Optimal System Design for an Implantable CW Doppler Ultrasonic Flowmeter

A totally implantable telemetry system utilizing custom micropower monolithic integrated circuits has been developed to measure instantaneous pulsatile blood flow in the major arteries of animals. The device utilizes the Doppler effect at ultrasonic frequencies to achieve a flowmeter possessing small size and weight, low power consumption, inherent accuracy, and long-term stability. The integrated circuit electronics package occupies a volume of 3.8 cc and requires a power consumption of 10 mW from a single 135 volt mercury cell. The volume of the entire implantable flowmeter package is less than 36 cc. As a micro-miniature radio-telemetry system, the flow-meter can be totally implanted within the body, thereby eliminating the need for wires penetrating the skin, a serious problem with "back-pack" flowmeters due to danger of infection. The implantable flow-meter system provides a new and necessary tool for accurate quantitative measurements in the study of cardiovascular disease. It has been used in the study of transplanted heart rejection to monitor blood velocity in the major arteries of doB     

A Servo-Controlled, Whole Body, Blood Perfusion System as a Pressure/Flow Clamp

To study the peripheral vascular system of anesthetized dogs, a whole body, blood perfusion system was developed to provide 1) a nonpulsatile output of 2) constant pressure (0-300 mm Hg), or 3) constant flow (0-3 liters/minute), or 4) any output characteristic between these extremes, and 5) the output controllable from a voltage command signal. Output is determined by pneumatic pressure, adjusted by a servo valve from the error signal, which drives the blood from a reservoir into the animal's aorta. The error signal is derived from the difference between either a flowmeter or pressure-gage signal and an adjustable set-point voltage, or any combination of these signals. Response time is less than 1 sec. Heat and gas exchange are provided by a double-walled disk oxygenator. Plasma hemoglobin accumulation is typically 0.2 mg/ml hour.     

An intelligent multiplexer/driver integrated circuit for animplantable multichannel blood flowmeter

A custom CMOS integrated circuit that extends the current implantable single-channel ultrasonic pulse Doppler blood flowmeter to three channels is discussed. By operating on a single 2.7-V battery with three existing custom bipolar ICs, the integrated circuit serves as an RF command receiver, controls the channel-multiplexing sequence, and multiplexes the piezoelectric transducers. A round-trip channel isolation of 38 dB is achieved with a novel transducer-multiplexing circuit that employs three on-chip power transistors for 6-MHz transducer excitation. Each power transistor is capable of switching a current of 200 mA with an on-resistance of 3 Ω and transition times of 10 ns. The power consumption in the implanted portion of the three-channel flowmeter is only 0.8 mW higher than the 30 mW in the single-channel flowmeter     

Design and Construction of a Pulsed Ultrasonic Air Flowmeter

The construction and specific function of a new ultrasonic flowmeter are described. The mean velocity of the respiratory air flow is calculated by measuring the transit times of short ultrasonic pulse-trains simultaneously transmitted upstream and downstream at a 650 Hz rate. The flowmeter system consists of a control unit and a separate flowhead. The former includes the power supplies, a controlling microprocessor, most of the signal processing circuitry, and three analog outputs for flow, volume, and temperature, respectively. The flowhead contains the respiratory tube with a constant circular cross section (length 90 mm, diameter 20 mm, dead space 35 cm3), a fast temperature sensor, two electronic circuits for processing of flow and temperature data, and a sound transmission channel with two capacitive ultrasonic wide-band transducers. This respiratory air flowmeter is extremely fast (response time 1-2 ms) and accurate, with low noise (below 9ml/s), with a wide flow range (bidirectional from 0 to 9 l/s) and with a linear frequency response up to 70 Hz.     

Integrated circuits for a bidirectional implantable pulsed Doppler ultrasonic blood flowmeter

The application of integrated circuits in medical implants and the complexity of these implants have increased at a rapid pace in the past few years. The need, however, still exists for a highly accurate and stable telemetry system for the measurement of blood flow. Two custom-designed ICs have been realized to resolve this problem. These ICs form the heart of a totally implantable pulsed Doppler ultrasonic bidirectional blood flowmeter; one circuit performs the basic timing functions, and the second implements low-level linear signal processing. For a small implanted package (3.8/spl times/2.8/spl times/0.8 cm/SUP 3/), these ICs must meet the stringent requirements of low-voltage operation (2.2-2.8 V), low power (<40 mW), high stability (short-term timing jitter <50 ppm), and the minimum of external components. Using a quadrature direction detecting technique, the circuits sense both positive and negative flow and produce a multiplexed telemetry signal. The approach used minimizes parts count and power drain and maximizes channel-to-channel matching in the multiplexed signal.     

Design and initial evaluation of an implantable sonomicrometer and CW Doppler flowmeter for simultaneous recordings with a multichannel telemetry system

We have developed a sonomicrometer and continuous wavelength (CW) Doppler flowmeter for a multichannel telemetry system. These developments will enable us to measure ventricular dimension and coronary artery blood velocity, which are valuable parameters to characterize sudden cardiac death (SCD) in ambulatory animal models of ventricular arrhythmias. The design goals for the sensors were accuracy, low power consumption, small size and compatibility with each other. The circuits were designed successfully and tested simultaneously in vivo. The CW Doppler flowmeter draws 9 mA and the sonomicrometer draws 28 mA on a 5-V supply. The ability to measure heart dimension and blood velocity will add significantly to our understanding of the sequence of events leading up to spontaneous sudden cardiac death.     

Low power integrated circuits for an implantable pulsed Doppler ultrasonic blood flowmeter

Describes two custom integrated circuits which were developed for an implantable pulsed Doppler ultrasonic blood flowmeter. Prime design goals were a minimum circuit volume, minimum power consumption, and operation at low supply voltages. The first of the two IC's performs system timing functions and produces the ultrasonic transmit burst. It can deliver up to 40 mW of peak output power at 50 percent efficiency and requires 3.7 mW standby power. The second IC, containing an RF amplifier, mixer and output amplifier, provides 54 dB conversion voltage gain for an 0.8 MHz bandwidth centered at 5.8 MHz, <3 dB noise figure, a dynamic range of 40 dB, and 1 /spl mu/s recovery time from a 1 V overload. This chip requires 2.7 mW power input.     

基于TDC-GP2的时差式超声流量计的设计

为实现流体流量测量高精度和低功耗的设计目的,采用TDC-GP2高精度低功耗测时模块,设计了一种基于ATmega32的时差式超声流量计。通过实验测量管径为20mm的管道中的家用自来水流量,得到系统测量精度为±1%,LCD上动态显示瞬时和累计流量以及电池电量等参数,同时可以通过RS 232与外部通信,便于大规模应用时由上位机对信息统一管理。     

A channel unit signal controller for shared codec D-type channel banks

The channel unit signal controller is a 2.56 mm/spl times/2.56 mm beam-leaded silicon integrated circuit fabricated using the complementary bipolar integrated circuit (CBIC) technology with buried injector logic (BIL). The circuit handles the distribution of signals within a channel unit of a digital telecommunications system. Several diverse circuit functions are incorporated on this device including high-speed emitter-coupled logic, lower speed buried injector logic. JFET switches, high-speed pulse amplifiers to drive the JFETs, a voltage limiter, and a comparator circuit. The channel unit signal controller is described from system and circuit points of view and the CBIC/BIL process is described.     

Micropower integrated circuits for an implantable bidirectional blood flowmeter

The measurement of bidirectional bloodflow on a chronic basis is of critical importance in research on cardiovascular and pulmonary diseases. An implantable bidirectional Doppler ultrasonic bloodflow system was designed to satisfy this need. The system utilized quadrature detection to provide the directional information and multiplexing to transmit the quadrature signals over one FM telemetry link. A new family of three 1 V micropower bipolar integrated circuits were designed to implement the RF amplifiers, square law detectors, /spl plusmn//spl pi//4 phase shifters, audio amplifiers, a multiplexer, and the FM transmitter required for this system. An implanted system was used to measure pulsatile bidirectional bloodflow on a canine descending aorta. The results compared well with those in the literature and with a percutaneous EM flowmeter.     

Theoretical Analysis of the CW Doppler Ultrasonic Flowmeter

The widespread application of ultrasonic techniques for the measurement of pulsatile blood flow has been hampered by the lack of a detailed theoretical understanding of the Doppler ultrasonic flowmeter. A general model for the Doppler flowmeter based upon stochastic considerations of the scattering of ultrasound by blood is introduced in this paper. The model characterizes the back- scattered ultrasound as a Gaussian random process and the expression for the autocovariance function is derived. For the CW Doppler flowmeter, the power spectral density function is computed, and its significance is emphasized: measurement of blood flow velocity corresponds to estimation of the average frequency of the Doppler power spectrum.     

Integrated optoelectronic probe including a vertical cavity surface emitting laser for laser Doppler perfusion monitoring

An integrated optoelectronic probe with small dimensions, for direct-contact laser Doppler blood flow monitoring has been realized. A vertical cavity surface emitting laser (VCSEL), and a chip with photodetectors and all necessary electronics are integrated in a miniature probe head connected to a laptop computer. The computer sound processor is utilized for acquisition and digital signal processing of the incoming Doppler signal. In this paper, the design of the laser Doppler perfusion monitor is described and its performance is evaluated. We demonstrate our perfusion monitor to be less sensitive to subject motion than a commercial fiber-optic device. For medium and high perfusion levels, the performance of our integrated probe is comparable to the fiberoptic flowmeter containing a normal edge-emitting laser diode. For very low perfusion levels, the signal-to-noise ratio of the fiber-optic device is higher. This difference can mainly be attributed to the shorter coherence length of the VCSEL compared with the edge-emitting laser diode.     

In Vivo Measurement of Brain Blood Flow in the Cat

A technique is described for measuring regional blood flows in the brain of the cat. The measuring system is based on the principle of photoelectric plethysmography, a method commonly used to measure skdn blood flow. To miniaturize the photoelectric flow probe to a size compatible with cerebral insertion, a light emitting diode (LED) was used as the light source and a photo-Darlington array was used as the photodetector, the entire structure being imbedded in the tip of a 22 gauge needle. To test the flow needle, blood flows were measured in the cerebrum and hypothalamus of the cat during nembutal infusion and CO2 breathing and were then compared to the blood flow measured by an electromagnetic flowmeter placed on the carotid artery. The results of these experiments showed the feasibility of using an indwelling photoelectric flow needle for measuring regional blood flows in the cat brain.     

一种医用智能型氧气流量计设计与实现

针对医院现有吸氧系统中金属浮球氧气流量计阀门手柄旋转角度和流量的对应关系,通过对手柄旋转角度进行编码,提出了一种基于单片机的医用智能氧气流量计的设计思想与实现方法,对病人吸氧时氧气流量和总吸氧量进行记录。实际应用表明,这种方法简单方便、安全可靠地解决了按吸氧量计费的问题。     

Chip-Scale Integration of Data-Gathering Microsystems

Integrated microsystems merging embedded computing with sensing and actuation are poised to dramatically expand our ability to gather information from the nonelectronic world. Examples include a microassembled multichip electronic interface to the brain, an integrated electrofluidic gas chromatography system for environmental monitoring, and a wireless intra-arterial microsystem for pressure and flow measurements. In general, such microsystems will consist of a few chips, integrated in generic platforms that are customized for a given application by the sensors selected and by software. This paper illustrates this approach with a 0.15-cm/sup 3/ multisensor microsystem for autonomously sensing and storing environmental and biological data. The microsystem is formed using on-board pressure/temperature/humidity sensors, off-board strain gauges and neural/EMG electrodes, a custom sensor-interface chip, a mixed-signal microcontroller, and a nonvolatile memory. These components allow the acquisition and storage of multidomain data at low power levels (< 50 /spl mu/W reading capacitive sensors at 1 Hz). The system is programmable in gain (0.4-3.2 mV/fF), offset (10b), accuracy (14b), and sampling rate (0.1 Hz-10 kHz) and is integrated in a micromachined silicon platform that implements through-wafer interconnects, solder-based microconnectors, and recessed cavities for chip-stacking. The microsystem is realized in 9.5 mm/spl times/7.6 mm/spl times/2.0 mm (0.15 cm/sup 3/) (< 0.5 cm/sup 3/ with a lithium battery).     

Clinical applications of the nuclear magnetic resonance (NMR) limb blood flowmeter

The principles of nuclear magnetic resonance (NMR) have been employed in the design of noninvasive blood flowmeters. This paper describes an NMR limb blood flowmeter which has been used in statistical studies of normal volunteers, and diagnostically on patients with a variety of circulatory problems. Quantitative blood flow measurements are comparable to those obtained by other methods such as indicitor dilution, radioactvive clearance, and water, strain gauge, capacitance, and air plethysmography.     

Nuclear magnetic resonance and transcutaneous electromagnetic blood flow measurement

Static and alternating magnetic fields are employed in blood flowmeters using nuclear magnetic resonance (NMR) principles and electromagnetic induction by a moving conductor (TEM). Both techniques require high steady magnetic fields, obtained either from permanent magnets or from electromagnets. A relatively homogeneous magnetic field is needed for NMR, but, though important for calibration, homogeneity is not critical for TEM. NMR is more complex than TEM since it requires radio-frequency and audio-frequency magnetic fields. However, the TEM method requires surface electrodes in contact with the skin, or needle electrodes placed subcutaneously, whereas NMR is contactless. The NMR flowmeter can be calibrated directly, but appropriate and approximate models must be assumed and then solved by computer to quantify blood flow by the TEM flowmeter. Flow in individual vessels is measured a priori in the TEM flowmeter by virtue of the assumed models. To measure flow in individual vessels by NMR, a scanning or ranging method is required, which logically leads to blood flow imaging. The levels of steady, radio-frequency, and audio-frequency magnetic fields used in the two types of flowmeters are low enough so as not to cause any apparent stimulus to human volunteers and patients tested.     

A 2.45-GHz Near-Field RFID System With Passive On-Chip Antenna Tags

The design of a 2.45-GHz near-field RF identification (RFID) system with passive on-chip antenna (OCA) tags is very challenging as the efficiency of RF power conversion is very low. It poses multidisciplinary research challenges such as ultra-low-power circuits design, semiconductor process technology, and integrated antenna design. This paper describes the designs of such an RFID system, the reader, and OCAs, as well as the passive tag integrated circuits in detail. The passive tag chip with 128-bit nonvolatile memory has been realized using CMOS 0.13- technology. The OCA is fabricated on top of the chip using post-processing technology. The complete RFID tag with an integrated OCA is smaller than 0.5- with a thickness of 0.1 mm. With the reader generating an output power of 0.5 W, the RFID system is able to perform with RF read/write functions at a distance of .     

The Performance of the Ultrasonic Flowmeter in Complex Velocity Profiles

The principle of operation of the ultrasonic flowmeter, detecting phase shifts or pulse transit times, is examined. It is shown both theoretically and experimentally that the sensitivity of the flowmeter depends on the fluid velocities averaged along the path of the ultrasound between the transducers. The instrument therefore overestimates the net fluid velocity by 33 percent in case of steady laminar flow and by approximately 7 percent in case of steady turbulent flow, provided the ultrasound traverses the entire lumen of the (cylindrical) vessel. The signal obtained in case of oscillatory flow generally is larger in amplitude than and lagging in phase behind the true flow. The errors are between 0 and 33 percent and between 0 and 7°, respectively. The effect of this on natural blood flow signals is discussed in detail. It is concluded that the flowmeter detects the waveform of aortic flows with a fidelity which should be satisfactory in most cases.