Frequency analysis of mathematical model for respiratory system's impedance

• Grant number: 18/00185-4
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: March 01, 2018
• End date: August 20, 2018
• Field of knowledge: Engineering - Biomedical Engineering - Medical Engineering
• Principal Investigator: Henrique Takachi Moriya
• Grantee: Henrique Tomaz Amorim
• Host Institution: Escola Politécnica (EP). Universidade de São Paulo (USP). São Paulo , SP, Brazil

Abstract

The respiratory impedance is an important tool for the lung mechanics branch of study because it allows the characterization of the respiratory system in terms of the relation between the airflow and tracheal pressure under different respiratory frequencies. In another words, the impedance is the frequency response of the system. For measuring and analyzing it, laboratory experiments with small animals will be developed, as mices for instance, through a fan for small animals that perform the forced oscillation technique, which provides an airflow stimulus that contains a specific group of frequencies to the lungs. It allows one to observe the respiratory systems' behavior to the spectral components of the stimulus. With the purpose of assigning more physiological significance to the impedance, it is used mathematical models, which are fit to the data. In this study, it is adopted the constant phase model, highly used in bibliography due to its easier physiological interpretation. This model is defined by some parameters: resistance of the airways (R), inertance (I) - related to air inertia, viscance (G) - related to energy dissipation through tissue and elastance (H) - related to elastic energy stored in tissue. It's possible to characterize different models of the respiratory system from different impedance profiles, which are fit by the constant phase model. For instance, there is the asthmatic model, which is obtained through ovalbumine infusion (OVA). Given the importance of the interpretation of the model, it's necessary to verify the model fit's quality, because often some measures of the impedance in certain frequencies might be compromised. It affects the model fit and the calculation of the parameters, which compromises the physiological interpretation of the data. Then it is necessary to define the model's sensitivity related to the exclusion of inappropriate frequencies for the fitting process. Even though, this process might compromise the content of the impedance data, because spectral information is lost. In this study, it is made an evaluation of the model's sensitivity to exclusion of inappropriate frequencies and it is verified how much these variations can affect the interpretations of the results. Furthermore, it will be evaluated the individual variations in the model's parameters and its uncertainty, which allows one to take enough mathematical criteria to justify the need of a new model fit. (AU)