What randomized controlled trials have compared specific VED pressures and session durations and reported both adherence and erectile function outcomes?
Executive summary
A systematic look at the literature finds no randomized controlled trial in humans that explicitly randomized patients to different vacuum erectile device (VED) negative pressures and different session durations while reporting both device adherence and validated erectile-function outcomes; systematic reviews that pooled VED trials note heterogeneous protocols and call for standardized RCTs [1] [2]. The only randomized experimental data that actually compared specific VED session durations (and reported physiologic and erectile outcomes) come from a controlled animal study in a rat cavernous‑nerve injury model, not from human RCTs [3].
1. The human randomized-trial landscape: lots of RCTs, but not the pressure-duration head‑to‑head the question seeks
Recent systematic and scoping reviews catalog VED trials after radical prostatectomy and in refractory ED and report that several randomized trials exist among the literature, but those trials used a wide range of schedules (daily vs intermittent, variable rehabilitation lengths) without standardized or clearly randomized comparisons of specific vacuum pressures and session durations tied to both adherence metrics and International Index of Erectile Function (IIEF) outcomes [4] [2]. The authors of a recent meta-analysis explicitly conclude VED appears effective as an adjunct but emphasize that future large randomized controlled trials with standardized objective measurements and longer follow‑up are needed—an implicit admission that the existing RCTs do not answer which pressure or session‑length regimen is optimal or how adherence interacts with efficacy [1] [2].
2. The one randomized experiment that did vary VED duration: an animal model, not human evidence
A randomized preclinical study in a bilateral cavernous nerve crush rat model compared multiple VED session durations (reported groups such as 2–3–2–3 min, 4–3–3 min, 5–5 min, and 10 min) and measured penile length, erectile function and tissue oxygenation, finding that prolongation of VED duration significantly decreased penile oxygen saturation and related oxygen metrics (P < 0.05) and influenced functional outcomes in that model [3]. That study demonstrates biologic plausibility that duration matters and that longer vacuum exposure may have adverse microvascular effects, but because it is an animal experiment its randomized comparisons cannot be taken as a direct clinical answer for humans [3].
3. What human trials typically report — and what they usually omit
Human trials cataloged in the scoping review and meta-analyses report a variety of endpoints—IIEF scores, intercourse success rate, patient satisfaction and adverse events like penile bruising—but most published trials adopted differing VED schedules (some daily, some several times per week) and mixed VED with other therapies; the reviews note inconsistent follow-up lengths and heterogeneity in protocol descriptions, and they do not identify trials that randomized participants specifically by vacuum pressure level or systematically recorded quantitative adherence alongside erectile-function outcomes for direct comparison [4] [1] [2]. Meta-analysts therefore could pool efficacy signals for “VED vs control” but were unable to extract a validated pressure-versus-duration dose–response or adherence‑adjusted effect estimate from randomized human data [1] [2].
4. Why this gap matters and what the literature signals about plausible harms and adherence issues
The heterogeneous human data plus the rat experiment together suggest two tensions: protocol intensity may influence both physiologic effect and tolerability, and side effects such as penile bruising—reported with notable pooled incidence in systematic reviews—could depress adherence, confounding efficacy measurement [1]. Systematic reviewers explicitly call for large RCTs with standardized objective measurements, longer follow-up, and presumably protocol arms that would let investigators test different negative pressures and session durations against adherence and IIEF outcomes—precisely the design the current evidence base lacks [1] [2].
5. Conclusion — a clear negative finding that directs next steps
No available human randomized controlled trial has directly compared specific VED negative‑pressure settings and precise session durations while reporting both adherence and validated erectile‑function outcomes; the only randomized comparisons of duration are in a rat model that found adverse oxygenation effects with longer sessions, and multiple systematic reviews confirm heterogeneity of human RCT protocols and call for standardized head‑to‑head trials to answer the exact question posed [3] [4] [1] [2].