Color Doppler ultrasound results of erectile dysfunction patients after an intracavernosal injection of prostaglandin E1: an analysis of 9,109 cases

Introduction

Erectile dysfunction (ED) is defined as the inability to achieve and/or maintain penile erection sufficient for satisfactory sexual performance, and affects a considerable proportion of men at least occasionally (1). At present, the incidence of ED varies from country to country. Some scholars estimated that approximately 322 million men would be affected by ED in 2025 (2). A population-based survey conducted in 2017 reported that the prevalence of ED in Chinese men aged over 40 years was approximately 40.56% and that ED was correlated with age (3). Many factors affect ED, including psychological, vascular, neurological, endocrine, and structural factors (4). Among them, vascular ED, which in clinical practice is usually classified as arterial ED, venous ED, or mixed ED according to the pathogenesis, is a common cause of ED.

Intracavernosal injection (ICI) combined with color Doppler ultrasound (CDU) examination can be used to diagnose the vascular ED, and is currently widely applied in clinical practice. This examination can be performed quickly and simply in the outpatient departments of hospitals (5-8). However, as examiners need to have a high level of professional expertise, the examination results of many hospitals lack accuracy and objectivity. Thus, the normal reference values of the parameters related to these examination results have not been standardized worldwide. For example, peak systolic velocity (PSV), which best reflects the blood supply capacity of the penile cavernous artery, has a reference lower limit of 25, 30, or 35 cm/s (9-11).

Previous studies involving more than 200 ED patients who underwent CDU after ICI have largely examined non-Asian populations (12,13), and large-scale results for Chinese populations are lacking. Xuan et al. (2016) examined the clinical data of 164 ED patients collected from 2002 to 2009 (14), and reported that the mean PSV value after ICI among ED patients with an Erection Hardness Score (EHS) of Grade 4 (non-vascular ED) was 38.47±8.54 cm/s. Conversely, another study of 200 patients published by Tang et al. in 2013 reported that the mean value of PSV in non-vascular ED patients was 76.5±29.6 cm/s (15). Thus, there was a notable difference in the PSV values of the non-vascular ED patients reported by the two studies.

In addition, reports of communicating branches between the bilateral cavernous arteries are common, and phases of persistent rigid erection have been frequently observed in some patients; however, most research, including the above-mentioned studies, has not addressed these findings. Thus, with standardized procedures, larger-scale data on CDU after ICI in Asian populations, including Chinese populations, may aid in the screening and diagnosis of vascular ED in Asia and worldwide.

In this study, we retrospectively analyzed the data of nearly 10,000 Chinese adult male ED patients who underwent CDU after ICI, and evaluated the cavernous artery blood flow-related parameters across different ED subtypes and age groups. We found that the CDU parameters were correlated with age. We also assessed the effects of communicating branches between the bilateral cavernous arteries and the presence of persistent rigid erection on the examination outcomes. We present this article in accordance with the STROBE reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-650/rc).

Methods

Patient data

The data of ED patients who underwent CDU examination after ICI for the first time at our Department of Andrology from October 2022 to July 2024 were collected. The examinations were conducted by a single andrologist with more than 5 years of working experience. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of Nanjing Drum Tower Hospital (No. 2025-0297-01), and written informed consent was obtained from all patients before the examination.

Inclusion criteria: Chinese male patients, aged 18 years and above, who had been diagnosed with ED by outpatient doctors after consultation or other examinations were included in the study.

Exclusion criteria: patients who had undergone penile thickening surgery, penile lengthening surgery, and sex-reassignment surgery were excluded from the study.

Study design

This was a single-center, retrospective study. All the patients underwent CDU examinations after ICI. A statistical analysis of the examination results of all patients was conducted. The results of patients across different age groups and ED subtypes were statistically analyzed and compared to identify patterns and summarize our clinical experience. Meanwhile, special examination results were analyzed separately to summarize our clinical experience and examine the potential causes and clinical significance of these results.

ICI and EHS

The ICI was administered to the patients in a quiet and private room as described previously (14). The vasoactive agent used was prostaglandin E1 (PGE1), and the injection dose for each patient was 10 µg. After ICI, the patients were exposed to audiovisual sexual stimulation while alone in an examination room. After 5–10 minutes, the examiner entered the room to start the examination. First, the penile EHS was assessed, with hardness between two grades recorded as 0.5 (e.g., hardness between grade 2 and grade 3 was recorded as grade 2.5). Meanwhile, a timer was used to record the erection duration. Patients who had not yet achieved a complete erection were allowed an additional 5–10 minutes, up to a maximum time of 30 minutes. None of the patients received repeated injections.

After the test, the patients were instructed to expedite detumescence by increasing their water intake, increasing their urination, stair climbing, jumping, and/or ice application. If the detumescence was not achieved within 4 hours, the patients received an injection of 200 µg of phenylephrine, which could be repeated or doubled based on the effect, until detumescence was achieved.

EHS was self-reported as: 0, penis is not enlarged; 1, penis is larger but not hard; 2, penis is hard but not hard enough for penetration; 3, penis is hard enough for penetration but not completely hard; 4, penis is completely hard and fully rigid (16).

CDU

After ICI, all patients underwent CDU examination using a Mindray TE7 machine (Shenzhen Mindray Bio-Medical Electronics Co., Ltd., Shenzhen, China). The operator sat on the right side of the patient (face to face), holding a high-frequency linear scanning probe, which was placed at the junction of the penis and scrotum on the left side of the penis. Parameters such as PSV, end diastolic velocity (EDV), and the resistance index (RI) of the bilateral cavernous arteries were measured. If the main artery of one side of the corpus cavernosum could not be detected, the strongest communicating branch with blood flow was recorded as the result for that side. Depending on the clinical situation, the probe was placed on the right side of the penis for detection if necessary. If the penis remained in the phase of persistent rigid erection and blood flow signal was not obviously detected, probing was continued for up to 20 minutes until slight detumescence occurred. If the normal blood flow signal was persistently undetectable, the findings were accurately described and recorded.

Statistical analysis

The data of patients who remained in the phase of persistent rigid erection with no detectable blood flow in the cavernous arteries were analyzed and reported separately. Separate analyses were conducted of the patients in whom one cavernous artery branched off from the contralateral side. Based on PSV and EDV, the remaining patients were allocated to the non-vascular ED group (PSV ≥35 cm/s and EDV <5 cm/s), arterial ED group (PSV <35 cm/s), and venous ED group (PSV ≥35 cm/s and EDV ≥5 cm/s). In the non-vascular ED group, the patients with an erection duration time ≥15 minutes were allocated to the persistent erection group, and those with an erection duration time <15 minutes were allocated to the non-persistent erection group. The data of each group were standardized and statistically analyzed based on the age gradient.

All the data were statistically analyzed using SPSS 22.0 software (IBM). The quantitative data are expressed as the mean ± standard deviation. The independent sample t-test was used to compare two groups of quantitative data. The Pearson correlation test was used to evaluate the associations between the hemodynamic parameters and age. A P value <0.05 was considered statistically significant.

Results

A total of 9,109 Chinese adult male ED patients were included in this study. The patients had an average age of 34.6 years (range, 18–90 years). Of the patients, 8,890 with normal bilateral cavernous artery anatomy and detectable blood flow signals were included in the study. These patients were divided into six age groups (<30, 30–39, 40–49, 50–59, 60–69, and ≥70 years), and the summary statistics for PSV, EDV, and the RI of each age group are presented in Table 1. Notably, the average PSV values of the non-vascular ED (persistent erection), arterial ED, and venous ED groups were 59.23±17.89, 22.52±5.77, and 43.72±9.08 cm/s, respectively, while the average EDV values of these groups were −4.13±4.25, 3.80±3.39, and 8.05±4.07 cm/s, respectively.

The correlation analysis between the hemodynamic parameters and age showed that PSV was negatively correlated with age, while EDV was positively correlated with age in both the arterial ED group and the venous ED group (Table 2).

A total of 200 cases were identified in which only one corpus cavernosum had a main cavernous artery trunk, while the other side had a main communicating branch trunk. The corresponding test data are shown in Table 3. The rest of 19 patients remained in a state of persistent rigid erection, with the unilateral or bilateral cavernous arteries showing no detectable blood flow signals. Detailed test parameters are provided in Table 4. Notably, five patients had no detectable blood flow signals on either side, seven patients exhibited weak blood flow signals bilaterally (PSV range, 0–35 cm/s), and seven patients showed normal blood flow signals on only one side of the cavernous artery (PSV ≥35 cm/s). Figure 1 shows various CDU spectrograms after ICI.

Figure 1 CDU spectrogram after ICI. (A,B) Non-vascular ED: (A) left cavernous artery (green arrow): PSV 73.12 cm/s, EDV −11.38 cm/s, RI 1.16; tunica albuginea of the septum (white arrow, same below); (B) left cavernous artery (green arrow): PSV 54.99 cm/s, EDV 0 cm/s, RI 1.0. (C) Arterial ED: left cavernous artery (green arrow): PSV 24.42 cm/s, EDV 0 cm/s, RI 1.0. (D) Venous ED: left cavernous artery (green arrow): PSV 43.11 cm/s, EDV 11.46 cm/s, RI 0.73. (E,F) Communicating branch: (E) the right cavernous artery is the main vessel (yellow arrow), and the left is the communicating branch (green arrow); (F) the left cavernous artery is the main vessel (green arrow), and the right is the communicating branch (yellow arrow). (G) Persistent rigid erection: left (green arrow) and right (yellow arrow) cavernous artery vessels were clearly visible, but no blood flow signal was detected. CDU, color Doppler ultrasound; ED, erectile dysfunction; EDV, end diastolic velocity; ICI, intracavernosal injection; PSV, peak systolic velocity; RI, resistance index.

Discussion

This study analyzed a large institutional database, comprising more than 9,000 ED patients, which represents the largest sample size examined in published research worldwide to date. The statistical analysis revealed that the CDU parameters were correlated with age across different subtypes of ED patients. Further, the communicating branches between the bilateral cavernous arteries and persistent rigid erection were found to significantly affect the examination results.

ICI is commonly used for the diagnosis and treatment of ED (17-20). The latest guidelines of the Italian Society of Andrology and Sexual Medicine recommend ICI combined with CDU examinations for all patients who present complaining of ED (21). In this study, young men aged under 40 years comprised a higher proportion of the study cohort (Table 1). This may be related to the greater willingness of younger men to seek medical consultation; aged men with ED may be less willing to seek medical help due to the influence of traditional Chinese beliefs. Notably, the study population only comprised ED patients who underwent this specific examination, and thus does not fully reflect the distribution of ED in the general population.

The study found that the mean PSV for the non-vascular ED patients who maintained an erection after ICI was 59.23±17.89 cm/s (Table 1 and Figure 1A,1B), and that PSV showed a negative correlation with age (Table 2). These findings are similar to those of a study conducted in 2020 involving 259 patients (13). However, there may be significant differences between the results of this study and those of Xuan et al. (14), who reported a mean PSV of 38.47±8.54 cm/s for patients with an EHS of grade 4. This might be related to differences in the detected regions of the penis and the Doppler angles used during the examination. The PSV magnitude may be related to the detection site, with blood flow varying at the head, middle, and base of the penis. The closer to the base, the higher the value (22-24). A recent review provided a detailed explanation, illustrated with diagrams, as to why changes in Doppler angles significantly affect CDU detection results (9). In the future, it is likely that more professional urologists and andrologists will conduct CDU examinations, and thus the results will be more reliable, which will also facilitate the standardization of CDU examination parameters.

Currently, a PSV >35 cm/s is considered normal, while a PSV of 25–35 cm/s may indicate moderate-to-mean arterial damage, and a PSV <25 cm/s may indicate severe arterial lesions (25). However, in the current study, a PSV cut-off <35 cm/s was used to diagnose arterial ED and an EDV cut-off >5 cm/s was used to diagnose venous ED based on the advice of other researchers (Table 1 and Figure 1C,1D) (26).

Anatomical variations need to be considered because they may result in PSV <35 cm/s, an effect which is especially evident when communicating branches are present (Table 3). While some studies have reported that the proportion of functional communicating arteries may reach 35% (27), this study did not focus on all types of communicating branches. Notably, mutual communication between bilateral cavernous arteries, as well as communication between dorsal and cavernous arteries, is often observed in some patients, especially if the penis is not fully erect, as the tunica albuginea cannot fully relax to compress the small arteries. However, as long as the bilateral cavernous arteries were clearly visible and the corresponding blood flow could be normally detected, we did not specifically examine their communication.

Because the erection of the penis ultimately depends on the complete filling of the two corpora cavernosa, the cavernous arteries remain the most important terminal functional vessels for penile erection. We only explored possible communicating branches and used the relatively higher flow velocity of the branches as the blood flow of the cavernous artery on that side when the main trunk of the cavernous artery on one side could not be clearly observed (Table 3, and Figure 1E,1F).

This study separately analyzed cases with only one main cavernous artery on one side, and found that the average PSV of the main cavernous artery in cases with an EHS ≥3 exceeded 70 cm/s (Table 3), which was significantly higher than the PSV of the cavernous artery in cases with normal cavernous vascular anatomy (the comparative results are not provided in this article). Of these 154 patients with an EHS ≥3, the left cavernous artery was the main trunk in 77 patients and the right cavernous artery was the main trunk in 77 patients. Thus, no left-right preference was found in relation to vascular anatomical variations. There was no statistically significant difference in the PSV between the left and right main arteries in both groups with an EHS ≥3 and an EHS <3, but the PSV of the main trunk of the cavernous arteries was about twice that of the communicating branch arteries in these two groups.

Additionally, the blood flow analysis of the communicating branches in both groups showed that the flow on the left side was better than that on the right side (Table 3). This was mainly due to the fact that the operator was positioned on the right side of the patient, and the probe was placed on the lower middle part of the patient’s penis on the left side for detection. If a communicating branch was encountered that passed through the tunica albuginea of the septum toward the left side (Figure 1E), the detection procedure did not different from that employed for a patient with normal vascular anatomy; the operator simply adjusted the Doppler angle so that the angle correction line was parallel to the blood vessel. Conversely, if a communicating branch passed through the tunica albuginea of the septum toward the right side, to ensure that the angle correction line was parallel to the measured blood vessel, the Doppler angle usually had to be greater than 60°, which might have led to biased results (Figure 1F). To avoid a Doppler angle greater than 60°, the probe needs to be placed on the lower middle part of the patient’s penis on the right side for detection, which can make the operator’s posture uncomfortable and may also lead to errors in results.

Clinically, the question of whether to intervene in patients with such large differences in bilateral blood flow requires comprehensive judgment based on doctors’ experience and patients’ condition. Some scholars believe that a difference of >10 cm/s in bilateral PSV may indicate vascular disease (9,28), while others suggest doctors should pay more attention to the vessel with poorer blood supply among the two cavernous arteries (29). Conversely, other researchers use the sum of bilateral blood flow values as a basis for determining whether blood supply is normal (30).

An abnormal PSV should not be considered an absolute indicator of systemic vascular disease (31). Currently, most clinical urologists primarily focus on whether the blood vessels of the penis itself affect erectile function. Phosphodiesterase type 5 (PDE5) inhibitors are generally the first-line treatment when the bilateral PSV is ≥35 cm/s, indicating normal cavernous vasodilation function; however, this approach overlooks cases in which the difference in bilateral PSV is >10 cm/s. Further screening of patients with an EHS ≥3 after ICI, who show normal blood supply in one cavernous artery but insufficient blood supply in the contralateral side, indicating morphological alterations, may be helpful for the early detection and management of cardiovascular diseases (12). As ED treatment technologies continue to advance, more personalized and precise treatment methods will gradually be employed (32). The existence of communicating branches represents a potential target of ED treatment.

As the penis transitions from flaccid to fully erect, the blood flow in the cavernous arteries undergoes dynamic changes, and the blood flow detection results vary with different phases of erection (33). The detection results obtained during the full erection phase are generally considered relatively objective and accurate. However, some patients may achieve rapid and complete erection, reaching the phase of rigid erection within a short period. At this point, as the internal pressure in the cavernosum exceeds blood pressure, the blood flow in the cavernous arteries may decrease or even cease (33). The PSV detected in this moment may be <35 cm/s or difficult to detect (Table 4 and Figure 1G). At this point, by distracting the patient’s attention or extending the detection time, normal blood flow values can often be detected when the penis is slightly flaccid.

For patients with persistent rigid erection in whom no obvious blood flow signals are detected, an accurate description should be provided, and further diagnosis and treatment can proceed based on a diagnosis of non-vascular ED. For patients who can maintain a rigid erectile state for a long time after ICI, CDU results are not necessary for further clinical diagnosis and treatment (34). We intend to conduct further research in this area in the future. In such cases, the prevention of possible priapism is more important than blindly focusing on CDU results. For clinicians, the clinical significance does not differ when PSV and EDV fall within the normal ranges, regardless of whether PSV is 40 or 100 cm/s, and whether EDV is −1 or −10 cm/s. Consequently, the next steps in diagnosis and treatment do not vary based on the values. However, normal CDU results are meaningful for both clinicians and patients, as they provide a basis for shared clinical decision making. This information is also useful in cases in which psychogenic ED is suspected, as normal results can alleviate patient anxiety (20).

This study had some limitations. First, this was a retrospective study and the patients were not screened. The duration of illness, medication use, diabetes, cardiovascular disease, and curvature are all unknown. Second, we analyzed the CDU results of patients after their first ICI test, without considering any dose-dependent effects (35) and the influence of psychological factors such as tension, fear, and anxiety during the first examination. Increasing the dose and using phentolamine in combination may improve the examination results for some patients. Third, since we did not conduct continuous testing within the 30-minute timeframe, the data obtained may not represent the optimal results for the patients. We intend to address these issues in future research. Fourth, this was a single-center study with all examinations performed by the same andrologist, which might have introduced potential bias. Finally, while the sample size was large, the study lacked data from healthy volunteers for comparison and was limited to Chinese men.

Conclusions

The CDU parameters were correlated with age. The PSV and EDV of non-vascular ED provide valuable reference data for normal adult males across different age groups. The communicating branches between bilateral cavernous arteries and persistent rigid erection significantly affected the CDU results. The presence of compensatory effects in the bilateral cavernous arteries of the penis suggests that further research needs to be conducted to determine whether differentiated and targeted treatment is necessary when the overall blood supply to the cavernosum is normal. For ED patients with persistent rigid erection, the focus should not be on the CDU results but on erection hardness and duration.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-650/rc

Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-650/dss

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-650/prf

Funding: This study was supported by the grants of Nanjing Medical Technology Development Project (No. YKK23071), and Clinical Trials from the Affiliated Drum Tower Hospital, Medical School of Nanjing University (No. 2023-LCYJ-PY-41).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-650/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Institutional Review Board of Nanjing Drum Tower Hospital (No. 2025-0297-01), and written informed consent was obtained from all patients before the examination.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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(English Language Editor: L. Huleatt)