Accurate assessment of pulmonary function is essential for understanding respiratory disease mechanisms and evaluating potential therapies in preclinical models. In mouse studies, forced oscillation technique (FOT) is widely used to characterize respiratory mechanics, including airway resistance and tissue elastance. However, translating these measurements to clinical respiratory endpoints can be challenging.
A study by Devos et al. (2017) demonstrated how negative pressure-driven forced expiration (NPFE) can complement conventional respiratory mechanics measurements by generating forced expiration parameters that resemble those commonly used in human spirometry.
The findings suggest that combining forced expiration measurements with respiratory mechanics can provide a more comprehensive characterization of lung function in mouse models of respiratory disease.
Respiratory diseases can produce complex changes in lung mechanics that may not always be apparent under normal tidal breathing conditions. Measurements performed during forced expiration place the respiratory system under greater functional stress, helping reveal abnormalities associated with airflow limitation and altered lung mechanics.
Using NPFE, researchers can generate flow-volume (FV) loops and quantify several clinically relevant parameters, including:
While these measurements are not identical to human spirometry, their ability to characterize changes in forced expiration makes them valuable complementary endpoints in preclinical respiratory research.
Devos et al. evaluated forced expiration in four established mouse models representing distinct pulmonary pathologies:
Respiratory mechanics and forced expiration measurements were performed concurrently, allowing disease-specific changes to be evaluated using multiple complementary endpoints.
Mice with bleomycin-induced pulmonary fibrosis demonstrated changes consistent with restrictive lung disease.
Forced expiration measurements showed significant reductions in:
The flow-volume loop also showed a characteristic reduction in overall volume and flow.
These findings corresponded with changes detected using respiratory mechanics, including increased tissue damping and tissue elastance and decreased static compliance.
Together, these measurements provided a more complete picture of the increased stiffness and reduced functional capacity associated with pulmonary fibrosis.
The emphysema model produced a different functional phenotype.
Mice treated with elastase demonstrated decreased tissue damping and tissue elastance, consistent with reduced elastic recoil. Forced expiration measurements showed:
The flow-volume loop exhibited a pronounced reduction in peak expiratory flow alongside increased forced vital capacity.
Interestingly, some of these findings differ from the typical pattern observed in human emphysema, highlighting an important consideration when translating pulmonary function measurements between species.
One of the advantages of combining forced expiration with respiratory mechanics is the ability to assess lung function under bronchoconstrictor challenge.
In the study, mice were exposed to increasing concentrations of aerosolized methacholine to evaluate airway responsiveness.
The HDM-induced asthma model demonstrated clear airway hyperresponsiveness. Increasing methacholine concentrations produced:
The changes in flow-volume loop shape reflected increasing airflow obstruction.
Importantly, the study also calculated PC20, PC30, and PC40 values, the methacholine concentrations required to produce defined reductions in FEV0.1. This provides a way to characterize the magnitude of airway hyperresponsiveness using endpoints with similarities to clinical assessments.
The LPS-induced acute lung injury model demonstrated another example of why multiple pulmonary function endpoints can be valuable.
At baseline, mice with acute lung injury showed an increase in central airway resistance and a decrease in PEF compared with control animals.
However, some other respiratory mechanics and forced expiration parameters showed relatively limited changes.
This highlights an important principle in preclinical respiratory research: no single lung function parameter necessarily captures every aspect of disease pathology.
Combining measurements can therefore improve the sensitivity and breadth of pulmonary phenotyping.
A major strength of the experimental approach was the ability to perform multiple lung function measurements in the same animal using a single measurement platform.
Using the flexiVent FX, researchers were able to perform:
This integrated approach eliminates the need to transfer animals between separate systems during an experiment and allows different aspects of respiratory function to be assessed within the same experimental workflow.
The result is a multidimensional assessment of pulmonary function that can capture both linear and nonlinear behavior of the respiratory system.
One of the ongoing challenges in respiratory drug development is translating findings from animal models to human disease.
Traditional respiratory mechanics parameters such as airway resistance, tissue damping, and tissue elastance provide valuable mechanistic information. However, endpoints that resemble clinical pulmonary function measurements can add another layer of translational relevance.
Forced expiration measurements offer an opportunity to bridge these approaches by providing parameters analogous to those routinely used in human pulmonary function testing.
The study found that lung function abnormalities could be detected in all four disease models using at least one forced expiration parameter at baseline or following methacholine challenge.
Although the authors emphasize that the translational interpretation of these parameters remains to be fully established, the findings support incorporating forced expiration into broader preclinical lung function assessments.
Respiratory diseases affect multiple components of the respiratory system, including the conducting airways, peripheral lung tissue, and mechanical properties of the lung.
For this reason, combining complementary techniques can provide a more complete understanding of disease phenotype.
Forced oscillation measurements can characterize respiratory mechanics and distinguish airway and tissue contributions, while forced expiration measurements can reveal changes in expiratory flow and volume under conditions that promote airflow limitation.
Together, these measurements can help researchers:
Forced expiration measurements provide a valuable complement to conventional respiratory mechanics in mouse models of respiratory disease.
Research by Devos et al. demonstrated that FEV0.1, FVC, FEV0.1/FVC, FEF0.1, and PEF can identify functional abnormalities across models of pulmonary fibrosis, emphysema, acute lung injury, and allergic asthma.
When integrated with forced oscillation, pressure-volume measurements, and bronchoprovocation testing, forced expiration can contribute to a more comprehensive assessment of pulmonary function.
For researchers developing and characterizing preclinical respiratory disease models, combining mechanistic respiratory mechanics with clinically relevant forced expiration endpoints may provide valuable additional insight into disease phenotype and improve the translational potential of pulmonary research.
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