Multi-frequency static imaging in electrical impedance tomography: Part 1. Instrumentation requirements.

Static images of the human body using electrical impedance tomography techniques can be obtained by measuring at two or more different frequencies. The frequencies used depend on the application, and their selection depends on the frequency behaviour of the impedance for the target tissue. An analysis using available data and theoretical models for tissue impedance yields the expected impedance and boundary voltage changes, therefore setting the measurement instrument specifications.

Reduction of motion artifacts using a two-frequency impedance plethysmograph and adaptive filtering.

We measured transthoracic impedance in nine presumed healthy adult subjects with a two-frequency plethysmograph at 57 kHz and 185 kHz. The measurement protocol included periods of normal breathing without motion and periods of motion without breathing. We analyzed the cross-correlation and the ratio between the signals at both frequencies for all the different maneuvers.

Errors in prolonged electrical impedance measurements due to electrode repositioning and postural changes.

Long-term electrical impedance measurements are affected by specific errors. Electrode failure, changes in its impedance due to aging, and postural changes are among the most important. We analyse errors due to electrode replacement and body postural changes.

Signal-to-motion artifact ratio versus frequency for impedance pneumography.

We measured transthoracic impedance between 12.5 and 185 kHz in nine adults. We used a system with two impedance channels, both simultaneously detecting the real part of impedance at two different frequencies.

Acute otitis media in childhood: a study of 20,532 cases.

We present a study of acute otitis media among 20,532 Spanish children during a 6-month period from January through June 1991. The study was done by distributing a questionnaire to all Spanish pediatricians. Of the patients 51.

Clinical, neuropathologic, and genetic studies of a large spinocerebellar ataxia type 1 (SCA1) kindred: (CAG)n expansion and early premonitory signs and symptoms.

We report the clinical, neuropathologic, and genetic studies of a large kindred (family M-ADCA1) with autosomal dominant spinocerebellar ataxia type 1 (SCA1), ascertained in 41 members, with clinical data available in twenty-two. The mean age of onset was 36.3 +/- 6.

A wide-band AC-coupled current source for electrical impedance tomography.

A current source suitable for application in electrical impedance tomography (EIT) is described. The first stage of the commercially available current-feedback amplifier AD844 constitutes a current-conveyor implementation and allows the construction of wide-bandwidth current sources, thus avoiding the mismatching and temperature-induced problems that arise in discrete realizations. The lack in gain accuracy of this circuit is overcome by the inclusion of its input buffer in an operational amplifier (op amp) feedback loop.

Presymptomatic analysis of spinocerebellar ataxia type 1 (SCA1) via the expansion of the SCA1 CAG-repeat in a large pedigree displaying anticipation and parental male bias.

Autosomal dominant cerebellar ataxia type 1 (ADCA1) is a clinical and genetic heterogeneous neurodegenerative disorder which leads to progressive cerebellar ataxia. One defective gene responsible for the disease was first localised to 6p (SCA1, spinocerebellar ataxia type 1) and the mutation has been more recently characterised. We have analysed the CAG-repeat mutation responsible for the SCA1 phenotype in a large Spanish kindred with 41 affected members, in which positive linkage with D6S89 was previously shown.

Exogenous growth hormone: effects on the catabolic response to surgically produced acute stress and on postoperative immune function.

The first purpose of the present prospective randomized study was to determine if the protein catabolic response after operation could be restrained by administration of hypocaloric parenteral nutrition (HPN) plus human growth hormone (hGH). Our second aim was to determine if the administration of hGH could improve the systemic host defenses, thereby reducing the risk of infection. We performed a placebo-controlled randomized double-blind trial in 180 patients after elective cholecystectomy with or without choledochoduodenostomy (placebo = control group, n = 93; hGH-treated group, n = 87).

[Effect of growth hormone and parenteral nutrition on the catabolic phase following major digestive surgery].

The purpose of the present study was to determine if the administration of a biosynthetic human growth hormone (bGH) was able to enhance the efficacy of total parenteral nutrition (PN). Patients (n = 38) who had undergone major gastrointestinal surgery were randomly divided in two groups. Group I (n = 20) treated only with PN and Group II (n = 18) treated as in Group I plus bGH (4 UI/daily).

Effects of growth hormone in patients receiving total parenteral nutrition following major gastrointestinal surgery.

The purpose of the present study was to determine whether the administration of a biosynthetic human growth hormone was capable of enhancing the efficacy of total parenteral nutrition. Patients (n = 38) who had undergone major gastrointestinal surgery were randomly divided into two groups. Group I (n = 20) treated only with PN, and Group II (n = 18) treated as in Group I plus human growth hormone (4 IU daily).

A broadband system for multifrequency static imaging in electrical impedance tomography.

A widely accepted method for static imaging in electrical impedance tomography (EIT) is to measure at two frequencies. The choice of measurement frequencies is application-dependent because some different tissues cannot be distinguished when using two fixed frequencies. We have developed a system that generates signals from 8-10(3) kHz and applies two of these signals simultaneously to the body through a broadband current mirror.

Common-mode feedback in electrical impedance tomography.

When a current is injected into a body, in addition to the voltage profile developed on the surface, a common-mode voltage (CMV) which produces errors in the measurement also appears. The great accuracy needed to reconstruct images in electrical impedance tomography (EIT) requires the use of differential amplifiers with a high common-mode rejection ratio (CMRR) to avoid this error. Nevertheless, the effective CMRR is lower than the differential amplifier ratio due to mismatches in the electrode impedances and other circuits in the measurement channel.

[Echinococcosis of the spleen. Its conservative surgical treatment].

Echinococcosis cysts in the spleen are very rare, even in endemic areas. We report here on 4 patients (0.5% of the total number of cases of echinococcosis disease) who have been treated in the University Hospital Granada from 1970 to 1990.

A study of prognostic factors in blast crisis of Philadelphia chromosome-positive chronic myelogenous leukaemia.

In 80 patients with Ph-positive chronic myelogenous leukaemia the main clinical, haematological and cytogenetical data were recorded at diagnosis of blast crisis and evaluated for prognostic significance. At the time of the analysis 73 patients had died, with a median survival of 4-8 months from diagnosis of blast crisis for the whole series. When analysed as a time-dependent variable, the achievement of a favourable response to chemotherapy resulted in a longer patient's survival.

Identification of a minor component of the sex pheromone ofLeucoptera malifoliella (Lepidoptera, lyonetiidae).

A new minor component in the female volatile extract ofLeucoptera malifoliella (Costa) (Lepidoptera, Lyonetiidae) has been identified as 5,9-dimethyloctadecane (2). The amount detected of the minor compound2 ranged from 4 to 8% in comparison with the major component 5,9-dimethylheptadecane (1). Neither compound has been found in the male volatile extract.

[Intraoperative autotransfusion in massive hemorrhage following thoracic-abdominal trauma].

In the University Hospital of Granada (Spain), 359 surgical trauma patients underwent intraoperative autotransfusion. The patients were divided into 2 groups, according to their blood loss: group I (blood loss less than or equal to 2000 ml) and group II (blood loss greater than 2000 ml). Patients from group I did not require homologous blood transfusion.

Two-frequency impedance plethysmograph: real and imaginary parts.

A four-channel impedance plethysmograph has been designed. Impedance signals are obtained at two frequencies by measuring both real and imaginary parts. Particular attention has been paid to the sine wave generation circuits that provide system versatility.

Benign osteoblastoma of vertebral column and skull. Report of two cases.

Osteoblastoma of the spine is a rare but important cause of back pain and the sciatica syndrome in young adults. Osteoblastoma of the skull is rare and the involvement of the orbital roof is very unusual. Clinical complaints and physical examination are not specific enough to provide a lead to the diagnosis.

[Intraoperative autotransfusion in massive hemorrhage after thoracic-abdominal trauma].

In the University Hospital of Granada (Spain), 359 trauma surgical patients underwent intraoperative autotransfusion. Patients from group I (blood loss less than 2000 ml) did not requiere homologous blood transfusion. So the high risk involved in the type of transfusion was avoided.

An improved buffer for bioelectric signals.

We propose an ac-coupled amplifier that offers a high input impedance, thus making it suitable for bioelectric signal amplification. We also present the necessary formulas for calculating its input impedance and transfer function in order to facilitate its adaptation to different applications.

[Complications in bland struma surgery. A retrospective study based on 2,035 personal cases].

In the present retrospective study we examine the complications arising from simple goiter operations based on the analysis of 2,035 cases. The mortality rate is extremely low (0.3%).

Analysis and assessment of errors in a parallel data acquisition system for electrical impedance tomography.

Three possible data collection configurations for electrical impedance tomography are considered. These are serial current but parallel voltage measurement or full parallel operations. Measurement errors due to stray capacitances, common mode signals and contact impedance are considered.