A dual control system for assisting respiration

A dual control system for assisting respiration was developed. The following features were included: (i) ventilation is controlled by the metabolic rate from continuously measured CO₂ output, (ii) physiologic dead space approximated as a linear function of tidal volume is used to estimate alveolar ventilation, and (iii) oxygen concentration in the inspired gas is regulated by the arterial oxygen saturation continuously measured with an ear oximeter. The ventilator was used on dogs with an inspired gas mixture of 85% N₂ and 15% O₂. Arterial P_co2 was maintained between 36 and 39 mmHg for a duration exceeding 60 minutes. Although an oscillatory variation was seen in the arterial P_o2 due to the adoption of an on-off control mode to regulate the O₂ fraction in the inspired gas, it remained between 80 and 136 mmHg. The dual control system of assisting respiration is capable of maintaining both the arterial P_co2 and P_o2 within normal levels at any level of metabolic rate and any respiratory frequency.     

Periodic respiration in patients with heart failure

Summary Patients with heart failure are known to demonstrate periodic respiration (PR) during sleep. The factors causing PR are not well known. We therefore studied 20 patients (aged 18–66 years) with idiopathic dilated cardiomyopathy. Full-night polysomnography and evaluation of respiration and transcutaneous oxygen saturation were performed. Hypercapnic ventilatory response (HCVR) was evaluated during daytime. The patients showed PR for 25 ± 26% (mean ± standard deviation) of total sleep time. During PR, oxygen desaturated 7.1±4.6%. Sleep was impaired. HCVR was normal. Oxygen desaturation during PR was predicted by HCVR (r=0.47, P<0.05) and left atrial diameter (r=0.60, P<0.05). The time period of PR expressed as a fraction of total sleep time was correlated with HCVR (r=0.45, P<0.05) and left atrial diameter (r=0.51, P<0.05). In conclusion, PR with oxygen desaturation, arousals, and impaired sleep was observed in stable heart failure. HCVR and left heart dimensions were related to PR. These findings confirm the concept of a feedback loop describing respiratory control in PR.Abbreviations PR periodic respiration - HCVR hypercapnic ventilatory response - LA left atrial diameter - LVED left ventricular end-diastolic diameter - REM rapid eye movement     

基于聚偏氟乙烯薄膜的穿戴式呼吸检测系统

【摘 要】 针对人体呼吸信号的特点设计一种基于聚偏氟乙烯（PVDF）压电薄膜材料的可穿戴式呼吸检测系统。人体呼吸时PVDF薄膜受力产生的感应电荷较少,经信号调理电路将电荷量转换成电压量。单片机通过模数转换器获得呼吸信号数据,通过蓝牙发送给上位机。上位机从获得的数据中提取呼吸波形,并进行平滑滤波、自适应双阈值来计算呼吸率。试验结果表明,本系统可以实时准确地检测出人体的呼吸波形,呼吸次数识别的准确率在90%以上,可以满足人体呼吸监护的需求。     

A stable wireless energy transmission system for gastrointestinal microsystems

A wireless energy transmission system using a Helmholtz primary coil outside and a 3-dimensional secondary coil inside the body is introduced. It is designed to transmit stable power to a gastrointestinal microsystem regardless of its position and orientation when working in the gastric tract. Up to 310 mW of usable DC power can be delivered under worst-case geometrical conditions. Measured data of the system performance are presented and evaluated.     

A magnetically actuated anchoring system for a wireless endoscopic capsule

In this study, we propose a new magnetically actuated anchoring system for wireless capsule endoscopes (WCE) by employing the principle of a switchable magnetic spring. A force model is derived to predict the magnetic force needed to support the interaction between the anchors and the intestinal lumen. The theoretical and experimental analysis conducted shows that the magnetic spring is capable of providing the force needed to activate the anchoring mechanism, which consists of four foldable legs. A prototype capsule with a size comparable with the size of a commercial WCE was designed, fabricated, and tested. The in-vitro tests with a real small intestine show that the proposed anchoring mechanism is able to raise the friction force between the anchoring legs and inner wall of the intestine by more than two times after its activation using an external magnetic field. Experimental results presented demonstrate that the proposed anchoring system, which has a low foot-print not taking up too much space on the capsule, can provide a reliable anchoring capability with the capsule inside the intestinal lumen.     

无线镇痛系统的研制

目的研制一套由镇痛泵泵头、路由基站和远程监控台组成的无线镇痛系统,以缓解术后患者的疼痛。方法镇痛泵泵头终端模块完成麻醉液输注的具体动作,并通过Wi-Fi与远程监控台进行无线数据通信。通过优化系统软件以及模块的电源管理等方面对镇痛泵泵头进行了低功耗软硬件设计;从机械装夹和软件校准等多方面提出了增大泵头精度的方法。基于压力模块和霍尔模块对镇痛泵报警方法进行研究并建立模型,根据不同的算法提取压力信号相应的特征,从而识别出管路堵塞、有气泡、无液和正常工作4种状态。结果通过对研制的无线镇痛系统进行精度和工作时长测试以及管路4种不同工作状态报警分析,可知本系统能够正常工作,压力模块可精确报警。结论本系统的功耗低、精度高,具有精确的报警提示功能,可实现患者自控镇痛。     

植入式无线能量传输系统

目的提出一种适用于植入式医疗设备的无线供电系统,引入磁谐振耦合供能的方法,并通过建立理论线圈仿真模型计算线圈尺寸与谐振频率,有效解决植入式装置无线供电距离远、尺寸小等难题,使植入式装置可无需更换电池而终生使用。方法首先通过MATLAB仿真耦合谐振线圈模型以及无线能量传输模型,并计算出满足条件的最优线圈设计。然后依据仿真结果制作发射线圈与接收线圈,设计植入式无线供电实际硬件系统,使系统在限定的距离等条件下有最优的传输效率。结果仿真算法能有效描述磁耦合谐振,计算与测量可以得到Q、L的理论与实际的平均相对误差E_Q=5.34%、E_L=4.42%,为实际供电系统的设计提供了参考依据。设计实现了适合于医疗植入的微型供电系统,增加了传输距离。该方案采用线圈大对小设计,植入部分尺寸仅有18 mm,体外线圈直径85mm,实际最高传输效率达到16.20%,80 mm距离可以供能2.642 m W。结论该仿真算法可为耦合谐振设计提供参考,为植入式医疗系统提供一种新的设计方案。     

A study on a non-contacting respiration signal monitoring system using Doppler ultrasound

We proposed non-contacting respiration signal monitoring system for sleep apnea syndrome. Experiments were conducted by emitting 40 kHz ultrasound beam, which is set tone burst mode by 1 ms period to a subject chest. Normal respiration condition and a simulated sleep apnea syndrome condition were measured while subjects were holding breath. To obtain the actual respiration signal from the raw signal, ultrasound attenuation characteristics were considered. The Doppler ultrasound signal was detectable once the received signal obtained by demodulation circuits passed through a low pass filter (LPF). The signal’s ripples were eliminated by moving average method and the signal’s peaks were detected by phase portrait reconstruction method to measure the respiration rate. This paper is the WC2006 special issue paper.     

Covert respiration measures for the detection of concealed information

A mock-theft experiment was designed to assess the efficiency of two covert respiration measures in detection of concealed information. The covert measures were further compared with three standard measures typically used for the detection of concealed knowledge (electrodermal, respiration and finger pulse measures). Results revealed that the covert respiration measures produced good discrimination between "guilty" (participants possessing concealed knowledge) and "innocent" participants. One of the covert measures produced detection efficiency that was similar to that of the standard respiration and finger pulse measures, but less than the electrodermal measure.     

A hybrid approach for continuous detection of sleep-wakefulness fluctuations: validation in patients with Cheyne-Stokes respiration

Fluctuations in sleep/wake state have been proposed as an important mechanism contributing to the development of oscillatory breathing patterns, including Cheyne-Stokes respiration in patients with heart failure. In order to properly assess the interactions between changes in state and changes in ventilatory parameters, a methodology capable of continuously and reliably detecting state transitions is needed. Traditional fixed-epoch analysis of polysomnographic recordings is not suitable for this purpose. Moreover, visual identification of changes in the dominant electroencephalogram activity at the transition from wakefulness to sleep and vice versa is often very subjective. We have therefore developed a hybrid approach--including both visual scoring and computer-based procedures--for continuous analysis of state transitions from polysomnographic recordings, specifically tailored for fluctuations between wakefulness and non-rapid eye movement-1 and -2 sleep. The overall analysis process comprises three major phases: (1) manual identification of relevant electroencephalogram/electrooculogram features and events, including a sample of unequivocal alpha and theta-delta activity; (2) automatic statistical discrimination of dominant electroencephalogram activity; and (3) state classification (wakefulness, non-rapid eye movement-1 and -2). The latter is carried out by merging information from visual scoring with the output of the discriminator. Validation has been carried out in 16 patients with heart failure during daytime Cheyne-Stokes respiration, using a training and testing set of electroencephalogram polysomnograms. The statistical discriminator correctly classified 99.1 ± 1.4% and 99.2 ± 1.1% of unequivocal alpha and theta-delta activity. This approach has therefore the potential to be used to reliably measure the incidence and location of sleep-wake transitions during abnormal breathing patterns, as well as their temporal relationship with major ventilatory events.     

A wireless power transmission system for implantable devices in freely moving rodents

Reliable wireless power delivery for implantable devices in animals is highly desired for safe and effective experimental use. Batteries require frequent replacement; wired connections are inconvenient and unsafe, and short-distance inductive coupling requires the attachment of an exterior transmitter to the animal’s body. In this article, we propose a solution by which animals with implantable devices can move freely without attachments. Power is transmitted using coils attached to the animal’s cage and is received by a receiver coil implanted in the animal. For a three-dimensionally uniform delivery of power, we designed a columnar dual-transmitter coil configuration. A resonator-based inductive link was adopted for efficient long-range power delivery, and we used a novel biocompatible liquid crystal polymer substrate as the implantable receiver device. Using this wireless power delivery system, we obtain an average power transfer efficiency of 15.2 % (minimum efficiency of 10 % and a standard deviation of 2.6) within a cage of 15 × 20 × 15 cm³.     

Cheyne-Stokes respiration in patients with congestive heart failure: causes and consequences

Cheyne-Stokes respiration is a form of periodic breathing in which central apneas and hypopneas alternate with periods of hyperventilation, producing a waxing and waning pattern of tidal volume. This review focuses on the causes and consequences of Cheyne-Stokes respiration in patients with congestive heart failure, in whom the prevalence is strikingly high and ranges from 30% to 50%. Several factors have been implicated in the genesis of Cheyne-Stokes respiration, including low cardiac output and recurrent hypoxia. The key pathophysiological mechanism triggering Cheyne-Stokes respiration is hyperventilation and low arterial CO2 (PaCO2) that when below the apneic threshold triggers a central apnea. Hyperventilation is associated with pulmonary congestion, and Cheyne-Stokes respiration is more prone to occur during sleep, when the respiratory system is mainly dependent on chemical control. It is associated with recurrent dips in oxygen saturation and arousals from sleep, with oscillations in blood pressure and heart rate, sympathetic activation and increased risk of ventricular tachycardia. Cheyne-Stokes respiration is an independent marker of poor prognosis and may participate in a vicious cycle, further stressing the failing heart.     

Provocation of ventricular ectopy by cheyne-stokes respiration in patients with heart failure

STUDY OBJECTIVES: Previous reports have suggested an association between Cheyne-Stokes respiration with central sleep apnea (CSR-CSA) and ventricular ectopy, but there has been relatively little evidence of a cause-effect relationship. The objective of this study was to determine whether CSR-CSA directly provokes ventricular ectopy and, if so, whether it is associated with any particular phase of the CSR-CSA breathing cycle. DESIGN: We compared the frequency of ventricular premature beats (1) between the apneic and hyperpneic phases of CSR-CSA, (2) between periods of CSR-CSA and periods of regular breathing during sleep, and (3) in response to the elimination of CSR-CSA by administration of a low concentration of inhaled CO2. SETTING: Hospital-based cardiopulmonary sleep laboratory. PATIENTS: Twenty-three patients with heart failure and CSR-CSA. MEASUREMENTS AND RESULTS: Ventricular premature beats were found to occur 40% more frequently during the hyperpneic phase than the apneic phase of CSR-CSA (mean+/-SD, 7.0+/-7.4 versus 4.9+/-5.7 ventricular premature beats per minute, P = .003). Ventricular premature beat frequency was also found to be higher during periods of CSR-CSA than during periods of regular breathing occurring either spontaneously (median [25th, 75th percentile], 2.2 [1.2, 6.5] versus 1.1 [0.8, 2.0] ventricular premature beats per minute, P = .027), or induced through inhalation of CO2 (from 4.7+/-3.8 to 3.3+/-4.0 ventricular premature beats per minute, P = .048). CONCLUSIONS: CSR-CSA provokes ventricular ectopy that is most pronounced during the hyperpneic phase. Such an increase in ventricular premature beats might contribute to the higher mortality rates reported in heart failure patients with CSR-CSA.     

A PC-aided optical foetal heart rate detection system

Safe monitoring of foetal heart rate is a valuable tool for the healthy evolution and wellbeing of both foetus and mother. This paper presents a non-invasive optical technique that allows for foetal heart rate detection using a photovoltaic infrared (IR) detector placed on the mother’s abdomen. The system presented here consists of a photoplethysmography (PPG) circuit, abdomen circuit and a personal computer equipped with MATLAB. A near IR beam having a wavelength of 880?nm is transmitted through the mother’s abdomen and foetal tissue. The received abdominal signal that conveys information pertaining to the mother and foetal heart rate is sensed by a low noise photodetector. The PC receives the signal through the National Instrumentation Data Acquisition Card (NIDAQ). After synchronous detection of the abdominal and finger PPG signals, the designed MATLAB-based software saves, analyses and extracts information related to the foetal heart rate. Extraction is carried out using recursive least squares adaptive filtration. Measurements on eight pregnant women with gestational periods ranging from 35–39 weeks were performed using the proposed system and CTG. Results show a correlation coefficient of 0.978 and a correlation confidence interval between 88–99.6%. The t test results in a p value of 0.034, which is less than 0.05. Low power, low cost, high signal-to-noise ratio, reduction of ambient light effect and ease of use are the main characteristics of the proposed system.