Handheld coandĂ effect uroflowmeter

Abstract

A uroflowmetry device includes a funnel; a cylinder attached to a bottom end of the funnel; a helical blade rotor positioned within the cylinder and adapted to freely rotate within the cylinder along a longitudinal axis of the cylinder; fiducials fixed to the rotor; a sensor fixed to the cylinder and adapted to sense movement of the fiducials as the rotor spins; and a microprocessor connected to the sensor that computes a urinary flow rate from a sensed rotation of the rotor. The device parameters are designed to ensure urine flows using the Coanda effect and avoids fluid detachment from the surface of the helical blade rotor.

Description

FIELD OF THE INVENTIONThe present invention relates generally to medical methods and devices. More specifically, it relates to uroflowmetry and devices for measurement of the flow of urine.BACKGROUND OF THE INVENTIONThe prevalence of lower urinary tract symptoms (LUTS) is about 60% in both men and women. Currently, the first step in diagnosis relies on uroflowmetry to measure urine flow rate in patients. However, uroflowmetry is prohibitively expensive, making it unaffordable for patients. Consequently, patients need to visit a hospital for the measurement, but hospitals typically have only one device, often unable to accommodate patients urination schedules.Conventional uroflowmetry uses a scale to measure the amount of urine. It is accurate and widely accepted by urologists, but is only available in hospital or clinical setting, needs the assistance of nurses / staff, and is not patient-friendly. Home uroflowmetry devices have been developed using various approaches to measurement such as scales, fluid height sensors, thermal sensors, and sound sensors. These can be expensive and complicated for some patients to use and clean.SUMMARY OF THE INVENTIONThe present invention provides a device and method for measuring clinically important parameters related to urination, such as maximum urine flow rate, average urine flow rate, voiding volume, voiding time, and voiding patterns. The approach is low cost, can be used at home, is patient-friendly, easy to clean, works with standard toilets, and has high accuracy. The device may be integrated in a system that provides urologists with frequent and accurate urination data from patients, without the need for patients to make hospital visits.In one aspect, the invention provides a uroflowmetry device comprising: a funnel; a cylinder attached to a bottom end of the funnel; a helical blade rotor, wherein the helical blade rotor is positioned within the cylinder and adapted to freely rotate within the cylinder along a longitudinal axis of the cylinder; fiducials (e.g., magnets) fixed to the rotor; a sensor fixed to the cylinder and adapted to sense movement of the fiducials as the rotor spins; and a microprocessor connected to the sensor that computes a urinary flow rate from a sensed rotation of the rotor.Preferably, a gap between the cylinder and the helical blade rotor is sufficiently small to ensure urine flow by the Coandă effect and avoid fluid detachment as urine flows along a surface of the helical blade rotor. Preferably, a pitch of the helical blade rotor is sufficiently small to ensure urine flow by the Coandă effect and avoid fluid detachment as urine flows along a surface of the helical blade rotor. Preferably, a pitch of the helical blade rotor corresponds to a helical angle in the range of 30° to 65°.For example, in one implementation, a pitch of the helical blade rotor corresponds to a helical angle of 57.6°. For example, in one implementation, the helical blade rotor has a height of 54.19 mm and a pitch of 63.3 mm, with 13 spokes. For example, in one implementation, the helical blade rotor fits within the cylinder with a gap of around 0.9 mm.The sensor may be a Hall effect sensor, a capacitive sensor, inductive sensor, magnetoresistive sensor, optical sensor, or a mechanical sensor.Preferably, the helical blade rotor has blades that form at least half of a full turn. More preferably, the helical blade rotor has blades that form at least three quarters of a full turn. Preferably, the helical blade rotor is a dual helical blade rotor. Preferably, the microprocessor is connected to the sensor via a wireless communication link.BRIEF DESCRIPTION OF THE DRAWINGSFig. 1A is a top view of a uroflowmetry device, according to an embodiment of the invention.Fig. 1B is a side view of a uroflowmetry device, according to an embodiment of the invention.Fig. 2A is a cross-sectional side view of a uroflowmetry device, according to an embodiment of the invention.Fig. 2B is a cross-sectional side view of a uroflowmetry device showing detail of a rotor and cylindrical housing, according to an embodiment of the invention.Fig. 2C is a side view of a helical rotor of a uroflowmetry device, according to an embodiment of the invention.Fig. 3 is a schematic diagram illustrating the connections between a sensor, microcontroller, battery module, and processors, according to an embodiment of the invention.Fig. 4 is a flowchart illustrating steps of data processing of raw sensor data to produce a urine flow measurement, according to an embodiment of the invention.DETAILED DESCRIPTIONIn one embodiment, shown in Fig. 1A and Fig. 1B, the device includes a wide-mouth funnel 100 designed for urine collection. The funnel may have a conical shape, but is not necessarily perfectly conical. It may have other shapes that are suitable to collect and guide urine into the device, i.e., a large opening at the top and small opening at the bottom. The funnel opening preferably is large enough for the patient to comfortably collect urine in a handheld manner. A bottom opening of the funnel is connected to the top of a transparent cylindrical barrel casing 120 which has a dual helical blade rotor 118 inside. The diameter of the funnel bottom opening is preferably greater than 5 mm to avoid urine accumulation in the funnel. The casing 120 has an upper cap 102 with central axial support pin 114 defining the rotation axis and mounting for the rotor 118. The casing 120 also has a lower cap 122 with a central axial support pin also defining the rotation axis and mounting for the rotor 118. The rotor is suspended along a central longitudinal axis using the axial pins protruding from the top and bottom caps. Low- friction interfaces are established using pairs of flat washers and O-rings on each end, minimizing mechanical resistance while ensuring fluid-tight operation. The bottom of the casing 120 has a slanted urine exhaust outlet 124. An upper O-ring 104 interfaces between the upper cap 102 and the barrel 120. A lower O-ring (not shown) interfaces between the lower cap 122 and the barrel 120.Embedded in or attached to the blades of the double-helical blade rotor are four neodymium N52 (1×1 mm) cylinder magnets 116 that serve as fiducials. Outside the casing 120 is a Hall effect sensor and other electronic components.Fig. 2A and Fig. 2B are cross-sectional schematics of the device, illustrating sensing of urine flow through the device. The urine 200 enters the top of the funnel 202 and flows down to the bottom opening of the funnel where it enters the top of the cylinder casing 204. Inside the cylindrical casing, the urine stream 212 is guided along the rotor blade surface 210 by the Coandă effect, which causes the stream to adhere to the curved helical blade surface as it flows. The movement of the stream on the surface of the blades applies a tangential force to the rotor, inducing rotor rotation.The rotation of the rotor is detected by the Hall effect sensor 208 positioned on the outer wall of the cylindrical housing. The Hall effect sensor detects the change in magnetic field due to the movement of the fiducial magnets 206 embedded in the rotor blades 210 and transduces this into an electrical signal. The electronics 214 are housed external to the cylindrical housing adjacent to the barrel. The electronics samples the sensor to produce raw sensor data. In one embodiment, the electronics performs pre-processing and processing to produce urine flow results. In other embodiments, the electronics transmits the raw data or pre-processed data to a smartphone for further processing, in which case the electronics is considered to be distributed electronics, encompassing the device and the smartphone electronics. The sensor is positioned on the barrel wall at the same axial height as the embedded magnets to ensure optimal magnetic signal detection during rotor spin. The two magnets are mounted symmetrically, one on each helical blade. The polarity of the magnets was selected to ensure an antiphase configuration.The Hall effect sensor can be digital or analog, but an analog sensor performs better when the urine flow rate is low. A Hall effect sensor is also not the only way to detect the rotation. Alternatively, a capacitive rotation speed sensor, inductive sensor or magnetoresistive sensor may be used. Optical or mechanical based sensors may also be used.The detection method used in the device takes advantage of the Coandă effect which causes the flowing urine stream to adhere to and be guided by the surface of a chiral rotor. When the stream is guided by the chiral rotor and flows between the wall of the barrel and the chiral rotor, it obtains angular momentum from the blade, and the reaction torque cause the rotor to spin. Note that the fluid guided between the surface of the rotor and inner wall of the barrel is important, so the chiral rotor design needs to ensure the smooth passage of fluid along the surface of the rotor and avoid early fluid detachment. This allows the device to operate even when the urine flow does not completely fill the cross-section of the barrel. Preferably, the rotor is a dual helical blade rotor, although it may have another chiral structure. The rotor preferably has two blades, although a triple or quadruple helical blade rotor is also possible. It is preferable in any case to have the number of blades different from the number of spokes on the cap inlet, so the rotor blades are not completely covered by the spokes on the cap inlet.The effectiveness of the Coandă effect in the device depends on the gap between the rotor and the barrel, which determines whether the urine jet remains attached to the rotor and the curved inner wall of the barrel. The separation between the rotor surface and the barrel wall, denoted w, preferably should satisfy a constraint based on the radius of curvature R of the inner wall of the barrel. To ensure jet attachment via the Coandă effect, the curvature-induced centrifugal force is preferably balanced by the pressure gradient generated across the gap. This leads to the approximate design constraint that w / R is less than a number selected in the range 0.01 to 0.25, depending on flow velocity and geometry.Additionally, the gap between the rotor and the barrel is preferably small enough for surface tension to maintain a continuous fluid bridge between the rotor and the inner wall of the barrel. Theoretical constraints based on the capillary length of water suggest that this gap should remain below 2.7 mm (e.g., a value of 1.8 mm) to prevent urine detachment during low flow states, particularly in scaled-up versions of the device.To ensure that the Coandă effect remains effective along the helical trajectory of the rotor, the helix preferably has a helical angle that is neither too shallow nor too deep. As illustrated in Fig. 2C, the helical angle is defined as the angle θ between the tangent of the helical path and the horizontal plane perpendicular to the rotor axis. A value of θ = 0° corresponds to a flat spiral (no axial rise), while θ = 90° corresponds to a vertical line (no azimuthal twist). If the helical angle is too small, corresponding to a shallow helix with a small axial pitch, the fluid tends to travel axially and may detach from the rotor blades 250, bypassing the intended spiral path. Conversely, if the angle is too large, the helix becomes nearly vertical and its surface curvature becomes too gentle to generate the lateral pressure gradient for Coandă attachment. Through empirical testing and geometric scaling, the inventors determined that a preferred helical angle lies within the range of 30° to 65°. As water flows through, the rotor is driven to spin, and magnets 252, 254 attached to the rotor blades allow sensing of the rotation. The magnets are oriented such that the surface of the North Pole or South Pole is tangential to the circumscribed circle of the double-helical blade rotor. Preferably, the weight of the magnets is sufficiently small that it does not significantly inhibit free rotation of the rotor. The vertical position of the magnet relative to the height of the rotor preferably leaves enough space to accommodate the sensor at the same position outside the barrel.ProcessingThrough high-speed imaging, the inventors have discovered a high correlation between the spinning rate of the helix-shaped rotor and the flow rate of the urine, provided the urine stream remains attached to the rotor blade. The interface between the rotor and the flat washer around the pin on the bottom is preferably designed in a way that permits spinning at low urine flow rate while preventing it from freely spinning after urine flow has stopped.Because the rotor spin in this design correlates directly with flow rate, we can objectively and accurately determine the urinary flow rate over time and the voiding pattern associated with different diseases, achieving the goal of diagnosing urinary diseases.As shown in Fig. 3, the analog output from the sensor 300 is sampled at 60 Hz or higher by a microcontroller 302, powered by a compact 3V, 1A battery module 304. A Bluetooth module 306 wirelessly transmits the signal to a smartphone 308 using an nRF Connect interface. The smartphone 308 stores and processes the data. Alternatively, or in addition, the smartphone can transmit the data, or pre-processed data, via an internet connection to a server 310 where processing can be performed and urine flow results made available to a medical professional. Alternatively, the electronics in the device itself can perform on-board processing and communicate or display results.To measure urine flow rate and / or other related parameters, the sensor data from the Hall sensor is denoised, and the cumulative rotation within every 0.5 or 1 sec is calculated to create an output with comparable time interval to the typical sampling rate of standard uroflowmetry. To calibrate the data, simultaneous detection of Hall sensor signal and conventional measurements while performing either standard uroflowmetry or other scale based method using water or urine is performed. The rotation of the device every 0.5 or 1 s can be plotted against the weight changes every 0.5 or 1 s on the scale. From the data we can identify the minimal flow rate that can cause the rotation in our device, and any data below that threshold will not be used for regression. Data above the threshold will be calibrated with data from scale using appropriate regression methods. After calibrating the rotation with scale-based measurement method either using water or urine, the urine flow rate can be calculated. Voided volume can be calculated as the integration of the urine flow rate. Other useful clinical outputs, such as maximum flow rate, average flow rate, time to maximum flow, and flow time, can also be calculated.A more detailed outline of the processing is shown in the signal processing pipeline of Fig. 4. The raw signal 400 from the Hall sensor first is re-centered to have zero mean and passed through a 20th-order Butterworth low-pass filter 402 with a 49 Hz cutoff frequency, selected to retain the rotor's physical dynamics while removing high-frequency noise. Spurious peaks were algorithmically removed 404. These included unidirectional peaks (i.e., deflections that lacked a zero crossing) and peaks whose magnitude was less than 45% of the full signal range relative to baseline. The result is denoised data 406.A Hilbert transform 408 is then applied to the denoised data obtain the analytic representation of the waveform. The phase of the analytic signal was unwrapped to ensure continuity across ±π discontinuities, producing phase data 410. Smoothing with Savitzky-Golay filter 412 and numerical differentiation with respect to the actual timestamps 414 are then applied to obtain instantaneous angular velocity data 416. Finally, using a calibration curve 418, the angular velocity is converted to a urine flow rate value 420.The calibration curve 418 is obtained by an initial calibration procedure using water as a surrogate fluid to simulate urination under controlled flow rates. A speed-variable peristaltic pump generated steady flows at discrete rates from 20 to 300 rpm in 10 rpm increments. At each flow rate setting, water was directed through the device. The average angular velocity of the rotor (in rad / s) was measured across the full duration of flow using the signal processing pipeline described above. In addition, the flow rate was measured using a standard clinical uroflowmeter.To convert angular velocity into urine flow rate, we fit the data using a thresholded linear model, y= a+ b•(x−k)·H(x−k), where y is the measured angular velocity(rad / s), x is the flow rate (mL / s) measured by the standard uroflowmeter, H is the Heaviside step function, and a, b, k are fitting parameters. This form accounts for an empirical threshold k below which the rotor remains stationary despite low flow, reflecting the minimum flow rate needed to overcome friction and initiate rotation.Calibration was performed across three independently assembled devices. For each device, triplicate measurements were taken at each flow rate. The resulting best-fit parameters were a=1.019 rad / s, b=1.006 rad / mL, k=2.378 mL / s, with a coefficient of determination R2 = 0.749.This calibration function is then used in the real time processing pipeline, described earlier, and enables reliable estimation of urine flow rate from the rotor's angular velocity. Specifically, the urine flow rate is calculated from the rotor's angular velocity using the inverse of the calibration model. Specifically, the flow rate x (mL / s) is computed from the angular velocity y (rad / s) as x = H(y-a)[ (y−a) / b + k]. This expression accounts for the empirically determined minimum angular velocity a, below which no flow is assumed. The Heaviside function H(y-a) ensures that flow rates are only reconstructed when the rotor motion exceeds this threshold.Example device materials and dimensionsVarious materials may be used for the components of the device, as long as they are waterproof, rustproof, and resistant to the acidity of urine, e.g., stainless steel or plastic. The components can be made with 3D printing, injection molding, or any appropriate manufacturing methods. For the dual helical blade rotor part and its associated components (such as O-rings, washers, and caps), a fine surface polish is used to reduce friction.The device can be scaled to various sizes and dimensions. In one specific example implementation of the device, the barrel inner diameter is larger than the circumscribed circle of the rotor by 1.82 mm, corresponding to a gap w of 0.91 mm on each side. This dimension ensures sufficient curvature for Coandă effect adherence without introducing excessive drag or rotor misalignment. In this specific implementation, the funnel has a wall thickness of 1 mm, rim of 4 mm, and a height of 67 mm. The top opening has a diameter of 82.98 mm, and the funnel tip has a diameter of 9.31 mm. In this specific implementation, the cap design for both upper and lower caps has a wall thickness of 1 mm, outer diameter of 23 mm. On its interface with the funnel, it has an opening with diameter of 11.5 mm. Each cap has an M22x1 threaded feature that allows it to be connected to the barrel, but it does not have to be this specific threading, as long as they can be held together. The cap has an inner elevation around the entry hole, with three spokes converge in the middle, forming a central platform. On top of the platform is a 1 mm pin with height of 6.6 mm that serves as the rotational axis of the double-helical blade rotor. In this specific implementation, there is a 2 mm-wide, 0.5 mm-deep indentation surrounding the pin, which serves as the space for the flat washer. The height of the inner elevation, the height of the pin, the number of the spokes forming the central platform are all adjustable as long as the dimension fits for the other components and allows the double-helical blade rotor to slide a little bit vertically (rather than being held tight on both ends). The width and the depth of the indentation around the pin is also adjustable, as long as it is slightly smaller than the flat washer and allows the helical blade rotor to be elevated above the central platform. In this specific implementation, there is an O-ring of outer diameter 21 mm and inner diameter of 15.5 mm between the barrel and the cap. The O-ring can be made out of any rubber material as long as it resists the acidity of urine. In this specific implementation, the flat washer design has an outer diameter of 2.5mm, inner diameter of 1.4mm and a thickness of 0.33 mm. It can be made of any material as long as it has a smooth polished surface and resist the acidity of urine. There are two washers on each side, four in total. The washers are important to reduce friction of the dual helical blade rotor. In this specific implementation, the barrel design has an inner diameter of 16.52 mm and a total height of 72.2mm. There is a transition zone of 12.6 mm of both ends of the barrel, which fit into the cap through the M22x1 thread and is cushioned by the O-ring. The barrel height is adjustable as long as it allows the double helical blade rotor to slide a bit on the vertical axis. The barrel has an outer diameter of 22 mm. It can be made of any plastic material as long as it resists the acidity of urine and is waterproof. In this specific implementation, the urine exhaust design has an outer diameter of 15.28 mm and inner diameter of 13.28 mm. The upper part of the exhaust is a full cylinder of height 20mm. The lower part of the exhaust also has a height of 20 mm, and is a cylinder cut half diagonally to create a slanted opening. The dimension of the urine exhaust is also adjustable, as long as it allows smooth exit of the urine from the lower cap, provide enough distance to prevent urine from contaminating the electronics, and guide the urine exhaust smoothly. In this specific implementation, the dual helical blade rotor has a height of 54.19 mm and a pitch of 63.3 mm, with 13 spokes in total. The end of the double-helical blade rotor has an opening with diameter of 2 mm to accommodate the pin on the cap. Around the hole is an indentation of diameter 3.08 mm and depth of 0.8 mm. Within that indentation fits an O-ring of outer diameter 3 mm and inner diameter 1.2 mm. The rotor is thus interfaced with the pin on the cap by one O-ring and two flat washers on each side. The dimension of the double helical blade rotor does not have to be exact, as long as the structure is chiral, fits within the barrel with a gap of around 0.9 mm, and is resistant to the acidity of urine. In this specific implementation, a pitch of 63.3 mm and a helix diameter along the center of the spoke of 12.7 mm corresponds to a helical angle of 57.6°. The total number of turns is determined by the pitch and the axial length of the rotor. In this specific implementation, the magnets are attached to the double-helical blade rotor at the height 11.5 mm below the top surface of the rotor.ConclusionEmbodiments of the present invention a timely, accurate, compact, user-friendly, and non-invasive solution for evaluating patients with LUTS, comparable to standard uroflowmetry. Its integration into routine urological clinical practice holds significant promise for enhancing diagnostic convenience and enabling home-based monitoring to support telemedicine. Furthermore, it facilitates real-time tracking of voiding patterns, which may assist in timely medication adjustments and provide early warnings for patients with poor voiding function to seek emergency care, thereby preserving renal function. By improving treatment adherence and enabling earlier detection and intervention, the device has the potential to reduce the need for invasive procedures such as surgery and substantially lower healthcare costs.

Claims

1. A uroflowmetry device comprising:a) a funnel;b) a cylinder attached to a bottom end of the funnel;c) a helical blade rotor, wherein the helical blade rotor is positioned within the cylinder and adapted to freely rotate within the cylinder along a longitudinal axis of the cylinder;d) fiducials fixed to the helical blade rotor;e) a sensor fixed to the cylinder and adapted to sense movement of the fiducials as the helical blade rotor spins;f) a microprocessor connected to the sensor that computes a urinary flow rate from a sensed rotation of the helical blade rotor.

2. The uroflowmetry device of claim 1, wherein a gap between the cylinder and the helical blade rotor is sufficiently small to ensure urine flow by the Coandă effect and avoid fluid detachment as urine flows along a surface of the helical blade rotor.

3. The uroflowmetry device of claim 1, wherein a pitch of the helical blade rotor is sufficiently small to ensure urine flow by the Coandă effect and avoid fluid detachment as urine flows along a surface of the helical blade rotor.

4. The uroflowmetry device of claim 1, wherein a pitch of the helical blade rotor corresponds to a helical angle in the range of 30° to 65°.

5. The uroflowmetry device of claim 1, wherein a pitch of the helical blade rotor corresponds to a helical angle of 57.6°.

6. The uroflowmetry device of claim 1, wherein the helical blade rotor has a height of 54.19 mm and a pitch of 63.3 mm, with 13 spokes.

7. The uroflowmetry device of claim 1, wherein the helical blade rotor fits within the cylinder with a gap of around 0.9 mm.

8. The uroflowmetry device of claim 1, wherein the sensor is a Hall effect sensor, a capacitive sensor, inductive sensor, magnetoresistive sensor, optical sensor, or a mechanical sensor.

9. The uroflowmetry device of claim 1, wherein the helical blade rotor has blades that form at least half of a full turn.

10. The uroflowmetry device of claim 1, wherein the helical blade rotor has blades that form at least three quarters of a full turn.

11. The uroflowmetry device of claim 1, wherein the helical blade rotor is a dual helical blade rotor.

12. The uroflowmetry device of claim 1, wherein the microprocessor is connected to the sensor via a wireless communication link.

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