Review Question - QID 106790

This patient presents with a severe asthma exacerbation which can cause pulsus paradoxus.

Asthma is an inflammatory airway disease that causes reversible airway obstruction and bronchospasm. It is commonly treated with beta-agonists, corticosteroids, and anticholinergics. During a severe asthma exacerbation, pulsus paradoxus may be observed. Pulsus paradoxus is a decrease in systolic blood pressure by > 10mmHg during inspiration (Illustration A). It is observed in severe cardiac tamponade, asthma, obstructive sleep apnea, pericarditis, and croup. It is caused by bulging of the interventricular septum into the left ventricle with decrease cardiac output and thus decreased blood pressure. This bulge is exacerbated by conditions such as asthma as a result of increased lung volume and vascular resistance that exaggerate the intrathoracic pressure swings during normal inspiration and expiration.

Hamzaoui review the pathophysiology of pulsus paradoxus and when it occurs. They state pulsus paradoxus is defined as a fall of systolic blood pressure of >10 mmHg during the inspiratory phase. Pulsus paradoxus can be observed in cardiac tamponade and in conditions where intrathoracic pressure swings are exaggerated or the right ventricle is distended, such as severe acute asthma or exacerbations of chronic obstructive pulmonary disease.

Xing et al. examine the mechanism of production of pulsus paradoxus. They state that it is primary caused by displacement of the interventricular septum into the left ventricular, thereby causing decreased CO. They find that the three major factors determining the respiratory displacement of the interventricular septum in normal and different pathophysiological conditions were the magnitude of respiratory intrathoracic pressure change, the pressure difference between the two ventricles, and the intrapericardial pressure.

Illustration A graphically demonstrates pulsus paradoxus.

Incorrect Answers:
Answer 1: Inspiratory stridor is characteristic of croup and is not generally characteristic of asthma. Of note, croup can also produce pulsus paradoxus.
Answer 2: Increased breath sounds are generally heard when a lung consolidation is present as occurs in a lobar pneumonia.
Answer 3: A friction rub is classically heard in acute pericarditis. It is not observed in an asthma exacerbation.
Answer 4: Kussmaul's sign, an increase in JVP on inspiration instead of a normal decrease, is not observed in asthma. Rather, it is observed in constrictive pericarditis, restrictive cardiomyopathies, right atrial or ventricular tumors, or cardiac tamponade.