Effects of Pulmonary Edema on Airway Reactivity

Abstract

Airway hyperreactivity can be defined as an extreme sensitivity of the airways to a wide variety of pharmacologic, chemical, or physical stimuli. It is a characteristic and consistent feature of patients with asthma and is present in some patients with chronic bronchitis. Airway hyperreactivity can be manifested clinically as cough, wheezing, and tachypnea. Airway reactivity to a stimulus is assessed objectively by measurements of pulmonary function that reflect airway constriction, such as the forced expiratory volume in one second (FEV1) or airway resistance (Raw)One method of measuring the degree of airway reactivity present in a patient or experimental animal is to administer increasing doses of a bronchoconstrictor material such as methacholine or histamine by inhalation and to make sequential measurements of pulmonary function. The results of such a study in a patient with hyperreactive airways (solid symbols) and in a patient with normal airways (open symbols) are depicted in Figure 1. The patient with airway hyperreactivity developed a significant degree of bronchoconstriction after inhaling relatively small amounts of histamine; the patient with normal airways reacted only slightly to large doses of histamine. Because airway hyperreactivity can be present in patients with normal spirometry, assessment of airway reactivity has been proposed as a diagnostic test of otherwise inapparent asthma. Despite the term "cardiac asthma," airway hyperreactivity has not been reported to accompany episodes of left ventricular failure, or to follow bouts of cardiogenic pulmonary edema. As discussed earlier in this issue, the wheezing present during cardiogenic pulmonary edema probably results from passive narrowing of the airways, and does not indicate the presence of airway hyperreactivity. However, there is suggestive evidence that noncardiogenic pulmonary edema, the adult 100