In order for an Autotitrating PAP to measure breathing patterns properly and detect abnormal events, flow and pressure must be communicated to the algorithm as a high-quality signal. The principle behind the use of pneumotachometers and flow sensors is that flow patterns indicate corresponding breathing patterns. Autotitrating PAPs also use a pressure transducer to deliver precise pressure levels.
Breathing events that, when present, trigger a response to increase pressure and, when absent, trigger a response to decrease pressure.
Obstructive apneas – occur when patient airways close and breathing cannot occur
Hypopneas – occur when patient airways are partially closed and breathing is limited
Snoring and flow limitation are similar in that both may occur prior to obstructive apneas and/or hypopneas. All Autotitrating PAPs are proactively programmed to increase pressure in response to snores or flow limitations to prevent the occurrence of obstructive apneas and hypopneas. There is conflicting evidence as to which parameter allows the earliest response.
Breathing events that are identified and logged without triggering a pressure response. Most Autotitrating devices have two non-responding events in common:
Leaks – usually caused by mouth breathing or mask fit/seal leaks
Non-obstructive apneas – caused by a PAP-induced reduction in CO2
Non-Obstructive Apneas (NOAs)
[poster's note: also called Clear Airway]
Cause: Non-obstructive apneas may occur during OSA therapy if the PAP pressure reduces the normal carbon dioxide accumulation and degrades the CO2 stimulus response. NOAs also may be primary central apneas that cannot be properly defined by an Autotitrating device alone.
NOTE: Non-obstructive apneas in excess of 10 per hour could indicate primary central apneas, not NOAs or obstructive apneas, and clinical intervention may be required.