In the classic theory of airway lumen narrowing in asthma, active force in airway smooth muscle is presumed to be in static mechanical equilibrium with the external load against which the muscle has shortened This theory is useful because it identifies the static equilibrium length toward which activated airway smooth muscle would tend if given enough time The corresponding state toward which myosin-actin interactions would tend is called the latch state But are the concepts of a static mechanical equilibrium and the latch state applicable in the setting of tidal loading, as occurs during breathing? To address this question, we have studied isolated, maximally contracted bovine tracheal smooth muscle subjected to tidal stretches imposed at 033 Hz We measured the active force (F) and stiffness (E), which reflect numbers of actin-myosin interactions, and hysteresivity ( η ), which reflects the rate of turnover of those interactions When the amplitude of imposed tidal stretch ( e ) was very small, 025

Airway smooth muscle, tidal stretches, and dynamically determined contractile states.

Excessive airway obstruction is the cause of symptoms and abnormal lung function in asthma. As airway smooth muscle (ASM) is the effecter controlling airway calibre, it is suspected that dysfunction of ASM contributes to the pathophysiology of asthma. However, the precise role of ASM in the series of events leading to asthmatic symptoms is not clear. It is not certain whether, in asthma, there is a change in the intrinsic properties of ASM, a change in the structure and mechanical properties of the noncontractile components of the airway wall, or a change in the interdependence of the airway wall with the surrounding lung parenchyma. All these potential changes could result from acute or chronic airway inflammation and associated tissue repair and remodelling. Anti-inflammatory therapy, however, does not "cure" asthma, and airway hyperresponsiveness can persist in asthmatics, even in the absence of airway inflammation. This is perhaps because the therapy does not directly address a fundamental abnormality of asthma, that of exaggerated airway narrowing due to excessive shortening of ASM. In the present study, a central role for airway smooth muscle in the pathogenesis of airway hyperresponsiveness in asthma is explored.

https://erj.ersjournals.com/content/erj/29/5/834.full.pdf

Airway smooth muscle dynamics: A common pathway of airway obstruction in asthma

Oscillometry (also known as the forced oscillation technique) measures the mechanical properties of the respiratory system (upper and intrathoracic airways, lung tissue and chest wall) during quiet tidal breathing, by the application of an oscillating pressure signal (input or forcing signal), most commonly at the mouth. With increased clinical and research use, it is critical that all technical details of the hardware design, signal processing and analyses, and testing protocols are transparent and clearly reported to allow standardisation, comparison and replication of clinical and research studies. Because of this need, an update of the 2003 European Respiratory Society (ERS) technical standards document was produced by an ERS task force of experts who are active in clinical oscillometry research.The aim of the task force was to provide technical recommendations regarding oscillometry measurement including hardware, software, testing protocols and quality control.The main changes in this update, compared with the 2003 ERS task force document are 1) new quality control procedures which reflect use of "within-breath" analysis, and methods of handling artefacts; 2) recommendation to disclose signal processing, quality control, artefact handling and breathing protocols (e.g. number and duration of acquisitions) in reports and publications to allow comparability and replication between devices and laboratories; 3) a summary review of new data to support threshold values for bronchodilator and bronchial challenge tests; and 4) updated list of predicted impedance values in adults and children.

https://erj.ersjournals.com/content/erj/55/2/1900753.full.pdf

Technical Standards for Respiratory Oscillometry

Spirometry is the main pulmonary function test and is essential for the evaluation and monitoring of respiratory diseases Its utility transcends the field of Respiratory Medicine, is becoming increasingly important in primary care and applications have even been described outside the field of respiratory diseases This document is therefore intended to serve as support for all health professionals who use spirometry, providing recommendations based on the best scientific evidence available An update of the indications and contraindications of the test is proposed The document sets out recommendations on the requirements necessary for conventional spirometers and portable office equipment, as well as on spirometer hygiene and quality control measures Spirometric parameters that must be considered, performance of manoeuvres, criteria for acceptability and repeatability of measurements and their quality control are defined A proposal is also established for presentation of the results and an evaluation and interpretation is proposed according to information generated in recent years Finally, lines of adaptation and integration of spirometry in the field of new technologies are considered

Spirometry. Spanish Society of Pulmonology and Thoracic Surgery (SEPAR).

Despite advancing knowledge of the pathophysiology and treatment of asthma, asthma morbidity and mortality are on the rise. To help avert this trend, clinicians and patients must focus their attention on the early identification and treatment of asthma exacerbations. As in the words of Dr. Thomas Petty: " ... the best treatment of status asthmaticus is to treat it three days before it occurs." (7) Still, there will be asthmatics with life-threatening attacks that require careful assessment and aggressive management. Inhaled beta-agonists, systemic corticosteroids, and oxygen remain the drugs of choice in SA. Anticholinergics play a lesser role in the treatment of acute asthma, and debate continues regarding the efficacy of theophylline in this setting. Available data do not support the routine use of magnesium sulfate or antibiotics in patients with SA. Patients failing drug therapy should be considered early for intubation and mechanical ventilation. A strategy of mechanical ventilation that prolongs TE by limiting VE and decreasing inspiratory time, and that tolerates hypercapnia, avoids excessive lung hyperinflation and barotrauma and should improve the outcome of these most critically ill asthmatics. Intubated and mechanically ventilated patients should be aggressively sedated. Paralytic agents should be used only if adequate control of the cardiopulmonary status cannot be achieved by sedation alone. Minimizing the use of paralytic agents may decrease risk of myopathy and other adverse consequences of muscle paralysis. Finally, after successful treatment of a life-threatening episode of asthma, the treatment team should address prevention of future episodes of SA prior to discharge.

The assessment and management of adults with status asthmaticus

Asthmatic patients who came to hospital for treatment of severe attacks were assessed for level of obstruction and the effects of a deep inhalation (DI) on degree of obstruction at various stages of their treatment and after recovery over several days. The more severe the obstruction, the greater was the constrictor effect of a DI; as lung function improved with intensive treatment, including corticosteroids, the constrictor effect diminished. Thus, we believe the constrictor effects of a DI relate to the degree of inflammation in the obstructive process. These longitudinal data relating severity to the effects of a DI were nearly identical to previously published cross-sectional data in a group of patients with spontaneous asthma with widely different levels of lung function. It is possible that the response to a DI in a given asthmatic subject serves as a functional marker for the predominant mechanism for obstruction.

T. H. Rossing

Papers

The effects of deep inhalation on maximal expiratory flow during intensive treatment of spontaneous asthmatic episodes.