Rationale: Methacholine and mannitol challenges are used clinically to assess airway hyperresponsiveness (AHR). Cough during (a) high-dose methacholine challenge in individuals with methacholine-induced cough and normal airway sensitivity and (b) mannitol challenge in some individuals with asthma both occur in the absence of significant declines in forced expiratory volume in one second (FEV1). We hypothesized mechanical responses to these challenges would reflect a continuum amongst subjects with: (i) asthma; (ii) cough variant asthma (CVA) and (iii) methacholine-induced cough and normal airway sensitivity due to varying degrees of impairment/preservation of the beneficial effects of deep inspirations. Purpose: To compare cough and airway responses to mannitol and high-dose methacholine challenges between these groups. Methods: Individuals with asthma or suspected CVA were invited to participate. Subjects were challenged with mannitol and high-dose methacholine in random order 2-14 days apart. Cough frequency, spirometry and esophageal-pressure were recorded at baseline and after each dose of mannitol and methacholine to a maximal decline in FEV1 of 15% and 50% respectively. Plethysmography was used to measure lung volumes at baseline, the dose nearest to a 15% decline in FEV1 during mannitol challenge (PD15) and 20% decline in FEV1 during methacholine challenge (PC20), and at the highest dose of methacholine. Measurements were compared: (a) between groups at PD15, PC20 and the highest dose of methacholine; and (b) within groups at PD15 and PC20, and the highest equivalent level of bronchoconstriction. Results: 22 subjects (17 female; 48.0±12.7 (mean±SD years)) who completed both challenges were included. All subjects coughed during both challenges. Mechanical responses to mannitol and high-dose methacholine challenges reflected a continuum amongst groups. Six of 8 subjects with asthma were mannitol postitive (PD15=115.2±100.0 mg) and were significantly more sensitive to mannitol compared to 3 of 5 mannitol positive subjects with CVA (PD15=533.6±88.3 mg; p=0.020) and 3 of 9 mannitol positive subjects with methacholine-induced cough and normal airway sensitivity (PD15=472.8±203.0 mg; p=0.037). At the highest equivalent level of bronchoconstriction, methacholine induced significant declines in FEF50% and FEF25-75% in all subjects groups while mannitol did not. Conclusion: Mechanical responses to mannitol and high-dose methacholine challenges reflected a continuum amongst groups. / Thesis (Master, Physiology) -- Queen's University, 2012-07-27 08:58:05.298

Rationale: The pathophysiologic differences between classic asthma (CA), cough variant asthma (CVA), and methacholine (MCh)-induced cough but normal airway sensitivity (COUGH) are poorly understood and may relate to differences in small airway function. We hypothesized that the bronchodilating and bronchoprotective effects of DIs are: (a) absent or impaired in individuals with CA; (b) impaired in individuals with CVA; and (c) preserved in those with COUGH. Purpose: To compare the effect of DIs in individuals with CA, CVA and COUGH using high-dose methacholine (MCh). Methods: Individuals aged 18-65 years with CA, or suspected CVA attended 3 visits. On visit 1, subjects performed body plethysmography and high-dose MCh testing to a maximum change (Δ) in FEV1 of 50% from baseline (MAX). On visits 2 and 3, subjects performed one of two modified single-dose MCh challenge tests with or without DIs prior to MCh administration. Partial and maximal-flow volume curves (used to calculated a DI index), impulse oscillometry (IOS) measurements and breathlessness (Borg scale) were recorded at baseline and at each dose of MCh. Lung volumes were measured by body plethysmography at baseline and MAX. Responses from baseline to a 20% decline in FEV1 (PC20) or MAX, and between visits with or without DIs were compared using paired t-tests. Between group differences were assessed by analysis of variance. Results: 19 subjects (14 female; 45.1±13.1 years (MEAN±SD)) completed the protocol (n=8 CA, n=7 CVA, and n=4 COUGH). At the dose nearest to PC20, the DI index was positive in all 3 groups, indicating preserved bronchodilation (CA: 0.88±0.67; CVA: 0.33±0.39; COUGH: 0.016±0.46; P=.0.076). There were no significant differences in: the Δs in spirometry, lung volumes, airway resistance, IOS measurements, closing indices, the DI index, or dyspnea when the single dose of MCh was preceded either by five DIs or by DI avoidance in CVA and COUGH. DIs in CA resulted in greater Δs in mid-to-late flows. Conclusion: The bronchodilating effect of DIs is preserved in CA, CVA and COUGH. The bronchoprotective effect may fall along a continuum. A larger study including subjects with more severe CA is required to definitively test the hypotheses. / Thesis (Master, Physiology) -- Queen's University, 2014-06-28 11:23:29.814

Methacholine (MCh) and mannitol challenges are tests used to assess airway responsiveness. It has been shown that airway responsiveness to direct bronchoconstrictors like MCh tends to increase following exposure to allergen but the response to mannitol an indirect stimuli, is not known. Furthermore, the provocative concentration causing a 20% decrease in Forced Expiratory Volume in one second (FEV1) for adenosine 5’ monophosphate (AMP) correlates better to sputum eosinophilia than MCh PC 20. Hence, we hypothesized that airway responsiveness will be greater when measured with mannitol than MCh. We studied airway responsiveness to MCh and mannitol first at 3 hours and then later at 24 hours after allergen challenge. The 3-hour study yielded results contrary to our hypothesis therefore a twenty-four hour study was undertaken. Ten mild atopic asthmatics who had a positive MCh challenge and an allergic response to allergen extracts such as cat, horse, and house dust mite completed the 3-hour study. Eleven mild atopic asthmatics with the criteria above completed the 24-hour study. Both studies were non-blinded, randomized clinical trials. Airway responsiveness to MCh was quantitated by changes in PC20. Airway responsiveness to mannitol was quantitated as PD15 in the 3-hour study and dose response ratio (DRR) in the 24-hour study. In both studies, the allergen challenges were separated by 14 days. Fractional exhaled nitric oxide measurements (FENO) were collected in both studies at varying time points to track airway inflammation. In the 3-hour study, the geometric mean MCh PC20 decreased significantly after allergen exposure from 0.88 mg/ml to 0.50 mg/ml (p = 0.02) indicating airway responsiveness to MCh increased. Conversely, the geometric mean mannitol PD15 increased significantly from 174 mg to 284 mg (p =0.02) indicating a decrease in airway responsiveness to mannitol. In the 24-hour study, the geometric mean MCh PC20 again decreased significantly from 5.9 mg/ml to 2.2 mg/ml (p= 0.01) after allergen exposure. The mannitol DRR increased significantly from 63 mg/∆%FEV1 to 158 mg/∆%FEV1 (p = 0.03). FENO levels increased significantly in MCh arm but not mannitol arm. That is pre allergen challenge versus 24 hours after allergen challenge (for MCh arm: 26 ppb pre to 55 ppb post; for mannitol arm: 31 ppb pre to 39 ppb post). In conclusion, at three and twenty-four hours after allergen challenge, a time when the airways are more responsive to MCh, there is a significant decrease in airway responsiveness to mannitol.

Microvascular dysfunction is believed to precede the development and contribute to the progression of obesity related diseases such as insulin resistance, hypertension, and coronary artery disease. Multiple studies have found impaired microvascular endothelium-dependent vasodilation occurs prior to the onset of disease in middle aged adults. In order to test the hypothesis that the cutaneous microvasculature of young obese (BMI>30kg/m²), but otherwise healthy, adults would exhibit impaired microvascular response, we recruited 12 obese and 12 lean (BMI<25 kg/m²) individuals. Each group was age-matched and consisted of 5 females and 7 males. Each participant was instrumented with two microdialysis probes inserted in the dermis of the non-dominant forearm for a wide dose range of infusions of either the endothelium-dependent vasodilator methacholine (MCh) or the endothelium-independent vasodilator sodium nitroprusside (SNP). Each microdialysis site was clamped at 33°C with a local heater and affixed with a laser Doppler flux (LDF) probe for determination of local red blood cell flux, an index of blood flow. LDF was recorded continuously while 7 doses of each drug (MCh: 10⁻³-10³mM; SNP: 5x10⁻⁵-50mM) were infused at a rate of 2 [mu]l/min for 8 minutes per dose. Both sites finished with heating to 43°C and infusion of 50mM SNP to confirm site specific maximal vasodilation. Blood pressure was recorded in the last minute of each stage and the corresponding LDF was used to calculate cutaneous vascular conductance (CVC). Dose response curves for CVC at each dose, as well as maximal CVC were analyzed. MCh dose response showed a trend toward endothelium–dependent impairment in obese (p=0.06) and maximal absolute CVC at the MCh site was attenuated in obese versus lean (2.70 ± 0.73 vs 3.30 ± 0.81 LDF/mmHg, p=0.027). Endothelium-independent vasodilation with SNP was impaired at the 4 highest doses of SNP (all P<0.006) and maximal CVC was attenuated in obese compared to lean (2.44 ± 0.74 vs 3.31 ± 0.65 LDF/mmHg, p=0.004). These results support the hypothesis that microvascular function is impaired in young, healthy obese, individuals; however they suggest the impairment is partially endothelium-independent. / text

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2006. / Härtill 4 uppsatser.

Pasture-associated severe equine asthma (EPA) is a progressive condition affecting horses in the southeastern United States. Pulmonary function testing with methacholine challenge (MC) provides a definitive diagnosis by eliciting airway hyper-responsiveness. Most horses require extensive conditioning to accept the instrumentation. Our hypothesis was that MC protocols designed to elicit airway hyper-responsiveness would yield equivalent results in the presence and absence of sedation. Sedated and unsedated MCs were performed on 8 EPA-affected horses, with each horse acting as its own control. Acepromazine was superior to xylazine/butorphanol, resulting in sedation and data collection. Based on American Thoracic Society guidelines, an acceptable ability to detect differences in lung resistance is less than a twofold difference in the provocative concentration of methacholine that elicited a 40% increase in lung resistance (PC40RL). Significant differences in PC40RL were not detected. Validation of a sedation protocol for use in MC will expand the application of this diagnostic.

No description available.

A viscoelasticidade do pulmão do mamífero é determinada principalmente pelas propriedades mecânicas, estrutura e regulação do músculo liso das vias aéreas. A exposição ao ar poluído pode deteriorar essas propriedades com consequências danosas à saúde individual. O formaldeído é um importante poluente presente em ambientes internos que adentra o músculo liso formando ligações covalentes entre proteínas da matriz extracelular e da estrutura intracelular deteriorando algumas funções do músculo liso das vias aéreas, alterando propriedades mecânicas e induzindo a hiperresponsividade. O primeiro objetivo desse trabalho foi desenvolver um modelo de rede viscoelástica bidimensional baseada na tesselação de Voronoi para reproduzir algumas propriedades mecânicas do músculo liso de via aérea a nível de tecido. O segundo objetivo foi comparar os resultados obtidos com o nosso modelo com aqueles previamente observados em experimentos com tiras de tecido após a exposição ao formaldeído. Nosso modelo simula as propriedades mecânicas do músculo liso de via aérea usando um conjunto de molas e amortecedores. Esse conjunto de molas e amortecedores não somente mimetiza as propriedades viscoeláticas do músculo liso mas também o aparato contrátil das células. Nós hipotetizamos que a formação de ligações covalentes, devido à ação do formaldeído, pode ser representada no modelo por uma alteração simples na constante elástica das molas, enquanto que a ação da metacolina reduz o tamanho da mola. Nosso modelo é hábil para reproduzir uma medida de força isométrica onde o músculo liso é sujeito a um agente contrátil, com e sem exposição in vitro ao formaldeído. Assim, a nossa nova abordagem mecanicista incorpora diversas propriedades bem conhecidas do sistema contrátil das células em um tecido a nível de modelo. O modelo pode também ser usado em diferentes escalas biológicas / The viscoelastic properties of the mammalian lung is mainly determined by the mechanical properties, structure and regulation of the airways smooth muscle. The exposure to polluted air may deteriorate these properties with harmful consequences to individual health. Formaldehyde is an important indoor pollutant that permeate through the smooth muscle tissue forming covalent bonds between proteins in the extracellular matrix and intracellular protein structure deteriorating some of the airways smooth muscle functions, changing mechanical properties, and inducing hyperresponsiveness. The first objectives of this work was to develop a two-dimensional viscoelastic network model based on Voronoi tessellation to reproduce some of the mechanical properties of airway smooth muscle at the tissue level. The second objective was to compare the results obtained with our model with those previously observed in tissue strip experiments after the tissue exposure to formaldehyde. Our model simulates the mechanical properties of airway smooth muscle using a set of springs and dashpot. This set of springs and dashpot not only mimic the viscoelastic properties of the smooth muscle but also the cells contractile apparatus. We hypothesize that the formation of covalent bonds, due to the action formaldehyde, can be represented in the model by a simple change in the elastic constant of the springs, while the action of methacholine reduce the size of the spring. Our model is able to reproduce an isometric force measurement, where the smooth muscle is subjected to a titration of a contractile agent, with and without an in vitro exposure to formaldehyde. Thus, our new mechanistic approaches incorporates several well know features of the contractile system of the cells in a tissue level model. The model can also be used in different biological scales

<p>We have developed a methacholine provocation method, which detects bronchial responsiveness in more than 80% of healthy subjects. The method enables us to detect differences in bronchial responsiveness within the normal range. </p><p>With this method FEV1 and Gaw had similar sensitivity in detecting small differences in bronchial responsiveness. Differences, between protocols when using doubling or fourfold concentration steps emphasize the importance to strictly adhere to a predefined protocol. </p><p>Deep inhalation associated with the FEV1 manoeuvre decreases bronchial tone induced by methacholine for up to 6 minutes, which emphasizes the importance of exact timing between successive FEV1 measurements in bronchial provocation tests. There is a substantial overlap in bronchial responsiveness between healthy and asthmatic subjects and a deep inhalation at the end of the methacholine test challenge could not discriminate between asthmatic and non-asthmatic subjects.</p><p>Inhalation of dust in a swine confinement building causes an intense airway inflammatory reaction with an extensive migration of inflammatory cells, predominantly neutrophils, into the upper and lower airways. Bronchial responsiveness to methacholine increased by about 3 doubling concentration steps and was normalized one week after exposure. However, exposure to dust in a swine confinement building did not yield increased bronchial responsiveness to eucapnic hyperventilation with dry air which is often observed in asthmatic subjects. Exhaled NO was approximately doubled five hours after exposure and in the present study we found no relationship between exhaled NO levels and bronchial responsiveness in healthy subjects. </p><p>Protection with half-mask inhibited the dust induced increase of exhaled NO whereas the increase in bronchial responsiveness was influenced only to a minor extent.</p><p>These findings, do not support the hypothesis that the increased bronchial responsiveness following organic dust exposure is directly caused by the inflammation. Instead, a possible direct effect on the smooth muscle and swelling of the airway mucosa and increased secretions due to the general inflammatory reaction probably leads to airway narrowing enhancing the post-exposure bronchial response to methacholine. </p>

We have developed a methacholine provocation method, which detects bronchial responsiveness in more than 80% of healthy subjects. The method enables us to detect differences in bronchial responsiveness within the normal range. With this method FEV1 and Gaw had similar sensitivity in detecting small differences in bronchial responsiveness. Differences, between protocols when using doubling or fourfold concentration steps emphasize the importance to strictly adhere to a predefined protocol. Deep inhalation associated with the FEV1 manoeuvre decreases bronchial tone induced by methacholine for up to 6 minutes, which emphasizes the importance of exact timing between successive FEV1 measurements in bronchial provocation tests. There is a substantial overlap in bronchial responsiveness between healthy and asthmatic subjects and a deep inhalation at the end of the methacholine test challenge could not discriminate between asthmatic and non-asthmatic subjects. Inhalation of dust in a swine confinement building causes an intense airway inflammatory reaction with an extensive migration of inflammatory cells, predominantly neutrophils, into the upper and lower airways. Bronchial responsiveness to methacholine increased by about 3 doubling concentration steps and was normalized one week after exposure. However, exposure to dust in a swine confinement building did not yield increased bronchial responsiveness to eucapnic hyperventilation with dry air which is often observed in asthmatic subjects. Exhaled NO was approximately doubled five hours after exposure and in the present study we found no relationship between exhaled NO levels and bronchial responsiveness in healthy subjects. Protection with half-mask inhibited the dust induced increase of exhaled NO whereas the increase in bronchial responsiveness was influenced only to a minor extent. These findings, do not support the hypothesis that the increased bronchial responsiveness following organic dust exposure is directly caused by the inflammation. Instead, a possible direct effect on the smooth muscle and swelling of the airway mucosa and increased secretions due to the general inflammatory reaction probably leads to airway narrowing enhancing the post-exposure bronchial response to methacholine.