Patent ID: 12194245

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A breathing assistance apparatus and method of controlling a breathing assistance apparatus is detailed below. Particularly, the breathing assistance apparatus is controlled such that it has a drying cycle to enable drying of the tubing that supplies gases to a user and prevent the harbouring of pathogens within the tube. The drying cycle is preferably operated automatically by internal controllers in the apparatus. However, it may be manually activated by pressing a button on the apparatus. The drying cycle is preferably activated at the end of a patient's treatment session.

The breathing assistance apparatus of the present invention is intended to typically deliver body temperature saturated gases (37.degree. C. and 44 mg/L) over a range of flows that could provide up to a patient's inspiratory flow requirements (that is, peak inspiratory flow) plus any bias flow requirement.

The breathing assistance apparatus operates as a flow controlled device, so it adjusts the flow of gases to the level set by the patient or user, such as a care giver. Therefore, this apparatus can be used to deliver humidified gas for patients with bypassed airways, such as tracheotomies or nasal cannula or masks.

Whether used in a hospital environment or in a home care environment, the breathing assistance apparatus of the present invention will generally have associated with it a gases supply means, such as ambient air, gases, such as oxygen from cylinders or other compressed gas supply, humidification means and a transport conduit from the humidification means to the patient, which is preferably heated to reduce condensation.

A heating element is preferably provided within the transport conduit to help prevent condensation of the humidified gases within the conduit. Such condensation is due to the temperature of the walls of the conduit being lower than to the dew point of the gases inside the conduit, which is usually lower than the temperature of the humidified gases within the conduit. The heating element effectively replaces the energy lost from the gases through conduction and convection during transit through the conduit and the patient interface. Thus the conduit heating element ensures the gases delivered are at an optimal temperature and humidity for patient treatment and to minimise condensation within the transport conduit and the patient interface.

The present invention provides a breathing assistance apparatus where the flow of gases passes in sequence through a gases supply means or flow driver (such as, a blower, fan or compressor), humidification chamber, heated delivery circuit and patient interface, such as that shown inFIG.1.

With reference toFIG.1the humidification apparatus of the present invention is shown in which a patient1is receiving humidified and pressurised gases through a nasal cannula20connected to a humidified gases transportation pathway or inspiratory conduit3that in turn is connected to a humidifier8(including humidification chamber5) that is supplied with gases from a blower15or other appropriate gases supply means. The inspiratory conduit3is connected to the outlet4of a humidification chamber5which contains a volume of water6. Inspiratory conduit3contains heating means or heater wires11that heat the walls of the conduit to reduce condensation of humidified gases within the conduit and the patient interface (e.g. nasal cannula20). The humidification chamber5is preferably formed from a plastics material and may have a highly heat conductive base (for example an aluminium base) which is in direct contact with a heater plate7of humidifier8. The humidifier8is provided with control means or electronic controller9which may comprise a microprocessor based controller executing computer software commands stored in associated memory.

Gases flowing through the inspiratory conduit3are passed to the patient by way of a patient interface20. The patient interface used with the apparatus of the present invention may be a full-face mask, nasal mask, nasal cannula, oral mouthpiece or tracheostomy connection.

Controller9receives input from sources such as user input means or dial10through which a user of the device may, for example, set a predetermined required value (preset value) of humidity or temperature of the gases supplied to patient1. In response to the user set humidity or temperature value input via dial (or buttons)10and other possible inputs such as internal sensors that sense gases flow or temperature, or by parameters calculated in the controller, controller9determines when (or to what level) to energise heater plate7to heat the water6within humidification chamber5. As the volume of water6within humidification chamber5is heated, water vapour begins to fill the volume of the chamber above the water's surface and is passed out of the humidification chamber5outlet4with the flow of gases (for example air) provided from a gases supply means or blower15which enters the chamber5through inlet16. It should be noted that it is possible to obtain the relationship between the humidity of the gases in humidification chamber5and the temperature of the heater plate7. Accordingly, it is possible to utilise the heater plate temperature in an algorithm or a look-up table to determine the humidity of the gases.

It is also possible to measure the chamber outlet gases temperature from the humidification chamber5using a temperature sensor12and use this to determine the humidity of the gases in the chamber5and conduit3.

The blower15may be provided with a variable speed pump or fan2which draws air or other gases through the blower inlet17. The speed of variable speed pump or fan2may be controlled by a further control means or electronic controller18(or alternatively the function of this controller18could be carried out by the other controller9) in response to inputs from controller9and a user set predetermined required value (preset value) of pressure or fan speed via dial19.

In the preferred embodiment shown inFIG.2the breathing assistance apparatus of the present invention the gases supply or blower is combined in one housing with the humidifier and humidification chamber. The humidification chamber35extends out from the housing30and is capable in use of being removed and replaced by the patient or other user. Also, the inlet port (not shown) to the humidification chamber35is internal within the housing30. The inlet31to the housing30where gases are drawn from the ambient air outside the housing30is located at the end of the housing30, but in actuality may be located at any appropriate point in the housing30. The gases exit from the humidification chamber35at the outlet33and water within the chamber35is heated by a heater plate36, similar to that described above. It must be appreciated that the embodiment described above in relation to the housing andFIG.2merely illustrates one form of the housing of the combined gases supply and humidifier of the present invention.

In one preferred form of the apparatus of the present invention, a nasal cannula20is used as the patient interface. The initial connection of a patient1to a blower and humidifier is an obstacle to patient compliance and negates a patient's comfort and tolerance due to the high pressure supply of gases through the cannula. Therefore, it would be advantageous if the gases flow was slowly increased to the patient, allowing their body time to adjust to the temperature, sensation of flow, and pressure in their nasopharynx. This slow increase in flow may be over a considerable time, such as 30 minutes, allowing the patient to slowly adjust to the therapy instead of feeling overwhelmed with the sudden delivery to the nasal passage, of up to 40 L/min of saturated gases.

As discussed earlier, high flows of non-humidified gases delivered to the patients airways causes dehydration and inflammation of the airways and nasal passages. At low flows (such as 5 litres per minute) a lower level of humidity is adequate. Because an active pass-over humidifier8holds a humidification chamber5which contains a volume of water6, this water has a large thermal mass and takes time to heat up enough to provide adequate humidity at high flows.

Warm Up Mode

The blower15may be controlled by a controller (18or9) such that on start-up or commencement of therapy by the patient1the flow rate of gases exiting the blower15is initially supplied as a low flow.

Under the warm up mode the aim is to deliver optimal gas to the patient. To do this, it is necessary to warm up the gases in the chamber as quickly as possible to a set value, most preferably 37.degree. C. As the temperature of the gases at the chamber outlet are measured by a sensor this is the temperature that is to be controlled to the set temperature value. In this way the patient is supplied with an optimal temperature of gases as soon as possible. This is achieved by; turning on the heater plate7to full heating output, providing a low flow of gases through the humidification chamber5and controlling the wall temperature of the heated conduit3to avoid condensation. When the gases temperature in the humidification chamber5reaches the set temperature the gases flow is increased to the predetermined therapy flow as fast as possible, while maintaining the gases temperature in the chamber at the set temperature. The increasing of the gases flow is performed by controlling (increasing) the speed of the fan21in the blower15. Alternatively, when the water chamber gases reach the set temperature the flow is increased to the target or predetermined flow for the therapy. As soon as the gases temperature in the water chamber recovers to approximately the set temperature, for example, 35.degree. C., a signal is given by the controller that the patient can now wear the interface.

As an example, gases flow is increased from the initial low flow (flow.sub.initial) to a flow that is optimal (flow.sub.opt) for the therapy being provided. It is preferred that the maximum or optimum flow level (flow.sub.opt) is selectable by the user or care provider by way of dial19. In this case, the controller18or9would control the flow rate, by controlling the fan21speed so that the gases flow is initially at a low flow rate of, for example, 5 L/min. Alternatively, the gases flow could be switched on for, for example, 1 to 15 seconds, at a low flow of, for example, 5 L/min to allow the temperature and humidity readings to be taken. Then the gases flow would be switched off for a period of time, for example, 5 to 60 seconds, to allow the humidity in the chamber to rise quicker.

Once the temperature the gases exiting the humidifier chamber reaches 37.degree. C. (the set temperature), the flow of the gases is ramped up over a predetermined time, for example, 30 minutes, to an optimum flow level (flow.sub.opt) of between 15 to 40 L/min, as selected by the patient.

The above sequence of events enables the humidity in the breathing circuit to reach the desired level as quickly as possible while minimising condensation and/or thermal overshoot.

Drying Mode

To overcome the problem of any condensation left in the conduit3or in the patient interface20at the end of a therapy treatment session, the breathing assistance apparatus of the present invention provides a mode or cycle of drying out the conduit3and potentially the interface20. This is carried out by providing a turn off process that facilitates the drying of the conduit3and the patient interface20.

A drying mode is critical in minimising the risk of pathogen transport via the conduit3and interface20to the patient1. A drying mode also ensures there will be no condensation left in the conduit or patient interface after a treatment session and in a next treatment session. Condensation can cause gurgling noises and surges in airflow at the beginning of the next humidification session making treatment uncomfortable for the patient.

Generally, the aim of the drying mode is to ensure the humidity of the gases in the chamber and conduit are at or below the ambient levels the apparatus is operating in. This is achieved by cooling the water in the humidification chamber5, while continuing to heat the conduit3and the interface20to a temperature that exceeds the chamber outlet gases temperature. This is continued until the humidifier water temperature and temperature of the gases at the chamber outlet reach or approximate room temperature. As the thermal mass of the water in the chamber5exceeds the thermal mass of the plastic walls of the conduit3, condensation may occur if the humidifier8and the blower fan21are turned off at the same time. To ensure this does not occur, at the end of treatment it is preferred that the heater plate7is turned off but power is maintained to a heater wire11in the conduit3.

The humidification means, humidifier8, is controlled by the control means (controller9or18) at the completion of a patient's treatment. Therefore, when the patient selects “off”, a button on the apparatus, or the controller detects the end of a therapy session, effectively only the heater plate7is powered down by the controller (9or18) and the humidification apparatus is placed in a drying mode. During the drying mode, it is preferred that power is maintained to the heater wire11and the gases supply means or blower15. As an example, the gases flow through the humidifier8and conduit3is a flow, such as 20 litres per minute for a period of time, for example 15 minutes, which will ensure the conduit has dried inside. The gases flow may be a fixed gases flow or pulses of gases flow.

A temperature sensor13is preferably provided at the end of the conduit, nearest the patient. This end of conduit temperature sensor13is connected to the controller9,18. The end of conduit sensor13may be used to optimise drying of the conduit3by ensuring the gases at the end of the breathing circuit are at the maximum safe operating temperature, so that the temperature of the gases does not obtain a level that might burn a patient or user.

Preferably it might be optimal to start at a low gases flow and then at a later stage increase the gases flow.

In some forms of the present invention the conduit may not include a heater wire. In this situation the controller would merely control the blower15, such that gases and not heat from the heater wire within the conduit alone would dry the conduit.

Deactivation of Drying Mode

The point in time that the drying mode is deactivated may be determined by a number of methods. The first of which is to measure the temperature of gases at the chamber outlet4. When the temperature of the gases at the chamber outlet4drops below or equals ambient temperature (which is preferably measured by an additional temperature sensor, for example, located at the blower15but connected to one of the controllers9,18) the blower15and heater wire11are powered off by the controller9,18. In this way gases flow through the humidification chamber6and as the heater plate7cools the humidity of the gases flowing through the conduit3reduces and the conduit3becomes drier.

A second method for determining when the drying mode is to be deactivated by the controller9,18is to turn off the power to the humidification chamber5and maintain a gases flow through the conduit3at a fixed speed or pulses and maintain power in the heater wire11to evaporate any condensate off the walls of the conduit3. After a predetermined time, preferably in excess of one minute, the heater wire11and flow source (blower) would be switched off.

Yet another method of controlling the drying of the conduit is to switch the gases supply (blower) off and switch off the power to the heater plate power. The controller9,18would then compare the heater plate7temperature with an ambient temperature that is measured either inside or outside the humidifier or blower (as previously described). When this temperature difference or comparison is within a predetermined limit, which typically approximates zero, a flow of gases is caused to flow in the same manner as described above.

It is possible that it could take longer to dry the condensate in the conduit than to cool the chamber. In this instance it may be necessary to extend the drying mode for some time, for example, up to 30 minutes depending on the ambient temperature of the water remaining in the chamber.

Alternative Methods of Activation of Drying Mode

It has been described that the drying mode is activated by the patient selecting or pressing an “off” button. An alternative method of activating the drying mode is to detect the patient1removing the interface20. This may be, for example, by detecting an increase in the flow from the blower due to decreased resistance at the patient interface at the end of a humidification session. After a predetermined time period has elapsed, which is long enough to ensure the patient does not put the interface back on, the drying mode is commenced.

As a further alternative method the time at which the patient stops breathing into the patient interface20may be detected. This may be detected by monitoring for a breathing pattern, for example using a flow sensor on the patient interface or in the blower. Once no breathing is found and after waiting a predetermined time period the drying mode is commenced.

In order for the apparatus to be fully powered down a user or patient must disconnect the apparatus from the electrical power supply or for example, hold a switch or power button down on the humidifier or blower for a period of time, for example, 5 seconds.