Detection of Intracardiac and Intrapulmonary Shunts at Rest and During Exercise Using Saline Contrast Echocardiography

Abstract

Ultrasound has become a valuable tool for making non-invasive physiological measurements that are clinically important, one of which is detection of anatomic shunts using saline contrast echocardiography. Right-to-left intrapulmonary and intracardiac shunts are clinically relevant for two reasons. First, they allow deoxygenated blood to mix with oxygenated blood, thereby reducing the overall efficiency of pulmonary gas exchange. Thus, the opening of either intrapulmonary or intracardiac shunts at rest and/or during exercise may play a role in determining pulmonary gas exchange efficiency (Sun et al., 2002; Stickland & Lovering, 2006; Lovering et al., 2011). The opening of these shunts may also explain why some people with pulmonary diseases such as chronic obstructive pulmonary disease (COPD) desaturate so profoundly during even mild exercise (Miller et al., 1984; Dansky et al., 1992). The second reason that these pathways are clinically relevant is that anatomic right-to-left shunts may allow for thrombi to bypass the pulmonary capillary filter. Indeed, a patent foramen ovale and pulmonary arteriovenous malformations are associated with increased risk for neurological sequelae such as migraines, transient ischemic attacks and stroke (Movsowitz et al., 1992; Petty et al., 1997; De Castro et al., 2000; Lamy et al., 2002).