Respiratory system dynamical mechanical properties: modeling in time and frequency domain

Abstract

The mechanical properties of the respiratory system are important determinants of its function and can be severely compromised in disease. The assessment of respiratory system mechanical properties is thus essential in the management of some disorders as well as in the evaluation of respiratory system adaptations in response to an acute or chronic process. Most often, lungs and chest wall are treated as a linear dynamic system that can be expressed with differential equations, allowing determination of the system's parameters, which will reflect the mechanical properties. However, different models that encompass nonlinear characteristics and also multicompartments have been used in several approaches and most specifically in mechanically ventilated patients with acute lung injury. Additionally, the input impedance over a range of frequencies can be assessed with a convenient excitation method allowing the identification of the mechanical characteristics of the central and peripheral airways as well as lung periphery impedance. With the evolution of computational power, the airway pressure and flow can be recorded and stored for hours, and hence continuous monitoring of the respiratory system mechanical properties is already available in some mechanical ventilators. This review aims to describe some of the most frequently used models for the assessment of the respiratory system mechanical properties in both time and frequency domain.

Parameter estimation of an artificial respiratory system under mechanical ventilation following a noisy regime

“…The respiratory system can be modelled as a first-order linear model, as shown in Equation 1 (Carvalho and Zin, 2011;Diong et al, 2007). It is an ordinary differential equation whose time-dependent variables are P, V and V. …”

“…Different methods have been developed to calculate the volume-dependent dynamic compliance, which may provide information to identify overdistension and recruitment without the need of obtaining the static pressure-volume curve (Zhao et al, 2012). Most of these methods are based on the linear first-order equation of motion (Carvalho and Zin, 2011;Diong et al, 2007). Linear respiratory system models, in which the respiratory system is represented by linear elements, have been used in frequency analysis and evaluated in the literature (Saatçi and Akan, 2008).…”

A new adaptive controller for volume-controlled mechanical ventilation in small animals

“…The CV of 30% was used because it was associated with an optimal response in gas exchange and respiratory system mechanics in an animal model of ARDS [8]; (N2) step increase in R by the factor of 10 (N2 low ) and 100 (N2 high ); (N3) step increase in E 1 and E 2 by a factor of 10 and 100, respectively, in N3 low and N3 high , at N3 high being 10 times the range of values between healthy and severely injured lungs [9]; (N4) two consecutive cycles of corrupted tidal volume measurement V T,m , a problem specific for the open chamber configured plethysmograph, with random errors of 25/50% of V T,s , in order to estimate the robustness of the control system; (N5) simultaneous step increase of R and E 1 /E 2 as a combination of N2 and N3, which reflect changes in respiratory mechanics in the HCl aspiration model of ARDS in rats [7].…”

An in vivo image acquisition system for the evaluation of tracheal mechanics in rats

“…Resistance and elastance parameters can be obtained with the linear single compartment model and are attributed to have physiological meaning . For example, resistance involves the frictional forces of the respiratory movement and elastance involves the forces necessary to overcome the elastic recoil . Both resistance and elastance are influenced by numerous factors such as bronchoconstriction, age, frequency of perturbation applied to the respiratory system, and disease …”