Resistance (R): dynamic resistance quantitatively assesses the level of constriction in the lungs.
Elastance (E): elastance captures the elastic stiffness of the respiratory system at the ventilation frequency. If measured under closed-chest conditions, it includes a contribution from the lung, the chest walls, and the airways. Elastance is the reciprocal of compliance and vice versa.
Compliance (C): compliance (also known as dynamic compliance) describes the ease with which the respiratory system can be extended. In a subject with intact chest walls, it provides a characterisation of the overall elastic properties that the respiratory system needs to overcome during tidal breathing to move air in and out of the lungs.
Coefficient of determination (COD): quality control parameter measuring the quality of the single compartment model fit.
Also referred to as the low-frequency forced oscillation technique, a broadband forced oscillation manoeuvre measures the subject’s response to a signal containing a wide range of frequencies both below and above the subject’s breathing frequency. The outcome, respiratory system input impedance (Zrs), is the most detailed assessment of respiratory mechanics currently available.
Input impedance can be further analyzed using the Constant Phase Model (CPM), introduced by Hantos et al., to obtain a parametric distinction between airway and tissue mechanics. This distinction is invaluable to obtain an accurate understanding of how diseases affect lungs.
Input Impedance (Zrs): the combined effects of resistance, compliance and inertance as a function of frequency.
Newtonian resistance (Rn): parameter of the CPM which represents the resistance of the central or conducting airways.
Tissue damping (G): parameter of the CPM closely related to tissue resistance and reflects the energy dissipation in the alveoli.
Tissue elastance (H): parameter of the CPM closely related to tissue elastance and reflects the energy conservation in the alveoli.
Coefficient of determination (COD): quality control parameter measuring the quality of the constant phase model fit.
A: estimate of inspiratory capacity. The parameter A of the SKE an upper bounds estimate of the difference between total lung capacity and zero volume.
B: the parameter B of the SKE is an estimate of the difference between the volume at total lung capacity and the predicted volume at zero pressure.
Note: the volume at zero pressure can only be obtained by extrapolating the SKE model fit, as a measurement at zero pressure is only possible if the lungs are fully degassed. While the SKE describes the upper portion of the PV loop, it deviates significantly at zero pressure, therefore B is a theoretical parameter and should not be interpreted physiologically or reported.
K: curvature of the upper portion of the deflation limb of the PV curve. This shape parameter has been shown to change with different chronic disease models.
Cst: quasi-static compliance is a classic parameter extracted from a PV curve. If measured under closed-chest conditions, it reflects the intrinsic elastic properties of the respiratory system (i.e. lung+chest wall) at rest.
Area: the area enclosed by the pressure volume loop provides an estimate of the amount of atelectasis (airspace closure) that existed before the PV loop manoeuvre.
Forced Expired Volume (FEVx): the volume expired during the first x seconds of a forced expiration, is indicative of obstructive airway disease and increased expiratory flow limitation.
Forced Expired Flow (FEFx): the expiratory flow calculated at a specific time or volume fraction into a forced expiration.
Forced Vital Capacity (FVC): is the total volume expired during a forced expiration, is typically reduced in many lung diseases.
Peak Expiratory Flow (PEF): the highest expiratory flow achieved during a forced expiration.
This is just one of the translational outcomes the flexiVent offers to help correlate clinical and preclinical research.
Learn more on how to obtain these measurements with the FEV extension.
The flexiVent is now capable of providing more measurements of lung volumes. In addition to measuring inspiratory capacity (IC) and forced vital capacity (FVC), the flexiVent now includes measurements of the total and residual lung volumes (TLC/RV). As with other techniques, this is done using a computer-controlled automated manoeuvre for standardization and control of parameters.
The acquisition of these new outcomes does not require the use of a separate device and can easily be preceded by comprehensive respiratory mechanics measurements typically performed with the flexiVent. Lung volume changes are sensitive to physiological or pathophysiological changes.
Please contact SCIREQ technical support should you be interested in obtaining other lung volumes.
Ventilator-Assisted Aerosol Delivery (VAAD) is a new innovative technique using the flexiVent, introduced to improve in vivo aerosol administrations for drug delivery and disease modelling. The VAAD approach minimizes subject-to-subject variability, and fosters a highly homogenous aerosol deposition within the lung. This optimized aerosol protocol is synced with mechanical ventilation to standardize features of the subject’s breathing pattern and to measure lung function prior to and post administration.
