Abstract: A system and method for identifying a disruption of a flow from an extracorporeal circuit to a patient circulatory system, such as a venous needle dislodgement or an access-bloodline separation, is based on flow rate data of the extracorporeal circuit. A patient contribution to the flow rate data can be identified as a harmonic and monitored to assess the presence of the disruption. The system can identify an inharmonic change, such as a spike, in the flow rate in the extracorporeal circuit, wherein the inharmonic change can be used alone or in conjunction with the identified harmonic to assess the existence of the disruption. The system can employ the spike in a blood flow rate as well as a spike in a dialysate flow rate fluidly connected to the extracorporeal circuit, wherein the spike can be used to identify the disruption.

Abstract: A system and method for measuring fluid flow and pressure in a flexible conduit is disclosed. An embodiment of the system and method uses an ultrasound sensor for determining volume of flow and a tonometric system for determining pressure along a common length of a flexible conduit.

Abstract: A surgical cassette have a rigid fluid channel formed into a rigid plastic component or housing. The piezoelectric crystals of an ultrasonic flow meter are positioned on one side of the fluid channel. The side wall of the fluid channel opposite the piezoelectric crystals is exposed to fluid in the flow channel on its interior side and is exposed to ambient air on its exterior side. The interface between the wall and the air acts as an acoustic reflector for the operation of the ultrasonic flow meter.

Abstract: A transcutaneous energy transfer system with subcutaneous non coupled coils is used to transmit power and signals to an implanted biological support device or sensor, such as a flow sensor for measuring relatively low flow rates, such as hydrocephalic shunt flow. The flow sensor is configured to convert a shear wave generated by a transducer to a longitudinal wave at the interface of a signal pathway and the flow, wherein the longitudinal wave travels parallel to the flow and exits a flow channel to convert to a shear wave which intersects a second transducer. The transcutaneous energy transfer employs a pair of inductive coupling coils, wherein the coils are disposed in zero coupling orientation which can include a perpendicular orientation of corresponding coil axes.

Abstract: A method is provided for employing a transit time ultrasound sensor, wherein the sensor can be used for the measurement of liquid flow in a conduit, the sensor having an acoustic path formed of materials matched in ultrasound properties to a flow under test, and designed to conform to the shape of the conduit. The transit time ultrasound sensor can be configured as a clamp on device, wherein the conduit walls are constructed from such an ultrasonically-matched material. Alternately, the transit time ultrasound sensor can be employed in a perivascular configuration, wherein the ultrasonically-matched material is operably intermediate the blood vessel and the sensor.

Abstract: A method and apparatus for determining an initial flow rate in a conduit is disclosed. A known change is made to the flow to be measured, resulting changes (or values corresponding to these changes), or relative changes in the flow to be measured are monitored and the initial flow in the conduit is calculated from the value of the known change and monitored changes. Devices to practice the method include catheters having one or two sensors and one or two sites for introducing the volume change.

Abstract: A method and apparatus for determining an initial flow rate in a conduit is disclosed. A known change is made to the flow to be measured, resulting changes (or values corresponding to these changes), or relative changes in the flow to be measured are monitored and the initial flow in the conduit is calculated from the value of the known change and monitored changes. Devices to practice the method include catheters having one or two sensors and one or two sites for introducing the volume change.

Abstract: A transit time ultrasound sensor is employed for the measurement of liquid flow in a conduit, the sensor having an acoustic path formed of materials matched in ultrasound properties to the flow under test, and designed to conform to the shape of the conduit. The sensor can be configured as a clamp on device, wherein the conduit walls are constructed from such an ultrasonically-matched material. Alternately, in a perivascular configuration, the ultrasonically-matched material is operably intermediate the blood vessel and the sensor.

Abstract: A method and apparatus for determining an initial flow rate in a conduit is disclosed. A known change is made to the flow to be measured, resulting changes (or values corresponding to these changes), or relative changes in the flow to be measured are monitored and the initial flow in the conduit is calculated from the value of the known change and monitored changes. Devices to practice the method include catheters having one or two sensors and one or two sites for introducing the volume change.

Abstract: A method and apparatus for determining an initial flow rate in a conduit is disclosed. A known change is made to the flow to be measured, resulting changes (or values corresponding to these changes), or relative changes in the flow to be measured are monitored and the initial flow in the conduit is calculated from the value of the known change and monitored changes. Devices to practice the method include catheters having one or two sensors and one or two sites for introducing the volume change.

Abstract: A transit time ultrasound sensor is employed for the measurement of liquid flow in a conduit, the sensor having an acoustic path formed of materials matched in ultrasound properties to the flow under test, and designed to conform to the shape of the conduit. The sensor can be configured as a clamp on device, wherein the conduit walls are constructed from such an ultrasonically-matched material. Alternately, in a perivascular configuration, the ultrasonically-matched material is operably intermediate the blood vessel and the sensor.

Abstract: The present invention provides a method for measuring the blood flow rate within an A-V shunt via indicator dilution techniques. Unknown flow resistance within the A-V shunt are addressed by adjusting a measured flow rate to provide a flow rate within a predetermined margin of error. The calculated flow rate can be rejected based upon flow conditions of the introduced indicator. Different indicator introduction rates can be used to enhance accuracy of the measured flow. The indicator flow path can include a flow restrictor to limit the flow rate of the indicator to below a predetermined value.

Abstract: The present invention provides a method and apparatus for measuring the blood flow rate within an A-V shunt via indicator dilution techniques. Unknown flow resistance within the A-V shunt are addressed by adjusting a measured flow rate to provide a flow rate within a predetermined margin of error. The calculated flow rate can be rejected based upon flow conditions of the introduced indicator. Different indicator introduction rates can be used to enhance accuracy of the measured flow. The indicator flow path can include a flow restrictor to limit the flow rate of the indicator to below a predetermined value.

Abstract: A transducer array and excitation circuitry for producing ultrasonic waves in a controlled pattern and for causing the waves to be scanned along the array. The array comprises a plurality of transducer elements coupled to each other in such a way as to produce a desired wave pattern when selected elements are activated. The array may be constructed from plural transducer elements or from a single plate of transducer material comprising a plurality of elements that can be individually activated, the plural elements being intercoupled to produce the desired wave pattern. The arrangement is such that a minimum number of electrical connections to the transducer elements are required to create the desired wave pattern and to scan that pattern across the face of the array.

Abstract: Methods and apparatus for calibrating terminated ultrasonic electroacoustic transducers are disclosed. The transducers are excited by a driving signal to emit an ultrasonic acoustic wave, which wave is received either by the same transducer after reflection or by a second transducer to produce an output signal. The driving signal and output signal are supplied to measuring circuitry deriving transducer performance calibration signals, such as transducer gain, transducer sensitivity, acoustic field pressure and intensity. These performance characteristics of the transducer are measured in absolute terms under conditions of actual termination. The transducer characteristics are obtained in order to determine the acoustical performance of transducers useful in biomedical and other fields.

Abstract: Methods and apparatus for calibrating terminated ultrasonic electroacoustic transducers are disclosed. The transducers are excited by a driving signal to emit an ultrasonic acoustic wave, which wave is received either by the same transducer after reflection or by a second transducer to produce an output signal. The driving signal and output signal are supplied to measuring circuitry deriving transdBACKGROUND OF THE INVENTIONThe invention described herein was made in the course of work under a grant or award from the Department of Health, Education and Welfare.

Abstract: An apparatus and method for direct measurement of the volume flow of fluids through a tube, using an interferometric transit time technique is disclosed. First and second transducers for producing and receiving waves which are capable of being modified by the flow of the fluid in the conduit are positioned so that the conduit is fully and evenly illuminated by the waves. The transducers are located with respect to the conduit so that there will be a component of fluid flow along the axis of the illuminating wave beam. Means are provided to first activate one transducer to transmit waves while the other is in a receive mode and thereafter to place the second transducer in a transmit mode while the first is switched to its receive mode. The received waves are converted to corresponding electric signals by the corresponding transducers, and these signals are periodically sampled and stored for comparison.