A 17-year-old student has experienced reversible, periodic attacks of chest tigh

Question

A 17-year-old student has experienced reversible, periodic attacks of chest tightness with coughing,wheezing, and hyperpnea. She states that expiration is more difficult than inspiration. She is mostcomfortable sitting forward with arms leaning on some support. X-rays revealed mild overinflationof the chest. Results from laboratory and pulmonary function tests are as follows:• Frequency: 20 breaths/min• Vital capacity (VC): 2.9 L• FEV1.0: 1.4 L• FEV1.0/FVC: 56%• Functional residual capacity (FRC): 3.89 L• Total lung capacity (TLC): 6.82 L• PaO2: 70 mm Hg• PaCO2: 26 mm Hg• Pulse: 108 b/min• BP: 120/76 mm HgIntermittent use of a bronchial smooth muscle dilator (1:1000 epinephrine by nebulizer) for severaldays caused marked improvement, resulting in the following laboratory and pulmonary functiontests:• VC: 4.15 L• FEV1.0: 3.1 L• FEV1.0/FVC: >75%• FRC: 3.7 L• TLC: 5.96L• PaO2: 89 mm Hg• PaCO2: 38 mm Hg• Pulse: 129 b/min• BP: 122/78 mm Hg

Questions:
1. What is the disorder of this 17-year-old student?2. Is this primarily a restrictive or an obstructive disorder? Why?3. Write the formula for determining residual volume (RV).4. Determine the residual volume (RV) before and after the use of the bronchodilator.

a. RV before using the bronchodilator:b. RV after using the bronchodilator:

5. Why is expiration more difficult than inspiration in this person?6. What does the change in pulmonary function after the bronchodilator therapy indicate?7. Why does the bronchodilator exaggerate the tachycardia?8. What causes the hypoxemia and the hypocalcemia in this person?

9. A beta2-adrenergic agent was prescribed for further use because it has less cardio stimulatory (beta1) effect. Based on your knowledge of beta1 and beta2 receptors, why is this a good suggestion?

10. An anticholinergic agent was also suggested as a possible nebulizer agent. How might this helps the breathing problem?

Explanation / Answer

1)The disorder is asthma .

2)This is primarily an obstructive disorder as evidenced by the reduced FEV1.0/FVC.

3).Residual volume RV = TLC - VC.

4)RV before using the bronchodilator = 3.92 L.

RV after using the bronchodilator=1.81L

5)Expiration is more difficult than inspiration in this person because of the following facts: Inspiration is an active process. Expiration is passive. Bronchoconstriction increases expiratory difficulty by further narrowing of the airways, thus increasing the work of expiration. Also, inspiration causes expansion of the airways during the negative pressure breathing, whereas expiration leads to further narrowing of the already narrowed airways.The decreased tidal volume is contributing to the decreased alveolar ventilation.

6)The change in pulmonary function after the bronchodilator therapy indicates that the airways were narrowed (bronchoconstriction) and relieved with bronchodilator therapy-a reversible process.

7)The bronchodilator exaggerates the tachycardia because epinephrine is a sympathomimetic agent (mimics the sympathetic nervous system) and therefore increases heart rate.

8)The hypoxemia (PaO2 = 70) is due to the bronchoconstriction, increased RV, and increased diffusion distance in the alveoli due to the mucus accumulation as evidenced by the wheezing. The hypocapnemia (PaCO2 = 26) is due to the increased frequency of breathing. CO2 also diffuses between the blood and the alveoli (the alveolar-capillary membrane) twenty times as fast as O2; therefore, CO2 is more easily removed from the blood.

9)The beta2-adrenergic agent was prescribed due to its reduced cardiostimulatory (beta1) effects based upon these facts: the heart has primarily beta1 receptors on cardiac muscle and the sinoatrial node, whereas bronchial smooth muscle has primarily beta2 receptors. A beta2-adrenergic agent causes relaxation of bronchial smooth muscle (bronchodilation) with minimal cardiostimulatory effect. (Epinephrine stimulates both beta1 and beta2 receptors.)

10)An anticholinergic agent might also help the breathing problem for the following reasons: Bronchial smooth muscle is innervated by both the parasympathetic (cholinergic) and sympathetic (adrenergic) divisions of the autonomic nervous system. Parasympathetic innervation causes bronchoconstriction. An anticholinergic agent would therefore cause bronchodilation.

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