No abstract available.
Electric Impedance* ; Plethysmography, Impedance*

A double feedback current source for biologic impedance measurement is designed in order to solve the problem on the poor constant-current characteristic under higher frequency and meet the request for the ability to eliminate the direct current signal. The voltage controlled current source based on the second generation current conveyor theory is presented, which has good output impedance and anti-direct current characteristics by using the direct current feedback unit and input buffer. The closed loop control of current amplitude is implemented by means of the direct digital synthesizer and multiplication demodulation technique, which improves the constant-current characteristic of the current source.
Equipment Design ; Plethysmography, Impedance ; instrumentation

Studying rheography of 32 patients with cerebrovascular insufficient treated by artificial magnetic fields at Central Military Hospital from June to December 2002. Results: treating by artificial magnetic fields gave significant improvements on the rheographic index such as reduce of  time and normalization of /T ratio, increase of Ri index and cerebrovascular volume to normal levels; artificial magnetic fields also improved imagines of rheographic waves. These results demonstrated the improvements in regulation of vascular tonicity, and promoting blood flow at treated areas
Plethysmography, Impedance ; Cerebrovascular Disorders ; Therapeutics ; Magnetics

OBJECTIVE: To investigate the diagnostic validity of doppler ultrasonography (US) and impedance plethysmography (IPG) using photoplethysmography for evaluation of varicose vein of the lower extremities. METHOD: One hundred sixty-six limbs in 83 consecutive patients with varicose vein were included. Venous reflux and deep venous lesions were assessed by doppler US. Venous filling time was evaluated using IPG. Diagnostic capabilities of two methods were analyzed using Receiver Operating Characteristic (ROC) curve. RESULTS: Doppler US identified superficial venous reflux in sixty-nine of 119 limbs with varicose vein and no abnor malities in 34 of 47 normal limbs (sensitivity, 58%; specifi-city, 75%). IPG demonstrated superficial venous insufficiency in 75 of the affected limbs and normal refill time in 38 of the normal limbs (sensitivity, 63%; specificity, 81%). Sensitivity was increased to 82% when both tests were used together. Area under the ROC curve was 0.66 in doppler US, 0.72 in IPG, and 0.76 in both tests. Deep venous lesion was found in 31 limbs using the both tests; 15 limbs with doppler US and 18 limbs with IPG. CONCLUSION: IPG was more superior to doppler US in diagnosing venous insufficiency. The combination of both tests provided more accurate diagnostic information in assessing venous valvular function
Electric Impedance* ; Extremities ; Humans ; Lower Extremity* ; Photoplethysmography ; Plethysmography ; Plethysmography, Impedance* ; ROC Curve ; Sensitivity and Specificity ; Ultrasonography ; Ultrasonography, Doppler* ; Varicose Veins* ; Venous Insufficiency

The current emphasis on the acquisition of physiological data by noninvasive means for mass medical screening and patient monitoring has increased interest in the use of electrical impedance for the measurement of physiological events. The technique has gained some degree of acceptance for monitoring respiration (Baker and Geddes, 1970), and much interest has been displayed recently in use of the technique to measure cardiac output including studies by Kubicek et al. (1966) Judy et al. (1969), and Mohapatra (1981). Other applications using the impedance technique include thoracic fluid accumulation, peripheral blood flow, cerebral blood flow, muscle contraction, eye movement, and uterine contraction, etc. The purpose of this article is to introduce the various impedance techniques for the measurement of physiological variables.
Cardiography, Impedance ; Cerebrovascular Circulation ; Extremities/blood supply ; Female ; Human ; *Plethysmography, Impedance ; Regional Blood Flow ; Respiration ; Uterine Contraction

In this paper, a simulation research software platform for EIT electrode structure and parameter optimizing design has been developed, which is based on the coercive equipotential node model of line electrode. By the method, which is presented for electrode structure and parameter optimizing design, the influences of electrode structure parameters on reconstructed image and measure sensitivity have been studied and the optimal structure parameters of electrode for the object in different depth have been determined.
Computer Simulation ; Electric Impedance ; Electrodes ; Electromagnetic Fields ; Equipment Design ; Humans ; Models, Biological ; Plethysmography, Impedance ; instrumentation ; methods ; Software ; Tomography ; methods

The in vivo techniques for studying human body composition have built up an important field and are continuing to be developed. This review provides an overview of the present status of this field and describes the in vivo techniques used in mearsuring human body composition such as anthropometry, metabolites method, densitometry, dilution method, total body potassium, neutron activation analysis, bioelectrical impedance analysis, dual energy X ray absorptiometry and imaging method. The review also introduces the principle, method and value of these techniques.
Anthropometry ; methods ; Body Composition ; Densitometry ; methods ; Humans ; Magnetic Resonance Spectroscopy ; methods ; Plethysmography, Impedance ; methods ; Whole Body Imaging ; methods

Piglets having each a body weight of 20-30 kg and an abdominal perimeter like human's were used in the experiment. Being guided by ultrasound, we stabbed the piglet's abdomen, placed a catheter on the liver's lower margin, then injected the anticoagulated blood through the catheter by electrical infusion pump with constant speed respectively, and monitored the whole process by EIT. We observed the image change, using Ultrasound and CT to examine the area of blood injection after the end of monitoring,and we dissected to check the result of observations. The results reveal: (1) Ultrasound, CT and dissection are all able to find out a large amount of blood in piglet's abdominal cavity; (2) The pixel value of EIT target area decreases with the increase of blood, and the change in impedance image can be obviously observed. Therefore, this animal model is suitable for simulating intraperitoneal bleeding, and the speed of bleeding therein can be controlled. We can get a limpid image when EIT is used for monitoring the intraperitoneal bleeding simulated by this animal model.
Animals ; Electric Impedance ; Female ; Hemorrhage ; diagnosis ; etiology ; physiopathology ; Image Interpretation, Computer-Assisted ; methods ; Male ; Monitoring, Physiologic ; methods ; Peritoneal Diseases ; diagnosis ; etiology ; physiopathology ; Plethysmography, Impedance ; methods ; Swine ; Tomography ; methods

The 4-layer sphere model of human head was built; the layers from outside to inside represented the scalp, the skull, the CFS and the brain, respectively. The point current source placed on the outmost layer was regarded as the boundary condition, and the method of separation of variables was used to solve the equations. The potential distribution and the current expression were given, and the isopotential-line map and current lines were drawn. The simulation result can be used to analyze head EIT problems.
Algorithms ; Brain ; anatomy & histology ; physiology ; Computer Simulation ; Electric Impedance ; Electrodes ; Electromagnetic Phenomena ; Head ; physiology ; Humans ; Image Interpretation, Computer-Assisted ; methods ; Models, Theoretical ; Plethysmography, Impedance ; methods ; Tomography ; methods

OBJECTIVE: To determine abnormal vascular response to cuff ischemia in patients with spinal cord injury (SCI). METHOD: Ankle blood pressure (ABP) and ankle-brachial index (ABI) in 20 SCI patients (14 men, 6 women, mean age 39.8 years) and control group (14 men, 6 women, mean age 40.2 years) were measured using impedance plethysmography at rest and after distal thigh cuff compression for 5 and 10 minutes. The patients were divided into tetraplegia (10), paraplegia (10), complete injury (8) and incomplete injury (12). RESULTS: There was no significant difference in ABP and ABI at rest and 5 minutes of ischemic compression between the patients and control groups. However, ABP and ABI decreased more at 10 minutes of ischemic compression in SCI compared to control groups (p<0.001). Changes of ABP and ABI between tetraplegia and paraplegia were not different. Complete injury of SCI decreased more than incomplete injury at 10 minutes of ischemia in the APB and ABI (p<0.001). CONCLUSION: Vascular control was significantly impaired in patients with spinal cord injury. Impedance plethysmography can be a useful and objective tool in evaluation of vascular response for the patients with spinal cord injury.
Animals ; Ankle ; Ankle Brachial Index ; Blood Pressure ; Electric Impedance ; Female ; Humans ; Ischemia ; Male ; Paraplegia ; Plethysmography, Impedance ; Quadriplegia ; Spinal Cord ; Spinal Cord Injuries ; Thigh