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

Assessing the influence of parameters on tissue welding in small bowel end-to-end anastomosis in vitro and in vivo

BACKGROUND

The use of high-frequency electric welding technology for intestinal end-to-end anastomosis holds significant promise. Past studies have focused on in vitro, and the safety and efficacy of this technology is uncertain, severely limiting the clinical application of this technology. This study investigates the impact of compression pressure, energy dosage, and duration on anastomotic quality using a homemade anastomosis device in both in vitro and in vivo settings.

METHODS

Two hundred eighty intestines and 5 experimental pigs were used for in vitro and in vivo experiments, respectively. The in vitro experiments were conducted to study the effects of initial pressure (50-400 kpa), voltage (40-60 V), and time (10-20 s) on burst pressure, breaking strength, thermal damage, and histopathological microstructure of the anastomosis. Optimal parameters were then inlaid into a homemade anastomosis and used for in vivo experiments to study the postoperative porcine survival rate and the pathological structure of the tissues at the anastomosis and the characteristics of the collagen fibers.

RESULTS

The anastomotic strength was highest when the compression pressure was 250 kPa, the voltage was 60 V, and the time was 15 s. The degree of thermal damage to the surrounding tissues was the lowest. The experimental pigs had no adverse reactions after the operation, and the survival rate was 100%. 30 days after the operation, the surgical site healed well, and the tissues at the anastomosis changed from immediate adhesions to permanent connections.

CONCLUSION

High-frequency electric welding technology has a certain degree of safety and effectiveness. It has the potential to replace the stapler anastomosis in future and become the next generation of new anastomosis device.

A Narrative Review on the Clinical Utility of Electrical Impedance Spectroscopy for Diagnosing High-Grade Cervical Intraepithelial Neoplasia

Colposcopy constitutes a pivotal step in the diagnosis and management of cervical intraepithelial neoplasia; nevertheless, the method has several inherent and external limitations. Electrical impedance spectroscopic (EIS) has been among the adjuncts that have been developed to increase the diagnostic accuracy of colposcopy. EIS is based on the principle that the trajectory of electrical current alters depending on the consistency of the tissues. In the present study, we investigate the diagnostic accuracy and clinical utility of EIS by means of searching the available evidence. Our search yielded 17 articles during the period 2005-2023. Subsequently, we focused on the performance metrics of the included studies. The general concept is that EIS, in combination with colposcopy, is a method with increased sensitivity and specificity in detecting high-grade cervical intraepithelial neoplasia as compared to colposcopy alone. However, we documented a heterogeneous distribution of these and other metrics, including the positive predictive value, the negative predictive value, and the area under the receiver operating characteristic curve (AUC). Additionally, we located potential confounders that might hamper the measurements of EIS and, as such, warrant further investigation in future research. We conclude that future studies should be directed towards randomized multicentric trials, whereas the advent of artificial intelligence might improve the diagnostic accuracy of the method by helping incorporate a large amount of data.

Piezoresistivity modeling of soft tissue electrical-mechanical properties: A validation study

In general, the electrical property of soft tissues is sensitive to the force applied to their surface. To further study the relationship between the force and the electrical property of soft tissues, this paper attempts to investigate the effect of static and higher-order stresses on electrical properties. Overall, a practical experimental platform is designed to acquire the force information and the electrical property of soft tissues during a contact procedure, which is featured different compression stimuli, such as constant pressing force, constant pressing speed, and step-force compression, etc. Furthermore, the piezoresistive characteristic is innovatively introduced to model the mechanical-electrical properties of soft tissue. Finite Element Modeling (FEM) is adopted to fit the static piezoresistivity of the soft tissue. Finally, experimental studies were performed to demonstrate the effect of stress on the electrical properties and the feasibility of the proposed piezoresistive model to describe soft tissues' mechanical and electrical properties.

Multi-Physical Tissue Modeling of a Human Urinary Bladder

A multi-physical model of a human urinary bladder is an essential element for the potential application of electrical impedance spectroscopy during transurethral resection surgery, where measurements are taken at different fill levels inside the bladder. This work derives a multi-physical bladder tissue model that incorporates the electrical impedance properties with dependence on mechanical deformation due to filling of the bladder. The volume and ratio of the intracellular to extracellular tissue fluid heavily influence the electrical impedance characteristics and thus provide the connection between the mechanical and electrical domains. Modeling the fluid within the tissue links both the physical and histological processes and enables useful inferences of the properties from empiric observations. This is demonstrated by taking impedance measurements at different fill volumes. The resulting model provides a tool to analyze impedance measurements during surgery at different stress levels. In addition, this model can be used to determine patient-specific tissue parameters.

Positron emission tomography study of effects of two pressure-relieving support surfaces on pressure ulcer development

OBJECTIVE

To study the pathophysiological cascade of pressure ulcer (PU) development consisting of tissue deformation, inflammation and hypoxia.

METHOD

In this crossover study, deformation was measured with computerised tomography (CT) linked with contact area reflecting immersion and envelopment. Inflammation and hypoxia were measured using subepidermal moisture (SEM), skin temperature and tissue perfusion with positron emission tomography. These variables were investigated under 90 minutes of pressure exposure caused by two functionally different support surfaces-a regular foam mattress and a minimum pressure air (MPA) mattress.

RESULTS

A total of eight healthy volunteers took part in the study. There was major tissue deformation when the participants lay on a foam mattress while the tissues retained their original shape on the MPA mattress (p<0.0001). During the pressure exposure, the skin temperature increased significantly on both support surfaces but the final temperature on the foam mattress was about 1oC higher than on the MPA mattress (p<0.0001). SEM increased on both support surfaces compared with an unexposed reference site, but the cause may be different between the two support surfaces. Tissue perfusion was lowest in the skin followed by subcutaneous tissues and highest in the muscles. The pressure exposure did not cause any substantial changes in perfusion. The results showed that tissue deformation was more pronounced, the support surface contact area (envelopment), was smaller and the skin temperature higher on the foam mattress than on the MPA mattress, without significant differences in tissue perfusion.

CONCLUSION

In this study, the MPA mattress support surface had mechanobiological properties that counteracted tissue deformation and thereby may prevent PUs.

Sub-epidermal moisture measurement: an evidence-based approach to the assessment for early evidence of pressure ulcer presence

This paper aims to discuss the literature pertaining to early pressure-shear induced tissue damage detection, with emphasis on sub-epidermal moisture measurement (SEM). The current method for pressure detection is visual skin assessment (VSA); however, this method is fraught with challenges. Advances in early detection of pressure ulcers are reported in the literature and mainly involve measuring inflammation markers on weight-bearing anatomical areas in order to capture the first signs of tissue damage. One novel technique currently in use is SEM measurement. This biophysical marker is the product of plasma that leaks as a response to local inflammation arising due to pressure-shear induced damage over bony prominences. The early detection of tissue damage is beneficial in two different ways. First, it enables early intervention when the damage is still microscopic and reversible and, therefore, has the potential to prevent further aggravation of healthy surrounding tissue. This arises by avoiding the causation of the problem and stopping the knock-on effect of inflammation, especially when the rapid pressure ulceration pathway of deformation is in place. Second, when the slow ischaemic-reperfusion related mechanism is undergoing, cell death can be avoided when the problem is identified before the cell reaches the "death threshold," completely averting a pressure ulcer.

Effect of Open-Ended Coaxial Probe-to-Tissue Contact Pressure on Dielectric Measurements

Open-ended coaxial probes are widely used to gather dielectric properties of biological tissues. Due to the lack of an agreed data acquisition protocol, several environmental conditions can cause inaccuracies when comparing dielectric data. In this work, the effect of a different measurement probe-to-tissue contact pressure was monitored in the frequency range from 0.5 to 20 GHz. Therefore, we constructed a controlled lifting platform with an integrated pressure sensor to exert a constant pressure on the tissue sample during the dielectric measurement. In the pressure range from 7.74 kPa to 77.4 kPa, we observed a linear correlation of - 0 . 31 ± 0 . 09 % and - 0 . 32 ± 0 . 14 % per kPa for, respectively, the relative real and imaginary complex permittivity. These values are statistically significant compared with the reported measurement uncertainty. Following the literature in different biology-related disciplines regarding pressure-induced variability in measurements, we hypothesize that these changes originate from squeezing out the interstitial and extracellular fluid. This process locally increases the concentration of membranes, cellular organelles, and proteins in the sensed volume. Finally, we suggest moving towards a standardized probe-to-tissue contact pressure, since the literature has already demonstrated that reprobing at the same pressure can produce repeatable data within a 1% uncertainty interval.

Determination of Tissue Thermal Conductivity as a Function of Thermal Dose and Its Application in Finite Element Modeling of Electrosurgical Vessel Sealing

OBJECTIVE

Electrosurgical vessel sealing is a process commonly used to control bleeding during surgical procedures. Finite element (FE) modeling is often performed to obtain a better understanding of thermal spread during this process. The accuracy of the FE model depends on the implemented material properties. Thermal conductivity is one of the most important properties that affect temperature distribution. The goal of this study is to determine the tissue thermal conductivity as a function of thermal dose. Methods: We developed an iterative approach to correlating tissue thermal conductivity to more accurately calculated thermal dose, which cannot be experimentally measured. The resulting regression model was then implemented into an electrosurgical vessel sealing FE model to examine the accuracy of this FE model. Results: The results show that with the regression model, more reasonable temperature and thermal dose prediction can be achieved at the center of the sealed vessel tissue. The resulting electrical current and impedance from the FE model match with the experimental results. Conclusion: The developed approach can be used to determine the correlation between thermal dose and thermal conductivity. Describing the thermal conductivity as a function of thermal dose allows modeling of irreversible changes in tissue properties. Significance: By having a more accurate temperature estimation at the center of the sealed vessel, more insight is provided into how the tissue reacts during the vessel sealing process.

Design, Construction and Validation of an Electrical Impedance Probe with Contact Force and Temperature Sensors Suitable for in-vivo Measurements

Bioimpedance spectroscopy measurements can be used for tissue characterization. These measurements can be performed in soft tissues by direct contact of a non-invasive probe consisting of two or four electrodes. The amount of force applied by users can be quite different, and the measurements can vary as a result. To compensate for this, we have built an electrical impedance probe (diameter 3.2 mm) with fibre optic contact-force and temperature sensors built in it. The different sensors of the probe were tested individually. The errors in magnitude and phase angle of the probe are <0.9% and <4°, respectively, for a 0.9% NaCl solution. The linear dynamic range of the force sensor was from 0 to 100 grams. An ex-vivo experiment on a section of proximal colon from a guinea-pig was performed. Twenty bioimpedance measurements were taken in a frequency range of 5 kHz to 1 MHz, while simultaneously recording the force applied. For an increase in contact pressure applied to tissue from 0 to 15.4 kPa, the maximum change in resistivity was 33% at 5 kHz and the minimum was 6.6% at 142 kHz. The probe is small enough to be introduced via the instrument port of an endoscope.

Effects of precompression time and strength on the physical characteristics of quasi-stapled porcine small intestinal tissue

Precompression is vital when performing gastrointestinal anastomosis with staplers. However, research on the internal changes in intestinal tissue under stapling is lacking, and the effects of precompression have not been clarified. In this study, a stapler was modified, and the multifrequency bioimpedance of porcine small intestinal tissue was measured from before clamping the tissue with the stapler until the release of the tissue after precompression without firing. The Cole _Y model was fitted to the bioimpedance, and the changes in the tissue were analyzed using the model parameters: G₀, extracellular fluid conductance, and Δ G, intracellular fluid conductance. The results show that the changes of G₀ and Δ G could be divided into four stages: rapid decrease, slow decrease, intense resilience, and slow recovery. During slow decrease stage, there was a greater decrease of G₀ and Δ G (1.02E-05 ± 1.12E-05 S and 1.73E-05 ± 2.12E-05 S in precompression time's increase, 1.68E-05 ± 8.74E-06 S and 1.20E-05 ± 1.09E-05 S in precompression strength's increase). On the contrary, during intense resilience stage, there was a less increase of G₀ and Δ G (0.88E-05 ± 4.86E-05 S and 9.15E-05 ± 9.37E-05 S in precompression time's increase, 2.72E-05 ± 3.53E-05 S and 1.02E-04 ± 8.54E-05 S in precompression strength's increase). In conclusion, the effects of precompression factors on tissue have been preliminary revealed: the tissue under precompression becomes thinner and less resilient. To improve the precompression effects and reduce any excessive pressure exerted on the staples by tissue resilience, the precompression time and strength should be increased appropriately.

Monitoring the Effect of Contact Pressure on Bioimpedance Measurements

This paper presents preliminary results on the effect of contact pressure on bioimpedance measurements in an excised section of human colon tissue. The impedance measurements were performed with a small diameter probe suitable for in-vivo use, which is capable of measuring contact force. Force measurements are performed by fiber optic sensor which consisted of a Fiber Bragg Grating. The obtained results highlight the importance on limiting the applied pressure during bioimpedance measurements.

Comparative study of separation between ex vivo prostatic malignant and benign tissue using electrical impedance spectroscopy and electrical impedance tomography

OBJECTIVE

Currently no efficient and reliable technique exists to routinely assess surgical margins during a radical prostatectomy. Electrical impedance spectroscopy (EIS) has been reported as a potential technique to provide surgeons with real-time intraoperative margin assessment. In addition to providing a quantified measure of margin status, a co-registered electrical impedance tomography (EIT) image presented on a surgeon's workstation could add value to the margin assessment process.

APPROACH

To investigate this, we conducted a comparative study between EIS and EIT to evaluate the potential these technologies might have for margin assessment. EIS and EIT data was acquired from ex vivo human prostates using a multi-electrode endoscopic impedance acquisition probe.

MAIN RESULTS

EIS and EIT show good predictive performance with a 0.76 and 0.80 area-under-curve (AUC), respectively, when considering discrete frequencies only. A machine learning (ML) algorithm is implemented to combine features, which improves the AUCs of EIS and EIT to 0.84 and 0.85, respectively. Single-step EIT takes significantly less time to reconstruct than multi-step EIT, yet provides similarly accurate classification results, making the single-step approach a potential candidate for real-time margin assessment. While the ML-based approach clearly exhibits benefits as compared to the single feature assessment, the decision to use EIS versus EIT is unclear since each approach performs better for different subsets of tissue classifications.

SIGNIFICANCE

The results presented in this paper corroborate our previous studies and present the strongest evidence yet that an intraoperative-capable impedance probe can be used to distinguish benign from malignant prostate tissues. An in vivo study with a large cohort will be necessary to definitively determine the preferred approach and to show the clinical effectiveness of using this technology for margin assessment.

Predicting burst pressure of radiofrequency-induced colorectal anastomosis by bio-impedance measurement

The present study investigates the relationship between bio-impedance and burst pressure of colorectal anastomosis created by radiofrequency (RF)-induced tissue fusion. Colorectal anastomosis were created with ex vivo porcine colorectal segments, during which 5 levels of compression pressure were applied by a custom-made bipolar prototype, with 5 replicate experiments at each compression pressure. Instant anastomotic tensile strength was assessed by burst pressure. Bio-impedance of fused tissue was measured by Impedance Analyzer across frequency that 100 Hz to 3 MHz. Statistical analysis shows only a weak correlation between bio-impedance modulus and burst pressures at frequency of 445 kHz ([Formula: see text]  =  -0.426, P  =  0.099  >  0.05). In contrast, results demonstrated a highly significant negative correlation between reactance modulus and burst pressures ([Formula: see text]  =  -0.812, P  =  0.000  <  0.05). The decrease in mean reactance modulus with increasing burst pressures was highly significant (P  =  0.019  <  0.05). The observed strong negative correlation between reactance modulus and burst pressures at frequency of 445 kHz indicates that reactance is likely to be a good index for tensile strength of RF-induced colorectal anastomosis, and should be considered for inclusion in a feedback loops in devices design.

Changes in Small Intestine Tissue Compressed by a Linear Stapler Based on Cole Y Model

Clarifying changes in gastrointestinal tissue compressed by surgical stapler is a crucial prerequisite for stapler design optimization. For this study, a stapler was modified, and multifrequency bioimpedance of a porcine small intestine tissue compressed by the stapler was measured. The Cole _Y model was fitted to the bioimpedance, and changes in tissue were analyzed using model parameters: G ₀, extracellular fluid conductance; ΔG, intracellular fluid conductance; C _cpeF, equivalent capacitance of cell membrane. The changes could be divided into two stages: first, all parameters decreased sharply with slopes more than 15.70 ± 2.67, 4.25 ± 1.23 μS/s and 72.68 ± 6.99 pF/s respectively; and subsequently, with an increase in compression strength, G ₀ decreased with slopes less than 2.54 ± 0.40 μS/s, ΔG decreased slightly with slope of 0.26 ± 0.04 μS/s after fluctuating mildly, and C _cpeF remained nearly invariant after initially increasing with slope of -2.94 ± 0.64 pF/s. In conclusion, when the stapler is closed, a portion of tissue is squeezed out of the measurement space, causing all parameters' sharp decrease. Subsequently, the stapler continues compressing the tissue, leading to extracellular fluid expulsion. The changes in intracellular fluid are related to the compression strength and may be explained by cell restoration. This study could provide a basis for stapler design optimization.

Subepidermal moisture (SEM) and bioimpedance: a literature review of a novel method for early detection of pressure-induced tissue damage (pressure ulcers)

Current detection of pressure ulcers relies on visual and tactile changes at the skin surface, but physiological changes below the skin precede surface changes and have a significant impact on tissue health. Inflammatory and apoptotic/necrotic changes in the epidermal and dermal layers of the skin, such as changes in interstitial fluid (also known as subepidermal moisture (SEM)), may precede surface changes by 3–10 days. Those same epidermal and subepidermal changes result in changes in the electrical properties (bioimpedance) of the tissue, thereby presenting an objective, non‐invasive method for assessing tissue damage. Clinical studies of bioimpedance for the detection of pressure ulcers have demonstrated that changes in bioimpedance correlate with increasing severity of pressure ulcer stages. Studies have also demonstrated that at anatomical locations with pressure ulcers, bioimpedance varies with distance from the centre of the pressure ulcers. The SEM Scanner, a handheld medical device, offers an objective and reliable method for the assessment of local bioimpedance, and therefore, assessment of tissue damage before signs become visible to the unaided eye. This literature review summarises pressure ulcer pathophysiology, principles of bioimpedance and clinical research using bioimpedance technology to assess pressure ulcers.

Diagnosing early Barrett's neoplasia and oesophageal squamous cell neoplasia by bioimpedance spectroscopy in human tissue

BACKGROUND

Detection of early oesophageal cancer in surrounding normal tissue can be challenging, but detection is essential to determine the subsequent treatment. Dysplastic tissue can be detected by using electrical impedance spectroscopy (EIS).

OBJECTIVE

The aim of the present study was to evaluate the feasibility and value of EIS in the diagnosis of oesophageal neoplasia.

METHODS

This prospective ex-vivo study included 23 patients with early oesophageal cancer (17 with Barrett's cancer and six with early squamous cell cancer). Immediately after endoscopic resection, the electrical properties of the resected specimens were investigated using a pencil probe (5 mm in diameter, frequency range from 100 Hz to 1 MHz). Punch biopsies were taken from the measured site in order to compare the results of EIS with histology.

RESULTS

EIS was able to detect dysplastic oesophageal mucosa with a high rate of accuracy (82% in Barrett's oesophagus and 100% in squamous oesophagus) A total of 54 different sites in 26 tumours were evaluated.

CONCLUSIONS

EIS was able to differentiate reliably between non-neoplastic and neoplastic oesophageal mucosa. Using EIS, it might be possible to use it for targeted biopsies and to avoid unnecessary biopsies during cancer surveillance in future.

Bioimpedance spectroscopy: a new tool to assess early esophageal changes linked to gastroesophageal reflux disease?

Bioimpedance spectroscopy can identify pathological changes related to precancerous lesions of the cervix uteri and esophagus. It therefore has the potential to detect early reflux-related changes in the esophageal mucosa, such as dilated intercellular spaces. The reliable detection of dilated intercellular spaces at the time of endoscopy would yield a significant diagnostic advantage for separating patients with functional heartburn from the large proportion of patients with gastroesophageal reflux symptoms but no macroscopic esophagitis or pathological acid exposure. The bioimpedance of the esophageal mucosa, measured with a small caliber probe, was evaluated in a series of preclinical experiments. First, sections of rabbit esophageal epithelium were mounted in Ussing chambers and exposed to solutions at pH 7.4 or pH 1.5 for 45 minutes. Impedance measurements were taken at varying probe pressures. Second, rabbit esophageal epithelia were perfused for 45 minutes in situ with pH 1.1 or control solutions and impedance measurements taken. Samples from both in vitro and in situ experiments were taken for morphological examination by light microscopy. Finally, esophageal bioimpedance was measured in awake dogs with permanent esophagocutaneous stoma. The in situ experiments demonstrated that morphological changes in the esophageal mucosa could be discerned by the use of bioimpedance spectroscopy. The variability in resistivity was species-independent but was affected by the pressure applied to the probe. The results suggest that evaluation of bioimpedance spectroscopy for use in a clinical setting is warranted. Small morphological differences in the esophageal mucosa may be detected by the use of bioimpedance spectroscopy.

The role of cervical Electrical Impedance Spectroscopy in the prediction of the course and outcome of induced labour

Background

Previous work by us and others had suggested that cervical electrical impedance spectroscopy (EIS) may be predictive of the outcome of induced labour. We sought to determine which probe configuration of the EIS device is predictive of the outcome of induced labour and compare this to digital assessment by the Bishop score.

Methods

In a prospective cohort of 205 women admitted for induction of labour, we used four probes of diameter 3, 6, 9 and 12 mm connected to an impedance meter to measure cervical resistivity (CR) in Ohm.meters at 14 electrical frequencies and compared their values to digital assessment of the cervix by the Bishop score for the prediction of the outcome of induced labour. We tested the association of labour characteristics and outcomes with CR and Bishop score by stepwise multilinear regression analyses, and the accuracy of prediction of categorical clinical outcomes by analysis of the area under the curves (AUC) of derived Receiver Operator Characteristic (ROC) curves.

Results

Of the four CR probe dimensions studied, only the 12 mm probe was predictive of any labour indices. In the frequency range 19 - 156 kHz, CR obtained with this probe was higher in women who delivered by caesarean section (CS) than those who delivered vaginally, and in labours lasting > 24 hrs. Cervical resistivity at 78.1 kHz best predicted vaginal delivery [optimal cut-off <2.25 Ohm.meter, AUC 0.66 (95% CI 0.59-0.72), sensitivity 71.0%, specificity 56.5%, LR+ 1.63, LR- 0.51, P < 0.01] and labour duration >24 hrs [optimal cut-off 2.27 Ω.m, AUC 0.65 (95% CI 0.58, 0.72), sensitivity 71%, specificity 59%, LR+ 1.72, LR- 0.50, P < 0.05]. In contrast digital assessment by the Bishop score neither predicted vaginal delivery nor the duration of labour. However, Bishop score predicted time to onset of labour > 12 hours and induction-delivery interval < 24 hrs [optimal cut-off ≤ 4, AUC 0.8 (95% CI 0.75, 0.86), sensitivity 77%, specificity 76%, LR+ 3.3, LR- 0.3, P < 0.05] whilst CR did not.

Conclusion

Cervical resistivity appears predictive of labour duration and delivery mode following induced labour. However the low predictive values obtained suggest that its current design proffers no immediate clinical utility.

Elastic scattering spectroscopy for detection of cancer risk in Barrett's esophagus: experimental and clinical validation of error removal by orthogonal subtraction for increasing accuracy

Elastic scattering spectroscopy (ESS) may be used to detect high-grade dysplasia (HGD) or cancer in Barrett's esophagus (BE). When spectra are measured in vivo by a hand-held optical probe, variability among replicated spectra from the same site can hinder the development of a diagnostic model for cancer risk. An experiment was carried out on excised tissue to investigate how two potential sources of this variability, pressure and angle, influence spectral variability, and the results were compared with the variations observed in spectra collected in vivo from patients with Barrett's esophagus. A statistical method called error removal by orthogonal subtraction (EROS) was applied to model and remove this measurement variability, which accounted for 96.6% of the variation in the spectra, from the in vivo data. Its removal allowed the construction of a diagnostic model with specificity improved from 67% to 82% (with sensitivity fixed at 90%). The improvement was maintained in predictions on an independent in vivo data set. EROS works well as an effective pretreatment for Barrett's in vivo data by identifying measurement variability and ameliorating its effect. The procedure reduces the complexity and increases the accuracy and interpretability of the model for classification and detection of cancer risk in Barrett's esophagus.

Reproducibility and repeatability of measuring the electrical impedance of the pregnant human cervix-the effect of probe size and applied pressure

Background

The utility of cervical electrical impedance spectroscopy (EIS) as a diagnostic tool is being investigated in clinical trials. We sought to assess the reliability of two different sizes of tetrapolar probes used in measuring cervical impedance.

Methods

Cervical transfer impedance was measured at 14 frequencies between 76 and 625 000 Hz from 11 pregnant subjects at term. Repeated measurements were taken with two probes (3 mm and 12 mm diameter) applied softly (approximately 0.7 Newton of force), and firmly (approximately 2.2 Newton) to the surface of the cervix by two observers. The intra-class correlation coefficient (ICC), coefficient of variation (CV) and repeatability standard deviations (SD) were derived from these measurements and compared.

Results

Measurements taken by one observer were highly repeatable for both probes as demonstrated by high ICC and low CV values. Probe performance was improved further by firm application. Firm application of the 3 mm probe resulted in ICC values that ranged from 0.936 to 0.986 (p = 0.0001) and CV values between 1.0 and 3.4%. Firm pressure with the 12 mm probe resulted in ICC values that ranged between 0.914 and 0.988 (p = 0.0001) with CV values between 0.7 and 2.1%. In addition, the repeatability SD was low across all frequencies implying that there was low intra-observer variability. Measurements taken by 2 observers with firm application of the 12 mm probe demonstrated moderate reproducibility between 9.8 and 156 kHz, the frequency range in which previous clinical studies have shown predictive association between high cervical resistivity and vaginal delivery: ICC values ranged between 0.528 and 0.638 (p < 0.05), CV values were between 3.3 and 5.2% and reproducibility SD values were also low. In contrast the 3 mm probe demonstrated poor reproducibility at all study frequencies.

Conclusion

Measuring cervical resistivity by a single observer with both the 3 and 12 mm probes is highly repeatable whilst inter-observer reproducibility is poor with the 3 mm probe but moderately good when the 12 mm probe is firmly applied to the cervix in the frequency range 9.8 to 156 kHz, consistent with our observations of probe performance in clinical trials.

Surface fluids effects on the bladder tissue characterisation using electrical impedance spectroscopy

The electrical impedance of the human urinary bladder in both benign and malignant areas can be measured using an electrical impedance spectroscopy system (EIS). Glycine is usually used in the bladder surgery in the theatre to make an insulation medium for electro-surgery and the extension of the mucosa. In addition, a saline solution is usually used to wash the inside of the bladder after bladder surgery and it is used to extend the bladder tissue mucosa. Therefore, the effect of glycine and the saline solution that fills the bladder is important, because it was expected that the application of common surface fluids (air, saline solution and glycine solution) in the bladder epithelium would affect the measured electrical impedance of the urothelium, to differentiate the malignant area from the normal bladder tissue. In this study, bladders were removed from the patients' bodies and then were moved from theatre to the histopathology department immediately after excision. These bladder samples were then opened and pinned to a corkboard to take the impedance readings, using the impedance spectroscopy system. Following this, the bladder and corkboard were completely submerged in a saline solution and readings were taken at about 1cm from the sutures. Subsequently, this procedure was repeated with the bladder submerged in glycine and then air, respectively. According to the statistical work, these fluids were found to have a significant effect on the measured impedance of the bladder tissue in benign and malignant areas. Furthermore, the best fluid between air, glycine and saline, to measure the impedance of the urinary bladder, is air (P<0.0001).

Monitoring Insertion Force and Electrode Impedance during Implantation of Microwire Electrodes

the electrical impedance and the insertion force were monitored during the implantation of the microwire electrodes. The data reveals distinct phases in the force and impedance profiles corresponding to the different mediums the electrodes pass through. The impedance is shown to be linearly related to the pressure exerted by the electrode on the dura (p < 0.05, R²>0.8). While both insertion force and the impedance could be used to determine when the electrode touches and breaks through the brain surface, the later, especially the phase angle of the impedance, is shown to be more consistent and sensitive. It is proposed that the electrode impedance be used to provide more objective and accurate estimation of 1) when the electrode touches the brain; 2) the load distribution among the wires of the microwire array, and 3) the mechanical and immunological interactions between the electrode and the tissue in-vivo. The method can potentially improve the accuracy of electrode placement, and enable the development of better surgical procedures and apparatus. The principle could also be applied to other situations, such as endoscopic and minimum invasive surgeries.