Apparatus for monitoring an arteri-ovenous fistula

Abstract

A probe for monitoring blood flow in a surgically created arterio-venous fistula (AVF) comprises sensing means 12 located at a distal end of the device body 11 for placing on the skin of a patient abo

Description

[0002] End Stage Renal Disease (ESRD) is a major global health concern and, according to The Global Burden of Disease (GBD), is among the leading causes of mortality worldwide. Current global statistics estimate that 843 million individuals are affected by ESRD. Kidney transplantation is the only cure, but this treatment is not feasible for most cases. Therefore, Renal Replacement Therapy remains the only option for these individuals.

[0003] “Renal Replacement Therapy,” or “Haemodialysis” or “artificial kidney” is conducted using a machine in clinical settings. To initiate haemodialysis, access to circulation is mandatory, and a surgeon must create an arteriovenous fistula (AVF) or arteriovenous graft (AVG). This allows individuals to be connected to the machine for haemodialysis or renal replacement therapy

[0004] Since the introduction of the arteriovenous fistula in 1966 by James E. Cimino and Michael J. Brescia, AVFs or AVGs have become the preferred method for vascular access for haemodialysis due to their superior durability, affordability, and reliability.

[0005] An AVF or AVG is created by a qualified surgeon by joining a suitable vein that is part of that individual’s anatomy “Autogenous” or Autologous” which is referred to as “outflow” to the same individual’s suitable artery also refed to as “inflow”. In the absence of a suitable vein, a prosthetic graft or so called “Synthetic graft” “artificial graft” “bioprosthetic graft” “vascular graft” is used. The AVF must be created in a location that allows for easy and repeated needle access to a dialysis machine whilst sitting or lying on a bed without limitations.

[0006] The AVF or AVG must undergo a clinical process of "Maturation" or "Suitability" to be deemed appropriate for dialysis. According to international standards, the criteria for a such is a vein diameter of at least 6 mm and in case of a prosthetic material, a minimum of 6 mm, a blood flow rate of 500-600 mL / min with a length of at least 6-8 cm positioned 6 mm under the skin surface for easy cannulation. The process generally takes 6-8 weeks post-surgery.

[0007] Maturation is confirmed by clinical signs of a strong, palpable thrill and an audible bruit upon physical examination, complemented by duplex ultrasound sonography and in majority of units 1-2 successful cannulation. Upon such the AVF or AVG is considered to be “patent” also referred to as “primary patency”

[0008] Upon affirmation of maturation, the AVF or AVG requires connection to the haemodialysis machine through access via needles or cannulation. In this process, only the “outflow” (the vein or the graft) is subjected to needling or cannulation, and not the artery at any point for haemodialysis.

[0009] The current national and international techniques for cannulation are the “rope-ladder” and “buttonhole techniques” with their own advantages and disadvantages to connect these AVFs or AVGs to the haemodialysis machine. On average, each AVF or AVG is subjected to 4-hour dialysis sessions three times a week. This repeated needling or cannulation leads to complications of stenosis, thrombosis, and aneurysm formation, and apart from cannulation, neointimal hyperplasia remains the leading cause of stenosis due to turbulence flow which is the consequence of any AVF or AVG creation.

[0010] The current life expectancy of individuals with AVF or AVG is around 7-9 years. Given the significant psychological and physiological implications of AVF / AVG creation alongside logistics of attendance for dialysis, AVF patency remains vital. Data suggests that each AVF or AVG is subjected to 1.9 surgical interventions over a 2-years to maintain its patency for effective dialysis. These statistics are pertinent to the 20-60% of AVFs or AVGs that have successfully passed the maturation phase and are used for dialysis. The remaining undetected cohort often requires formation of a new AVF, effectively retracing the steps of the prior clinical journey.

[0011] The literature reveals a direct link between the failure of AVFs, frequent interventions (to ensure functionality or patency), increased hospital visits (including surveillance and dialysis sessions), failure of the dialysis procedure, and resorting to bridging modalities, all of which contribute to all cause mortality within the ESRD cohort. Furthermore, these outcomes are most prominently observed in patients from average to high socioeconomic states (SES).

[0012] The current modern monitoring techniques, such as Duplex ultrasound (DUS), Handheld Doppler, Computed Tomography Angiography (CTA) or venography (CTV), Magnetic Resonance Imaging (MRI), and histogram, are instrumental in detecting early signs of stenosis, thrombosis or failure. However, a significant challenge in any surveillance program is embedded in determining the ideal timing for surveillance, the intervals between them and those following each haemodialysis sessions

[0013] Therefore, the lack of an active and ongoing surveillance or monitoring device for the detection of adversities in AVFs and / or AVGs has become more apparent. Such innovation will reduce the psychological &physiological burdens associated with AVF failure thus enhancing the quality of life (QALY). This also leads to significant reduction cost implications associated with multiple surveillance programmes, availability of scares expertise and multiple visits to hospitals and dialysis units.

[0014] These prior art methods of determining arteriovenous fistula (AVF) maturation and measuring blood flow parameters are inefficient for the reasons disclosed above.

[0015] It is an aim of the present invention to overcome these problems and to provide apparatus for monitoring a surgically created arteriovenous fistula (AVF). Summary of the Invention

[0016] According to a first non-limiting embodiment of the present invention there is provided apparatus for monitoring a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis comprising: a body; and a controller; and at least one at least one sensing means on a distal end of the body for placing on the skin of a user above a venous or graft component of a surgically created arteriovenous fistula; and wherein the at least one sensing means collects data indicative of the presence of a pulse in the venous or graft component of a surgically created arteriovenous fistula.

[0017] This is advantageous because the use of a sensor to investigate the success or failure of a surgically created arteriovenous fistula (AVF) allows for the early detection of functional maturation, and thus early cannulation, will reduce the requirement for further expensive dialysis sessions than is required. A reduction in expensive ultrasound assessment of the fistula. A shorter follow up and reduction in resource management due to a reduction in the use of outpatient follow up and specialist sonographers. As such, it will allow for an increase in the availability of outpatient appointment services, thus offering an increase in efficiency and efficacy. It also offers early detection of failure / impairment of the AVF, thus offering early intervention and a potential limitation of emergency operating surgery. This will also offer cost reductions as it will potentially result in a reduction in the use of central venous access, infection rates associated with such lines, and a potential limited use of resources for their care. It will allow earlier creation of another AVF if required, potentially optimising the cost of dialysis substantially. The use of a sensor also allows patients to selfmonitor their surgically created AVF. Over time, this offers the potential optimisation of AVF care and reduction in use of haemodialysis appointments for incidental finding of malfunctioning AVF.

[0018] Further, one at least one sensing means may be configured so as to be suitable for placing on the skin of a user substantially 6mm or less above a venous or graft component of a surgically created arteriovenous fistula. Further still, the at least one sensing means may be configured so as to be suitable for placing on the skin of a user substantially 3cm or less downstream from a surgically created arteriovenous fistula above the venous or graft component. This is advantageous because in order to measure the success of a surgically created arteriovenous fistula (AVF), “thrill” must be measured a certain distance from the surgically created arteriovenous fistula (AVF), a measurement taken too close results in measurements being unreliable due to turbulence of blood flow upon exiting the surgically created arteriovenous fistula (AVF). Further, the sensing element may comprise a sensor measuring external force, preferably a sensor whose resistance varies when displaced, more preferably an at least one strain gauge or silicon sensor. A silicon sensor is this application refers to a silicon pressure sensor comprising a silicon-based diaphragm as is known in the art.

[0019] As the at least one sensing means is specifically 6mm or less above a venous or graft component of a surgically created AVF and substantially 3cm or less downstream of a surgically created AVF, the controller will be able to determine from this data a number of parameters which will aid in detecting the functional maturation of a surgically created AVF. This is because the specific depth of the venous or graft component of a surgically created AVF will have a known wall thickness, and as such, due to the already known depth, the controller is able to determine parameters relating to blood vessels based on the displacement of the skin - relating to the maximum and minimum diameter of blood vessels. This is only possible as the depth of the venous or graft component of a surgically created AVF is known and would not work at simply any location in the body.

[0020] Further, the sensing element may transmit collected data to the controller. Further still, the controller may comprise a processor. Further still, the controller may comprise a memory.

[0021] Even further still, the controller may be configured to determine at least one property of blood flow through an arteriovenous fistula (AVF). Even further still the controller may be configured to determine multiple properties of blood flow through an arteriovenous fistula (AVF). Further, the controller may comprise a filtering module.

[0022] Further still, a property of the blood flow determined by the controller may be the presence of a pulse. Even further still, a property of the blood flow determined by the controller may be blood flow rate. Further, the controller may be configured to determine a systolic blood pressure and a diastolic blood pressure.

[0023] Further, the controller may be configured to determine the presence of stenosis. Further still, the controller may be configured to determine a degree of stenosis. Further, the controller may be configured to determine a blood flow volume.

[0024] Further still, the controller may be configured to compare determined values to threshold values. Preferably, the controller may be configured to compare the degree of stenosis to a threshold degree of stenosis. Preferably, the controller may be configured to compare the blood flow volume to a threshold blood flow volume.

[0025] Further, the controller may be configured to determine the maturation of a surgically created arteriovenous fistula (AVF). Further still, the controller may be configured to determine a level of risk based on the determined information.

[0026] Further, the apparatus for investigating the success or failure of a surgically created arteriovenous fistula (AVF) may comprise a data transmittal means for transmitting data to an external apparatus.

[0027] Further, the controller may comprise a display. Further, the controller may comprise a speaker. Further, the controller may comprise haptic feedback means. Further, the controller may comprise a data transmission means for use with an external device or network.

[0028] Further, there is provided a method of using the apparatus for monitoring a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis, comprising the steps of: placing the apparatus on a user’s skin; with the at least one sensing means above a venous or graft component of a surgically created arteriovenous fistula; and wherein the at least one sensing means collects data indicative of the presence of a pulse in the venous or graft component of a surgically created arteriovenous fistula.

[0029] Further, the at least one sensing means may be placed on the skin of a user substantially 6mm or less above a venous or graft component of a surgically created arteriovenous fistula.

[0030] Further, the at least one sensing means may transmit collected data to the controller.

[0031] Even further still, the controller may determine at least one property of blood flow through an arteriovenous fistula (AVF). Even further still the controller may determine multiple properties of blood flow through an arteriovenous fistula (AVF).

[0032] Further still, a property of the blood flow determined by the controller may be the presence of a pulse. Even further still, a property of the blood flow determined by the controller may be blood flow rate. Further, the controller may be configured to determine a systolic blood pressure and a diastolic blood pressure.

[0033] Further, the controller may determine the presence of stenosis. Further still, the controller may determine a degree of stenosis. Further, the controller may determine a blood flow volume.

[0034] Further still, the controller may compare determined values to threshold values. Preferably, the controller may compare the degree of stenosis to a threshold degree of stenosis. Preferably, the controller may compare the blood flow volume to a threshold blood flow volume.

[0035] Further, the controller may determine the maturation of a surgically created arteriovenous fistula (AVF). Further still, the controller may determine a level of risk based on the determined information.

[0036] Further, the controller may comprise a display. Further, the controller may comprise a speaker. Further, the controller may comprise haptic feedback means. Further, the controller may comprise a data transmission means for use with an external device or network.

[0037] Further, the controller may relay any of the above information to the user via any one or a plurality of the speaker, display, or haptic feedback means.

[0038] According to a further non-limiting embodiment of the present invention there is provided apparatus for monitoring a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis comprising: a body; and a controller; and a at least one sensing means on a distal end of the body for placing on the skin of a user above a venous or graft component of a surgically created arteriovenous fistula; and wherein the at least one sensing means collects data indicative of the presence of a pulse in the venous or graft component of a surgically created arteriovenous fistula.

[0039] Further, the at least one sensing means may be configured so as to be suitable for placing on the skin of a user substantially 6mm or less above a venous or graft component of a surgically created arteriovenous fistula. Further still, the at least one sensing means may be configured so as to be suitable for placing on the skin of a user substantially 3cm or less downstream of a venous or graft component of a surgically created arteriovenous fistula.

[0040] Further, the at least one sensing means may comprise a sensor measuring external force, preferably a sensor whose resistance varies when displaced, more preferably a at least one strain gauge or silicon sensor. This is advantageous because it allows the collection of data regarding the presence of a pulse, and not thrill,

[0041] Further, the sensing element may transmit collected data to the controller. Further still, the controller may comprise a processor. Further still, the controller may comprise a memory.

[0042] Even further still, the controller may be configured to determine at least one property of blood flow through an arteriovenous fistula (AVF). Even further still the controller may be configured to determine multiple properties of blood flow through an arteriovenous fistula (AVF).

[0043] Further, the controller may comprise a filtering module.

[0044] Further still, a property of the blood flow determined by the controller may be the presence pulse. Even further still, a property of the blood flow determined by the controller may be blood flow rate. Further, the controller may be configured to determine a systolic blood pressure and a diastolic blood pressure.

[0045] Further, the controller may be configured to determine the presence of stenosis. Further still, the controller may be configured to determine a degree of stenosis. Further, the controller may be configured to determine a blood flow volume.

[0046] Further, the controller may comprise a display. Further, the controller may comprise a speaker. Further, the controller may comprise haptic feedback means. Further, the controller may comprise a data transmission means for use with an external device or network.

[0047] Further, there is provided a method of using the above apparatus for monitoring a surgically created arteriovenous fistula (AVF), comprising the steps of: placing the apparatus on a user’s skin; with the at least one sensing means above a venous or graft component of a surgically created arteriovenous fistula; and wherein the at least one sensing means collects data indicative of the presence of a pulse in the venous or graft component of a surgically created arteriovenous fistula.

[0048] Further, the at least one sensing means may be placed on the skin of a user substantially 6mm or less above a venous or graft component of a surgically created arteriovenous fistula.

[0049] Further, the at least one sensing means may transmit collected data to the controller.

[0050] Even further still, the controller may determine at least one property of blood flow through an arteriovenous fistula (AVF). Even further still the controller may determine multiple properties of blood flow through an arteriovenous fistula (AVF).

[0051] Further still, a property of the blood flow determined by the controller may be the presence pulse. Even further still, a property of the blood flow determined by the controller may be blood flow rate. Further, the controller may be configured to determine a systolic blood pressure and a diastolic blood pressure.

[0052] Further, the controller may determine the presence of stenosis. Further still, controller may determine a degree of stenosis. Further, the controller may determine a blood flow volume.

[0053] According to a further non-limiting embodiment of the present invention there is provided apparatus for monitoring a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis comprising: a body; and a controller; and a at least one sensing means on a distal end of the body for placing on the skin of a user above a venous or graft component of a surgically created arteriovenous fistula; and wherein the at least one sensing means collects data indicative of the presence of a pulse in the venous or graft component of a surgically created arteriovenous fistula.

[0054] Further, the at least one sensing means may be configured so as to be suitable for placing on the skin of a user substantially 6mm or less above a venous or graft component of a surgically created arteriovenous fistula. Further still, the at least one sensing means may be configured so as to be suitable for placing on the skin of a user substantially 3cm or less downstream of a venous or graft component of a surgically created arteriovenous fistula. This is advantageous because

[0055] Further, the at least one sensing means may comprise a sensor measuring external force, preferably a sensor whose resistance varies when displaced, more preferably a at least one strain gauge or silicon sensor. This is advantageous because it allows the collection of data regarding the presence of a pulse, and not thrill,

[0056] Further, the sensing element may transmit collected data to the controller. Further still, the controller may comprise a processor. Further still, the controller may comprise a memory.

[0057] Even further still, the controller may be configured to determine at least one property of blood flow through an arteriovenous fistula (AVF). Even further still the controller may be configured to determine multiple properties of blood flow through an arteriovenous fistula (AVF). Further, the controller may comprise a filtering module.

[0058] Further still, a property of the blood flow determined by the controller may be the presence pulse. Even further still, a property of the blood flow determined by the controller may be blood flow rate. Further, the controller may be configured to determine a systolic blood pressure and a diastolic blood pressure.

[0059] Further, the controller may comprise a display. Further, the controller may comprise a speaker. Further, the controller may comprise haptic feedback means. Further, the controller may comprise a data transmission means for use with an external device or network.

[0060] Further, there is provided a method of using the above apparatus for investigating the success or failure of a surgically created arteriovenous fistula (AVF), comprising the steps of: placing the apparatus on a user’s skin; with the at least one sensing means above a venous or graft component of a surgically created arteriovenous fistula; and wherein the at least one sensing means collects data indicative of the presence of a pulse in the venous or graft component of a surgically created arteriovenous fistula.

[0061] Further, the at least one sensing means may be placed on the skin of a user substantially 6mm or less above a venous or graft component of a surgically created arteriovenous fistula.

[0062] Further, the at least one sensing means may transmit collected data to the controller.

[0063] Even further still, the controller may determine at least one property of blood flow through an arteriovenous fistula (AVF). Even further still the controller may determine multiple properties of blood flow through an arteriovenous fistula (AVF).

[0064] Further still, a property of the blood flow determined by the controller may be the presence pulse. Even further still, a property of the blood flow determined by the controller may be blood flow rate. Further, the controller may be configured to determine a systolic blood pressure and a diastolic blood pressure.

[0065] It will be appreciated that the embodiments of the invention described above have been given by way of example only and that modifications or combinations of features of the device in its various embodiments may be affected. The invention also extends to the individual components mentioned above, taken singly or in combination. Description of the Drawings

[0066] Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which:

[0067] Figure 1 a schematic view of the device according to the present invention; and

[0068] Figure 2 shows a signal output of a at least one sensing means according to the present invention; and

[0069] Figure 3 shows a Fast Fourier Transform (FFT) spectrogram according to the present invention; and

[0070] Figure 4 shows a schematic of a blood vessel including a stenotic region; and

[0071] Figure 5 shows a series of signal outputs of a at least one sensing means according to the present invention; and

[0072] Figure 6 shows a method of using the device according to the present invention. Detailed Description of the Invention

[0073] An arteriovenous fistula (AVF) is surgically created by joining the vein and artery primarily on the non-dominant hand, as a method of circulation access for haemodialysis as a treatment for end stage renal disease. The first choice of AVF is Radiocephalic Arteriovenous Fistulae (RCAVF) that is created at the wrist joint. The second choice is Brachiocephalic Arteriovenous Fistula (BCAVF) which is created at the elbow joint in the same fashion as RCAVF in practice. Irrespective of the type of the fistula, Functional maturation is a necessity and remains a standard for all type of fistula.

[0074] In order to create an AVF or AVG, a normal blood flow is mandatory. The artery should be of a good calibre 1.8-2.5 mm that could handle the increase in pressure, velocity and flow. The artery should possess a good elasticity and not be calcified as this results in stiffness and failure of AVF. The artery should be located in an accessible area and relatively superficial. The artery should be in the close proximity of the vein for approximation and creation of an AVF or AVG as the artery cannot be mobilised. The artery should not be located at a joint as this does not permit anastomosis and constant movement of the joint results in failure of AVF / AVG. The artery contains a constant pressure (the systolic &diastolic blood pressure) and flow as it is connected to a close system (the heart). The artery does not dilate significantly after creation of AVF / AVG as it has muscular wall structure (smooth muscle &elastic fibres). The artery used to create an AVF continues to supply other areas of the body alongside the course of the AVF / AVG so the monitoring of blood flow through that artery would not be useful for the purposes of monitoring a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis. The artery is not cannulated for dialysis. The pressure at arteries is constant as the normal pressure (systolic and diastolic). Therefore, monitoring the AVF at the arterial component would not be useful, and would therefore simply replicate the state of the art.

[0075] To create an apparatus for monitoring a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis the monitoring must take place at a venous component. This is because veins do not have a constant pressure like that of an artery. The pressure in veins ranges from 5-20 mmHg. Veins have thinner walls compared to arteries, allowing them to stretch and expand more easily in response to increased blood flow and pressure. Veins have higher compliance (ability to change volume with pressure changes) compared to arteries, which makes them more capable of accommodating increased blood volume. The baseline pressure in veins is lower than in arteries, so they are more responsive to changes in pressure and can dilate more effectively. Veins contain valves that prevent backflow of blood, which can help in maintaining consistent pressure and facilitating dilation when necessary. Veins have less smooth muscle content compared to arteries, making them less resistant to dilation. Veins are more capable of undergoing structural remodelling in response to chronic changes in hemodynamic forces. The endothelial cells in veins can respond to increased wall shear stress (WSS). The extracellular matrix of veins is more adaptable to changes in pressure and flow, aiding in dilation. Veins have a unique compliance mechanism that allows them to store and release blood volume efficiently, aiding in their dilation under increased flow conditions. Therefore, monitoring the AVF at the venous component would to be useful, and would allow monitoring to be performed successfully. From AVF Creation to Maturation and Changes in The Vein Immediate Changes (Days)

[0076] The following changes occur in the days after the creation of an AVF:

[0077] Increased Blood Flow: The connection between the high-pressure artery and the low-pressure vein results in a significant increase in blood flow through the vein, this is governed by Poiseuille’s Law: LPnr4 827 /

[0078] Where Q is the flow rate, AP is the pressure gradient, is the vessel radius, q is the blood viscosity, and I is the length of the vessel. The implication of this is that an increase in the radius (r) of the vein significantly increases the flow rate, facilitating venous dilation in AVF.

[0079] Elevated Shear Stress: The increased flow velocity leads to higher shear stress on the endothelial cells lining the vein. Shear stress is the tangential force per unit area exerted by the flowing blood on the vessel wall. This is governed by the Shear Stress Formula: T = —T nr5

[0080] Where t is the shear stress, p is the blood viscosity, Q is the flow rate, and r is the radius of the vessel. The increased flow velocity leads to higher shear stress on the endothelial cells lining the vein.

[0081] Pressure Gradient: The pressure within the vein rises due to the direct connection with the high-pressure arterial system. This pressure gradient drives the initial dilation of the vein, this is governed by Ohm’s Law for Fluid Dynamics:

[0082] Where Q is the flow rate, AP is the pressure difference, and R is the resistance. The pressure within the vein rises due to the direct connection with the high-pressure arterial system, increasing the pressure gradient. Short-Term Adaptations (Days to Weeks)

[0083] The following changes occur in the days to weeks after the creation of an AVF:

[0084] Endothelial Cell Activation: Increased shear stress activates endothelial cells, leading to the release of vasodilatory substances of nitric oxide (NO) and prostacyclin. These substances induce vasodilation and reduce vascular resistance.

[0085] Vasodilation: The immediate response to increased shear stress and endothelial activation is the dilation of the vein. Vasodilation reduces resistance and allows for higher blood flow; this is governed by Poiseuille’s Law (adapted for vasodilation): APn(r + Ar)4

[0086] Where Ar represents the change in radius due to vasodilation.

[0087] Vascular Remodelling: Structural changes occur in the vein wall, including the proliferation and migration of smooth muscle cells (SMCs) and changes in the extracellular matrix (ECM). This remodelling increases the vein's diameter and wall thickness, adapting it to the increased hemodynamic load. Intermediate Changes (6-8 weeks)

[0088] The following changes occur between 6 and 8 weeks after the creation of an AVF:

[0089] Wall Tension and Compliance: The vein’s compliance (its ability to expand with increased pressure) helps accommodate the higher blood flow and pressure without excessive stress on the wall, this is governed by Laplace’s Law: T = P x r

[0090] Where T is the wall tension, P is the intraluminal pressure, and r is the radius of the vessel. Increased radius due to dilation results in higher wall tension.

[0091] Smooth Muscle Cell Response: SMCs undergo phenotypic changes from a contractile to a synthetic state, promoting ECM production and structural reinforcement. This helps the vein to stabilize and maintain its increased diameter.

[0092] Extracellular Matrix Remodelling: The composition and organization of the ECM change to support the increased vessel size and maintain structural integrity. Collagen and elastin fibbers are remodelled to provide strength and elasticity. AVF Maturation

[0093]

[0097] In order for an arteriovenous fistula (AVF) to be useable it needs to achieve functional maturation. The term "functional maturation" is defined in accordance with the "rules of sixes" evaluation of the fistula. The fistula is required to be a 6 mm vein, 6mm under the skin, 500^600 ml / min and at least 6 mm long.

[0094] When functional maturation is achieved the vein dilates and remodels, shear stress normalizes to levels similar to those in normal physiological conditions. This is crucial for preventing excessive endothelial activation and potential damage to the vein.

[0095] The vein reaches a new steady state where it has adapted to the increased blood flow and pressure. The diameter of the vein is significantly larger, and its wall is thicker and stronger, making it suitable for repeated needle insertions which are required for haemodialysis. The vein's structural and functional changes make it capable of handling the demands of dialysis without collapsing or causing complications. Hemodynamic stability is achieved, and the vein can sustain high blood flows necessary for efficient dialysis treatment.

[0096] Failure of functional maturation refers to a fistula that has not gained functional maturation and does not have the necessary blood flow for successful haemodialysis and requires further intervention to gain functional maturation otherwise referred to assisted functional maturation.

[0097] Once functional maturation of the AVF has been achieved we can monitor the AVF or arteriovenous graft for the purposes of haemodialysis. The at least one sensing means will monitor the outflow (venous) component only, not the arterial component as discussed above. The at least one sensing means needs to be positioned at least 3 cm from the anastomosis (the area where the artery and vein has joined) on the vein component. Any at least one sensing means placed near the anastomosis site (3cm below from vein aspect) will give false flow, turbulence flow and more which is not predictor of anything useful for monitoring a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis.

[0098] There needs to be at least 6cm long vein for this purpose, which mut be 6 mm under the skin. There may be a plurality sensing means, at least one applied before the cannulation site and at least one after. The at least one sensing means is for detection of stenosis and not for the detection of a blockage.

[0099] There might be combination of more than one stenosis (cannulation sites), therefore the average of two stenosis can also be evaluated.

[0100] The at least one sensing means has to be applied longitudinally &transverse. The reason for the position of the at least one sensing means is because Oscillatory Shear Stress, radial and longitudinal changes. The Oscillatory Shear Stress happens when the pressure of artery comes to the vein and there is gap in the next cycle of the heart and given vein does not have a pressure there is vacuum like or syphon like event. Oscillatory Shear Stress (OSI) is calculated by: 1 / |t|\ 0 SI = I 1........................................| 2\ Ri /

[0101] The Oscillatory Shear Index (OSI) is defined as: r is the time averaged shear stress over a cardiac cycle. |f | is the time-averaged magnitude of the shear stress over a cardiac cycle.

[0102] Time-averaged shear stress: This is the average value of shear stress considering its direction over a period. 1 T = ~ T(t) dt 1 Jo

[0103] Time-averaged magnitude of shear stress: This is the average value of the absolute magnitude of shear stress, ignoring its direction, over a period. — 1 fT kl =- |t(0 I dt 1 Jo

[0104] OSI Value Range: The OSI ranges from 0 to 0.5:

[0105] OSI = 0 indicates a unidirectional shear stress with no oscillation.

[0106] OSI = 0.5 indicates a highly oscillatory shear stress, where the flow is changing direction frequently.

[0107] Shear stress and flow Rate Along the length of the vein:3 nr3

[0108] Where: t is the shear stress, p is the blood viscosity, Q is the flow rate, r is the radius of the vessel.

[0109] Flow Rate (Q): The flow rate Q increases due to the connection with the high-pressure arterial system.

[0110] Radius (r): The radius of the vein changes along its length due to dilation.

[0111] Shear Stress (t): Shear stress varies along the length of the vessel as a function of changes in radius and flow rate.

[0112] Combined Formula for Longitudinal Changes: APwr4 8rjl

[0113] The flow rate along the length of the vessel can be affected by changes in the vessel's diameter and pressure gradient. Poiseuille's Law can be adapted to describe these changes:

[0114] Where: AP is the pressure gradient along the length of the vessel.

[0115] tt is a constant (Pi, approximately 3.14159).

[0116] r is the radius of the vessel.

[0117] n is the blood viscosity.

[0118] I the length of the vessel.

[0119] Following the surgical creation of an arteriovenous fistula the patient is regularly followed up in outpatient clinic for clinical and ultrasonography assessment. On clinical examination presence of "Bruit" or" Thrill" remains an important clinical predictor of Functional Maturation, however, this is not an independent marker. Ultrasound examination of the fistula assess the flow and pressure alteration of the AVF. A flow rate of more than 200-600 ml / minute remains essential for successful functional maturation thus cannulation for haemodialysis. The presence of a pulse in a venous or graft component downstream of a surgically created AVF suggests the development of stenosis.

[0120] Stenosis, the abnormal narrowing or blockage of a blood vessel, slows and reduces blood flow through an arteriovenous fistula (AVF), causing problems with the quality of the patient’s dialysis treatment, prolonged bleeding after puncture, or pain at the fistula site. Stenosis can also lead to blocked or clotted access of the arteriovenous fistula (AVF), suggesting that functional maturation of the arteriovenous fistula (AVF) has not been achieved and that the arteriovenous fistula (AVF) has not been successful.

[0121] Generally disclosed herein are monitoring a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis generally indicated 1 comprising a body 11, a controller 13, and a at least one sensing means 12 on a distal end of the body 11 for placing on the skin of a user above a venous or graft component of a surgically created arteriovenous fistula; wherein the at least one sensing means 12 collects data indicative of the presence of a pulse in the venous or graft component of a surgically created arteriovenous fistula.

[0122] The use of at least one sensing means 12 to monitor a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis generally indicated 1 is advantageous for a number of reasons. The early detection of functional maturation, and thus early cannulation, will reduce the requirement for further expensive dialysis sessions than is required. A reduction in expensive ultrasound assessment of the fistula. A shorter follow up and reduction in resource management due to a reduction in the use of outpatient follow up and specialist sonographers. As such, it will allow for an increase in the availability of outpatient appointment services, thus offering an increase in efficiency and efficacy. It also offers early detection of failure I impairment of the AVF, thus offering early intervention and a potential limitation of emergency operating surgery. This will also offer cost reductions as it will potentially result in a reduction in the use of central venous access, infection rates associated with such lines, and a potential limited use of resources for their care. It will allow earlier creation of another AVF if required, potentially optimising the cost of dialysis substantially. The use of a sensor also allows patients to selfmonitor their surgically created AVF. Over time, this offers the potential optimisation of AVF care and reduction in use of haemodialysis appointments for incidental finding of malfunctioning AVF.

[0123] The at least one sensing means 12, in an exemplary embodiment, may comprise an at least one strain gauge or silicon sensor 12 configured to be placed 6mm or less above a venous or graft component of a surgically created arteriovenous fistula. The at least one strain gauge or silicon sensor 12 must be 6mm or less below the above a venous or graft component of a surgically created arteriovenous fistula, or below the surface of the skin, as this is the working length for a successful two needle dialysis when the patient requires such, and as a result this is the working depth at which a surgically created arteriovenous fistula (AVF) is created.

[0124] The at least one strain gauge or silicon sensor 12 may be placed substantially 3cm or less downstream of a surgically created arteriovenous fistula. This is because in order to measure the success of a surgically created arteriovenous fistula (AVF), “thrill” must be measured a certain distance from the surgically created arteriovenous fistula (AVF), a measurement taken too close results in measurements being unreliable due to turbulence of blood flow upon exiting the surgically created arteriovenous fistula (AVF).

[0125] The at least one strain gauge or silicon sensor 12, when placed 6mm or less above a venous or graft component of a surgically created AVF, and substantially 3cm or less downstream of a surgically created AVF will be able to measure the displacement of skin and transmit this data to a controller 13.

[0126] As the at least one strain gauge or silicon sensor 12 is specifically 6mm or less above a venous or graft component of a surgically created AVF and substantially 3cm or less downstream of a surgically created AVF, the controller 13 will be able to determine from this data a number of parameters which will aid in detecting the functional maturation of a surgically created AVF. This is because the specific depth of the venous or graft component of a surgically created AVF will have a known wall thickness, and as such, due to the already known depth, the controller 13 is able to determine parameters relating to blood vessels based on the displacement of the skin - relating to the maximum and minimum diameter of blood vessels. This is only possible as the depth of the venous or graft component of a surgically created AVF is known and would not work at simply any location in the body.

[0127] In the exemplary apparatus for investigating the success or failure of a surgically created arteriovenous fistula (AVF), the sensor means comprises an at least one strain gauge or silicon sensor 12 configured to collect data indicative of the movement of the skin of the user when placed 6mm or less above a venous or graft component of a surgically created AVF, and substantially 3cm or less downstream of a surgically created AVF. The at least one strain gauge or silicon sensor 12 is configured to measure strain, as will be explained below. As such, in the at least one strain gauge or silicon sensor 12 collects data indicative of strain applied to the at least one strain gauge or silicon sensor 12 caused by movement of the skin of the user. As the skin of the user moves, due to blood flowing through the AVF, the at least one strain gauge or silicon sensor 12 deforms, which causes the resistance of the sensing element of the at least one strain gauge or silicon sensor 12 to change in proportion to the amount of strain being applied to the at least one strain gauge or silicon sensor 12. Based on the measured change in resistance, strain may be determined, as explained below.

[0128] Strain, E, is defined as the ratio of the change in length of a material to the original, unaffected length: △L

[0129] Each at least one strain gauge or silicon sensor 12 possesses a gauge factor (GF), defined as the ratio between the fractional change in electrical resistance (AR / R) and the fractional change in length (AL / L) of the at least one strain gauge or silicon sensor 12. This gauge factor is a constant value specified by the manufacturer. Consequently, the strain (e) can be calculated based on the change in resistance observed in the at least one strain gauge or silicon sensor 12, as shown below: A / ? / A / ? / rn - 'R _ 'R ur — — — --- 4 p

[0130] The at least one strain gauge or silicon sensor 12 gathers data over a specified duration. In exemplary configurations, this duration may be approximately 30 seconds, 45 seconds, 60 seconds, or 90 seconds, though alternative time periods may be employed as understood by skilled practitioners. In some configurations, the specified duration may fall within a range, such as substantially 30 to 45 seconds, 30 to 60 seconds, 45 to 60 seconds, or 45 to 90 seconds, with the understanding that other ranges may also be used.

[0131] Figure 2 illustrates a plot of the at least one strain gauge or silicon sensor 12 output when positioned against the skin over a blood vessel, such as an arteriovenous fistula (AVF). The plot displays the strain measured by the at least one strain gauge or silicon sensor 12 on the y-axis and time on the x-axis. As evident from Figure 2, the at least one strain gauge or silicon sensor 12 output consists of a waveform with a series of peaks (202a-d) and valleys (204a-d). Between each peak (202a-d) and valley (204a-d), there are intermediate peaks (206a-d), such as intermediate peaks 206b located between peak 202b and valley 204b. Similar waveforms can be generated using alternative sensors, including Fiber Bragg Gratings (FBG) optical, at least one strain gauge or silicon sensor 12, other optical technology at least one strain gauge or silicon sensors 12, or stretch sensors or a silicon sensor. In exemplary arrangements, the raw data collected by the at least one strain gauge or silicon sensor 12 may be filtered by a filtering module of the controller 13. The filtering module may use a filter, such as the Butterworth filter, to smooth the waveform output of the sensor before determination of the blood flow parameters, as described below. Figure 2 shows a signal output that has been filtered by the filtering module.

[0132] The controller 13 determines one or more blood flow parameters based on the data collected by the at least one strain gauge or silicon sensor 12.

[0133] The blood flow parameters may comprise one or more of the following: the maximum diameter (dm,,) of the blood vessel over which the at least one strain gauge or silicon sensor 12 is placed, the minimum diameter (dmin) of the blood vessel over which the at least one strain gauge or silicon sensor 12 is placed, systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (w), and the estimated diameter of the stenotic portion (d) of the blood vessel over which the at least one strain gauge or silicon sensor 12 is placed.

[0134] The blood flow parameters are determined from the signal output of the at least one strain gauge or silicon sensor 12 as shown in Figure 2.

[0135] The blood flow parameters include the maximum diameter of the blood vessel over which the at least one strain gauge or silicon sensor 12 is placed (dmax) can be determined based on the average height of the signal peaks 202a-d from the signal mean (i.e. from y = signal mean).

[0136] The blood flow parameters further include the minimum diameter of the blood vessel over which the sensor 102 is placed (dmin) can be determined based on the average height of the signal valleys 204a-d from the signal mean.

[0137] The blood flow parameters further include the systolic blood pressure (SBP) can be determined based on the average height of the signal peaks 202a-d from the x-axis (i.e. from y=0).

[0138] The blood flow parameters further include the diastolic blood pressure (DBP) can be determined based on the average height of the signal valleys 204a-d from the x-axis (i.e. from y=0).

[0139] The blood flow parameters further include the heart rate (co) may be determined based on the time interval between signal peaks 202a-d divided by the number of signal peaks.

[0140] The blood flow parameters further include an estimated diameter of the stenotic portion (d) can be determined based on the signal mean (the signal mean may also be referred to as signal running mean or signal moving average).

[0141] The blood flow parameters may be determined by the controller 13 using a peak detection algorithm or alternative methods, as will be familiar to the skilled person.

[0142] The controller 13 may alternatively, or additionally, determine systolic and diastolic blood pressure by applying a Fast Fourier Transform (FFT) to the at least one strain gauge or silicon sensor 12's signal output, creating an FFT spectrogram of the signal. Figure 3 illustrates an FFT spectrogram of the signal output shown in Figure 2. The FFT spectrogram features a series of peaks (P1 to P5 as shown in Figure 3). These peaks (P1 to P5) correspond to the intermediate peaks 206a-d located between each signal peak (202a-d) and the respective signal valley (204a-d). Thus, the FFT spectrogram enables the extraction of data from the at least one strain gauge or silicon sensor 12 output related to the intermediate peaks (206a-d).

[0143] The controller 13 is configured to determine the amplitude of each of the peaks from the FFT spectrogram (i.e. the amplitude of peaks P1, P2, P3, P4, P5 as shown in Figure 3), for example using a peak detection algorithm. The controller 13 determines the systolic and diastolic blood pressure based on the determined amplitudes of the peaks from the FFT. The systolic blood pressure can be determined from the ratio of P1 / P5. The diastolic blood pressure can be determined from the ratio of P4 / P5.

[0144] The controller 13 determines if blood flow through the AVF is compromised using the determined blood flow parameters. It specifically evaluates impairment by analysing the maximum and minimum diameters of the venous or graft segment of the AVF, measured 6mm above the skin where the at least one strain gauge or silicon sensor 12 is placed, along with the systolic and diastolic blood pressures derived from the at least one strain gauge or silicon sensor 12 data.

[0145] Determining if the AVF has achieved functional maturation or if it is impaired may involve calculating the degree of stenosis (DOS) and / or the blood flow volume (BFV) using the blood flow parameters identified by the controller 13, as described below. Degree of Stenosis (DOS)

[0146] The degree of stenosis (DOS) is determined by determining the ratio of the cross-sectional area between a normal unaffected venous or graft component of a surgically created AVF and a stenotic region of the venous or graft component of a surgically created AVF. DOS = d2\ 1 - X 100% D2 /

[0147] Where d is the blood vessel / AVF diameter at the stenotic region, and D is the diameter of the normal, unaffected AVF. The above equation may be expressed using the thickness of the venous or graft component of a surgically created AVF, as below: d2 .2 DOS = 1 - 7-----77 X100% = 1 - 7---------77 X100% \ (d + 2 / i2)2 / \ (d + 2h-2hiy I

[0148] Where d is the diameter of the stenosis, hi is the thickness of the blood vessel / AVF wall, h2 is the thickness of the stenotic region, and h is the total thickness of the blood vessel wall and the stenotic region (i.e. h = hi + h?). These parameters are shown in Figure 4, where 402 is the blood vessel wall and 404 is the stenotic region.

[0149] Using the Telegrapher model / equations to relate the hemodynamics of the venous or graft component of a surgically created AVF to strain gauge theory, the total thickness may be expressed based on the definition of the at least one strain gauge or silicon sensor 12 capacitance: 4 — A nmax ^min SBP - DBP (1 — <j2)7rd| 4hE

[0150] Wherein Amax is the maximum cross sectional area of the venous or graft id \2 component of a surgically created AVF (i.e. n ) and Amin is the minimum cross sectional area of the venous or graft component of a surgically created AVF (i.e.Tr(^)2).

[0151] As such, the total thickness, h, may be expressed as: (1 - a2)ndl SBP - DBP h =-- Ed2- d2 ^max ^min

[0152] Where o is the Poissons ratio of the venous or graft component of a surgically created AVF, do is the initial diameter of the venous or graft component of a surgically created AVF (that is, the initial diameter of the vein before creation of the AVF), and E is the Young's modulus of the venous or graft component of a surgically created AVF.

[0153] o, do and E are constants that can be determined for the venous or graft component of a surgically created AVF from medical guidelines (for example, the National Kidney Foundation). For example, typically do is within a certain range for most patients, specifically 1,5mm to 2.5mm, E is approximately 0.5MPa and a is approximately 0.45 to 0.55. Furthermore, the systolic and diastolic blood pressures (SBP and DBP), and the maximum and minimum diameters of the venous or graft component of a surgically created AVF (dmax and dmin) which is at least one strain gauge or silicon sensor 12 is placed 6m above on the user’s skin can be determined as described above based on the data collected by the at least one strain gauge or silicon sensor 12. As such, the maximum thickness, h, may be determined.

[0154] The degree of stenosis (DOS) may therefore be calculated using the below equation: / d2 \ DOS = 1 - 73-----7--7 % 100% \ (d + 2h - 2 / iJ2 /

[0155] As described above, the diameter of the stenotic region, d, may be determined based on the data collected by the at least one strain gauge or silicon sensor 12 (that is, from the signal mean). The thickness of the wall of the venous or graft component of a surgically created AVF, hi, can be determined from medical guidelines (for example, the National Kidney Foundation). The thickness of the wall of the venous or graft component of a surgically created AVF typically falls within the range of 0.2mm to 0.4mm for most patients. Bood Flow Volume

[0156] The blood flow volume of the blood vessel / AVF can be determined based on the definition of the at least one strain gauge or silicon sensor 12 impedance, Z, (equation [1] given below) and the Telegrapher equations (equations [2] and [3] given below). P(z) = P^ = R+jmL °Q(z) Qo Jg+jmc p(z, t) = p+e-az cos(—pz + Mt) [2] q(z, t) = Qq e~az cos(—pz + a>t) [3]

[0157] Where Zo is the average impedance of the at least one strain gauge or silicon sensor 12 circuit, P(z) is the blood flow pressure, Q(z) is the blood flow volume, Po+ is the average blood flow pressure, Qo+ is the average blood flow volume, R is the resistance of the at least one strain gauge or silicon sensor 12 circuit, L is the inductance of the at least one strain gauge or silicon sensor 12 circuit, C is the capacitance of the at least one strain gauge or silicon sensor 12 circuit, and G is the conductance of the at least one strain gauge or silicon sensor 12 circuit.

[0158] Equation [3] may be written with Zo is the average impedance of the at least one strain gauge or silicon sensor 12 circuit, as below: P+ q(z, t) = — cos(—pz + (ut) 0

[0159] Assuming that the at least one strain gauge or silicon sensor 12 is positioned as z = 0, the equation becomes: q(O.t) = Pq cos(<ot) G + ja)L R + ja)c

[0160] The average blood pressure 130+ (or mean blood pressure, MPB) can be calculated based on the systolic and diastolic blood pressures determined from the data collected by the at least one strain gauge or silicon sensor 12 as 5 below 1 2 Po+ = MBP = — SBP + -DBP 0 3 3

[0161] As such, the average blood flow volume may be determined using the 10 following equation: Qavg G + jdjL MBP -—-— R + jo)c

[0162] Where G, R, C and L may all be determined using the following equations: 128n 4p (1 — r = c1-^-,l = c2^,g = q,c=-— ' d^ tuIq 4hE

[0163] Where: R Dynamic viscosity (0.035 9 / cm3) P Blood density (1.056 9 / cm3) a Poisson's ratio of blood vessel w Heart rate frequency h The thickness of the blood vessel wall E Young's elastic modulus of blood vessel do The initial diameter of the blood vessel W Womersley number equal to W = d0 Ci Heart rate constant equal to: Ci = 0.18W+0.45 c2 Heart rate constant equal to: C2 = -0.018W+ 1.39

[0164] As such, the degree of stenosis (DOS) and / or the blood flow volume (BFV) may be determined based on the blood flow parameters determined by the controller 13.

[0165] Using the degree of stenosis (DOS) and / or the blood flow volume (BFV), the controller 13 assesses the extent of blood flow impairment. This involves comparing the DOS to a stenosis threshold and / or the BFV to a flow volume threshold. Based on these comparisons, the controller 13 assigns a risk level, which could be high, moderate, or low. For instance, the stenosis threshold might be substantially 25%, 30%, or 35%, while the blood flow volume threshold could be substantially 600 ml / min, 650 ml / min, 700 ml / min, or 750 ml / min.

[0166] Based on the degree of stenosis (DOS) and / or the blood flow volume (BFV), the controller 13 may determine the functional maturation, or failure of a surgically created AVF. This may comprise comparing the determined degree of stenosis to a stenosis threshold and / or comparing the determined blood flow volume to a blood flow volume threshold. Based on the comparison of the determined degree of stenosis to the stenosis threshold and / or the comparison of the determined blood flow volume to the blood flow volume threshold, the controller 13 may determine a risk level. The risk level may be one of: high risk, moderate risk or low risk. In one example, the stenosis threshold may be one of substantially 25%, substantially 30% and substantially 35% (i.e. a degree of stenosis of one of substantially 25%, substantially 30%, and substantially 35%), and the blood flow threshold may be one of substantially 600 ml / min, substantially 650 ml / min, substantially 700 ml / min and substantially 750 ml / min.

[0167] For example, the controller 13 might classify the user as high risk if the degree of stenosis surpasses the stenosis threshold and the blood flow volume falls below the flow volume threshold. The user might be categorized as moderate risk if the degree of stenosis exceeds the threshold but the blood flow volume is above the threshold. The user would be considered low risk if the degree of stenosis is below the threshold and the blood flow volume is above the threshold.

[0168] In exemplary arrangements, the blood flow threshold may consist of a first and a second threshold, where the second threshold is higher than the first. In such configurations, the controller 13 may identify the user as high risk if the degree of stenosis surpasses the stenosis threshold and the blood flow volume falls below the first blood flow threshold. If the degree of stenosis exceeds the threshold and the blood flow volume exceeds the second blood flow threshold, the controller 13 may classify the user as moderate risk. Conversely, the controller 13 may assess the user as low risk if the degree of stenosis is below the stenosis threshold and the blood flow volume exceeds the second blood flow threshold. For instance, in one scenario, the stenosis threshold could be approximately 30%, the first blood flow threshold around 600 ml / min, and the second blood flow threshold approximately 750 ml / min.

[0169] Figure 5 shows a series of output plots generated from data captured by the at least one strain gauge or silicon sensor 12 positioned over various blood vessels, such as AVFs, each exhibiting different degrees of stenosis. The plots on the left column display the raw data collected by the at least one strain gauge or silicon sensor 12, while those on the right column illustrate the filtered data, processed by the filtering module. These plots illustrate the strain measured by the gauge on the y-axis against time on the x-axis. Figure 5 demonstrates how waveforms (and consequently blood flow parameters) may alter in the presence of stenosis. It's important to note that the waveforms depicted in Figure 5 are exemplary and are intended for illustrative purposes, this would be understood by the skilled person.

[0170] The determined risk level regarding the degree of stenosis or blood flow volume will be indicated to the user. The indication may be visual, auditory, or haptic, provided singly or in combination through a display 15, speaker 14, or haptic feedback means 16 respectively. This information may be transmitted to an external device or network, such as a computer, external monitoring system, or mobile phone.

[0171] The display may show the user any of the blood flow parameters determined by the controller 13. The display may also indicate whether or not the user should seek medical attention regarding their surgically created AVF, and the reasons why based on the blood flow parameters determined by the controller 13.

[0172] Figure 6 shows a method of using the above apparatus for monitoring a surgically created Arteriovenous Fistula (AVF) and arteriovenous grafts for purpose of haemodialysis, comprising the steps of:

[0173] 601 placing the apparatus on a user’s skin; with the at least one sensing means above a venous or graft component of a surgically created arteriovenous fistula; and 602 wherein the at least one sensing means collects data indicative of the presence of a pulse in the venous or graft component of a surgically created arteriovenous fistula.

[0174] The at least one sensing means is placed on the skin of a user substantially 6mm or less above a venous or graft component of a surgically created arteriovenous fistula and will transmit collected data to the controller 13.

[0175] 603 The controller 13 determines at least one property of blood flow through an arteriovenous fistula (AVF). The controller 13 may determine multiple properties of blood flow through an arteriovenous fistula (AVF). A property of the blood flow determined by the controller 13 may be the presence of a pulse, blood flow rate, a systolic blood pressure, and a diastolic blood pressure.

[0176] 604 The controller 13 determines the presence of stenosis, a degree of stenosis, and a blood flow volume.

[0177] 605 The controller 13 compares determined values to threshold values, the degree of stenosis to a threshold degree of stenosis, and the blood flow volume to a threshold blood flow volume.

[0178] 606 The controller 13 determines the maturation of a surgically created arteriovenous fistula (AVF) and determines a level of risk based on the determined information. The controller 13 relays this information, and the determined blood flow parameters, to the user.

[0179] 607 The controller 13 relays any of the above information to the user via any one or a plurality of the speaker 14, display 15, or haptic feedback means 16.

[0180] It is to be appreciated that the embodiments of the invention described 5 above with reference to the accompanying drawings have been given by way of example only and that modifications may be affected. Other constructions may be employed. Individual components shown in the drawings are not limited to use in their drawings and they may be used in other drawings and in all aspects of the invention. The invention also extends to the individual components mentioned 10 and / or shown above, taken singly or in any combination.

Claims

1. An apparatus for monitoring a surgically created arteriovenous fistula (AVF) comprising:a body; anda controller; anda at least one sensing means on a distal end of the body for placing on the skin of a user above a venous or graft component of a surgically created arteriovenous fistula; and whereinthe at least one sensing means collects data indicative of the presence of a pulse in the venous or graft component of a surgically created arteriovenous fistula.

2. An apparatus for monitoring a surgically created arteriovenous fistula (AVF) according to claim 1 wherein, the at least one sensing means is configured so as to be suitable for placing on the skin of a user substantially 6mm or less above a venous or graft component of a surgically created arteriovenous fistula.

3. An apparatus for monitoring a surgically created arteriovenous fistula (AVF) according to claims 1 or 2 wherein the at least one sensing means is be configured so as to be suitable for placing on the skin of a user substantially 3cm or less downstream from a surgically created arteriovenous fistula above the venous or graft component.

4. An apparatus for monitoring a surgically created arteriovenous fistula (AVF) according to claims 1 to 3 wherein the at least one sensing means comprises a sensor measuring external force whose resistance varies when displaced.

5. An apparatus for monitoring a surgically created arteriovenous fistula (AVF) according to claim 4 wherein the at least one sensing means comprises a at least one strain gauge or silicon sensor.

6. An apparatus for monitoring a surgically created arteriovenous fistula (AVF) according to claims 1 to 6 wherein the controller is configured to determine at least one property of blood flow through an arteriovenous 5 fistula (AVF).

7. An apparatus for monitoring a surgically created arteriovenous fistula (AVF) according to claim 6 wherein the controller is be configured to determine a plurality of properties of blood flow through an arteriovenous 10 fistula (AVF).

8. An apparatus for monitoring a surgically created arteriovenous fistula (AVF) according to claims 6 or 7 wherein a property of blood flow through an arteriovenous fistula (AVF) comprises the presence of a pulse, blood 15 flow rate a systolic blood pressure, or a diastolic blood pressure.

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