Adaptive control of closed-circuit anesthesia

Closed-circuit anesthesia (CCA) is more economical and ecologically safer than open circuit anesthesia. However, gas concentrations are more difficult to control. Computer control of CCA has been proposed to facilitate its use. Past efforts have either been limited to the control of anesthetic gas concentrations or apply only to a small group of patients. This paper describes a comprehensive control system applicable to a large class of patients. This system controls the end-tidal oxygen and anesthetic gas concentrations, and the circuit volume. The CCA process was modeled by writing mass balance equations. Simplifying assumptions yielded a bilinear single-input-single-output model for the anesthetic gas concentration and a bilinear multiple-input-multiple-output model for the circuit volume and oxygen concentration. One-step-ahead controllers were used to control these two subsystems. Simulations showed that the control performance was most sensitive to the gas uptakes. Three independent, least-mean-squares estimation schemes were implemented to estimate the uptakes of oxygen, nitrous oxide, and anesthetic gas. These estimates were used in the control law and resulted in explicit adaptive control. The performance of the adaptive controller was compared to that of a fixed controller (with precalculated gas uptakes) in five animal experiments. The adaptive controller performed better than the fixed controller in all cases. The most significant difference was in the anesthetic gas response time 3.6 +/- 0.70 min for adaptive control and 7.04 +/- 5.62 min for fixed control. The adaptive controller was also robust with respect to variations in the system parameters such as the functional residual capacity, leak, deadspace and gas uptakes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Instrumentation for Measuring Continuous Oxygen Consumption of Surgical Patients

A system has been developed for continuously monitoring the oxygen consumption (V02) of surgical patients. A replenishment technique is used whereby the oxygen removed by the patient from a closed rebreathing circuit is replaced. This is accomplished using a feedback-controlled pump to add oxygen at a rate necessary to maintain a constant inspired oxygen percent. A second feedback loop adds nitrous oxide to the circuit at a rate equal to the patient's nitrous oxide uptake rate, thus maintaining a constant circuit volume. These two feedback loops constitute a system to monitor oxygen and nitrous oxide uptake during nitrous oxide anesthesia. The instrument responds to a step change in V02 in 4 min. System accuracy has been shown to be ±6% in an in vivo comparison, the major error resulting from oxygen sensor or electronics dnift, leaks in the system, or changes in residual volume. The record of a surgical patient's VO2 while under balanced anesthesia shows a practical application of the system.     

Piezoelectric Sorption Anesthetic Sensor

The piezoelectric sorption detection method is evaluated for use in construction of an inexpensive, rugged, compact, and fast sensor for measuring the concentration of inhalation anesthetics. 10 MHz quartz crystals were coated with various substances and their frequency shifts measured upon exposure to varying concentrations of halothane, enflurane, and nitrous oxide. For a silicone rubber coating, the response was found to be linear with concentration, with sufficient signal to allow resolution to approximately 0.05 volume percent for either halothane or enflurane, or to 4 percent for nitrous oxide. The devices were sensitive to halothane and enflurane in proportion to their anesthetic potencies, but were slightly less sensitive to equally potent concentrations of nitrous oxide. They were insensitive to CO2 in the physiologic range, but had a significant response to water vapor. The response time of the detector was primarily a function of washout of the sensing chamber. At a 200 ml/min sample flow rate, the time constant was approximately 100 ins. It is concluded that this detection method is suitable for a variety of applications in anesthesia, although, with the coatings presented here, control of or correction for sample humidity is required.     

The Use of the Time Domain Analyzed EEG in Conjunction with Cardiovascular Parameters for Monitoring Anesthetic Levels

A simple time domain method of EEG analysis based upon the computation of the frequency and the amplitude of the zeroth, first, and second derivative of the EEG wave has been developed for monitoring the anesthetic level of patients undergoing general anesthesia. This study explores the effectiveness of this EEG analytical system working in conjunction with cardiovascular parameters in discriminating among commonly used anesthetic dosages. EEG features and cardiovascular features were used as variables in a stepwise discriminant analysis on two patient group sets each using a light, medium, and deep dosage level of the agents halothane/nitrous oxide and enflurane/nitrous oxide, respectively. The best overall discriminant prediction of the three 30-patient groups using halothane and nitrous oxide was 86.7 percent correct. The best overall discriminant prediction of the three 30-patient groups using enflurane and nitrous oxide was 90 percent correct. It was felt that these accuracies were sufficient to continue development of this sytem, the next step being the determination of a suitable anesthetic depth scale based upon the use of these and perhaps additional physiological features.     

Depth of anesthesia estimation and control [using auditory evokedpotentials]

A fully automated system was developed for the depth of anesthesia estimation and control with the intravenous anesthetic, Propofol. The system determines the anesthesia depth by assessing the characteristics of the mid-latency auditory evoked potentials (MLAEP). The discrete time wavelet transformation was used for compacting the MLAEP which localizes the time and the frequency of the waveform. Feature reduction utilizing step discriminant analysis selected those wavelet coefficients which best distinguish the waveforms of those responders from the nonresponders. A total of four features chosen by such analysis coupled with the Propofol effect-site concentration were used to train a four-layer artificial neural network for classifying between the responders and the nonresponders. The Propofol is delivered by a mechanical syringe infusion pump controlled by Stanpump which also estimates the Propofol effect-site and plasma concentrations using a three-compartment pharmacokinetic model with the Tackley parameter set. In the animal experiments on dogs, the system achieved a 89.2% accuracy rate for classifying anesthesia depth. This result was further improved when running in real-time with a confidence level estimator which evaluates the reliability of each neural network output. The anesthesia level is adjusted by scheduled incrementation and a fuzzy-logic based controller which assesses the mean arterial pressure and/or the heart rate for decrementation as necessary. Various safety mechanisms are implemented to safeguard the patient from erratic controller actions caused by external disturbances. This system completed with a friendly interface has shown satisfactory performance in estimating and controlling the depth of anesthesia     

Design of a recognition system to predict movement duringanesthesia

The need for a reliable method of predicting movement during anesthesia has existed since the introduction of anesthesia. This paper proposes a recognition system, based on the autoregressive (AR) modeling and neural network analysis of the electroencephalograph (EEG) signals, to predict movement following surgical stimulation. The input to the neural network will be the AR parameters, the hemodynamic parameters blood pressure (BP) and heart rate (HR), and the anesthetic concentration in terms of the minimum alveolar concentration (MAC). The output will be the prediction of movement. Design of the system and results from the preliminary tests on dogs are presented here. The experiments were carried out on 13 dogs at different levels of halothane. Movement prediction was tested by monitoring the response to tail clamping, which is considered to be a supramaximal stimulus in dogs. The EEG data obtained prior to tail clamping was processed using a tenth-order AR model and the parameters obtained were used as input to a three-layer perceptron feedforward neural network. Using only AR parameters the network was able to correctly classify subsequent movement in 85% of the cases as compared to 65% when only hemodynamic parameters were used as the input to the network. When both the measures were combined, the recognition rate rose to greater than 92%. When the anesthetic concentration was added as an input the network could be considerably simplified without sacrificing classification accuracy. This recognition system shows the feasibility of using the EEG signals for movement during anesthesia     

Opioid-induced respiratory depression: a mathematical model for fentanyl

In this paper, respiratory depressant effects of fentanyl are described quantitatively by a mathematical model. The model is an extension of a previous one, which reproduces the human ventilatory control system on a physiological basis. It includes the following: three compartments for gas storage and exchange (lungs, body tissue, and brain tissue); the main mechanisms involved in ventilation control (peripheral chemoreceptors, central chemoreceptors, and the central hypoxic depression); and local blood flow regulation. The effects of fentanyl on the respiratory system include a decrease in peripheral and central chemoreceptor gains on ventilation and a direct inhibition of respiratory neural activity. All parameters in the model were chosen according to the literature. The model is able to reproduce the ventilatory effects of fentanyl in several conditions: 1) constant levels of fentanyl; 2) after a bolus injection; 3) at fixed levels of P(ETCO2); and 4) after artificial ventilation. According to the model, in spontaneously breathing subjects, minute ventilation depends on two opposing actions: fentanyl inhibitory influences, which depress ventilation, reducing oxygen tension and increasing CO2 tension, and the consequent activation of chemoreceptors, which stimulates ventilation. Simulations of anesthetized patients resuming spontaneous breathing after artificial ventilation demonstrate the risk of prolonged apnea and tissue hypoxemia. A safe transition can be achieved by increasing patient PCO2 toward the end of artificial ventilation, because an advanced chemoreceptor stimulation is produced, which promptly counteracts fentanyl-induced inhibition at cessation of artificial ventilation.     

A fast, digitally controlled flow proportional gas injection system for studies in lung function

The aim of this paper is to describe a device for flow proportional injection of tracer gas in the lungs of mechanically ventilated patients. This device may then be used for the study of the multiple breath indicator gas washout technique to determine the end-expiratory lung volume. Such a tracer gas injection device may also be used in the study of other techniques that rely on uptake and elimination of tracer gas by the lungs. In this paper, an injector is described which enables injection of indicator gas at a predetermined concentration in a breathing circuit independent of the type of breathing. The presented setup uses a control computer to produce steering signals to a multivalve array in proportion to the input breathing signals. The multivalve array consists of ten circular valves, each with a different diameter, which can be opened or closed individually according to the input signal of the array. By opening of a certain combination of valves an amount of sulphur hexafluoride gas proportional to the inspiratory breathing signal is released. The rate of transmission between the components of the injection system was 80 Hz. The injector has a full flow range between 0-10 L/min. The delay time between the breathing signal and the flow response was 70 ms. The aimed washin gas concentration of 1% SF6 was achieved after 0.5 s. The study describes the results of tests to determine valve-flow ratios, step response and dynamic response of the injector. The flow output response of the injector system was shown to increase in input frequencies above 3 Hz. The valve flow ratios showed the largest relative deviation in the two smallest valves of the 10 valve array, respectively 0.005 L/min (25%) and 0.002 L/min (20%). We conclude that the injector can achieve a stable concentration of indicator gas in a breathing system with an accuracy of 0.005 L/min to execute the multiple breath indicator washout test in human subjects. The results of the study indicate that the injector may be of use in other application fields in respiratory physiology in which breathing circuit injection of indicator gas is required.     

便携式家用呼吸机的研制

介绍了一种便携式家用呼吸机的软硬件设计。通过精密的元器件,稳定可靠的气流量、气压测量电路,静音风机,人性化的通气策略和模拟电路PID电磁阀的控制电路,以及各类报警措施和简捷的人机界面等,使呼吸机达到较强的可靠（安全）性、经济性和舒适性,并且具备简单的操控特性,适合进入普通家庭,以维持老年人正常呼吸之用。该呼吸机同样适合于各类急救场合。     

A Microcomputer-Based Differential Lung Ventilation System

In order to provide a versatile means of delivering differential lung ventilation (DLV), a computer-controlled system was constructed to allow a variety of ventilation protocols as well as to record and monitor relevant physiologic parameters. Two Siemens servo ventilators were modified for synchronous operation and computer control of minute volume and respiratory rate. Twenty-five parameters on the two lungs were collected every breath. Feedback control was used to adjust respiratory rate to maintain PaCO2 = 35 torr and to keep total tidal volume equal to 15 mI/kg. Three differential volume delivery protocols were established. The DLV system was evaluated in a study involving eighteen mongrel dogs (six dogs for each volume delivery protocol), each with a unilateral lung injury caused by an infusion of 0.1 N HOC through the endobronchial tube. This system has proven to be a highly effective and versatile means of providing differential ventilation as well as precise feedback control of essential physiologic parameters such as PaCO2 and tidal volume. The system handles automated data collection of all relevant physiological parameters, making graphical as well as statistical analysis extremely easy.     

置换通风条件下室内空气品质研究

通过建立一模型房间,从室内空气温度分布、PPD、悬浮颗粒分布及CO2浓度几方面模拟研究了置换通风条件下室内空气品质。结果显示置换通风条件下的IAQ完全能满足相关规范规定,达到人体对健康的要求。小微粒有很好的跟随性,大微粒在重力作用下下沉到地面,CO2的浓度随高度的增加而增大,呼吸区的空气清新。     

The transient absorption characteristics of the two-phase blood/gassystem: a comparison to the Danckwerts model

The transient gas absorption characteristics of a motionless two-phase system consisting of blood and air were investigated. The data were compared to the general liquid/gas system model developed by Danckwerts (1970). The results have shown that the amount of change in concentration of the gases in the gas phase of the system is linearly proportional to the square root of the time the two phases are in contact with each other. This relationship is consistent with the Danckwerts model. The results have revealed the potential of the transient two-phase absorption phenomenon for measuring blood gas tensions clinically. Empirical equations were derived from the data which yielded blood gas concentration estimates for nitrous oxide and oxygen from absorption time and the concentration of the gas phase of the system     

头高15°倾斜位吸氧去氮对肥胖患者耐受呼吸暂停安全时限的影响

目的;探讨全麻诱导插管期间,头高15°倾斜位与平卧位吸氧去氮两种给氧方式对肥胖患者耐受呼吸暂停安全时限的影响。方法：选择年龄21-63岁,BMI〉28 kg/m2,ASAI-II级择期手术的全麻插管病人62例。将其随机分为平卧位（30例）和头高15°倾斜位（32例）两组,常规静脉麻醉诱导,诱导期以10L/min的氧流量...     

Design and control of a demand flow system assuring spontaneous breathing of a patient connected to an HFO ventilator

Lung protective ventilation is intended to minimize the risk of ventilator induced lung injury and currently aimed at preservation of spontaneous breathing during mechanical ventilation. High-frequency oscillatory ventilation (HFOV) is a lung protective ventilation strategy. Commonly used high-frequency oscillatory (HFO) ventilators, SensorMedics 3100, were not designed to tolerate spontaneous breathing. Respiratory efforts in large pediatric and adult patients impose a high workload to the patient and may cause pressure swings that impede ventilator function. A Demand Flow System (DFS) was designed to facilitate spontaneous breathing during HFOV. Using a linear quadratic Gaussian state feedback controller, the DFS alters the inflow of gas into the ventilator circuit, so that it instantaneously compensates for the changes in mean airway pressure (MAP) in the ventilator circuit caused by spontaneous breathing. The undesired swings in MAP are thus eliminated. The DFS significantly reduces the imposed work of breathing and improves ventilator function. In a bench test the performance of the DFS was evaluated using a simulator ASL 5000. With the gas inflow controlled, MAP was returned to its preset value within 115 ms after the beginning of inspiration. The DFS might help to spread the use of HFOV in clinical practice.     

Derived fuzzy knowledge model for estimating the depth of anesthesia

Reliable and noninvasive monitoring of the depth of anesthesia (DOA) is highly desirable. Based on adaptive network-based fuzzy inference system (ANFIS) modeling, a derived fuzzy knowledge model is proposed for quantitatively estimating the DOA and validate it by 30 experiments using 15 dogs undergoing anesthesia with three different anesthetic regimens (propofol, isoflurane, and halothane). By eliciting fuzzy if-then rules, the model provides a way to address the DOA estimation problem by using electroencephalogram-derived parameters. The parameters include two new measures (complexity and regularity) extracted by nonlinear quantitative analyses, as well as spectral entropy. The model demonstrates good performance in discriminating awake and asleep states for three common anesthetic regimens (accuracy 90.3 % for propofol, 92.7 % for isoflurane, and 89.1% for halothane), real-time feasibility, and generalization ability (accuracy 85.9% across the three regimens). The proposed fuzzy knowledge model is a promising candidate as an effective tool for continuous assessment of the DOA.     

Controlling deep transient depletion of an m.o.s. capacitor

The transient surface potential ?s of an m.o.s. capacitor is regulated to a given value ?0 by controlling the gate voltage. Simultaneously, the oxide voltage drop, depletion layer charge and generation current are measured. We present an application of this circuit to the determination of the deep doping profile in a silicon substrate.     

Low temperature plasma enhanced chemical vapor deposition of silicon oxide films using disilane and nitrous oxide

Silicon oxide films have been deposited between room temperature and 300°C using disilane and nitrous oxide by plasma enhanced chemical vapor deposition. Film deposition was investigated as a function of the gas flow ratio of nitrous oxide to disilane, the substrate temperature, the total gas flow rate, the radio frequency discharge power, and the process pressure. The stoichiometric SiO₂ films were obtained when the gas ratio of nitrous oxide to disilane was in the range of 50-150. The deposition was found to be nearly temperature independent indicating the mass transport limited regime.     

Compact helium speech unscrambler using charge-transfer devices

Helium speech is the term commonly used for the distorted speech uttered by deep-sea divers breathing in a helium/oxygen mixture. Present unscrambler designs use pitch synchronous time-expansion signal processing with digital storage. The compact unscrambler reported here has been configured using analogue charge-transfer devices for waveform storage and c.m.o.s. digital circuitry for control logic as a precursor to development of the whole system as a single integrated circuit. The compact unscrambler itself is shown to offer distinct engineering and operational advantages.     

Realization of intrinsic p-type ZnO thin films by metal organic chemical vapor deposition

P-type ZnO thin films were grown on sapphire substrates with and without nitrous oxide (N₂O) by metal organic chemical vapor deposition (MOCVD). The intrinsic p-type ZnO films were achieved by controlling the Zn:O ratio in the range of 0.05–0.2 without N₂O flow. Secondary ion mass spectroscopy (SIMS) showed that the films contained little or no nitrogen (N) impurities for all samples. The p-type behavior of the samples should be due to the intrinsic acceptor-like defects V_Zn, for ZnO film grown without nitrous oxide, and N, occupying O sites as acceptors for ZnO film grown with nitrous oxide. The best p-type ZnO film has low resistivity of 0.369 Ω-cm, high carrier density of 1.62×10¹⁹ cm⁻³, and mobility of 3.14 cm²/V-s. The obtained p-type ZnO films possess a transmittance of nearly 100% in the visible region and strong near-band-edge emission.     

CO2激光热处理工作台控制电路

本文叙述CO2激光热处理工作台用的1．5KWDC马达正，反向调速，稳速反馈控制电路。给出控制原理设计的依据和实际线路总图，对线路工作原理特别是自行设计计的电压控制移相调压可控硅驱动电路作了说明，最后给出拖动610r型铣床工作台的实验结果。