Phase angle of bioimpedance at 50 kHz is associated with cardiovascular diseases: systematic review and meta-analysis

Biomarkers of aging: from molecules and surrogates to physiology and function

Many countries face an unprecedented challenge in aging demographics. This has led to an exponential growth in research on aging, which, coupled to a massive financial influx of funding in the private and public sectors, has resulted in seminal insights into the underpinnings of this biological process. However, critical validation in humans has been hampered by the limited translatability of results obtained in model organisms, additionally confined by the need for extremely time-consuming clinical studies in the ostensible absence of robust biomarkers that would allow monitoring in shorter time frames. In the future, molecular parameters might hold great promise in this regard. In contrast, biomarkers centered on function, resilience, and frailty are available at the present time, with proven predictive value for morbidity and mortality. In this review, the current knowledge of molecular and physiological aspects of human aging, potential antiaging strategies, and the basis, evidence, and potential application of physiological biomarkers in human aging are discussed.

Phase angle as a reproducible bedside tool to assess reduced muscle mass in patients with decompensated cirrhosis and ascites: An observational cross-sectional study

BACKGROUND

Reduced muscle mass in patients with cirrhosis is linked to poor clinical outcomes. Bioimpedance analysis estimates fat mass (FM), fat-free mass (FFM), and phase angle (PhA), a marker of cell membrane integrity correlating with computed tomography-based muscle mass assessments. We hypothesized that PhA would remain stable after paracentesis.

METHODS

Bioelectrical impedance was measured in patients with cirrhosis immediately before and after paracentesis using a 256-frequency bioimpedance spectroscopy device. We assessed median paired differences (with 95% confidence intervals) for FM, FFM, and PhA. Reduced muscle mass was diagnosed using PhA thresholds of 5.4 for women and 5.6 for men, based on previous cross-sectional validation against skeletal muscle index.

RESULTS

The study included 32 participants with median age of 60 (IQR: 55-67), 60% male, median model for end stage liver disease Na (MELD-Na) score of 18 (IQR: 14-21), and median paracentesis volume of 6 liters (loss of 5.7 kg). At baseline, 97% had reduced muscle mass based on PhA thresholds. Significant differences were observed between pre-paracentesis and post-paracentesis measurements for FM and FFM (P < 0.05). PhA remained stable (P = 0.208), with a slight nonsignificant increase of 0.1° from pre-paracentesis to post-paracentesis. Sensitivity analysis showed change in reduced muscle mass diagnosis for only one participant.

CONCLUSIONS

FM and FFM levels before and after paracentesis were significantly different, suggesting that these tests would not be accurate in patients with large fluid shifts. PhA measurements were not significantly affected by ascitic fluid shifts after paracentesis, suggesting that PhA may reliably monitor muscle mass in patients, regardless of ascites.

Association between segmental phase angles and functional independence measure scores in hospitalized adults following stroke: A retrospective cohort study

BACKGROUND

This study investigated the association between segmental phase angles and functional outcomes in patients after stroke, hypothesizing that increased segmental phase angle correlates with improved functional status.

METHODS

A retrospective cohort study of 1012 patients after stroke was conducted. Whole body and segmental phase angles were measured using bioelectrical impedance analysis within 3 days of admission. Our exposure of interest was segmental phase angle measured via a multifrequency bioelectrical impedance analyzer and calculated as phase angle = arctangent (Xc/R) × (180/π), where R is the resistance of the right half of the body and Xc is the reactance measured at 50 kHz. The primary outcomes were the motor subscale of the functional independence measure (FIM) at discharge and FIM change between admission and discharge. Secondary outcomes included FIM scores for specific activities. Multiple linear regression analysis was performed to assess associations.

RESULTS

Phase angles of the healthy upper and lower limbs demonstrated stronger associations with discharge FIM motor scores (β = 0.175 and β = 0.105, respectively) and FIM motor gain (β = 0.242 and β = 0.092, respectively) compared with whole body or paretic limb phase angles. Upper limb phase angles were more closely related to grooming and toileting abilities, whereas lower limb phase angles were associated with both toileting and locomotion at discharge.

CONCLUSION

Segmental phase angles, particularly those of the nonparetic limbs, are promising predictors of functional outcomes in patients after stroke. Assessing segmental phase angles may guide targeted interventions and rehabilitation strategies for improving specific activities of daily living.

Fat-Free Mass: Friend or Foe to Metabolic Health?

BACKGROUND

Fat mass (FM) and fat-free mass (FFM) are body composition estimates commonly reported in research studies and clinical settings. Recently, fat-free mass indexed to height (fat-free mass index; FFMI) has been shown to be positively associated with impaired insulin sensitivity or insulin resistance. Consequently, hypertrophic resistance training which can increase FFM was also questioned. This paper sets out to evaluate these propositions.

METHODS

In this narrative review, we discuss possible reasons that link FFMI to adverse metabolic health outcomes including the limitations of the body composition model that utilizes FFM. The safety of resistance training is also briefly discussed.

RESULTS

Approximately 50% of FFM is comprised of skeletal muscle (SM), with the other 50% being viscera, skin, and bone; FFM and SM cannot be conflated. FFM and fat mass (FM) can both rise with increasing body weight and adiposity, indicating a positive correlation between the two compartments. Risk assessment models not adequately adjusting for this correlation may cause erroneous conclusions, however which way FM and FFM are indexed. Adipose tissue accumulation with weight gain, measured by dual-energy X-ray absorptiometry or bioelectrical impedance, can inflate FFM estimates owing to increased connective tissue. Increased adiposity can also result in fat deposition within skeletal muscle disrupting metabolic health. Importantly, non-skeletal muscle components of the FFM, i.e., the liver and pancreas, both critical in metabolic health, can also be negatively affected by the same lifestyle factors that impact SM. The most frequently used body composition techniques used to estimate FM and FFM cannot detect muscle, liver or pancreas fat infiltration. Prospective evidence demonstrates that resistance training is a safe and effective exercise modality across all ages, especially in older adults experiencing age- or disease-related declines in muscle health.

CONCLUSIONS

The association between FFM and insulin resistance is largely an artefact driven by inadequate assessment of skeletal muscle. If FM and FFM are used, at the minimum, they need to be evaluated in context with one another. Body composition methods, such as magnetic resonance imaging, which measures skeletal muscle rather than fat-free mass, and adipose tissue as well as muscle ectopic fat, are preferred methods. Resistance training is important in achieving and maintaining good health across the lifespan. While strength and power are critical components of resistance training, the reduction of skeletal mass through ageing or disease may require hypertrophic training to mitigate and slow down the progression of this often-inevitable process.

Phase angle in bioelectrical impedance analysis for assessing congestion in acute heart failure

BACKGROUND

The phase angle (PhA) in bioelectrical impedance analysis (BIA) reflects the cell membrane integrity or body fluid equilibrium. We examined how the PhA aligns with previously known markers of acute heart failure (HF) and assessed its value as a screening tool.

METHODS

PhA was measured in 50 patients with HF and 20 non-HF controls along with the edema index (EI), another BIA parameter suggestive of edema. Chest computed tomography-measured lung fluid content (LFC) was used to assess pulmonary congestion. A correlation analysis was conducted to evaluate the relationships between PhA and EI, NT-proBNP, and LFC. Receiver operating characteristic (ROC) curve analysis was used to determine the cut-off values for PhA and EI for classifying patients with HF. The area under the curve (AUC) was compared using the DeLong test to evaluate the performance of PhA and EI compared to that of LFC in correctly classifying HF.

RESULTS

The PhA levels were significantly lower in the HF group. Whole-body PhA was 4.49° in the HF group and 5.68° in the control group. Moderate and significant correlation was observed between PhA measured at 50-kHz and both NT-proBNP (-0.56 to -0.27, all p-values<0.05) and LFC (-0.52 to -0.41, all p-values <0.05). The AUC for whole-body PhA was 0.827 (confidence interval [CI] 0.724-0.931, p<0.01) and was 0.883 (CI 0.806-0.961, p<0.01) for EI, and the optimal cutoffs were estimated as 5° (sensitivity 0.84, specificity 0.80) and 0.394 (sensitivity 0.78, specificity 0.95), respectively. When both PhA and EI were included in the model, the AUC increased to 0.905, and this was comparable to that of LFC (AUC = 0.913, p = 0.857).

CONCLUSIONS

PhA exhibited a correlation with known markers of HF and demonstrated its potential as a non-invasive screening tool for the early detection of HF exacerbation. The combined use of PhA and EI can provide a robust alternative for routine self-monitoring in patients with HF, thereby enhancing early intervention.

Associations of socio-demographic, anthropometric and behavioural factors with phase angle in older adults: a cross-sectional study in Taiwan

OBJECTIVE

Phase angle (PhA) is a prognostic factor for predicting and monitoring geriatric syndromes. However, multiple factors associated with increased PhA values as an outcome remain unclear in the older population. This study aimed to examine the association of socio-demographic, anthropometric and behavioural factors with PhA among older Taiwanese adults.

DESIGN

This cross-sectional study was conducted between May and August 2023.

SETTING

The study was carried out in northern Taiwan, specifically Taipei city and Yilan county.

PARTICIPANTS

Participants aged ≥65 years who were able to walk independently and had no artificial implants, such as cardiac pacemakers or joint replacements, were recruited using convenience sampling. A total of 198 participants were initially recruited for this study.

PRIMARY OUTCOME MEASURES

Data on socio-demographic and behavioural variables were collected using self-administered questionnaires. Anthropometric variables and PhA were measured using a multi-frequency bioelectrical impedance analyser (MC-780MA, TANITA). PhA was categorised into 'high' and 'low' using gender-specific cut-off points. A logistic regression analysis was performed.

RESULTS

A total of 152 participants (mean age: 72.0±5.5 years; 121 women (79.6%)) were included. Male (OR=0.72, 95% CI=0.02 to 0.33), unmarried (OR=0.22, 95% CI=0.06 to 0.82) and unemployed older adults (OR=0.16, 95% CI=0.03 to 0.87) were less probable to achieve high PhA values. After adjusting for potential confounders, older individuals with an increased body mass index (BMI) (OR=2.56, 95% CI=1.61 to 4.07) and greater muscle mass (OR=1.34, 95% CI=1.12 to 1.60) may have higher PhA values, whereas those with a greater fat mass may have lower PhA values (OR=0.61, 95% CI=0.48 to 0.78). No significant associations were observed between behavioural factors and PhA values.

CONCLUSIONS

The interventions designed to improve PhA should prioritise strategies tailored to male, unmarried or unemployed older adults, as well as those with low BMI, low muscle mass and high fat mass. Future studies with larger sample sizes are needed to confirm and strengthen our findings.

Bioelectrical Impedance Analysis (BIA) detects body resistance increase in dogs undergoing blood donation

Using raw parameters of bioelectrical impedance analysis (BIA) and derived Phase Angle (PhA) has emerged as an alternative to conventional predictive BIA for body fluid volumes and body composition estimation in human patients, offering an approach independent of predictive equations. Classic predictive equation-based BIA remains unsuitable for veterinary clinical practice due to the high morphological variability within the canine species. This study aimed to validate the feasibility of BIA in dogs and assess its utility in detecting changes in body fluid volumes, particularly in blood donation. Sixty healthy blood donor dogs and ten controls were longitudinally assessed using BIA raw parameters with a portable analyzer at a 50 kHz frequency. Measurements were performed before and after blood donation in donor dogs, whereas in controls, they were carried out at two time points, approximating the timing of a donation. Significant increases in raw bioelectrical parameters were observed after blood donation in the donor group, while differences were not statistically significant in controls. Hematocrit values did not significantly differ between the two time points in both groups. These findings suggest the feasibility of using BIA to detect changes in body fluid volumes in dogs undergoing blood donation, highlighting its potential application in veterinary medicine. Further research should explore the applicability of BIA in spontaneous pathological conditions involving fluid loss or retention and investigate the potential utility of PhA as a prognostic or monitoring tool in veterinary clinical practice. This study provides valuable insights into using BIA in canine medicine, paving the way for enhanced diagnostic and monitoring strategies in clinical practice.

Association of bio-impedance phase angle and a nutritional indicator in community-dwelling patients with type 2 diabetes mellitus

Purpose

Although the bio-impedance phase angle is a relevant factor in nutritional assessment, studies with community-dwelling patients with type 2 diabetes mellitus have not been identified. The purpose of this study was to determine the association between phase angle and nutritional status in community-dwelling patients with type 2 diabetes mellitus according to gender and accounting for related factors other than nutritional status.

Methods

This study included 122 patients (mean age 52.1 ± 13.5 years, 63 males and 59 females) with type 2 diabetes mellitus living in the community who used our Endocrinology and Metabolism medical clinic. The phase angle was measured using bioelectrical impedance analysis. Albumin was an independent variable and the covariates were age, hemoglobin A1c, skeletal muscle index (SMI), and body mass index. Statistical analysis was performed using linear regression with a significance level of 5%.

Results

The linear regression model results showed a significant association between phase angle and albumin in both males and females (males: β = 0.26, females: β = 0.16). Age was also a relevant factor (male: β = -0.25, female: β = -0.51), and a significant association was found between phase angle and SMI in males (β = 0.54).

Conclusion

Phase angle was positively associated with albumin, a nutritional assessment index. These results suggest that phase angle can be a simple and noninvasive measure of nutritional status.

Exploring the association between phase angle of bioimpedance at 50 kHz and cardiovascular risk

BACKGROUND

Cardiovascular diseases are characterized by chronic inflammation, leading to increased inflammatory markers that can cause cell damage and death. Phase angle has emerged as a marker of cellular health. It is considered a prognostic factor in various acute and chronic conditions. However, few studies have examined its association with cardiovascular disease risk measures. This study aims to investigate the relationship between phase angle, the general Framingham risk score, and the HEARTS cardiovascular risk score.

METHODS

This cross-sectional study included a convenience sample of adult patients of 2 primary health care services. Phase angle was measured using multifrequency bioimpedance analysis at 50 kHz. The risk of cardiovascular events was calculated using the Framingham and HEARTS risk scores. Statistical analysis included generalized linear regression models, unadjusted and adjusted according to sex and age, to determine the association between scores, risk factors, and phase angle.

RESULTS

The study included 164 individuals with a mean age 52.2 (SD 17.9). According to the HEARTS score, low-risk patients had higher phase angle values than those with high or very high risk [ß = -0.57 (95% CI -0.95; -0.19), P = 0.003]. Framingham scores showed a trend toward significance for higher mean phase angle values in low-risk than high-risk patients [ß = -0.43 (95% CI -0.88 to 0.02), P = 0.06].

CONCLUSION

Phase angle values were lower in high and very high-risk patients than in low-risk patients, which shows that phase angle is a promising risk predictor for patients with cardiovascular diseases.

Comparing Device-Generated and Calculated Bioimpedance Variables in Community-Dwelling Older Adults

Despite BIA emerging as a clinical tool for assessing older adults, it remains unclear how to calculate whole-body impedance (Z), reactance (Xc), resistance (R), and phase angle (PhA) from segmental values using modern BIA devices that place electrodes on both sides of the body. This investigation aimed to compare both the whole-body and segmental device-generated phase angle (PhADG) with the phase angle calculated using summed Z, Xc, and R from the left, right, and combined sides of the body (PhACalc) and to compare bioelectric variables between sides of the body. A sample of 103 community-dwelling older adults was assessed using a 50 kHz direct segmental multifrequency BIA device. Whole-body PhACalc values were assessed for agreement with PhADG using 2.5th and 97.5th quantile nonparametric limits of agreement and Spearman's rho. Bioelectrical values between sides of the body were compared using Wilcoxon rank and Spearman's rho. A smaller mean difference was observed between PhADG and right PhACalc (-0.004°, p = 0.26) than between PhACalc on the left (0.107°, p = 0.01) and on the combined sides (0.107°, p < 0.001). The sum of Z, R, and PhACalc was significantly different (p < 0.01) between the left (559.66 ± 99.55 Ω, 556.80 ± 99.52 Ω, 5.51 ± 1.5°, respectively) and the right sides (554.60 ± 94.52 Ω, 552.02 ± 94.23 Ω, 5.41 ± 0.8°, respectively). Bilateral BIA values do not appear to be interchangeable when determining whole-body measurements. Present data suggest that using right-sided segmental values would be the most appropriate choice for calculating whole-body bioelectrical variables.

Phase angle and donor type are determinants of coronary artery calcification in stable kidney transplant recipients at twelve months after transplantation

BACKGROUND AND AIM

Coronary artery calcification (CAC) partially explains the excess cardiovascular morbidity and mortality after kidney transplantation. This study aimed to investigate determinants of CAC in stable kidney transplant recipients at 12 months post-transplantation.

METHODS AND RESULTS

CAC-score was quantified by the Agatston method using non-contrast enhanced computed tomography, and age- and sex-standardized CAC-percentiles were calculated. Univariable and multivariable multinomial logistic regression was performed to study potential determinants of CAC. The independent determinants were included in multivariable multinomial logistic regression adjusting for potential confounders. 203 KTRs (age 54.0 ± 14.7 years, 61.1% male) were included. Participants were categorized into four groups according to CAC percentiles (p = 0 [CAC-score = 0], n = 68; p ≥ 1%-p ≤ 50% [CAC score = 29.0 (4.0-166.0)], n = 31; p > 50 ≤ 75% [CAC score = 101.0 (23.8-348.3)], n = 26; and p>75% [CAC score = 581.0 (148.0-1652)], n = 83). Upon multivariable multinomial logistic regression, patients with a narrower phase angle and patients who had received a graft from a deceased donor had a higher risk of being in the >75th CAC-percentile.

CONCLUSIONS

This study identifies not only metabolic and transplant-related factors, but also phase angle, a composite marker of cell integrity, as an independent determinant of CAC at 12 months after kidney transplantation. This study offers new perspectives for future research into the value of bioelectrical impedance analysis in relation to vascular calcification in kidney transplant recipients.

Impact of CFTR modulator therapy on body composition as assessed by thoracic computed tomography: A follow-up study

OBJECTIVE

Treatment with cystic fibrosis transmembrane conductance regulator (CFTR) modulators in individuals with cystic fibrosis (CF) has brought a significant change in forced expiratory volume in 1 second (FEV1) and clinical parameters. However, it also results in weight gain. The aim of our study is to evaluate the effect of CFTR modulator treatment on body composition, measured by computed tomography (CT).

METHODS

Adult subjects with CF under follow-up at La Princesa University Hospital were recruited. All of them were on elexacaftor-tezacaftor-ivacaftor (ELX/TEZ/IVA) treatment. Body composition analysis was conducted using CT scans and an open-source software. The results were then compared with bioimpedance estimations, as well as other clinical and spirometry data.

RESULTS

Our sample consisted of 26 adult subjects. The fat mass compartments on CT scans correlated with similar compartments on bioimpedance, and normal-density muscle mass exhibited a strong correlation with phase angle. Higher levels of very low-density muscle prior to treatment were associated with lower final FEV1 and less improvement in FEV1 after therapy. We observed an increase in total body area (P < 0.001), driven by increases in total fat mass (P < 0.001), subcutaneous fat (P < 0.001), visceral fat (P = 0.002), and intermuscular fat (P = 0.022). The only muscle compartment that showed an increase after treatment was very low-density muscle (P = 0.032).

CONCLUSIONS

CT scans represent an opportunity to assess body composition on CF. Combination treatment with CFTR modulators, leads to an improvement in FEV1 and to an increase in body mass in all compartments primarily at the expense of fat mass.

Conflicting Associations among Bioelectrical Impedance and Cardiometabolic Health Parameters in Young White and Black Adults

PURPOSE

The purpose of this cross-sectional evaluation was to determine the associations between raw bioelectrical impedance and cardiometabolic health parameters in a sample of young non-Hispanic White and African American adults.

METHODS

A total of 96 (female: 52, male: 44) non-Hispanic White ( n = 45) and African American adults ( n = 51) between the ages of 19 and 37 yr (22.7 ± 3.83 yr) completed several fasted assessments including resting systolic blood pressure (rSBP), blood glucose (FBG), blood lipids, and bioelectrical impedance spectroscopy. Bioelectrical impedance spectroscopy-derived measurements included phase angle, bioimpedance index (BI), impedance ratio (IR), reactance index (XCi), fat-free mass (FFM), FFM index (FFMi), and absolute (a) and relative (%) total body water (TBW) and extracellular (ECF) and intracellular fluid (ICF). All bioelectric variables were collected at 50 kHz other than IR (250 kHz/5 kHz). Multiple regressions were conducted and adjusted for sex, age, and body mass index.

RESULTS

rSBP was positively, and HDL was inversely, associated with all bioelectrical impedance and absolute hydration variables (all P ≤ 0.050) other than XCi for rSBP and XCi and FFMi for HDL. rSBP ( P < 0.001) was inversely, and HDL ( P = 0.034) was positively, associated with IR. FBG was positively associated with BI, XCi, FFM, TBWa, and ECFa (all P < 0.050). Metabolic syndrome severity was positively associated with BI, FFM, TBWa, and ECFa for women (all P ≤ 0.050) and with ICFa for African American women ( P = 0.016).

CONCLUSIONS

Given the rapid increase in the prevalence of cardiometabolic health risks among young adults and the broad use of bioelectrical impedance in practice, the conflicting associations we observed in this age group suggest that bioelectrical impedance parameters should be used with caution in the context of cardiometabolic health risks and age.

Relationship between phase angle and lower-extremity function in older adults: Itabashi Longitudinal Study on Aging

OBJECTIVE

Evaluating muscle quality instead of its mass has gained attention in diagnosing sarcopenia. The aim of this study was to examine whether phase angle (PhA) as a bioelectrical impedance analysis (BIA)-derived muscle quality indicator is associated with overall lower extremity function better than appendicular skeletal muscle mass index (ASMI) in community-dwelling older adults.

METHODS

This cross-sectional study used data from the Itabashi Longitudinal Study on Aging, a community-based cohort study. A sex-stratified multivariate logistic regression analysis was conducted using PhA and ASMI as exposures, and low physical function defined as short physical performance battery score <10 as the outcome, adjusted for age, being overweight, knee pain, and non-communicable diseases. Discrimination of low physical function was compared using the receiver operating characteristic curve.

RESULTS

This study included 1464 participants (age 76 [73-80] y; 757 women), with 58 men (8%) and 66 women (9%) exhibiting low physical function. The multivariate odds ratio (OR; 95% confidence interval [CI]) for low physical function among the highest quartile, compared with the lowest quartile were significant in PhA in multiple sites (e.g., OR, 0.09; 95% CI, 0.03-0.32] for men and 0.12; 95% CI, 0.04-0.33 for women in the left leg) but not in ASMI (OR, 0.51; 95% CI, 0.19-1.34 for men and 0.56; 95% CI, 0.21-1.47 for women). Legs and whole-body PhA outperformed the ASMI in discriminating low physical function (P < 0.001).

CONCLUSION

PhA reflected physical function better than ASMI; using PhA instead of ASMI in BIA-based morphometric evaluation may add information on low physical function and enhance the diagnostic value of sarcopenia.

Bioelectrical impedance analysis as a clinical marker of health status in adult patients with benign gastrointestinal disease: A systematic review

BACKGROUND

Body composition reflects nutritional status, disease status and progression, and treatment responses. Mounting evidence supports the use of bioelectrical impedance analysis (BIA) as a non-invasive tool to assess body composition. Patients with benign gastrointestinal (GI) disease experience disease-related alterations in their body composition, and bioimpedance outcomes in patients with benign GI diseases have not previously been summarized. We aimed to evaluate BIA as a clinical body composition marker for benign GI diseases and describe its association with physical health status.

METHODS

We systematically searched PubMed, Scopus, Web of Science, Embase, and CINAHL from inception to October 2023 (PROSPERO registration: CRD42021265866). Of 971 screened studies, 26 studies were included in the final analysis, comprising a total of 2398 adult patients with benign GI disease. The main outcome was raw impedance data.

RESULTS

The most frequently reported BIA outcome was phase angle (PhA) (reported in 18 of 26 studies), followed by fat-free-mass (FFM) (reported in 13 of 26 studies). The consensus view of the included studies illustrates that BIA can be a useful tool for evaluating body composition in patients with benign GI diseases, and low PhA and FFM were associated with increased nutritional risk, abnormal physical characteristics, and increased mortality risk.

CONCLUSION

To fully utilize BIA as a clinical marker of health in patients with benign GI disease, standardized protocols specific to this population are needed and prospective studies testing cut-offs and ranges, accuracy, and other raw BIA parameters for classifying disease status.

Body Composition Evaluation and Clinical Markers of Cardiometabolic Risk in Patients with Phenylketonuria

Cardiovascular diseases are the main cause of mortality worldwide. Patients with phenylketonuria (PKU) may be at increased cardiovascular risk. This review provides an overview of clinical and metabolic cardiovascular risk factors, explores the connections between body composition (including fat mass and ectopic fat) and cardiovascular risk, and examines various methods for evaluating body composition. It particularly focuses on nutritional ultrasound, given its emerging availability and practical utility in clinical settings. Possible causes of increased cardiometabolic risk in PKU are also explored, including an increased intake of carbohydrates, chronic exposure to amino acids, and characteristics of microbiota. It is important to evaluate cardiovascular risk factors and body composition in patients with PKU. We suggest systematic monitoring of body composition to develop nutritional management and hydration strategies to optimize performance within the limits of nutritional therapy.

Associations of phase angle with platelet-activating factor metabolism and related dietary factors in healthy volunteers

Introduction

Phase angle (PA) is derived from bioelectrical impedance analysis (BIA). It reflects cell membrane function and decreases in disease. It is affected by inflammation, oxidative stress, and diet. Platelet-activating factor (PAF) is a potent inflammatory lipid mediator. Its levels, along with the activity of its metabolic enzymes, including CDP-choline:1-alkyl-2-acetyl-sn-glycerol-cholinephosphotransferase, acetyl-CoA:lyso-PAF-acetyltransferases, and PAF-AH/Lp-PLA2 are also related to dietary factors, such as the dietary antioxidant capacity (DAC). The aim of the study was to estimate whether the PAF metabolic circuit and related dietary factors are associated with PA in healthy volunteers.

Methods

In healthy subjects, PAF, its metabolic enzyme activity, and erythrocyte fatty acids were measured, while desaturases were estimated. Food-frequency questionnaires and recalls were used, and food groups, macronutrient intake, MedDietScore, and DAC were assessed. Lifestyle and biochemical variables were collected. DXA and BIA measurements were performed.

Results

Lp-PLA2 activity was positively associated with PA (rho = 0.651, p < 0.001, total population; rho = 0.780, p < 0.001, women), while PAF levels were negatively associated with PA only in men (partial rho = -0.627, p = 0.012) and inversely related to DAC. Estimated desaturase 6 was inversely associated with PA (rho = -0.404, p = 0.01, total sample). Moreover, the DAC correlated positively with PA (rho = 0.513, p = 0.03, women). All correlations were adjusted for age, body mass index, and sex (if applicable).

Conclusion

PA is associated with PAF levels and Lp-PLA2 activity in a gender-dependent fashion, indicating the involvement of PAF in cell membrane impairment. The relationship of PA with DAC suggests a protective effect of antioxidants on cellular health, considering that antioxidants may inhibit PAF generation.

Bioelectrical Impedance Analysis and Body Composition in Cardiovascular Diseases

Nutritional status and body composition in cardiovascular (CV) patients are important aspects of their performance. Bioelectrical impedance analysis (BIA) is a noninvasive method that provides reliable information about bioelectrical parameters which reflect nutritional status and body composition data. The aim of this paper was to describe BIA, its advantages, limitations, and clinical applications in CV patients. The PubMed database was searched for all papers showing the use of BIA in CV conditions until January 1, 2023. A total of 42 papers regarding BIA application in CV patients were identified. Phase angle, Z200/5 parameter, and membrane capacitance are the BIA parameters that can be used for nutritional status assessment in CV patients, mainly in heart failure and after myocardial infarction. Among secondary body composition parameters, fat mass can be used for obesity assessment which is a CV risk factor. Body cell mass can be used together which the direct BIA parameters for nutritional status assessment which is an important factor in treatment outcome, quality of life, and disease prognosis. Total body water can be used for hydration assessment in heart failure and during invasive procedures. To conclude, BIA is a noninvasive method that provides essential information about the general condition of the body which is the result of nutritional and hydration status in CV patients.

The role of bioelectrical phase angle in patients with heart failure

The most challenging feature of heart failure (HF) still remains the evaluation of congestion. Residual congestion at discharge and the difficulties in perfectly dosing therapies in order to balance the hydration status of the patient are the most worrisome issues when dealing with HF.The use of bioimpedance vector analysis (BIVA) might promote a different approach in the general management of patients with HF. BIVA is a reliable, fast, bedside tool able to assess the congestion status. It proved to be helpful to physicians for diagnosing congestive status, managing therapies, and providing prognostic information in the setting of HF.Bioelectrical Phase Angle (PhA) - as derived from equations related to the parameters of BIVA - recently surged as a possible biomarker for patients with HF. Studies provided data about the application of PhA in the clinical management and in the overall risk stratification of HF patients.Basically, the use of PhA might be considered as a holistic evaluation of patients with HF which includes the need for a multiparametric approach able to effectively depict the clinical status of patients. There is no definite biomarker able to comprehensively describe and identify all the features of HF patient, but scores based on molecules/techniques able to explore the different pathogenetic mechanisms of HF are desirable.The aim of this review was to provide a comprehensive evaluation of literature related to PhA role in HF and the impact of this biomarker on clinical management and risk stratification of HF patients.

Phase angle of bioimpedance as a marker of inflammation in cardiovascular diseases: A systematic review

OBJECTIVE

The aim of this systematic review was to investigate whether phase angle (PhA) of bioelectrical impedance is associated with inflammatory markers in cardiovascular diseases (CVDs).

METHODS

A search was performed in the following databases: MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), Latin American Caribbean Health Sciences Literature (LILACS), Cumulative Index to Nursing and Allied Health Literature (CINAHL), Web of Science and Scopus; and in the gray literature up to January 2022. Studies with individuals with CVDs were included, to evaluate the association between PhA and the inflammatory markers interleukin (IL)-6, IL-10, IL-18, IL-1β, IL-33, tumor necrosis factor (TNF)-α, C-reactive protein (CRP), toll-like receptor (TLR) 2, TLR 4, nuclear factor κB, pathogen-associated molecular pattern molecules, lipopolysaccharides, interferon-γ-inducing factor, and JAK STAT.

RESULTS

We identified 755 articles and, after an eligibility analysis, 5 studies were included. The inflammatory markers investigated in the studies were CRP, TNF-α, and IL-33. In patients with CVDs, PhA was negatively associated with CRP and TNF-α in 80% and 100% of the studies, respectively.

CONCLUSIONS

The present results suggested that PhA is inversely associated with inflammatory markers in individuals with CVDs, and its clinical use is encouraged for better therapeutic planning.

Future lines of research on phase angle: Strengths and limitations

Bioelectrical impedance analysis (BIA) is the most widely used technique in body composition analysis. When we focus the use of phase sensitive BIA on its raw parameters Resistance (R), Reactance (Xc) and Phase Angle (PhA), we eliminate the bias of using predictive equations based on reference models. In particular PhA, have demonstrated their prognostic utility in multiple aspects of health and disease. In recent years, as a strong association between prognostic and diagnostic factors has been observed, scientific interest in the utility of PhA has increased. In the different fields of knowledge in biomedical research, there are different ways of assessing the impact of a scientific-technical aspect such as PhA. Single frequency with phase detection bioimpedance analysis (SF-BIA) using a 50 kHz single frequency device and tetrapolar wrist-ankle electrode placement is the most widely used bioimpedance approach for characterization of whole-body composition. However, the incorporation of vector representation of raw bioelectrical parameters and direct mathematical calculations without the need for regression equations for the analysis of body compartments has been one of the most important aspects for the development of research in this area. These results provide new evidence for the validity of phase-sensitive bioelectrical measurements as biomarkers of fluid and nutritional status. To enable the development of clinical research that provides consistent results, it is essential to establish appropriate standardization of PhA measurement techniques. Standardization of test protocols will facilitate the diagnosis and assessment of the risk associated with reduced PhA and the evaluation of changes in response to therapeutic interventions. In this paper, we describe and overview the value of PhA in biomedical research, technical and instrumental aspects of PhA research, analysis of Areas of clinical research (cancer patients, digestive and liver diseases, critical and surgical patients, Respiratory, infectious, and COVID-19, obesity and metabolic diseases, Heart and kidney failure, Malnutrition and sarcopenia), characterisation of the different research outcomes, Morphofunctional assessment in disease-related malnutrition and other metabolic disorders: validation of PhA with reference clinical practice techniques, strengths and limitations. Based on the detailed study of the measurement technique, some of the key issues to be considered in future PhA research. On the other hand, it is important to assess the clinical conditions and the phenotype of the patients, as well as to establish a disease-specific clinical profile. The appropriate selection of the most critical outcomes is another fundamental aspect of research.

Raw bioelectrical impedance measurements are not different between White and Black adults when matched for sex, age, BMI, and other physical characteristics

Raw bioelectrical impedance measurements are often used as a prognosticator of health status because of their association with disease states and malnutrition. Although studies consistently show the effect of physical characteristics on bioelectrical impedance, few investigations describe the effect of race, particularly for Black adults, and many bioelectrical impedance standards were produced from primarily White adults almost 2 decades ago. Therefore, this study sought to evaluate the racial differences in bioelectrical impedance measurements using bioimpedance spectroscopy between non-Hispanic White and non-Hispanic Black adults matched for age, sex, and body mass index. We hypothesized that Black adults would have a lower phase angle from higher resistance and lower reactance compared with White adults. One hundred non-Hispanic White (n = 50) and non-Hispanic Black (n = 50) males (n = 34) and females (n = 66) matched for sex, age, and body mass index completed this cross-sectional study. Participants underwent several anthropometric assessments, including height, weight, waist circumference, hip circumference, bioimpedance spectroscopy, and dual-energy X-ray absorptiometry. Bioelectrical impedance measures of resistance, reactance, phase angle, and impedance were all collected at frequencies of 5, 50, and 250 kHz and bioelectrical impedance vector analysis was performed using 50-kHz data. There were no significant differences for any anthropometric variable between Black and White participants in the total sample or by sex groups. In addition, there were no significant racial differences for any bioelectrical impedance assessment, including bioelectrical impedance vector analysis. Differences in bioelectrical impedance are likely not a function of race between Black and White adults and concerns regarding its utility should not be based on this characteristic.

Nutritional Status of Coronary Artery Disease Patients-Preliminary Results

INTRODUCTION

Malnutrition is a condition that negatively impacts the clinical outcomes of numerous diseases. The aim of this study was to assess the nutritional status of coronary artery disease (CAD) patients and to investigate its relationship with the main clinical aspects of CAD.

MATERIAL AND METHODS

50 CAD patients undergoing coronary angiography were enrolled in this study. The nutritional status assessment was based on Nutritional Risk Score 2002 (NRS 2002), body mass index (BMI), and bioelectrical impedance analysis (BIA) measurements.

RESULTS

The analysis showed a moderate inverse correlation between NRS 2002 and BIA phase angle measured at 50 kHz (R: -0.31; p = 0.03) and Z200/5 parameter (R: 0.34; p = 0.02). The analysis of CAD clinical parameters showed a significant correlation between NRS 2002 and Canadian Cardiovascular Society (CCS) class (R: 0.37; p = 0.01). Left ventricle ejection fraction (LVEF) was correlated with BMI (R: 0.38; p = 0.02), however further BIA revealed hydration changes as LVEF was correlated to intracellular (ICF) and extracellular fluid (ECF) proportion: positively with ICF (R: 0.38; p = 0.02) and negatively with ECF (R: -0.39; p = 0.02).

CONCLUSIONS

NRS 2002 and BIA are valuable tools for nutritional status assessment in CAD patients. Malnutrition is related to the severity of CAD symptoms, particularly in women. Maintaining proper nutritional status can have a potentially important role in this group of patients.

Phase Angle as a Potential Screening Tool in Adults with Metabolic Diseases in Clinical Practice: A Systematic Review

BACKGROUND

Phase angle (PhA) has been used as mortality prognostic, but there are no studies about its possible use as a screening tool. Therefore, an assessment of the possible utility of PhA in clinical practice is required. The aim of this systematic review was to explore all recent available evidence of PhA, and its possible utility as a screening tool in clinical practice in subjects with chronic metabolic diseases.

MATERIALS AND METHODS

This systematic review was performed and written as stated in the PRISMA 2020 guidelines. The search was conducted in PubMed, ScienceDirect and SciElo. In order to be considered eligible, within the entire search, only articles involving PhA and their utility in metabolic diseases were included.

RESULTS

PhA was associated with hyperuricemia and vitamin D deficiency in obese subjects, and decreased cardiovascular risk and malnutrition in hospitalized patients.

CONCLUSION

PhA may be a potential screening tool in clinical practice to evaluate different biomarkers, cardiovascular risk, and nutritional diagnosis in metabolic diseases in adults.

Prognostic value of combined preoperative phase angle and handgrip strength in cardiac surgery

OBJECTIVES

Phase angle (PA) constitutes a bioelectrical impedance measurement, indicating cell membrane health and integrity, hydration, and nutritional status. Handgrip strength (HS) has been also associated with body composition, nutritional status, inflammation, and functional ability in several chronic diseases. Although their prognostic significance as independent biomarkers has been already investigated regarding the outcomes of a cardiac surgery, our study is the first one to assess the combined predictive value of preoperative PA and HS.

DESIGN AND METHODS

HS and PA measurements were performed preoperativelyin 195 patients undergoing cardiac surgery. The association ofthe combination of HS and PAwith all-cause mortality rates was the primary study outcome, while its association with the intensive care unit (ICU) length of stay (LOS) was the secondary one.

RESULTS

PA was positively correlated with HS (r = 0.446, p < 0.005) and negatively with EuroSCORE II (r = - 0.306 p < 0.005). The combination of PA < 5.15 and HS < 25.5 was associated with higher one-year all-cause mortality (OR = 9.28; 95% CI 2.50-34.45; p = 0.001) compared to patients with PA > 5.15 and HS > 25.5, respectively. Patients with combined lower values of PA and HS (PA < 5.15 and HS < 30.7) were at higher risk of prolonged ICU LOS (OR = 4.02; 95% CI 1.53-10.56; p = 0.005) compared to those with higher PA-HS (PA > 5.15-HS > 30.7). The combination of PA-HS was also significantly linked with EuroSCORE II.

CONCLUSION

The combination of low preoperative PA and HS values was significantly associated with higher risk of all-cause mortality at 12 months and prolonged ICU LOS; thereby it might serve as a clinically useful prognostic biomarker after cardiac surgery procedures.

Brazilian Reference Percentiles for Bioimpedance Phase Angle of Healthy Individuals

Objectives

The present study was designed to estimate phase angle percentile curves for a broad age range of healthy individuals.

Methods

This is a cross-sectional study of healthy Brazilian individuals aged five to 80. InBodyS10 was used to assess phase angle. Reference curves were stratified by sex and estimated using Generalized additive models for location, scale, and shape as a continuous function of age. The phase angle determinants analyzed were physical activity, age, BMI, and SES variables.

Results

Data were analyzed from 2,146 individuals, 1,189 (55.2%) of whom were female. In both sexes, the phase angles showed a similar pattern (an increasing trend from childhood to the teenage phase, followed by stabilization during adult ages and a decrease in old adults). In female, the relationship between phase angle and age were associated with BMI and family income. In the male, the relationship between phase angle and age were associated with skin color and family income.

Conclusions

To the best of our knowledge, it is the first attempt to apply the GAMLSS technique to estimate phase angle percentiles in a healthy population covering most of the life cycle. We also showed that there are different phase angle determinants according to sex.

Proteomics of the phase angle: Results from the population-based KORA S4 study

BACKGROUND & AIMS

The phase angle (PhA) measured with bioelectrical impedance analysis is considered to reflect the interrelated components body cell mass and fluid distribution based on technical and physical aspects of the PhA measurement. However, the biomedical meaning of the PhA remains vague. Previous studies mainly assessed associations of the PhA with numerous diseases and health outcomes, but few connected protein markers to the PhA. To broaden our understanding of the biomedical background of the PhA, we aimed to explore a proteomics profile associated with the PhA and related biological factors.

METHODS

The study sample encompassed 1484 participants (725 women and 759 men) aged 55-74 years from the population-based Cooperative Health Research in the Region of Augsburg (KORA) S4 study. Proteomics measurements were performed with a proximity extension assay. We employed boosting with stability selection to establish a set of markers that was strongly associated with the PhA from a group of 233 plasma protein markers. We integrated the selected protein markers into a network and enrichment analysis to identify gene ontology (GO) terms significantly overrepresented for the selected PhA protein markers.

RESULTS

Boosting with stability selection identified seven protein markers that were strongly and independently associated with the PhA: N-terminal prohormone brain natriuretic peptide (NT-proBNP), insulin-like growth factor-binding protein 2 (IGFBP2), adrenomedullin (ADM), myoglobin (MB), matrix metalloproteinase-9 (MMP9), protein-glutamine gamma-glutamyltransferase 2 (TGM2), and fractalkine (CX3CL1) [beta coefficient per 1 standard deviation increase in normalized protein expression values on a log 2 scale (95% confidence interval): -0.12 (-0.15, -0.08), -0.13 (-0.17, -0.09), -0.14 (-0.18, -0.10), 0.10 (0.07, 0.14), 0.07 (0.04, 0.10), 0.08 (0.05, 0.11), -0.06 (-0.10, -0.03), respectively]. According to the enrichment analysis, this protein profile was significantly overrepresented in the following top five GO terms: positive regulation of cell population proliferation (p-value: 1.32E-04), extracellular space (p-value: 1.34E-04), anatomical structure formation involved in morphogenesis (p-value: 2.92E-04), regulation of multicellular organismal development (p-value: 5.72E-04), and metal ion homeostasis (p-value: 8.86E-04).

CONCLUSION

Implementing a proteomics approach, we identified six new protein markers strongly associated with the PhA and confirmed that NT-proBNP is a key PhA marker. The main biological processes that were related to this PhA's protein profile are involved in regulating the amount and growth of cells, reinforcing, from a biomedical perspective, the current technical-based consensus of the PhA to reflect body cell mass.

Preoperative Phase Angle as a Risk Indicator in Cardiac Surgery-A Prospective Observational Study

Background: The phase angle (PhA) can be used for prognostic assessments in critically ill patients. This study describes the perioperative course of PhA and associated risk indicators in a cohort of elective cardiac surgical patients. Methods: The PhA was measured in 168 patients once daily until postoperative day (POD) seven. Patients were split into two groups depending on their median preoperative PhA and analyzed for several clinical outcomes; logistic regression models were used. Results: The PhA decreased from preoperative (6.1° ± 1.9°) to a nadir on POD 2 (3.5° ± 2.5°, mean difference −2.6° (95% CI, −3.0°; −2.1°; p < 0.0001)). Patients with lower preoperative PhA were older (71.0 ± 9.1 vs. 60.9 ± 12.0 years; p < 0.0001) and frailer (3.1 ± 1.3 vs. 2.3 ± 1.1; p < 0.0001), needed more fluids (8388 ± 3168 vs. 7417 ± 2459 mL, p = 0.0287), and stayed longer in the ICU (3.7 ± 4.5 vs. 2.6 ± 3.8 days, p = 0.0182). Preoperative PhA was independently influenced by frailty (OR 0.77; 95% CI 0.61; 0.98; p = 0.0344) and cardiac function (OR 1.85; 95%CI 1.07; 3.19; p = 0.028), whereas the postoperative PhA decline was independently influenced by higher fluid balances (OR 0.86; 95% CI 0.75; 0.99; p = 0.0371) and longer cardiopulmonary bypass times (OR 0.99; 95% CI 0.98; 0.99; p = 0.0344). Conclusion: Perioperative PhA measurement is an easy-to-use bedside method that may critically influence risk evaluation for the outcome of cardiac surgery patients.

Cardiovascular Diseases Diagnosis by Impedance Cardiography

Cardiovascular disease (CVD) represents the leading cause of mortality worldwide. In order to diagnose CVDs, there are a range of detection methods, among them, the impedance cardiography technique (ICG). It is a non-invasive and low-cost method. In this paper, we highlight recent advances and developments of the CDVs diagnosis mainly by the ICG method. We considered papers published during the last five years (from 2017 until 2022). Based on this study, we expressed the need for an ICG database for the different CDVs.