Thanks for the in-depth reply. I mean it all sounds perfectly logical...I suppose my interest was the issue as to whether the 'in-rushed' blood that causes an erection becomes completely devoid of any circulatory mechanism and is essentially pooled then eventually oxygen depleted.
I've tried numerous dosing regimes but can't seem to find a 'sweet spot.' Either the Trimix dosage has no measurable effect or it results in the 3-4 hour erections. Been using it for about 3 years and haven't experienced any obvious deterous outcomes, but it's something I obviously would want to avoid.
Correct, that would be my concern, pooled blood eventually becoming deoxgenated. It could be that the sheer volume of blood which enters the penis during an erection, means that it will last longer in this regard. How long is the question. We know how important constant circulation is to all our tissues.
I am not sure how much "leakage" there may be when the penis is fully hard, that is some blood leaving and some entering, but I have read many times, when the penis is at the full erection stage; the bulbocavernosus and ischiocavernosus muscles contract at the base inside the body, almost creating a closed circuit. This is when the penis is at its most firm, I think we all know this feeling

. It must have to create this very effective "seal" in order to reach the pressures required to keep the penis fully rigid.
As I discuss, most guys will have periods of time during sex (depending on how long that sex or masturbation session is) when this intensity of erection changes, essentially allowing more blood to leave and fresh blood to enter.
When the pressure declines its obvious this is occurring.
It sounds like your erection is at this very hard stage for the full 3 plus hours?
Have you tried Bimix instead?
You could try talking to the guys at Frank talk, on the injection forum. They are very well versed in the use of these drugs. I have not taken the "plunge" with injections as yet, but I am getting close to trying and was considering Bimix first for the very reasons we have been discussing.
We have not evolved to have full erections that last for 3 hours normally. Doing this artificially is changing the function of one of our most sensitive organs. Suddenly changing the function of a an organ in this manner which has taken an enormity of time to evolve, is asking for trouble in my humble opinion.