Radiographic inversion of pulmonary blood flow in acute asthma.

Chest radiographs are obtained routinely in children hospitalized with asthma but are considered to be of low utility. We describe a previously unreported radiographic inversion of pulmonary artery flow patterns in the chest films of a majority of children and young adults hospitalized for asthma. Seventy-five hospital records of 65 patients aged 2 to 25 years (mean 9.2) admitted for asthma during the calendar year 1991 were reviewed. As compared with the normal pattern, patients with inverted vascularity were younger (mean age 6.75 years), tended to be admitted through the emergency department, and had significantly more signs of labored breathing, such as tachypnea, retractions, nasal flaring, and tachycardia. We propose that the exaggerated respiratory effort in these children raises the transmural pulmonary artery pressure, impeding pulmonary blood flow. This results in distension of the right ventricle, which then compresses the left ventricle in the confines of the pericardium by posterior displacement of the interventricular septum. The resultant loss of left-sided compliance raises the left atrial and pulmonary venous pressures, leading to inversion of vascular markings through the same mechanism as seen in left-heart failure. We conclude that attention to this easily recognized sign will detect presence of the hemodynamically significant respiratory obstruction in asthmatic patients.