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Physiology of the respiratory system and mechanical models 1.4.3 High frequency linear models When the frequencies are higher than typical of traditional mechanical ventilation, the models above described lose their validity because they do not consider the peculiar feature of the system. If we limit our attention between 4 to 32 Hz, it has been proved [Dorkin et al, 1988] that a satisfactory approximation is given by simple one-compartment second-order linear model RIC (Fig. 1.8). Figure 1.8 One-compartment second-order linear model. The RIC model is a series combination of a resistance, a compliance and an inertance according to: 1 p ( t) = ⋅ v( t) + R ⋅ v& ( t) + I ⋅ v& ( t) C where p (t) is the pressure applied to the respiratory system, v (t) is the pulmonary volume, 1 v& (t) is the airflow and v&(t & ) its derivative that represents flow acceleration. The term v( t) C ⋅ corresponds to the pressure necessary to balance elastic forces; it depends on both the volume insufflated in excess of resting volume and the elastance of the respiratory system. On the other hand the term R ⋅ v(t & ) corresponds to the pressure necessary to balance frictional forces; it is mainly due to the resistance offered to the airflow. Lastly, the product I ⋅ v(t & ) corresponds to the pressure necessary to overcome the system’s inertia (the inertance of the respiratory system) which depends on the airflow derivative. 18
Physiology of the respiratory system and mechanical models However, extending further on the frequencies field up to 200 Hz, it is suitable to use models more sophisticated than the simple RIC, utilizing models with more elements (Fig. 1.8). Figure 1.8 Six elements, high frequency linear model. 19
Page 1 and 2: UNIVERSITÀ DEGLI STUDI DI TRIESTE
Page 3 and 4: Index 2.2.7 Pressure-Controlled Ven
Page 5 and 6: Introduction Introduction The lungs
Page 7 and 8: Introduction The study was carried
Page 9 and 10: Physiology of the respiratory syste
Page 21: Physiology of the respiratory syste
Page 25 and 26: Chapter 2 - Intensive care: mechani
Page 39 and 40: Chapter 3 - The pulmonary function
Page 47 and 48: Chapter 4 - State of the art of met
Page 53 and 54: Chapter 5 - Development of innovati
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Chapter 5 - Development of innovati
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Chapter 6 - High Frequency Percussi
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Chapter 7 - Gas distribution in a t
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Conclusions and future developments
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References References Annane D, Orl
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References Lucangelo U, Antonaglia
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