Disorders of Ventilation and Gas Exchange
Emmanuel and his mother live in an urban community housing complex. The building is worn down and dirty from the urban dust, cockroaches, and mold. Emmanuel is five years of age and has suffered from asthma for the last two years. One evening, his mother poured him some milk and put him to bed. Shortly afterward, Emmanuel woke up wheezing and coughing. As he gasped for air, he became more and more anxious. His mother ran for his inhaler, but he was too upset and restless to use it. Emmanuel’s skin became moist with sweat, and as he began to tire, his wheezing became quieter. His mother called 911 and waited anxiously for the ambulance to arrive.
- Emmanuel uses a corticosteroid inhaler for the management of his asthma. What is the mechanism of action of this drug? How is its action different from the β2-agonist inhalants?
- Why does someone with severe asthma become physically fatigued during a prolonged attack? What are the physiological events that occur during an attack?
- One of the complications of respiratory fatigue is the development of hypercapnia. How does the body compensate for an increase in CO2? What are the effects of hypercapnia on the central nervous system?
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Expert Solution Preview
Introduction:
This case study is about a five-year-old boy named Emmanuel who suffers from asthma. The following questions will focus on the mechanism of action of corticosteroid inhalers and β2-agonist inhalants, the physiological events that occur during a severe asthma attack, and the effects of hypercapnia on the central nervous system.
1) Mechanism of action of corticosteroid inhalers and β2-agonist inhalants:
Corticosteroid inhalers work by reducing inflammation in the airways, leading to decreased swelling and mucus production. This reduction in inflammation helps to decrease the severity of asthma symptoms by relaxing the airway muscles, making it easier to breathe. On the other hand, β2-agonist inhalants work by dilating the airways, which allows more air to flow in and out of the lungs. These drugs work quickly to provide immediate relief from asthma symptoms, making them useful during an acute asthma attack. The mechanism of action of corticosteroids is different from β2-agonists because corticosteroids treat the underlying inflammation causing the symptoms, while β2-agonists provide immediate symptom relief.
2) Physiological events during a severe asthma attack:
During a severe asthma attack, the muscles surrounding the airways become highly contracted, leading to narrowing of the airways. As a result, there is a decrease in air supply and an increase in airway resistance, making breathing difficult. The body responds to this by increasing respiratory rate and tidal volume, which can lead to exhaustion and fatigue. Additionally, the increased work of breathing can cause metabolic acidosis, leading to an increased level of carbon dioxide in the blood (hypercapnia). This can affect the oxygen supply to the brain, causing confusion, headaches, and even loss of consciousness.
3) Effects of hypercapnia on the central nervous system:
To compensate for hypercapnia, the body increases ventilation, which can lead to a respiratory alkalosis. However, as compensation mechanisms fail, hypercapnia sets in, leading to decreased cerebral perfusion and cerebral vasodilation. This can cause an influx of intracellular calcium and a loss of cell membrane integrity, leading to cell dysfunction and even death. The central nervous system can also be affected, leading to confusion, lethargy, and seizures. In extreme cases, hypercapnia can lead to respiratory failure and death.
In conclusion, understanding the underlying mechanisms of asthma and its complications is crucial for medical students. This knowledge can help health professionals provide appropriate treatment for patients suffering from this condition.
