Vitamin A deficiency alters the pulmonary parenchymal elastic modulus and elastic fiber concentration in rats

BACKGROUND: Bronchial hyperreactivity is influenced by properties of the conducting airways and the surrounding pulmonary parenchyma, which is tethered to the conducting airways. Vitamin A deficiency (VAD) is associated with an increase in airway hyperreactivity in rats and a decrease in the volume density of alveoli and alveolar ducts. To better define the effects of VAD on the mechanical properties of the pulmonary parenchyma, we have studied the elastic modulus, elastic fibers and elastin gene-expression in rats with VAD, which were supplemented with retinoic acid (RA) or remained unsupplemented. METHODS: Parenchymal mechanics were assessed before and after the administration of carbamylcholine (CCh) by determining the bulk and shear moduli of lungs that that had been removed from rats which were vitamin A deficient or received a control diet. Elastin mRNA and insoluble elastin were quantified and elastic fibers were enumerated using morphometric methods. Additional morphometric studies were performed to assess airway contraction and alveolar distortion. RESULTS: VAD produced an approximately 2-fold augmentation in the CCh-mediated increase of the bulk modulus and a significant dampening of the increase in shear modulus after CCh, compared to vitamin A sufficient (VAS) rats. RA-supplementation for up to 21 days did not reverse the effects of VAD on the elastic modulus. VAD was also associated with a decrease in the concentration of parenchymal elastic fibers, which was restored and was accompanied by an increase in tropoelastin mRNA after 12 days of RA-treatment. Lung elastin, which was resistant to 0.1 N NaOH at 98°, decreased in VAD and was not restored after 21 days of RA-treatment. CONCLUSION: Alterations in parenchymal mechanics and structure contribute to bronchial hyperreactivity in VAD but they are not reversed by RA-treatment, in contrast to the VAD-related alterations in the airways

A theoretical model of inflammation- and mechanotransduction- driven asthmatic airway remodelling

Inflammation, airway hyper-responsiveness and airway remodelling are well-established hallmarks of asthma, but their inter-relationships remain elusive. In order to obtain a better understanding of their inter-dependence, we develop a mechanochemical morphoelastic model of the airway wall accounting for local volume changes in airway smooth muscle (ASM) and extracellular matrix in response to transient inflammatory or contractile agonist challenges. We use constrained mixture theory, together with a multiplicative decomposition of growth from the elastic deformation, to model the airway wall as a nonlinear fibre-reinforced elastic cylinder. Local contractile agonist drives ASM cell contraction, generating mechanical stresses in the tissue that drive further release of mitogenic mediators and contractile agonists via underlying mechanotransductive signalling pathways. Our model predictions are consistent with previously described inflammation-induced remodelling within an axisymmetric airway geometry. Additionally, our simulations reveal novel mechanotransductive feedback by which hyper-responsive airways exhibit increased remodelling, for example, via stress-induced release of pro-mitogenic and procontractile cytokines. Simulation results also reveal emergence of a persistent contractile tone observed in asthmatics, via either a pathological mechanotransductive feedback loop, a failure to clear agonists from the tissue, or a combination of both. Furthermore, we identify various parameter combinations that may contribute to the existence of different asthma phenotypes, and we illustrate a combination of factors which may predispose severe asthmatics to fatal bronchospasms

Identificación de equipos y procedimientos utilizados por fisioterapeutas brasileños para pruebas de endurance muscular inspiratoria

A avaliação da função dos músculos inspiratórios por meio do teste de endurance muscular inspiratória (EMI), definida como a capacidade de sustentação dessa tarefa ao longo do tempo, atualmente apresenta ampla variedade de instrumentos e procedimentos para sua mensuração. Este estudo teve como objetivo identificar os diferentes equipamentos, procedimentos e forma de avaliação dos testes de EMI entre fisioterapeutas brasileiros. É um estudo transversal realizado por meio de questionário enviado por correio eletrônico individualmente a cada participante. Cento e treze fisioterapeutas de diferentes regiões do país, grande parte com atuação conjunta na clínica e na docência (52,1%), responderam realizar poucas vezes a medida de EMI (48,7%). O manovacuômetro aneroide foi o aparelho mais utilizado por 42,5% dos profissionais. O clipe nasal e o bocal tubular de plástico rígido ou papel foram os acessórios mais utilizados durante o teste, correspondendo a 51,8% e 33%, respectivamente. O teste de ventilação voluntária máxima foi o mais utilizado para avaliação da endurance inspiratória, relatado por 23% dos respondentes. O teste de carga constante para avaliação da endurance foi adotado por 51,2% dos fisioterapeutas, sendo que 54,9% associaram comandos verbais à demonstração para explicação do teste. A interpretação dos valores aferidos era feita através de valores de referência por 25,7% dos entrevistados. Identificou-se que os fisioterapeutas brasileiros entrevistados não apresentaram a mesma conduta para os testes de EMI. No entanto os equipamentos, procedimentos e a forma de avaliação são utilizados com base nas diretrizes sobre o tema e de acordo com a disponibilidade de recursos do serviço.La evaluación de la función de los músculos inspiratorios a través del entrenamiento muscular inspiratorio (EMI), definida como la capacidad de sustentación de esta tarea a lo largo del tiempo, actualmente presenta una amplia variedad de instrumentos y procedimientos para su medición. Este estudio tuvo como objetivo identificar los diferentes equipos, procedimientos y forma de evaluación de las pruebas de EMI entre fisioterapeutas brasileños. Es un estudio transversal realizado por medio de un cuestionario enviado por correo electrónico a cada participante. Ciento trece fisioterapeutas de diferentes regiones del país, que en gran parte actúan a la vez en la clínica y en la enseñanza (52,1%), dijeron realizar pocas veces la medida de EMI (48,7%). El manovacuómetro aneroide fue el aparato más utilizado por el 42,5% de los profesionales. El clip nasal y la boquilla tubular de plástico rígido o papel fueron los accesorios más utilizados durante la prueba, correspondiendo al 51,8% y al 33%, respectivamente. La prueba de ventilación voluntaria máxima fue la más utilizada para la evaluación de la resistencia respiratoria, reportada por el 23% de los entrevistados. La prueba de carga constante para la evaluación de la resistencia se adoptó por el 51,2% de los fisioterapeutas, siendo que el 54,9% asoció comandos verbales a la demostración para la explicación de la prueba. La interpretación de los valores evaluados se hacía a través de valores de referencia por el 25,7% de los entrevistados. Se identificó que los fisioterapeutas brasileños entrevistados no presentaron la misma conducta para las pruebas de EMI. Sin embargo, los equipos, procedimientos y la forma de evaluación se utilizan con base en las directrices sobre el tema y de acuerdo con la disponibilidad de recursos del servicio.The assessment of inspiratory muscles through the inspiratory muscle endurance test (IME), defined as the ability to support this task over time, currently presents wide range of instruments and procedures for its measurement. This study aimed to identify the different equipment, procedures and assessments of IME tests among Brazilian physical therapists. It is a cross-sectional study carried out through a questionnaire sent individually by electronic mail to each participant. One hundred and thirteen physical therapists from different regions of the country, many practicing in the clinic and in the teaching field (52.1%), said they measured IME a few times (48.7%). The aneroid manovacuometer was used by 42.5% of the professionals. The nose clip and the hard plastic or paper tubular incentive spirometer were the most used accessories during the test, corresponding to 51.8% and 33%, respectively. The maximum voluntary ventilation test was used to assess the inspiratory endurance, reported by 23% of the respondents. The constant load test for endurance assessment was adopted by 51.2% of the physical therapists, and 54.9% associated verbal commands with the demonstration for the test application. The interpretation of the measured values was made with reference values by 25.7% of respondents. We identified that Brazilian physical therapists interviewed did not show the same conduct for IME tests. However, the equipment, procedures and assessment form are used based on the guidelines on the subject and according to the availability of resources of the service

Circulatory effects of expiratory flow-limited exercise, dynamic hyperinflation and expiratory muscle pressure

This article reviews recent research in normal subjects exercising with and without expiratory flow limitation at 1 L·s–1 imposed by a Starling resistor in the expiratory line, and in patients with chronic obstructive pulmonary disease (COPD), using optoelectronic plethysmography to measure respiratory kinematics, combined with mouth, pleural and abdominal pressure measurements, to assess work of breathing and respiratory muscle performance. In normal subjects, flow-limited exercise resulted in the following: 1) Impaired exercise performance due to intolerable dyspnoea; 2) hypercapnia; 3) excessive respiratory muscle recruitment; 4) blood shifts from trunk to extremities; 5) a 10% reduction in cardiac output and a 5% reduction in arterial oxygen saturation, decreasing energy supplies to working respiratory and locomotor muscles. In both normal subjects and in COPD patients, dynamic hyperinflation did not always occur. Those patients that hyperinflated had worse lung function and less work of breathing, but better exercise performance than the others, in whom expiratory muscle recruitment prevented dynamic hyperinflation at the cost of increased work of breathing and excessive oxygen cost of breathing. This established an early competition between respiratory and locomotor muscles for available energy supplies. Dynamic hyperinflation is a better exercise strategy in chronic obstructive pulmonary disease than expiratory muscle recruitment, but the benefit it confers is small