Surgery – Diagnostic testing – Respiratory
Reexamination Certificate
1999-08-02
2002-06-04
Casler, Brian L. (Department: 3737)
Surgery
Diagnostic testing
Respiratory
C600S484000, C128S204180, C128S207180, C128S204230
Reexamination Certificate
active
06398739
ABSTRACT:
BACKGROUND OF THE INVENTION
A particular application of the present invention is to the diagnosis and/or treatment of snoring and sleep apnea. Sleep apnea is characterized by complete occlusion of the upper airway passage during sleep while snoring is characterized by partial occlusion. Obstructive sleep apnea sufferers repeatedly choke on their tongue and soft palate throughout an entire sleep period resulting in lowered arterial blood oxygen levels and poor quality of sleep. It should be realized that although the following specification discusses sleep apnea in detail, the present invention also applies to the diagnosis and treatment of other forms of upper airway disorders.
Reference to international patent publication WO 82/03548 will show that the application of continuous positive airway pressure (CPAP) has been used as a means of treating the occurrence of obstructive sleep apnea. The patient is connected to a positive pressure air supply by means of a nose mask or nasal prongs. The air supply breathed by the patient, is at all times, at slightly greater than atmospheric pressure. For example, gauge pressures will typically be within the range of 2 cm to 25 cm. It has been found that the application of continuous positive airway pressure provides what can be described as a “pneumatic splint”, supporting and stabilizing the upper airway and thus eliminating the occurrence of upper airway occlusions. It is effective in eliminating both snoring and obstructive sleep apnea and in many cases, is effective in treating central and mixed apnea.
The airway pressure required for effective CPAP therapy differs from patient to patient. In order to discover the airway pressure which is most effective for a particular individual, the practice has been for the patient to undergo two sleep studies at an appropriate observation facility such as a hospital, clinic or laboratory. The first night is spent observing the patient in sleep and recording selected parameters such as oxygen saturation, chest wall and abdominal movement, air flow, expired CO
2
, ECG, EEG, EMG and eye movement. This information can be interpreted to diagnose the nature of the sleeping disorder and confirm the presence or absence of apnea and where present, the frequency and duration of apneic episodes and extent and duration of associated oxygen desaturation. Apneas can be identified as obstructive, central or mixed. The second night is spent with the patient undergoing nasal CPAP therapy. When apnea is observed the CPAP setting is increased to prevent the apnea. The pressure setting at the end of the sleep period, i.e., the maximum used, is deemed to be the appropriate setting for that patient. For a given patient in a given physical condition there will be found different minimum pressures for various stages of sleep in order to prevent occlusions. Furthermore, these various pressure will, in fact, vary from day to day depending upon the patient's physical condition, for example, nasal congestion, general tiredness, effects of drugs such as alcohol, as well as their sleeping posture. Thus the appropriate pressure found in the laboratory is necessarily the maximum of all these minimum pressures for that particular night and is not necessarily the ideal pressure for all occasions nor for every night. It will generally be higher than necessary for most of the night.
Also patients must be able to operate a CPAP system to deliver appropriate airway pressure at their home where their general physical condition state of health may be quite different to that in the sleep clinic, and will certainly vary from day to day. The patient's physical condition often improves due to CPAP therapy. It is often the case that after a period of therapy the necessary airway pressure can be reduced by some amount while preventing the occurrence of obstructive sleep apnea. However, the prior art provides no facility to take advantage of this fact other than by regular diagnostic sleep periods in a sleep clinic or hospital.
The long term effects of CPAP therapy are unknown so it is desirable to keep the airway pressure as low as practicable, particularly if a patient requires long term treatment. Lower airway pressures also result in a lower face mask pressure which is generally more comfortable for the patient. It has been found that CPAP induces patients to swallow and this inducement to swallow can be reduced by lowering the airway pressure. This it is desirable to use the lowest practicable airway pressure that is effective in preventing airway occlusion during CPAP therapy for the comfort and, possibly, the long term safety of the patient. Also, a lower airway pressure requires less energy consumption and a less complex and therefore less expensive apparatus which is generally quieter.
Low airway pressures are also desirable before and during the early stage of each sleep period as the increased comfort of an initially lower airway pressure allows the patient to more easily fall asleep. When a patient undergoing CPPA opens his mouth with pressurized air being forced through the nose the pressured air exits out of the mouth producing an unpleasant sensation. This can occur when the patient puts on the mask connected to the pressured air supply before falling a sleep and some patients will therefore leave the mask off for as long as possible and may in fact fall asleep without wearing the mask and therefore without the benefits of the CPAP therapy.
Presently available CPAP units do not address this problem and so there is a need to provide a CPAP device which will b, more acceptable to the patient before and during initial sleep by operating at an initially low pressure but automatically increasing to an appropriate therapeutic pressure before apnea occurs.
In addition to the problems associated with administering CPAP therapy there exists the inconvenience and cost of diagnosis which is currently undertaken by overnight observation at a sleep clinic or the like. Hence a simple means whereby a patient's apnea problem can be diagnosed at home without supervision is clearly desirable as well as a CPAP device which will deliver a continuously minimum appropriate pressure for substantially the entire period of therapy.
Devices are available to detect apnea. For example, International Patent publication WO/86/05965 discloses an apparatus which includes acoustic respiration sensors, background sound sensors and movement sensors. Such apparatus are capable of detecting breathing sounds, comparing those sounds with body movements and background noises and by further comparing the results with a data base of information, to indicate whether the patient is undergoing a normal or abnormal breathing pattern. Such apparatus can sound an alarm on the occurrence of apnea.
Another device which could be readily adapted to detect and record the occurrence of apneic episodes is disclosed in U.S. Pat. No. 4,537,190. That apparatus is responsive to the CO
2
levels in exhaled air during respiration and is also responsive to the absence of respiration (i.e., apnea) in which case it can switch on a ventilator.
These devices are deficient in that they do not take advantage of the indication of apnea obtained exclusively from a recording from a single sound transducer (microphone) preferably located in the CPAP nose mask or prongs that can be interpreted by a skilled physician. The sound transducer, in its most general form, consists of a pressure transducer which, in addition to detecting snoring sounds, can detect other respiratory para such as the rate of breathing, inhaled air flow inhaled air flow rate. The inherent simplicity of this form of measurement makes it safe and practicable for anybody to use in their own home with a minimum of prior instruction.
Although diagnosis in a sleep clinic as outlined above is beneficial, it has some deficiencies. A patient is likely not to sleep in a fully relaxed state in an unfamiliar environment and a single night is insufficient to obtain a pressure setting that will be optimal in the long run. Thu
Lynch Christopher
Sullivan Colin E.
Casler Brian L.
Pillsbury & Winthrop LLP
ResMed Limited
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