Comparison of transthoracic electrical bioimpedance cardiac output measurement with thermodilution method in post coronary artery bypass graft patients.

Transthoracic electrical bioimpedance (TEB) has been proposed as a non-invasive, continuous, and cost-effective method of cardiac output (CO) measurement. In this prospective, non-randomized, clinical study, we measured CO with NICOMON (Larsen and Toubro Ltd., Mysore, India) and compared it with thermodilution (TD) method in patients after off-pump coronary artery bypass (OPCAB) graft surgery. We also evaluated the effect of ventilation (mechanical and spontaneous) on the measurement of CO by the two methods. Forty-six post-OPCAB patients were studied at five predefined time points during controlled ventilation and at five time points when breathing spontaneously. A total of 230 data pairs of CO were obtained. During controlled ventilation, TD CO values ranged from 2.29 to 6.74 L/min (mean 4.45 ± 0.85 L/min), while TEB CO values ranged from 1.70 to 6.90 L/min (mean 4.43 ± 0.94 L/min). The average correlation (r) was 0.548 (P = 0.0002), accompanied by a bias of 0.015 L/min and precision of 0.859 L/min. In spontaneously breathing patients, TD CO values ranged from 2.66 to 6.92 L/min (mean 4.66 ± 0.76 L/min), while TEB CO values ranged from 3.08 to 6.90 L/min (mean 4.72 ± 0.82 L/min). Their average correlation was relatively poor (r = 0.469, P= 0.002), accompanied by a bias of −0.059 L/min and precision of 0.818 L/min. The overall percent errors between TD CO and TEB CO were 19.3% (during controlled ventilation) and 17.4% (during spontaneous breathing), respectively. To conclude, a fair correlation was found between TD CO and TEB CO measurements among post-OPCAB patients during controlled ventilation. However, the correlation was weak in spontaneously breathing patients.

Image reconstruction of conductivity on magnetoacoustic tomography with magnetic induction / 生物医学工程学杂志

The electric characteristics such as impedance and conductivity of the organization will change in the case where pathological changes occurred in the biological tissue. The change in electric characteristics usually took place before the change in the density of tissues, and also, the difference in electric characteristics such as conductivity between normal tissue and pathological tissue is obvious. The method of magneto-acoustic tomography with magnetic induction is based on the theory of magnetic eddy current induction, the principle of vibration generation and acoustic transmission to get the boundary of the pathological tissue. The pathological change could be inspected by electricity characteristic imaging which is invasive to the tissue. In this study, a two-layer concentric spherical model is established to simulate the malignant tumor tissue surrounded by normal tissue mutual relations of the magneto-sound coupling effect and the coupling equations in the magnetic field are used to get the algorithms for reconstructing the conductivity. Simulation study is conducted to test the proposed model and validate the performance of the reconstructed algorithms. The result indicates that the use of signal processing method in this paper can image the conductivity boundaries of the sample in the scanning cross section. The computer simulating results validate the feasibility of applying the method of magneto-acoustic tomography with magnetic induction for malignant tumor imaging.

A preliminary study of piglet intraperitoneal bleeding model and electrical impedance tomography monitoring / 生物医学工程学杂志

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.

Analytical method for the potential distribution of head sphere model under the stimulation of point current source / 生物医学工程学杂志

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.

Evaluation of Vascular Response using Impedance Plethysmography in Patients with Spinal Cord Injury

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.

Menopause, estrogens, and endothelial dysfunction: current concepts

Menopause is defined as the permanent cessation of menses. Cardiovascular disease is the leading cause of death among postmenopausal women in developed countries. The disparity between the incidence of cardiovascular disease among women in pre- and postmenopause has been ascribed to the actions of endogenous estrogen on the cardiovascular system and, particularly, on the vascular endothelium. The endothelium plays an important role in cardiovascular homeostasis, either through the vascular tonus and its regulation, or through coagulation and the inflammatory response. Endothelial dysfunction is implicated in the genesis of atherosclerosis and other chronic disorders, such as diabetes mellitus and hypertension. The pharmacological use of estrogen exerts influence on the circulating levels of markers of vascular tonus, and inflammation, as well as prothrombotic, and fibrinolytic markers, but the impact of these changes on the atherosclerotic disease is still uncertain.

A menopausa é definida como a cessação permanente das menstruações. A doença cardiovascular é a principal causa de mortalidade em mulheres na pós- menopausa, em países desenvolvidos. A disparidade entre a incidência de doença cardiovascular entre mulheres na pré e pós menopausa tem sido atribuída a ações do estrogênio endógeno sobre o sistema cardiovascular e, em especial, sobre a função do endotélio vascular. O endotélio tem importante papel na homestase cardiovascular, seja no controle do tônus e permeabilidade vascular, ou da coagulação e resposta inflamatória. A disfunção endotelial está implicada na gênese da aterosclerose e de outras doenças crônicas, como diabete melito e hipertensão arterial. O uso farmacológico de estrogênio exerce influência sobre concentrações circulantes de marcadores do tônus vascular, inflamatórios, pró-trombóticos e fibrinolíticos, porém o impacto destas alterações sobre a doença aterosclerótica ainda não está determinado.

Measurement of human body composition: in vivo techniques and related evaluation / 生物医学工程学杂志

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.

Simulation study of line electrode for electrical impedance tomography / 生物医学工程学杂志

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.

Study on double feedback current source for biologic impedance measurement / 生物医学工程学杂志

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.

Algoritmo de separación de latidos de pulso arterial / Separation algorithm arterial pulse beats

An algorithm is described to extract cardiac from a pletysmographic signal based on the maximum value of the second derivative. An initial set of points is detected and filtered with two consecutive temporal analyses...

Some changes of rheograph index in the patients with cerebro-vascular insufficient treated with artificial magnetic fields

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

Desarrollo de un pletismografo de impedancia para evaluar la hiperemia reactiva en el antebrazo / Design of an impedance pletismograph for reactive hyperemia evaluation in the forearm

La pletismografía de impedancia se basa en medición del cambio de voltaje que ocurre por las variaciones de volumen que suceden en una sección de tejido. La corriente aplicada es del tipo alterna, débil y de alta frecuencia para evitar la estimulación de tejidoseléctricamente excitables como músculo y nervio. Los cambios de flujo sanguíneo son susceptibles de medición por este método y el mismo se ha aplicado en el diagnóstico de la oclusión venosa de los miembros. Se diseñó y construyó un medidor de impedancia para aplicarlo al antebrazo, el cual consta de un regulador de voltaje TPS76150 con registro simultaneo de la derivación DII del ECG. La señal de inyección generada fue de 50 KHz (puente de Wien) y registrada con dos amplificadores operacionales de transconductancia LM 3080 (1mA). Laseñal fue demodulada y reamplificada. Se usaron electrodos de banda de plata aplicados sobre la piel del antebrazo con gel de conducción eléctrica y sujetados con bandas de goma. El circuito y el software de adquisición fueron desarrollados en el centro de Bioingeniería de laUSB. Se hicieron registros en 15 sujetos sanos de 18-30 años de edad con protocolos de oclusión de la arteria braquial y registro de flujo sanguíneo en el antebrazo. Se hicieron oclusiones con un brazalete a presiones subdiastólica (oclusión venosa), supradiastólica ysuprasistólica; durante 60 y 90 segundos con liberación brusca de la oclusión. El gráfico se observó y registró en una computadora portátil (laptop). Durante la oclusión suprasistólica se halló un aumento inicial de impedancia progresivo hasta su estabilización y la aparición de unpico correspondiente a la hiperemia reactiva del antebrazo al momento de liberar la oclusión, el cual se ha relacionado con la liberación de sustancias vasodilatadores de origen endotelial. En conclusión, el aparato diseñado es de aplicación clínica sencilla, permite evaluar las variables hemodinámicas típicas de la hiperemia reactiva y es potencialmente utilizable en el diagnóstico de oclusiones venosas.

Correlation between Doppler Ultrasonography and Impedance Plethysmography in Lower Extremity Varicose Vein

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

Validación de la pletismografía de impedancia como pruba diagnóstica de la trombosis venosa profunda proximal de miembros inferiores: estudio de concordancia entre venografía y pletismografía

Introducción: La trombosis venosa profunda proximal de miembros inferiores (TVPPMI) es una entidad potencialmente mortal; de la rapidez del diagnóstico y la intervención depende el curso y complicaciones de la enfermedad. El diagnóstico por pletismografía de impedancia facilita el seguimiento y la conducta terapéutica; sin embargo, su sensibilidad y especificidad ha sido cuestionada y se propone el reemplazo por otros métodos no invasivos (doppler venoso). Objetivos: Determinar la sensibilidad y especificidad de la pletismografía de impedancia de miembros inferiores en el diagnóstico de la TVPPMI en pacientes con clínica o con factores de riesgo para esta enfermedad en el Hospital Universitario San Ignacio. Diseño: estudio de concordancia entre la venografía (patrón de oro) y la pletismografía de impedancia (IPG). Pacientes y Métodos: Entre febrero de 1994 y marzo de 1995 ingresaron 62 pacientes con clínica de TVPPMI o con factores de riesgo para la enfermedad al servicio de Medicina Interna o al Departamento del Radiología del Hospital Universitario San Ignacio. Se diligenció una historia clínica haciendo énfasis en los factores de riesgo y en el diagnóstico; se les realizó pletismografía de impedancia de miembros inferiores y posteriormente una venografía. Resultados: Se incluyeron 62 sujetos, de los cuales ocho se excluyen y se analizan un total de 54 pacientes. El 11 por ciento presentaban historia clínica de trombosis venosa profunda y el grupo restante, factores de riesgo para adquirir la enfermedad. La sensibilidad de la IPG en el diagnóstico de TVPPMI del grupo en general fue del 100 por ciento con especificidad de 92 por ciento, con un valor predictivo positico del 33 por ciento. En pacientes con sospecha clínica la sensibilidad fue del 100 por ciento y la especificidad del 90 por ciento; en pacientes sin clínica pero con factores de riesgo no se pudo calcular la sensibilidad y la especificidad fue del 90 por ciento. Conclusión: En pacientes con sospecha clínica de TVPPMI, la IPG tiene alta sensibilidad como método diagnóstico; su valor predictivo positivo en este estudio es bajo por el tamaño de la muestra. Se debe continuar el estudio incluyendo más pacientes con clínica o con alto riesgo de tener TVPPMI.

Diagnóstico de las trombosis venosas profundas de las extremidades / Diagnosis of deep venous thrombosis of the extremities

La trombosis venosa profunda de las extremidades es una entidad relativamente frecuente, especialmente en los miembros inferiores. Su complicación más temida es la embolia pulmonar, por el riesgo potencial de muerte cuando es masiva. Se revisan los métodos diagnósticos actuales de las trombosis venosas profundas de las extremidades, fundamentales para realizar un tratamiento oportuno y completo, y para planificar métodos preventivos apropiados. En la actualidad el método ideal es el Eco-Doppler color, o en su defecto el Eco-Doppler en blanco y negro, ya que no sólo entrega información anatómica y funcional de la circulación venosa, sino porque permite evidenciar trombos no oclusivos, trombos flotantes (de alto riesgo embolígeno), y también porque logra discriminar trombos agudos de aquellas oclusiones antiguas, estableciendo el diagnóstico preciso para definir el tratamiento apropiado

Monitoraçäo da hemodiálise através da pletismografia elétrica com prediçäo da pressäo arterial / Monitoring of hemodialysis by electrical plethysmography with arterial pressure prediction

A monitoraçäo contínua de oito hemodiálises através da pletismografia elétrica, ECG e da variaçäo do peso corporal permitiu a obtençäo de de um alogaritmo para a estimativa de valores futuros da pressäo arterial média (PAM) com vistas à reduçäo da ocorrência de hipotensäo clínica durante a hemodiálise (HD). Através de regressäo múltipla, verificou-se que valores futuros da PAM säo determinados (p < 0,05) por valores atuais de PAM, pelo valor máximo da derivada do pulso de impedância e pela variaçäo percentual do peso corporal. Vários outros parâmetros hemodinâmicos considerados näo apresentaram influência significativa para a prediçäo da PAM. Para intervalos de tempo futuros de até 30min, durante a fase crítica da HD, a prediçäo da PAM apresentou erro médio de 6,5 ñ 4,0%. Substituindo-se a variaçäo percentual de peso (PE) pela impedância basal (Zo esse erro aumenta para 7,4 ñ 8,8%

Measurement of digital blood flow using impedance plethysmography

No abstract available.

Evaluation of state of circulation in radiation injury using impedance plethysmography.

Seven patients with history of radiation burn were subjected to impedance plethysmographic investigation at Non-invasive Vascular Laboratory, K. E. M. Hospital. Impedance plethysmograms were recorded from various locations in both the upper extremities in supine and digits of both the hands in supine as well as on hyper-abduction in sitting position. Control values of blood flow index (BFI) and differential pulse arrival time (DPAT) were derived from similar data in 15 normal subjects. It was observed that digits having thinning of epidermis of skin recorded marked decrease in values of BFI and significant change in value of DPAT and these observations correlated well with thermography and vascular scintigraphy. Digits recording significant decrease in BFI, which were clinically normal, were found to have changes in the skin during follow up examination. Thus IPG provided a sensitive modality for detecting ischaemia in early stages in patients with history of radiation injury.

Coitus induced changes in oviductal motility & effect of progesterone.

Motility of different oviductal segments of conscious rabbits was recorded through permanently implanted sensors using the technique of impedance plethysmography. The implants were around the oviductal wall and therefore did not obstruct its lumen. Pre-ovulatory ampullary motility was always less than the isthmic motility. Coitus induced ovulation produced a characteristic oviductal motility pattern consisting of (i) initial relaxation of both isthmus and ampulla (4-12 h) followed by (ii) increased isthmic motility in the face of a continually relaxed ampulla (36-48 h), and finally phase (iii) leading to restitution of both ampullary and isthmic motility to the base-line at 72-96 h. Estimation of ova positions indicated the presence of fertilized eggs in the ampulla and ampullo-isthmic junction at 48 h and the ova could come to the end of the isthmic segment only at 72 h or after. Increased isthmic motility thus served to counter the transportation of ova and their retention in the ampulla. Rabbits in which oviducts were not taken out for ova positioning achieved normal pregnancy. Administration of progesterone (im, 2.5 mg) produced complete relaxation of both isthmus and ampulla, did not produce increased isthmic contractility on coitus, accelerated the ovum transport rate and inhibited pregnancy, again emphasising the ova retentive role of oviductal motility.