Obstructive sleep apnea (OSA) is common sleep disorder suffered by a large number of people. When a person who suffers from OSA has an event, the airway collapses and is blocked, primarily during inspiration. The airway may remain blocked for a few seconds to more than one minute while the person struggles to breath. The person may wake or may move to change his or her sleep position to until the blockage is opened. Severe snoring is frequently a precursor to OSA. During severe snoring, the airflow to the patient's lungs may be restricted, but not totally blocked. One treatment for OSA is the application of a continuous positive airway pressure (CPAP) to the patient's respiratory system. This is most frequently accomplished by the patient wearing a nasal mask during sleep which is connected to a source of pressurized air. When a sufficient air pressure is applied to the nasal mask, the patient's airways become sufficiently inflated and remain open for unrestricted breathing. While evaluating a patient for CPAP treatment, a clinician determines the lowest effective pressure needed for keeping the patient's airway open during sleep.
Various types of CPAP apparatus are well known in the art. The basic CPAP apparatus has a blower which is connected through a pressurized air hose to a nasal mask. The CPAP apparatus is adjusted to provide the lowest effective pressure to the patient for preventing abnormal sleep events. More sophisticated CPAP apparatus includes features such as a ramp delay which applies a reduced pressure to the nasal mask for a period while the patient falls asleep, and then gradually increases the pressure to a programmed level. The CPAP apparatus also may vary the applied pressure to gradually increase the applied pressure in response to sensed sleep events, and to gradually decrease the applied pressure when no sleep events are sensed. In a bi-level form of CPAP apparatus, an effective therapeutic pressure is applied to the nasal mask when the patient begins to inhale and the pressure is reduced when the patient begins to exhale. Bi-level apparatus can increase the comfort of CPAP therapy by reducing the work of exhaling against the therapeutic pressure, particularly for patients who require a high therapeutic pressure.
Some patients do not comply with the prescribed CPAP treatment due to mask discomfort where it contacts the face, especially at the bridge of the nose. There has been significant work by CPAP equipment manufacturers to improve mask comfort, since the mask must be worn whenever the patient is sleeping. To be effective, the mask requires a comfortable seal which will adjust to a wide differences in facial configurations of different patients. The seal also must adjust to facial changes when a user changes sleep positions. A number of different seal configurations have been used in the past. These include flexible membranes which can conform to the face and the bridge of the nose, foam filled seals, inflated seals, and seals filled with a gel type material. Each type of seal has positive and negative features.
The mask is secured to the patient with headgear which typically is in the form of straps which extend around the head. Preferably, the headgear is designed so that it is easily adjusted by the patient and is easily attached to the patient. The patient should be able to remove the mask during the night and to easily reattach the mask, for example, if the patient needs to go to the toilet. However, many mask/headgear configurations are not easy for the patient to attach and remove.