Reactance Measurements Research Articles

Classification of Hydration in Clinical Conditions: Indirect and Direct Approaches Using Bioimpedance.

Although the need to assess hydration is well recognized, laboratory tests and clinical impressions are impractical and lack sensitivity, respectively, to be clinically meaningful. Different approaches use bioelectrical impedance measurements to overcome some of these limitations and aid in the classification of hydration status. One indirect approach utilizes single or multiple frequency bioimpedance in regression equations and theoretical models, respectively, with anthropometric measurements to predict fluid volumes (bioelectrical impedance spectroscopy—BIS) and estimate fluid overload based on the deviation of calculated to reference extracellular fluid volume. Alternatively, bioimpedance vector analysis (BIVA) uses direct phase-sensitive measurements of resistance and reactance, measured at 50 kHz, normalized for standing height, then plotted on a bivariate graph, resulting in a vector with length related to fluid content, and direction with phase angle that indexes hydration status. Comparison with healthy population norms enables BIVA to classify (normal, under-, and over-) and rank (change relative to pre-treatment) hydration independent of body weight. Each approach has wide-ranging uses in evaluation and management of clinical groups with over-hydration with an evolving emphasis on prognosis. This review discusses the advantages and limitations of BIS and BIVA for hydration assessment with comments on future applications.

Comparison of Forced and Impulse Oscillometry Measurements: A Clinical Population and Printed Airway Model Study

The use of commercialised forced oscillation (FOT) devices to assess impedance in obstructive diseases such as asthma has gained popularity. However, it has yet to be fully established whether resistance and reactance measurements are comparable across different FOT devices, particularly in disease. We compared two commercially available FOT devices: Impulse Oscillometry (IOS) and TremoFlo FOT (Thorasys) in a) clinical adult population of healthy controls (n = 14), asymptomatic smokers (n = 17) and individuals with asthma (n = 73) and b) a 3D printed CT-derived airway tree model resistance, as well as a 3 L standardised volume reactance. Bland-Altman Plots and linear regressions were used to evaluate bias between the devices. Resistance measurements at both 5 and 20 Hz were numerically higher with IOS compared to FOT, with evidence of small and statistically significant proportional systematic bias and a positive Bland-Altman regression slope at both 5 and 20 Hz. In contrast, the IOS device recorded reactances that were less negative at both 5 Hz and 20 Hz and significantly smaller reactance areas when compared to TremoFlo. Larger statistically significant proportional systematic biases were demonstrated with both reactance at 5 Hz and reactance area (AX) between the devices with a negative Bland-Altman regression slope. The printed airway resistance and standardised volume reactance confirmed the observations seen in patients. We have demonstrated that the impulse oscillation system and TremoFlo FOT demonstrate comparative bias, particularly when comparing airway reactance in patients. Our results highlight the need for further standardisation across FOT measurement devices, specifically using variable test loads for reactance standardisation.

Therapeutic reactance in adolescents: the psychometrics of the Therapeutic Reactance Scale in adolescents.

Background:The Therapeutic Reactance Scale (TRS) is a classic measure of psychological reactance, yet only two studies have evaluated its factorial structure. Both proposed different multidimensional structures based on exploratory analyses. Not only is the factorial structure of the TRS unclear, but the scale has yet to be validated in adolescents.Objective:This study aimed to test the factorial structure of the TRS in adolescents.Methods:The authors conducted exploratory and confirmatory factor analyses, and analyses of reliability and validity, with a sample of 1,344 adolescents.Results:A four-factor model fits well to the data. Three of the four TRS dimensions (not susceptibility to influence, SI) were correlated with the Hong Psychological Reactance Scale (HPRS). These three dimensions were also correlated with novelty seeking, cooperativeness and persistence components of personality (Cloninger’s psychobiological model of personality), while SI showed a different pattern.Conclusions:Overall, this study demonstrates that the TRS is a suitable and potentially useful tool for measuring reactance in adolescents, but the authors propose that practitioners may wish to consider excluding items pertaining to the SI dimension.

Safety and Results of Bioelectrical Impedance Analysis in Patients with Cardiac Implantable Electronic Devices

Objective To analyze the dual interference between cardiac implantable electronic devices (CIEDs) and bioelectrical impedance analysis (BIA).Methods Forty-three individuals admitted for CIEDs implantation were submitted to a tetrapolar BIA with an alternating current at 800 microA and 50 kHz frequency before and after the devices’ implantation. During BIA assessment, continuous telemetry was maintained between the device programmer and the CIEDs in order to look for evidence of possible electric interference in the intracavitary signal of the device.Results BIA in patients with CIEDs was safe and not associated with any device malfunction or electrical interference in the intracardiac electrogram of any electrode. After the implantation of the devices, there were significant reductions in BIA measurements of resistance, reactance, and measurements adjusted for height resistance and reactance, reflecting an increase (+ 1 kg; P<0.05) in results of total body water and extracellular water in liter and, consequently, increases in fat-free mass (FFM) and extracellular mass in kg. Because of changes in the hydration status and FFM values, without changes in weight, fat mass was significantly lower (-1.2 kg; P<0.05).Conclusion BIA assessment in patients with CIEDs was safe and not associated with any device malfunction. The differences in BIA parameters might have occurred because of modifications on the patients’ body composition, associated to their hydration status, and not to the CIEDs.

Impulse oscillometry reference values and correlation with predictors in Turkish preschool children.

Er İ, Günlemez A, Baydemir C, Kılıçbay F, Ersu R, Uyan ZS. Impulse oscillometry reference values and correlation with predictors in Turkish preschool children. Turk J Pediatr 2019; 61: 560-567. Impulse oscillometry (IOS) is a noninvasive, rapid technique requiring passive cooperation that allows for evaluation of lung function through the measurement of airway resistance and reactance. There are no available reference values for Turkish children. This study is aimed to determine the reference values of IOS parameters and to study their correlation with height, weight, body mass index, and age as predictors in healthy Turkish preschool children. Healthy children between 3-7 years of age who were selected according to ERS/ATS criteria and followed at Kocaeli University outpatient clinic performed IOS. The correlation between the anthropometric predictor variables and resistance and reactance at 5-20 hertz (R5-R20 and X5-X20), the respiratory impedance at 5 hertz (Z5), resistance area (AX) and resonance frequency (Fres) were assessed by regression analysis and stepwise method. 151 children (93 female) with the mean age of 67.9±16.2 months participated in the study. Multilinear regression analysis for IOS values of all children revealed that resistance was significantly correlated with height and reactance was significantly correlated with age (p < 0.05). For girls, height had a negative effect on R5-20, Z5, AX values, while age had a positive effect on X5-20 and a negative effect on Fres (p < 0.05). For boys, weight had a negative effect on R5- 20, Z5 values, while age had a positive effect on X15-20 and a negative effect on AX, Fres (p < 0,05). This study provided reference values of IOS in healthy Turkish children that would be a useful guide for diagnosing and following respiratory diseases in preschool children.

Lung function and CT lung densitometry in 37- to 39-year-old individuals with alpha-1-antitrypsin deficiency.

BackgroundAlpha-1-antitrypsin (AAT) deficiency is a hereditary disorder that predisposes to emphysema. A cohort of severe (PiZZ) and moderate (PiSZ) AAT-deficient newborn infants was identified by the Swedish national neonatal AAT screening program in 1972–1974 and has been followed-up since birth. Our aim was to study whether the cohort has signs of emphysema in pulmonary function tests (PFTs) and computed tomography (CT) densitometry at 38 years of age in comparison with an age-matched control group, randomly selected from the population registry.MethodsForty-one PiZZ, 18 PiSZ, and 61 control subjects (PiMM) underwent complete PFTs, measurement of resistance and reactance in the respiratory system by impulse oscillometry (IOS)/forced oscillation technique (FOT), and CT densitometry. The results were related to self-reported smoking habits.ResultsThe total lung capacity (TLC) % of the predicted value was significantly higher in the PiZZ ever-smokers than in the PiZZ never-smokers (P<0.05), PiSZ never-smokers (P=0.01) and the PiMM never-smokers (P=0.01). The residual volume (RV) % of the predicted value was significantly higher in the PiZZ ever-smokers compared to the PiMM never-smokers (P<0.01). The PiZZ ever-smokers had a significantly lower carbon monoxide transfer coefficient (Kco) than the PiSZ never-smokers (P<0.01) and PiMM never-smokers (P<0.01). Respiratory system resistance at 5 Hz (P<0.01), at 20 Hz (P<0.01), and the area of low reactance (Alx; P<0.05) were significantly lower and respiratory system reactance at 5 Hz (P<0.05) was significantly higher in PiZZ subjects compared to the PiMM subjects. No statistically significant differences in the CT densitometry parameters were found between the Pi subgroups.ConclusionThe physiological parameters in the PiZZ ever-smokers showed evidence of hyperinflation and emphysema before the age of 40 years.

Bioelectrical Impedance Analysis Measures and Clinical Outcomes in CKD

Bioelectrical impedance analysis (BIA) provides a noninvasive assessment of body composition. BIA measures of cell integrity (phase angle) and hydration (vector length) have been associated with mortality among patients receiving dialysis. Whether these measures are associated with clinical outcomes in patients with chronic kidney disease (CKD) is unknown. Observational study. We studied 3,751 participants with CKD in the prospective multicenter Chronic Renal Insufficiency Cohort (CRIC) who had baseline single-frequency BIA performed. Predictors included phase angle and vector length, which were calculated from measurements of resistance and reactance from BIA. We ranked phase angle and vector length into quartiles and compared the 2 narrower quartiles of phase angle and shorter quartiles of vector length with the 2 upper quartiles. Mortality, heart failure, atherosclerotic cardiovascular disease, and progression of CKD (30% decline in estimated glomerular filtration rate or end-stage kidney disease). We tested associations of phase angle and vector length with risks for mortality and progression of CKD using Cox proportional hazard models and the association with heart failure and atherosclerotic cardiovascular disease using Fine and Gray models. All models were adjusted for demographics, comorbidconditions, and kidney function. Mean phase angle and vector length were 6.6°±1.8° and 470 ± 96 Ω/m, respectively. Relative to phase angle≥ 6.40o, narrower phase angle (<5.59o) was significantly associated with mortality (HR, 1.31; 95% CI, 1.09-1.58). Relative to vector length≥ 459 Ω/m, shorter vector length (<401 Ω/m) was significantly associated with heart failure (HR, 1.28; 95% CI, 1.01-1.61). Neither measure was associated with atherosclerotic cardiovascular disease or a composite renal end point. Observational study. Adjusted for key confounders, BIA-derived measures of cellular integrity and tissue hydration were significantly associated with death and incident heart failure, respectively.

Bronchodilator Responses in Respiratory Impedance, Hyperinflation and Gas Trapping in COPD

ABSTRACTHyperinflation, gas trapping and their responses to long-acting bronchodilator are clinically important in COPD. The forced oscillation technique (FOT) measures of respiratory system resistance and reactance are sensitive markers of bronchodilator response in COPD. The relationships between changes in resistance and reactance, and changes in hyperinflation and gas trapping, following long-acting bronchodilator (LA-BD) have not been studied.15 subjects with mild-moderate COPD underwent FOT, spirometry then body plethysmography, before and 2 hours after a single 150 microg dose of the LA-BD indacaterol. Hyperinflation was quantified as the inspiratory capacity to total lung capacity ratio (IC/TLC), and gas trapping as residual volume to TLC ratio (RV/TLC).At baseline, FOT parameters were moderately correlated with IC/TLC (|r| 0.53–0.73, p < 0.05). At 2 hours post-LA-BD, there were moderate correlations between change in FOT and change in RV/TLC (|r| 0.60–0.82, p < 0.05). Baseline FOT parameters also correlated with the subsequent post-LA-BD change in both IC/TLC (|r| 0.54–0.62, p < 0.05) and RV/TLC (|r| 0.57–0.76, p < 0.05).FOT impedance reflects hyperinflation and gas trapping in COPD, and the potential for long-acting bronchodilator responsiveness. These results provide us with further insight into the physiological mechanisms of action of long-acting bronchodilator treatment, and may be clinically useful for predicting treatment responses.

Effect of omega-3 fatty acids supplementation during pregnancy on lung function in preschoolers: a clinical trial

ABSTRACTRationale: Prenatal omega-3 fatty acids improve alveolarization, diminish inflammation, and improve pulmonary growth, but it is unclear whether these outcomes translate into improved postnatal lung function. Objective: We assessed the effect of prenatal supplementation with docosahexaenoic acid (DHA) on offspring lung function through 60 months of age. Methods: We included a cohort of 772 Mexican preschoolers whose mothers participated in a clinical trial (NCT00646360) of supplementation with DHA or a placebo from week 18–22 of gestation through delivery. Measurements: The children were followed after birth and anthropometric measurements and forced oscillation tests were performed at 36, 48, and 60 months of age. The effect of DHA was tested using a longitudinal mixed effect models. Results: Overall, mean (Standard Deviation) of the measurements of respiratory system resistance and respiratory system reactance at 6, 8, and 10 Hz during follow up period were 11.3 (2.4), 11.1 (2.4), 10.3 (2.2) and –5.2 (1.6), –4.8 (1.7), –4.6 (1.6), respectively. There were no significant differences in pulmonary function by treatment group. DHA did not affect the average lung function or the trajectories through 60 months. Conclusions: Prenatal DHA supplementation did not influence pulmonary function in this cohort of Mexican preschoolers.

Biceps tissue bioimpedance changes from isotonic exercise-induced fatigue at different intensities

Electrical impedance measurements of biological tissues, also referred to as bioimpedance, quantify the passive electrical properties of these materials. The motivation behind collecting these measurements is to provide details regarding the electrochemical structures and processes within these tissues. Bioimpedance measures have recently been investigated as a method to monitor morphological and physiological changes that occur in skeletal muscle during contraction as well as result from fatigue. Objective: To investigate the effect of exercise intensity during a fatiguing protocol of the biceps brachii on the electrical impedance changes of biceps tissue due to an isotonic protocol. Approach: Resistance (R) and reactance (X) measurements were collected from the right and left biceps of 18 participants pre and post execution of a fatiguing protocol using an isotonic exercise to task failure at two intensities, either 60% (N = 10) or 75% (N = 8) of their assessed one-repetition maximum strength. Main Results: There were significant differences (p < 0.05) between the pre and post fatigue R and X within groups due to the exercise protocol. But no significant differences (p > 0.05) of the R and X between groups at different intensities and no significant differences (p > 0.05) of changes between the left and right biceps in both groups. Significance: These results show that the level of exercise intensity did not significantly impact the changes in electrical impedance of the biceps tissue between the two intensity groups in this study when the same fatigue criteria are used, which is an important consideration when using EIM to monitor changes as a result of fatigue and exercise related injury.

Reactance to Electronic Surveillance: a Test of Antecedents and Outcomes

Organizations are increasingly using electronic surveillance to observe their employees’ behavior. This controversial practice has yet-unknown effects on employee behavior or attitudes. We seek to examine the effects of electronic surveillance on contextual performance, drawing from the perspective of psychological reactance theory. Data were collected from employees of a variety of organizations (n = 238). Respondents indicated the ways their organizations used electronic surveillance and described their reactions using open-ended comments, and then completed measures of state and trait reactance, organizational citizenship behavior (OCB), and counterproductive work behavior (CWB). Invasion of privacy was linked with state reactance. Anger, one component of state reactance, was associated with increased CWB-O and decreased OCB-O. Further, not only did trait reactance predict invasion of privacy perceptions, but it also explained significant variance in CWB and OCB. After controlling for trait reactance, anger was no longer a significant predictor of these outcomes. This study provides evidence that perceptions of monitoring systems affect contextual performance and that individual differences affect reactions to surveillance. This knowledge can be used to inform the design, implementation, and communication of monitoring systems. This study contributes to the electronic monitoring and reactance literatures by being the first to link invasion of privacy, trait and state reactance, and contextual performance. People experience state reactance in response to invasion of privacy; this suggests that psychological reactance theory can be used to inform the design of monitoring systems. We provide evidence that surveillance is associated with negative consequences.

Small-airway dysfunction precedes the development of asthma in children with allergic rhinitis

BackgroundEpidemiological evidence suggests the existence of a direct link between allergic rhinitis (AR) and asthma. Several studies also support the presence of small-airway dysfunction (SAD) in non-asthmatic children with AR. However, it remains unknown whether SAD can predict the progression of AR to asthma. Our objective was to explore the existence of SAD in non-asthmatic children with AR and to assessed its ability to predict the development of asthma. MethodsSeventy-three 6-year-old children with intermittent moderate-severe AR but without asthma symptoms/medication within the last two years, underwent spirometry and measurement of respiratory resistance (Rrs) and reactance (Xrs) before and after bronchodilation (BD) (300mcg salbutamol). Lung function measurements were performed in the absence of nasal symptoms and repeated at AR exacerbation. SAD was defined as >30% decrease in Rrs or >50% increase in Xrs at 6 or 8Hz post-BD. Participants were followed for five years. ResultsTwenty-three children (31.5%) developed asthma; this group presented significant post-BD changes in Rrs and Xrs, but only at AR exacerbation. The ability of these changes to predict the development of asthma was exceptional and superior to that of the spirometric parameters. SAD (22 children, 30.1%), emerged as the single most efficient predictor of asthma, independently of other risk factors such as parental asthma, personal history of eczema and type of allergic sensitisation. ConclusionSAD precedes the development of asthma in children with AR. Changes in respiratory impedance at AR exacerbation may assist in identifying those at risk to progress to asthma.

Sensitivity of Lung Resistance and Compliance to Beta-Blocker Induced Bronchoconstriction and Long Acting Beta-Agonist Withdrawal in COPD

Little is known about impulse oscillometry (IOS) in COPD. IOS is an effort independent measure of lung resistance and reactance (compliance). We assessed how frequency dependence of resistance (R) and reactance (X) changed in response to bronchoconstriction with carvedilol followed by long acting beta-agonist (LABA) withdrawal. N = 12 patients with moderate to severe COPD were analysed, who had ≥ 100 ml fall in FEV1 with carvedilol. Compared to baseline taking ICS/LABA there were 21, 59, and 135% significant changes in resistance at 5 Hz (R5), reactance at 5 Hz (X5), and reactance area (AX), respectively, with carvedilol, while after LABA withdrawal only AX showed a further significant increase to 210% (i.e. reduced compliance). Hence changes in lung compliance rather than resistance play a more important role in the beta-2 receptor-mediated responses in COPD.

Determinants of peripheral airway function in adults with and without asthma.

Peripheral airway involvement in asthma remains poorly understood. We investigated impulse oscillometry (IOS) measures of peripheral airway function in a population-based birth cohort. Pre- and post-bronchodilator spirometry and IOS measures of respiratory resistance and reactance were measured in 915 participants at age 38 years. Current asthma was associated with impairments in both spirometry and IOS parameters. These impairments were greater in men and in those with childhood persistent asthma. Spirometry and IOS values for those whose asthma was in remission were not different to non-asthmatic participants. There were significant changes in IOS in both asthmatic and non-asthmatic participants after bronchodilator, but between-group differences persisted. Higher BMIs were associated with impairments in IOS but not spirometry. Cumulative tobacco use was associated with spirometric airflow obstruction in both sexes, whereas cannabis use was associated with impairments in IOS in women. Despite higher lifetime exposure, there were few associations between cannabis and IOS in men. Asthma is associated with abnormalities in IOS measures of peripheral airway dysfunction. This association is stronger in men and in those with asthma persisting since childhood. Tobacco and cannabis use are associated with different patterns of spirometry and IOS abnormalities and may affect the bronchial tree at different airway generations with differences in susceptibility between sexes.

Assessing the Unidimensionality of Trait Reactance Using a Multifaceted Model Assessment Approach

ABSTRACTThis study employed a multifaceted model assessment approach to investigate the dimensionality and nomological network of a popular measure of trait reactance, the Hong Psychological Reactance Scale (HPRS; Hong & Page, 1989). To address confusion regarding the scoring and modeling of the HPRS as well as its limited external validity evidence, we tested competing factor models, diagnosed model–data misfit, examined relationships between competing factor models and key personality traits, and cross-validated the results. Confirmatory factor analytic results supported modeling the HPRS via a bifactor model and, when this model was applied, trait reactance was negatively related to agreeableness, conscientiousness, and conformity, and positively related to entitlement, as expected. However, we also demonstrated the consequences of championing a 1-factor model by highlighting differences in relationships with external variables. Specifically, although modeling the HPRS scores with the bifactor model resulted in greater model–data fit than the 1-factor model, relationships with external variables based on the 2 models differed negligibly. Moreover, bifactor statistical indexes indicted that scores were essentially unidimensional, providing some support that HPRS scores can be treated as unidimensional in structure. Implications for using and scoring the HPRS are discussed.

A brief measure of reactance to health warnings.

Reactance to persuasive messages involves perceived threat to freedom, anger, and counterarguing that may undermine the impact of health warnings. To understand reactance's effects, reliable and valid assessment is critical. We sought to develop and validate a brief Reactance to Health Warnings Scale (RHWS). Two independent samples of US adults completed the brief RHWS in studies that presented warnings on cigarette packs that smokers carried with them for 4weeks (Study 1; n=2149) or as digital images of cigarette packs that participants viewed briefly (Study 2; n=1413). The three-item Brief RHWS had good internal consistency and test-retest reliability. The scale correlated with higher trait reactance and exposure to pictorial warnings, supporting its convergent validity. With respect to predictive validity, the Brief RHWS predicted perceived message effectiveness, quit intentions, avoidance of the warnings, and number of cigarettes smoked per day. The Brief RHWS can serve as an efficient adjunct to the development of persuasive messages.

Interference of heart and transcutaneous oxygen monitoring in the measurement of bioelectrical impedance analysis in preterm newborns

ObjectiveTo verify if the connection between electrodes for heart and transcutaneous oxygen monitoring interfere with the measurement of electrical bioimpedance in preterm newborns. MethodsThis was a prospective, blinded, controlled, cross‐sectional, crossover study that assessed and compared paired measures of resistance (R) and reactance (Xc) by BIA, obtained with and without monitoring wires attached to the preterm newborn. The measurements were performed in immediate sequence, after randomization to the presence or absence of electrodes. The sample size calculated was 114 measurements or tests with monitoring wires and 114 without monitoring wires, was calculated for a difference between the averages of 0.1 ohms, with an alpha error of 10% and beta error of 20%, with significance<0.05. ResultsNo differences were observed between the R (677.37±196.07 vs. 677.46±194.86) and Xc (31.15±9.36 vs. 31.01±9.56) values obtained with and without monitoring wires, respectively, with good correlation between them (R: 0.997 and Xc: 0.968). ConclusionThe presence of heart and/or transcutaneous oxygen monitoring wires connected to the preterm newborn did not affect the values of R or Xc measured by BIA, allowing them to be carried out in this population without risks.

Role of IOS in evaluation of patients with interstitial lung diseases

AimIn patients with ILD, a static expiratory pressure–volume curve of the lung is generally shifted downward and rightward and spirometry results reveal reduced vital capacity (Thompson et al., 1989). However, reduced vital capacity may occur even in patients with obstructive lung diseases and in other situations, such as chest wall restriction, lung resection, inspiratory muscle weakness, or poor cooperation with spirometry. In addition, spirometry is sometimes difficult to perform with elderly, cognitively impaired patients, or severe respiratory distress (Kubota et al., 2009). IOS is a simple, noninvasive method requiring only passive patient cooperation that allows for the evaluation of lung function through the measurement of both airway resistance and airway reactance. The aim of this study is to assess the role of IOS in the evaluation of the cases of interstitial lung diseases. MethodologyThis study included 48 patients with interstitial lung diseases of different causes. Pulmonary function test by spirometry was done to measure FEV1, FVC, FEV1/FVC, MEF25-75 and pulmonary function test by impulse oscillometry (IOS). We measured R5, R20, X5, RF. Oxygen saturation and 6MWT. ResultsIn our study 87% were females. The mean age in our study was 50.75±11.1. Mean X5 was low in ILD denoting restrictive pattern, and there was a negative correlation between X5andFEV1/FVC. There was a positive correlation between X5and6MWT. The mean R5 was 150.33±while mean R20 was 108.33±48.66 this is within normal then this is considered an index of mild small airways obstruction.

Interference of heart and transcutaneous oxygen monitoring in the measurement of bioelectrical impedance analysis in preterm newborns

ObjectiveTo verify if the connection of electrodes for heart and transcutaneous oxygen monitoring interfere with the measurement of electrical bioimpedance in preterm newborns. MethodsThis was a prospective, blinded, controlled, cross-sectional, crossover study that assessed and compared paired measures of resistance (R) and reactance (Xc) by BIA, obtained with and without monitoring wires attached to the preterm newborn. The measurements were performed in immediate sequence, after randomization to the presence or absence of electrodes. The sample size calculated was 114 measurements or tests with monitoring wires and 114 without monitoring wires, considering for a difference between the averages of 0.1 ohms, with an alpha error of 10% and beta error of 20%, with significance <0.05. ResultsNo differences were observed between the R (677.37±196.07 vs. 677.46±194.86) and Xc (31.15±9.36 vs. 31.01±9.56) values obtained with and without monitoring wires, respectively, with good correlation between them (R: 0.997 and Xc: 0.968). ConclusionThe presence of heart and/or transcutaneous oxygen monitoring wires connected to the preterm newborn did not affect the values of R or Xc measured by BIA, allowing them to be carried out in this population without risks.

Hyperpolarized 3He magnetic resonance imaging ventilation defects in asthma: relationship to airway mechanics.

In patients with asthma, magnetic resonance imaging (MRI) provides direct measurements of regional ventilation heterogeneity, the etiology of which is not well‐understood, nor is the relationship of ventilation abnormalities with lung mechanics. In addition, respiratory resistance and reactance are often abnormal in asthmatics and the frequency dependence of respiratory resistance is thought to reflect ventilation heterogeneity. We acquired MRI ventilation defect maps, forced expiratory volume in one‐second (FEV 1), and airways resistance (Raw) measurements, and used a computational airway model to explore the relationship of ventilation defect percent (VDP) with simulated measurements of respiratory system resistance (Rrs) and reactance (Xrs). MRI ventilation defect maps were experimentally acquired in 25 asthmatics before, during, and after methacholine challenge and these were nonrigidly coregistered to the airway tree model. Using the model coregistered to ventilation defect maps, we narrowed proximal (9th) and distal (14th) generation airways that were spatially related to the MRI ventilation defects. The relationships for VDP with Raw measured using plethysmography (r = 0.79), and model predictions of Rrs>14 (r = 0.91, P < 0.0001) and Rrs>9 (r = 0.88, P < 0.0001) were significantly stronger (P = 0.005; P = 0.03, respectively) than with FEV 1 (r = −0.68, P = 0.0001). The slopes for the relationship of VDP with simulated lung mechanics measurements were different (P < 0.0001); among these, the slope for the VDP‐Xrs0.2 relationship was largest, suggesting that VDP was dominated by peripheral airway heterogeneity in these patients. In conclusion, as a first step toward understanding potential links between lung mechanics and ventilation defects, impedance predictions were made using a computational airway tree model with simulated constriction of airways related to ventilation defects measured in mild‐moderate asthmatics.