Application of Forced Breath Technique While CPAP Therapy for Apnea Classification

Obstructive sleep-disordered breathing is usually treated by positive airway pressure (PAP) therapy with respective devices.The devices detect, classify and store respiratory events as apneas, hypopneas and snoring to adapt the therapy pressure according to patients needs and/ or to validate therapy efficacy.

Since several years the Forced Breath Technique (FBT) is standard practice in PAP devices with a BiLevel pressure profile and a background rate to classify apneas as central or obstructive. In case of an interruption of the respiratory flow within an apnea the devices background rate applies so called "mandatory breaths" with neither a manually or by device defined pressure gap between exhalation and inhalation pressure (PDIFF). If a mandatory breath generates respiratory flow patients airways are open and the patient gets ventilated. In this case the detected apnea is classified as central. If a mandatory breath generates no or insufficient respiratory flow patients airways are impassable and the apnea is classified as an obstructive event.

Usually the size of the applied therapeutic pressure gap PDIFF is >= 4 hPa. If patients airways are open the mandatory breaths with PDIFF>= 4 hPa generate an obvious flow that submits a valid classification of apneas. Therefore the pressure gap should be preferably large. So, too, the pressure gap size should be defined as small as possible to prevent the impairment of patients sleep quality.

This pilot study targets to analyze if the application of FBT with a minor gap between inhalation and exhalation pressure (IPAP [inspiratory positive airway pressure] - EPAP [expiratory positive airway pressure] = PDIFF = 1,0 to 2,0 hPa) qualifies for an equal classification of apneas as with a PDIFF >= 4 hPa. Subsequently it serves to define the minimum size of this pressure gap.

To this effect the study is subdivided in to phases: an optimization phase and an evaluation phase.

The optimization phase targets to define the PDIFF size that enables the valid classification of apneas. The evaluation phase serves to compute the accuracy of the classification, the optimized algorithm and the determined classification criteria. Therefore this phase only takes place if the optimization phase yielded a result.

The optimization phase starts with a PDIFF of 1,5 hPa. If this PDIFF serves the purpose, the phase continues with a PDIFF of 1,0 hPa to analyze if a smaller pressure gap yields similar results. Otherwise the phase continues with a PDIFF of 2,0 hPa. Afterwards the optimization phase ends.

The review of the matching of the apneas classified by the device vs the manual scoring takes place after the synchronization of both sources.

Within every PDIFF round in the optimization phase patient recruitment takes place as long as at least 60 obstructive and 60 central apneas have been collected. To guarantee an equal dispersion of apneas on the patient population only 10 obstructive and 10 central apneas of each patient go down in the pool of apneas of the respective PDIFF round. The apnea extraction is made by randomization.

The evaluation phase runs with the determined PDIFF until at least 80 obstructive and 80 central apneas are collected.

The data evaluation occurs by use of descriptive statistics and based on fourfold tables.