Control system design for a continuous positive airway pressure ventilator

Nasal continuous positive airway pressure is a prevalent and effective treatment for patients with obstructive sleep apnea syndrome (OSAS) characterized by repetitive episodes of complete or partial upper airway obstruction that occurs during sleep [1-3]. CPAP devices delivered a positive trans-mural pressure during the throughout respiratory cycle to prevent the collapse of the upper airway. Actually, constant CPAP levels affect the impedance of airway circuit and gas leak, especially the tidal volume and breathing frequency. The key problem to be resolved in designing CPAP devices with good compliance is how to synchronize them with patient's spontaneous breathing, that is, CPAP devices should automatically increase pressure levels at the beginning of inspiration to maintain therapeutic pressure and decrease pressure at the beginning of expiration to facilitate patient's expiration. The present work aims to develop the CPAP ventilator with better pressure stability. The study also tries to come up with some parameters to objectively evaluate the performance of different CPAP devices in an attempt to make CPAP therapy more comfortable and acceptable.According to British Standards/European Norm/International Organization for Standardization 17510-1:2009 Sleep apnoea breathing therapy-Sleep apnoea breathing therapy equipment, two basic design specifications area. Pressure range: 4-20 hPa (4-20 cmH2O)b. Sound levels: ≤30 dB (at 10 hPa)In order to meet the above design requirements, it is very important to select a sensitive pressure sensor and a motor and blower with good performances such as fast response time and low noise level. In this design, we use an integrated silicon pressure transducer (model MPXV5004GC7U by Freescale Semiconductor, Inc., USA) with pressure range from 0 to 40 hPa and an application-specific CPAP blower (ebm-papst, Germany) that is able to change its speed rapidly to respond to the requirement of the patient. The blower's maximum air flow is