Is there a role of radial rigidity in the evaluation of erectile dysfunction?

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1 (2001) 13, 200±204 ß 2001 Nature Publishing Group All rights reserved /01 $ Is there a role of radial rigidity in the evaluation of erectile dysfunction? JH Ku 1 *, YS Song 2, ME Kim 2,NKLee 2 and YH Park 2 1 Department of Urology, Military Manpower Administration, Teajeon, Korea; and 2 Soonchunhyang University School of Medicine, Seoul, Korea RigiScan has been the most widely utilized device for measuring erectile rigidity. However, the use of the RigiScan in the evaluation of erectile dysfunction has questionable because the RigiScan device does not directly determine axial rigidity. The aim of this study is to clarify that radial rigidity measured by RigiScan re ects the intracorporeal pressure and erectile capability ef ciently. From January 1998 to May 1999, a total of 23 patients with erectile dysfunction were involved in the study. They were evaluated by RigiScan and duplex ultrasonography after intracorporeal injection of prostaglandin E1. We investigated the relationship between radial rigidity and the resistance index. The results of radial rigidity were also compared with that of the degree of erection. For the entire group, signi cant correlations were found between radial rigidity and the resistance index (r ˆ 0.680, P < for tip rigidity; r ˆ 0.703, P < for base rigidity). In addition, for 12 patients whose tip rigidity exceeded 60% and for 10 whose base rigidity exceeded 60%, the correlations between radial rigidity and the resistance index remained (r ˆ 0.659, P ˆ for tip rigidity; r ˆ 0.759, P ˆ for base rigidity). Based on the response determined by patients, radial rigidity represented the degree of erection ef ciently. Our ndings suggest that RigiScan is a useful diagnostic tool. Radial rigidity represents the intracorporeal pressure ef ciently and has an acceptable role in the evaluation of erectile dysfunction. (2001) 13, 200±204. Keywords: erectile dysfunction; impotence; radial rigidity; RigiScan; penile duplex ultrasonography Introduction Oral therapy is considered as the rst-line management strategies for erectile dysfunction and intracavernous injection therapy is offered as the rst-choice treatment if oral therapy fails or is contraindicated. 1 A diagnosis of erectile dysfunction is important because oral therapy may not be the proper therapy with underlying major diseases. 2 Evaluation of male erectile dysfunction ideally should include measurement of axial rigidity. Unfortunately, this test cannot be done frequently and an alternative method of determining rigidity is to use RigiScan, which makes repetitive measurements of radial rigidity at the tip and base of the penis. However, when tip and base rigidity exceed 60%, these are poor correlations with axial rigidity and observer rating. 3 This nding can be explained by the fact that axial and radial rigidity share a common *Correspondence: JH Ku, Department of Urology, Military Manpower Administration, 1-6, Moonhwa-dong, Joong-Ku, Taejeon , Korea. randyku@korea.com Received 1 August 2000; accepted 26 February 2001 dependency upon intracarvernosal pressure but for axial rigidity, additional dependent variables include cavernosal erectile tissue properties and penile geometry, while for radial rigidity, this may include tunical surface wall tension properties. 4 So, should axial rigidity instead of radial rigidity be measured in all the patients with erectile dysfunction? To clarify this problem, we investigated the relationship between radial rigidity and the resistance index. The results of radial rigidity were also compared with that of the degree of erection. Our goal of the study was to determine whether radial rigidity measured by RigiScan re- ected the intracorporeal pressure and erectile capability of the patients with erectile dysfunction ef ciently. Patients and methods Patients From January 1998 to May 1999, we evaluated patients with erectile dysfunction by RigiScan and duplex ultrasonography after intracorporeal

2 injection of prostaglandin E1. The nature of the study was fully explained to each participant before informed consent was obtained. All patients participated in our multidisciplinary sexual dysfunction evaluation program, jointly coordinated by the department of urology. A history was obtained and a careful physical examination was performed and appropriate laboratory studies were obtained. The intracavernous injection test with RigiScan and duplex ultrasonography was performed. If the erectile response was different during RigiScan and duplex ultrasonography, the results were excluded and a total of 23 patients, 24 to 70-y-old (mean age 48 y) with erectile dysfunction were involved in the study. Methods Each patient after voiding was injected intracorporeally with 10 mg prostaglandin E1. The RigiScan was placed on the penis immediately after injection, and radial and axial rigidity measurements were made for 30 min following injection. RigiScan was placed on the patient in the standard manner with one band near the base and the other just below the glans penis. At the same time, erectile response was evaluated and judged by the clinician and patient. The response was classi ed as positive Ð a fully rigid erection, negative Ð absent or slight erection when no tumescence or tumescence without any rigidity suf cient for vaginal intromission was obtained. The following day, the duplex Doppler examination was performed with the patient supine and the sonographic probe placed on the dorsal side at the base of the penis. Flow measurements can be evaluated accurately by a combination of B-mode imaging and pulsed Doppler spectrum analysis. High-frequency (7.5 ± 10 MHz) linear-array ultrasound transducers are used to image the penis in the longitudinal and transverse planes to exclude plaque material along the tunica albuginea and within the corpora cavernosa. The peak systolic velocity and the end diastolic velocity in both cavernous arteries were measured by duplex sonography 5 ± 30 min after an intracavernous injection of 10 mg prostaglandin E1. The resistance index was calculated as follows: resistance index ˆ (peak systolic velocity 7 end diastolic velocity)=(peak systolic velocity). 5 Throughout the scanning period the degree of rigidity and tumescence were determined by palpation of the penis as well as by questioning the patient, and the interval to achieve the maximum response. The same method was performed to evaluate the degreee of erection during RigiScan measurement. Each study was conducted by the same investigator in an isolated quiet rooom that ensured warmth and privacy. Statistical analysis used to determine whether there is a correlation between the resistance index and radial rigidity of the penis included Spearman's correlation coef cient with P < 0.05 considered with signi cance. Using the degree of erection as the criterion standard, the ability of radial rigidity was assessed by sensitivity, speci city and positive and negative predictive values (PPV and NPV, respectively). Statistical analyses were performed using a commercially available analysis program. Results The results of peak systolic velocity, end diastolic velocity, resistance index, and radial rigidity at the tip and base in the 23 patients are summarized in the Table 1. Overall, there was an excellent correlation between the resistance index measured with duplex ultrasonography, and radial rigidity measured with the RigiScan at the tip (Figure 1A) and base (Figure 1B) of the penis. For the entire group, signi cant correlations were found between radial rigidity and the resistance index (r ˆ 0.680, P < for tip rigidity; r ˆ 0.703, P < for base rigidity). In addition, for 12 patients whose tip rigidity exceeded 60% and 10 whose base rigidity exceeded 60%, there was also a correlation with the resistance index and radial rigidity at the tip (Figure 1C) and base (Figure 1D) of the penis. The correlations between radial rigidity and the resistance index remained (r ˆ 0.659, P ˆ for tip rigidity; r ˆ 0.759, P ˆ for base rigidity). Furthermore, based on the degree of response determined by patients, RigiScan tip and base rigidity represents the degree of erection ef ciently. The receiver operating characteristic (ROC) curve had an area under the curve (AUC) of 96.7% in tip rigidity and 100% in base rigidity (not shown). Radial rigidity at the tip of the penis was greater than 70 in seven patients, 60 ± 70 in ve, and less than 60% in 11. The seven patients with tip rigidity of greater than 70% had a full erection and the 11 with tip rigidity of less than 60% had an incomplete erection. Of the remaining ve with tip rigidity of 60 ± 70%, one had a full erection. Seven, three and 13 patients had base rigidity greater than 70, 60 ± 70, and less than 60%, respectively. The seven patients Table 1 Patients' characteristics Parameters (unit) Mean s.d. Minimum Maximum Peak systolic velocity (cm=s) End diastolic velocity (cm=s) Resistance index Tip radial rigidity Base radial rigidity

3 202 Figure 1 Correlation between the resistance index and radial rigidity. (A) Tip radial rigidity (r ˆ 0.680, P < 0.001). (B) Base radial rigidity (r ˆ 0.703, P < 0.001). (C) Tip radial rigidity exceeded 60% (r ˆ 0.659, P ˆ 0.020). (D) Base rigidity exceeded 60% (r ˆ 0.759, P ˆ 0.011). Table 2 erection Ability of radial rigidity to represent the degree of Discussion Cut-off Sensitivity Radial rigidity (tip=base) Speci city PPV NPV = = = = = = = =100.0 PPV: Positive predictive value, NPV: Negative predictive value. with base rigidity of greater than 70% had a full erection and the 13 with base rigidity of less than 60% had an incomplete erection. Of the remaining three with base rigidity from 60 ± 70%, one had a full erection. Sensitivity, speci city, PPV and NPV are shown in Table 2. The resistance index has been used routinely by many investigators to screen patients for cavernous leakage. Because this parameter is assumed to re ect best the penile hemodynamic change after vasodilator stimulation, the value of the resistance index less than 0.85 is often considered indicative of the degree of leakage. 6 However, there is a direct correlation between the resistance index and the intracorporeal pressure increase provoked by intracavernous injection of vasodilators but not between the resistance index and the intracorporeal pressure provoked by cavernosometry. 7 As the intracavernous pressure at cavernosometry is only in uenced by cavernous wall resistance but not by arterial

4 ow, 8 there is no clear correlation between the value of the resistance index and the degree of cavernous wall resistance. The value of the resistance index was only related to the corporeal pressure. In the phase of erectile response, the tone of the trabecular smooth muscle regulates venous out ow resistance in the corpora. Following complete smooth muscle relaxation, the out ow resistance from the corporal bodies increases by approximately 100-fold and it is constant and independent of intracavernous pressure. 9 Therefore, under physiological conditions, arterial pressure rather than arterial ow appears to govern penile rigidity. A positive erectile response merely re exes an intracavernous pressure 80 mmhg. In this study, we tested two hypotheses that radial rigidity measured with the RigiScan represents the intracorporeal pressure ef ciently and may discriminate the degree of erection. We compared radial rigidity at the tip and base with the resistance index, not cavernosometry because the value of resistance index is only in uenced by corporeal pressure but not by the degree of cavernous wall resistance. We found that there was a correlation between the resistance index and radial rigidity at the tip and base of the penis and when RigiScan base tip and base radial rigidity exceeded 60%, there was also a correlation with the resistance index and radial rigidity at the tip and base of the penis. Although the number of patients were small, this nding demonstrated that radial rigidity might have a correlation with the intracorporeal pressure in circumstances when it exceeded 60%. Then, we compared the results of radial rigidity at the tip and base with the degree of erection for investigating the second hypothesis. All the patients with radial rigidity at the tip and base rigidity of greater than 70% had a full erection and all with radial rigidity at the tip and base rigidity of less than 60% had an incomplete erection. Radial rigidity at the tip and base rigidity from 60 to 70% was a gray zone in our series. Allen et al 3 stated that when RigiScan base and tip radial rigidity exceeded 60% of maximum, there was a poor correlation with axial rigidity and observer rating. They concluded since the RigiScan might not be able to detect mild abnormalities in erectile dysfunction, the RigiScan measurement of radial rigidity in excess of 60% of maximum should be interpreted cautiously and not necessarily regarded as normal. Udelson et al 4 explained this nding. They demonstrated that radial rigidity asymptotically approached a maximum nite value while axial rigidity increased continuously towards in nity, since axial and radial rigidity share a common dependency upon intracavernosal pressure but for axial rigidity, additional dependent variables include cavernosal erectile tissue properties and penile geometry, while for radial rigidity, this may include tunical surface wall tension properties. However, it is unclear which surrogate measure of erection is the most accurate one. The goal of evaluating an individual penile erectile capacity is to determine how that individual's erection compares to the pressure necessary to accomplish intromission with his partner but no measures of intromission pressure have been accepted. 10 Axial buckling force measurements fail to record the ability of an individual to maintain an erection and give no indication of location of penile buckling which could be useful in assessing penile shaft abnormalities. 11 Furthermore, these measurements have the operator dependence and impractical nature. Above all, for radial rigidity above 60 ± 70%, the individual had an unbuckleable penis and the sensitivity to increase in intracavernal pressure is of unknown clinical value or no useful clinical signi cance. 10,11 To date, several accurate tests for diagnosing erectile dysfunction may be chosen. Each method has its pros and cons, related to validity, costs, invasiveness and availability. The choice of tests should always depend on the purpose of testing: assessing erectile capacity, locating a speci c vascular lesion for surgical treatment, or de ning the vascular status in groups of patients with a speci c disease. A practical purpose for diagnostic testing may be assessment of erectile capacity. Another purpose may be that the physician wishes to select patients for speci c surgical treatments such as revascularization or veno-restrictive surgery. Furthermore, it may be important for scienti c and clinical reasons to de ne the cause of erectile dysfunction in groups of patients with a chronic disease, such as diabetes mellitus or renal failure. It is necessary to be well aware of the purpose of testing. 12 Because the RigiScan device is used for a screening purpose, but not con rmatory one, its use seems to be reasonable for the diagnosis of erectile dysfunction. Our ndings suggest that RigiScan is a useful diagnostic tool. Radial rigidity represents the intracorporeal pressure ef ciently and has an acceptable role in the evaluation of erectile dysfunction. However, our tests had the shortcoming that they were not performed synchronously, although our patients had the same response during RigiScan and duplex ultrasonography measurement. Generally, comparison of different techniques to evaluate veno-occlusion is valid if the tests are performed synchronously. This is due to the fact that circumstances of the test and the interval after pharmacological stimulation are critical factors in venoocclusive function. References 1 Shabsigh R et al. Intracavernous alprostadil alfadex is more ef cacious, better tolerated and preferred over intraurethral alprostadil plus optional actis: a comparative, randomized, crossover, multicenter study. Urology 2000; 55: 109 ±

5 204 2 Weiske WH. Invasive diagnostic and therapy Ð are they still reasonable in the age of sildena l? Andrologia 1999; 31(Suppl 1): 95 ± Allen RP, Smolev JK, Engel RM, Brendler CB. Comparison of Rigiscan and formal nocturnal penile tumescence testing in the evaluation of erectile rigidity. JUrol1993; 149: 1265 ± Udelson D et al. Axial penile buckling vs Rigiscan TM radial rigidity as a function of intracavernosal pressure: why Rigiscan does not predict functional erections in individual patients. Int J Impot Res 1999; 11: 327 ± Fronek A, Coel M, Bernstein EF. Qualtitative ultrasonographic studies of lower extremity ow velocities in health and disease. Circulation 1976; 53: 957 ± Meuleman EJ et al. Assessment of penile blood ow by duplex ultrasonography in 44 men with normal erectile potency in different phases of erection. J Urol 1992; 147: 51 ± de Meyer JM, Thibo P. The resistance index represents the corporeal pressure and not the cavernous wall resistance. J Urol 1997; 157: 830 ± Puech-Leao P, Chao S, Glina S, Reichelt AC. Gravity cavernosometry Ð a simple diagnostic test for cavernal incompetence. Br J Urol 1990; 65: 391 ± Saenz de Tejada I et al. Trabecular smooth muscle modulates the capacitor function of the penis. Studies on a rabbit model. Am J Physiol 1991; 260: 1590 ± Levine LA. Editorial comment. Axial penile buckling vs Rigiscan TM radial rigidity as a function of intracavernosal pressure: why Rigiscan does not predict functional erections in individual patients. Int J Impot Res 1999; 11: 337 ± Gerald T. Editorial comment. Axial penile buckling vs Rigiscan TM radial rigidity as a function of intracavernosal pressure: why Rigiscan does not predict functional erections in individual patients. Int J Impot Res 1999; 11: 338 ± Meuleman EJ, Diemont WL. Investigation of erectile dysfunction: diagnostic testing for vascular factors in erectile dysfunction. Urol Clin N Amer 1995; 22: 803 ± 819. Editorial Comment The authors state `...the use of the RigiScan in the evaluation of erectile function has questionable because the RigiScan device does not directly determine axial rigidity'. The RigiScan system measures radial rigidity by recording the displacement that occurs in the compressive loops in response to a 10 ounce tug force. To the extent the penis can be approximated as a thin-walled, cylindrical pressure vessel, the hoop stress which is measured by the RigiScan compressive loops is twice as large as the longitudinal stress measured by an axial buckling force load and is independent of the length to diameter aspect ratio or internal pressure, as long as the wall thickness is signi cantly less than the vessel radius. 1 Therefore, radial rigidity as measured by the RigiScan system is equivalent, by a constant factor, to axial rigidity within the range of measurements in which a 10 ounce tug force is suf cient to compress the penile wall. 2,3 Despite acknowledging the shortcoming of their study in that the tests were not performed synchronously, the authors demonstrated a high correlation between radial rigidity as measured by the RigiScan system and the resistance index as measured by duplex ultrasonography for base and tip rigidities exceeding 60%. These high rigidity values coincide with the time in a penile erection when the tunica are in tension, both radially and axially, producing stress in the tunica wall. This data demonstrates the equivalence of radial rigidity to erectile capacity as measured by resistance index, which has been shown to be correlated with intracavernosal pressure. The authors note that an investigator must be well aware of the clinical or scienti c purpose of patient testing before determining which tests to perform. Their study further con rms the validity of radial rigidity measurements, whether measured continuously or intermittently, as a useful tool in assessing an individual's pathophysiology and his responsiveness to various therapeutic regimens. References 1 Beer FP and Johnston ER. Stresses in thin-walled pressure vessels. In: Mechanics of Materials, Second Edn. McGraw-Hill: New York, 1992, pp 377 ± Bradley WE, Timm GW, Gallagher JM, Johnson B. New method for continuous measurement of nocturnal penile tumescence and rigidity. Urology 1985; 26: 4 ± 9. 3 Frohrib DA et al. Characterization of penile erectile states using external computer-based monitoring. J Biomech Eng 1987; 109: 110 ± 114. GW Timm

D Udelson, A Nehra, DG Hatzichristou, K Azadzoi, RB Moreland, RJ Krane, I Saenz de Tejada and I Goldstein

D Udelson, A Nehra, DG Hatzichristou, K Azadzoi, RB Moreland, RJ Krane, I Saenz de Tejada and I Goldstein International Journal of Impotence Research (1998) 10, 89±99 ß 1998 Stockton Press All rights reserved 0955-9930/98 $12.00 http://www.stockton-press.co.uk/ijir Engineering analysis of penile hemodynamic