Nesta dissertação, apresenta-se o projeto e a implementação de um instrumento portátil para captação dos sons respiratórios adventícios de forma não invasiva, a partir das vias aéreas, em animais submetidos a ventilação mecânica e com lavagem previa com solução salina. Descrevem-se os ensaios para avaliação da resposta em frequência e sensibilidade do microfone de eletreto que foi fixado nos tubos de um ventilador mecânico de uma Unidade de Terapia Intensiva – UTI, o comportamento da propagação dos sons nos tubos do aparelho de ventilação mecânica e as características dos circuitos eletrônicos projetados para realizar a adequação e digitalização dos sinais sonoros captados pelos microfones e transferidos para um software de gravação instalado em um computador pessoal. Os testes do sistema eletrônico de captação dos sons foram realizados em três porcos submetidos a ventilação mecânica e com monitoramento em tempo real da quantidade de ar nos pulmões através de um tomógrafo de impedância elétrica. Como resultado das gravações, foi possível identificar ruídos de crepitação, induzidos nos animais através de manobras ventilatórias. Conclui-se que o circuito desenvolvido e a fixação do microfone nos tubos possibilitam a captação dos ruídos de crepitação em animais submetidos a ventilação mecânica, evidenciando a boa propagação dos sons ao longo das vias aéreas do sistema respiratório. Discute-se também a possibilidade de utilizar esse sistema em conjunto com o sistema de tomografia por impedância elétrica para identificar a duração e a extensão das alterações no recrutamento pulmonar durante a ventilação mecânica. / This essay presents the project of a portable equipment to capture adventitious respiratory sounds, inside the airways, in animals submitted at mechanical ventilation. It is described the tests for assessment of frequency response and sensitivity of the microphone that was fixed in the tubes of a mechanical ventilator, the behavior of sound propagation in tubes of the system and the characteristics of electronic circuits designed to acquire sound signals by microphones and transferred them to a recording software installed on a personal computer. Tests with the electronic system were performed in three pigs submitted to mechanical ventilation and monitoring in real time the amount of air into the lungs through electrical impedance tomography. Through the recorded sound, it was possible to identify crackles induced in animals by ventilator maneuvers. It was possible to conclude that the developed circuit and setting the microphone in the tube allows to capture crackle sounds on animals with mechanical ventilation, showing a good sound propagation along the airways of the respiratory system. It is also discussed the possibility of using this system with the Electric Impedance Tomography - EIT - to identify the duration and extent of changes in alveolar recruitment during pulmonary ventilation.

Yip Lung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2001. / Includes bibliographical references. / Abstracts in English and Chinese. / Chapter 1 --- Introduction / Chapter 1.1 --- Heart and Lung Diseases --- p.1 / Chapter 1.1.1 --- Hong Kong --- p.1 / Chapter 1.1.2 --- China --- p.2 / Chapter 1.1.3 --- the United States of America (USA) --- p.3 / Chapter 1.2 --- Auscultation --- p.3 / Chapter 1.2.1 --- Introduction of Auscultation --- p.4 / Chapter 1.2.2 --- Comparison between Auscultation and Ultrasound --- p.6 / Chapter 1.3 --- Stethoscope --- p.7 / Chapter 1.3.1 --- History of Stethoscope --- p.7 / Chapter 1.3.2 --- New Electronic Stethoscope --- p.14 / Chapter 1.4 --- Main Purpose of the Study --- p.16 / Chapter 1.5 --- Organization of Thesis --- p.16 / References --- p.18 / Chapter 2 --- A New Electronic Stethoscope's Head / Chapter 2.1 --- Introduction --- p.20 / Chapter 2.2 --- Biopotential Electrode --- p.21 / Chapter 2.2.1 --- Flexible Electrode --- p.21 / Chapter 2.2.2 --- Laplacian Electrocardiogram --- p.22 / Chapter 2.3 --- Transducer --- p.25 / Chapter 2.4 --- Design of the Head of Stethoscope --- p.26 / Chapter 2.5 --- Experimental Results --- p.27 / Chapter 2.5.1 --- Bias Voltage of Condenser Microphone --- p.27 / Chapter 2.5.2 --- Frequency Response of New Stethoscope's Head --- p.29 / Chapter 2.6 --- Discussion --- p.30 / Chapter 2.7 --- Section Summary --- p.31 / References --- p.33 / Chapter 3 --- Signal Pre-processing Unit / Chapter 3.1 --- Introduction --- p.35 / Chapter 3.2 --- High Input Impedance IC Amplifier --- p.36 / Chapter 3.3 --- Voltage Control Voltage Source High Pass Filter Circuit --- p.37 / Chapter 3.4 --- Multiple Feed Back Low Pass Filter Circuit --- p.39 / Chapter 3.5 --- Overall Circuit --- p.41 / Chapter 3.6 --- Experimental Results --- p.43 / Chapter 3.7 --- Discussion --- p.46 / Chapter 3.8 --- Section Summary --- p.47 / References --- p.48 / Chapter 4 --- Central Platform / Chapter 4.1 --- Introduction --- p.49 / Chapter 4.2 --- Adaptive Filter --- p.49 / Chapter 4.2.1 --- Introduction to Adaptive Filtering --- p.49 / Chapter 4.2.2 --- Least-Mean-Square (LMS) Algorithm --- p.51 / Chapter 4.2.3 --- Applications --- p.52 / Chapter 4.3 --- Offline Processing --- p.54 / Chapter 4.3.1 --- WINDAQ and MATLAB --- p.55 / Chapter 4.3.2 --- Direct Reference Algorithm --- p.57 / Chapter 4.3.3 --- Determination of Parameters in DRA --- p.62 / Chapter 4.3.4 --- Experimental Results of DRA --- p.67 / Chapter 4.3.5 --- Acoustic Waveform Based Algorithm --- p.72 / Chapter 4.3.6 --- Experimental Results of AWBA --- p.81 / Chapter 4.4 --- Online Processing --- p.85 / Chapter 4.4.1 --- LABVIEW --- p.85 / Chapter 4.4.2 --- Automated Gain Control --- p.88 / Chapter 4.4.3 --- Implementation of LMS adaptive filter --- p.89 / Chapter 4.4.4 --- Experimental Results of Online-AGC --- p.92 / Chapter 4.5 --- Discussion --- p.93 / Chapter 4.6 --- Section Summary --- p.97 / References --- p.98 / Chapter 5 --- Conclusion and Further Development / Chapter 5.1 --- Conclusion of the Main Contribution --- p.100 / Chapter 5.2 --- Future Works --- p.102 / Chapter 5.2.1 --- Modification of the Head of Stethoscope --- p.102 / Chapter 5.2.2 --- Validation of Abnormal Breath --- p.102 / Chapter 5.2.3 --- Low Frequency Analysis --- p.102 / Chapter 5.2.4 --- AGC-AWBA Approach --- p.102 / Chapter 5.2.5 --- Standalone Device --- p.103 / Chapter 5.2.6 --- Demand on Stethoscope --- p.109 / References --- p.110 / Appendix / Chapter A.1 --- Determination of parameters in VCVS High Pass Filter --- p.106 / Chapter A.2 --- Determination of parameters in MFB Low Pass Filter --- p.110 / Chapter A.3 --- Source code of DRA (MATLAB) --- p.114 / Chapter A.4 --- Source code of AWBA (MATLAB) --- p.129 / Chapter A.5 --- Source code of online AGC (LABVIEW) --- p.134