CORP: Measurement of lung function in small animals

Comparison of the respiratory effects of commonly utilized general anaesthesia regimes in male Sprague-Dawley rats

Background: Respiratory parameters in experimental animals are often characterised under general anaesthesia. However, anaesthesia regimes may alter the functional and mechanical properties of the respiratory system. While most anaesthesia regimes have been shown to affect the respiratory system, the effects of general anaesthesia protocols commonly used in animal models on lung function have not been systematically compared. Methods: The present study comprised 40 male Sprague-Dawley rats divided into five groups (N = 8 in each) according to anaesthesia regime applied: intravenous (iv) Na-pentobarbital, intraperitoneal (ip) ketamine-xylazine, iv propofol-fentanyl, inhaled sevoflurane, and ip urethane. All drugs were administered at commonly used doses. End-expiratory lung volume (EELV), airway resistance (Raw) and tissue mechanics were measured in addition to arterial blood gas parameters during mechanical ventilation while maintaining positive end-expiratory pressure (PEEP) values of 0, 3, and 6 cm H2O. Respiratory mechanics were also measured during iv methacholine (MCh) challenges to assess bronchial responsiveness. Results: While PEEP influenced baseline respiratory mechanics, EELV and blood gas parameters (p < 0.001), no between-group differences were observed (p > 0.10). Conversely, significantly lower doses of MCh were required to achieve the same elevation in Raw under ketamine-xylazine anaesthesia compared to the other groups. Conclusion: In the most frequent rodent model of respiratory disorders, no differences in baseline respiratory mechanics or function were observed between commonly used anaesthesia regimes. Bronchial hyperresponsiveness in response to ketamine-xylazine anaesthesia should be considered when designing experiments using this regime. The findings of the present study indicate commonly used anaesthetic regimes allow fair comparison of respiratory mechanics in experimental animals undergoing any of the examined anaesthesia protocols.

Prolonged smoldering Douglas fir smoke inhalation augments respiratory resistances, stiffens the aorta, and curbs ejection fraction in hypercholesterolemic mice

While mounting evidence suggests that wildland fire smoke (WFS) inhalation may increase the burden of cardiopulmonary disease, the occupational risk of repeated exposure during wildland firefighting remains unknown. To address this concern, we evaluated the cardiopulmonary function in mice following a cumulative exposure to lab-scale WFS equivalent to a mid-length wildland firefighter (WLFF) career. Dosimetry analysis indicated that 80 exposure hours at a particulate concentration of 22 mg/m3 yield in mice the same cumulative deposited mass per unit of lung surface area as 3600 h of wildland firefighting. To satisfy this condition, male Apoe-/- mice were whole-body exposed to either air or smoldering Douglas fir smoke (DFS) for 2 h/day, 5 days/week, over 8 consecutive weeks. Particulate size in DFS fell within the respirable range for both mice and humans, with a count median diameter of 110 ± 20 nm. Expiratory breath hold in mice exposed to DFS significantly reduced their minute volume (DFS: 27 ± 4; Air: 122 ± 8 mL/min). By the end of the exposure time frame, mice in the DFS group exhibited a thicker (DFS: 109 ± 3; Air: 98 ± 3 μm) and less distensible (DFS: 23 ± 1; Air: 28 ± 1 MPa-1) aorta with reduced diastolic blood augmentation capacity (DFS: 53 ± 2; Air: 63 ± 2 kPa). Cardiac magnetic resonance imaging further revealed larger end-systolic volume (DFS: 14.6 ± 1.1; Air: 9.9 ± 0.9 μL) and reduced ejection-fraction (DFS: 64.7 ± 1.0; Air: 75.3 ± 0.9 %) in mice exposed to DFS. Consistent with increased airway epithelium thickness (DFS: 10.4 ± 0.8; Air: 7.6 ± 0.3 μm), airway Newtonian resistance was larger following DFS exposure (DFS: 0.23 ± 0.03; Air: 0.20 ± 0.03 cmH2O-s/mL). Furthermore, parenchyma mean linear intercept (DFS: 36.3 ± 0.8; Air: 33.3 ± 0.8 μm) and tissue thickness (DFS: 10.1 ± 0.5; Air: 7.4 ± 0.7 μm) were larger in DFS mice. Collectively, mice exposed to DFS manifested early signs of cardiopulmonary dysfunction aligned with self-reported events in mid-career WLFFs.

Lung function measurements in preclinical research: What has been done and where is it headed?

Due to the close interaction of lung morphology and functions, repeatable measurements of pulmonary function during longitudinal studies on lung pathophysiology and treatment efficacy have been a great area of interest for lung researchers. Spirometry, as a simple and quick procedure that depends on the maximal inspiration of the patient, is the most common lung function test in clinics that measures lung volumes against time. Similarly, in the preclinical area, plethysmography techniques offer lung functional parameters related to lung volumes. In the past few decades, many innovative techniques have been introduced for in vivo lung function measurements, while each one of these techniques has their own advantages and disadvantages. Before each experiment, depending on the sensitivity of the required pulmonary functional parameters, it should be decided whether an invasive or non-invasive approach is desired. On one hand, invasive techniques offer sensitive and specific readouts related to lung mechanics in anesthetized and tracheotomized animals at endpoints. On the other hand, non-invasive techniques allow repeatable lung function measurements in conscious, free-breathing animals with readouts related to the lung volumes. The biggest disadvantage of these standard techniques for lung function measurements is considering the lung as a single unit and providing only global readouts. However, recent advances in lung imaging modalities such as x-ray computed tomography and magnetic resonance imaging opened new doors toward obtaining both anatomical and functional information from the same scan session, without the requirement for any extra pulmonary functional measurements, in more regional and non-invasive manners. Consequently, a new field of study called pulmonary functional imaging was born which focuses on introducing new techniques for regional quantification of lung function non-invasively using imaging-based techniques. This narrative review provides first an overview of both invasive and non-invasive conventional methods for lung function measurements, mostly focused on small animals for preclinical research, including discussions about their advantages and disadvantages. Then, we focus on those newly developed, non-invasive, imaging-based techniques that can provide either global or regional lung functional readouts at multiple time-points.

Understanding the fundamentals of oscillometry from a strip of lung tissue

Metrics used in spirometry caught on in respiratory medicine not only because they provide information of clinical importance but also because of a keen understanding of what is being measured. The forced expiratory volume in 1 s (FEV₁), for example, is the maximal volume of air that can be expelled during the first second of a forced expiratory maneuver starting from a lung inflated to total lung capacity (TLC). Although it represents a very gross measurement of lung function, it is now used to guide the diagnosis and management of many lung disorders. Metrics used in oscillometry are not as concrete. Resistance, for example, has several connotations and its proper meaning in the context of a lung probed by an external device is not always intuitive. I think that the popularization of oscillometry and its firm implementation in respiratory guidelines starts with a keen understanding of what exactly is being measured. This review is an attempt to clearly explain the basic metrics of oscillometry. In my opinion, the fundamentals of oscillometry can be understood using a simple example of an excised strip of lung tissue subjected to a sinusoidal strain. The key notion is to divide the sinusoidal reacting force from the tissue strip into two sinusoids, one in phase with the strain and one preceding the strain by exactly a quarter of a cycle. Similar notions can then be applied to a whole lung subjected to a sinusoidal flow imposed at the mouth by an external device to understand basic metrics of oscillometry, including resistance, elastance, impedance, inertance, reactance and resonant frequency.

Update on the Features and Measurements of Experimental Acute Lung Injury in Animals: An Official American Thoracic Society Workshop Report

Advancements in methods, technology, and our understanding of the pathobiology of lung injury have created the need to update the definition of experimental acute lung injury (ALI). We queried 50 participants with expertise in ALI and acute respiratory distress syndrome using a Delphi method composed of a series of electronic surveys and a virtual workshop. We propose that ALI presents as a "multidimensional entity" characterized by four "domains" that reflect the key pathophysiologic features and underlying biology of human acute respiratory distress syndrome. These domains are 1) histological evidence of tissue injury, 2) alteration of the alveolar-capillary barrier, 3) presence of an inflammatory response, and 4) physiologic dysfunction. For each domain, we present "relevant measurements," defined as those proposed by at least 30% of respondents. We propose that experimental ALI encompasses a continuum of models ranging from those focusing on gaining specific mechanistic insights to those primarily concerned with preclinical testing of novel therapeutics or interventions. We suggest that mechanistic studies may justifiably focus on a single domain of lung injury, but models must document alterations of at least three of the four domains to qualify as "experimental ALI." Finally, we propose that a time criterion defining "acute" in ALI remains relevant, but the actual time may vary based on the specific model and the aspect of injury being modeled. The continuum concept of ALI increases the flexibility and applicability of the definition to multiple models while increasing the likelihood of translating preclinical findings to critically ill patients.

Signal processing to remove spurious contributions to the assessment of respiratory mechanics

Signal disruptions in small animals during the realization of the Forced Oscillation Technique are a well-known cause of data loss as it leads to non-reliable estimations of the respiratory impedance. In this work, we assessed the effects of removing the disrupted epoch when a 3-seconds input signal composed of one and a half 2-seconds full cycle is used.

We tested our hypothesis in 25 SAMR1 mice under different levels of bronchoconstriction due to methacholine administration by iv bolus injections in different doses (15 animals) and by iv continuous infusion in different infusion rates (10 animals). Signal disruptions were computationally simulated as sharp drops in the pressure signal within a short timescale, and signal processing was performed using own developed algorithms.

We found that the model goodness of fit worsens when averaging techniques to estimate the input respiratory impedance are not used. However, no statistically significant differences were observed in the comparison between Constant Phase Model parameters of the full 3-s signal and the 2-s non disrupted epoch in all doses or infusion rates for both methacholine delivery strategies.

The proposed technique presents reliable outcomes that can reduce animal use in Forced Oscillation Technique realization.

Double-chamber plethysmography versus oscillometry to detect baseline airflow obstruction in a model of asthma in two mouse strains

AIM OF THE STUDY

The current gold standard to assess respiratory mechanics in mice is oscillometry, a technique from which several readouts of the respiratory system can be deduced, such as resistance and elastance. However, these readouts are often not altered in mouse models of asthma. This is in stark contrast with humans, where asthma is generally associated with alterations when assessed by either oscillometry or other techniques. In the present study, we have used double-chamber plethysmography (DCP) to evaluate the breathing pattern and the degree of airflow obstruction in a mouse model of asthma.

MATERIALS AND METHODS

Female C57BL/6 and BALB/c mice were studied at day 1 using DCP, as well as at day 11 using both DCP and oscillometry following a once-daily exposure to either house-dust mite (HDM) or saline for 10 consecutive days.

RESULTS

All DCP readouts used to describe either the breathing pattern (e.g., tidal volume and breathing frequency) or the degree of airflow obstruction (e.g., specific airway resistance) were different between mouse strains at day 1. Most of these strain differences persisted at day 11. Most oscillometric readouts (e.g., respiratory system resistance and elastance) were also different between strains. Changes caused by HDM were obvious with DCP, including decreases in tidal volume, minute ventilation, inspiratory time and mid-tidal expiratory flow and an increase in specific airway resistance. HDM also caused some strain specific alterations in breathing pattern, including increases in expiratory time and end inspiratory pause, which were only observed in C57BL/6 mice. Oscillometry also detected a small but significant increase in tissue elastance in HDM versus saline-exposed mice.

CONCLUSIONS

DCP successfully identified differences between C57BL/6 and BALB/c mice, as well as alterations in mice from both strains exposed to HDM. We conclude that, depending on the study purpose, DCP may sometimes outweigh oscillometry.

Noninvasive Measurement of Pulmonary Function in Experimental Mouse Models of Airway Disease

Mouse models have become an indispensable tool in translational research of human airway disease and have provided much of our understanding of the pathogenesis of airway disease such as asthma. In these models the ability to assess pulmonary function and particularly airway responsiveness is critically important. Existing methods for testing pulmonary function in mice in vivo include noninvasive and invasive technologies. Noninvasive head-out body plethysmography is a well-established and widely accepted technique which has been proven as a reliable method to measure lung function on repeated occasions in intact, conscious mice. We have performed several validation studies in allergic mice to compare the parameter midexpiratory flow (EF₅₀) as a noninvasive marker of airflow limitation with invasively measured gold standard parameters of lung mechanics. The results of these studies showed a good agreement of EF₅₀ with the invasive assessment of lung resistance and dynamic compliance with a somewhat lower sensitivity of EF₅₀. The measurement of EF₅₀ together with basic respiratory parameters is particularly appropriate for simple and repeatable screening of pulmonary function in large numbers of mice or if noninvasive measurement without use of anesthesia is required. Beyond known applications, head-out body plethysmography also provides a much-needed high-throughput screening tool to gain insights into the impact and kinetics of respiratory infections such as SARS-COV-2 on lung physiology in laboratory mice.

Oscillometry of the respiratory system: a translational opportunity not to be missed

Airway oscillometry has become the de facto standard for quality assessment of lung physiology in laboratory animals and has demonstrated its usefulness in understanding diseases of small airways. Nowadays, it is seeing extensive use in daily clinical practice and research; however, a question that remains unanswered is how well physiological findings in animals and humans correlate? Methodological and device differences are obvious between animal and human studies. However, all devices deliver an oscillated airflow test signal and output respiratory impedance. In addition, despite analysis differences, there are ways to interpret animal and human oscillometry data to allow suitable comparisons. The potential with oscillometry is its ability to reveal universal features of the respiratory system across species, making translational extrapolation likely to be predictive. This means that oscillometry can thus help determine if an animal model displays the same physiological characteristics as the human disease. Perhaps more importantly, it can also be useful to determine whether an intervention is effective as well as to understand if it affects the desired region of the respiratory system, e.g., the periphery of the lung. Finally, findings in humans can also inform preclinical scientists and give indications as to what type of physiological changes should be observed in animal models to make them relevant as models of human disease. The present article will attempt to demonstrate the potential of oscillometry in respiratory research, an area where the development of novel therapies is plagued with a failure rate higher than in other disease areas.

An oropharyngeal device for airway management of conscious and semiconscious patients: A randomized clinical trial

OBJECTIVE

No oropharyngeal devices exist for use in conscious and semiconscious trauma patients during emergency evacuation, transport, or resuscitation. We aimed to test the hypotheses that the ManMaxAirway (MMA) is better tolerated than the standard Guedel-style device in awake volunteers and that it produces a jaw thrust and improves air flow.

METHODS

This was a randomized cross-over study of healthy volunteers with either the MMA or standard device. The primary outcome of tolerability was defined as maintaining the device in place for 60 seconds. Secondary outcomes included respiratory system function and jaw thrust. Resistance to airflow through the device lumen was measured in situ and when placed in subjects in the pulmonary laboratory alone. Jaw thrust was quantified as displacement between the mandibular condyle and condylar fossa apex relative to baseline visualized with magnetic resonance imaging (MRI).

RESULTS

We enrolled 19 subjects. Of these, a convenience sample of 5 individuals was selected for MRI; the remaining individuals (n = 14) were randomized for the cross-over study. All 14 subjects were able to maintain the MMA for 60 seconds compared with 2/14 (14%) with the standard device (odds ratio, 145; 95% confidence interval, 6.3-3314). Subjects reported that the experimental device was more comfortable and its placement did not trigger the gag reflex. Airway resistance produced by the MMA in an oscillatory flow model was nearly an order of magnitude lower than that of the standard device (experimental vs standard, 8 Hz-0.092 vs 0.786 cmH20·s/L; 15 Hz-0.193 vs 1.321 cmH20·s/L). Rapid induction of the gag reflex precluded further measurements with the standard device. Forced oscillation pulmonary testing in conscious volunteers with and without the MMA demonstrated that the device decreased respiratory system resistance to airflow and reduced respiratory elastance (31% ± 8% and 44% ± 13.4%, respectively; P < 0.05). MRIs of the subjects (n = 5) with the MMA in place showed a significant jaw thrust compared with baseline (7 ± 1 mm).

CONCLUSIONS

The MMA proved well tolerated in conscious subjects, resulting in an opening of the anatomic airway and a decreased resistance to airflow.

Drug class effects on respiratory mechanics in animal models: access and applications

Assessment of respiratory mechanics extends from basic research and animal modeling to clinical applications in humans. However, to employ the applications in human models, it is desirable and sometimes mandatory to study non-human animals first. To acquire further precise and controlled signals and parameters, the animals studied must be further distant from their spontaneous ventilation. The majority of respiratory mechanics studies use positive pressure ventilation to model the respiratory system. In this scenario, a few drug categories become relevant: anesthetics, muscle blockers, bronchoconstrictors, and bronchodilators. Hence, the main objective of this study is to briefly review and discuss each drug category, and the impact of a drug on the assessment of respiratory mechanics. Before and during the positive pressure ventilation, the experimental animal must be appropriately sedated and anesthetized. The sedation will lower the pain and distress of the studied animal and the plane of anesthesia will prevent the pain. With those drugs, a more controlled procedure is carried out; further, because many anesthetics depress the respiratory system activity, a minimum interference of the animal's respiration efforts are achieved. The latter phenomenon is related to muscle blockers, which aim to minimize respiratory artifacts that may interfere with forced oscillation techniques. Generally, the respiratory mechanics are studied under appropriate anesthesia and muscle blockage. The application of bronchoconstrictors is prevalent in respiratory mechanics studies. To verify the differences among studied groups, it is often necessary to challenge the respiratory system, for example, by pharmacologically inducing bronchoconstriction. However, the selected bronchoconstrictor, doses, and administration can affect the evaluation of respiratory mechanics. Although not prevalent, studies have applied bronchodilators to return (airway resistance) to the basal state after bronchoconstriction. The drug categories can influence the mathematical modeling of the respiratory system, systemic conditions, and respiratory mechanics outcomes.

Measuring Breathing Patterns in Mice Using Whole-body Plethysmography

Respiratory dysfunction is among the main cause of severe and fatal pathologies worldwide. The use of effective experimental models and methodologies for the study of the pulmonary pathophysiology is necessary to prevent, control and cure these diseases. Plethysmography, a technique for the assessment of lung function, has been widely applied in mice for the characterization of respiratory physiology. However, classical plethysmography methods present technical limitations such as the use of anesthesia and animal immobilization. Whole-body plethysmography (WBP) avoids these issues providing a non-invasive approach for the assessment of the respiratory function in conscious animals. WBP relies on the recording of pressure changes that are produced by the spontaneous breathing activity of an animal placed inside an airtight chamber. During normal respiration, pressure variation is directly proportional to the respiratory pattern of the animal allowing the measurement of the respiratory rate and tidal volume. These parameters are commonly used to evaluate pulmonary function in different physiological and disease models. In contrast to classical plethysmography methods, WBP technique allows reproducible serial measurements as it avoids animal restraint or the use of anesthesia. These key features rend WBP a suitable approach for longitudinal studies allowing the assessment of progressive respiratory alterations in physiological and pathological conditions. This protocol describes the procedures for the measurement of the breathing patterns in mice using the WBP method, the data analysis and results interpretation.

N6-methyladenosine-dependent primary microRNA-126 processing activated PI3K-AKT-mTOR pathway drove the development of pulmonary fibrosis induced by nanoscale carbon black particles in rats

The pulmonary fibrosis could be caused by long-term inhalation of carbon black (CB) particles. Studies on the mechanisms of pulmonary fibrosis induced by CB are required to develop the stratagem of prevention and treatment on fibrosis. The RNA-binding protein DiGeorge syndrome critical region gene 8 (DGCR8)-dependent pri-miRNAs processing is regulated by N⁶-methyladenosine (m⁶A) modification, which targets the downstream signal pathway. However, its role in pulmonary fibrosis has not been known clearly. In the present study, rats inhaled CB at dose of 0, 5 or 30 mg/m³ for 28 days, 6 h/day, respectively. The rats inhaled CB at dose of 0 or 30 mg/m³ for 14 days, 28 days and 90 days, respectively. In vitro experiments, the normal human bronchial epithelial cell line (16HBE) was treated with CB (0, 50, 100 and 200 μg/mL) for 24 h. In vitro and vivo study, the levels of fibrosis indicators including α-SMA, vimentin, collagen-I and hydroxyproline in CB treatment groups statistically increased in dose- or time- dependent manners compared with the control. After CB treatment, PI3K-AKT-mTOR pathway was activated and regulated by miRNA-126. We found that both of m⁶A modifications of pri-miRNA-126 and its binding with DGCR8 were decreased after CB treatment, which resulted in the reduction of mature miRNA-126 accompanied by accumulation of unprocessed pri-miRNA-126. This work demonstrated that m⁶A modification of pri-miRNA-126 and its binding with DGCR8 decreases blocked miRNA-126 maturation, and then activated the PI3K/AKT/mTOR pathway, which drove the fibro genesis in the lung after CB exposure.

Feasibility of forced oscillatory assessment of respiratory mechanics across a laryngeal mask airway in rabbits

OBJECTIVES

The forced oscillation technique (FOT) is the method of choice for assessment of respiratory tissue mechanics. A laryngeal mask airway (LMA) is increasingly used to secure the airways in subjects under sedation or general anesthesia. While FOT is routinely performed using an endotracheal tube (ETT), the accuracy of information about airway and tissue mechanics obtained with FOT using a LMA has not been characterized. Therefore, we compared the mechanical parameters obtained with FOT using LMA and ETT in rabbits.

APPROACH

FOT was performed through a LMA at normal and reduced oscillatory amplitudes in anesthetized and mechanically ventilated rabbits (n  =  9) at positive end-expiratory pressures (PEEP) of 3 and 6 cmH₂O. These measurements were repeated at normal amplitude for the same animal using an ETT. Airway resistance, inertance, respiratory tissue damping (G) and elastance (H) were measured under each condition by FOT. The potential bias of the distensible upper airways when FOT was applied using LMA was assessed with a simulation study.

MAIN RESULTS

Values of parameters reflecting airway mechanics were significantly higher when measured using LMA at both PEEPs and oscillatory amplitudes than with ETT. Conversely, regardless of the condition, there was a correlation (r  =  0.89 both at normal and reduced amplitudes; p   <  0.0001) with good agreement (mean bias of 8.8 cmH₂O/l and 11.3 cmH₂O/l) in H, whereas G was systematically lower when obtained with LMA than with ETT at PEEP 3 (21.1%  ±  7.2% and 9.6%  ±  6.9% at normal and reduced oscillatory amplitudes, respectively) and 6 cmH₂O (15.1%  ±  8.2%, 1.6%  ±  9.4%, p   <  0.05 for all).

SIGNIFICANCE

Mechanical properties of the airways and the respiratory tissues, particularly for respiratory tissue stiffness, can be reliably assessed using LMA. However, the involvement of a longer laryngo-tracheo-bronchial pathway when using LMA should be considered for airway resistance and inertance, whereas upper airway shunting may affect the assessment of respiratory tissue damping.

Assessment of Respiratory Function in Conscious Mice by Double-chamber Plethysmography

Air volume changes created by a conscious subject breathing spontaneously within a body box are at the basis of plethysmography, a technique used to non-invasively assess some features of the respiratory function in humans as well as in laboratory animals. The present article focuses on the application of the double-chamber plethysmography (DCP) in small animals. It provides background information on the methodology as well as a detailed step-by-step procedure to successfully assess respiratory function in conscious, spontaneously breathing animals in a non-invasive manner. The DCP can be used to monitor the respiratory function of multiple animals in parallel, as well as to identify changes induced by aerosolized substances over a chosen time period and in a repeated manner. Experiments on control and allergic mice are used herein to demonstrate the utility of the technique, explain the associated outcome parameters, as well as to discuss the related advantages and shortcomings. Overall, the DCP provides valid and theoretically sound readouts that can be trusted to evaluate the respiratory function of conscious small animals both at baseline and after challenges with aerosolized substances.

Quantitative Imaging of Regional Aerosol Deposition, Lung Ventilation and Morphology by Synchrotron Radiation CT

To understand the determinants of inhaled aerosol particle distribution and targeting in the lung, knowledge of regional deposition, lung morphology and regional ventilation, is crucial. No single imaging modality allows the acquisition of all such data together. Here we assessed the feasibility of dual-energy synchrotron radiation imaging to this end in anesthetized rabbits; both in normal lung (n = 6) and following methacholine (MCH)-induced bronchoconstriction (n = 6), a model of asthma. We used K-edge subtraction CT (KES) imaging to quantitatively map the regional deposition of iodine-containing aerosol particles. Morphological and regional ventilation images were obtained, followed by quantitative regional iodine deposition maps, after 5 and 10 minutes of aerosol administration. Iodine deposition was markedly inhomogeneous both in normal lung and after induced bronchoconstrition. Deposition was significantly reduced in the MCH group at both time points, with a strong dependency on inspiratory flow in both conditions (R² = 0.71; p < 0.0001). We demonstrate for the first time, the feasibility of KES CT for quantitative imaging of lung deposition of aerosol particles, regional ventilation and morphology. Since these are among the main factors determining lung aerosol deposition, we expect this imaging approach to bring new contributions to the understanding of lung aerosol delivery, targeting, and ultimately biological efficacy.