Multifrequency Bioimpedance Measurements Research Articles

Multimodal breast cancer risk classifier based on biomaterial impedance analysis

Purpose of the research. Breast cancer is the most common malignant tumor among women in Europe and its early detection plays a leading role in reducing mortality rates. Currently, X-ray mammography is the standard screening method for detecting breast cancer. However, due to the morphological similarities between benign and malignant lesions, many of the positive screening mammograms are false positive (up to 40%). Therefore, automation and intellectualization of this process is an urgent task.Methods. The presented studies examine the problems of finding new, highly sensitive, prompt and non-invasive methods for detecting malignant tumors, based on the use of modern computer and telecommunication technologies, which make it possible not only to identify early manifestations of a pathological focus, but also to monitor the process of the effectiveness of therapy without significant harm to the patient’s health.Results. The presented model of a multi-channel classifier integrates the capabilities of multi-frequency bioimpedance measurements and matrix acquisition of information from the surface of human skin through multi-electrode matrix systems. To do this, based on a matrix of electrodes, 3D mapping of the skin surface in problem areas is carried out. Through multi-frequency scanning, we obtain a three-dimensional bioimpedance image, which is analyzed by a convolutional neural network and/or by a decision maker. The proposed solution allows simultaneous analysis of data by an expert (bioimpedance image) and a convolutional neural network (trained classifier), which leads to a reduction in false positive results.Conclusion. The possibilities of multichannel monitoring open up prospects for constructing impedance multidimensional "portraits" of malignant tumors. To classify “portraits” (diagnostics and preclinical diagnostics), methods and algorithms for image recognition and classification are used.

#2118 Monitoring hemodynamics in dialysis: on the feasibility of semi-continuous and multifrequency thoracic bioimpedance measurements by a wearable device

Abstract Background and Aims Hemodialysis patients face a high hemodynamic variability in blood pressure and fluid status, which contributes to their cardiovascular mortality. Currently, intradialytic hemodynamic monitoring has to rely on cuff-based blood pressure measurements. During the interdialytic interval, no monitoring system is applied. An interesting alternative to monitor hemodynamics continuously can be found in the bioimpedance technique, and more specifically in bioimpedance measurements of the thoracic segment. Repeated single-point measurements of thoracic bioimpedance at single (low)-frequency are strongly related to fluid changes during hemodialysis. Extension to semi-continuous measurements may provide longitudinal details in the time pattern of the bioimpedance signal, and multifrequency measurements may add in-depth information on the distribution between intra- and extracellular fluid. This study aims to investigate the feasibility of semi-continuous multifrequency thoracic bioimpedance measurements by a wearable device in hemodialysis patients. Method Thoracic bioimpedance was recorded semi-continuously (i.e. every ten minutes) at nine frequencies (8–160 kHz) in 68 patients during two consecutive hemodialysis sessions, complemented by an interdialytic single-point measurement at home. The wearable bioimpedance device was provided by imec, The Netherlands (Fig. 1). A linear mixed model was built to integrate all measurements at frequencies 8 and 160 kHz, incorporating the different dialysis sessions up until 240 minutes after the start of dialysis as well as the home measurement that was performed. Results On average, the thoracic resistance signals increased during the first hemodialysis session, decreased during the interdialytic interval, and increased again during the second hemodialysis session, at all frequencies. The average intradialytic increase was larger at 8 kHz (∆ 32.6 Ω during session 1 and ∆ 10 Ω during session 2) compared to 160 kHz (∆ 29.5 Ω during session 1 and ∆ 5.1 Ω during session 2). By measuring semi-continuously and at multiple frequencies, a different time pattern became clear within and between frequencies. The resistance at 8 kHz followed a linear time pattern, whereas the evolution of the resistance at 160 kHz showed a significant quadratic trend in the first dialysis session (p < 0.0001). During the first interdialytic interval (from the end of the first dialysis session towards the home measurement), the decrease in resistance was more distinct at 8 kHz (∆ −2.27 Ω) compared to a small increase of 0.84 Ω in 160 kHz. This finding reveals a certain inertia in the higher frequencies, mirroring the changes in intracellular volume. Finally, the statistical model could create individual predicting profiles over time, including as well the intradialytic as the interdialytic interval (Fig. 2). Conclusion In this study, we showed that it is feasible to perform semi-continuous and multifrequency bioimpedance measurements by a wearable device during hemodialysis. Semi-continuous and multifrequency measurements provided a broader, and respectively profounder knowledge on the trend of the bioimpedance signal during fluid changes compared to single-point and single-frequency measurements. Measuring thoracic bioimpedance semi-continuously and with a multifrequency current is a major step forward in the understanding of fluid dynamics in hemodialysis patients, by which the road is paved towards remote fluid monitoring and the prevention of hemodynamic instabilities.

The Feasibility of Semi-Continuous and Multi-Frequency Thoracic Bioimpedance Measurements by a Wearable Device during Fluid Changes in Hemodialysis Patients.

Repeated single-point measurements of thoracic bioimpedance at a single (low) frequency are strongly related to fluid changes during hemodialysis. Extension to semi-continuous measurements may provide longitudinal details in the time pattern of the bioimpedance signal, and multi-frequency measurements may add in-depth information on the distribution between intra- and extracellular fluid. This study aimed to investigate the feasibility of semi-continuous multi-frequency thoracic bioimpedance measurements by a wearable device in hemodialysis patients. Therefore, thoracic bioimpedance was recorded semi-continuously (i.e., every ten minutes) at nine frequencies (8-160 kHz) in 68 patients during two consecutive hemodialysis sessions, complemented by a single-point measurement at home in-between both sessions. On average, the resistance signals increased during both hemodialysis sessions and decreased during the interdialytic interval. The increase during dialysis was larger at 8 kHz (∆ 32.6 Ω during session 1 and ∆ 10 Ω during session 2), compared to 160 kHz (∆ 29.5 Ω during session 1 and ∆ 5.1 Ω during session 2). Whereas the resistance at 8 kHz showed a linear time pattern, the evolution of the resistance at 160 kHz was significantly different (p < 0.0001). Measuring bioimpedance semi-continuously and with a multi-frequency current is a major step forward in the understanding of fluid dynamics in hemodialysis patients. This study paves the road towards remote fluid monitoring.

Differentiation using minimally-invasive bioimpedance measurements of healthy and pathological lung tissue through bronchoscopy.

To use minimally-invasive transcatheter electrical impedance spectroscopy measurements for tissue differentiation among healthy lung tissue and pathologic lung tissue from patients with different respiratory diseases (neoplasm, fibrosis, pneumonia and emphysema) to complement the diagnosis at real time during bronchoscopic procedures. Multi-frequency bioimpedance measurements were performed in 102 patients. The two most discriminative frequencies for impedance modulus (|Z|), phase angle (PA), resistance (R) and reactance (Xc) were selected based on the maximum mean pair-wise Euclidean distances between paired groups. One-way ANOVA for parametric variables and Kruskal-Wallis for non-parametric data tests have been performed with post-hoc tests. Discriminant analysis has also been performed to find a linear combination of features to separate among tissue groups. We found statistically significant differences for all the parameters between: neoplasm and pneumonia (p < 0.05); neoplasm and healthy lung tissue (p < 0.001); neoplasm and emphysema (p < 0.001); fibrosis and healthy lung tissue (p ≤ 0.001) and pneumonia and healthy lung tissue (p < 0.01). For fibrosis and emphysema (p < 0.05) only in |Z|, R and Xc; and between pneumonia and emphysema (p < 0.05) only in |Z| and R. No statistically significant differences (p > 0.05) are found between neoplasm and fibrosis; fibrosis and pneumonia; and between healthy lung tissue and emphysema. The application of minimally-invasive electrical impedance spectroscopy measurements in lung tissue have proven to be useful for tissue differentiation between those pathologies that leads increased tissue and inflammatory cells and those ones that contain more air and destruction of alveolar septa, which could help clinicians to improve diagnosis.

Bioimpedance Spectroscopy as a potential technique to detect label-free PCR products

PCR is a molecular technique that multiplies DNA fragments in a logarithmical way. qPCR uses fluoroscopic dyes or probes to quantify amplicons but it is a complex and expensive technique that should be performed by highly trained personnel. PCR has been used in a wide variety of disciplines such as in food sciences, organ transplant, odontology, oncology and lately, as the standard diagnostic technique for COVID-19. Even when qPCR is a reliable and robust technique, it is hardly accessible for developing countries for its complex labelling procedures and expensive instrumentation, for that, it is of big relevance to search for simpler and cheaper alternative technologies for the detection and analysis of DNA. In this work, we explore the feasibility of using multifrequency bioimpedance measurements to detect label-free PCR products as a proof of principle for the future development of a gene biosensor on the basis of PCR and bioimpedance measurements.

Threshold and Trend Artifacts in Localized Multi-Frequency Bioimpedance Measurements.

Localized tissue bioimpedance is being widely investigated as a technique to identify physiological features in support of health focused applications. In support of this method being translated into wearable systems for continuous monitoring, it is critical to not only collect measurements but also evaluate their quality. This is necessary to reduce errors in equipment or measurement conditions from contributing data artifacts to datasets that will be analyzed. Two methods for artifact identification in resistance measurements of bioimpedance datasets are presented. These methods, based on thresholding and trend detection, are applied to localized knee bioimpedance datasets collected from two knee sites over 7 consecutive days in free-living conditions. Threshold artifacts were identified in 0.04% (longitudinal and transverse) and 0.69% (longitudinal) /3.50% (transverse) of the total data collected.

Параметры биоэлектрического импеданса легких у самок крыс линии Вистар при экспериментальной легочной гипертензии

The aim of the study was to reveal changes in bioelectrical impedance of the lung and body in female Wistar rats with monocrotaline-induced pulmonary hypertension. Multifrequency bioimpedance measurements were taken in rats a month before and after of administration of monocrotaline (100 mg/kg). Histological lung tissue sections of 5 μm thickness were stained with hematoxylin and eosin. Monocrotaline-induced pulmonary vascular remodeling that confirmed the development of pulmonary hypertension, emphysematous changes, and the inflammatory process in the lung were histologically shown in rats. At low frequencies, a significant increase of active resistance, amplitude of bioelectrical impedance of the lung revealed in monocrotaline-treated rats in comparison to the rats in the control group may testify to emphysematous changes, and at higher frequencies, that may be connected with the inflammatory process and narrowing of the lumen of blood vessels in the lung. In monocrotaline-treated rats, a significant decrease of the phase angle of pulmonary electrical bioimpedance and reactive resistance of bioelectrical impedance of the body at low frequency may indicate cell membrane injury.

Bioimpedance and Fluid Status in Children and Adolescents Treated With Dialysis

Assessment of hydration status in patients with chronic kidney failure treated by dialysis is crucial for clinical management decisions. Dilution techniques are considered the gold standard for measurement of body fluid volumes, but they are unfit for day-to-day care. Multifrequency bioimpedance has been shown to be of help in clinical practice in adults and its use in children and adolescents has been advocated. We investigated whether application of multifrequency bioimpedance is appropriate for total-body water (TBW) and extracellular water (ECW) measurement in children and adolescents on dialysis therapy. A study of diagnostic test accuracy. 16 young dialysis patients (before a hemodialysis session or after peritoneal dialysis treatment) from the Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy, and the Emma Children's Hospital-Academic Medical Center, Amsterdam, the Netherlands. TBW and ECW volumes assessed by multifrequency bioimpedance. TBW and ECW volumes measured by deuterium and bromide dilution, respectively. Mean TBW volumes determined by multifrequency bioimpedance and deuterium dilution were 19.2±8.7 (SD) and 19.3±8.3L, respectively; Bland-Altman analysis showed a mean bias between the 2 methods of-0.09 (95% limits of agreement,-2.1 to 1.9) L. Mean ECW volumes were 8.9±4.0 and 8.3±3.3L measured by multifrequency bioimpedance and bromide dilution, respectively; mean bias between the 2 ECW measurements was+0.6 (95% limits of agreement,-2.3 to 3.5). Participants ingested the deuterated water at home without direct supervision by investigators, small number of patients, repeated measurements in individual patients were not performed. Multifrequency bioimpedance measurements were unbiased but imprecise in comparison to dilution techniques. We conclude that multifrequency bioimpedance measurements cannot precisely estimate TBW and ECW in children receiving dialysis.

Compression-dependency of soft tissue bioimpedance for in-vivo and in-vitro tissue testing

Abstract The present study determines the effect of compression over bioimpedance of healthy soft tissue (in-vitro and in-vivo). Electrical impedance spectroscopy (EIS) is a promising tissue characterization and tumor detection technique that uses tissue impedance or admittance to characterize tissue and identify tissue properties as well as cell structure. Variation in EIS measurements while applying pressure suggests that compression tends to affect soft tissue bioimpedance. Moreover, the displacements in tissue caused by applied compression may provide useful information about the structure and state of the tissue. Thus combining the changes to the electrical properties of tissue resulted by applied compression, with the changes in tissue displacements caused by applied compression, and consequently measuring the effect that electrical and mechanical properties have on each other, can be useful to identify tissue structure. In this study, multifrequency bioimpedance measurements were performed on in-vitro and in-vivo soft tissue at different pressure levels. Increasing compression on the in-vitro tissue results in an increase in both extracellular resistance and membrane capacitance while it causes a reduction in the intracellular resistance. However, as the compression over the in-vivo samples increases, the intracellular and extracellular resistance increase and the membrane capacitance decreases. The in-vivo measurements on human body are also tested on contra-lateral tissue sites and similar tissue impedance variation trends are observed in the contra-lateral sites of human body. The evidence from these tests suggests the possibility of using this EIS-Pressure combined measurement method to improve tumor detection in soft tissue. Based upon the observations, the authors envision developing an advanced model based upon the Cole model, which is dependent on tissue displacements.

Agreement of Single- and Multi-Frequency Bioimpedance Measurements in Hemodialysis Patients: An Ancillary Study of the Frequent Hemodialysis Network Daily Trial

Background: Bioimpedance analysis (BIA) is well established to assess body composition. Agreements between single- and multi-frequency bioimpedance (SF-BIA, MF-BIS) measurements in subjects undergoing 6 or 3 times/week hemodialysis (HD) were analyzed. Methods: Total body water (TBW) and intra- and extracellular fluid (ICF, ECF) of subjects enrolled in the Frequent Hemodialysis Network (FHN) Daily Trial (www.clinicaltrials.gov No. NCT00264758) were measured with a Hydra 4200 at baseline (BL) and at 5 months (M5). Volumes were computed using SF (at 50 kHz) and MF approaches. Agreement was assessed by means of linear regression and Bland-Altman analysis and treatment effects by t test. Results: 35 subjects (17 on the more frequent regimen, 26 males, 20 African-American, 48 ± 9 years, pre-HD weight 84 ± 19 kg) were studied. Assessments with SF-BIA and MF-BIS correlated significantly at BL and M5 in both arms. No proportional errors, but systematic biases over the entire range of values were found at BL and M5. Agreement did not differ between subjects randomized to either HD treatment arm at both time points. MF-BIS appears to have better precision than SF-BIA allowing the observation of a significant treatment effect by the intervention [-1.5 (95% CI -2.5 to -0.5) l] on ECF, not found for ECF SF-BIA. Precision also affected the statistical power of the SF-BIA data in the current analysis. Conclusion: Both methods showed agreement without significant proportional errors regardless of HD frequency and can be used for longitudinal analyses. SF-BIA has lower precision which needs thorough consideration in the design of future trials with similar outcomes.

An Integrated Analog Readout for Multi-Frequency Bioimpedance Measurements

Bioimpedance spectroscopy is used in a wide range of biomedical applications. This paper presents an integrated analog readout, which employs synchronous detection to perform galvanostatic multi-channel, multi-frequency bioimpedance measurements. The circuit was fabricated in a 0.35-μm CMOS technology and occupies an area of 1.52 mm2. The effect of random dc offsets is investigated, along with the use of chopping to minimize them. Impedance measurements of a known RC load and skin (using commercially available electrodes) demonstrate the operation of the system over a frequency range up to 1 MHz. The circuit operates from a ±2.5 V power supply and has a power consumption of 3.4-mW per channel.

Body composition monitoring to manage fluid status in haemodialysis

Haemodialysis patients with little or no urine output usually experience periods of overhydration as they accumulate fluid between treatments through intake of salt and water. Many are also dehydrated when fluid is removed during dialysis. The time-averaged deviation from normal hydration will depend on the patient's fluid status after dialysis and his or her interdialytic fluid gains. Attempts to minimise the adverse effects of abnormal hydration begin by setting patients' ‘target’ weight to optimise their post-dialysis fluid status. However, the clinical indicators that are traditionally used to adjust target weight can be ambiguous or misleading. Body composition monitoring using multifrequency bioimpedance measurements can now provide an objective assessment of fluid status. The measurements are non-invasive and can be made in a few minutes before or after dialysis. If added to the complete clinical picture, this technology can improve outcomes and quality of life for patients.

Changes in N-Terminal Pro-Brain Natriuretic Peptide Correlate with Fluid Volume Changes Assessed by Bioimpedance in Peritoneal Dialysis Patients

Background/Aims: Both brain natriuretic peptide (BNP) and volume overload are reported to be powerful predictors of survival for peritoneal dialysis patients. The usefulness of single BNP determinations in helping determine volume status in peritoneal dialysis patients remains controversial, so we reviewed serial BNP and multifrequency bioimpedance measurements to determine whether changes in BNP reflected changes in volume status. Methods: Prospective measurements of fluid volume by multifrequency bioimpedance and serum N-terminal pro-BNP (NTproBNP) were conducted in stable adult peritoneal dialysis outpatients attending for routine assessments of peritoneal dialysis adequacy and transport status. Results: A total of 189 serial measurements were made in 92 patients, and NTproBNP increased from a median of 162.5 pmol/l (interquartile range 82–385.4) to 195 pmol/l (interquartile range 101.9–348.6; p < 0.05). Changes in NTproBNP correlated with changes in extracellular water (ECW), total body water (TBW) and ECW/TBW (r = 0.38, 0.31 and 0.45, respectively; all p < 0.0001). Patients were divided into quartiles depending upon NTproBNP changes; those with the greatest fall in NTproBNP had significant falls in ECW (p < 0.001), TBW (p = 0.001) and ECW/TBW (p < 0.001) compared to the quartile with the greatest increase in NTproBNP, who also had an increase in systolic blood pressure from 133.5 ± 22.7 to 142.7 ± 28.8 mm Hg (p = 0.0078), whereas it fell in the quartile with the greatest fall in NTproBNP (143.8 ± 24.6 vs. 136.5 ± 18.7 mm Hg). Conclusions: Serial measurements of NTproBNP correlated with changes in volume assessments made by multifrequency bioimpedance in peritoneal dialysis outpatients. As multifrequency bioimpedance measures total ECW, rather than effective plasma volume, serial NTproBNP determinations may prove an adjunct to the clinical assessment of volume status in peritoneal dialysis patients.

Extracellular Volume Expansion in Peritoneal Dialysis Patients

Cardiovascular mortality remains high among peritoneal dialysis (PD) patients. Several small studies have suggested that PD patients are volume expanded, and as such this could be a cardiovascular risk factor. We therefore wished to investigate factors which could lead to extracellular water (ECW) expansion. Retrospective cross-sectional audit of 600 prevalent, adult PD patients attending two tertiary university PD centers, with corresponding assessments of PD adequacy, transport status, and multifrequency bioimpedance measurements of extracellular water to total body water (ECW/TBW). 600 PD patients, median age 57.5 (46.9-67.9) years, 54% male, 31% diabetic, 47.6% Caucasoid, median PD vintage 16 (3.7-38) months, (64% prescribed icodextrin, 34% hypertonic glucose dialysates, and 74% antihypertensive medications). Mean ECW 15.1±0.2 L, ICW 20±0.2 L, ECW/TBW ratio 0.437±0.007. On multivariate analysis %ECW/TBW was associated with age (F=13.1 ß=0.045 p=0.000), number of antihypertensive medications (F=10.3 ß=0.43 p=0.001), log CRP (F=12.9 ß=1.3 p=0.000), and negatively with serum albumin (F=25 ß=-0.22 p=0.000), and residual renal function (urine volume mL F=9.96 ß=-0.001 p=0.002) (weekly Kt/Vurine F=8.82 ß=-2.05, p=0.003). Overhydration as assessed by ECW/TBW is prevalent in adult PD patients, and is associated with loss of residual renal function, inflammation, malnutrition and hypertension - as assessed by antihypertensive medications. As this was a retrospective cross-sectional audit, whether loss of residual renal function, inflammation, and protein energy wasting lead to volume expansion remains to be determined in prospective longitudinal studies.

Comparison of Volume Status in Asymptomatic Haemodialysis and Peritoneal Dialysis Outpatients

Background: The majority of haemodialysis (HD) patients gain weight between dialysis sessions and thereby become volume overloaded, whereas peritoneal dialysis (PD) is a more continuous technique. Cardiovascular mortality and hypertension is increased with both treatment modalities. We therefore wished to compare volume status in PD and HD to determine whether PD patients are chronically volume overloaded, as a risk factor for cardiovascular mortality. Study Design, Setting and Participants:We retrospectively audited 72 healthy HD patients and 115 healthy PD patients attending a university hospital dialysis centre for routine outpatient treatment, who had multi-frequency bioimpedance measurements of extracellular water to total body water (ECW/TBW). Results: The groups were well matched for age, sex, weight and ethnicity, PD patients had greater urine output [1,075 (485–1,613) vs. 42.5 (0–1,020) ml/day, p < 0.001], but there was no difference in antihypertensive prescription (63.5 vs. 76.4%), mean arterial blood pressure (post-dialysis 101.6 ± 1.5 mm Hg vs. pre-dialysis 102 ± 2.4 mm Hg), although post-dialysis arterial blood pressure was lower than in PD patients (96.4 ± 3.1 mm Hg, p < 0.05). The ratio of ECW/TBW fell after HD (pre-dialysis 0.394 ± 0.001 vs. post-dialysis 0.389 ± 0.004, p < 0.001) and was similar in the PD group to the group before HD (0.393 ± 0.001), and greater than that in the group after HD (p < 0.001). ECW/TBW was greater than the normal reference range in 30% PD patients, 28% patients before HD and 20% patients after HD. Conclusions: Overhydration is common in healthy stable PD outpatients, and ECW volumes in PD patients are not dissimilar to those of pre-dialysis HD patients. The role of chronic volume overload as a risk factor for cardiovascular disease needs further investigation.

Do Changes in Relative Blood Volume Monitoring Correlate to Hemodialysis-Associated Hypotension?

Introduction: Intradialytic hypotension remains the most common complication for outpatient hemodialysis, and relative blood volume monitoring was designed to reduce hypotension. Reports of the usefulness of this technology, however, have been variable. Methods: We audited the usefulness of relative blood volume monitoring recorded throughout the mid-week dialysis in 72 stable adult outpatients who had multifrequency bioimpedance measurements. Results: The blood volume measurement (BVM) at the end of the session was 91.6 ± 0.6% and was not different from the nadir BVM recorded (90.7 ± 0.5). The BVM was strongly correlated with change in hematocrit (r = –0.56, p < 0.001) and albumin (r = –0.69, p < 0.001), but had no relationship with pre-, intra- or postdialysis blood pressure recordings. The BVM was not associated with ultrafiltration volume, but did correlate with a postdialysis change in extracellular fluid volume (r = –0.39, p = 0.006). Conclusion: In this audit, although the BVM at the end of the dialysis session was correlated with changes in hematocrit, serum albumin and extracellular fluid volume, the change in the relative BVM did not mirror changes in intradialytic blood pressure.

The association between vascular endothelial growth factor levels and clinically evident peripheral edema in dogs with systemic inflammatory response syndrome

To determine the relationship between plasma vascular endothelial growth factor (VEGF) levels, severity of illness, and edema formation in critically ill dogs. Prospective, observational, descriptive, clinical study. University Teaching Hospital. Twenty-eight dogs. None. Physical examination and multifrequency bioimpedance (MFBIA) measurements were performed daily on 28 critically ill dogs with evidence of severe inflammatory disease and compared with the corresponding plasma VEGF levels. The change in VEGF values and the relationship between MFBIA measurements and clinical evidence of edema were also examined. Eighteen dogs had a positive VEGF level, 12 dogs had clinical evidence of edema, and 7 dogs had both a positive VEGF level and clinical evidence of edema. There was no statistically significant correlation between VEGF levels and the presence of edema on physical examination (P=0.2). VEGF values were also evaluated with respect to WBC count, survival prediction index, presence of known sepsis, change in extracellular water, and outcome. No statistical relationship could be identified between VEGF levels in the blood of dogs with inflammatory disease and their survival prediction index (P=0.1), the WBC count (P=0.2), or presence of sepsis (P=0.2). Dogs with a VEGF level >70 pg/mL (n=3) were less likely to survive (P=0.04). Because of high variability within and between animals, conclusions regarding changes in MFBIA could not be made, suggesting that this technology requires further refinement and investigation in critically ill dogs. A relationship between VEGF and clinically evident increased vascular permeability was not found in this study. Dogs with markedly elevated VEGF levels may be more likely to die, but further studies are needed to determine the diagnostic and prognostic value of VEGF in critically ill dogs.

Multi-frequency bioimpedance measurements of rabbit shanks with stress fracture

Purpose: The objective of this research is to investigate whether bioimpedance is useful to indicate a shank’s physical condition during training. Methods: Bioimpedance was applied to monitor the condition of 8 rabbits’ shanks in 3 weeks, during which the rabbits were trained for regular excessive jump daily. Nine tibias in 16 developed stress fracture after the 3-week training. Results: According to the analysis of the bioimpedance data, we found that changing pattern of bioimpedance properties of shanks which were more liable to suffer from SF was different from that of shanks which were not during training. Conclusions: This suggests that bioimpedance may be used to monitor the physical condition of a limb, imply its liability to develop stress fracture, and indicate stress fracture during training.

Impact of oedema on recovery after major abdominal surgery and potential value of multifrequency bioimpedance measurements (Br J Surg 2006; 93: 354–361)

Impact of oedema on recovery after major abdominal surgery and potential value of multifrequency bioimpedance measurements (<i>Br J Surg</i> 2006; 93: 354–361)

Authors' reply: impact of oedema on recovery after major abdominal surgery and potential value of multifrequency bioimpedance measurements (Br J Surg 2006; 93: 354–361)

Authors' reply: impact of oedema on recovery after major abdominal surgery and potential value of multifrequency bioimpedance measurements (<i>Br J Surg</i> 2006; 93: 354–361)