32

32 CASE 32


A 10-year-old boy is brought to the emergency department because of difficulty breathing that developed during soccer practice.


The boy has a history of allergies, including a pollen allergy, but never previously showed this level of respiratory difficulty. He now complains of tightness in the chest. There is no family history of allergies or asthma. Both parents smoke cigarettes.



PHYSICAL EXAMINATION



VS: T 37°C, P 120/min, R 30/min and shallow, BP 110/95 mm Hg

PE: Patient is wheezing, anxious, and short of breath. The wheezing is more prominent on exhalation, and there is an extended forced expiratory phase. The chest anteroposterior diameter appears large for age and size. The nasal mucosa is edematous, and the pharynx is coated with a clear postnasal discharge. A beta2-adrenergic agent was administered by an inhaler, and the symptoms quickly subsided. The patient’s anxiety was relieved, and heart rate and breathing rate returned to normal. The patient was scheduled for pulmonary function tests.


LABORATORY STUDIES



Spirometry: Normal values. When challenged with methacholine, however, a hyperreactive bronchoconstriction occurred with decreased FEV1, decreased forced vital capacity, and increased residual volume.

Forced spirometry flow/volume loop: Scooping, diminished peak flow.


DIAGNOSIS


Asthma



PATHOPHYSIOLOGY OF KEY SYMPTOMS


Asthma is characterized by a chronic inflammation of the pulmonary airways. The bronchiolar smooth muscle becomes hyperresponsive to allergens, irritants, or other agents. Exposure to these substances triggers a strong bronchoconstriction. The symptoms of an asthmatic attack result from the bronchoconstriction and are characteristic of an “obstructive” pulmonary disease. The bronchoconstriction, inflammation, and excess mucus all act to obstruct the lumen of the bronchioles.


The increased resistance to airflow in the bronchioles accounts for the wheezing, abnormal spirometry volumes, and shortness of breath.


Wheezing is due to the premature closing of airways during expiration. During inspiration, the negative intrapleural pressure helps to expand both the alveoli and the small pulmonary bronchioles. Consequently, inflation of the lungs is not diminished during an asthmatic attack. During exhalation, however, contraction of the accessory respiratory muscles acts to increase pleural pressure. This increased pleural pressure provides an external compression of the small bronchioles. Airflow past these narrowed airways can be heard as a wheeze that is more prominent during exhalation.


Increased resistance to airflow through the narrowed airways also causes a diminished peak expiratory flow rate. In spirometry, the same effect is indicated by a diminished FEV1. During active exhalation, the increase in pleural pressure is acting to collapse the airways. Consequently, additional respiratory effort does not result in improved exhalation volumes (Fig. 32-1).


image

FIGURE 32–1 Recordings during the forced vital capacity maneuver in a healthy person (A) and in a person with partial airway obstruction (B). (The “zero” on the volume scale is residual volume.)

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 32

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