In duplex imaging after injection, which resistivity pattern is observed in the penile arteries?

• A. High-resistivity
• B. Low-resistivity
• C. No change
• D. Venous flow predominant

Answer: (B)

After pharmacologic erection, the penile cavernosal arteries dilate and the erectile tissue offers less resistance to flow. This produces a low-resistance Doppler pattern characterized by increased diastolic flow and a reduced resistive index (RI). Since RI = (PSV − EDV) / PSV, the rise in EDV with the low downstream resistance lowers the RI, often with prominent diastolic flow. This pattern indicates adequate arterial inflow after injection.

High-resistivity would reflect constricted or high-resistance flow, which isn’t expected after successful erection. No change would imply the injection didn’t affect flow, and venous flow predominant points more to venous leakage rather than the arterial response being evaluated.