Thanks Stuart - we need more studies of fistulas and how to best use them.
My specific concern is about people cutting their blood pump speeds for the sake of cutting their blood pump speeds. I did it myself incenter in 1996 (and lengthened my time) but without data and in the absence of a wide spread increase in stenosis among people using SHHD with a high Qb, I just can't say lowering the pump speed is, in itself, a good idea.
It is hard to parse out the effects of Qb considering the large impact on the circulatory system of just having a fistula in the first place and the effect of regular cannulation. The question seems to be does high Qb increase the incidence of stenosis. This NDT article is fully available http://ndt.oxfordjournals.org/content/19/2/309.full , it discusses stenosis and puts the potential problem due to Qb in context
If it is true that 80% of stenoses occur at the anastomosis, and the remaining 20% are a mixed bag, that include stenoses resulting from the cannulation directly, I have to wonder how big a problem stenosis due to Qb could be. I haven't heard anything that amounts to an uptick in access interventions from people using NxStage with Qb=500. The only only uptick I've heard about is sepsis among people using buttonholes. This has been a relatively small sepsis increase in the nominal cases but it does suggest that any increase in stenoses would be reported.
The reason I am asking about blood flows, especially blood flows in terms of actual speed rather than volume, is to try to imagine the turbulence caused by the out flow of the venous needle. If the blood coming out of the needle is going slower than the blood in the fistula that would suggest to me that there would be less turbulance than if the venous outflow was faster than the fistula.
To me it is confusing to compare the fistula with the blood circuit in terms of ml/min. ml is a volume measure but when we talk about speed we normally put it in terms of distance. The fistula is much larger so if both the fistula and the blood circuit were said to have the same flow in ml/min it would mean the fistula flow speed, call it centimeters/second, would have to be much slower. It would be like comparing a garden hose and a stream- if they were going the same speed - cm/min - the stream's ml/min rate would be much greater than the hose's.
So I'm not sure this is true but in general my understanding is that blood exiting the needle at Qb=500 is entering the fistula at a slower speed: cm/min, than the natural fistula flow. Whether or not that is true would say a lot about the potential for turbulence damage, it seems to me. That's what I am hoping to clarify.
It would be nice to hear from others who read this board and have some insight on what the data shows and what data we need to develop. I've participated in email exchanges about this and had useful discussions ... hopefully some of that can move to the forum.