This prospective study was approved by the research ethics board of our institution, and informed consent was obtained. Participants recruited from our hospital consented to receive this noninvasive US examination, and this aspect of the study was approved by the Ethical Committee of the First Affiliated Hospital of Sun Yat-Sen University as IRB_2011  entitled “Assessment of cavernous endothelial dysfunction in patients consulting for sexual dysfunction”. From October 2014 to October 2016, a consecutive series of 310 Chinese male patients consulting for sexual dysfunction were referred. Among them, 6 patients declined the US examination. Another 44 patients were excluded if (a) US data were not collected according to the standard protocol (n = 25), (b) no reference standard was obtained (n = 13), or (c) clinical or US data were missing (n = 6).The remaining 260 eligible patients underwent color Doppler sonographic examination. Fifty-four healthy adult volunteers who did not have a history of sexual dysfunction were examined by US and served as a control group for which the same US parameters were obtained. No volunteers had taken any medication or drugs at the time of the US examination. The mean ages of the two groups were 32.9 ± 8.3 years (range 19–72 years) and 29.9 ± 8.9 years (range 19–40 years), respectively (P = 0.200). All patients were in a stable monogamous relationship with a female partner and had made at least one attempt at sexual intercourse over the last 8 weeks. All patients underwent an erectile dysfunction evaluation that included IIEF-5 and EHGS.
All patients in each group were examined using an Aplio XV or 500 (Toshiba Medical Systems, Tokyo, Japan) or Mylab Twice (Esaote Medical Systems, Genoa, Italy) by three operators (W.W., Z. W., L.Y Z.). To ensure patient privacy, all exams were performed in a quiet, comfortable room. Excessive compression with the transducer was avoided. First, in grayscale US, the penis was evaluated in both the longitudinal and transverse planes in the flaccid state. Then, color Doppler sonography was optimized to obtain the best longitudinal plane of the cavernosal arteries. In this longitudinal plane, spectral analysis of the cavernosal arteries was performed in the proximal part of the penis. The optimal site for spectral analysis was the proximal part of the cavernosal arteries where the vessels curved. This location allowed an angle of insonation as low as < 30° for accurate angle-corrected velocity calculations. The PSV, resistance index (RI) and diameters of both cavernosal arteries were recorded. When analyzing the spectral Doppler, the optimized pulse repetition frequency and wall filter were selected, and the width of the Doppler sample size was set at 0.5 mm - 1 mm. Three consecutive similar waveforms were considered to constitute a satisfactory test.
IIEF-5 and EHGS
The IIEF-5, a 5-item questionnaire, is used for clinical diagnosis of the severity of ED, including scores on the 5-item form (that is, Erection confidence, Penetration ability, Maintenance frequency, Maintenance ability, Intercourse satisfaction) . These items focus on erectile function and intercourse satisfaction. This tool has become the ‘gold standard’ for the clinical evaluation of therapy efficacy. The degree of ED is classified as follows: grade1 = severe ED (scores between 5 and 7), grade2 = mild ED (scores between 8 and 11), grade 3 = moderate ED (scores between 12 and 21), grade 4 = no ED (scores between 22 and 25).
The erection hardness grading scale (EHGS) was developed in 1998 by Goldstein et al. . It is a convenient, four-grade scale for ED that provides a reliable measure of the degree and duration of penile rigidity, according to data reported at the European Association of Urology. The erection hardness of the penis is graded according to the EHGS as follows: grade 1 = increased in size without hardness, grade 2 = hard but not hard enough for penetration, grade 3 = hard enough for penetration but not completely hard, and grade 4 = completely hard and fully rigid.
The data were expressed as the mean ± SD or median and inter-quartile range (IQR), as appropriate. The chi-square test or Fisher’s exact test was used to evaluate the difference between the IIEF-5 and EHGS groups in PSV, diameter and RI. Receiver operating characteristic (ROC) curves were compared to evaluate the diagnostic performance of PSV using the MedCalc version 9.0 software (MedCalc Software, Mariakerke, Belgium). The diagnostic performance was expressed as the area under the ROC curve (AUROC). The sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) were calculated. Figures were drawn using the Origin 8.5 software (OriginLab, Northampton, MA, USA). P < 0.05 was considered to indicate statistical significance.