Such breathing masks are used especially to supply a patient with oxygen, the feed port being connected to a breathing gas supply and especially to an oxygen supply, which has an inhalation valve, which controls a flow of breathing gas into the cavity and which is designed such that it will open when the pressure in the cavity is below the pressure prevailing in the breathing gas supply by a preset value. A gas or oxygen bag, which is, in turn, connected to the oxygen supply, is usually provided in this case in the breathing gas supply. The oxygen bag is thus used as a buffer, and it is not necessary for the oxygen supply to provide such a large volume flow as this would be necessary during the inhalation phase, when the patient is breathing in. It is rather sufficient for the oxygen supply to provide a volume flow that corresponds to the time average of the patient's oxygen intake.
In addition, an exhalation valve is provided in the breathing mask, and this valve opens when a pressure that is higher than the ambient pressure builds up in the interior of the cavity during the exhalation phase. The exhalation valve is consequently designed such that it only allows a flow from the cavity to the outside, i.e., a higher pressure must prevail in the cavity than in the surrounding area.
Such breathing masks, which have only an exhalation valve in conjunction with an inhalation valve in the breathing gas supply, have the drawback that there is a risk that the patient will not be sufficiently supplied with breathing gas when the volume flow of the breathing gas supply is lower than the patient's demand or fails to materialize altogether. It may happen in such a situation that the volume present in the oxygen bag is consumed by the patient and the patient will then no longer be supplied with more breathing gas.
To avoid this problem, it is known from EP 1 854 494 B1 that an emergency breathing valve is also provided besides the inhalation valve and the exhalation valve. The emergency breathing valve provides for a connection between the cavity and the area surrounding the breathing mask and is designed such that it only opens when a pressure that is lower than the pressure at which the inhalation valve would already open prevails in the cavity of the breathing mask. This causes the emergency breathing valve to open only when the patient is no longer receiving breathing gas from the breathing gas supply during the inhalation phase and a lower pressure is therefore building up in the cavity than is necessary to open the inhalation valve.
The valve body, which closes or opens the inhalation valve, the valve body, which closes or opens the exhalation valve, and the valve body of the emergency breathing valve are made in one piece from a flat, flexible material in the design described on EP 1 854 494 B1, on which the present invention is based. However, this is associated with the drawback that the pressure thresholds at which the inhalation valve and the emergency breathing valve open and which must be coordinated with one another can be set with highly insufficient precision only.