CPAP THERAPY AND EQUIPMENT
The most effective and least invasive means of treating sleep apnea is with positive airway pressure (PAP). Positive airway pressure works by keeping the airway open while a person sleeps, allowing them to breathe properly. Positive airway pressure is the treatment of choice for all patients with moderate or severe sleep apnea and for most with mild but symptomatic obstructive sleep apnea.
Under the Obstructive Sleep Apnea section of this website, we described what it is and how it affects a person who suffers from it. This portion of the site is designed to introduce the treatment of obstructive sleep apnea with positive airway pressure.
GOALS OF TREATMENT
The goals of treatment with positive airway pressure are to improve health and overall well-being. The specific objectives are to improve the quality of sleep and to reduce the number of apnea events to safe levels. Improved sleep quality usually alleviates the symptoms caused by sleep apnea. The most common symptoms of sleep apnea that improve are sleepiness and fatigue. However, PAP can also eliminate or at least improve other problems such as snoring, insomnia, lack of concentration, nighttime urination and frequent nighttime awakenings.
Treatment with PAP is known to lessen the risk of developing long-term health conditions such as hypertension, stroke, diabetes, elevated cholesterol and heart disease. Studies have shown that when the number of obstructive events are reduced to normal, the risk of these long-term complications returns to the risk of the general population without obstructive sleep apnea.
When PAP therapy has been recommended to you, remember that the objectives of treatment are to improve symptoms and to control the obstructive apnea events. PAP will improve symptoms most of the time (greater than eighty percent) and the obstructive events, almost all the time (greater than ninety-five percent).
HOW POSITIVE AIRWAY PRESSURE WORKS
Positive airway pressure is the most effective form of treatment for obstructive sleep apnea. PAP is almost universally effective at correcting the obstructive breathing events. Most sleep apnea is caused by the collapse of the throat when the muscles relax during sleep. When the air pressure in the throat is increased, collapse does not occur as the muscles relax. The pressure acts as a brace or stent and holds it open.
Positive airway pressure causes one to breathe air at a slightly higher pressure than that of room air. For the patient with sleep apnea, the pressure is usually kept at a constant level above normal atmospheric pressure. The pressurized air has to be held in place, contained by a mask of some type. To achieve this pressure, a machine forces air through a connecting tube into the mask. The masks are designed to continually leak air in a limited controlled amount. To maintain the pressure, air is forced into the system constantly. When the person inhales, the air pressure will start to drop. Then the machine will sense the change and increase the air it forces through the system to maintain the pressure at the constant level.
There are different types of air pressure systems used to treat apnea. In each system the general concepts are the same. The air pressure at the mask is set and maintained by the machine pumping air into the system. Most of the time it is constant, however, modern technology has developed equipment capable of adjusting pressures automatically.
COMPONENTS OF POSITIVE AIRWAY PRESSURE THERAPY
There are several components involved in positive airway pressure therapy: A pressure source, a humidification source, a form of interface (mask) and tubing to connect the system. The system is designed to create a small world of carefully controlled, elevated air pressure for you to breathe.
The most commonly used form of pressure source is called CPAP, or Constant Positive Airway Pressure. As its name suggests, a CPAP machine delivers a single, constant level of pressure to keep the airway open. The person using CPAP will inhale and exhale at the same pressure. Most CPAP machines can be set as low as 4cm of pressure or as high as 20cm. The amount of pressure needed to keep an airway open is usually determined during a sleep study where the positive airway pressure is gradually adjusted to a level that controls the obstructive events.
The second common pressure source is Bi-level. A Bi-level machine delivers two set levels of positive pressures. A higher pressure is delivered during inhalation, and a lower pressure during exhalation. When relatively high pressures are required to keep the obstructive apneas from occurring, a Bi-level machine allows a person to exhale more comfortably and to adapt more easily to the use of the pressure.
There are additional types of pressure sources which have been developed for very specific medical needs. These pressure machines have been designed to support breathing, not just to keep airways open and prevent apnea. These machines adopt some of the techniques employed in hospital critical care units that provide artificial ventilation to extremely ill individuals. The technique of using external air pressure to artificially breathe for a person is over fifty years old. Modifications of the positive air pressure machines with specific upgraded functions, both CPAP and Bi-level, can provide for some limited types of artificial ventilation support.
The pressures generated by the CPAP and Bi-level machines are determined by your physician and the machine is set to deliver those pressures.
Pressure Source Special Features
There are several special features available in many, if not most, pressure machines.
The most common feature is a ‘pressure ramp.’ The ramp feature allows the machine to gradually increase the pressure delivered over a period of five to forty-five minutes. This permits the person to fall asleep at a low pressure. Then it is slowly increased to the set therapeutic pressure. It is particularly helpful when someone first starts using CPAP.
‘Auto altitude adjustment’ will adjust the pressure the machine generates so that it is appropriate for the altitude were it is being used. The pressure machine is generating air pressure which is set to deliver pressure a certain level above the atmospheric pressure. The atmospheric pressure changes with the altitude, so if you travel to the mountains from the seashore, the pressure of the machine should be adjusted. All machines are manually adjustable, but the auto altitude adjustment feature makes the changes when a machine’s location and altitude changes.
‘Memory card’ options are available for many machines. The card records certain information on the machine’s performance and can be ‘read’ by your physician. The information explains how the machine is being used and what happens while it is used. It is particularly helpful if the person is having problems. The problems can often be identified and corrected from the information on the card. This may help one avoid another sleep test.
‘End exhalation pressure reduction’ is a relatively new feature that is available on some pressure machines. The machines equipped with this feature allow for a rapid, brief drop in the set pressure during exhalation. Respironics developed C-Flex™ technology, the first commercially available form of this feature. CPAP with C-Flex delivers a set pressure, such as 10cm, upon inhalation. However, the exhalation pressure may be lowered by 1, 2, or 3cm to increase patient comfort. For instance, if the CPAP setting is 10cm and the C-Flex setting is 3cm, the person will always inhale at 10cm and exhale at 7cm. ResMed has a similar product available that they call EPR™. The settings on the different machines with exhalation pressure reduction work the same, although there are some technical differences.
The second component involved in PAP therapy is the interface, also called a mask. This is the component that contains the pressurized air for the person to breathe. A single tube connects the pressure machine to the interface. The mask is designed to provide air under positive pressure by forming a seal at the nose or at both the nose and mouth. As the air is pumped under pressure to the mask, it is held under positive pressure while the person breathes. There are five basic mask designs available: the nasal mask, the nasal pillows mask, the full-face mask, the hybrid mask, and the oral mask. For each of these designs there are many different styles available.
The nasal mask covers the nose and a seal is formed against the face. An example of a nasal mask is the Respironics Comfort Gel™. The nasal pillows mask rest just inside the nostrils and create a seal at the outer edge of each nostril. The ResMed Swift II™ is an example of a nasal pillows type of mask.
There are many people who breathe through their mouths when asleep for a variety of reasons. Some may have a chronic nasal obstruction and some people have learned to breathe through their mouths as a response to sleep apnea itself. Since the mouth needs to be closed when using a nasal mask to maintain the therapeutic pressure, there are two solutions. First, a person with a nasal mask may add a chin strap to aid in keeping the mouth closed. The other alternative is to use a full-face mask. The full-face mask is designed to cover both the nose and mouth while maintaining an adequate seal. The newest type of full-face mask is a combination of mouth cushion and nasal pillows. The Fisher & Paykel FlexiFit 432™ and ResMed Liberty™ are examples of a full-face and full-face hybrid mask.
The final mask type is an oral mask. Fisher & Paykel Oracle™ is the only variety available on the market. This mask is not used very often, but may be of benefit to a person who has severe skin reactions to the materials of some masks, or who has severe airflow obstruction through the nose
Our respiratory tract has to be able to adapt to many types of air as we move from season to season and travel to many places. One major factor that affects our respiratory system is the humidity of the air we breathe. Ideally, our air would be of a constant temperature and humidity, but that just never occurs. When air is breathed through a CPAP machine, humidity can be added to the air making the positive air pressure more easily tolerated. As a result, humidifiers are available for almost all of the commercially available CPAP machines.
The addition of extra humidity to the air supplied through the CPAP machine improves the person’s ability to use positive air pressure. The units, a water reservoir and heater, are generally connected directly to the pressure source. The heater is designed to heat the water just enough to add humidity to the air. The heating scale is a simple range from ‘off’ to ‘warm.’ The setting and the ideal amount of humidity is that which the person using the system finds comfortable.
SELF REGULATING POSITIVE AIRWAY PRESSURE THERAPY
The two main types of positive airway pressure, CPAP and Bi-level, were described above. Within the categories of CPAP and Bi-level there are more specialized forms of PAP as well.
Another type of pressure therapy machine is the Auto-Titration machine. Auto-titration means that the machine will estimate and deliver the amount of pressure needed at each breath. The machine has a pressure range from low to high and it will deliver pressure at any level within that range as needed to prevent the obstructive events. The sensors in the machine are designed to identify the apnea events and adjust the pressure to correct the problems. These machines are of most value when the physician cannot determine the ideal treatment pressure.
Auto-Titration machines are available in both the CPAP and Bi-Level forms of positive airway pressure machines.