What is the Forced Oscillation Technique (FOT)?
Simply put, the forced oscillation technique is:
- Pausing ventilation
- Sending a test signal to the lungs
- Measuring the subject’s response
The test signal is either a single frequency (matching the breathing frequency of the subject) or made up of multiple frequencies. When adding complexity to the signal, it provides additional insight about lung function.
Why use a Broadband Forced Oscillation?
The broadband signal or low-frequency forced oscillation technique, measures the subject’s response to a wide range of frequencies that extend above and below the subject’s breathing frequency. As a result, it provides respiratory system input impedance (Zrs), which is the most detailed assessment of respiratory mechanics available.
Hantos et al.¹ introduced the Constant Phase Model to analyze input impedance, providing a separation between airway and tissue mechanics. This distinction is invaluable in gaining an accurate understanding of lung diseases.
Broadband FOT with the flexiVent.
The flexiVent is considered by many researchers to be the gold-standard for respiratory mechanics assessment in small animal models. One of its many strengths is its unique ability to provide this detailed assessment of airway and lung tissue contributions.
DID YOU KNOW?
Although the broadband forced oscillation manoeuvre may appear noisy during execution, it is in fact a precisely constructed signal containing specific frequencies relevant to the subject being studied.
FOT in preclinical respiratory studies.
The benefits of this detailed approach are exemplified in a number of scientific publications. For example, North et al.2, highlights the power of the broadband forced oscillations in their study analyzing the impact of concentrated air pollution (CAP) and ozone (O3), on asthma exacerbation in models of allergen-induced airway hyperresponsiveness. Subjects were administered increasing concentrations of aerosolized methacholine and the data collected during the maximal response offered some new insight for their experiments.
Using the single-frequency Snapshot signal to assess sub-acute and chronic sensitization models, ovalbumin-treated subjects show an increase in total respiratory system resistance (Rrs). Following that treatment, an arginase inhibitor (BEC) abrogates the effect.
Extending the analysis to the Quickprime offered new insights:
Running the broadband Quickprime signal shows increases in both central airway resistance (Rn) and Tissue Damping (G) in the chronically sensitized group. However the sub-acute model indicates localized effects through an increase in Tissue Damping (G) only, but not in the central airway resistance (Rn).
Secondly, introducing the arginase inhibitor attenuates the central airway resistance (Rn) increase in the chronic model. However, it is noteworthy that this effect only appears on the increased tissue damping in the sub-acute model, not in the chronic model.
North et al.2 study outcome:
Their results highlight functional differences not detected by the classic resistance and compliance, which are only detected with the broadband signal. Moreover, this publication offers scientific insight into two models often studied (sub-acute, chronic), while demonstrating variations in the site of action of a therapeutic agent.
- Hantos Z, Daroczy B, Suki B, Nagy S, Fredberg JJ. Input impedances and peripheral inhomogeneity in dog lungs. J Appl Physiol. 1992, 72: 168-178.
- North ML, Amatullah H, Khanna N, et al. Augmentation of arginase 1 expression by exposure to air pollution exacerbates the airways hyperresponsiveness in murine models of asthma. Respir Res. 2011, 12: 19. doi:10.1186/1465-9921-12-19. Images are published with permission.