[Diagnosis of oesophageal reflux by PH, impedance, and bilirubin measurement: recommendations of the German Society of Neurogastroenterology and of the working group for neurogastroenterology of the German Society for Digestive and Metabolic Diseases]. / Ösophageale Refluxdiagnostik - pH-Metrie, Impedanzmessung, Bilirubin-Messung: Empfehlungen der Deutschen Gesellschaft für Neurogastroenterologie und Motilität und der Arbeitsgruppe Neurogastroenterologie der Deutschen Gesellschaft für Verdauungs- und Stoffwechselkrankheiten.

The current recommendations on indications, technical performance, and interpretation of diagnostic techniques for oesophageal reflux update the German recommandations about 24 hour pH measurement of 2003. The recommendations encompass conventional pH measurement, wireless pH measurement, pH and impedance measurements, and bilirubin measurement (duodenogastro-oesophageal reflux).

A Versatile Noise Performance Metric for Electrical Impedance Tomography Algorithms.

Electrical impedance tomography (EIT) is an emerging technology for real-time monitoring of patients under mechanical ventilation. EIT has the potential to offer continuous medical monitoring while being noninvasive, radiation free, and low cost. Due to their ill-posedness, image reconstruction typically uses regularization, which implies a hyperparameter controlling the tradeoff between noise rejection and resolution or other accuracies. In order to compare reconstruction algorithms, it is common to choose hyperparameter values such that the reconstructed images have equal noise performance (NP), i.e., the amount of measurement noise reflected in the images. For EIT many methods have been suggested, but none work well when the data originate from different measurement setups, such as for different electrode positions or measurement patterns. To address this issue, we propose a new NP metric based on the average signal-to-noise ratio in the image domain. The approach is validated for EIT using simulation experiments on a human thorax model and measurements on a resistor phantom. Results show that the approach is robust to the measurement configuration (i.e., number and position of electrodes, skip pattern) and the reconstruction algorithm used. We propose this novel approach as a way to select optimized measurement configurations and algorithms.

Standardisation of bioelectrical impedance analysis for the estimation of body composition in healthy paediatric populations: a systematic review.

BACKGROUND: Bioelectrical impedance analysis (BIA) requires a high degree of standardisation in order to ensure valid and reproducible impedance measurements. The overall aim of this review was to study the degree to which BIA papers conducted in healthy paediatric populations (aged 0-17 years) were standardised. METHODS: Literature was identified on the basis of a systematic search of internationally-recognised electronic databases and hand searching of the reference lists of the included papers in order to identify additional relevant papers. The review was limited to lead-type BIA devices for whole-body, segmental- and focal impedance measurements. In total, 71 papers published between 1988 and 2016 were included. To evaluate the degree of standardisation of the papers, a recently published review detailing critical factors that may impact on BIA measurements in children was used as a model for structuring and extracting data. RESULTS: There was a general lack of BIA standardisation, or its reporting, in the papers under review, which hinders comparison of data between studies and could potentially lead to erroneous measurements. CONCLUSIONS: If the BIA technique should be accepted clinically for routine use in paediatric populations, there is a need for an increased focus on the importance of improved standardisation and its reporting in future studies. Consequently, this review contains recommendations for performing and reporting BIA measurements in a standardised manner.

Validating Reference Equations for Impulse Oscillometry in Healthy Mexican Children.

BACKGROUND: The impulse oscillometry system (IOS) measures the impedance (Z) of the respiratory system, but proper interpretation of its results requires adequate reference values. The objectives of this work were: (1) to validate the reference equations for the IOS published previously by our group and (2) to compare the adjustment of new available reference equations for the IOS from different countries in a sample of healthy children. METHODS: Subjects were healthy 4-15-y-old children from the metropolitan area of Mexico City, who performed an IOS test. The functional IOS parameters obtained were compared with the predicted values from 12 reference equations determined in studies of different ethnic groups. The validation methods applied were: analysis of the differences between measured and predicted values for each reference equation; correlation and concordance coefficients; adjustment by Z-score values; percentage of predicted value; and the percentage of patients below the lower limit of normality or above the upper limit of normality. RESULTS: Of the 224 participants, 117 (52.3%) were girls, and the mean age was 8.6 ± 2.3 y. The equations that showed the best adjustment for the different parameters were those from the studies by Nowowiejska et al (2008) and Gochicoa et al (2015). The equations proposed by Frei et al (2005), Hellinckx et al (1998), Kalhoff et al (2011), Klug and Bisgaard (1998), de Assumpção et al (2016), and Dencker et al (2006) overestimated the airway resistance of the children in our sample, whereas the equation of Amra et al (2008) underestimated it. In the analysis of the lower and upper limits of normality, Gochicoa et al equation was the closest, since 5% of subjects were below or above percentiles 5 and 95, respectively. The study found that, in general, all of the equations showed greater error at the extremes of the age distribution. CONCLUSIONS: Because of the robust adjustment of the present study reference equations for the IOS, it can be recommended for both clinical and research purposes in our population. The differential adjustment of other equations underlines the need to obtain local reference values.

Measurement of Aortic Pulse Wave Velocity With a Connected Bathroom Scale.

BACKGROUND: Measurement of arterial stiffness should be more available. Our aim was to show that aortic pulse wave velocity can be reliably measured with a bathroom scale combining the principles of ballistocardiography (BCG) and impedance plethysmography on a single foot. METHOD: The calibration of the bathroom scale was conducted on a group of 106 individuals. The aortic pulse wave velocity was measured with the SphygmoCor in the supine position. Three consecutive measurements were then performed on the Withings scale in the standing position. This aorta-leg pulse transit time (alPTT) was then converted into a velocity with the additional input of the height of the person. Agreement between the SphygmoCor and the bathroom scale so calibrated is assessed on a separate group of 86 individuals, following the same protocol. RESULTS: The bias is 0.25 m·s-1 and the SE 1.39 m·s-1. This agreement with Sphygmocor is "acceptable" according to the ARTERY classification. The alPTT correlated well with cfPTT with (Spearman) R = 0.73 in pooled population (cal 0.79, val 0.66). The aorta-leg pulse wave velocity correlated with carotid-femoral pulse wave velocity with R = 0.76 (cal 0.80, val 0.70). CONCLUSION: Estimation of the aortic pulse wave velocity is feasible with a bathroom scale. Further investigations are needed to improve the repeatability of measurements and to test their accuracy in different populations and conditions.

Design and calibration of a compact multi-frequency EIT system for acute stroke imaging.

A new, compact UCLH Mk 2.5 EIT system has been developed and calibrated for EIT imaging of the head. Improvements include increased input and output impedances, increased bandwidth and improved CMRR (80 dB) and linearity over frequencies and load (0.2% on a single channel, +/-0.7% on a saline tank over 20 Hz-256 kHz and 10-65 Omega). The accuracy of the system is sufficient to image severe acute stroke according to the specification from recent detailed anatomical modelling (Horesh et al 2005 3rd European Medical and Biological Engineering Conference EMBEC'05). A preliminary human study has validated the main specifications of the modelling, the range of trans-impedance from the head (8-70 Omega) using a 32 electrode, 258 combination protocol and contact impedances of 300 Omega to 2.7 kOmega over 20 Hz to 256 kHz.

Meta-analysis of plethysmography and rheography in the diagnosis of deep vein thrombosis.

BACKGROUND: Plethysmography and rheography techniques have been widely studied as diagnostic tests for deep vein thrombosis (DVT). This study aimed to systematically review the accuracy of these tests for diagnosing clinically suspected DVT. METHODS: The following databases were searched: Medline, EMBASE, CINAHL, Web of Science, Cochrane Database of Systematic Reviews, Cochrane Controlled Trials Register, Database of Reviews of Effectiveness, the ACP Journal Club (1966 to 2004), and citation lists of retrieved articles. Studies that compared plethysmography or rheography to a reference standard of ultrasound or contrast venography were selected. Standardised data were extracted and study quality determined against validated criteria. Data were analysed by random effects meta-analysis and meta-regression. RESULTS: The meta-analysis included 78 studies, reporting 82 patient cohorts. Sensitivity and specificity (95% CI) were: 75% (73% to 77%) and 90% (89% to 91%) for impedance plethysmography, 83% (81% to 85%) and 81% (79% to 82%) for strain-gauge plethysmography, 85% (79% to 90%) and 91% (81% to 95%) for air plethysmography, 91% (87% to 94%) and 71% (66% to 75%) for light-reflex rheography, and 86% (83% to 89%) and 93% (91% to 95%) for phleborheography. Meta-regression was limited by poor reporting of studies. There was some evidence that diagnostic performance depended on the proportion of males in the cohort and reporting of study setting. CONCLUSIONS: Although plethysmography and rheography techniques add diagnostic value, they have inadequate diagnostic performance to act as a stand-alone test in DVT diagnosis. Evaluation of their role in combination with other tests, or standardised clinical assessment, is required.

Reevaluation of the sensitivity of impedance plethysmography for the detection of proximal deep vein thrombosis.

BACKGROUND: To reevaluate the sensitivity of impedance plethysmography (IPG) for proximal deep vein thrombosis (DVT) and to establish a relationship between the location and size of thrombi and the results of IPG. DESIGN: Prospective cohort study. METHODS: One hundred thirty-two consecutive patients with clinically suspected DVT underwent IPG testing and most (n = 118) underwent contrast-enhanced venography; in 14 patients, venous ultrasonography was performed and demonstrated definitive proximal DVT in which the size and extent of the thrombus could be delineated. All patients with dubious or normal ultrasound results underwent contrast-enhanced venography. All tests were performed and test results were interpreted without knowledge of the results of the other tests. Patients were considered to have proximal DVT if this was demonstrated on venography or ultrasound, calf DVT if this was demonstrated on venography, or no DVT if venography yielded normal findings. The sensitivity and specificity of IPG for DVT were calculated. RESULTS: Of the 132 patients, 40 (30%) had proximal DVT, seven (5%) had calf DVT, and 85 (64%) had no DVT. The sensitivity of IPG for proximal DVT was 65% and the specificity was 93%. Of the proximal vein thrombi, IPG detected three (23%) of 13 that involved the popliteal vein but not the superficial femoral vein and 23 (85%) of 27 proximal vein thrombi that involved the superficial femoral vein. CONCLUSIONS: Our study demonstrated that the sensitivity of IPG for proximal DVT at our center is only 65%, a figure that is much lower than those reported in earlier studies from our institution. We hypothesize that because of a change in referral practice, an increased proportion of patients with less severe symptoms are now referred to our center than in the past. These patients have thrombi that are smaller, less likely to be occlusive, and therefore less likely to yield abnormal IPG findings.

Phleborheography--results of a ten-year experience.

Phleborheography (PRG) is a physiologic volumetric plethysmographic technique that was developed for the diagnosis of lower extremity deep venous thrombosis. During the past 10 years, 21, 626 extremities have been studied with 709 corresponding venograms. Overall data reveal a sensitivity of 92% (247/268) and specificity of 95% (418/441). There were 21 false negative PRG results, and 12 of these were due to isolated calf vein thrombosis. There were 23 false positive results, and 11 of these were considered true errors of the technique. When isolated calf vein thrombosis was disregarded, the sensitivity increased to 95%. PRG detected 45 of 57 (79%) isolated calf vein thrombi. The modified criteria for interpretation included respiratory waves and baseline elevation as the major criteria and prominent arterial pulsation and foot emptying as the minor criteria. PRG has recently been used to monitor the duration of thrombolytic therapy. While data are limited, this appears to be a promising contribution to the quantification of individual response to lytic therapy and may indicate an objective end point for treatment. PRG is a sensitive and specific method of detecting deep vein obstruction. It is a painless, reproducible, repeatable technique that requires minimal patient cooperation. PRG is a versatile laboratory technique that can be used for a variety of applications in addition to the diagnosis of deep vein thrombosis.

Quantification of intracranial contribution to rheoencephalography by a numerical model of the head.

OBJECTIVES: Partial contributions of intracranial and extracranial circulation to rheoencephalography (REG) remain uncertain. The main goal of this work is to determine theoretically the capability of REG techniques to reflect intracranial blood flow. METHODS: Head and current injection electrodes were computationally modeled to assess REG sensitivity to brain and scalp conductivity changes. Data obtained were related to tissue perfusions to calculate the partial contribution of cerebral blood perfusion to REG I, REG II and monopolar REG and to assess their amplitudes. RESULTS: When REG I and monopolar REG were used, the theoretical maximum of intracranial contribution was reached with large current injection electrodes, being 8% for REG I and 12% for monopolar REG. However, some specific REG II electrode arrangements showed a nil contribution of the extracranial circulation and a minimum influence of the electrode size. CONCLUSIONS: These results may explain the disagreement on REG origin and suggest a theoretically optimum electrode arrangement.

Limitation of impedance plethysmography in assessing efficacy of dihydroergotamine-heparin prophylaxis of deep vein thrombosis.

The sensitivity of impedance plethysmography (IPG) for diagnosing deep vein thrombosis was evaluated in the presence of dihydroergotamine, an agent with significant venoconstrictor activity. In a prospective, randomized, controlled clinical trial, 105 patients undergoing total hip replacement surgery were investigated to evaluate the thromboprophylactic efficacy of DHE-Heparin using IPG and 125I-Fibrinogen Leg Scanning to monitor the incidence of DVT. Retrospective analysis of the IPG data indicated that DHE-Heparin impaired the sensitivity of impedance plethysmography by decreasing venous capacitance and venous outflow. Although the patient sample size was relatively small, the results showed trends which suggested that the utility of impedance plethysmography for diagnosing DVT was limited in the presence of a vasoactive agent. Alternate noninvasive diagnostic methods may need to be considered in select patients receiving concomitant medications possessing venoconstrictor activity.

A randomized management study of impedance plethysmography vs. contrast venography in patients with a first episode of clinically suspected deep vein thrombosis.

OBJECTIVES: In this randomized management study, we examined the safety of withholding anticoagulation on the basis of negative impedance plethysmography (IPG) compared to negative contrast venography (CV) in symptomatic patients with a first episode of clinically suspected deep vein thrombosis (DVT), and we determined the impact of the limitations of IPG or CV on their clinical utility. METHODS: Patients at a university teaching hospital presenting with a first episode of clinically suspected DVT were randomized to one of two management strategies at study entry: (1) IPG: if positive, confirmatory CV was performed. If CV was positive, anticoagulants were administered, if CV was negative, anticoagulants were held. If negative, IPG was repeated serially and if it remained negative, anticoagulants were held (n = 165). (2) CV: if positive, anticoagulants were administered, if negative, anticoagulants were held (n = 159). The negative predictive value (NPV) of IPG and CV, positive predictive value (PPV) of IPG, and the failure rate of each strategy were assessed. RESULTS: Among IPG patients, 28 of 37 with positive IPG initially or during serial testing and evaluable CV had confirmed DVT (PPV 76%; 95% confidence interval, CI [62%, 90%]). DVT was diagnosed during serial testing in 2.1% of patients with initially negative IPG who completed testing. The NPV overall of negative IPG was 98.3%. During follow-up, two patients in the IPG group (1.2%) and two patients in the CV group (1.3%) developed venous thromboembolism (VTE). Death during follow-up occurred in 11% of IPG patients compared to 6% of CV patients (P =.13) The investigation strategy failed in 25% of IPG patients and in 14% of CV patients. CONCLUSIONS: Our findings demonstrate that the two diagnostic strategies we studied are equivalent methods for ruling out DVT in patients with a first episode of suspected DVT. The PPV of IPG was too low to permit its use alone as a test to rule in DVT. Both strategies had surprisingly high failure rates.

Distinguishability in impedance imaging.

Impedance imaging systems apply currents to the surface of a body, measure the induced voltages on the surface, and from this information, reconstruct an approximation to the electrical conductivity in the interior. This paper gives a detailed discussion of several ways to measure the ability of such a system to distinguish between two different conductivity distributions. The subtle differences between these related measures are discussed, and examples are provided to show that these different measures can give rise to different answers to various practical questions about system design.

Electrical impedance of layered atherosclerotic plaques on human aortas.

Electrical impedance measurements were performed on 13 atherosclerotic human aortic segments at 67 measuring spots in order to determine whether or not on the basis of these data a distinction can be made between atherosclerotic lesions and normal tissue. Stenosis localization and guidance of interventional techniques could be among the applications of an impedance measuring technique implemented on a catheter system. The experimental results, obtained with a two-electrode measuring technique, show that the apparent resistivity of an atherosclerotic spot does not necessarily deviate much from the resistivity of normal tissue. This is clarified by histology which shows that the majority of lesions has a surface layer of connective, fibrous tissue having almost similar conducting properties as the normal arterial wall. For gaining a deeper understanding of the way in which the measured data come about, a physical model of an atherosclerotic lesion is presented and confronted with the data. Both experimental data and theoretical considerations lead to the conclusion that only when the superficial fibrous layer is absent or very thin in relation to the size of the measuring electrode, the measured resistivity at a lesion is much higher than at normal spots. This occurs as a consequence of the high ohmic properties of the calcified or lipid deposits in the atherosclerotic lesion.

Using compound electrodes in electrical impedance tomography.

In electrical impedance tomography, we inject currents and measure voltages to estimate an object's resistivity distribution. The electrode configuration affects measured voltage data because the electrode-skin contact impedance is high and varies with electrode location. We developed a compound electrode which is composed of two electrodes: a large outer electrode to inject current and a small inner electrode to sense voltage. We used these compound electrodes to measure voltages from a physical phantom. We showed that the measured voltages from the compound electrodes are smaller in amplitude than those from conventional electrodes. This demonstrates that the compound electrode can minimize contact impedance voltage drop from the measured data. We used a finite element model for the compound electrode and incorporated the model into the regularized Newton-Raphson reconstruction algorithm. We performed a sensitivity study and showed that the reconstructed resistivity distributions are less dependent on the unknown contact resistance values for a compound electrode than a conventional electrode and that the use of a compound electrode results in improved images for the reconstruction algorithm.

Axillary subclavian vein thrombosis. Changing patterns of etiology, diagnostic, and therapeutic modalities.

Fifty-two patients with axillary-subclavian vein thrombosis were treated in the last 10 years and were available for follow-up for at least 1 year. Eighteen of these were treated in the first 5 years, Group A, and 34 in the last 5 years, Group B. The causes in both Group A and Group B included respectively: effort or spontaneous 28 per cent and 29 per cent, catheter insertion related 17 per cent and 47 per cent, and malignancy or systemic disease 55 per cent and 24 per cent. None of the patients in Group A had noninvasive vascular testing (NIT). However, 27 patients in Group B had IPG/duplex imaging (NIT). All 18 cases in Group A and 27 cases in Group B were treated conventionally (anticoagulants). Seventy-three per cent of these had residual pain on exertion (venous claudication) and/or swelling. Fourteen of these cases had posttreatment NIT/venography. Four of these showed total resolution of the thrombus and all were symptom free. Ten had no resolution, and nine were symptomatic. Seven cases in Group B were treated with thrombolytic therapy. Five of these had total resolution of thrombus and were symptom free (71%). Two had no resolution with residual symptoms (29%) (statistically significant). In conclusion (1) More patients with axillary-subclavian vein thrombosis seen recently are catheter insertion related; 2) Diagnosis should be initiated with duplex imaging; and (3) Thrombolytic therapy significantly decreased residual symptoms and yielded better resolution than anticoagulants.

Validation of a polyvinylidene fluoride impedance sensor for respiratory event classification during polysomnography.

STUDY OBJECTIVES: The AASM has recommended specific sensors in measuring apnea and hypopnea based on published reliability and validity data. As new technology emerges, these guidelines will need revision. Polyvinylidene fluoride (PVDF) measures impedance and can be incorporated into a belt to approximate airflow and respiratory effort. We compared respiratory event detection using PVDF impedance belts (PVDFb), respiratory inductance plethysmography (RIP), and nasal-oral pneumotachography (PNT). METHODS: First, in a clinical setting, 50 subjects (median AHI 26) undergoing polysomnography were fitted with PVDFb and standard sensors. Studies were scored in 4 independent passes using 4 respiratory montages (M); M1: nasal pressure transduction (NPT), thermistry, and RIP; M2: NPT, thermistry, and PVDFb; M3: thermistry and PVDFb; M4: PVDFb alone. Each experimental montage (M2-M4) was compared to the reference standard (M1) for total apneas and hypopneas. In a second experimental study, respiratory event detection was compared across a series of breathing trials for PVDFb, RIP, and PNT in normal subjects. Agreement was evaluated with intraclass correlation coefficient (ICC), κ statistics, and Bland-Altman plots. RESULTS: ICCs comparing event numbers by M1 to M 2, 3, and 4 were: 0.99, 0.93, and 0.91, respectively. Almost identical numbers of events were identified for M 1 and M2 (177.5 ± 122.7 vs 177.6 ± 123.2). Event subtypes also were comparable. PVDFb was less sensitive than PNT but no different than RIP in detecting decreased breathing amplitude. CONCLUSIONS: PVDFb was comparable to standard RIP in determining respiratory events during polysomnography and in detecting decreased breathing amplitude, suggesting that PVDFb can be used as an alternative to RIP for apnea/hypopnea evaluation.

Obstructive sleep apnea devices for out-of-center (OOC) testing: technology evaluation.

Guidance is needed to help clinicians decide which out-of-center (OOC) testing devices are appropriate for diagnosing obstructive sleep apnea (OSA). A new classification system that details the type of signals measured by these devices is presented. This proposed system categorizes OOC devices based on measurements of Sleep, Cardiovascular, Oximetry, Position, Effort, and Respiratory (SCOPER) parameters.Criteria for evaluating the devices are also presented, which were generated from chosen pre-test and post-test probabilities. These criteria state that in patients with a high pretest probability of having OSA, the OOC testing device has a positive likelihood ratio (LR+) of 5 or greater coinciding with an in-lab-polysomnography (PSG)-generated apnea hypopnea index (AHI) ≥ 5, and an adequate sensitivity (at least 0.825).Since oximetry is a mandatory signal for scoring AHI using PSG, devices that do not incorporate oximetry were excluded. English peer-reviewed literature on FDA-approved devices utilizing more than 1 signal was reviewed according to the above criteria for 6 questions. These questions specifically addressed the adequacy of different respiratory and effort sensors and combinations thereof to diagnose OSA. In summary, the literature is currently inadequate to state with confidence that a thermistor alone without any effort sensor is adequate to diagnose OSA; if a thermal sensing device is used as the only measure of respiration, 2 effort belts are required as part of the montage and piezoelectric belts are acceptable in this context; nasal pressure can be an adequate measurement of respiration with no effort measure with the caveat that this may be device specific; nasal pressure may be used in combination with either 2 piezoelectric or respiratory inductance plethysmographic (RIP) belts (but not 1 piezoelectric belt); and there is insufficient evidence to state that both nasal pressure and thermistor are required to adequately diagnose OSA. With respect to alternative devices for diagnosing OSA, the data indicate that peripheral arterial tonometry (PAT) devices are adequate for the proposed use; the device based on cardiac signals shows promise, but more study is required as it has not been tested in the home setting; for the device based on end-tidal CO(2) (ETCO(2)), it appears to be adequate for a hospital population; and for devices utilizing acoustic signals, the data are insufficient to determine whether the use of acoustic signals with other signals as a substitute for airflow is adequate to diagnose OSA.Standardized research is needed on OOC devices that report LR+ at the appropriate AHI (≥ 5) and scored according to the recommended definitions, while using appropriate research reporting and methodology to minimize bias.