Resistance in the distal penile circulation depends on the helicine arterioles, cavernosal lacunae and draining venules.
Method:
(1) An erection is achieved, often by injecting papaverine HCl (usually 60 mg) into a cavernosal body.
(2) Systolic blood flow is measured in cm per second (cm/s).
(3) End-diastolic blood flow is measured in cm per second (cm/s).
resistance index =
= ((peak systolic velocity in cm/s) - (end-diastolic velocity in cm/s)) / (peak systolic velocity)
Interpretation:
• The normal RI is > 0.8. A value of 0.8 is borderline.
• The RI is abnormal if < 0.8.
• If the peak systolic velocity is normal then a low RI indicates veno-occlusive dysfunction.
• Valiji and Bookstein found a low RI in patients with arteriogenic impotence. A large percentage of the patients with arteriogenic impotence also had veno-occlusive disease.
