Ear oximetry measures the oxygen saturation of circulating blood. The oximeter transmits a beam of light through the earlobe or pinna to a receiver on the other side. By analyzing the amount of light received relative to the amount of light transmitted, the percentage of oxygen saturation of the blood can be calculated. A positive finding involves transient drops in oxygen saturation following techniques that provoke right-to-left cardiac shunting, such as the Valslava maneuver.
The technique is both a sensitive and specific method for the detection of PFO. It's noninvasive, inexpensive and causes no discomfort for the patient, unlike the current gold standard for the detection of PFO, transesophageal echocardiography (TEE) with bubble contrast. And, yes, it generally is readily available in the USA.