What is a CPAP/BiPAP Machine?

CPAP and BiPAP machines perform similar but different functions, but both use a mask connected by a tube to the machine, which pumps and circulates the air.    

CPAP, or Continuous Positive Airway Pressure, is the most common treatment for obstructive sleep apnea. These devices use air pressure to keep the airway open and prevent it from collapsing as an individual sleeps.   

BiPAP machines, or Bilevel Positive Airway Pressure, is a variation on the CPAP treatment. BiPAP machines deliver air at two alternating pressures: the inspiratory positive airway pressure (IPAP) supports a breath as it’s taken in, while expiratory positive airway pressure (EPAP) is delivered at a lower level and allows the individual to breathe out.   

CPAP or BiPAP - Which is the Right Choice?

Sleep is universal; everyone sleeps.

While it’s true that many people don’t get enough sleep because of overwork, stress, school obligations, and social schedules, others may be staying in bed long enough but, in fact, aren’t getting the quality of sleep necessary to maintain health. Sleep apnea is a common condition affecting millions of people in this country and worldwide. Many people suffer from it but don’t even know that they have it.

Before we talk about the different types of mechanical treatments for sleep apnea – CPAP, APAP, BiPAP, and ASV machines – a bit of background on sleep apnea is necessary. (You can find a more in-depth treatment of sleep apnea elsewhere on this website.)

Sleep Apnea – a Thief of Breath in Three Disguises

A person suffering from severe sleep apnea stops breathing periodically during the night – not once or twice, but dozens of times an hour, hundreds of times each night. Even moderate sleep apnea can significantly disrupt sleep and prevent the patient from getting the rest they need.

The most common type is obstructive sleep apnea, in which the tongue, soft palate, and other structures in the upper airway collapse and restrict the space through which air flows. Usually, this blockage results in loud snoring, which can be symptomatic of obstructive sleep apnea.

A less prevalent type of sleep apnea is so-called central sleep apnea, characterized by the brain failing to send appropriate signals to the muscles required for breathing.

A third type of sleep apnea, complex sleep apnea (sometimes abbreviated CompSA so as to not be confused with central sleep apnea), is a combination of obstructive sleep apnea and central sleep apnea. Complex sleep apnea has only been recognized by sleep medicine practitioners as an independent diagnostic entity since 2006.

Obstructive sleep apnea is by a large measure the most common type of sleep apnea. The study that led to the classification of complex sleep apnea as a distinct condition found that 84% of the patients involved had obstructive sleep apnea, 15% suffered from complex sleep apnea, and only 0.4% were afflicted with central sleep apnea.

Sometimes, sleep apnea is caused by underlying conditions like chronic nasal congestion or congestive heart failure. If that is the case, ameliorating the underlying condition may effectively resolve the sleep apnea. Far more often, however, the sleep apnea itself must be the focus of treatment.

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Positive Airway Pressure Therapy – Treatment for Sleep Apnea

By far, the most common and effective treatment for sleep apnea is positive airway pressure (PAP). PAP therapy utilizes a machine to keep air in the patient’s upper airway (for simplicity’s sake, think nasal passages and throat above the vocal cords) at a higher-than-normal pressure. Picture a support system of timbers in a mine shaft preventing the shaft from caving in on itself. Positive airway pressure acts as a kind of pneumatic support system for the throat and soft palate, keeping the upper airway structure from collapsing and impeding airflow.

All of the machines we’ll be discussing utilize some form of positive airway pressure, but they do so in different ways. And the type of sleep apnea is important because the type dictates the treatment. A medical professional sleep specialist will determine both the kind of sleep apnea and the appropriate treatment regimen through a sleep study.

Air Delivery – Full-Face or Nasal Mask – Measuring Pressure

All PAP machines deliver air to the patient using a hose attached to the machine on one end and a mask worn by the patient on the other. The mask can be a nasal mask that covers the nostrils only or a full-face mask that encompasses the patient’s nose and mouth. Usually, when a nasal mask is worn, a chin strap or some other method needs to be used to prevent the mouth from opening during sleep, thereby ensuring that the patient breathes only pressurized air being delivered through the nasal mask.

A full-face mask doesn’t require any additional mechanism for keeping the mouth closed. Some patients, however, find the full-face mask confining to the point of claustrophobia and prefer the smaller nasal mask.

The amount of pressure that a PAP machine delivers is measured in centimeters of water or cmH2O, signifying how far up a column of water will be elevated by a given pressure. Exactly why that measurement is used is a matter of some mystery, but it is the standard unit of measure for medical ventilators and respirators, as well as PAP machines. In more familiar terms, one cmH2O is equal to 2.05 pounds per square foot. For an additional frame of reference, recall that normal air pressure on earth at sea level is 14.7 pounds per square inch.

CPAP and BiPAP – Different Treatments for Different Conditions

The difference between CPAP machines and BiPAP machines is that a CPAP machine delivers air to the patient at a continuous, single, level pressure, while a BiPAP machine varies the air pressure depending upon whether the patient is breathing in or out. A BiPAP machine is set to deliver air at two different pressures: a higher inhalation positive airway pressure and a lower exhalation positive airway pressure.

Continuous positive airway pressure, or CPAP, is the treatment of choice for obstructive sleep apnea. A CPAP machine delivers a steady, constant singular pressure of air to the patient’s airway, whether the patient is inhaling or exhaling. The maximum pressure that a CPAP machine can deliver is 20 cmH2O, although most are set in the neighborhood of 12-14 cmH2O.

Bi-level positive airway pressure, or BiPAP, is the treatment for central sleep apnea and sometimes complex sleep apnea. Also, if a patient simply can’t withstand the struggle of exhaling against the relentless pressure of their CPAP machine, a BiPAP machine offers the option of a fixed, lower exhalation positive airway pressure. As we’ll see in a minute, this inability to tolerate the constant singular pressure of the CPAP machine may have to be confirmed in a sleep study.

Additionally, some sleep apnea patients require additional oxygenation because of the nature of their condition. The sleep specialist can set a BiPAP machine to deliver up to 25 cmH2O during the inhalation cycle, five cmH2O higher than is available with a CPAP machine. BiPAP is also used to treat more esoteric sleep disorders such as obesity hypoventilation syndrome, COPD (chronic obstructive pulmonary disease) overlap syndrome, and others.

Some CPAP devices feature a function that automatically lowers the pressure somewhat during exhalation. These are sometimes called APAP (automatic positive airway pressure) or VPAP (variable positive airway pressure) machines. While these might sound like BiPAP machines, the exhalation pressure adjustment is “sensed” by the machine and is an automatic, mechanical response. On the other hand, the BiPAP machine utilizes two distinct pressures determined by the sleep medicine specialist for optimum therapeutic effect.

Other Differences Between CPAP and BiPAP

Another thing a BiPAP machine can do that a CPAP machine cannot is prompt the patient to breathe utilizing a “spontaneous timed mode” of operation. This can be especially important in central sleep apnea and some complex sleep apnea cases, in which part of the problem is a disconnect between the central nervous system and the musculature responsible for respiration.

Even if the patient suffers from what otherwise might be considered relatively moderate sleep apnea, the neurological malfunction is troublesome and requires medical intervention. The sleep specialist sets the BiPAP machine to a threshold criterion of breaths per minute (the spontaneous timed mode setting). If the patient’s respiration falls below that level, the device kicks in and prompts the patient to breathe. In this way, the BiPAP machine regulates not only the volume of air getting to the patient using the inhalation position airway pressure and exhalation position airway pressure settings but also the consistency and frequency of inhalation and exhalation.

It’s important to note that neither BiPAP machines nor CPAP machines are ventilators; they do not breathe for the patient. Rather, in the spontaneous timed mode, the BiPAP device prompts the patient to breathe on their own.

A Significant Difference in Price

All positive airway pressure devices require a doctor’s prescription. As you might expect, given the more complicated nature of a BiPAP machine, BiPAP devices are substantially more expensive than CPAP devices. Not only do they incorporate two independent systems for regulating and timing respirations, essentially doubling the mechanical complexity involved, but the continual variation in pressures requires more durable materials.  

While the price of a CPAP machine may range from around $500 to $1000 or more, depending upon its features, a patient can expect to pay between $1500 and $2000 for a BiPAP device, although many sites reflect retail prices up to $4000 or more.  

As a result of the significant price differential, if insurance is involved in the purchase process for the apparatus, the sleep specialist must document the medical necessity for BiPAP as opposed to CPAP for positive airway pressure therapy. 

Another significant difference between CPAP and BiPAP machines is in terms of portability. While standard CPAP and BiPAP devices are roughly the same size – about the size of a shoebox – one can obtain CPAP machines that are quite small, not much bigger than a coffee cup. Such diminutive BiPAP machines are not currently available.

Both CPAP and BiPAP machines come with humidifier options to reduce the drying effect of continuous positive airway pressure. Some also include heaters to warm the air before it reaches the mask.

As a general proposition, there is no difference in the masks and hoses that a patient will use with either CPAP or BiPAP machines. The choice between a nasal mask and a full-face mask is one of patient comfort.

Other respiratory assist devices exist, most notably the recently-developed Adaptive Sero-Ventilation (ASV) machines. While ASV machines can be counted as positive airway pressure devices, they are quite sophisticated in their operation. Rather than delivering pressurized air at fixed settings (even considering CPAP devices that “auto-adjust” to accommodate exhalation), the ASV device is designed to utilize a target pressure that varies continually with the patient’s needs and breathing patterns. ASV machines currently are used only with complex sleep apnea, but the technology behind them may represent the future of positive airway pressure respiratory assist devices.

If you suffer from severe or even moderate sleep apnea, the decision of whether to incorporate PAP therapy into your health care regimen is one that must be made in conjunction with your professional medical care providers. The available options, however, are comprehensive. Whether CPAP or BiPAP is the correct choice, a suitable machine is out there, waiting you help you breathe easy.

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