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Journal of Applied Physiology... Jul 2022Mice are a valuable model for elegant studies of complex, system-dependent diseases, including pulmonary diseases. Current tools to assess lung function in mice are...
Mice are a valuable model for elegant studies of complex, system-dependent diseases, including pulmonary diseases. Current tools to assess lung function in mice are either terminal or lack accuracy. We set out to develop a low-cost, accurate, head-out variable-pressure plethysmography system to allow for repeated, nonterminal measurements of lung function in mice. Current head-out plethysmography systems are limited by air leaks that prevent accurate measures of volume and flow. We designed an inflatable cuff that encompasses the mouse's neck preventing air leak. We wrote corresponding software to collect and analyze the data, remove movement artifacts, and automatically calibrate each dataset. This software calculates volume, inspiratory/expiratory time, breaths per minute, mid-expiratory flow, and end-inspiratory pause. To validate the use, we established that our plethysmography system accurately measured tidal breathing, the bronchoconstrictive response to methacholine, sex- and age-associated changes in breathing, and breathing changes associated with house dust mite sensitization. Our estimates of volume, flow, and timing of breaths are in line with published estimates, we observed dose-dependent decreases in volume and flow in response to methacholine ( < 0.05), increased lung volume, and decreased breathing rate with aging ( < 0.05), and that house dust mite sensitization decreased volume and flow ( < 0.05) while exacerbating the methacholine-induced increase in inspiratory time ( < 0.05). We describe an accurate, sensitive, low-cost, head-out plethysmography system that allows for longitudinal studies of pulmonary disease in mice. We describe a low-cost, variable-pressure head-out plethysmography system that can be used to assess lung function in mice. A balloon cuff is inflated around the mouse's neck to prevent air leak, allowing for accurate measurements of lung volume and air flow. Custom software facilitates system calibration, removes movement artifacts, and eases data analysis. The system was validated by measuring tidal breathing, responses to methacholine, and changes associated with house dust mite sensitization, sex, and aging.
Topics: Animals; Bronchoconstriction; Lung; Lung Volume Measurements; Methacholine Chloride; Mice; Plethysmography; Tidal Volume
PubMed: 35608203
DOI: 10.1152/japplphysiol.00835.2021 -
Journal of Applied Physiology... Jun 2022Specific ventilation imaging (SVI) measures the spatial distribution of specific ventilation (SV) in the lung with MRI by using inhaled oxygen as a contrast agent....
Specific ventilation imaging (SVI) measures the spatial distribution of specific ventilation (SV) in the lung with MRI by using inhaled oxygen as a contrast agent. Because of the inherently low signal-to-noise ratio in the technique, multiple switches between inspiring air and O are utilized, and the high spatial resolution SV distribution is determined as an average over the entire imaging period (∼20 min). We hypothesized that a trade-off between spatial and temporal resolution could allow imaging at a higher temporal resolution, at the cost of a coarser, yet acceptable, spatial resolution. The appropriate window length and spatial resolution compromise were determined by generating synthetic data with signal- and contrast-to-noise characteristics reflective of that in previously published experimental data, with a known and unchanging distribution of SV, and showed that acceptable results could be obtained in an imaging period of ∼7 min (80 breaths), with a spatial resolution of ∼1 cm. Previously published data were then reanalyzed. The average heterogeneity of the temporally resolved maps of SV was not different from the previous overall analysis, however, the temporally resolved maps were less effective at detecting the amount of bronchoconstriction resulting from methacholine administration. The results further indicated that the initial response to inhaled methacholine and subsequent inhalation of albuterol were largely complete within ∼22 min and ∼9 min, respectively, although there was a tendency for an ongoing developing effect in both cases. These results suggest that it is feasible to use a shortened SVI protocol, with a modest sacrifice in spatial resolution, to measure temporally dynamic processes. Dynamic imaging providing maps of specific ventilation with a temporal resolution of ∼7 min with a spatial resolution of ∼1 cm using MRI was shown to be practical. The technique provides an ionizing radiation free means of temporally following the spatial pattern of specific ventilation. Reanalysis of previously published data showed that the effects of inhaled methacholine and albuterol were largely complete at ∼22 min and ∼9 min, respectively after administration.
Topics: Albuterol; Bronchoconstriction; Lung; Magnetic Resonance Imaging; Methacholine Chloride; Oxygen
PubMed: 35482322
DOI: 10.1152/japplphysiol.00652.2021 -
Pediatric Allergy and Immunology :... Apr 2022Onset of wheeze is the endpoint often used in the determination of a positive bronchial challenge test (BCT) in young children who cannot perform spirometry. We sought...
BACKGROUND
Onset of wheeze is the endpoint often used in the determination of a positive bronchial challenge test (BCT) in young children who cannot perform spirometry. We sought to assess several clinical endpoints at the time of a positive BCT in young children with recurrent wheeze compared to findings in school-aged children with asthma.
METHODS
Positive BCT was defined in: (1) preschool children (n = 22) as either persistent cough, wheeze, fall in oxygen saturation (SpO ) of ≥5%, or ≥50% increase in respiratory rate (RR) from baseline; and (2) school-aged children (n = 22) as the concentration of methacholine (MCh) required to elicit a 20% decline in FEV (PC ).
RESULTS
All preschool children (mean age 3.4 years) had a positive BCT (median provocative MCh concentration 1.25 mg/ml [IQR, 0.62, 1.25]). Twenty (91%) school-aged children (mean age 11.3 years) had a positive BCT (median PC 1.25 mg/ml [IQR, 0.55, 2.5]). At the time of the positive BCT, the mean fall in SpO (6.9% vs. 3.8%; p = .001) and the mean % increase in RR (61% vs. 22%; p < .001) were greater among preschool-aged than among school-aged children. A minority of children developed wheeze at time of positive BCT (23% preschool- vs. 15% school-aged children; p = .5).
CONCLUSIONS
The use of wheeze as an endpoint for BCT in preschool children is unreliable, as it rarely occurs. The use of clinical endpoints, such as ≥25% increase in RR or fall in SpO of ≥3%, captured all of our positive BCT in preschool children, while minimizing undue respiratory distress.
Topics: Asthma; Bronchial Provocation Tests; Child; Child, Preschool; Humans; Methacholine Chloride; Respiratory Sounds; Spirometry
PubMed: 35470941
DOI: 10.1111/pai.13767 -
Role of hyperpnea in the relaxant effect of inspired CO on methacholine-induced bronchoconstriction.Journal of Applied Physiology... May 2022Inhaling carbon dioxide (CO) in humans is known to cause inconsistent effects on airway function. These could be due to direct effects of CO on airway smooth muscle or...
Inhaling carbon dioxide (CO) in humans is known to cause inconsistent effects on airway function. These could be due to direct effects of CO on airway smooth muscle or to changes in minute ventilation (V̇e). To address this issue, we examined the responses of the respiratory system to inhaled methacholine in healthy subjects and subjects with mild asthma while breathing air or gas mixtures containing 2% or 4% CO. Respiratory mechanics were measured by a forced oscillation technique at 5 Hz during tidal breathing. At baseline, respiratory resistance (R) was significantly higher in subjects with asthma (2.53 ± 0.38 cmHO·L·s) than healthy subjects (2.11 ± 0.42 cmHO·L·s) ( = 0.008) with room air. Similar values were observed with CO 2% or 4% in the two groups. V̇e, tidal volume (V), and breathing frequency (BF) significantly increased with CO-containing mixtures ( < 0.001) with insignificant differences between groups. After methacholine, the increase in R and the decrease in respiratory reactance (X) were significantly attenuated up to about 50% with CO-containing mixtures instead of room air in both asthmatic ( < 0.001) and controls ( < 0.001). Mediation analysis showed that the attenuation of methacholine-induced changes in respiratory mechanics by CO was due to the increase in V̇e ( = 0.006 for R and = 0.014 for X) independently of the increase in V or BF, rather than a direct effect of CO. These findings suggest that the increased stretching of airway smooth muscle by the CO-induced increase in V̇e is a mechanism through which hypercapnia can attenuate bronchoconstrictor responses in healthy subjects and subjects with mild asthma. The main results of the present study are as follows: ) breathing gas mixtures containing 2% or 4% CO significantly attenuated bronchoconstrictor responses to methacholine, not differently in healthy subjects and subjects with mild asthma, and ) the causal inhibitory effect of CO was significantly mediated via an indirect effect of the increment of V̇e in response to intrapulmonary hypercapnia.
Topics: Airway Resistance; Asthma; Bronchoconstriction; Bronchoconstrictor Agents; Carbon Dioxide; Humans; Hypercapnia; Hyperventilation; Methacholine Chloride
PubMed: 35358399
DOI: 10.1152/japplphysiol.00763.2021 -
American Journal of Physiology. Lung... May 2022Excessive production, secretion, and retention of abnormal mucus is a pathological feature of many obstructive airways diseases including asthma. Azithromycin is an...
Excessive production, secretion, and retention of abnormal mucus is a pathological feature of many obstructive airways diseases including asthma. Azithromycin is an antibiotic that also possesses immunomodulatory and mucoregulatory activities, which may contribute to the clinical effectiveness of azithromycin in asthma. The current study investigated these nonantibiotic activities of azithromycin in mice exposed daily to intranasal house dust mite (HDM) extract for 10 days. HDM-exposed mice exhibited airways hyperresponsiveness to aerosolized methacholine, a pronounced mixed eosinophilic and neutrophilic inflammatory response, increased airway smooth muscle (ASM) thickness, and elevated levels of epithelial mucin staining. Azithromycin (50 mg/kg sc, 2 h before each HDM exposure) attenuated HDM-induced airways hyperresponsiveness to methacholine, airways inflammation (bronchoalveolar lavage eosinophil and neutrophils numbers, and IL-4, IL-5, IL-6, IL-10, IL-12, IL-13, and RANTES levels), and epithelial mucin staining (mucous metaplasia) by at least 50% (compared with HDM-exposed mice, < 0.05). Isolated tracheal segments of HDM-exposed mice secreted Muc5ac and Muc5b (above baseline levels) in response to exogenous ATP. Moreover, ATP-induced secretion of mucins was attenuated in segments obtained from azithromycin-treated, HDM-exposed mice ( < 0.05). In additional ex vivo studies, ATP-induced secretion of Muc5ac (but not muc5b) from HDM-exposed tracheal segments was inhibited by in vitro exposure to azithromycin. In vitro azithromycin also inhibited ATP-induced secretion of Muc5ac and Muc5b in tracheal segments from IL-13-exposed mice. In summary, azithromycin inhibited ATP-induced mucin secretion and airways inflammation in HDM-exposed mice, both of which are likely to contribute to suppression of airways hyperresponsiveness.
Topics: Adenosine Triphosphate; Allergens; Animals; Asthma; Azithromycin; Disease Models, Animal; Inflammation; Interleukin-13; Metaplasia; Methacholine Chloride; Mice; Mucins; Mucus; Pyroglyphidae
PubMed: 35348023
DOI: 10.1152/ajplung.00487.2021 -
Respiratory Care Jun 2022There are several tests recommended by the American Thoracic Society (ATS) to evaluate for airway hyper-responsiveness (AHR), one of which is methacholine challenge...
BACKGROUND
There are several tests recommended by the American Thoracic Society (ATS) to evaluate for airway hyper-responsiveness (AHR), one of which is methacholine challenge testing (MCT). Few studies have examined the correlation of baseline spirometry to predict AHR in MCT, especially in the younger, relatively healthy military population under clinical evaluation for symptoms of exertional dyspnea. The study aim was to retrospectively correlate baseline spirometry values with MCT responsiveness.
METHODS
This study is a retrospective review of all MCT performed at Brooke Army Medical Center/Wilford Hall Medical Center over a 12-y period; all completed studies were obtained from electronic databases. The following parameters were analyzed from the studies: baseline FEV, FVC, FEV/FVC, mid-expiratory flow (FEV), FEV/FVC. Studies were categorized based on baseline obstruction, restriction, FEF lower limit of normal, and response to bronchodilator testing (if completed); these values were compared based on methacholine reactivity and severity.
RESULTS
Methacholine challenge studies ( 1,933) were reviewed and categorized into reactive ( 577) and nonreactive ( 1,356) as determined by ATS guidelines. The mean baseline FEV (% predicted) with MCT reactivity was 88.0 ± 13.0% versus no MCT reactivity was 92.7 ± 13.0% ( < .001). The mean baseline FVC (% predicted) was 93.1 ± 13.7% versus 95.3 ± 13.5% ( < .001). The mean baseline FEV (% predicted) was 80.0 ± 22.1% versus 89.0 ± 23.4% ( < .001). Based on partition analysis, methacholine reactivity was most prevalent with baseline obstruction, 115 (43%), and in the absence of obstruction, when the FEF (% predicted) was below 0.70, 111 (40%). The negative predictive value with normal spirometry was 73%.
CONCLUSIONS
The analysis of baseline spirometry prior to MCT proved useful in the evaluation of exertional dyspnea in a military population. The presence of airways obstruction (FEV/FVC < lower limit of the normal range) followed by a reduction in FEV < 70% predicted showed a positive correlation with underlying AHR. In patients with exertional dyspnea and normal baseline spirometry, the use of the FEF may be a useful surrogate measurement to predict reactivity during MCT and consideration for additional testing or treatment.
Topics: Bronchial Provocation Tests; Dyspnea; Forced Expiratory Volume; Humans; Methacholine Chloride; Retrospective Studies; Spirometry
PubMed: 35042746
DOI: 10.4187/respcare.09163 -
Pulmonary Medicine 2021To clarify whether in adults with a nonobstructive spirometry a reduced FEF25-75% is associated with a positive methacholine challenge test (MCT). (Observational Study)
Observational Study
OBJECTIVE
To clarify whether in adults with a nonobstructive spirometry a reduced FEF25-75% is associated with a positive methacholine challenge test (MCT).
METHODS
Data was collected for all the patients who had a MCT done between April 2014 and January 2020 but had nonobstructive baseline spirometry. Logistic regression was utilized to estimate the log odds of a positive methacholine test as a function of FEF25-75% and also for age, gender, BMI, FEV1, and FEV1/FVC.
RESULTS
Out of 496 patients, 187 (38%) had a positive MCT. Baseline characteristics in two groups were similar except that patients with positive MCT were younger (32 ± 11.57 vs. 38 ± 13.25 years, respectively, < 0.001). Mean FEF25-75% was lower in MCT positive (3.12 ± 0.99 L/s) vs. MCT negative (3.39 ± 0.97 L/s) patients, = 0.003. Logistic regression results suggest that MCT outcome is inversely related to FEF25-75%, age, and gender. Specifically, as FEF25-75% percentage of predicted value increases, the log odds of a positive MCT decrease (odds ratio (OR) = 0.90, 95% confidence intervals (CI) = 0.84-0.96, = 0.002). Also, as age increases, the log odds of a positive MCT decrease (OR = 0.95, 95%CI = 0.94-0.97, < 0.001).
CONCLUSIONS
Reduced FEF25-75% in adults with nonobstructive spirometry can predict a positive response to MCT in younger patients. However, this relationship becomes weaker with increasing age.
Topics: Adult; Asthma; Bronchial Provocation Tests; Female; Forced Expiratory Volume; Humans; Male; Methacholine Chloride; Middle Aged; Retrospective Studies; Spirometry
PubMed: 35003806
DOI: 10.1155/2021/6959322 -
American Journal of Physiology. Lung... Feb 2022There are renewed interests in using the parameter K of Salazar-Knowles' equation to assess lung tissue compliance. K either decreases or increases when the lung's...
There are renewed interests in using the parameter K of Salazar-Knowles' equation to assess lung tissue compliance. K either decreases or increases when the lung's parenchyma stiffens or loosens, respectively. However, whether K is affected by other common features of respiratory diseases, such as inflammation and airway smooth muscle (ASM) contraction, is unknown. Herein, male C57BL/6 mice were treated intranasally with either saline or lipopolysaccharide (LPS) at 1 mg/kg to induce pulmonary inflammation. They were then subjected to either a multiple or a single-dose challenge with methacholine to activate ASM to different degrees. A quasi-static pressure-driven partial pressure-volume (P-V) maneuver was performed before and after methacholine. The Salazar-Knowles' equation was then fitted to the deflation limb of the P-V loop to obtain K, as well as the parameter A, an estimate of lung volume (inspiratory capacity). The fitted curve was also used to derive the quasi-static elastance (E) at 5 cmHO. The results demonstrate that LPS and both methacholine challenges increased E. LPS also decreased A, but did not affect K. In contradistinction, methacholine decreased both A and K in the multiple-dose challenge, whereas it decreased K but not A in the single-dose challenge. These results suggest that LPS increases E by reducing the open lung volume (A) and without affecting tissue compliance (K), whereas methacholine increases E by decreasing tissue compliance with or without affecting lung volume. We conclude that lung tissue compliance, assessed using the parameter K of Salazar-Knowles' equation, is insensitive to inflammation but sensitive to ASM contraction.
Topics: Airway Resistance; Animals; Inflammation; Lipopolysaccharides; Lung; Lung Compliance; Male; Methacholine Chloride; Mice; Mice, Inbred C57BL; Muscle Contraction; Respiratory Mechanics
PubMed: 34936511
DOI: 10.1152/ajplung.00384.2021 -
American Journal of Physiology. Lung... Feb 2022Obese asthmatics tend to have severe, poorly controlled disease and exhibit methacholine hyperresponsiveness manifesting in proximal airway narrowing and distal lung...
Obese asthmatics tend to have severe, poorly controlled disease and exhibit methacholine hyperresponsiveness manifesting in proximal airway narrowing and distal lung tissue collapsibility. Substantial weight loss in obese asthmatics or in mouse models of the condition decreases methacholine hyperresponsiveness. Ketone bodies are rapidly elevated during weight loss, coinciding with or preceding relief from asthma-related comorbidities. As ketone bodies may exert numerous potentially therapeutic effects, augmenting their systemic concentrations is being targeted for the treatment of several conditions. Circulating ketone body levels can be increased by feeding a ketogenic diet or by providing a ketone ester dietary supplement, which we hypothesized would exert protective effects in mouse models of inherent obese asthma. Weight loss induced by feeding a low-fat diet to mice previously fed a high-fat diet was preceded by increased urine and blood levels of the ketone body β-hydroxybutyrate (BHB). Feeding a ketogenic diet for 3 wk to high-fat diet-fed obese mice or genetically obese mice increased BHB concentrations and decreased methacholine hyperresponsiveness without substantially decreasing body weight. Acute ketone ester administration decreased methacholine responsiveness of normal mice, and dietary ketone ester supplementation of high-fat diet-fed mice decreased methacholine hyperresponsiveness. Ketone ester supplementation also transiently induced an "antiobesogenic" gut microbiome with a decreased ratio. Dietary interventions to increase systemic BHB concentrations could provide symptom relief for obese asthmatics without the need for the substantial weight loss required of patients to elicit benefits to their asthma through bariatric surgery or other diet or lifestyle alterations.
Topics: 3-Hydroxybutyric Acid; Animals; Asthma; Bronchial Hyperreactivity; Diet, High-Fat; Diet, Ketogenic; Disease Models, Animal; Esters; Gastrointestinal Microbiome; Ketone Bodies; Ketosis; Male; Methacholine Chloride; Mice, Inbred C57BL; Obesity; Weight Loss; Mice
PubMed: 34936508
DOI: 10.1152/ajplung.00309.2021 -
Respiratory Care Dec 2021Methacholine bronchoprovocation or challenge testing (MCT) is commonly performed to assess airway hyper-responsiveness in the setting of suspected asthma. Nebulization...
BACKGROUND
Methacholine bronchoprovocation or challenge testing (MCT) is commonly performed to assess airway hyper-responsiveness in the setting of suspected asthma. Nebulization is an aerosol-generating procedure, but little is known about the risks of MCT in the context of the ongoing coronavirus disease 2019 (COVID-19) pandemic. We aimed to quantify and characterize aerosol generation during MCT by using different delivery methods and to assess the impact of adding a viral filter.
METHODS
Seven healthy subjects performed simulated MCT in a near particle-free laboratory space with 4 different nebulizers and with a dosimeter. Two devices continuously sampled the ambient air during the procedure, which detected ultrafine particles, from 0.02-1 μm, and particles of sizes 0.3, 0.5, 1.0, 2.0, 5.0, and 10 µm, respectively. Particle generation was compared among all the devices, with and without viral filter placement.
RESULTS
Ultrafine-particle generation during simulated MCT was significant across all the devices. Ultrafine-particle (0.02-1 μm) concentrations decreased 77%-91% with the addition of a viral filter and varied significantly between unfiltered < .001) and filtered devices < .001). Ultrafine-particle generation was lowest when using the dosimeter with filtered Hudson nebulizer (1,258 ± 1,644 particle/mL). Ultrafine-particle concentrations with the filtered nebulizer devices using a compressor were higher than particle concentrations detected when using the dosimeter: Monaghan (3,472 ± 1,794 particles/mL), PARI (4,403 ± 2,948), Hudson (6,320 ± 1,787) and AirLife (9,523 ± 5,098).
CONCLUSIONS
The high particle concentrations generated during MCT pose significant infection control concerns during the COVID-19 pandemic. Particle generation during MCT was significantly reduced by using breath-actuated delivery and a viral filter, which offers an effective mitigation strategy.
Topics: Aerosols; COVID-19; Humans; Infection Control; Methacholine Chloride; Nebulizers and Vaporizers; Pandemics; Particle Size; SARS-CoV-2
PubMed: 34789516
DOI: 10.4187/respcare.09236