Self Adjusting Venous Equalizing Graft for Hemodialysis
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Solution Overview
Problem
Current venous grafts for hemodialysis have poor patency rates due to unnatural flow dynamics, leading to scarring and reduced lifespan, and often cause 'stealing' of blood flow, compromising circulation and increasing healthcare costs.
Innovation Solution
A self-adjusting venous equalizing graft (SAVE graft) with a self-regulating stenosis that creates increased pressure at the inflow end and decreased pressure at the outflow end, mimicking natural venous pressure, preventing scarring and reducing blood flow 'stealing', and automatically adjusts based on venous and arterial blood pressures without operator intervention.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a conventional venous graft is used to provide hemodialysis access, then large volume blood flow is achieved, but the graft has poor patency rates due to unnatural flow dynamics causing scarring
Solution Approach 1:
The graft incorporates a stenotic segment with a specific diameter (0.5-1.5 cm) that creates localized high velocity flow and turbulence. This localized modification changes the flow dynamics only in the critical region where blood enters the graft, while the rest of the graft maintains normal flow characteristics. This local quality change prevents scarring and improves patency without compromising overall blood flow volume.
Solution Approach 2:
The invention changes the flow velocity parameter by introducing a stenotic segment. The reduced diameter of the stenotic segment increases flow velocity and creates turbulence, which prevents blood stasis and scarring. This parameter change (velocity increase through diameter reduction) transforms the unnatural laminar flow into a more physiological turbulent flow pattern that maintains graft patency.
2Quantity of substance
If a conventional venous graft is used to provide hemodialysis access, then blood access is established, but blood flow is stolen from downstream body parts
Solution Approach 1:
The stenotic segment creates a localized region of high resistance to flow. This local quality change ensures that the majority of arterial blood flow continues downstream to supply the arm and hand, while only a controlled portion is diverted into the graft for dialysis. The stenosis acts as a flow regulator that prevents excessive blood stealing.
Solution Approach 2:
The stenotic segment provides partial action by allowing only a portion of the arterial blood flow to enter the graft, rather than allowing all blood to be shunted. This partial diversion maintains adequate flow for dialysis while preserving sufficient flow for downstream tissue perfusion, preventing the harmful effect of complete blood stealing.
3Ease of operation
If a conventional venous graft is used, then dialysis access is provided, but the vein scars and the graft lifespan is reduced
Solution Approach 1:
The stenotic segment changes the flow parameters (velocity, turbulence) to match more natural physiological conditions. This parameter change prevents the high pressure and stasis that cause venous scarring and graft failure, thereby extending the functional lifespan of the graft while maintaining dialysis access capability.
Solution Approach 2:
The stenotic segment creates a pressure gradient that provides feedback control of blood flow into the graft. The high velocity flow through the stenosis regulates the amount of blood entering the graft, preventing overload that would cause scarring. This self-regulating mechanism protects the vein and extends graft life.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The SAVE graft extends the life of the graft by preventing scarring, reducing venous pressure, and minimizing blood flow diversion, thereby improving hemodialysis efficiency and reducing the need for frequent access point creation, while maintaining optimal arterial pressure for dialysis.
Implementation Method 1
A collapsible portion of the conduit configured to provide a stenosis for the blood flow. The outflow pressure increasing relative to the reservoir pressure collapses the collapsible portion and the outflow pressure decreasing relative to the reservoir pressure returns the collapsible portion to a substantially uncollapsed state.
Data Source
AI summary
A self adjusting venous equalizing graft (SAVE graft) which provides a self regulating stenosis is provided herein. The SAVE graft responds to increases or decreases in blood pressure which allows a higher pressure at the graft's arterial end and a lower pressure at the graft's venous end. This is ideal in that it mimics the natural pressure of a patient's circulatory system. A dialysis machine may draw blood at the arterial end, dialyze the blood, and return the blood to the patient at the graft's venous end. The lower pressure at the venous end prevents damage to the patient's vein. The SAVE graft may comprise a deformable stenosis control diaphragm or a venous controlled pressure nozzle which may expand or contract in response to blood pressure to self regulate the stenosis provided by the SAVE graft.