[I]Dear David
My apologies for the lateness of this reply … i have had some family issues to deal with and my atention has been elsewhere.
I have replied to each question segment below …[/I]
Thank you for this John, I was actually familiar with your explanation to MikeB - and see nothing to argue with there. However it is the possible cardiovascular impact of pump speed that has raised my interest and the fact that the dialysis m/c pump of whatever manufacturer is inevitably out of synch with the heart.
True … and I do not know of any studies - recent or old - that specifically test this hypothesis. However, most current systems use effectively continuous flow … I know the pumps are peristaltic but the roller distribution makes it near as continuous … And as most AVF access is peripheral, and in a relatively isolated distal circulation, I am not sure that the counter-pressure effects would be significant. Not a very good answer, I fear, but maybe the best I can give.
This can be seen with NxStage as the digital readout with that machine has less damping than the conventional analogue instrumentation and so shows a range of pressures at each reading of venous and arterial pressure - these revolve at about 30sec intervals.
Also true, but, again, i suspect (but don’t know) that the summation effect on the circulation and the heart are ( likely) small in totality … And the effects of short, hard, volume altering dialysis on myocardial perfusion and contractility (myocardial stun) are proportionately far greater and of much greater potential harm. I hear what you say, agree there must ba ‘an effect’ but suspect the effect is small.
It seems to me that the dialysis machine peristaltic pump design as commonly used throughout all manufactures is inherently not favorable to the human heart and should be assessed and an alternative found.
As above … though most newer designs that I am aware of and that are in the development pipeline are going down the hydraulically-driven, dual-chamber, diaphragm-dependent, vacuum pump design pathway.
The advantage with the peristaltic pump is of course that it does not come into contact with the patients blood.
Nor does the vacuum pump system.
The alternatives are either positive displacement diaphragm pump - this still having pulsations that are out of synch with the heart but they would be smaller and more frequent pulses.
tThank you for this John, I was actually familiar with your explanation to MikeB - and see nothing to argue with there. However it is the possible cardiovascular impact of pump speed that has raised my interest and the fact that the dialysis m/c pump of whatever manufacturer is inevitably out of synch with the heart.
True … and I do not know of any studies - recent or old - that specifically test this hypothesis. However, most current systems use effectively continuous flow … I know the pumps are peristaltic but the roller distribution makes it near as continuous … And as most AVF access is peripheral, and in a relatively isolated distal circulation, I am not sure that the counter-pressure effects would be significant. Not a very good answer, I fear, but maybe the best I can give.
This can be seen with NxStage as the digital readout with that machine has less damping than the conventional analogue instrumentation and so shows a range of pressures at each reading of venous and arterial pressure - these revolve at about 30sec intervals.
Also true, but, again, i suspect (but don’t know) that the summation effect on the circulation and the heart are ( likely) small in totality … And the effects of short, hard, volume altering dialysis on myocardial perfusion and contractility (myocardial stun) are proportionately far greater and of much greater potential harm. I hear what you say, agree there must ba ‘an effect’ but suspect the effect is small.
It seems to me that the dialysis machine peristaltic pump design as commonly used throughout all manufactures is inherently not favorable to the human heart and should be assessed and an alternative found.
As above … though most newer designs that I am aware of and that are in the development pipeline are going down the hydraulically-driven, dual-chamber, diaphragm-dependent, vacuum pump design pathway.
The advantage with the peristaltic pump is of course that it does not come into contact with the patients blood.
Nor does the vacuum pump system.
The alternatives are either positive displacement diaphragm pump - this still having pulsations that are out of synch with the heart but they would be smaller and more frequent pulses.
Again true … but to self-synch via ECG tracing may introduce a range of other issues that may prove worse, I suspect (or of greater threat) than does the problem trying to be solved.
Or a centrifugal pump which would give a constant pressure - the major disadvantage of either is probably that the impeller or diaphragm would need to be changed and throw away after each use; so cost and time implications are disadvantageous but I suggest they would be a safer application for the patient.
Red cell fragility might be an issue there too.
I think some manufacturer should research this.[I]
It is certainly well worth raising and discussing at a think-tank roundtable, I agree[/I].
Needle direction - i insert both arterial and venous needles in the same direction - point with natural flow - but turn the arterial needle so that the eye is towards the direction in which the blood is flowing from (black spot up red down). It seems that this reduces arterial suction pressure by about 5%[/I]
Or a centrifugal pump which would give a constant pressure - the major disadvantage of either is probably that the impeller or diaphragm would need to be changed and throw away after each use; so cost and time implications are disadvantageous but I suggest they would be a safer application for the patient.
Red cell fragility might be an issue there too.
I think some manufacturer should research this.
It is certainly well worth raising and discussing at a think-tank roundtable, I agree.
Needle direction - i insert both arterial and venous needles in the same direction - point with natural flow - but turn the arterial needle so that the eye is towards the direction in which the blood is flowing from (black spot up red down). It seems that this reduces arterial suction pressure by about 5%.
[I]I absolutely agree with you needle direction - of both needles - perhaps you have read my stuff on this at this site … though there are ‘flippers’ and ‘non-flippers’, and we are - in most patients - non-flippers.
However, that said, there are patients who do better flipped … so, I think it is ‘horses for courses’ there.[/I]
Sent from my Ipad en route to give a talk in Madrid!