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Mike is sitting in his athletic training suite feeling sorry for himself. He moved from Southern California to play soccer at Northern Minnesota University (NMU) as a highly recruited player. All was well until he got sick with a miserable cold. He soon recovered, but now he finds himself with a lingering dry cough and difficulty catching his breath any time he exerts himself, which is every day! He also notices it has gotten worse as the weather has become colder. To make things worse, Mike feels, and looks, like he's out of shape, so his coach has been criticizing him for dogging it.
A few days later, Mike relays his story to JP, the head athletic trainer at NMU. "I'm thinking my cold is coming back, or something else is wrong with me. When I'm just hanging out, like now, I feel fine. But as soon as I start to run I get winded and can't stop coughing." JP listens to Mike's breathing sounds with his stethoscope, but hears nothing abnormal. So he tells Mike to come back as soon as the symptoms return during soccer practice. Twenty minutes later, Mike is back in the athletic training suite, audibly wheezing, coughing, and short of breath. The team physician, Dr. McInnis, happens to be there and performs a complete physical exam. He also does pulmonary function tests with Mike using spirometry, including a forced vital capacity (FVC) and forced expiratory volume in one second (FEV1). He instructs Mike to take a maximal inhalation and then exhale as forcefully and maximally as possible into the spirometer.
Based on his findings, Dr. McInnis tells Mike he thinks he is experiencing cold-induced bronchoconstriction (also called cold-induced asthma), which is made worse by exertion. The doctor explains to Mike that his recent upper respiratory infection probably inflamed his airways, making them hypersensitive and reactive to irritants, such as cold and physical exertion. When Mike exercises in the cold, autumn afternoons of Minnesota, his sensitive airways temporarily bronchoconstrict, causing the symptoms he is experiencing. Asthma is almost always a reversible condition. Dr. McInnis prescribes two puffs of an albuterol inhaler, to be used 10 minutes before a bout of exercise in the cold.
Short Answer Questions
- Describe the relationship between intrapulmonary pressure, atmospheric pressure, and air flow during normal inspiration and expiration, referring to Boyle's law.
- Resistance varies in Mike's conducting airways. Using your understanding of respiratory anatomy, explain where in his airway the resistance is highest and why.
- Several physical factors that influence the efficiency of pulmonary ventilation are compliance, alveolar surface tension, and airway resistance. Briefly describe each factor and identify the one that is affecting Mike's efficiency of breathing.
- What must happen to Mike's intrapulmonary pressure in order for him to maintain normal air flow during inhalation and exhalation when he is having one of his asthma attacks?
- How does Mike's body make the necessary changes in intrapulmonary pressure to maintain normal air flow when he is experiencing cold-induced asthma?
- When Mike is experiencing an asthmatic attack, his forced vital capacity (FVC) is 65%, and his FEV1 is 65%. Are these values normal? Knowing how one performs FVC tests, explain these test results in Mike's case. (Assume that Mike and the doctor have performed an accurate test.)
- Albuterol is a selective beta-2 adrenergic agonist, which means it specifically activates beta-2 adrenergic receptors on smooth muscle in the airways. How does this improve Mike's asthma?
Clinical Case Study I Can't Stop Coughing: A Case Study on the Respiratory System
Short Answer Questions
1. Describe the relationship between intrapulmonary pressure, atmospheric pressure, and air flow during normal inspiration and expiration, referring to Boyle's law.
According to Marieb & Hoehn, Boyle's law gives the relationship between pressure and volume of a gas: At constant temperature, Pressure (P) varies inversely with volume (V).
That is, P1V1 = P2V2, where P is the pressure of the gas, V is its volume, and subscripts 1 and 2 represent the initial and resulting conditions respectively. (Marieb & Hoehn, 2013, p. 817-819)
During normal inspiration
Inspiratory muscles contract (diaphragm descends; rib cage rises). Thoracic cavity volume increases → Intrapulmonary pressure drops (to -1 mm Hg). Lungs are stretched and intrapulmonary volume increases. Air (gases) flows into lungs down its pressure gradient until intrapulmonary pressure is equal to atmospheric pressure. (Marieb & Hoehn, 2013, p. 817-819)
During normal expiration
Inspiratory muscles relax (diaphragm rises; rib cage descends due to recoil of costal cartilages). Thoracic cavity volume decreases. Elastic lungs recoil and intrapulmonary volume decreases → pressure increases (Ppul rises to +1 mm Hg) →Air flows out of lungs down its pressure gradient until Ppul = 0. (Marieb & Hoehn, 2013, p. 817-819)
2. Resistance varies in Mike's conducting airways. Using your understanding of respiratory anatomy, explain where in his airway the resistance is highest and why.
In Mike’s case, airway resistance is highest in trachea, in middle-sized bronchi and bronchioles. The contraction of respiratory muscles causes airway resistance in and out of the lungs. The contraction occurs due to an excess concentration of ionic calcium within the cells. Narrow of conducting airways → increase airway resistance → Mike breathing problems. In addition, the mediators from mast cells trigger bronchospasm;...
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