Value of cervical electrical impedance spectroscopy to predict spontaneous preterm delivery in asymptomatic women: the ECCLIPPx prospective cohort study

OBJECTIVES

Preterm birth (PTB) accounts for two-thirds of deaths of structurally normal babies and is associated with substantial lifetime healthcare costs. Prevention of PTB remains limited by the modest accuracy of prediction methods, namely transvaginal ultrasound (TVS) cervical length (CL) measurement and quantitative cervicovaginal fetal fibronectin (FFN) estimation. We report the first substantive study detailing the predictive performance of a cervical probe device based on electrical impedance spectroscopy (EIS) for PTB - the EleCtriCaL Impedance Prediction of Preterm birth by spectroscopy of the cervix (ECCLIPPx) study. We aimed to compare the accuracy of cervical EIS-based prediction of spontaneous PTB with that of prediction using TVS-CL and FFN in asymptomatic women in the mid-trimester.

METHODS

We studied asymptomatic women with a singleton pregnancy at 20-22 weeks' and 26-28 weeks' gestation. EIS was performed using a Sheffield Mark 5.0 device that makes measurements in the frequency range 76 Hz to 625 kHz using a small probe housing tetrapolar electrodes. TVS-CL and FFN were also measured. The associations of cervical EIS, TVS-CL and FFN with spontaneous delivery before 37 weeks and before 32 weeks were determined by multivariate linear and non-linear logistic regression analysis. Areas under the receiver-operating-characteristics curves (AUC) plots of sensitivity against specificity were used to compare the predictive performance of all parameters, both in isolation and in combination.

RESULTS

Of the 365 asymptomatic women studied at 20-22 weeks who were not receiving treatment, 29 had spontaneous PTB, 14 had indicated PTB and 322 had term birth. At the higher frequencies assessed, cervical EIS predicted spontaneous PTB before 37 weeks with an AUC of 0.76 (95% CI, 0.71-0.81), compared with AUCs of 0.72 (95% CI, 0.66-0.76) for TVS-CL and 0.62 (95% CI, 0.56-0.72) for FFN. Combining all three assessments improved the prediction of spontaneous PTB before 37 weeks (AUC, 0.79 (95% CI, 0.74-0.83)) compared with TVS-CL and FFN alone. Incorporating a history of spontaneous PTB (defined as previous mid-trimester miscarriage or spontaneous PTB (14 to < 37 weeks)) into the cervical EIS prediction model improved the accuracy of prediction of spontaneous PTB before 37 weeks (AUC, 0.83 (95% CI, 0.78-0.87)) and before 32 weeks (AUC, 0.86 (95% CI, 0.82-0.90)).

CONCLUSIONS

Mid-trimester cervical EIS assessment predicts spontaneous PTB. Larger confirmatory studies investigating its potential clinical utility and to inform effective preventive interventions are required. © 2020 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.

Chromosomal rearrangements in holocentric organisms lead to reproductive isolation by hybrid dysfunction: The correlation between karyotype rearrangements and germination rates in sedges

PREMISE OF THE STUDY

Understanding the drivers of speciation is a central task of evolutionary biology. Chromosomal rearrangements are known to play an important role in species diversification, but the role of rearrangements of holocentric chromosomes-chromosomes without localized centromeres-is poorly understood.

METHODS

We made numerous artificial crosses between Carex scoparia individuals of different diploid chromosome numbers and, for comparison, between individuals of the same chromosome number. We studied chromosome pairing and chromosomal rearrangements in the F1 individuals using light microscopy. We then estimated germination rates as a function of geographic distance, genetic distance, chromosome number differences in parents, and pairing irregularities in F1 individuals, using generalized least squares to fit alternative regression models.

KEY RESULTS

The most informative predictors of germination rates in the F1 generation are chromosome number differences and minimum number of chromosome pairing irregularities in the F1 individuals. Genetic and geographic distances between parents are not significant predictors.

CONCLUSIONS

Holocentric chromosomal rearrangements play an important role in postzygotic reproductive isolation in Carex through F1 hybrid inviability and sterility. Hybrid dysfunction seems to be a suitable model for chromosomal speciation when there are several chromosomal rearrangements between parents. However, we have not tested the hypothesis that genome rearrangements may also play an important role in suppressing recombination between cytogenetically divergent populations.

White-tailed deer are a biotic filter during community assembly, reducing species and phylogenetic diversity

Community assembly entails a filtering process, where species found in a local community are those that can pass through environmental (abiotic) and biotic filters and successfully compete. Previous research has demonstrated the ability of white-tailed deer (Odocoileus virginianus) to reduce species diversity and favour browse-tolerant plant communities. In this study, we expand on our previous work by investigating deer as a possible biotic filter altering local plant community assembly. We used replicated 23-year-old deer exclosures to experimentally assess the effects of deer on species diversity (H'), richness (SR), phylogenetic community structure and phylogenetic diversity in paired browsed (control) and unbrowsed (exclosed) plots. Additionally, we developed a deer-browsing susceptibility index (DBSI) to assess the vulnerability of local species to deer. Deer browsing caused a 12 % reduction in H' and 17 % reduction in SR, consistent with previous studies. Furthermore, browsing reduced phylogenetic diversity by 63 %, causing significant phylogenetic clustering. Overall, graminoids were the least vulnerable to deer browsing based on DBSI calculations. These findings demonstrate that deer are a significant driver of plant community assembly due to their role as a selective browser, or more generally, as a biotic filter. This study highlights the importance of knowledge about the plant tree of life in assessing the effects of biotic filters on plant communities. Application of such knowledge has considerable potential to advance our understanding of plant community assembly.

Accuracy of detection of high-grade cervical intraepithelial neoplasia using electrical impedance spectroscopy with colposcopy

Objective

To determine if electrical impedance spectroscopy (EIS) improves the diagnostic accuracy of colposcopy when used as an adjunct.

Design

Prospective, comparative, multi-centre clinical study.

Setting

Three colposcopy clinics: two in England and one in Ireland.

Population

Women referred with abnormal cytology.

Methods

In phase 1, EIS was assessed against colposcopic impression and histopathology of the biopsies taken. In phase 2, a probability index and cut-off value for the detection of high-grade cervical intraepithelial neoplasia (HG–CIN, i.e. grade CIN2+) was derived to indicate sites for biopsy. EIS data collection and analyses were performed in real time and blinded to the clinician. The phase-2 data were analysed using different cut-off values to assess performance of EIS as an adjunct.

Main outcome measure

Histologically confirmed HG–CIN (CIN2+).

Results

A total of 474 women were recruited: 214 were eligible for analysis in phase 1, and 215 were eligible in phase 2. The average age was 33.2 years (median age 30.3 years, range 20–64 years) and 48.5% (208/429) had high-grade cytology. Using the cut-off from phase 1 the accuracy of colposcopic impression to detect HG–CIN when using EIS as an adjunct at the time of examination improved the positive predictive value (PPV) from 78.1% (95% CI 67.5–86.4) to 91.5%. Specificity was also increased from 83.5% (95% CI 75.2–89.9) to 95.4%, but sensitivity was significantly reduced from 73.6% (95% CI 63.0–82.5) to 62.1%, and the negative predictive value (NPV) was unchanged. The positive likelihood ratio for colposcopic impression alone was 4.46. This increased to 13.5 when EIS was used as an adjunct. The overall accuracy of colposcopy when used with EIS as an adjunct was assessed by varying the cut-off applied to a combined test index. Using a cut-off set to give the same sensitivity as colposcopy in phase 2, EIS increased the PPV to detect HG–CIN from 53.5% (95% CI 45.0–61.8) to 67%, and specificity increased from 38.5% (95% CI 29.4–48.3) to 65.1%. NPV was not significantly increased. Alternatively, applying a cut-off to give the same specificity as colposcopy alone increased EIS sensitivity from 88.5% (95% CI 79.9–94.4) to 96.6%, and NPV from 80.8% (95% CI 67.5–90.4) to 93.3%. PPV was not significantly increased. The receiver operator characteristic (ROC) to detect HG–CIN had an area under the curve (AUC) of 0.887 (95% CI 0.840–0.934).

Conclusions

EIS used as an adjunct to colposcopy improves colposcopic performance. The addition of EIS could lead to more appropriate patient management with lower intervention rates.

Glucose 6-phosphate dehydrogenase deficiency increases redox stress and moderately accelerates the development of heart failure

BACKGROUND

Glucose 6-phosphate dehydrogenase (G6PD) is the most common deficient enzyme in the world. In failing hearts, G6PD is upregulated and generates reduced nicotinamide adenine dinucleotide phosphate (NADPH) that is used by the glutathione pathway to remove reactive oxygen species but also as a substrate by reactive oxygen species-generating enzymes. Therefore, G6PD deficiency might prevent heart failure by decreasing NADPH and reactive oxygen species production.

METHODS AND RESULTS

This hypothesis was evaluated in a mouse model of human G6PD deficiency (G6PDX mice, ≈40% normal activity). Myocardial infarction with 3 months follow-up resulted in left ventricular dilation and dysfunction in both wild-type and G6PDX mice but significantly greater end diastolic volume and wall thinning in G6PDX mice. Similarly, pressure overload induced by transverse aortic constriction (TAC) for 6 weeks caused greater left ventricular dilation in G6PDX mice than wild-type mice. We further stressed transverse aortic constriction mice by feeding a high fructose diet to increase flux through G6PD and reactive oxygen species production and again observed worse left ventricular remodeling and a lower ejection fraction in G6PDX than wild-type mice. Tissue content of lipid peroxidation products was increased in G6PDX mice in response to infarction and aconitase activity was decreased with transverse aortic constriction, suggesting that G6PD deficiency increases myocardial oxidative stress and subsequent damage.

CONCLUSIONS

Contrary to our hypothesis, G6PD deficiency increased redox stress in response to infarction or pressure overload. However, we found only a modest acceleration of left ventricular remodeling, suggesting that, in individuals with G6PD deficiency and concurrent hypertension or myocardial infarction, the risk for developing heart failure is higher but limited by compensatory mechanisms.

Marine n3 polyunsaturated fatty acids enhance resistance to mitochondrial permeability transition in heart failure but do not improve survival

Mitochondrial dysfunction in heart failure includes greater susceptibility to mitochondrial permeability transition (MPT), which may worsen cardiac function and decrease survival. Treatment with a mixture of the n3 polyunsaturated fatty acids (n3 PUFAs) docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) is beneficial in heart failure patients and increases resistance to MPT in animal models. We assessed whether DHA and EPA have similar effects when given individually, and whether they prolong survival in heart failure. Male δ-sarcoglycan null cardiomyopathic hamsters were untreated or given either DHA, EPA, or a 1:1 mixture of DHA + EPA at 2.1% of energy intake. Treatment did not prolong survival: mean survival was 298 ± 15 days in untreated hamsters and 335 ± 17, 328 ± 14, and 311 ± 15 days with DHA, EPA, and DHA + EPA, respectively (n = 27-32/group). A subgroup of cardiomyopathic hamsters treated for 26 wk had impaired left ventricular function and increased cardiomyocyte apoptosis compared with normal hamsters, which was unaffected by n3 PUFA treatment. Evaluation of oxidative phosphorylation in isolated subsarcolemmal and interfibrillar mitochondria with substrates for complex I or II showed no effect of n3 PUFA treatment. On the other hand, interfibrillar mitochondria from cardiomyopathic hamsters were significantly more sensitive to Ca(2+)-induced MPT, which was completely normalized by treatment with DHA and partially corrected by EPA. In conclusion, treatment with DHA or EPA normalizes Ca(2+)-induced MPT in cardiomyopathic hamsters but does not prolong survival or improve cardiac function. This suggest that greater susceptibility to MPT is not a contributor to cardiac pathology and poor survival in heart failure.

Effects of glucose-6-phosphate dehydrogenase deficiency on the metabolic and cardiac responses to obesogenic or high-fructose diets

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common human enzymopathy that affects cellular redox status and may lower flux into nonoxidative pathways of glucose metabolism. Oxidative stress may worsen systemic glucose tolerance and cardiometabolic syndrome. We hypothesized that G6PD deficiency exacerbates diet-induced systemic metabolic dysfunction by increasing oxidative stress but in myocardium prevents diet-induced oxidative stress and pathology. WT and G6PD-deficient (G6PDX) mice received a standard high-starch diet, a high-fat/high-sucrose diet to induce obesity (DIO), or a high-fructose diet. After 31 wk, DIO increased adipose and body mass compared with the high-starch diet but to a greater extent in G6PDX than WT mice (24 and 20% lower, respectively). Serum free fatty acids were increased by 77% and triglycerides by 90% in G6PDX mice, but not in WT mice, by DIO and high-fructose intake. G6PD deficiency did not affect glucose tolerance or the increased insulin levels seen in WT mice. There was no diet-induced hypertension or cardiac dysfunction in either mouse strain. However, G6PD deficiency increased aconitase activity by 42% and blunted markers of nonoxidative glucose pathway activation in myocardium, including the hexosamine biosynthetic pathway activation and advanced glycation end product formation. These results reveal a complex interplay between diet-induced metabolic effects and G6PD deficiency, where G6PD deficiency decreases weight gain and hyperinsulinemia with DIO, but elevates serum free fatty acids, without affecting glucose tolerance. On the other hand, it modestly suppressed indexes of glucose flux into nonoxidative pathways in myocardium, suggesting potential protective effects.

Improved mitochondrial function with diet-induced increase in either docosahexaenoic acid or arachidonic acid in membrane phospholipids

Mitochondria can depolarize and trigger cell death through the opening of the mitochondrial permeability transition pore (MPTP). We recently showed that an increase in the long chain n3 polyunsaturated fatty acids (PUFA) docosahexaenoic acid (DHA; 22:6n3) and depletion of the n6 PUFA arachidonic acid (ARA; 20:4n6) in mitochondrial membranes is associated with a greater Ca²⁺ load required to induce MPTP opening. Here we manipulated mitochondrial phospholipid composition by supplementing the diet with DHA, ARA or combined DHA+ARA in rats for 10 weeks. There were no effects on cardiac function, or respiration of isolated mitochondria. Analysis of mitochondrial phospholipids showed DHA supplementation increased DHA and displaced ARA in mitochondrial membranes, while supplementation with ARA or DHA+ARA increased ARA and depleted linoleic acid (18:2n6). Phospholipid analysis revealed a similar pattern, particularly in cardiolipin. Tetralinoleoyl cardiolipin was depleted by 80% with ARA or DHA+ARA supplementation, with linoleic acid side chains replaced by ARA. Both the DHA and ARA groups had delayed Ca²⁺-induced MPTP opening, but the DHA+ARA group was similar to the control diet. In conclusion, alterations in mitochondria membrane phospholipid fatty acid composition caused by dietary DHA or ARA was associated with a greater cumulative Ca²⁺ load required to induced MPTP opening. Further, high levels of tetralinoleoyl cardiolipin were not essential for normal mitochondrial function if replaced with very-long chain n3 or n6 PUFAs.

High-sugar intake does not exacerbate metabolic abnormalities or cardiac dysfunction in genetic cardiomyopathy

OBJECTIVE

A high-sugar intake increases heart disease risk in humans. In animals, sugar intake accelerates heart failure development by increased reactive oxygen species (ROS). Glucose-6-phosphate dehydrogenase (G6PD) can fuel ROS production by providing reduced nicotinamide adenine dinucleotide phosphate (NADPH) for superoxide generation by NADPH oxidase. Conversely, G6PD also facilitates ROS scavenging using the glutathione pathway. We hypothesized that a high-sugar intake would increase flux through G6PD to increase myocardial NADPH and ROS and accelerate cardiac dysfunction and death.

METHODS

Six-week-old TO-2 hamsters, a non-hypertensive model of genetic cardiomyopathy caused by a δ-sarcoglycan mutation, were fed a long-term diet of high starch or high sugar (57% of energy from sucrose plus fructose).

RESULTS

After 24 wk, the δ-sarcoglycan-deficient animals displayed expected decreases in survival and cardiac function associated with cardiomyopathy (ejection fraction: control 68.7 ± 4.5%, TO-2 starch 46.1 ± 3.7%, P < 0.05 for TO-2 starch versus control; TO-2 sugar 58.0 ± 4.2%, NS, versus TO-2 starch or control; median survival: TO-2 starch 278 d, TO-2 sugar 318 d, P = 0.133). Although the high-sugar intake was expected to exacerbate cardiomyopathy, surprisingly, there was no further decrease in ejection fraction or survival with high sugar compared with starch in cardiomyopathic animals. Cardiomyopathic animals had systemic and cardiac metabolic abnormalities (increased serum lipids and glucose and decreased myocardial oxidative enzymes) that were unaffected by diet. The high-sugar intake increased myocardial superoxide, but NADPH and lipid peroxidation were unaffected.

CONCLUSION

A sugar-enriched diet did not exacerbate ventricular function, metabolic abnormalities, or survival in heart failure despite an increase in superoxide production.

High intake of saturated fat, but not polyunsaturated fat, improves survival in heart failure despite persistent mitochondrial defects

AIMS

The impact of a high-fat diet on the failing heart is unclear, and the differences between polyunsaturated fatty acids (PUFA) and saturated fat have not been assessed. Here, we compared a standard low-fat diet to high-fat diets enriched with either saturated fat (palmitate and stearate) or PUFA (linoleic and α-linolenic acids) in hamsters with genetic cardiomyopathy.

METHODS AND RESULTS

Male δ-sarcoglycan null Bio TO2 hamsters were fed a standard low-fat diet (12% energy from fat), or high-fat diets (45% fat) comprised of either saturated fat or PUFA. The median survival was increased by the high saturated fat diet (P< 0.01; 278 days with standard diet and 361 days with high saturated fat)), but not with high PUFA (260 days) (n = 30-35/group). Body mass was modestly elevated (∼10%) in both high fat groups. Subgroups evaluated after 24 weeks had similar left ventricular chamber size, function, and mass. Mitochondrial oxidative enzyme activity and the yield of interfibrillar mitochondria (IFM) were decreased to a similar extent in all TO2 groups compared with normal F1B hamsters. Ca(2+)-induced mitochondrial permeability transition pore opening was enhanced in IFM in all TO2 groups compared with F1B hamsters, but to a significantly greater extent in those fed the high PUFA diet compared with the standard or high saturated fat diet.

CONCLUSION

These results show that a high intake of saturated fat improves survival in heart failure compared with a high PUFA diet or low-fat diet, despite persistent mitochondrial defects.

Role of adiponectin in the development of high fat diet-induced metabolic abnormalities in mice

The adipokine adiponectin is decreased in severe obesity and is inversely associated with adipose mass. Adiponectin is associated with insulin sensitivity and cardioprotection. Obesity frequently results in the development of a "cardiometabolic syndrome" characterized by increased circulating insulin and leptin, and cardiac hypertrophy and dysfunction. This study examined if adiponectin-deficiency affects the development of metabolic and cardiac abnormalities in response to modest obesity. Mice were studied under normal conditions and with mild cardiac pressure-overload induced by abdominal aortic banding. After surgery, wild type and adiponectin-deficient mice were fed a high-fat diet for 8 weeks (45% energy from fat vs. 10%). In wild type mice the high-fat diet increased fat and whole body mass, which corresponded with elevated circulating insulin and leptin and a decrease the glucose/insulin ratio. On the other hand, in adiponectin-deficient mice the high-fat diet had less impact on body mass and no effect on fat mass, insulin, leptin, or glucose/insulin. There was modest cardiac hypertrophy with aortic banding, but no cardiac dysfunction or effects of adiponectin deficiency or diet. The results suggest that the increase in adipose mass, leptin and insulin induced by a high fat diet is dependent on adiponectin. The lack of accelerated cardiac hypertrophy and dysfunction in the adiponectin-deficient mice subjected to aortic banding and the high-fat diet suggest that adiponectin may not play a major role in protecting the heart during the early stages of diet-induced obesity.

Treatment with docosahexaenoic acid, but not eicosapentaenoic acid, delays Ca2+-induced mitochondria permeability transition in normal and hypertrophied myocardium

Intake of fish oil containing docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) prevents heart failure; however, the mechanisms are unclear. Mitochondrial permeability transition pore (MPTP) opening contributes to myocardial pathology in cardiac hypertrophy and heart failure, and treatment with DHA + EPA delays MPTP opening. Here, we assessed: 1) whether supplementation with both DHA and EPA is needed for optimal prevention of MPTP opening, and 2) whether this benefit occurs in hypertrophied myocardium. Rats with either normal myocardium or cardiac hypertrophy induced by 8 weeks of abdominal aortic banding were fed one of four diets: control diet without DHA or EPA or diets enriched with either DHA, EPA, or DHA + EPA (1:1 ratio) at 2.5% of energy intake for 17 weeks. Aortic banding caused a 27% increase in left ventricular mass and 25% depletion in DHA in mitochondrial phospholipids in rats fed the control diet. DHA supplementation raised DHA in phospholipids ∼2-fold in both normal and hypertrophied hearts and increased EPA. DHA + EPA supplementation also increased DHA, but to a lesser extent than DHA alone. EPA supplementation increased EPA, but did not affect DHA compared with the control diet. Ca(2+)-induced MPTP opening was delayed by DHA and DHA + EPA supplementation in both normal and hypertrophied hearts, but EPA had no effect on MPTP opening. These results show that supplementation with DHA alone effectively increases both DHA and EPA in cardiac mitochondrial phospholipids and delays MPTP and suggest that treatment with DHA + EPA offers no advantage over DHA alone.

Electrical impedance measurements: an objective measure of prelabor cervical change

OBJECTIVE

To investigate the use of electrical impedance measurements of the pregnant cervix as an objective measure of cervical favorability (Bishop score > or = 5).

METHODS

A prospective study of 86 women, investigating electrical impedance measurements of the pregnant cervix at the time of induction of labor. Transfer electrical impedance measurements were made by placing a tetrapolar pencil probe of 8 mm in diameter on the surface of the cervix. A Bishop score was determined simultaneously.

RESULTS

A mean resistivity (standard error of the mean) of 7.03 (6.01-8.04) omega(m) was measured for the unfavorable group and 5.34 (4.61-6.07) omega(m) for the favorable group. This was a statistically significant difference (p = 0.016).

CONCLUSION

We highlight the ability of this safe, painless technique to differentiate the favorable from the unfavorable cervix at induction of labor.

Impedimetric sensing of cells on polypyrrole-based conducting polymers

Polypyrrole (PPy) is a conducting polymer that may be electrochemically generated with the incorporation of any anionic species, including net-negatively charged biological molecules such as proteins and polysaccharides. In this article, dermatan and chloride-loaded PPy films were prepared on gold sputter-coated coverslips and various skin derived cells were studied on them by electrochemical impedance spectroscopy. Impedance spectra in the frequency range 1-100 kHz were either determined at specific times or impedance was monitored continuously at specific frequencies. An equivalent impedance circuit was fitted to the recorded impedance spectra to obtain parameters whose contributions could be mapped to intracellular and intercellular current pathways, and the membrane properties of cells. Results show cell-induced impedance changes were detected over PPy modified electrodes and were dependent on cell density and type, monitoring frequency, material composition, and treatment. Lower cell densities were detected on PPy when compared with bare gold. Keratinocyte confluence, as determined by impedimetric analysis, was reached more rapidly on PPy than on gold. This was consistent with previous, more cumbersome, biochemical assays. Electrical equivalent circuit analysis provided evidence that the technique may be extended to discriminate cell type because of the intracellular and intercellular resistance, and cell membrane capacitance being related to cell morphology.

The use of electrical impedance spectroscopy in the detection of cervical intraepithelial neoplasia

The objective of this study was to assess the performance of cervical impedance spectroscopy in the detection of cervical intraepithelial neoplasia (CIN) using the new MKIII impedance probe. A prospective observational study recruited women referred to colposcopy with an abnormal Papanicolaou smear. A pencil probe incorporating four gold electrodes was used to measure electrical impedance spectra from cervical epithelium. Colposcopy examinations, including probe positioning, were video recorded to allow for correlation between results obtained from colposcopic impression, histopathologic examination of colposcopic punch biopsies, and impedance measurements. Cervical impedance-derived parameters R, S, R/S, C, and Fc were assessed to see if significant difference in values obtained in CIN and normal epithelium existed. The performance of the probe in identifying women with CIN was also assessed. One hundred seventy-six women were recruited and 1168 points analyzed. Parameters R, S, and Fc showed significant separation of CIN or squamous intraepithelial lesion (SIL) from squamous, mature metaplastic, and columnar epithelium. Sensitivities of 74% and specificity of 53% can be achieved in identifying CIN 2/3 (High-grade SIL) in screened women. We conclude that cervical impedance spectrometry provides a potentially promising real-time screening tool for CIN with similar sensitivity and specificity to currently used screening tests. Further research is ongoing to develop the probe for potential clinical use.

Study of the optimum level of electrode placement for the evaluation of absolute lung resistivity with the Mk3.5 EIT system

Inter-subject variability has caused the majority of previous electrical impedance tomography (EIT) techniques to focus on the derivation of relative or difference measures of in vivo tissue resistivity. Implicit in these techniques is the requirement for a reference or previously defined data set. This study assesses the accuracy and optimum electrode placement strategy for a recently developed method which estimates an absolute value of organ resistivity without recourse to a reference data set. Since this measurement of tissue resistivity is absolute, in Ohm metres, it should be possible to use EIT measurements for the objective diagnosis of lung diseases such as pulmonary oedema and emphysema. However, the stability and reproducibility of the method have not yet been investigated fully. To investigate these problems, this study used a Sheffield Mk3.5 system which was configured to operate with eight measurement electrodes. As a result of this study, the absolute resistivity measurement was found to be insensitive to the electrode level between 4 and 5 cm above the xiphoid process. The level of the electrode plane was varied between 2 cm and 7 cm above the xiphoid process. Absolute lung resistivity in 18 normal subjects (age 22.6 +/- 4.9, height 169.1 +/- 5.7 cm, weight 60.6 +/- 4.5 kg, body mass index 21.2 +/- 1.6: mean +/- standard deviation) was measured during both normal and deep breathing for 1 min. Three sets of measurements were made over a period of several days on each of nine of the normal male subjects. No significant differences in absolute lung resistivity were found, either during normal tidal breathing between the electrode levels of 4 and 5 cm (9.3 +/- 2.4 Omega m, 9.6 +/- 1.9 Omega m at 4 and 5 cm, respectively: mean +/- standard deviation) or during deep breathing between the electrode levels of 4 and 5 cm (10.9 +/- 2.9 Omega m and 11.1 +/- 2.3 Omega m, respectively: mean +/- standard deviation). However, the differences in absolute lung resistivity between normal and deep tidal breathing at the same electrode level are significant. No significant difference was found in the coefficient of variation between the electrode levels of 4 and 5 cm (9.5 +/- 3.6%, 8.5 +/- 3.2% at 4 and 5 cm, respectively: mean +/- standard deviation in individual subjects). Therefore, the electrode levels of 4 and 5 cm above the xiphoid process showed reasonable reliability in the measurement of absolute lung resistivity both among individuals and over time.

First case of septicemia due to a strain belonging to enteric group 58 (Enterobacteriaceae) and its designation as Averyella dalhousiensis gen. nov., sp. nov., based on analysis of strains from 20 additional cases

When enteric group 58 was first described as a distinct new group of Enterobacteriaceae in 1985, there were only five known human isolates: four from wounds and one from feces. In 1996, we investigated the first blood isolate of enteric group 58, a case of sepsis in a 33-year-old woman receiving total parenteral nutrition. Fifteen additional clinical isolates have since been identified at CDC, including several recognized from a collection of "unidentified" strains dating back to 1973. All strains were characterized with a standard set of 49 biochemical tests used for Enterobacteriaceae, and the results were analyzed to determine phenotypic relatedness and best taxonomic fit. Antibiograms were determined as a taxonomic tool. Original identifications provided by submitting laboratories encompassed a wide variety of Enterobacteriaceae, including 14 species in eight genera, the most common being Enterobacter spp., Salmonella spp., Serratia spp., Kluyvera spp., or Escherichia spp. Enteric group 58 strains have been most frequently isolated from traumatic injuries, fractures, and wounds and rarely from feces. Defining its clinical significance and distinguishing infection from colonization requires further study, but our case report indicates that serious systemic infection can occur. The vernacular name enteric group 58 was used from 1985 to 2004. In this paper, we formally name it Averyella dalhousiensis gen. nov., sp. nov., on the basis of its unique phenotype and its unique 16S rRNA gene sequence. These data indicate that enteric group 58 is not closely related to any of the existing genera or species of Enterobacteriaceae. The type strain is designated CDC 9501--97, and a phenotypic definition is given based on all 21 strains.

Detection of emboli in vessels using electrical impedance measurements--phantom and electrodes

A phantom was constructed to simulate the electrical properties of the neck. A range of possible electrode configurations was then examined in order to improve the sensitivity of the impedance measurement method for the in vivo detection of air emboli. The neck phantom consisted of simulated skin, fat and muscle layers made of agar and a conductive rubber tube mimicking the common carotid artery. The ring-shaped electrodes with a guard electrode showed the highest sensitivity to emboli at short distances.

Electrical bioimpedance readings increase with higher pressure applied to the measuring probe

Electrical bioimpedance spectroscopy (EBIS) is a technique that uses a probe to calculate the transfer impedance from tissues. This transfer impedance can give information about the normal or pathological condition of the tissue. To take readings, pressure has to be applied to the probe in order to get a good contact between the electrodes and the tissue. We have been using EBIS to investigate the early diagnosis of dysplasia and cancer in the human cervix, oesophagus and bladder. We have found that, with increasing pressure (range used here was approximately 1 kPa to approximately 50 kPa), the resistivity readings increase in a consistent way up to 80%. In this paper, we show how this is a case in three different tissue types (oesophageal, gastric and vesical samples). These increases can be higher than those associated with the pathological changes that we are investigating (non-inflamed columnar tissue, for instance, shows values 50% higher than dysplastic columnar tissue). Finite-element modelling was also used to investigate the effect of volume reduction in the connective tissue or stroma. This simulation suggests no strong correlation between reduction of this structure and increase in resistivity. We hypothesize therefore that these changes may be mainly associated with the squeezing of water from the extracellular space. Finally, as pressure is difficult to control by hand, we raise the issue of the necessity of considering this variable when making EIS measurements.

Estimation of the size of air emboli detectable by electrical impedance measurement

Non-invasive detection of air emboli in blood is investigated in vitro using a tetrapolar electrical impedance measurement. A cubic tank with a linear array of four electrodes, spaced approximately 1 cm apart down one side, was filled with 0.2 Sm(-1) saline. Bubbles were generated by carbon dioxide gas. Electrical transfer impedance was measured every 8.2 ms at 1.25 MHz. The movement of bubbles was recorded by a video camera, and their sizes and depths from the middle of the array were measured using captured video images. Changes in transfer impedance caused by passage of bubbles were clearly observed and almost identical with those calculated theoretically. Using lead field theory and experimental results, the fundamental limit on the detectable size of bubbles was estimated at the carotid artery, the great saphenous vein and the cephalic vein. The theoretical results showed that a 0.5 mm diameter bubble is detectable at a depth of 5.3 mm, similar to the depth of the great saphenous and the cephalic veins, and a 2.3 mm diameter bubble is detectable at a depth of 21 mm, similar to the depth of the common carotid artery.

Electrical impedance tomography (EIT): a review

Electrical impedance tomography (EIT) has been the subject of quite intensive research for about 20 years but has yet to become established as a routine tool in healthcare. None the less the volume of published research work in this area is still rising. This review takes a broad look at what has been achieved and attempts to give the reader sufficient information to form an opinion as to the likely future for this interesting area of research.

Low frequency electrical bioimpedance for the detection of inflammation and dysplasia in Barrett's oesophagus

Biological tissues undergoing inflammation and dysplasia seem to exhibit changes in the intercellular space that can be sensed using low frequency electrical impedance methods. Basically, low frequency electric current flows through this space and its widening as well as the disruption of the tight junction decrease the resistance, facilitating current flow. The electrical changes accompanying structural changes from columnar tissue to adenocarcinoma in Barrett's metaplastic mucosa and gastric tissue are illustrated using resected tissue from 32 patients. Two hundred and fifty-eight biopsies were analysed, correlating their electrical resistivity (R) at 9.6 kHz and their histopathological interpretation. Compared to non-inflamed non-dysplastic columnar tissue (R = 4.9 ohms m), the results suggest a small but statistically significant decrease of electrical impedance in columnar tissue showing inflammation (R = 4.2 ohms m, p = 0.016) and a larger decrease when dysplasia is present (R = 3.4 ohms m, p = 0.040). If this method is validated further, this technique could be used to obtain guided biopsies from patients undergoing surveillance programmes for Barrett's oesophagus. We aim to refine this technique using a new system with lower frequencies and, possibly, in vitro (cultured cells) and in vivo (rats) models of Barrett's oesophagus.

Modelling of epithelial tissue impedance measured using three different designs of probe

Impedance measurement is a promising technique for detecting pre-malignant changes in epithelial tissue. This paper considers how the design of the impedance probe affects the ability to discriminate between tissue types. To do this, finite element models of the electrical properties of squamous and glandular columnar epithelia have been used. The glandular tissue model is described here for the first time. Glandular mucosa is found in many regions of the gastrointestinal tract, such as the stomach and intestine, and has a large effective surface area. Firstly, the electrical properties of a small section of gland, with epithelial cells and supportive tissue, are determined. These properties are then used to build up a three-dimensional model of a whole section of mucosa containing many thousands of glands. Measurements using different types of impedance probe were simulated by applying different boundary conditions to the models. Transepithelial impedance, and tetrapolar measurement with a probe placed on the tissue surface have been modelled. In the latter case, the impedance can be affected by conductive fluid, such as mucus, on the tissue surface. This effect has been investigated, and a new design of probe, which uses a guard electrode to counteract this potential source of variability, is proposed.

A study of the morphological parameters of cervical squamous epithelium

Electrical impedance spectroscopy is a technique that has been investigated as a potential method for the diagnosis of epithelial carcinomas. Finite element modelling can provide an insight into the patterns of current flow in normal and pathological epithelium and hence aid in the process of probe design optimization. In order to develop a finite element model of the structure of normal and precancerous cervical squamous epithelium, it was first necessary to obtain the mean values and ranges of a number of morphological tissue parameters. The most important parameters in discriminating normal from neoplastic tissue were identified as being cell size and shape distribution, nuclear-to-cytoplasmic volume ratio and volume of extracellular space. A survey of the literature revealed an absence of reliable quantitative data for these parameters. We therefore present the results of our own basic image analysis on normal and pathological tissue sections, which we hope will be of use to other workers wishing to model cervical squamous epithelium, or other similar tissue structures.

Accuracy of an optically isolated tetra-polar impedance measurement system

Accurate electrical transfer impedance measurement at the high frequencies (> 1 MHz) required to characterise blood and intracellular structures is very difficult, owing to stray capacitances between lead wires. To solve this problem, an optically isolated measurement system has been developed using a phase-locked-loop technique for synchronisation between current injection (drive) and voltage measurement (receive) circuits. The synchronisation error between drive and receive circuits was less than 1 ns. The accuracy and reproducibility of the developed system was examined using a tissue equivalent Cole model consisting of two resistors and one capacitor. The absolute value Z and phase shift theta in impedance of the Cole model was measured at 1.25 MHz by both an LCR meter and the isolated measurement system. The difference between the values measured by the isolated measurement system and those measured by the LCR meter was less than 0.27omega (2.9%) in Z and 0.79 degree in theta. The standard deviation was less than 0.09 omega in Z and 0.60 degree in theta.

Neonatal lungs: maturational changes in lung resistivity spectra

The electrical resistivity of lung tissue can be related to the structure and composition of the tissue and also to the air content. Electrical impedance tomographic measurements have been used on 155 normal children over the first three years of life and 25 pre-term infants, to determine the absolute resistivity of lung tissue as a function of frequency. The results show consistent changes with increasing age in both lung tissue resistivity (5.8 ohm m at birth to 20.9 ohm m at 3 years of age) and in the changes of resistivity with frequency (Cole parameter ratio R/S=0.41 at birth and 0.84 at 3 years of age). Comparison with a lung model showed that the measurements are consistent with maturational changes in the number and size of alveoli, the extracapillary blood volume and the size of the extracapillary vessels. However, the results show that the process of maturation is not complete at the age of three years.

Neonatal lungs--can absolute lung resistivity be determined non-invasively?

The electrical resistivity of lung tissue can be related to the structure and composition of the tissue and also to the air content. Conditions such as pulmonary oedema and emphysema have been shown to change lung resistivity. However, direct access to the lungs to enable resistivity to be measured is very difficult. We have developed a new method of using electrical impedance tomographic (EIT) measurements on a group of 142 normal neonates to determine the absolute resistivity of lung tissue. The methodology involves comparing the measured EIT data with that from a finite difference model of the thorax in which lung tissue resistivity can be changed. A mean value of 5.7 +/- 1.7 omega(m) was found over the frequency range 4 kHz to 813 kHz. This value is lower than that usually given for adult lung tissue but consistent with the literature on the composition of the neonatal lung and with structural modelling.

Resistivity changes in conductive silicone sheets under stretching

This paper reports a preliminary finding associated with an investigation of how tissues respond to mechanical stress. The stress distribution within the tissue may be the result of normal function, for example, joint forces, or it may result from interventions such as tissue suturing during or after surgery. We sought to combine electrical and mechanical computational models in order to better understand the interaction between the two. For example, if mechanical stress is applied to tissue this may change the cell arrangements within the tissue matrix and hence change the electrical properties. If this interaction could be determined, then it should be possible to use electrical impedance tomography measurements to identify stress patterns in tissues. Measurements of resistivity changes have been made in conductive silicone rubber sheets when subject to a uniaxial stress of up to 10%. Relatively large changes in resistivity are produced (up to 200%). These changes are far larger than those predicted arising from topological changes alone. It is suggested that under stress the conductive islands of carbon within the silicone rubber sheet undergo a reversible disassociation from their neighbours and that the material's electrical properties change under load. If similar stress-resistivity relationships occur within biological materials it may be possible to recover the stress fields within tissues from transfer impedance measurements and thereby predict if actions such as inappropriate suture tension will compromise tissue viability.

Modelled current distribution in cervical squamous tissue

The electrical properties of cervical squamous epithelium have been modelled in the frequency range 100 Hz to 10 MHz. The hierarchical modelling process comprises a cellular level stage, which includes detailed models of cells typical of different depths within the epithelium and a tissue model, which utilizes electrical properties obtained from the cellular models. The fit between the modelled and measured impedance spectra and the distribution of current with depth depends on the macroscopic model structure. Both the properties of the basement membrane and the presence of a surface mucus layer are shown to have a significant effect. The best fit with measured data is obtained when a 10 microm thick, high-conductivity surface layer is included in the tissue model.

Surface electromyography using electrode arrays: a study of motor neuron disease

The use of electromyography (EMG) is limited, particularly in the investigation of children, by the invasive nature of needle electrodes. Surface electrode techniques are an attractive alternative but the detected signals are greatly influenced by volume conductor effects, thus making their interpretation problematic. Using finite element analysis we investigated the relationship between surface potential distribution and motor unit depth, incorporating anisotropic conductivity to model muscle tissue and a range of subcutaneous fat thicknesses. The modeling results were used to analyze data recorded with a 16-channel surface electrode array, from 10 normals subjects and 12 patients with motor neuron disease. Differences in the motor units between the two groups were statistically significant (P < 0.01) and are consistent with reinnervation and increased motor unit territory in the patient group. This noninvasive technique shows promise as a more acceptable alternative to the use of conventional needle electrodes for neurophysiological investigations.

Mk3.5: a modular, multi-frequency successor to the Mk3a EIS/EIT system

This paper describes the Sheffield Mk3.5 EIT/EIS system which measures both the real and imaginary part of impedance at 30 frequencies between 2 kHz and 1.6 MHz. The system uses eight electrodes with an adjacent drive/receive electrode data acquisition protocol. The system is modular, containing eight identical data acquisition boards, which contain DSPs to generate the drive frequencies and to perform the FFT used for demodulation. The current drive is in three sequentially applied packets, where each packet contains ten summed sine waves. The data acquisition system is interfaced to a host PC through an optically isolated high speed serial link (RS485) running at 2 Mbaud (2 Mbits s(-1)). Measurements on a saline filled tank show that the average signal to noise performance of the system is 40 dB measured across all frequencies and that this figure is independent of frequency of measurement. These results suggest that the current system is 10 dB better in absolute terms than the previous Sheffield (Mk3a) system.

An in vivo comparative study of the pregnant and nonpregnant cervix using electrical impedance measurements

Electrical impedance may be measured using electrodes on the surface of the cervix and recording the potential that results when an electrical current is passed. Increased hydration of the cervix has been described throughout pregnancy and occurs most dramatically before labour. This study compared tissue impedance measurements of the pregnant and non-pregnant cervix and found a statistically significant lower value (P < 0.001) in pregnancy. Further work may show that such measurements alter in relation to labour onset.

Assessing the conditions for in vivo electrical virtual biopsies in Barrett's oesophagus

It has previously been shown that it is possible to differentiate between squamous and columnar epithelia in rat and resected human tissues using an impedance probe to make in vitro measurements. This probe can be passed down an endoscope allowing measurements to be made in patients. However, the probe emerges parallel to the oesophageal wall, with little room to manoeuvre. The conditions of control required to give reliable readings have been investigated. The importance of pressure applied and the angle of approach to the oesophagus was assessed. Pressures in the range 26.6 Pa to 46.3 kPa and angles in the range 15-90 degrees were considered. In in vitro studies it was observed that it was possible to obtain consistent readings with pressures greater than 2.9 kPa and with angles greater than 15 degrees between the probe and the oesophagus. These conditions can be achieved in vivo, and readings obtained from twelve patients are shown (45 readings on normal squamous, 34 on Barrett's oesophagus and 22 on stomach). At low frequencies (9.6-153.2 kHz), a Mann-Whitney test shows a significant difference (p < 0.001) when comparing the means from squamous and columnar, and also when readings from Barrett's and normal gastric epithelia are compared (p < 0.001).

Relation between tissue structure and imposed electrical current flow in cervical neoplasia

BACKGROUND

When an electrical potential is applied to human tissue, the pattern of the resulting current flow is determined by the shapes, arrangements, and internal structure of the tissue cells. By measurement of the electrical current patterns over a range of frequencies, and use of an inverse modelling procedure, electrical variables describing the tissue structure can be calculated. We used this method to develop a screening technique for the detection of cervical precancers.

METHODS

We used a pencil probe (diameter 5 mm) to measure electrical impedance spectra from eight points on the cervix in 124 women with abnormal cervical smears. Variables that should be sensitive to the expected tissue changes were calculated. These were compared with the colposcopic results.

FINDINGS

The measured electrical impedance changes were those predicted on the basis of the expected tissue structures. Measurements made on normal squamous tissues were well separated from those made on precancerous tissues. We constructed receiver-operating-characteristic curves, comparing measurements made on normal tissue and that showing cervical intraepithelial neoplasia grade 2/3; the area under the curve was 0.951. These groups of women could be separated with a sensitivity of 0.92 and a specificity of 0.92.

INTERPRETATION

Characteristics of the electrical impedance spectra of tissues can be explained by changes in cell arrangements (layering) and in the size of the nuclei. This relation opens the way to deriving tissue structure from electrical impedance spectral measurements. We show that this approach can be used to give good separation of normal and precancerous cervical tissues.

Movement artefact rejection in impedance pneumography using six strategically placed electrodes

In this paper, we have proposed a technique for reducing movement artefacts in impedance pneumography by placing six electrodes at appropriate locations and suitably combining the measurements obtained. The strategy for electrode placement was based on the observation that the electrodes appeared to slide over the rib cage along with the skin, during movement. A volume conductor model of the thoracic cavity was developed and movement artefacts were simulated by shifting the electrodes to a different location on the surface. The impedance changes due to movement in one of the measurements of a 'symmetrical pair' were 180 degrees out of phase with respect to those observed in the other measurement of that pair. However, the impedance changes due to breathing were in phase in both these measurements. Thus, it was possible to reduce movement artefacts by taking a mean of these measurements without affecting the breathing related changes. The six electrodes could be configured into two such symmetrical pairs. The same observation was made in experimental data recorded from human subjects. This indicated that movement artefacts were caused by sliding of electrodes along with the skin and could be reduced by using the six-electrode configuration.

Diuretic induced change in lung water assessed by electrical impedance tomography

Monitoring patients with left ventricular failure can be difficult. Electrical impedance tomography (EIT) produces cross-sectional images of changes in the impedance of the thorax. We measured changes in the electrical impedance of the lung in nine volunteers following a diuretic challenge. The hypothesis was that lung impedance would increase with diuretic induced fluid loss. Heart rate, blood pressure and urine output were also recorded. After diuretic the mean urine output was 1220 ml compared with 187 ml after placebo. Following diuretic administration, mean thoracic impedance increased by 13.6% (p < 0.01) and lung impedance increased by 7.8% (p < 0.05). Taken as a group there was a correlation between overall impedance change and total urine output. However, for each individual, the time course of change in impedance and urine output did not correlate significantly. Our findings show that EIT may offer a better guide to the response of the lung to diuretic treatment than simply measuring urine output. The urine output is neither specific nor sensitive in the assessment of lung water. Mean lung impedance, however, is largely determined by lung water. The study showed that lung impedance can be recorded at supra-normal values. EIT may help in the management of patients with excess lung water.

A comparison of modified Howland circuits as current generators with current mirror type circuits

Multi-frequency electrical impedance tomography (EIT) systems require stable voltage controlled current generators that will work over a wide frequency range and with a large variation in load impedance. In this paper we compare the performance of two commonly used designs: the first is a modified Howland circuit whilst the second is based on a current mirror. The output current and the output impedance of both circuits were determined through PSPICE simulation and through measurement. Both circuits were stable over the frequency ranges 1 kHz to 1 MHz. The maximum variation of output current with frequency for the modified Howland circuit was 2.0% and for the circuit based on a current mirror 1.6%. The output impedance for both circuits was greater than 100 kohms for frequencies up to 100 kHz. However, neither circuit achieved this output impedance at 1 MHz. Comparing the results from the two circuits suggests that there is little to choose between them in terms of a practical implementation.

Cole equation modelling to measurements made using an impulse driven transfer impedance system

Electrical impedance measurements are used to obtain information about a subject, tissue sample or tissue model under test. There are several ways of obtaining these impedance data and thereafter analysing the data to obtain relevant parameters. This paper shows how a completely isolated drive and receive system using current pulses, as opposed to sine waves, achieves good fitted results with resistor-capacitor Cole phantoms.

Monitoring patients with left ventricular failure by electrical impedance tomography

Acute left ventricular failure (LVF) is a common medical emergency but detection and monitoring of pulmonary oedema remains problematic. Fluid is an important determinant of tissue impedance. Electrical impedance tomography (EIT) is a non-invasive technique allowing localisation of impedance changes within tissue. We have investigated the relationship between LVF and the electrical impedance of lung tissue. Twenty patients with a clinical diagnosis of acute left ventricular failure were compared with 30 normal subjects. Patients were monitored using serial chest radiographs and electrical impedance tomography measurements of lung impedance during hospital admission. Radiographs were graded according to the severity of pulmonary oedema by two independent radiologists. Lung impedance was significantly (P<0.0001) lower than normal in patients with left ventricular failure. Values returned towards the normal range as LVF resolved. There was a similar improvement in the score of the chest radiographs. The electrical impedance of the lung is low in left ventricular failure and increases following treatment.

A comparison of neonatal and adult lung impedances derived from EIT images

An objective method of extracting respiratory data from lung images is presented, together with a technique for automatically generating regions of interest delineating the anterior and posterior regions of the lungs. The method is used to extract data on the change in lung impedance with frequency, and on calculated Cole parameters, from 19 normal neonates (gestational age 32 to 42 weeks) and 8 normal adults (age 21 to 82 years). A comparison of the impedance properties of neonatal and adult lungs was made. The variation of lung impedance with frequency in neonates, as derived from EIT images, is significantly different from that found for adults. The implications for a model of the electrical impedance of lung tissue are discussed.

Anatomical and physiological models for surgical simulation

A considerable amount of effort has been aimed towards developing real-time deformable objects for surgical simulation, but very little work has been aimed towards including physiology within the soft tissue models. A simulator that links the structural and functional aspects of the human body would allow the user to develop a better understanding of the intrinsic link between anatomy and physiology. This positional paper discusses the challenges facing the creation of and the development of an integrated physiological and anatomical soft tissue model for use in surgical simulators. It explores the artificial dichotomy between anatomy and physiology and the issues it raises, by considering a suturing simulator capable of modelling ischaemia.