Real-Time Lung Mechanics Identification During Mechanical Ventilation

The model-based approach incorporates a physiologically relevant and validated recruitment model [17 (link),20 (link)] with the use of a single compartment linear lung model that captures fundamental lung mechanics and properties in real-time to identify patient-specific constant lung elastance (E_lung) and dynamic lung elastance (E_drs) during MV. The model uses transpulmonary pressure (P_tp), volume (V) and flow (Q) and offset pressure (P₀), to identify lung elastance (E_lung) and resistance (R_lung). Patient-specific lung elastance, E_lung reflects the lung stiffness (1/Compliance). Therefore, a lower E_lung is a more compliant lung. E_lung is identified from measured data using an integral-based method [21 (link)]. The model is defined:
$P_{tp}=E_{lung}V+R_{lung}Q+P_{\mathit{0}}$
Airway pressure is related to transpulmonary pressure (P_tp) and pleural pressure (P_pl) by:
$P_{tp}=P_{aw}-P_{pl}$
When the patient is sedated and fully dependant on the ventilator to breathe, it can be assumed that there is no chest wall activity, allowing P_pl to be omitted in this case. Equation 1 is then further modified to eliminate P_pl, yielding:
$P_{aw}=E_{lung}V+R_{lung}Q+P_{\mathit{0}}$
Patient-specific dynamic lung elastance, E_drs, is identified as a time-variant lung elastance and Equation (3) is defined:
$P_{aw}\left(t\right)=E_{drs}\left(t\right)V\left(t\right)+R_{lung}Q\left(t\right)+P_{\mathit{0}}$
To ensure that the identified parameters of constant E_lung and time-variant E_drs (E_drs(t)) are valid, the absolute percentage error between the identified model and measured clinical pressure data is reported.