Impedance cardiography revisited

Continuous non-invasive measurement of cardiac output in neonatal intensive care using regional impedance cardiography: a prospective observational study

OBJECTIVES

To compare agreement between echocardiography and regional impedance cardiography (RIC)-derived cardiac output (CO), and to construct indicative normative ranges of CO for gestational age groups.

DESIGN, SETTING AND PARTICIPANTS

Prospective cohort observational study performed in a tertiary centre in London, UK, including neonates born between 25 and 42 weeks' gestational age.

EXPOSURES

Neonates on the postnatal ward had 2 hours of RIC monitoring; neonates in intensive care had RIC monitoring for the first 72 hours, then weekly for 2 hours, with concomitant echocardiography measures.

MAIN OUTCOMES AND MEASURES

RIC was used to measure CO continuously. Statistical analyses were performed using R (V.4.2.2; R Core Team 2022). RIC-derived CO and echocardiography-derived CO were compared using Pearson's correlations and Bland-Altman analyses. Differences in RIC-derived CO between infants born extremely, very and late preterm were assessed using analyses of variance and mixed-effects modelling.

RESULTS

127 neonates (22 extremely, 46 very, 29 late preterm and 30 term) were included. RIC and echocardiography-measured weight-adjusted CO were correlated (r=0.62, p<0.001) with a Bland-Altman bias of -31 mL/min/kg (limits of agreement -322 to 261 mL/min/kg). The RIC-derived CO fell over 12 hours, then increased until 72 hours after birth. The 72-hour weight-adjusted mean CO was higher in extremely preterm (424±158 mL/min/kg) compared with very (325±131 mL/min/kg, p<0.001) and late preterm (237±81 mL/min/kg, p<0.001) neonates; this difference disappeared by 2-3 weeks of age.

CONCLUSIONS

RIC is valid for continuous, non-invasive CO measurement in neonates. Indicative normative CO ranges could help clinicians to make more informed haemodynamic management decisions, which should be explored in future studies.

TRIAL REGISTRATION NUMBER

NCT04064177.

Comparing elective and emergency caesarean section by using bioimpedance method

BACKGROUND

There are limited studies focusing on hemodynamic changes between elective and emergent C/S cases. We considered that a better understanding of the alterations and physiological reactions in both situations with non-invasive novel technologies might be useful in managing maternal and fetal sides.

METHODS

In this prospective observational study, non-invasive hemodynamic changes were observed by using the whole-body impedance method using the NICaS™ device. CO, cardiac index (CI), stroke volume (SV), stroke index (SI), total peripheric resistance (TPR), and cardiac reserve (GGI) parameters were evaluated with a non-invasive method. Measurements were done initiating before surgery, 9 times of 5 min intervals.

RESULTS

All 95 patients finished the study. 47 cesarean sections were in the elective group, 48 were in the emergent group. SV in 4.5.6. time intervals were statistically increased in the elective group (p values: SvMl4: 0.025, SvMl5: 0.049, SvMl6: 0.044) (p < 0.05). SI in the second-time interval was statistically increased in the emergent group (p-value SI2: 0.047) (p < 0.05). SI in the 4th time interval was statistically increased in the elective group (p-value SI4: 0.047) (p < 0.05). CO measurements were not statistically different between groups in all time intervals for all comparisons. CI in the second time interval was statistically decreased in the elective group (p-value CI2: 0.012) (p < 0.05). GGI in the 4th time interval was statistically increased in the elective group (p-value GGI4: 0.035) (p < 0.05). TPRI in the second time interval was statistically increased in the elective group (p-value TPRI 2: 0.014) (p < 0.05).

CONCLUSIONS

Understanding normal hemodynamic values before, during, and after C/S is feasible and might help the clinician assess patients' cardiac performance with a reliable noninvasive technique. NICaS might be a reliable tool to evaluate patients' baseline values and diagnose complications earlier during the surgery.

Noninvasive Hemodynamic Evaluation Following TAVI for Severe Aortic Stenosis

Background Various hemodynamic changes occur following transcatheter aortic valve implantation (TAVI) that may impact therapeutic decisions. NICaS is a noninvasive bioimpedance monitoring system aimed at hemodynamic assessment. We used the NICaS system in patients with severe aortic stenosis (AS) to evaluate short-term hemodynamic changes after TAVI. Methods and Results We performed hemodynamic analysis using NICaS on 97 patients with severe AS who underwent TAVI using either self-expandable (68%) or balloon-expandable (32%) valves. Patients were more often women (54%) and had multiple comorbidities including hypertension (83%), coronary artery disease (46%), and diabetes (37%). NICaS was performed at several time points-before TAVI, soon after TAVI, at hospital discharge, and during follow-up. Compared with baseline NICaS measurements, we observed a significant increase in systolic blood pressure and total peripheral resistance (systolic blood pressure 132±21 mm Hg at baseline versus 147±23 mm Hg after TAVI, P<0.001; total peripheral resistance 1751±512 versus 2084±762 dynes*s/cm⁵, respectively, P<0.001) concurrent with a decrease in cardiac output and stroke volume (cardiac output 4.2±1.5 versus 3.9±1.3 L/min, P=0.037; stroke volume 61.4±14.8 versus 56.2±15.9 mL, P=0.001) in the immediate post-TAVI period. At follow-up (median 59 days [interquartile range, 40.5-91]) these measurements returned to values that were not different from the baseline. A significant improvement in echocardiography-based left ventricular ejection fraction was observed from baseline to follow-up (55.6%±11.6% to 59.4%±9.4%, P<0.001). Conclusions Unique short-term adaptive hemodynamic changes were observed using NICaS in patients with AS soon after TAVI. Noninvasive hemodynamic evaluation immediately following TAVI may contribute to the understanding of complex hemodynamic changes and merits favorable consideration.

A fresh look at sports PSM-systems

The aim of the proposed study is to reveal the correlations between the dynamics of Respiratory Rate (RR) and Heart Rate (HR) during intermittent physical work at maximum power on a cycle ergometer. The stage of investigating the General functional athlete readiness (GFAR) was conducted using the sports standard "R-Engine" and the cycle ergometer in 16 volunteers (10 men, 6 women) whose average age was 21±1.17 years. To determine the athletic potential of the volunteers in this study, we used our own Coefficient of Anaerobic Capacity (CANAC Q, beats). Continuous registration of the heart rate and respiratory rate of volunteers in the maximum power sports test was performed by the "RheoCardioMonitor" system with a module of the athlete functional readiness based on the method of Transthoracic electrical impedance rheography (TEIRG). The degree of correlation of functional indicators (M, HRM, GFAR) with CANAC Q in all experimental series of the study group as a whole (n=80) was at a very high level, which confirmed the effectiveness of using the Coefficient of Anaerobic Capacity (CANAC Q) in assessing the general functional athlete readiness of the volunteers. CANAC Q is measured in "beats" of the heart and is recorded very accurately using the method of transthoracic electrical impedance rheography (TEIRG). For this reason, as a promising sports PSM-system, CANAC Q can replace the methods for determining the functional athlete readiness by blood lactate concentration and maximum oxygen consumption.

Comparative study of cardiac output measurement by regional impedance cardiography and thermodilution method in patients undergoing off pump coronary artery bypass graft surgery

Background:

An ideal CO monitor should be noninvasive, cost effective, reproducible, reliable during various physiological states. Limited literature is available regarding the noninvasive CO monitoring in open chest surgeries.

Aim:

The aim of this study was to compare the CO measurement by Regional Impedance Cardiography (RIC) and Thermodilution (TD) method in patients undergoing off pump coronary artery bypass graft surgery (OPCAB).

Settings and Design:

We conducted a prospective observational comparative study of CO measurement by the noninvasive RIC method using the NICaS Hemodynamic Navigator system and the gold standard TD method using pulmonary artery catheter in patients undergoing OPCAB. A total of 150 data pair from the two CO monitoring techniques were taken from 15 patients between 40-70 years at various predefined time intervals of the surgery.

Patients and Methods:

We have tried to find out the accuracy, precision and cost effectiveness of the newer RIC technique. Mean CO, bias and precision were compared for each pair i.e.TD-CO and RIC-CO as recommended by Bland and Altman. The Sensitivity and specificity of cutoff value to predict change in TD-CO was used to create a Receiver operating characteristic or ROC curve.

Results:

Mean TD-CO values were around 4.52 ± 1.09 L/min, while mean RIC- CO values were around 4.77± 1.84 L/min. The difference in CO change was found to be statistically not significant (p value 0.667). The bias was small (-0.25). The Bland Altman plot revealed a mean difference of -0.25 litres. The RIC method had a sensitivity of 55.56 % and specificity of 33.33 % in predicting 15% change in CO of TD method and the total diagnostic accuracy was 46.67%.

Conclusion:

A fair correlation was found between the two techniques. The RIC method may be considered as a promising noninvasive, potentially low cost alternative to the TD technique of hemodynamic measurement.

Cross-Entropy Learning for Aortic Pathology Classification of Artificial Multi-Sensor Impedance Cardiography Signals

An aortic dissection, a particular aortic pathology, occurs when blood pushes through a tear between the layers of the aorta and forms a so-called false lumen. Aortic dissection has a low incidence compared to other diseases, but a relatively high mortality that increases with disease progression. An early identification and treatment increases patients’ chances of survival. State-of-the-art medical imaging techniques have several disadvantages; therefore, we propose the detection of aortic dissections through their signatures in impedance cardiography signals. These signatures arise due to pathological blood flow characteristics and a blood conductivity that strongly depends on the flow field, i.e., the proposed method is, in principle, applicable to any aortic pathology that changes the blood flow characteristics. For the signal classification, we trained a convolutional neural network (CNN) with artificial impedance cardiography data based on a simulation model for a healthy virtual patient and a virtual patient with an aortic dissection. The network architecture was tailored to a multi-sensor, multi-channel time-series classification with a categorical cross-entropy loss function as the training objective. The trained network typically yielded a specificity of (93.9±0.1)% and a sensitivity of (97.5±0.1)%. A study of the accuracy as a function of the size of an aortic dissection yielded better results for a small false lumen with larger noise, which emphasizes the question of the feasibility of detecting aortic dissections in an early state.

Exposure to acute normobaric hypoxia results in adaptions of both the macro- and microcirculatory system

Although acute hypoxia is of utmost pathophysiologic relevance in health and disease, studies on its effects on both the macro- and microcirculation are scarce. Herein, we provide a comprehensive analysis of the effects of acute normobaric hypoxia on human macro- and microcirculation. 20 healthy participants were enrolled in this study. Hypoxia was induced in a normobaric hypoxia chamber by decreasing the partial pressure of oxygen in inhaled air stepwisely (pO₂; 21.25 kPa (0 k), 16.42 kPa (2 k), 12.63 kPa (4 k) and 9.64 kPa (6 k)). Macrocirculatory effects were assessed by cardiac output measurements, microcirculatory changes were investigated by sidestream dark-field imaging in the sublingual capillary bed and videocapillaroscopy at the nailfold. Exposure to hypoxia resulted in a decrease of systemic vascular resistance (p < 0.0001) and diastolic blood pressure (p = 0.014). Concomitantly, we observed an increase in heart rate (p < 0.0001) and an increase of cardiac output (p < 0.0001). In the sublingual microcirculation, exposure to hypoxia resulted in an increase of total vessel density, proportion of perfused vessels and perfused vessel density. Furthermore, we observed an increase in peripheral capillary density. Exposure to acute hypoxia results in vasodilatation of resistance arteries, as well as recruitment of microvessels of the central and peripheral microcirculation. The observed macro- and microcirculatory effects are most likely a result from compensatory mechanisms to ensure adequate tissue oxygenation.

Cardiac Function and Hemodynamic Changes during Minimally Invasive Hysterectomy with Pneumoperitoneum and Steep Trendelenburg Position for Patients with Endometrial Cancer Who Are Obese

STUDY OBJECTIVE

To assess the effect of carbon dioxide (CO₂) pneumoperitoneum and steep Trendelenburg position on patients' cardiac function and hemodynamics during minimally invasive staging surgery for endometrial cancer.

DESIGN

Single-center prospective longitudinal study.

SETTING

University-affiliated tertiary hospital.

PATIENTS

Patients with endometrial cancer undergoing minimally invasive surgery.

INTERVENTIONS

After consent, the patients' hemodynamic parameters were assessed by the Non-Invasive Cardiac System (NI Medical, Petah Tikva, Israel) at 5 time points: before general anesthesia, after induction of general anesthesia, after CO₂ insufflation of the peritoneum, after steep Trendelenburg position, and at the end of surgery.

MEASUREMENTS AND MAIN RESULTS

Twenty-three women were recruited. The median age of the patients was 68 years (interquartile range [IQR] 62-75), with a median body mass index of 34.9 kg/m² (IQR 31.2-39.5) and an American Society of Anesthesiologists score ≥2. The initial median mean arterial pressure was 108 mmHg (IQR 101-113), and the baseline median cardiac output was 7.2 L/min (IQR 5.6-8.7). The median mean arterial pressure significantly decreased by 18% after insufflation (p = .001), again after Trendelenburg position (p = .003), and did not fully recover at the end of surgery in comparison with the preanesthesia baseline (p = .001). The median stroke volume significantly decreased by 17% after insufflation compared with the baseline (p = .01) and then gradually recovered to the baseline levels by the end of surgery. The median cardiac power significantly decreased by 35% after insufflation (0.009), remained low during Trendelenburg position (p = .009), and recovered by the end of surgery to 18% below the baseline levels (p = .035).

CONCLUSION

Significant hemodynamic changes occur during minimally invasive staging surgery for endometrial cancer. CO₂ insufflation is accompanied by the most dramatic hemodynamic deterioration during surgery, and this does not get affected much with Trendelenburg. Knowledge of the hemodynamic values of women classified as high risk when using a noninvasive technique during surgery is obtainable and may assist both surgeon and anesthesiologist to ensure a safer procedure.

The repeatability of estimated systolic time intervals in healthy subjects using seismocardiogram and electrocardiogram

OBJECTIVE

We investigated the repeatability of systolic time intervals (STIs) in healthy subjects using a combination of seismocardiogram (SCG) and electrocardiogram (ECG). STIs have been extensively used in the past to quantify heart performance, particularly the left ventricle. In this study, STIs included pre-ejection period (PEP), left ventricular ejection time (LVET), and their ratio.

APPROACH

We conducted the repeatability test of STI estimation through two experiments. The first involved three consecutive one-minute recordings separated by one-minute intervals, and the second involved two one-minute recordings separated by 24 h. Twenty healthy subjects participated in our study. We considered the coefficient of variation (CV) to quantify the repeatability. As there was no agreed upon values for optimal CV values, we compared our results with an alternative method using a combination of impedance cardiography (ICG) and ECG. Similar to our method, the alternative method was noninvasive and could be employed for personal heart monitoring. We also studied the repeatability after STIs were corrected for heart rate using two approaches. The first approach used a multiplicative factor per subject based on the heart rates in each recordings of that subject. The second approach employed sex-specific regression models for all subjects (Weissler's equations).

MAIN RESULTS

We found that the repeatability of our method (SCG and ECG) was in agreement with the alternative method (ICG and ECG) in both experiments. Moreover, the Weissler's equations approach for heart rate increased the repeatability.

SIGNIFICANCE

It can be concluded that estimation of PEP, LVET and their ratio through SCG and ECG signals was repeatable in healthy subjects.

Hemodynamic response to fluid removal during hemodialysis: categorization of causes of intradialytic hypotension

Background

Intradialytic hypotension is a clinically significant problem, however, the hemodynamics that underlie ultrafiltration and consequent hypotensive episodes has not been studied comprehensively.

Methods

Intradialytic cardiac output, cardiac power and peripheral resistance changes from pretreatment measurements were evaluated using a novel regional impedance cardiographic device (NICaS, NI Medical, Peta Tikva, Israel) in 263 hemodialysis sessions in 54 patients in dialysis units in the USA and Brazil with the goal of determining the various hemodynamic trends as blood pressure decreases.

Results

Hypotensive episodes occurred in 99 (13.5%) of 736 intra- and postdialytic evaluations. The hemodynamic profiles of the episodes were categorized: (i) The cardiac power index significantly decreased in 35% of episodes by 36%, from 0.66 [95% confidence interval (CI) 0.60-0.72] to 0.43 (95% CI 0.37-0.48) [w/m2] with a small reduction in the total peripheral resistance index. (ii) The total peripheral resistance index significantly decreased in 37.4% of episodes by 33%, from 3342 (95% CI 2824-3859) to 2251 (95% CI 1900-2602) [dyn × s/cm5 × m2] with a small reduction in the cardiac power index. (iii) Both the cardiac power index and total peripheral resistance index significantly decreased in 27.3% of episodes, the cardiac power index by 25% from 0.63 (95% CI 0.57-0.70) to 0.48 (95% CI 0.42-0.53) [w/m2] and the total peripheral resistance index by 23% from 2964 (95% CI 2428-3501) to 2266 (95% CI 1891-2642).

Conclusions

The hemodynamic profiles clearly define specific hemodynamic mechanisms of cardiac power reduction and/or vasodilatation as underlying intradialytic hypotensive episodes. A reduction in cardiac power (reduction of both blood pressure and cardiac output) could be the result of preload reduction due to a high ultrafiltration rate with not enough refilling or low target weight. A reduction in peripheral resistance (reduction in blood pressure and increase in cardiac output) could be the result of relative vasodilatation as arteries do not contract to compensate for volume reduction due to autonomous dysfunction. As both phenomena are independent, they may appear at the same time. Based on these results, a reduction of ultrafiltration rate and an increase in target weight to improve preload or immediate therapeutic actions to increase peripheral resistance are rational measures that could be taken to maintain blood pressure and prevent hypotensive ischemic complications in dialysis patients.

The value of non-invasive measurement of cardiac output and total peripheral resistance to categorize significant changes of intradialytic blood pressure: a prospective study

Background

Blood pressure (BP) is currently the main hemodynamic parameter used to assess the influence of fluid removal during hemodialysis session. Since BP is dependent on cardiac output (CO) and total peripheral resistance (TPRI), investigating these parameters may help to better understand the influence of fluid removal on patient’s hemodynamics. We used a novel non-invasive whole-body bio-impedance cardiography device, recently validated in hemodialysis patients, to examine mechanisms of intradialytic hemodynamics in a Chinese dialysis population.

Methods

Chronic hemodialysis patients in Sichuan Provincial People’s Hospital were enrolled. Demographic data and dialysis prescriptions were collected. Hemodynamic measurements were made pre-treatment, every 20 min during treatment and immediately after treatment in each random dialysis session. These included blood pressure, cardiac index (CI), total peripheral resistance (TPRI) and cardiac power index (CPI). Patients were divided into 5 hemodynamic groups as per their major hemodynamic response to fluid removal: low CPI, low TPRI, high TPRI, High CPI and those with normal hemodynamics.

Results

Twenty-seven patients were enrolled, with 12 (44.4%) males. The average age was 65 ± 12 y. The average body mass index (BMI) was 23.7 ± 3.9 kg/m2. 12 (44.4%) patients were diabetic. Three hundred twenty-four hemodynamic measurements were made. Weight, BMI, total fluid removal, pretreatment systolic BP, CI, TPRI and CI differed significantly among the 5 hemodynamic groups.11.1% of patients had low CPI, 25.9% had low TPRI, 18.5% had high CPI, 3.7% had high TPRI and 40.7% had normal hemodynamics. Hemodynamic differences among the 5 subgroups were significant.

Conclusion

This technology provides multi-dimensional insight into intradialytic hemodynamic parameters, which may be more informative than blood pressure only. Using hemodynamic parameters to describe patients’ status is more specific and accurate, and could help to work out specific and effective therapeutic actions according to underlying abnormalities.

Maternal cardiovascular hemodynamics in normotensive versus preeclamptic pregnancies: a prospective longitudinal study using a noninvasive cardiac system (NICaS™)

BACKGROUND

Preeclampsia is among the most common medical complications of pregnancy. The clinical utility of invasive hemodynamic monitoring in preeclampsia (e.g., Swan-Ganz catheter) is controversial. Thoracic impedance cardiography (TIC) and Doppler echocardiography are noninvasive techniques but they both have important limitations. NICaS™ (NI Medical, PetachTikva, Israel) is a noninvasive cardiac system for determining cardiac output (CO) that utilizes regional impedance cardiography (RIC) by noninvasively measuring the impedance signal in the periphery. It outperformed any other impedance cardiographic technology and was twice as accurate as TIC.

METHODS

We used the NICaS™ system to compare the hemodynamic parameters of women with severe preeclampsia (PET group, n = 17) to a cohort of healthy normotensive pregnant women with a singleton pregnancy at term (control group, n = 62) (1/2015-6/2015). Heart rate (HR), stroke volume (SV), CO, total peripheral resistance (TPR) and mean arterial pressure (MAP) were measured 15-30 min before CS initiation, immediately after administering spinal anesthesia, immediately after delivery of the fetus and placenta, at the abdominal fascia closure and within 24-36 and 48-72 h postpartum.

RESULTS

The COs before and during the CS were significantly higher in the control group compared to the PET group (P < .05), but reached equivalent values within 24-36 h postpartum. CO peaked at delivery of the newborn and the placenta and started to decline afterwards in both groups. The MAP and TPR values were significantly higher in the PET group at all points of assessment except at 48-72 h postpartum when it was still significantly higher for MAP while the TPR only exhibited a higher trend but not statistically significant. The NICaS™ device noninvasively demonstrated low CO and high TPR profiles in the PET group compared to controls.

CONCLUSIONS

The immediate postpartum period is accompanied by the most dramatic hemodynamic changes and fluid shifts, during which the parturient should be closely monitored. The NICaS™ device may help the clinician to customize the most optimal management for individual parturients. Our findings require validation by further studies on larger samples.

Systematic Variability in ICG Recordings Results in ICG Complex Subtypes - Steps Towards the Enhancement of ICG Characterization

The quality of an impedance cardiography (ICG) signal critically impacts the calculation of hemodynamic parameters. These calculations depend solely on the identification of ICG characteristic points on the ABEXYOZ complex. Unfortunately, contrary to the relatively constant morphology of the PQRST complex in electrocardiography, the waveform morphology of ICG data is far from stationary, which causes difficulties in the accuracy of the automated detection of characteristic ICG points. This study evaluated ICG recordings obtained from 10 volunteers. The results indicate that there are several different waveforms for the ABEXYOZ complex; there are up to five clearly distinct waveforms for the ABEXYOZ complex in addition to those that are typically reported. The differences between waveform types increased the difficulty of detecting ICG points. To accurately detect all ICG points, the ABEXYOZ complex should be analyzed according to the corresponding waveform type.

Maternal hemodynamics in late gestation and immediate postpartum in singletons vs. twin pregnancies

PURPOSE

Differences in hemodynamic changes during a cesarean section (CS) between twin and singleton pregnancies are poorly defined. The Non-Invasive Cardiac System (NICaS) is an impedance device that measures cardiac output (CO) and its derivatives. We compared maternal cardiac parameters using NICaS™ in singleton and twins before and during delivery, as well at the early puerperium in healthy women undergoing CS at term.

METHODS

This prospective longitudinal study included women with twin (n = 27) or singleton pregnancies (n = 62) whose hemodynamic parameters were assessed by NICaS before an elective CS, after spinal anesthesia, immediately after delivery, after fascia closure, and within 24-36 and 48-72 h postpartum.

RESULTS

By 24-36 h postpartum, the mean arterial pressure and the total peripheral resistance equaled preoperative values in both groups. The CO increased throughout the CS and peaked immediately after delivery in the singleton group (P < 0.0001), after which it abruptly began to decline until reaching a nadir 24-36 h after delivery (P < 0.0001), while it remained steady throughout the CS and then dropped until 24-36 h after delivery in the twin group (P < 0.05). None of the studied parameters differed significantly between the groups for the 24-36 and 48-72 h postpartum measurements.

CONCLUSIONS

Hemodynamic parameters immediately before, during and shortly after CS in singleton and twin pregnancies are equivalent. Further evaluations of the value of NICaS™ in assessing cardiovascular-related pregnancy complications are warranted.

Comparison of stroke volume measurements during hemodialysis using bioimpedance cardiography and echocardiography

BACKGROUND

Fluid management remains a major challenge of hemodialysis (HD) care, with serious implications for morbidity and mortality. Intradialytic fluid management is typically guided by blood pressure, an indirect resultant of hemodynamics status. Direct measurements of hemodynamic parameters may improve cardiovascular outcomes by providing rational bases for intervention. We compare stroke volume (SV) measurements using a noninvasive, regional biompedance cardiography device (NiCaS) with Doppler echocardiography (Echo) in HD setting.

METHODS

Stroke volumes were simultaneously measured using the devices in 17 patients receiving maintenance HD. Measurements were made during 2 weekly HD treatments, and twice within each HD treatment during the first and last hour of each treatment, for a total of 64 SV measurements. Agreement between devices was assessed using linear regression, a Pearson's correlation coefficient, and a Bland-Altman plot all adjusted for repeated measures within patients.

RESULTS

Echo and NiCaS SV mean and 95% CIs were 58.0 (50.1, 65.8) and 56.7 (49.4, 64.0) mL, respectively. NiCaS SV correlated strongly with Echo SV during the first and last hours of treatments (r = 0.93, P < 0.001 and r = 0.92, P < 0.001, respectively). Linear regression of NiCaS on Echo showed a slope of 0.97, 95% CI (0.91, 1.02) which did not differ from 1, P = 0.20. A Bland-Altman plot and 4-Quadrant plot confirmed that the 2 methods produced comparable measurements.

CONCLUSION

NiCaS SV measurements are similar to and strongly correlated with Echo SV measurements. This suggests that noninvasive NiCaS technology may be a practical method for measuring SV during HD.

Cardiac hemodynamics before, during and after elective cesarean section under spinal anesthesia in low-risk women

OBJECTIVE

The aim of this study was to describe maternal central hemodynamic parameters before and during delivery as well at the early puerperium in healthy women undergoing elective cesarean section (CS) at term.

STUDY DESIGN

The noninvasive Cardiac System (NICaS, NI Medical, Petah-Tikva, Israel) is a regional impedance device that measures cardiac output (CO) and its derivatives with a good correlation with the gold standard Swan-Ganz catheter. We performed a prospective longitudinal study of healthy women with a singleton pregnancy at term. Maternal hemodynamic parameters were assessed by the NICaS at six time points: a few minutes before undergoing an elective CS, immediately after receiving spinal anesthesia, immediately after delivery of the fetus and placenta, after abdominal fascia closure, and within 24 to 36 and 48 to 72 h postpartum.

RESULT

Sixty-one consenting women were recruited during the study period (January 2015 to June 2015). Baseline (pre-CS) mean arterial pressure (MAP) was 87.7±7.9 mm Hg, baseline CO was 7.5±1.7 l per min and baseline total peripheral resistance (TPR) was 994±301 dyne × s per cm⁵. After spinal anesthesia CO significantly increased by 13%, no significant changes were observed in MAP or TPR. Immediately after delivery, a nadir for all parameters was reached: MAP and TPR were significantly reduced by 8% and 26%, respectively (comparing to pre-CS), and CO further increased by 9% (24% comparing to pre-CS). After fascia closure, partial recoveries of all parameters were observed. Twenty-four to thirty-six hours postpartum MAP returned to pre-CS values, while CO and TPR reached -9% and +11% comparing to baseline, respectively. None of the parameters differed significantly between 24 to 36 and 48 to 72 h postpartum.

CONCLUSION

Significant hemodynamic changes (reduction of TPR and increase of CO) take place at the time of delivery of fetus and placenta. Knowledge of normal hemodynamic values using a reliable noninvasive technique during various stages of pregnancy and the postpartum period is feasible, and might assist clinicians in assessing the level of patient deviation from expected cardiac performance, especially in high-risk women.

Influence of electrode positioning on accuracy and reproducibility of electrical velocimetry cardiac output measurements

Electrical velocimetry (EV) is one of the most recent adaptions of impedance cardiography. Previous studies yielded diverging results identifying several factors negatively influencing accuracy. Although electrode arrangement is suspected to be an influencing factor for impedance cardiography in general, no data for EV is available. We aimed to prospectively assess the influence of electrode position on the accuracy and reproducibility of cardiac output (CO) measurements obtained by EV. Two pairs of standard electrocardiographic electrodes were placed at predefined positions of the thorax in 81 patients. The inter-electrode gap was varied between either 5 or 15 cm by caudal movement of the lowest electrode. Measurements were averaged over 20 s and performed twice at each electrode position. Reference values were determined using cardiac magnetic resonance imaging (CMR). Mean bias was 1.2  ±  1.6 l min(-1) (percentage error 22  ±  28%) between COCMR and COEV at the 5 cm gap significantly improving to 0.5  ±  1.6 l min(-1) (8  ±  28%) when increasing the gap (p  <  0.0001). The mean difference between repeated measurements was 0.0  ±  0.3 l min(-1) for the 5 cm and 0.1  ±  0.3 l min(-1) for the 15 cm gap, respectively (p  =  0.3). The accuracy of EV can be significantly improved when increasing the lower inter-electrode gap still exceeding the Critchley and Critchley recommendations. Therefore, absolute values should not be used interchangeably in clinical routine. As the reproducibility was not negatively affected, serial hemodynamic measurements can be reliably acquired in stable patients when the electrode position remains unchanged.

A multichannel bioimpedance monitor for full-body blood flow monitoring

The design, properties, and possible diagnostic contribution of a multichannel bioimpedance monitor (MBM) with three independent current sources are presented in this paper. The simultaneous measurement of bioimpedance at 18 locations (the main part of the body, legs, arms, and neck) provides completely new information, on the basis of which more precise haemodynamic parameters can be obtained. The application of the MBM during various haemodynamic stages, such as resting in a supine position, tilting, exercise stress, and various respiration manoeuvres, is demonstrated. Statistical analysis on a group of 34 healthy volunteers is presented for demonstration of blood flow monitoring by using the proposed method.

Development of a wearable multi-frequency impedance cardiography device

Cardiovascular diseases as well as pulmonary oedema can be early diagnosed using vital signs and thoracic bio-impedance. By recording the electrocardiogram (ECG) and the impedance cardiogram (ICG), vital parameters are captured continuously. The aim of this study is the continuous monitoring of ECG and multi-frequency ICG by a mobile system. A mobile measuring system, based on 'low-power' ECG, ICG and an included radio transmission is described. Due to the high component integration, a board size of only 6.5 cm×5 cm could be realized. The measured data can be transmitted via Bluetooth and visualized on a portable monitor. By using energy-efficient hardware, the system can operate for up to 18 hs with a 3 V battery, continuously sending data via Bluetooth. Longer operating times can be realized by decreased transfer rates. The relative error of the impedance measurement was less than 1%. The ECG and ICG measurements allow an approximate calculation of the heart stroke volume. The ECG and the measured impedance showed a high correlation to commercial devices (r=0.83, p<0.05). In addition to commercial devices, the developed system allows a multi-frequency measurement of the thoracic impedance between 5-150 kHz.

Evaluation of changes in cardiac output from the electrical impedance waveform in the forearm

We tested the validity of regional impedance cardiography (RIC) for measuring changes in both cardiac output and stroke volume by comparing the values with a 2D ultrasound technique in response to the breath-hold manipulation. Among 13 subjects, changes in the maximum amplitude of the regional impedance waveform from the forearm conformed to those in stroke volume (r = 0.86, p < 0.001) and cardiac output (r = 0.76, p < 0.003) measured with the ultrasound technique in baseline and immediately after a 30 s breath-hold maneuver. We also found that the per cent change in cardiac output (r = 0.73, p < 0.005) and the per cent change in stroke volume (r = 0.84, p < 0.0003) by the echocardiography were both positively correlated with the per cent change in the peak impedance amplitude. In addition, both the change and the per cent change in the mean area under the impedance curve were consistent with those in the stroke volume, respectively. Accordingly, the regional electrical impedance waveform from lower limbs may be helpful in providing a non-invasive and continuous assessment of left ventricular output, especially during cardiac procedures.