MSFinals-6792
A 56-year-old man visits his doctor with complaints of difficulty maintaining an erection, which has been ongoing for some time and is causing problems in his relationship. He is generally healthy, except for high blood pressure that is managed with amlodipine. He reports still experiencing morning erections and has not noticed any changes in his sex drive. During the examination, his blood pressure is measured at 145/78 mmHg, and his BMI is 30 kg/m2. His abdominal, genital, and prostate exams are all normal. What is the most crucial test to rule out any organic causes for his difficulty maintaining an erection?