In the past 15 years sildenafil citrate-induced penile Doppler has emerged as a technique for evaluating erectile dysfunction. It has greater patient acceptability than the usual papaverine-induced colour Doppler and is safer.
Sildenafil citrate is a popular vasodilator drug used in treatment of erectile dysfunction and can achieve an erection in as many as 85% of cases irrespective of the cause.
Erectile dysfunction (ED) is the occasional or consistent inability of a male to attain and maintain a penile erection sufficiently firm and for a long enough duration to permit vaginal penetration.
Erectile dysfunction has a multifactorial aetiology. In general, erectile dysfunction increases with age, type 2 diabetes mellitus, hypertension, history of smoking, stressful lifestyle and also as a complication following pelvic surgeries.
Papaverine-induced colour Doppler
Penile duplex Doppler using intracorporeal pharmacoactive agents, e.g. papaverine, has traditionally been the investigation of choice. The most troublesome side-effects have been discomfort related to intracorporeal injection, anxiety and priapism, a state of persistent and painful erection which may require treatment with blood aspiration, irrigation and injection of alpha-agonist medications.
NB: for complete discussion on the aetiologies of erectile dysfunction and details of papaverine-induced colour Doppler please see penile Doppler: role in erectile dysfunction.
The sildenafil protocol involves a baseline study without administration of pharmacological agent and includes:
- measurement of cavernosal artery diameter bilaterally
- 0.3 - 0.5 mm is considered normal
- evaluate calcification in cavernosal artery wall (atherosclerotic or diabetic) and tunica albuginea (Peyronie disease)
- peak systolic velocity, acceleration time, resistive index of cavernosal artery
- end diastolic flow and presence or absence of diastolic reversal of flow
50 mg of sildenafil citrate is administered orally to the patient. The parameters are measured without manual or audiovisual stimulation at 60 minutes post-administration as the serum levels reach peak value by this time. Since sildenafil citrate requires a direct sexual stimulus for maximum effectiveness, an audiovisual stimulus (15 minutes of private continuous visualisation of an erotic video) is given. After that, clinical and Doppler evaluations are again performed at five-minute intervals for another 20 minutes with the patient still receiving the audiovisual stimulus.
The main side-effects are mild headaches and occasional blurring of vision which should be explained to the patient prior to the procedure.
Semiquantitative clinical grading of an erection:
- score of 0: flaccid
- score of 1: mild engorgement of the penis without adequate rigidity
- score of 2: partial erection allowing minimal compression
- score of 3: full visible erection with turgidity and complete stiffness of the penis
Duplex Doppler evaluation of erection:
Cut-off values to define sufficient arterial response are:
- peak systolic velocity (PSV) >25 cm/s
- 60% increase in cavernosal artery diameter
- acceleration time (AT) <72 ms
Cut-off value to define sufficient veno-occlusion are:
- end diastolic forward flow velocity <5 cm/s
- resistance index >1.00
Sildenafil citrate-induced penile Doppler offers a safer alternative to the traditional papaverine-induced study with 90% sensitivity and 100% selectivity. It is more acceptable to patients than intracorporeal injections.
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