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Relationship between erectile function and sexual self-confidence: a path analytic model in men being treated with tadalafil

Abstract

Sexual self-confidence has been shown to be associated with erectile function (EF) in men receiving PDE-5 inhibitor therapy; however, few studies have investigated the pathways (for example, sexual satisfaction, communication, time concerns and spontaneity) through which improvements in sexual self-confidence occur. This study examined this relationship using a path analysis model in men with ED enrolled in an open-label clinical trial of 20 mg tadalafil, administered on-demand over 12 weeks. International Index of Erectile Function and Psychological and Interpersonal Relationship Scales data were used to assess improvement in EF, sexual confidence and mediating variables. Controlling for baseline measures and covariates, the model indicated that change in sexual self-confidence was significantly associated with changes in EF (P<0.0001), sexual communication conflict (P=0.01), time concerns (P<0.0001) and spontaneity (P<0.0001). The total effect of EF on sexual self-confidence was 0.85, with 0.08 of this relationship indirectly mediated through time concerns and spontaneity. These data suggest that improved sexual confidence in men receiving treatment with a long-acting PDE-5 inhibitor occurs both directly via improved EF and indirectly via improved spontaneity and diminished time concerns.

Introduction

ED is a complex and multidimensional condition, associated with psychological and relationship concerns, including decreased quality of life, self-esteem, and an increased incidence of depression and interpersonal relationship problems.1, 2, 3 ED is defined as the persistent inability to achieve or maintain an erection sufficient enough for satisfactory sexual performance.4 Approved PDE-5 inhibitors have an established efficacy and safety profile.5 However, the multifactorial nature of ED suggests that effective treatment of impaired erectile function (EF) may have benefits that extend beyond improved ability for sexual performance. Previous research indicates that EF improvements in men on PDE-5 inhibitors are associated with improved psychosocial outcomes, including sexual confidence, sexual relationship, depression and quality of life.6, 7, 8, 9, 10, 11, 12

The relationship between the physiological (that is, erection hardness and maintenance) and various psychosocial (for example, self-esteem, sexual self-confidence and relationships) aspects of ED and its treatment have been studied using statistical modeling of validated patient-reported outcome measures. A cognitive-emotional model for ED was developed and tested with path analysis by Nobre13, supporting the role of psychosocial factors on predisposition and maintenance of ED. Earlier psychosocial ED paradigms emphasized the role of performance anxiety, an inhibitory mechanism, in the development and maintenance of sexual dysfunction.14, 15 However, Althof et al.16 demonstrated that performance anxiety is ameliorated by improved sexual confidence, an excitatory mechanism, in men with ED treated with sildenafil. Their model suggested that sexual confidence might be the main psychosocial driver in ED treatment. In this study, improved sexual confidence was mediated mainly by improvements in erection hardness and maintenance, although other mediating variables were not tested.16 The mechanisms involved, and the role of specific mediating variables, which may underlie improvements in sexual self-confidence with PDE-5 inhibitor treatment, remain unclear.

The purpose of the current analysis was to explore the links between improved sexual self-confidence and EF through analyses of efficacy outcomes including sexual satisfaction, sexual relationship satisfaction, sexual communication conflict, time concerns and spontaneity. This was achieved by developing a conceptual model of the causal relation among these variables and subsequently testing the strength of this model using path analytical procedures. This analysis builds directly on work by Althof and on a similar investigation examining pathways linking EF with overall quality of life.16; 17

Materials and methods

Study design

This was a retrospective analysis of a multicenter open-label study designed to evaluate the efficacy and safety of tadalafil for the treatment of ED over 12 weeks, on an as-needed basis.18 Following a 4-week run-in phase with no ED treatment, subjects entered a 12-week treatment period of on-demand dosing of 20 mg tadalafil. Institutional review boards at each center reviewed and approved the protocol, and all men gave written informed consent.

Study subjects

This study enrolled 1911 patients with ED into eight predefined groups based on demographic characteristics and comorbidities (Hispanic, African American, Caucasian, depressed, diabetes, over 65 years old, with spinal cord injury and other). Eligibility criteria have been previously described.18 In brief, eligible subjects were 18 years of age with a self-reported minimum of 3 months with ED. Subjects were excluded if they met any of the following criteria: use of nitrates or cancer chemotherapy, unstable cardiovascular disease, recent history of stroke, or failure to achieve any erection following radical prostatectomy or pelvic surgery. Subjects were required to report on sexual attempts with the same adult female partner.

Definitions of predictor, mediating and outcome variables

Predictor, mediating and outcome variables were constructed from items in the International Index of Erectile Function (IIEF)19 and the Psychological and Interpersonal Relationship Scales (PAIRS),20 which were administered at baseline and the 12-week study end point (Table 1). The IIEF consists of 15 questions that assess EF, intercourse satisfaction, overall satisfaction, orgasmic function and sexual desire. PAIRS is a self-administered questionnaire that assesses broader psychosocial outcomes (sexual self-confidence, time concerns and spontaneity) associated with the treatment of ED.20, 21, 22 A hypothetical model comprised of predictor, mediating and outcome variables was constructed as described in Table 1. These latent variables correspond to the underlying factors or constructs of observed variables and were used to model the relationship between these theoretical constructs using a structural equation modeling approach as described below.23, 24 We hypothesized that improved sexual satisfaction, sexual relationship satisfaction, sexual communication conflict, spontaneity and reduced time concerns will mediate the association between changes in EF and changes in sexual self-confidence.

Table 1 Predictor, mediating and outcome variables in hypothesized model

Statistical analyses

The study population was split 75:25, in which 75% of the sample (the development sample) was used to develop the path model (n=1433) and 25% of the sample (validation sample) was used to validate the model (n=478). Statistical analyses were carried out in a series of stages. First, difference scores (week 12–week 0) were calculated for predictor (EF), mediating (sexual relationship satisfaction and sexual satisfaction), and outcome (sexual self-confidence) variables. End point values were used for sexual communication conflict and time concerns, as these items assume that subjects are on medication. These scores were used to create latent variables (via factor analysis) for inclusion in the path model.

Several covariates, including age, ED severity, previous use of PDE-5 inhibitors, comorbidity, smoking history (yes/no), alcohol use (14 units per week), concomitant medications, ED etiology (psychogenic, organic and mixed), and baseline values to the outcome, predictors and mediating variables measured as deltas (sexual relationship satisfaction, sexual satisfaction and spontaneity items) were considered in this analysis. A series of linear regressions were performed to reduce this list of covariates before building the path model. Covariates not associated with at least one measure in the model were excluded. Five covariates were considered for path analyses (P<0.05 in three or more outcomes): baseline value, age, ED severity, concomitant medications and diabetes.

The full path model (Figure 1) was developed using MPLUS software (version 4.21), Los Angeles, CA, USA, and contains all paths from the predictors and mediating variables to sexual self-confidence. The full model also includes all paths from the final list of covariates to the latent variables. Model fit indices were assessed in the latent variables construction, as well as in the full path model, using common cutoffs to assess model fit (comparative fit index>0.90 and root mean square error<0.05). Finally, the full path model as constructed using the development sample was assessed in the validation sample.

Figure 1
figure1

Conceptual model linking improvements in erectile function with sexual self-confidence. Squares represent observed measures and circles represent latent variables. Arrows indicate regression coefficients (β) for paths. Regression coefficients are shown for latent variables. A positive coefficient indicates that an improvement on one measure is associated with an improvement on another measure. Significant regression (P0.05) are denoted by an *. Regression coefficients for the development sample are shown in black and coefficients for the validation sample are shown in gray. Correlations between the covariates are estimated in the model but are not presented. Separate pathways (shown in gray) are fit for age, ED severity, concomitant medications, diabetes, and baseline erectile function to sexual relationship satisfaction, sexual satisfaction, sexual communication conflict, time concerns, spontaneity, and sexual self-confidence. Beta estimates for covariate pathways are reported elsewhere.

Results

Characteristics of the development and validation samples

Patient demographic and baseline clinical characteristics of the entire sample are presented in previous reports.18 The characteristics of the development (N=1433) and validation (N=478) samples are shown in Table 2. Overall, characteristics were comparable between the two samples.

Table 2 Characteristics of the development and validation samples

Latent variable correlations

Latent variables were first created using the items as specified in Table 1. Items that were found to correlate with other latent variables were allowed to load on multiple factors. Specifically, IIEF question (Q)15 ‘Over the past four weeks, how do you rate your confidence that you can get and keep your erection?’ was allowed to load on both sexual self-confidence and EF domains. There are two items that were deleted because of inadequate variable loadings (<0.40): IIEF Q6 in the sexual satisfaction latent variable and PAIRS Q6 in the time concerns domain. Items from the time concerns and spontaneity domains did not cluster together. When the items were restricted to one latent factor, the items had low loadings (<0.40). The loadings increased when two factors were specified instead of one (analyses not shown); therefore, these two domains were analyzed separately in the path model. In addition, the single item in the sexual relationship satisfaction domain (IIEF Q14) was found to correlate with the items from the sexual satisfaction domain (IIEF Q6, Q7 and Q8). We therefore combined these items to create a single sexual satisfaction latent variable. IIEF item Q13 ‘Over the past 4 weeks, how satisfied have you been with your overall sex life?’ was found to correlate highly with IIEF item 14 ‘Over the past 4 weeks, how satisfied have you been with your sexual relationship with your partner?’ and was deleted from the sexual satisfaction latent variable. PAIRS Q8 ‘My partner sometimes feels some pressure to have sex with me’ was highly correlated with the items in the sexual communication conflict domain, and therefore was removed from the time concerns latent variable and added to the set of items in the sexual communication conflict latent variable. IIEF Q1 and IIEF Q2 were found to correlate highly with IIEF Q15 and showed co-linearity with one another, and as a result, were deleted from the EF domain. Correlations among the latent variables for the development and validation samples are shown in Table 3. The model with the new construction of latent variables has a good model fit based on comparative fit index=0.934 and root mean square error=0.0437. See Table 4 for a comparison of fit and factor loadings in the hypothesized and final models (both of these models were run on the development data set). The magnitude of correlations among the main variables of interest in the development and validation samples was similar and the correlations among the main variables of interest were notably high. Sexual communication conflict was poorly correlated (r<0.10) with both changes in EF and changes in sexual satisfaction.

Table 3 Correlations among latent variables in both development (N=1279) and validation (N=421) samples
Table 4 Path analysis model: the effect of erectile function on sexual self-confidence

Final path model

The final path model (Figure 1) includes baseline value, age, ED severity, concomitant medications, and diabetes as covariates, and sexual self-confidence, EF, sexual communication conflict, sexual satisfaction, time concerns and spontaneity as latent variables. Latent variables measuring change (EF, sexual satisfaction, spontaneity and sexual self-confidence) were significantly predicted by their baseline values. The negative regression coefficients indicate that subjects who scored low on these domains at baseline were more likely to show improvement in these outcomes. The main outcome variable, change in sexual self-confidence, was significantly associated with changes in EF (P<0.0001), sexual communication conflict (P=0.01), time concerns (P<0.0001) and changes in spontaneity (P<0.0001; Table 4). Subjects who scored higher on these domains were more likely to have increased sexual self-confidence. Conversely, the association between sexual communication conflict and sexual self-confidence was negative (P=0.01) in the development sample, suggesting that subjects who performed worse on communication were more likely to have higher sexual self-confidence. The negative association in the validation sample was marginally significant (regression coefficient=–0.12, P=0.06).

Improved EF was a significant predictor of sexual self-confidence both directly (P<0.0001) with an effect of 0.77 and indirectly through sexual communication conflict (P=0.02), time concerns (P<0.0001) and spontaneity (P<0.0001) paths, with total indirect effect of 0.08. In addition, improved EF was also directly associated with improved sexual satisfaction, better sexual communication conflict, reduced time concerns and improved spontaneity (all P<0.0001).

Baseline EF was significantly associated with all latent variables except for spontaneity, whereas the other covariates did not show a significant association with sexual satisfaction, sexual communication conflict, time concerns, spontaneity and sexual self-confidence. Age and diabetes were significantly associated with EF, indicating that men without diabetes and younger men were more likely to have increased EF.

Validation of the path model

The path model in the validation sample had adequate model fit. EF remained a significant predictor of sexual self-confidence directly (P<0.0001). With the exception of sexual communication, its indirect association with sexual self-confidence remained significant. The percentage of variance explained in sexual self-confidence in the validation model was comparable to the development model (R2=0.89).

Discussion

Treatment of ED in men affects both the physiological and psychosocial components of sexual function, including emotional and sexual intimacy in the couple and sexual self-confidence in the male. This retrospective study used path analysis to examine the pathways through which improvements in EF resulting from PDE-5 inhibitor treatment influence sexual self-confidence. Our model demonstrated that improved EF accounted for the majority (77%) of the downstream effect of improved sexual self-confidence. The path model constructed in this study also considered the roles of various other efficacy measures, including sexual satisfaction and sexual relationship satisfaction, sexual communication conflict, time concerns and spontaneity. This approach allowed identification and quantification of the pathways through which PDE-5 inhibitor treatment might have distal influences on other variables that may affect sexual self-confidence, the most important of which were determined to be time concerns and spontaneity.

The association of the physiological and psychosocial aspects of the treatment of ED was previously investigated by Althof et al.16 using statistical mediation modeling, a quantitative method similar to the path analytic approach described in this report. Their model estimated that erection hardness and erection maintenance accounted for approximately two-thirds of the treatment effect of sildenafil on sexual confidence. However, the purpose of the Althof study was to determine the contributions of improved EF on several different psychosocial end points rather than to understand the role of mediating variables on improved sexual self-confidence. Nonetheless, the Althof study demonstrates that improvements in EF alone do not account for all changes in sexual self-confidence. The findings of our study are consistent with those of Althof et al. and further add to the understanding of psychosocial elements of ED and its treatment.

These results highlight the potential benefits of long-acting PDE-5 inhibitors in improved sexual confidence in men with ED via both the direct effects of treatment in improved EF and the indirect effects on sexual spontaneity and lower time concerns. In a randomized cross-over trial comparing tadalafil once daily, tadalafil on demand, and sildenafil on demand, time concerns and spontaneity were improved for both tadalafil groups but not for sildenafil. All three groups had significant improvements in sexual self-confidence, but improvements were greater for both tadalafil groups as compared with sildenafil.25 Similar results were observed in an earlier randomized cross-over trial comparing sildenafil on demand and tadalafil on demand in which improvements in EF were similar for the two treatment arms,26 but tadalafil was associated with better improvements in sexual self-confidence, time concerns and spontaneity as compared with sildenafil.27 These results are consistent with the findings from our analysis, demonstrating that, while improved EF is the major driver for improved sexual self-confidence, additional gains in self-confidence may be obtained via improvements in time concerns and spontaneity associated with long-acting PDE-5 inhibitor treatment. As such, the current analysis has important implications for clinicians involved in the day-to-day management of ED. The use of long-acting PDE-5 inhibitors such as tadalafil may have particular benefits in improving patients’ self-confidence in their ability to perform sexually via the direct effect of the drug on improved EF, but also by indirect effects on other factors such as decreased time demands and increased spontaneity. With this new information in mind, clinicians may wish to encourage their patients with ED being treated with long-acting PDE-5 inhibitors to make use of their improved EF to be more sexually spontaneous and to initiate sexual activity more freely with their partner. By doing so, patients with ED are likely to increase their sexual confidence which, in turn, is likely to lead to more frequent sexual activity, further benefits in EF, and additional gains in sexual confidence. This clinically important ‘positive feedback cycle’ may yield further benefits for these patients in reinforcing and maintaining their improved sexual performance and more frequent and satisfying sexual activity with their partner.

There are several potential limitations to this study. First, the cross-sectional modeling strategy limits the ability to establish cause and effect; however, this analysis is still capable of providing estimates of both direct and indirect influences of improvements in EF on changes in sexual self-confidence. These estimates support the role of these variables in mediating positive changes in sexual confidence in patients with ED using long-acting PDE-5 inhibitors. In addition, the mediating variables and covariates in this study are limited by the measures included in the study design and represent only some of the factors involved in sexual self-confidence. Second, the negative association between sexual communication conflict and sexual self-confidence is inconsistent with previous research and does not comport with theory. When assessed alone, sexual communication conflict is positively correlated with sexual self-confidence (r=0.31); however, in the presence of time concerns, this association becomes negative. It is possible that the reverse in direction is the result of time concerns and sexual communication conflict being correlated (r=0.72); however, this finding requires further investigation and/or replication. Finally, the nature of this study required a large number of statistical tests, potentially resulting in a higher type 1 error rate. However, applying the path model to the validation sample indicated good fit and generally consistent results, which provide assurance against this potential.

In conclusion, our findings provide support for the hypotheses that important pathways by which improved EF influences sexual self-confidence are via time concerns and spontaneity. These results also point to important potential benefits of long-acting PDE-5 inhibitors in improving sexual self-confidence both directly through improved EF and indirectly through improved spontaneity and diminished time concerns. For clinicians, these findings may have implications for therapy selection wherein long-acting therapy or daily dose treatment may offer additional benefits, particularly for those patients who exhibit decreased sexual confidence.

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Acknowledgements

We acknowledge New England Research Institutes employees May Yang, MPH and Heather Litman, PhD for statistical analysis and interpretation and Andre Araujo, PhD for scientific consultation on the statistical analysis plan and data interpretation. We also acknowledge Stephanie Brillhart of PharmaNet/i3 for writing and editorial support for the manuscript. This study was sponsored by Eli Lilly.

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Correspondence to A Sontag.

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Dr Sontag is an employee of and stockholder in Eli Lilly. Dr Ni is an employee of and stockholder in Eli Lilly. Dr Althof has consulted for Abbott, Bayer, Eli Lilly, Palitan Pharmaceuticals and Promenescent. Dr Rosen has consulted for Auxilium, Bayer Healthcare, Eli Lilly and Palatin Pharmaceuticals.

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Sontag, A., Ni, X., Althof, S. et al. Relationship between erectile function and sexual self-confidence: a path analytic model in men being treated with tadalafil. Int J Impot Res 26, 7–12 (2014). https://doi.org/10.1038/ijir.2013.31

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Keywords

  • ED
  • path analytic model
  • PDE-5 inhibitor
  • sexual self-confidence
  • tadalafil

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