a source of infec-tion. It is also desirable that the humidifiers should be capable of supplying the patient with effectively 100% humidi-fied gas at the different flow rates required by the medical profession. These flow-rates can vary greatly in accordance . with the size and age of the patient in anesthesia and inten-,~ sive care.
~, A high degree of cleanliness is possible in a simple ,~i humidifier tank which can provide a certain percentage humidi-; fication of gas at a particular temperature and flow rate.
However, an increase in the flow-rate of the gas diminishes its dwell time in the humidifying chamber with the result that its percentage humidification falls as gas flow is increased.

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~07l)609 The patient is then fed with gas which is substantially less than 100% saturated. This is undesirable. For this reason, although a simple tank humidifier has the advantage of clean-liness, there are limitations imposed upon its usefulness.
These limitations can be reduced by lengthening the gas flow path through the hum;d~fying chamber by introducing baffles, and by suspending vapour generating surfaces in it. An almost 100% saturation of the gas leaving the humidifying chamber can then be achieved over a wider range of gas flows than is pos-sible with a simple tank structure. Baffles also induce tur-bulence in the gas flow path so that saturated gas adjacent the liquid is thoroughly mixed with the incoming gas to in-crease its saturation. Scrolls of blotting paper or other porous material may be placed in the water in the tank and ex-tend into the gas space in the humidifying chamber to provide the vapour generating surfaces so that the saturation of the gas by the time it leaves the tank is in the region of 100%
over a relatively wide range of gas flows. The disadvantages of such a system is that the introduction of baffles and vapour generating surfaces results in the interior of the chamber having a complicated shape which is difficult to clean and which therefore represents a possible source of dangerous infaction.
The humidifier tank assembly of the invention com-bines the advantages of both of the above prior techniques without their disadvantages. The use of a gas flow-path de-; void of baffles, vapour generating surfaces or sharp bends enables the humidifying chamber to be easily cleaned between uses ~o that it no longer represents a possible source of infection. The orientation of the gas inlet so that it dis-charges the gas entering the chamber obliquely towards the liquid surface together with the spatial separation between ~13 ~070609 the liquid surface and the gas inlet and gas outlet, in addi-tion to other factors such as the length and cross-sectional area of the gas~flow-path and it being devoid of sharp bends all help in producing a curve of percentage humidification against gas flow which is very much flatter over the useful range of gas flows than is possible with prior art humidifiers.
It is believed that this result stems from the movement of the gas through the humidifying chamber being different at differ-ent gas flow-rates.
At low gas flow-rates, the dwell time of the gas in the chamber is longer than at high flow-rates. However, it appears that the bulk of the gas flowing between the inlet and outlet travels through the chamber without contacting the sur-face of the liquid or disturbing the gas layer immediately above it. Because the gas-flow path between the inlet and the outlet is free of baffles or sharp bends there is only a small amount of turbulence occurring in it and therefore the extent of mixing of different levels of gas in the chamber is limited.
At higher gas flow-rates, the downward direction of the gas entering the chamber causes a greater proportion of it to mix with and scour away the gas layer adjacent to the water surface. This layer is the most highly saturated with water vapour in the tank. It will thus be appreciated that by suitably designing the tank assembly with particular attention being taken to the cross-sectional areas of the gas inlet and gas outlet and the cross-sectional area of the gas flow-path between them, the height of the water level in the tank under normal operating conditions, and the angle at which the in-coming gas is discharged downwardly towards the water surface, one can obtain a humidifying tank structure which is easy to clean and which will produce a substantially constant degree '~`

~ 070609 of saturation of gas flowing through it over a wide range of useful gas flows and at a range of useful temperatures.
The invention will now be described in more detail, by way of example, with reference to the accompanying drawings in which:
FIGURE 1 shows diagrammatically a humidifying tank assembly mounted on a heater stand FIGURE 2 is a vertical section through the tank assembly which is shown partially broken away and partly diagrammatic;
FIGURE 3 is a plan view of a part of the tank assembly shown in Figure 2 with its top cap and base plate moved:
FIGURE 4 is an underview of the part of the assembly shown in Figure 3; and FIGURE 5 shows the variation of relative humidity at the delivery end of a flexible tube connected be-tween the tank assembly and the patient, at con-stant delivery temperature but with widely dif~-ferent rates of gas flow.
The above figures are diagrammatic and are not to scale.
Figure 1 shows a stand 1 having feet 2 and an elec-trical socket connector 3. The stand 1 contains electrical control circuitry designed to maintain the temperature and humidity of the gas output at the desired levels. A panel 4 ; on the face of the stand has a pair of switches 5, a set of six indicating lamps 6, and a dial 7 from which the tempera-ture of the gas delivered to a patient is read. Mounted on top of stand 1 within a plate 8 is an electrical heater which is thermostatically controlled in accordance with the temper-ature of the water in a humidifying tank assembly 9 which rests on the plate 8.

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~.o70609 The tank assembly 9 is shown fitted with a gas inlet tube 11 and a humidified gas outlet tube 12 in the wall of which is embedded a coiled heater 13 and which terminates in a delivery nozzle 14 containing a temperature sensing probe 15 from which electrical leads 16 extend to the control cir-cuitry in the stand 1. Ties 18 are used to tie the leads 16 to the wall of the tube 12 between the patient and the tank assembly 9. The dissipation of the heater 13 is controlled by the electrical circuitry in the stand 1 in the manner des-cribed in detail in the above-mentioned British patent specifications.
A water temperature sensing unit 19 is mounted inside the tank assembly and has electrical leads 21 which extend out of the tank assembly 9 and into the control circuitry in the stand 1.
The tank assembly 9 is closed at its top end by a re-movable cap 22 which provides an airtight seal when closed.
The lower end of the tank assembly 9 is closed by a base plate 23 made of stainless steel and which is provided with four equally spaced turnbuckles 24.
Figure 2 shows the tank assembly in more detail. It comprises a methylpentene polymer moulding 31 providing in its upper portion a cylindrical reservoir 32 and in its lower por-tion a cylindrical enclosure 33 surrounded by an annular humi-difying chamber 34. The enclosure 33 is separated from the ; chamber 34 by a wall partition 35 which terminates above the level of the base plate 23 so as to leave a gap 36 there-between. A vertical slot 37 is provided in the partition 35 which has the same internal and external radii as the wall of the reservoir chamber 32 immediately above. A horizontal web 38 separates the enclosure 33 from the reservoir 32 and has a central port 39 for the reception of a seating (not shown) _ ~ _ of a float-controlled valve not illustrated but described in my above-mentioned patent specifications. The float which controls the release of water through the port 39 from the reservoir into the enclosure 33, is located inside the enclo-sure and floats on the water level therein which is diagram-matically indicated at 41.
The humidifying chamber 34 comprises an annulus formed between the concentrically arranged partition 35 and an outside wall 43 of the moulding. These two walls are paral-lel and the outside wall 43 terminates in an outwardly direc-ted rim flange 44 which is engaged by the four turnbuckles 24 to clamp the moulding tightly against the top face of the base plate 23. An annular groove 45 is formed in the under-side of the rim flange 44 and receives a compressible O-ring which provides a watertight seal between the base plate 23 and the flange 44. The turnbuckles can be quickly operated ~y finger pressure to enable the base plate to be detached from the moulding for cleaning. As is clear from Figure 2, when the base plate and the top cap 22 are removed, all parts of the reservoir 32, enclosure 33 and humidifying chamber 34 are readily available for cleaning.
The upper portion of the chamber 34 is defined by a ~ sloping wall portion 46 of the moulding. It is provided, at; diametrically opposite positions, with a downwardly inclined gas inlet 47 and a gas outlet 48 into which the outlet tube 12 is normally coupled. Adjacent the gas outlet 48 is a verti-cal opening 49 which is normally closed by a stopper through which the leads 21 extend to the water temperature sensing unit 19. It will be noticed that the gas inlet and outlet openings 47, 48 slope inwardly and downwardly so that gas dis-charged through the inlet 47 is deflected by the partition 35 downwardly and around the two arcuate flow paths indicated by D

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the arrows 50 in Figure 3 and which extend to the gas outlet ~8.
The top of the moulding is provided with four equi-spaced blocks 51 which provide a bayonet type fitting for the top cap 22. An annular groove 53 is provided in the top rim of the moulding to receive an O-ring providing a seal between the top cap 22 and the top of the moulding providing the reservoir wall.
The tank assembly is stored dismantled. It is assembled by fitting resiliently deformable sealing rings to the top and bottom grooves of the moulding of Figure 2 and inserting the float-controlled valve into the enclosure 33 prior to attaching the base plate 23 by means of the turn-buckles 24.
The reservoir 32 is then filled with water, a portion of which flows through the port 39 and into the enclosure 33 which, being in communication with the humidifying chamber 34 allows the water level to rise therein until the float closes the valve. The cap 22 is placed on the reservoir 32 and the assembly placed on the stand 1. The gas inlet tube 11 is fitted to the inlet 47 and the gas outlet tube 12 is fitted to the outlet 48. The bore 49 is also plugged by inserting temperature sensing unit 19.
When power is connected to the stand 1 the electrical circuitry is switched on to raise the temperature of the heater until the water in the humidification chamber has reached the desired operating temperature which is determined by the temperature sensing unit 19.
As the humidifier is operated in the way described in my above-mentioned patent specifications, the temperature of the water is raised above that required at the delivery end of the tube 12. The temperature drop through the tube 12 is ,~

controlled by the coiled heater 13 ~ ensure that by the time the gas delivered to the patient reaches the delivery end, it has cooled to the temperature of the patient and its percent-age saturation has increased.to 100~ or nearly so. The above described humidifier can operate to provide an acceptably stable level of saturation of the gas at the temperature de-sired at the gas outlet 48, over a significantly larger range of gas flows than is possible with other currently available equipment which has the same level of cleanliness.
At low rates of gas flow through the humidifying chamber, typically 1 litre per minute, the incoming gas stream is deflected downwardly and around the two parallel arcuate gas flow paths 50 around the partition 35. Because of the large cross-sectional area of the gas flow path and its free-dom from baffles, sharp corners or bends, the incoming gas tends to follow an arcuate flow-path between the inlet 47 and the outlet 48 and only a relatively small portion of the gas stream contacts the surface of the water 41 as is shown by the path bounded by the lines X - X in Figure 2. If the demand for humidified gas is more, the downward discharge of gas at the inlet 47 is at an increased velocity and therefore has a greater component in the direction of the water level 41. In consequence, the incoming gas follows the path bounded by the lines Y - Y in Figure 2, and, as is apparent from the arrows, is in contact with the surface of the water 41 for a greater part of its passage through the humidifying chamber. The amount of moisture it entrains is therefore increased which - compensates for its shorter dwell time in the humidifying chamber at the higher flow rate.
As shown in Figure 5, the above-described humidifier is able to provide gas at the delivery end of the tube 12 at a constant temperature and with a sensibly constant level of _ g _ , '~ `i .~

10706~9 saturation approaching, or at, 100% over a wide range of gas flows ranging from 1/2 litre/min. to 20 litres/min. Moreover, the operating curves are much the same if the humidifier assembly is providing gas intermittently rather than contin-uously.
It is believed that the advantages of the invention over the prior art simple tank humidifier stem from the dis-tinctive gas flow patterns which occur in the humidifying chamber at different gas flow rates. These patterns result from the absence of baffles or sharp corners in the humidi-fying chamber which could cause turbulence so that the amount of water vapour entrained in the gas is less an uncontrolled function of the rate of gas flow through the chamber. The partition wall 35 is important in this regard because from - time to time it is necessary for the float-controlled valve to -~ open to release water into the enclosure 33 from the reservoir ; 32. This is inevitably accompanied by surface waves. The partition wall 35 prevents these from reaching the chamber 34 and possiby disrupting the gas flow patterns through it in an unpredictable manner. The dimensions of the slot 37 are so small that its influence on the gas flow path between the inlet and the outlet 48 is negligible.
In an example of the apparatus described in the drawings, the moulding is transparent and has the following dimensions:
- height of gas inlet and outlet from water = 38.0 mm :
external radius of partition 35 = 48.64 mm internal radius of chamber wall 43 = 76.2 mm ' ~

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~o70609 angle between horizontal and axis of gas inlet = 60~
bore of gas inlet tube fitted to inlet = 22 mm dia.
width of slot 37 = 3.3 mm height of gap 36 = 1.57 mm radius of top corners of chamber 34:-inner corner - 4.75 mm outer corner = 4.75 mm The above-describea humidifying chamber provide~ gas at 90 - 100~ saturation over gas flow rates from 0.3 litres/
min. to 40 litres/min. under ambient temperature conditions of 10 to 30C with a gas delivery temperature of 37C at the patient. The water temperature in the humidifying chamber is maintained at about 46C which produces a gas temperature at the outlet of the chamber of 41C.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A humidifier tank assembly comprising an enclosure containing a float-controlled valve, a humidification chamber surrounding the enclosure and having an upper portion which defines a gas flow path between a gas inlet to the chamber and a gas outlet therefrom, partitioning means defining the enclo-sure and partitioning the enclosure from the chamber, means permitting fluid flow between the enclosure and the chamber, a reservoir located above the enclosure and arranged to supply liquid to a lower portion of the chamber by way of the valve and the enclosure, the valve being operable to maintain a sub-stantially constant level of liquid within the chamber, the gas inlet being arranged to direct gas which enters the chamber downwardly toward a surface of the liquid which, under operating conditions, is within the chamber and spaced a dis-tance below the gas inlet and outlet, and the gas flow path extending between the inlet and the outlet being free of baffles and sharp bends and being disposed about the parti-tioning means.

2. An assembly as claimed in claim 1, in which the chamber is cylindrical, the partitioning means is a cylindrical partition projecting concentrically downwards within the chamber and terminating at its lower end beneath the substan-tially constant liquid level therein, and the gas flow path is provided by two semi-circular passages extending around the partition between the inlet and the outlet.

3. An assembly as claimed in claim 2, in which the chamber has a detachable base which is spaced beneath the lower end of the partition.

4. An assembly as claimed in claim 3, in which the base is a metal plate clipped against the underside of the chamber wall which is provided with a groove in its rim con-taining a resiliently deformable sealing ring providing a water-tight seal between the base and the chamber wall.

5. An assembly as claimed in claim 2 in which the partition defining the enclosure and the walls defining the outer boundary of the chamber are formed from a plastics material.

6. An assembly as claimed in claim 2 in which the partition defining the enclosure, the walls defining the outer boundary of the chamber, and the reservoir are integrally moulded from a plastics material, and in which an integrally moulded apertured web separates the reservoir from the enclosure.