A 31-Year-Old Man Arrives at the Office After Experiencing Progressive

A 31-year-old man arrives at the office after experiencing progressive dyspnea for several months. According to the patient, shortness of breath improved initially with supine positioning, but it is now present even with recumbency and minimal exertion. He has had recurring nosebleeds since childhood but has no other medical conditions. The temperature is 36.7 degrees Celsius (98.1 degrees Fahrenheit) , the blood pressure is 110/50 mm Hg, the pulse is 102/min, and the respirations are 20 per minute. On room air, oxygen saturation is 96 percent. An accentuated S2 over the upper left sternal border is discovered during a cardiac examination. Auscultation reveals that the lungs are clear. There is electronic clubbing. The results of the skin examination are depicted in the exhibit. Which of the following is the most likely underlying cause of this patient's dyspnea?

A) Airway obstruction
B) Endocardial infection
C) Pulmonary fibrosis
D) Valvular dysfunction
E) Vascular malformation