Modern Continuous Positive Airway Pressure Therapy An Overview

Modern Continuous Positive Airway Pressure Therapy An Overview

Andreas C Happel, Georg Nilius, Karl-Heinz Ruehle
European Respiratory Disease 2007 - Issue I
Published: October 2008
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Obstructive sleep apnoea syndrome (OSAS) is characterized by repetitive episodes of upper airway obstruction during sleep, resulting in cyclic oxygen desaturation,1,2 sleep fragmentation, impaired quality of life,3,4 excessive daytime sleepiness and an increased risk of road traffic accidents.5

Moreover, patients suffering from OSAS show increased incidence of arterial hypertension, increased risk of developing cardiovascular disease6 and higher five-year mortality rates.7 It is estimated that OSAS occurs in 2% of women and 4% of men in the middle-aged work force.8

Since its first description by Sullivan,9 treatment with continuous positive airway pressure (CPAP) during sleep, usually administered through a nasal mask,10 is now established as the preferred treatment option for OSAS. Using CPAP therapy can lower increased blood pressure,11 and OSAS patients who use CPAP have higher survival rates7 and a better quality of life compared with untreated patients.

No severe adverse effects have been reported for this therapy. However, a considerable number of patients complain about problems with upper airways, mostly referred to as a sensation of dryness in the nose, mouth or throat.12,13 Furthermore, a subgroup of about 20% of patients complains of a sensation of exhaling against a high pressure. Up to now there are no precise data available concerning the necessary duration of daily CPAP use.14,15,16 Many experts advise usage during total bed-time every night. Others, however, regard a use of three and a half hours per night as sufficient compliance.17

About 20–50% of patients do not use therapy regularly; in particular, there is scarce information about long-term usage after 10 years or more. Compliance is influenced by a number of different factors independent of the pressure mode employed. Such psychosocial factors as living alone,18 major life events18 in the recent past, high anxiety or depression scores19 or unfavourable coping strategies20 have an influence on the use of CPAP. Patients with a higher apnoea/hypopnoea score have a better CPAP compliance,21 and the quality of sleep during the first night predicts subsequent compliance.21 Compliance can be improved by group work with the patients22 or by intensive support at the start of CPAP therapy.23 In contrast, less intensive support at the beginning of therapy may reduce CPAP usage.24 There have been numerous efforts to reduce side effects and thus improve acceptance of therapy. No data are available defining the optimal CPAP use.

OSAS is caused by increased collapsibility of the upper airways. The patency of the pharyngeal airway is a function of the balance of forces promoting collapse and antagonising factors.25 One factor promoting pharyngeal collapse is the amount of pressure placed on the muscular pharynx by the soft parts of the throat (increased fatty portion). Anatomic factors are hereditary proportions in the larynx, the position of the lower jaw, the size of the tonsils and many others. Also, lung volume, intraluminary pressure and the activity of the pharyngeal dilatator muscles influence collapsibility. The balance of these factors results in changing collapsibility during the breathing cycle, during one night and during longer periods of time. Crucial for developing pharyngeal obstruction is collapsibility at the beginning of inspiration.26 This results in the need for variable levels of pressure during the breathing cycle. Other factors, such as position of sleep and muscular tonus according to sleep stages, produce a need for variable levels of pressure during one night.

In order to reduce side effects of therapy, technical variations of constant positive airway pressure have been developed.27 Automatically adjusting positive airway pressure (APAP) devices measure the amount of obstruction by various signals (e.g. flow, forced oscillation28 or oscillations due to snoring) and adjust the necessary amount of positive airway pressure in the course of the night. The required pressure can thus be reduced by about 1.5cmH2O29. No significant advantage has been proven over constant PAP to improve compliance or to reduce side effects, although some studies were able to show patients´ preferences for APAP devices.30,31,32 Possibly, only patients requiring a therapeutic pressure above 10cmH2O benefit from APAP therapy.33

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