Environments for real-time measurement and control: A study of HFJV in anaesthesia.
thesisposted on 19.11.2015, 08:59 by Salih. Kabay
This thesis is concerned with intelligent computer-based instrumentation which can be easily adapted for measurement, modelling and control in a range of application domains. The particular application area selected for study and used to illustrate the main features of the scheme was in anaesthesia for measurement and control of high-frequency jet ventilation (HFJV). The analytical methods and experimental procedures required for this area are also applicable to many other areas throughout engineering and biomedicine. A prototype general-purpose signal processing computer (SPC) encompassing many new design concepts was built to provide a flexible and user-friendly system for performing dedicated measurement and control tasks - as specified by the application program interface. The other objective of this study was to develop a new measurement and control environment for investigating the underlying respiratory dynamics of patient airways during HFJV - to facilitate a study of the efficacy of this mode of ventilation. Drawing on past experience with the SPC, a new computer-system was designed which overcame the bandwidth limitations of the original SPC. Based around powerful, modem and cost- effective commercial system hardware it is shown that this second-generation SPC can perform real-time measurement, modelling and control in HFJV as required. Modifications were carried out on an existing high-frequency jet ventilator to allow new modes of respiratory excitation. The signal processing system described together with these modifications to the jet ventilator coupled with the development of a new non- invasive fibre-optic chest-wall displacement transducer forms a complete environment which permits systematic identification of respiratory dynamics with extremely high precision in a fraction of the time taken by previous workers in this field. This is achieved with only minor changes to existing jet ventilation equipment and procedures. The system is intended to cope with the volume of information that needs to be considered during HFJV and the level of complexity that this method of ventilation entails. The measurement environment has undergone clinical trials on a small population of patients. The study clearly validated the hypothesis that the respiratory airways exhibit characteristics similar to an acoustic resonant circuit over the range of frequencies covered by HFJV. Based on this study, a Lyapunov model-reference adaptive control (MRAC) system has been designed and simulated for performing automatic control of HFJV and tested for stability and convergence over a wide range of operating conditions. The thesis concludes with a consideration of how the presented approach can be extended to take account of new hardware and software developments.