Asthma is a serious health and socioeconomic problem affecting more than 300 people worldwide (Kudo et al. , 2013). Asthma exacerbations are manageable with effective, regular therapy and patient education. Nevertheless, a significant proportion of the global population continues to experience asthma exacerbations. In the US, approximately 12 million people experience an acute exacerbation of asthma with a quarter of them requiring hospitalization (Fergeson & Leakey, 2015). Asthma exacerbation refers to an asthma attack due to inflammation and swelling of the airways. During asthma exacerbation, muscles around the airways contract and excess mucus is produced, resulting in narrowing of bronchiole tubes. Understanding the pathophysiology of asthma exacerbations and the role of different risk factors is critical in diagnosis and treatment.
Pathophysiological Mechanisms of Chronic Asthma and Acute Asthma Exacerbation
Kudo et al. (2013) observed that asthma is considered an inflammatory disease of the airway that causes airway hyper-responsiveness, hyper-production of mucus, obstruction, and remodeling. The pathophysiology of the disease is understood via the paradigms of immunology and molecular biology. Asthma exacerbations occur following exposure of the power respiratory airway to environmental agents, particularly viral infections. The patterns of inflammation differ according to trigger factors and the respective immunohistopathologic factors involved in inflammatory cell infiltration. Common airway responses include neutrophilic bronchitis caused by epithelial chemokine activation, eosinophilic bronchitis due to Th2 lymphocyte activation with IL‐5 release, a combination of the two, or severe bronchospasm caused by arachidonic acid shunting via 5‐LO pathway, increased leukotriene production.
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Pathophysiology of asthma is dominantly caused by bronchoconstriction which causes narrowing of the airway and subsequent impairment of airflow. Bronchoconstriction responses to allergen and other antigens have been demonstrated in model animals (Li et al. , 2013) In acute asthma exacerbations, bronchoconstriction occurs rapidly after exposure to allergen with the resulting smooth muscle contraction causing narrowing of the airway. Chronic asthma exacerbations are due to advanced complications including airway edema from persistent and progressive inflammation. Other factors limiting airflow in chronic asthma exacerbations are inflammation, mucus hypersecretion and the formation of inspissated mucus plugs, as well as structural changes including hypertrophy and hyperplasia of the airway smooth muscle. Airway hyper-responsiveness occurs in both acute and chronic cases of asthma exacerbations. Severity of the attack in hyper-responsiveness correlates to the degree to which contractile responses to challenges with methacholine can be defined. Hyper-responsiveness of airways is influenced by a number of mechanisms including inflammation, dysfunctional neuroregulation, and structural changes. Inflammation remains a dominant factor in hyper-responsiveness progression. Airway remodeling is a dominant feature in chronic asthma exacerbations where in some cases, airflow limitation may only be partially reversible. Airway remodeling is an outcome of the activation of numerous structural cells, resulting to permanent changes in airway that increase obstruction and hyper-responsiveness. Structural changes that take place in airway remodeling include thickening of the sub-basement membrane, subepithelial fibrosis, airway smooth muscle hypertrophy and hyperplasia, blood vessel proliferation and dilation, and mucous gland hyperplasia and hypersecretion.
Shiber and Santana (2006) demonstrated how the severity of asthma exacerbations affect airflow rate. In mild exacerbations during acute attacks, the peak expiratory flow rate (PEFR) is equal to or more than 200L/minute, which translates to ≥50% of the predicted best. In moderate attacks, PEFR IS between 80 and 200 L/min, or 25% and 50% of the predicted best. On the other hand, chronic cases are defined by severe airflow impairment resulting to PEFR of severe is defined as ≤ 80 L/min, or ≤25% of the predicted best.
Impact of Age on the Pathophysiology of the Disorders
Asthma affects people of all ages with equal incidence rates across age groups, though it is often underdiagnosed and undertreated among the elderly. Data presented by the Center for Disease Control and Prevention shows that 1 in 11 children and 1 in 12 adults in the US had asthma. A study conducted by Smith et al. (2012) established older adults with asthma to have a higher rate of allergic sensitization, decreased lung function, and significantly worse quality of life. Consequently, elderly patients with asthma face disproportionate morbidity, mortality and cost when compared with younger patient groups. Asthma in people aged over 65 can have serious health implication if not managed properly. On the other hand, in children below age 5, diagnosis techniques are unavailable, making it difficult to establish asthma exacerbations. However, it can be argued that the decreased lung function and worse quality of life among the elderly exacerbates progressive of pathophysiology including bronchoconstriction, hypersensitiveness, airways edema, and airway remodeling.
Diagnosis and Prescription of Treatment for a Patient Based on Age
Asthma is the most common childhood chronic disease that occurs in the first years of life. However, the situation in children is complicated by the absence of diagnostic frameworks for asthma for children under the age of 5. Manifestation of clinical symptoms in toddlers and preschoolers usually requires treatment given for the disease followed by critical evaluation. Diagnosis of asthma in the early ages is complex and predominantly clinical. Inhaled corticosteroids are used as effective treatment, but their benefits and effects need careful evaluation. Allergen sensitization among the elderly improves diagnosis outcomes and treatment efficacy. However, Dunn et al. (2015) established that old age is a major risk factor for failure of treatment, especially in patients taking inhaled corticosteroids. The findings contrast sharply with those from children under five years where these therapy has been established to be effective. The differential treatment outcomes based on age can be attributed to pathophysiology of asthma exacerbation which is influence by the health condition of the patient and their respiratory system.
Conclusion
The pathophysiology of asthma exacerbations is influence by immunohistological responses to allergens and antigens. The responses usually leading to diagnosis include bronchoconstriction, hypersensitiveness, airways edema, and airway remodeling. These exacerbations differ with age and are easier to diagnose in adults than children are. However, treatment of the asthma attacks with commonly inhaled corticosteroids has been demonstrated to be effective in children compared to adults. The overall health status of the patients in the two age groups is linked to their health status, with the elderly showing decreased lung function and lower life span that are risks to progression of the disease and failure of treatment.
References
Dunn, R. M., Lehman, E., Chinchilli, V. M., Martin, R. J., Boushey, H. A., Israel, E., ... & Peters, S. P. (2015). Impact of age and sex on response to asthma therapy. American journal of respiratory and critical care medicine , 192 (5), 551-558.
Fergeson, J., & Lockey, R. (2015). Acute asthma. World Allergy Organization. Retrieved from https://www.worldallergy.org/education-and-programs/education/allergic-disease-resource-center/professionals/acute-asthma.
Kudo, M., Ishigatsubo, Y., & Aoki, I. (2013). Pathology of asthma. Frontiers in microbiology , 4 , 263.
Li, S., Aliyeva, M., Daphtary, N., Martin, R. A., Poynter, M. E., Kostin, S. F., ... & Lundblad, L. K. (2013). Antigen-induced mast cell expansion and bronchoconstriction in a mouse model of asthma. American Journal of Physiology-Lung Cellular and Molecular Physiology , 306 (2), L196-L206.
Shiber, J. R., & Santana, J. (2006). Dyspnea. Medical Clinics , 90 (3), 453-479.
Smith, A. M., Villareal, M., Bernstein, D. I., & Swikert, D. J. (2012). Asthma in the elderly: risk factors and impact on physical function. Annals of Allergy, Asthma & Immunology , 108 (5), 305-310.
