I Can’t Stop Coughing: A Case Study on the Respiratory System Mike is sitting in
ID: 217693 • Letter: I
Question
I Can’t Stop Coughing: A Case Study on the Respiratory System 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.
Questions to Think About:
1. Describe the relationship between intrapulmonary pressure, atmospheric pressure, and air flow during normal inspiration and expiration, referring to Boyle’s law.
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.
3. 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
4. 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?
5. How does Mike’s body make the necessary changes in intrapulmonary pressure to maintain normal air flow when he is experiencing cold-induced asthma?
6. 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.)
7. 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?
Explanation / Answer
1. Boyles law state that the volume of a gas in a container is inversely proportional to the pressure of the gas.
When the lung volume increases, the intrapulmonary pressure drops below the atmospheric pressure, and air rushes into the lungs. When the muscles of inspiration relax, the thoracic volume decreases and intrapulmonary pressure rises above atmospheric pressure. Therefore, air flows out of the lungs.
2. Air travels into lower diameter leads to face greater resistance like medium-sized bronchi. Then air moves to terminal bronchi but here resistance is low compared to medium size bronchi because there are many smaller bronchi are present to much greater cross-sectional area than the medium-sized airways. The greater the total cross-sectional area of airways, the lower the resistance through that region.
3. Lung compliance=measure of change in lung volume that occurs with given change in transpulmonary pressure
(higher compliance > easier to breath). Alveolar surface tension=attracts liquid molecules to one another at gas-liquid interface (resists any force that tends to increase surface area of liquid). Airway resistance=gas flow changes inversely with resistance Mike is experiencing airway resistance because his bronchioles are constricting.
4. Intrapulmonary pressure needs to decrease to allow more air in. Exhalation, the intrapulmonary pressure must increase more than usual to move air out against the same resistance.
5. Accessory muscles, such as the sternocleidomastoid, pectoralis minor, and scalenes, are recruited to help increase the thoracic cage dimensions on inspiration. They do so by assisting in drawing the thoracic cage upward. Expiration is normally a passive process, but with the increased resistance in asthma abdominal muscles and internal intercostals must be recruited to force air out against resistance. Contracting the abdominal muscles increase intra-abdominal pressure, pushing up on the diaphragm, and contracting the internal intercostals depresses the thoracic cage; these actions assist in decreasing thoracic volume.
6. Both the FVC and FEV1 should be ³ 80%, so Mike's values indicate respiratory dysfunction. Asthma is classified as an obstructive disease because the reactive airways narrow and increase resistance, thus obstructing normal air flow. Despite a maximal effort, Mike cannot generate enough intrapulmonary pressure to compensate entirely for the excessive resistance, so normalized air flow on exhalation, particularly in the first second, cannot happen.
7. Activation of beta-2 adrenergic receptors on bronchial smooth muscle sets into motion a second messenger system, which leads to relaxation of smooth muscle. This causes the bronchi and bronchioles to dilate. Bronchodilation decreases resistance and ameliorates the wheezing, coughing, and shortness of breath.
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