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Asthma

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Description

Chapter 1: Definition of asthma
Chapter 2: Pathophysiology of asthma
Chapter 3: The aetiology of asthma
Chapter 4: Prevalence of asthma
Chapter 5: Symptoms of asthma
Chapter 6: Asthma diagnosis
Chapter 7: Assessment of asthma severity and control
Chapter 8: Severe asthma and/or problematic asthma
Chapter 9: Prevention of asthma
Chapter 10: Management of asthma
Chapter 11: Drug treatment of asthma
Chapter 12: Asthma education
Chapter 13: Management of acute exacerbations of asthma
Chapter 14: Comorbid conditions impacting and asthma
Chapter 15: Associated medical conditions and asthma
Chapter 16: Airway remodeling
Chapter 17: Conclusions

 

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INTRODUCTION

Asthma is one of the most common respiratory complaints in the world today. It affects approximately one in five children (20%) and one in ten adults (10%). Asthma can occur for the first time at any age, even in adulthood, but most commonly starts in childhood. Although it usually begins before the age of five years, a few children affected will become largely asymptomatic during their teenage years but asthma symptoms usually persist if asthma is present in adulthood. It tends to run in families as do related allergic conditions such as hay fever and eczema. It cannot, as yet, be cured, but if kept under control those affected will be able to live normal lives enjoying full involvement in sport and all other activities. It must be treated primarily with anti-inflammatory therapy.

2015-11-13 11-20-07 AM

Professor Charles Feldman Professor of Pulmonology and Chief Physician, Head Pulmonology Division, Department of Internal Medicine, Charlotte Maxeke Johannesburg Academic Hospital and University of the Witwatersrand MBBCh, DSc, PhD, FRCP, FCP (SA)

2015-11-13 11-20-49 AM

Professor Robin Green Professor and Head: Department of Paediatrics and Child health, University of Pretoria PhD, FCCP, FAAAAI, FRCP President of the College of Paediatricians of South Africa

Summary DEFINITION OF ASTHMA

The Global Initiative For Asthma have defined Asthma as “a chronic inflammatory disorder of the airways, most commonly allergic in origin, in which many cells and cellular elements play a role. The chronic inflammation causes an associated increase in airway hyper-responsiveness causing the airways to constrict readily in response to a number of stimuli that then leads to recurrent episodes of wheezing, breathlessness, chest tightness, and coughing, particularly at night or in the early morning. These episodes are usually associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment”.

PATHOPHYSIOLOGY OF ASTHMA The primary function of the lungs is to breathe. When air is inhaled, it passes through the mouth and nose, the larynx and then down the trachea. The trachea branches into the two main bronchi which then divide further and further, becoming increasingly smaller until eventually air is conducted into the alveoli (air sacs) where gas exchange takes place together with gases carried in the bloodstream. With each breath a myriad of potentially harmful substances may be inhaled into the airways, including various particles, microorganisms, vapours and toxins. The airway has a number of well developed mechanisms to help protect it from these environmental factors, including mechanical, reflex and immunological factors. The protective role of epithelia in many areas of the body is well recognised, and in the case of the airway, much of the upper and lower respiratory tract is lined by a specialised ciliated respiratory epithelium, that also contains goblet cells. The coordinated action of the beating cilia, together with the mucus layer secreted primarily by the goblet cells constitute the mucocilary escalator, which is the first line mechanical defence of the lower airway and helps to clear the lower airway of particles and secretions and to keep it sterile. The epithelium rests on a thin basement membrane, and in the tissues below that are nerve fibres, muscles and even cartilage, depending on the size of the airways and therefore how far down they are in the lower respiratory tract. It is the abnormalities of this airway epithelium that underlie the fundamental changes that occur in the asthmatic patient.

THE BASIC AIRWAY PROCESS The central problem in asthma is ‘inflammation’ in the airways of the lungs. Asthma affects the entire airway from the very upper part of the airway through to the smaller bronchioles. This inflammation produces all the symptoms found in asthmatics. Inflammation can best be understood as:
  • Swelling of the lining of the airways (mucosal oedema)
  •  Secretions of mucus into the airways (mucus hypersecretion)
  • Spasm of the muscles of the airways (bronchospasm)
  • Asthma is characterised by narrowing of the bronchi caused by the inflammation:
  • The swelling and increased secretions are a consequence of airway inflammation
  •  Bronchospasm occurs only when there is ongoing airway inflammation
  • When the bronchi become too narrow or are partially obstructed from inflammation and bronchospasm, the typical symptoms of asthma will develop. These symptoms include:
  •  Cough which often occurs more frequently at night and with activity, can be dry or productive, and is persistent or recurrent
  •  Wheezing, which is a whistling noise in the chest
  •  Tightness of the chest, with breathing difficulty
Shortness of breath, especially after exercise Figure 1a depicts the anatomy of a normal airway and Figure 1b the anatomical changes in the airway of an asthmatic patient, showing the various manifestations of the airway inflammation. 2015-11-12 11-56-54 AM