COPD & Emphysema Support Group

The acronyms 'CPAP' and 'BiPAP' stand for Continuous Positive Airway Pressure and 'Bi-level' - Positive Airway Pressure. BiPAP, incidentally is a registered/protected term owned by Respironics, Inc; makers of some of the earliest machines and accessories for these therapies. Therefore, as difficult as we find it to do, we must be careful in what context we use the term "BiPAP", as they have been known to litigate for infringement. They were the first to introduce 'bi-level positive airway pressure', the term we most often use, which is NOT protected.

To begin with, Positive Airway Pressure breathing seeks to 'augment' the user's breathing efforts to improve their ability to achieve normalized ventilation. It has also been found effective in helping to maintain patency (open, un-obstructed) of the upper portion of the airway. We think it does this through at least two mechanisms. One mechanism is through simple physical 'splinting' such that the soft palate (behind the 'roof' of your mouth, where your throat begins) is 'lifted' off that part of the tongue. The other mechanism is neurologic, in that there is thought to be some 'stimulus' by way of the nervous system to keep the tongue from closing off the airway.

There is a distinct difference between the two therapies. CPAP provides a single-level of constant pressure against the airway and is used to treat folks who need the benefit of 'airway splinting' and stimulus to keep the tongue from blocking the oral, or 'upper' airway. It is applied as a means to reduce or prevent snoring and periods of 'apnea' (no effective breathing)
in folks who have been diagnosed with OSA - - the acronym for Obstructive Sleep Apnea. As a single-level pressure device, it exerts a constant pressure against which the user breathes during both inspiration and expiration (synonymous with 'inhalation' and 'exhalation') - - or, throughout the entire 'respiratory cycle', which is defined as one inspiration plus it's corresponding expiration.

It is usually applied using either a small, soft mask which seals over the nose, or another apparatus with two small cone-like attachments, called 'nasal pillows'. Both devices are held in place by one of several choices of 'head gear' - - a series of straps assembled like a harness, or a 'cap-gear', similar to the old bathing caps, but made of much lighter cloth materials and much more comfortable, too.

There are conditions for which single level positive airway pressure is not effective, and some cases when folks with conditions that do respond to single-level positive pressure cannot find comfortable tolerance of CPAP.
This is where the role of BiPAP comes in. There are several ways in which BiPAP may be applied. There is a 'spontaneous' mode (only the user's breathing efforts 'trigger' the machine to cycle), and depending upon the particular machine used, along with its particular features, there are other modes with combinations of arbitrary ventilatory support at parameters selected by the physician, according to the patient's needs and tolerances, or according to the desired benefit the physician wants to exact. These other modes can be set such that the machine will cycle between pressure settings in coordination with the user's breathing efforts, or may be set independently of (but usually to synchronize with) the user's breathing efforts.

By definition, bi-level PAP is distinct from CPAP because there are (two)
different pressures imposed upon the airway during the inspiratory and expiratory phases of the respiratory cycle. Most often, a higher level of pressure is imposed during the inspiratory phase so as to provide support for achieving a deeper inhalation. When the inspiratory cycle is finished and the user is ready to exhale, the machine is triggered to drop the pressure it exerts to that level which is selected for the expiratory phase.
Bi-level PAP, therefore allows the selection of an appropriate, but different pressure to help the user achieve a deeper breath during inspiration, than that which is needed to keep the airway splinted ('patent', open) during expiration. Bi-level PAP may be applied using the devices as described with CPAP and more. In some cases, it is being employed connected to 'artificial airways' such as tracheostomies.

As mentioned earlier, positive pressure ventilatory support is employed to help overcome the difficulties of obstructive sleep apnea. It is also used to improve various conditions that have 'ventilatory insufficiency' as a component. More recently, bi-level PAP is being shown to help improve energy levels, sleep and possibly even gas exchange in folks with advanced emphysema and carbon dioxide retention. However, the jury remains out as the evidence is still very anecdotal and obtaining objective evidence is difficult and will require considerable time.
Posted on 11/13/07, 06:11 pm