Physiology Of Asthma

Physiology Of Asthma



Physiology Of Asthma

Introduction

Severe or difficult asthma afflicts a small percentage (probably about 5%) of the asthma population. These patients, however, remain difficult to treat and prone to severe exacerbations, therefore contributing disproportionately to the overall cost of asthma. The introduction of high-potency inhaled corticosteroids had a marked impact on the numbers of patients dependent on oral corticosteroids, probably reducing the overall number of severe or refractory asthmatics. Beyond those medications, however, little further progress has been made in understanding the disease or its pathobiology.

Definitions

Before considering the pathology of difficult asthma, some definition must be assigned to this concept. Severe persistent asthmahas been defined in recent guidelines but the definitions have been somewhat limited in scope and difficult to apply. “Refractory” or “difficult” asthma was given a working definition by the American Thoracic Society - sponsored workshop, the proceedings of which were published in 2000.This definition included one of two major criteria (continuous high-dose inhaled corticosteroids or oral corticosteroids for more than 50% of the previous year), with two of seven additional minor criteria required. The minor criteria included aspects of lung function, exacerbations, disease stability and the amount of additional medications. Patients must also have had compliance and exacerbating factors fully addressed. Although these definitions are a start, they may still not be the definitive list and it is likely that revisions will be required over the ensuing years.

Discussion

Asthma is a common chronic inflammatory condition in which the airway narrows reversibly in response to certain stimuli. In asthma, airway obstruction may be caused by abnormal sensitivity to cholinergic and peptidergic receptors. These two receptors respond to acetylcholine and neurokinins respectively, causing underlying smooth muscles to contract and thus altering the flow of air. In an asthmatic attack there is abnormal sensitivity to cholinergic and peptidergic receptors which result in abnormal contraction of the smooth muscles of the airways.

Mast cells are thought to be mainly responsible for initiating the airway narrowing. Mast cells release substances such as histamines and leukotrienes, which casue smooth muscles to contract, mucous secretion to increase, and white blood cells to migrate to the area.

During an asthma attack, there is bronchoconstriction of the muscles of the airways, and the tissues lining the airways become inflamed and secrete mucous resulting in narrowing of the airways. Symptoms may include shortness of breath, coughing, wheezing, chest tightness and production of a mucoid phlegm.Possible triggers of asthma attacks may include allergens such as pollens, dust particles, animal dander, cigarette smoking, cold air and viral infections.

Risks and Benefits of Written Drug Information

A survey of 32 community pharmacies in New York reflected that two thirds of patients who received written medication leaflets reported actually reading the leaflets that were provided. (Patients use and perception of medication information leaflets). A European survey was also found to reflect similar results. (A telephone survey of patients' use of medicine information leaflets). These figures are very promising as it may result in a potential increase in patients' knowledge, with regards to ...