Recent developments in cardiac output determination by bioimpedance: comparison with invasive cardiac output and potential cardiovascular applications

Vascular limitations in blood pressure regulation with age in women: Insights from exercise and acute cardioselective β-blockade

Younger women rely on altering cardiac output (Q ̇ $\dot{Q}$ ) to regulate blood pressure (BP). In contrast, older women rely more on altering vascular tone. However, evidence suggests that the ability to alter systemic vascular conductance (SVC) is diminished in older women. In the present study, cardioselective β-blockade was utilized to diminish the relative contribution ofQ ̇ $\dot{Q}$ to BP regulation and thereby evaluate age-related vascular limitations in women at rest and during large muscle dynamic exercise. Younger (n = 13, mean age 26.0 years) and older (n = 14, mean age 61.8 years) healthy women performed submaximal bouts of semi-recumbent cycling exercise at varying intensities while receiving an intravenous infusion of esmolol, a β1-antagonist, or saline control in a repeated-measures crossover design.Q ̇ $\dot{Q}$ was attenuated during esmolol infusion, with greater reductions during exercise (moderate, -1.0 (95% CI, -1.6 to -0.5) L/min, P < 0.001; heavy, -2.0 (95% CI, -2.6 to -1.5) L/min, P < 0.001) than seated rest (-0.5 (95% CI, -1.1 to 0.0) L/min, P = 0.048), and this reduction was not significantly different between age groups (P = 0.122). Older women exhibited a greater attenuation in mean arterial pressure (MAP) during esmolol (-7 (95% CI, -9 to -4) mmHg, P < 0.001) relative to younger women (-2 (95% CI, -5 to 0) mmHg, P = 0.071). These changes coincided with a greater reduction of SVC in the younger women during esmolol (-15 (95% CI, -20 to -10) mL/min/mmHg, P < 0.001) compared to older women (-3 (95% CI, -9 to 2) mL/min/mmHg, P = 0.242). Together, these findings provide evidence that older, postmenopausal women have a diminished ability to adjust SVC in order to regulate MAP.

3D morphable systems via deterministic microfolding for vibrational sensing, robotic implants, and reconfigurable telecommunication

DNA and proteins fold in three dimensions (3D) to enable functions that sustain life. Emulation of such folding schemes for functional materials can unleash enormous potential in advancing a wide range of technologies, especially in robotics, medicine, and telecommunication. Here, we report a microfolding strategy that enables formation of 3D morphable microelectronic systems integrated with various functional materials, including monocrystalline silicon, metallic nanomembranes, and polymers. By predesigning folding hosts and configuring folding pathways, 3D microelectronic systems in freestanding forms can transform across various complex configurations with modulated functionalities. Nearly all transitional states of 3D microelectronic systems achieved via the microfolding assembly can be easily accessed and modulated in situ, offering functional versatility and adaptability. Advanced morphable microelectronic systems including a reconfigurable microantenna for customizable telecommunication, a 3D vibration sensor for hand-tremor monitoring, and a bloomable robot for cardiac mapping demonstrate broad utility of these assembly schemes to realize advanced functionalities.

Central and Peripheral Oxygen Distribution in Two Different Modes of Interval Training

In high-intensity interval training the interval duration can be adjusted to optimize training results in oxygen uptake, cardiac output, and local oxygen supply. This study aimed to compare these variables in two interval trainings (long intervals HIIT3m: 3 min work, 3 min active rest vs. short intervals HIIT30s: 30 s work, 30 s active rest) at the same overall work rate and training duration. 24 participants accomplished both protocols, (work: 80% power output at VO₂peak, relief: 85% power output at gas exchange threshold) in randomized order. Spirometry, impedance cardiography, and near-infrared spectroscopy were used to analyze the physiological stress of the cardiopulmonary system and muscle tissue. Although times above gas exchange threshold were shorter in HIIT3m (HIIT3m 1669.9 ± 310.9 s vs. HIIT30s 1769.5 ± 189.0 s, p = 0.034), both protocols evoked similar average fractional utilization of VO₂peak (HIIT3m 65.23 ± 4.68% VO₂peak vs. HIIT30s 64.39 ± 6.78% VO₂peak, p = 0.261). However, HIIT3m resulted in higher cardiovascular responses during the loaded phases (VO₂p < 0.001, cardiac output p < 0.001). Local hemodynamics were not different between both protocols. Average physiological responses were not different in both protocols owning to incomplete rests in HIIT30s and large response amplitudes in HIIT3m. Despite lower acute cardiovascular stress in HIIT30s, short submaximal intervals may also trigger microvascular and metabolic adaptions similar to HIIT3m. Therefore, the adaption of interval duration is an important tool to adjust the goals of interval training to the needs of the athlete or patient.

Agreement of Bioreactance Cardiac Output Monitoring With Thermodilution in Healthy Standing Horses

Bioreactance is the continuous analysis of transthoracic voltage variation in response to an applied high frequency transthoracic current and was recently introduced for non-invasive cardiac output measurement (NICOM). We evaluated NICOM compared to thermodilution (TD) in adult horses. Six healthy horses were used for this prospective, blinded, experimental study. Cardiac output (CO) measurements were performed simultaneously using TD and the bioreactance method. Different cardiac output scenarios were established using xylazine (0.5 mg/kg IV) and dobutamine (1.5-3 mcg/kg/min). Statistical analysis was performed by calculating the concordance rate, performing a regression analysis, Pearson correlation, and Bland Altman. The TD-based CO and NICOM values were highly correlated for low, normal and high CO values with an overall correlation coefficient. A 4-quadrant plot showed an 89% rate of concordance. The linear regression calculated a relationship between NICOM and TDCO of Y = 0.4874 · X + 0.5936. For the corrected Bland Altman agreement, the mean bias and lower/upper limits of agreement were -0.26 and -3.88 to 3.41 L/min, respectively. Compared to TD, bioreactance- based NICOM showed good accuracy at induced low, normal, and high CO states in normal horses. Future studies performed under more clinical conditions will show if this monitor can help to assess hemodynamic status and guide therapy in horses in ICU settings and under general anesthesia.

Non-invasive evaluation of macro- and microhemodynamic changes during induction of general anesthesia – A prospective observational single-blinded trial

BACKGROUND: Hypotension and bradycardia are known side effects of general anesthesia, while little is known about further macro- and microhemodynamic changes during induction. Intriguing is furthermore, why some patients require no vasopressor medication to uphold mean arterial pressure, while others need vasopressor support. OBJECTIVE: Determination of macro- and microhemodynamic changes during induction of general anesthesia. METHODS: We enrolled 150 female adults scheduled for gynaecological surgery into this prospective observational, single-blinded trial. Besides routinely measuring heart rate (HR) and mean arterial blood pressure (MAP), the non-invasive technique of thoracic electrical bioimpedance was applied to measure cardiac output (CO), cardiac index (CI), stroke volume (SV), stroke volume variability (SVV) and index of myocardial contractility (ICON) before induction of anesthesia, 7 times during induction, and, finally, after surgery in the recovery room. Changes in microcirculation were assessed using sidestream dark field imaging to establish the perfused boundary region (PBR), a validated gauge of glycocalyx health. Comparisons were made with Friedman’s or Wilcoxon test for paired data, and with Mann-Whitney-U test for unpaired data, with post-hoc corrections for multiple measurements by the Holm-Bonferroni method. RESULTS: 83 patients did not need vasopressor support, whereas 67 patients required therapy (norepinephrine, atropine or cafedrine/theodrenaline) to elevate MAP values to ≥70mmHg during induction, 54 of these receiving norepinephrine (NE) alone. Pre-interventional (basal) values of CO, CI, ICON, SV and SVV were all significantly lower in the group of patients later requiring NE (p < 0.04), whereas HR and MAP were identical for both groups. HR, MAP and CO decreased from baseline to 12 min after induction of general anesthesia in both the patients without and those with NE support. Heart rate decreased significantly by about 25% in both groups (–19 to –21 bpm). The median individual decrease of MAP amounted to –26.7% (19.7/33.3, p < 0.001) and –26.1% (11.6/33.2, p < 0.001), respectively, whereas for CO it was –40.7% (34.1/50.1, p < 0.001) and –43.5% (34.8/48.7). While these relative changes did not differ between the two groups, in absolute values there were significantly greater decreases in CO, CI, SV and ICON in the group requiring NE. Noteably, NE did not restore ICON or the other cardiac parameters to levels approaching those of the group without NE. PBR was measured in a total of 84 patients compiled from both groups, there being no intergroup differences. It increased 6.4% (p < 0.001) from pre-induction to the end of the operation, indicative of damage to microvascular glycocalyx. CONCLUSION: Non-invasive determination of CO provides additional hemodynamic information during anesthesia, showing that induction results in a significant decrease not only of MAP but also of CO and other cardiac factors at all timepoints compared to baseline values. The decrease of CO was greater than that of MAP and, in contrast to MAP, did not respond to NE. There was also no sign of a positive inotropic effect of NE in this situation. Support of MAP by NE must consequently result from an increase in peripheral arterial resistance, posing a risk for oxygen supply to tissue. In addition, general anesthesia and the operative stimulus lead to an impairment of the microcirculation.

Noninvasive Cardiac Output Monitoring Using Electrical Cardiometry and Outcomes in Critically Ill Children

Cardiac output (CO) measurement is an important element of hemodynamic assessment in critically ill children and existing methods are difficult and/or inaccurate. There is insufficient literature regarding CO as measured by noninvasive electrical cardiometry (EC) as a predictor of outcomes in critically ill children. We conducted a retrospective chart review in children <21 years, admitted to our pediatric intensive care unit (PICU) between July 2018 and November 2018 with acute respiratory failure and/or shock and who were monitored with EC (ICON monitor). We collected demographic information, data on CO measurements with EC and with transthoracic echocardiography (TTE), and data on ventilator days, PICU and hospital days, inotrope score, and mortality. We analyzed the data using Chi-square and multiple linear regression analysis. Among 327 recordings of CO as measured by EC in 61 critically ill children, the initial, nadir, and median CO (L/min; median [interquartile range (IQR)]) were 3.4 (1.15, 5.6), 2.39 (0.63, 4.4), and 2.74 (1.03, 5.2), respectively. Low CO as measured with EC did not correlate well with TTE (p = 0.9). Both nadir and mean CO predicted ventilator days (p = 0.05 and 0.01, respectively), and nadir CO was correlated with peak inotrope score (correlation coefficient of –0.3). In our cohort of critically ill children with respiratory failure and/or shock, CO measured with EC did not correlate with TTE. Both nadir and median CO measured with EC predicted outcomes in critically ill children.

The accuracy of electrical cardiometry for the noninvasive determination of cardiac output before and after lung surgeries compared to transthoracic echocardiography

Background:

The anatomical changes associated with lung surgeries may decrease cardiac output and heart function. Therefore, monitoring of cardiac output (CO) is of significant value in these patients for clinical decision-making.

Objective:

This study is to evaluate the reliability of electrical cardiometry (EC) for the noninvasive continuous determination of CO after lobectomy or pneumonectomy compared to transthoracic echocardiography (TTE).

Patients and Methods:

This study was carried out on 60 patients, age ≥18 years scheduled for elective lung surgery (lobectomy or pneumonectomy). All patients underwent simultaneous measurement by EC using the ICON_ device and by TTE by measuring left ventricle outflow tract diameter (LVOT) and velocity time integral (VTI). Heart rate (HR), systolic and diastolic blood pressure (SBP and DBP), stroke volume (SV), stroke volume index (SVI), CO, and cardiac index (CI) were measured 1 day before the surgery and 7 days after the surgery.

Results:

There was no significant difference between TTE and EC regarding preoperative and postoperative HR, SV, SVI, CO, and CI. There was a strong positive correlation between TTE and EC as regard preoperative and postoperative HR, SV, SVI, CO, and CI. Bland and Altman analysis showed low bias with accepted limits of agreement of HR, SV, SVI, CO, and CI. Postoperative readings showed a significant increase in HR and a significant decrease in SV and CO (either by TTE or EC), SBP, and DBP as compared to preoperative reading.

Conclusion:

Compared to the TTE, EC provides accurate and reliable CO, SV, and HR measurements before and even after lung surgeries.

Measurement of hemodynamics immediately after vaginal delivery in healthy pregnant women by electrical cardiometry

Few reports have focused on hemodynamics around delivery in pregnant women because of the difficulty of continuous and noninvasive measurement. Electrical cardiometry allows noninvasive continuous monitoring of hemodynamics and has recently been used in non-pregnant subjects. We compared the use of electrical cardiometry versus transthoracic echocardiography in healthy pregnant women and evaluated hemodynamics immediately after vaginal delivery. In Study 1, electrical cardiometry and transthoracic echocardiography were used to measure cardiac output in 20 pregnant women with threatened premature delivery. A significant correlation was found between the two methods, with electrical cardiometry showing the higher cardiac output. In Study 2, heart rate, stroke volume, and cardiac output were continuously measured in 15 women during vaginal delivery up to 2 h postpartum. Cardiac output increased markedly because of an increased heart rate and stroke volume at the time of newborn delivery. The heart rate then immediately returned to baseline, while cardiac output remained elevated for at least 2 h after delivery because of a sustained high stroke volume. Electrical cardiometry was as readily available as transthoracic echocardiography for evaluating hemodynamics and allowed for continuous measurement during labor. High intrapartum cardiac output was sustained for at least 2 h after vaginal delivery. J. Med. Invest. 66 : 75-80, February, 2019.

Autonomic Cardiovascular Dysregulation at Rest and During Stress in Chronically Low Blood Pressure

Abstract. Chronic low blood pressure (hypotension) is accompanied by symptoms such as fatigue, reduced drive, faintness, dizziness, cold limbs, and concentration difficulties. The study explored the involvement of aberrances in autonomic cardiovascular control in the origin of this condition. In 40 hypotensive and 40 normotensive subjects, impedance cardiography, electrocardiography, and continuous blood pressure recordings were performed at rest and during stress induced by mental calculation. Parameters of cardiac sympathetic control (i.e., stroke volume, cardiac output, pre-ejection period, total peripheral resistance), parasympathetic control (i.e., heart rate variability), and baroreflex function (i.e., baroreflex sensitivity) were obtained. The hypotensive group exhibited markedly lower stroke volume, heart rate, and cardiac output, as well as higher pre-ejection period and baroreflex sensitivity than the control group. Hypotension was furthermore associated with a smaller blood pressure response during stress. No group differences arose in total peripheral resistance and heart rate variability. While reduced beta-adrenergic myocardial drive seems to constitute the principal feature of the autonomic impairment that characterizes chronic hypotension, baroreflex-related mechanisms may also contribute to this state. Insufficient organ perfusion due to reduced cardiac output and deficient cardiovascular adjustment to situational requirements may be involved in the manifestation of bodily and mental symptoms.

Identification of the State of Maximal Hyperemia in the Assessment of Coronary Fractional Flow Reserve Using Non-Invasive Electrical Velocimetry

Previous research revealed that, in patients with coronary pressure-derived fractional flow reserve (FFR) in the 'grey zone' (0.75-0.85), repeated FFR assessments sometimes yield conflicting results. One of the causes of the fluctuations in FFR values around the grey zone may be imprecise identification of the point where maximal hyperemia is achieved. Identification of the state of maximal hyperemia during assessment of FFR can be challenging. This study aimed to determine whether non-invasive electrical velocimetry (EV) can be used to identify the state of maximal hyperemia.Stroke volume (SV), SV variation (SVV), and systemic vascular resistance index (SVRI) were determined by EV in 15 patients who underwent FFR assessment. Time intervals from initiation of adenosine infusion to achieving maximal hyperemia (time^mFRR), as well as to achieving maximal cardiac output (CO), SV, SVV, and SVRI (time^mCO, time^mSV, time^mSVV, and time^mSVRI, respectively), were determined. Time^mCO and time^mSVV were closer to time^mFRR than other values (time^mSVV/time^mFRR versus time^mSVRI/time^mFRR = 1.03 ± 0.2 versus 1.36 ± 0.4, P < 0.05). The maximum of SV was difficult to determine owing to considerable variations, but the maximum of SVV was clearly recognized. Time^mCO and time^mSVV were significantly correlated with time^mFFR, with time^mSVV showing a stronger correlation than time^mSV (time^mSVV: r = 0.92, P < 0.01; time^mCO: r = 0.80, P < 0.01).Maximal SVV is reached close to maximal hyperemia. Monitoring of SVV with non-invasive EV during FFR assessment can help identify the state of maximal hyperemia.

Hemodynamic monitoring in the critically ill: an overview of current cardiac output monitoring methods

Critically ill patients are often hemodynamically unstable (or at risk of becoming unstable) owing to hypovolemia, cardiac dysfunction, or alterations of vasomotor function, leading to organ dysfunction, deterioration into multi-organ failure, and eventually death. With hemodynamic monitoring, we aim to guide our medical management so as to prevent or treat organ failure and improve the outcomes of our patients. Therapeutic measures may include fluid resuscitation, vasopressors, or inotropic agents. Both resuscitation and de-resuscitation phases can be guided using hemodynamic monitoring. This monitoring itself includes several different techniques, each with its own advantages and disadvantages, and may range from invasive to less- and even non-invasive techniques, calibrated or non-calibrated. This article will discuss the indications and basics of monitoring, further elaborating on the different techniques of monitoring.

Correlation between impedance cardiography and 6 min walk distance in atrial fibrillation patients

Background

The correlation between impedance cardiography (ICG) and 6 min walk distance (6MWD) in atrial fibrillation (AF) patients remains unknown.

Methods

We recruited 49 subjects in the study (21 AF patients and 28 patients without AF) and estimated hemodynamic parameters: cardiac output (CO), stroke volume (SV), stroke volume index (SVI), left stroke work (LSW), left stroke work index (LSWI), stroke systemic vascular resistance (SSVR), stroke systemic vascular resistance index (SSVRI); 6MWD, left ventricle ejection fraction (LVEF), NT-pro brain natriuretic peptide (NT-pro BNP) for the two groups.

Results

The AF group have apparently lower CO (2.26 ± 0.14 VS 4.11 ± 0.20 L/min, p = 0.039) and distinctly higher SVR (677.60 ± 69.10 VS 344.41 ± 22.98 dynes/cm⁵, p = 0.001), SSVRI (396.97 ± 36.80 VS 199.01 ± 11.72 dynes/cm⁵/m², p < 0.001) than the control group. NT-pro BNP (1409.48 ± 239.90 VS 332.59 ± 68.85 pg/ml, p = 0.001) in the AF group was significantly higher than the control group and 6MWD (264.33 ± 14.55 VS 428.79 ± 29.98 m, p < 0.001) in the AF group was lower than the control group. There was no significant difference in LVEF between the two groups (62.67 ± 7.62 % VS 63.93 ± 5.03 %, p = 0.470). Pearson correlation analysis revealed that CO (R = 0.494, p = 0.023), SV (R = 0.633, p = 0.002), LSW (R = 0.615, p = 0.003) and LSWI (R = 0.491, p = 0.024) significantly correlated positively with 6MWD in AF patients.

Conclusions

AF patients had lower cardiac output, shorter 6MWD and higher NT-pro BNP than patients with sinus rhythm. The cardiac output measured by impedance cardiography significantly correlated positively with 6MWD in AF patients.

Noninvasive cardiac output measurement using bioreactance in postoperative pediatric patients

BACKGROUND

Thoracic bioreactance is a noninvasive and continuous method of cardiac output (CO) measurement that is being developed in adult patients. Very little information is available on thoracic bioreactance use in children.

OBJECTIVE

The aim of the study was to evaluate the ability of a bioreactance device (NICOM(®) ; Cheetah Medical, Tel Aviv, Israel) to estimate CO and to track changes in CO induced by volume expansion (VE) in children.

METHODS

Cardiac output values obtained using the NICOM(®) device (CONICOM ) and measured by trans-thoracic echocardiography (COTTE ) were compared in pediatric neurosurgical patients during the postoperative period.

RESULTS

Seventy-three pairs of measurements of CO obtained in 30 children were available for analysis. The bias (lower and upper limits of agreement) between CONICOM and COTTE was -0.11 (-1.4 to 1.2) l·min(-1). The percentage error (PE) was 55%. The precision of the NICOM(®) device was 45%. A significant correlation was observed between the CO values obtained using the two methods (r = 0.89, <0.001). The concordance percentage between changes in COTTE and CON icom induced by VE was 84% following exclusion of patients with changes in CO <15% (n = 5).

CONCLUSIONS

The PE observed is too large, and the limits of agreement too wide, to enable us to comment on the equivalence of the two techniques of CO measurements. However, the NICOM(®) device performs well in tracking changes in CO following VE.

New therapeutic options in heart failure. What's on the horizon? An overview

Heart failure is a complex clinical syndrome responsible for high morbidity and mortality in the world. Despite advances in the management of heart failure, the prognosis of these patients remains poor and there is a critical need for new treatment strategies improving the clinical outcomes. New approaches in heart failure therapies target cellular mechanisms, as well as mechanical and structural aspects of heart failure that are not addressed by recent therapies. These include abnormalities in molecular mechanisms, electrical conduction and ventricular remodeling. This review presents the pathophysiological basis, mechanisms of action and available clinical efficacy and safety data of drugs and mechanical therapies that are currently under development.

The utility of novel non-invasive technologies for remote hemodynamic monitoring in chronic heart failure

Monitoring a patient's hemodynamic status may be a revolutionary way to aid a 'health maintenance' strategy in which the physician strives to therapeutically keep the patient in an ideal hemodynamic range. Currently, home telemonitoring employs a 'crisis-prevention' approach. This strategy is still based on easily acquired measures such as heart rate, weight and blood pressure--measurements that are useful to help implement guideline-directed therapy but provide little information about impending decompensation or the risk of hospitalisation. Current systems provide limited information to personalize and adapt medication therapy for heart failure. Several innovative technologies that can remotely monitor estimates of cardiovascular hemodynamics, such as cardiac index, systemic vascular resistance, augmentation index and added heart sounds may enable earlier detection of heart failure decompensation. This editorial presents an overview of the innovative technologies that are available for non-invasive hemodynamic monitoring and maybe adapted for home telemonitoring for chronic heart failure.

Detecting variations of blood volume shift due to heart beat from respiratory inductive plethysmography measurements in man

The simultaneous study of the cardiac and respiratory activities and their interactions is of great physiological and clinical interest. For this purpose, we want to investigate if respiratory inductive plethysmography (RIP) can be used for cardiac functional exploration. We propose a system, based on RIP technology and time-scale approaches of signal processing, for the extraction of cardiac information. This study focuses on the monitoring of blood volume shift due to heart beat, noted ▵Vtr_c and investigates RIP for the detection of ▵Vtr_c variations by comparison to stroke volume (SV) variations estimated by impedance cardiography (IMP). We proposed a specific respiratory protocol assumed to induce significant variations of the SV. Fifteen healthy volunteers in the seated and supine positions were asked to alternate rest respiration and maneuvers, consisting in blowing into a manometer. A multi-step treatment including a variant of empirical mode decomposition was applied on RIP signals to extract cardiac volume signals and estimate beat-to-beat ▵Vtr_c. These were averaged in quasi-stationary states at rest and during the respiratory maneuvers, and analysed in view of SV estimations from IMP signals simultaneously acquired. Correlation and statistical tests over the data show that RIP can be used to detect variations of the cardiac blood shift in healthy young subjects.

Comparison of cardiac output derived from FloTrac™/Vigileo™ and impedance cardiography during major abdominal surgery

Objectives

Impedance cardiography (ICG) is a noninvasive technique that provides reasonably accurate measurements of cardiac output, but the usefulness of ICG in patients undergoing open abdominal surgery has not been validated.

Methods

Cardiac output was measured while patients underwent open gastrectomy using an ICG monitor ( niccomo™; ICG-CO); the results were compared with those measured using a FloTrac™/Vigileo™ monitor (Flo-CO), which measures cardiac output by analysing the arterial waveform. Data collection commenced at the beginning of anaesthetic induction and continued until the patient was awake. Data were compared using the Bland–Altman analysis, and the clinical significance of the difference between the two methods was evaluated by calculating the percentage error (%).

Results

Eleven patients were monitored during surgery. The bias of the Flo-CO and ICG-CO values was −0.45 l/min. The upper and lower limits of agreement were 0.96 l/min and −1.85 l/min, respectively. The percentage error was 28.5%. Electrocautery induced interference that transiently impaired the performance of the ICG monitor.

Conclusions

ICG provided useful information in evaluating the cardiac output of patients during abdominal surgery.

Assessment of cardiac stroke volume in patients with implanted cardiac pacemaker using parametric electrical impedance tomography: a theoretical 2D study

The present theoretical study examines the ability to estimate cardiac stroke volume (CSV) in patients with implanted cardiac pacemaker using parametric electrical impedance tomography (pEIT) in a 2D computerized model of the thorax. CSV is a direct indicator of the cardiac pumping efficiency. The commonly used methods for measuring CSV require the invasive procedure of right heart catheterization or use expensive imaging techniques (i.e., MRI). Hence, experience with these techniques for diagnosis and monitoring has been limited to hospitalized patients. In the present study, pEIT scheme was applied in a computerized 2D model of the human thorax with implanted cardiac device to determine the left ventricular (LV) volume at different cardiac cycle phases. The LV was simulated as a prolate ellipse with its axes' lengths as the reconstruction parameters while all other geometries and conductivity values remained constant. An optimization was carried out in order to ensure that the ellipse is the appropriate model for the LV at each cardiac cycle phase. LV volumes calculated by both the pEIT algorithm and the ellipsoid model are consistent. A high correlation (ρ = 0.99) between the true and reconstructed volumes was found. The SV calculation error was ∼1%. The results suggest that the LV volume can be estimated using the pEIT method in a 2D computerized model, and that the method has the potential to be used for monitoring patients with implanted cardiac pacemaker.

A Wearable Technology Revisited for Cardio-Respiratory Functional Exploration

The objective of the present study is to extract new information from complex signals generated by Respiratory Inductive Plethysmography (RIP). This indirect cardio-respiratory (CR) measure is a well-known wearable solution. The authors applied time-scale analysis to estimate cardiac activity from thoracic volume variations, witnesses of CR interactions. Calibrated RIP signals gathered from 4 healthy volunteers in resting conditions are processed by Ensemble Empirical Mode Decomposition to extract cardiac volume signals and estimate stroke volumes. Averaged values of these stroke volumes (SVRIP) are compared with averaged values of stroke volumes determined simultaneously by electrical impedance cardiography (SVICG). There is a satisfactory correlation between SVRIP and SVICG (r=0.76, p<0.001) and the limits of agreement between the 2 types of measurements (±23%) satisfies the required criterion (±30%). The observed under-estimation (-58%) is argued. This validates the use of RIP for following stroke volume variations and suggests that one simple transducer can provide a quantitative exploration of both ventilatory and cardiac volumes.

Empirical mode decomposition of respiratory inductive plethysmographic signals for stroke volume variations monitoring: respiratory protocol and comparison with impedance cardiography

We investigate Respiratory Inductive Plethysmography (RIP) to estimate cardiac activity from thoracic volume variations and study cardio-respiratory interactions. The objective of the present study is to evaluate the ability of RIP to monitor stroke volume (SV) variations, with reference to impedance cardiography (IMP). Five healthy volunteers in seated and supine positions were asked to blow into a manometer in order to induce significant SV decreases. Time-scale analysis was applied on calibrated RIP signals to extract cardiac volume signals. Averaged SV values, in quasi-stationary states at rest and during the respiratory maneuvers, were then estimated from these cardiac signals and from IMP signals simultaneously acquired. SV variations between rest and maneuvers were finally evaluated for both techniques. We show that SV values as well as SV variations are correlated between RIP and IMP estimations, suggesting that RIP could be used for SV variations monitoring.

Hemodynamically complicated ST-segment elevation myocardial infarction: presentation and treatment

When ST-segment elevation myocardial infarction is complicated by hemodynamic instability, clinical evaluation alone cannot be relied upon for accurate assessment. Invasive hemodynamic monitoring with a pulmonary artery catheter and intra-arterial catheter should, therefore, be performed to gauge impaired hemodynamics in such patients and make necessary changes in therapy. There are several hemodynamic disturbances that can occur after ST-segment elevation myocardial infarction including pulmonary congestion, cardiogenic shock and mechanical complications such as left-ventricular free-wall rupture, ventricular-septal defect or papillary muscle rupture. Patients with hemodynamic compromise should be admitted to the coronary care unit and therapy should be initiated with drugs such as vasodilators, diuretics and positive-inotropic agents, based on hemodynamic data provided by the invasive catheter. Intra-aortic balloon counterpulsation should be used for those who fail to achieve hemodynamic stability with medical therapy. Coronary angiography should be considered for all patients who are hemodynamically unstable provided they are candidates for aggressive care, followed by coronary revascularization in those with suitable anatomy. Operative repair should be performed promptly when a surgically correctable mechanical lesion is identified.

Impedance cardiography facilitates differentiation of severe and superimposed preeclampsia from other hypertensive disorders

OBJECTIVE

To determine if hemodynamic profiling using noninvasive impedance cardiography (ICG) reliably identifies the patient with severe (SPRE) or superimposed (SuPRE) preeclampsia.

METHODS

Late gestation hypertensive pregnant patients underwent immediate ICG evaluation. Findings were compared between patients subsequently achieving or not achieving American College of Obstetricians and Gynecologists criteria for SPRE or SuPRE.

RESULTS

Patients with severe disease were more likely to have depressed cardiac function and higher systolic blood pressure, mean arterial blood pressure, systemic vascular resistance, and thoracic fluid content compared to nonsevere hypertensive disease.

CONCLUSION

ICG hemodynamic profiling of late gestation hypertensive patients can rapidly and reliably identify those with SPRE or SuPRE.

Persistent arterial stiffness and endothelial dysfunction following successful pancreas-kidney transplantation in Type 1 diabetes

OBJECTIVE

Successful simultaneous pancreas-kidney transplantation (SPK) in Type 1 diabetic (T1DM) patients results in improved cardiovascular outcome and survival. However, it is doubtful whether the impairment of cardiovascular and endothelial function in T1DM can be completely reversed.

METHODS

Pulse-wave velocity, stroke volume, heart rate, serological markers of endothelial dysfunction (soluble intercellular, vascular cell-adhesion molecules, E-selectin, and plasminogen-activator-inhibitor-1) were measured in 10 T1DM patients after SPK with non-diabetic glucose levels, 10 T1DM patients with poor [T1DM>8; glycated haemoglobin (HbA1c)>8%], and 10 with good glucose control (T1DM<7, HbA1c<7%), in 6 non-diabetic patients after kidney transplantation (KT) and 9 non-diabetic control subjects (CON), matching for major anthropometric characteristics.

RESULTS

Pulse-wave velocity was increased in SPK (P < 0.02 vs. CON, KT, T1DM<7) and in T1DM>8 (P < 0.02 vs. T1DM<7). Systolic blood pressure was increased in SPK (P < 0.05 vs. CON). Stroke volume was reduced in SPK, T1DM>8 and T1DM<7 and KT (P < 0.01 vs. CON). Heart rate was elevated in SPK and in T1DM>8 (P < 0.0003 vs. CON and T1DM<7). In SPK, soluble intercellular and vascular cell-adhesion molecules were 100% and 44% higher (P < 0.03 vs. CON), respectively, while plasminogen-activator-inhibitor-1 was decreased in SPK (P < 0.02 vs. CON).

CONCLUSION

T1DM patients after SPK experience arterial stiffness, a higher heart-rate and blood pressure, reduced stroke volume and serological signs of endothelial dysfunction. Thus, functional and structural cardiovascular alterations as a result of glucotoxicity, uraemia and hypertension in T1DM might not be completely resolved by SPK.

Evaluation of a commercial ultrasonographic hemodynamic recording system for the measurement of cardiac output in dogs

OBJECTIVE

To evaluate the accuracy of a commercial ultrasonographic cardiac output (CO) monitoring system (UCOMS) in anesthetized Beagles as assessed by comparison with thermodilution CO (TDCO).

ANIMALS

8 healthy anesthetized Beagles.

PROCEDURES

Simultaneous UCOMS and TDCO measurements of CO were obtained during 4 hemodynamic states: baseline anesthesia (0.5% to 1.5% isoflurane), a higher depth of anesthesia (2% to 3.5% isoflurane) to yield a >or= 15% reduction in systolic arterial blood pressure, IV infusion of colloidal solution to a mean right atrial pressure of >or= 15 mm Hg, and IV infusion of dobutamine at 5 microg/kg/min. Measurements were obtained at 2 probe positions: the subxiphoid region and the right thoracic inlet. Correlation and agreement of results between methods were determined via linear regression analysis and Bland-Altman plots.

RESULTS

A significant positive correlation was detected between UCOMS andTDCO measurements obtained at the subxiphoid (R = 0.86) and thoracic inlet (R = 0.83) positions. Bland-Altman plots revealed minimal bias between methods (bias +/- SD, -0.03 +/- 0.73 L/min and -0.20 +/- 0.80 L/min for subxiphoid and thoracic inlet measurements, respectively). However, the percentage error associated with UCOMS measurements made at the 2 positions was > 45%.

CONCLUSIONS AND CLINICAL RELEVANCE

When compared with the results of TDCO, CO measured with the UCOMS exceeded commonly accepted limits of error in healthy dogs. The UCOMS was, however, able to track changes in CO across hemodynamic states. Additional research is needed to assess the usefulness of the UCOMS for monitoring CO in critically ill dogs.

Hemodynamic monitoring in acute heart failure

Hemodynamic monitoring has moved in the last few years from being the holy grail of evaluating patients with acute heart failure to being all but extinct. Recent studies have not demonstrated any sustained benefits from right heart catheterization, and some studies have even suggested harm due to adverse events related to this invasive procedure. It is possible that this lack of efficacy is related to multiple inherent deficiencies in the design of these studies, including the inclusion of patients with chronic heart failure or mild acute heart failure, use of the reduction in pulmonary artery occlusion pressure as the main hemodynamic target for intervention, choice of treatment algorithms, and selection of ambitious long-term efficacy and safety end points. This review discusses the role of hemodynamic monitoring in patients with acute heart failure. We suggest that right heart catheterization should be reserved for patients with acute heart failure and impending respiratory or circulatory failure especially in the presence of a diagnostic or therapeutic dilemma or when encountering acute heart failure or hemodynamic lability refractory to conventional therapy. Therapeutic algorithms emphasizing modern variables for cardiovascular performance and using safer and more efficacious individualized therapies and possibly noninvasive measurement of certain hemodynamic variables may enhance the likelihood of a beneficial effect for hemodynamic guided therapy.

Prognostic significance and measurement of exercise-derived hemodynamic variables in patients with heart failure

The peak VO2 is an important prognostic measurement in the evaluation of patients with heart failure and is used to monitor the progress of the condition, especially in selecting patients for cardiac transplantation. However, peak VO2 may be influenced by noncardiac factors such as age, sex, motivation, anemia, and muscle deconditioning. These confounding factors may diminish somewhat the prognostic power of peak VO2. Several groups have looked at exercise-derived variables beyond peak VO2 to assess whether a more direct assessment of cardiac function, using exercise-derived hemodynamic variables, may yield more precise prognostic information than standard cardiopulmonary-derived data. This article reviews the evidence that cardiac work related to exercise may enhance the prognostic value of peak VO2 in the evaluation of patients with heart failure and briefly discusses the available methods for measuring these parameters.

Comparison of electrical velocimetry and thermodilution techniques for the measurement of cardiac output

AIM

To compare a new method of non-invasive determination of cardiac output based on electrical velocimetry (EV-CO) with invasive thermodilution methods.

METHODS

Fifty critically ill patients were enrolled into the study. EV-CO was compared with cardiac output measured by a pulmonary artery catheter (PA-CO) in one group (n= 25) and by a femoral artery catheter (PiCCO-CO) in a second group (n= 25), by simultaneous measurements. Standard electrocardiography electrodes were used for non-invasive measurements, and EV-CO was calculated using the Bernstein-Osypka equation. The invasive measurements of PA-CO and PiCCO-CO were made by the injection of iced 0.9% saline and the recording of thermodilution curves.

RESULTS

The precision values of EV-CO, PA-CO and PiCCO-CO measurements were +/- 0.46 [95% confidence interval (95% CI), +/- 0.06], +/- 0.57 (95% CI, +/- 0.09) and +/- 0.48 l/min (95% CI, +/- 0.08 l/min), respectively. The mean differences between EV-CO and PA-CO or PiCCO-CO were -0.05 +/- 0.71 and 0.22 +/- 0.78 l/min, respectively. The lower and upper limits of agreement for the comparison of EV-CO with PA-CO were -1.47 and 1.37 l/min (95% CI, +/- 0.25 l/min), respectively. In the comparison of EV-CO and PiCCO-CO, lower and upper limits of -1.34 and 1.78 l/min (95% CI, +/- 0.27 l/min) were found. The percentage errors between EV-CO and PA-CO or PiCCO-CO were 26.5% and 26.4%, respectively.

CONCLUSIONS

The values of cardiac output were statistically comparable between the groups. Therefore, electrical velocimetry is a suitable method to evaluate haemodynamic variables with clinically acceptable accuracy.

Atrial natriuretic peptide serum concentration decreases in donors undergoing discontinuous plasmapheresis involving a large extracorporeal blood volume

BACKGROUND

In donor plasmapheresis, circulatory reactions occur at a similar frequency as in whole-blood donation although the large extracorporeal blood volume (ECV) occurring during discontinuous plasmapheresis might predispose donors to hypovolemic reactions. The regulatory mechanisms compensating for this intradonation blood volume (BV) deficit are not well understood. It was the aim of this study to delineate whether atrial natriuretic peptide (ANP) is involved in the BV regulation of plasmapheresis donors. Because ANP regulates volume overload, it might decrease during BV decrease in plasmapheresis.

STUDY DESIGN AND METHODS

ANP serum concentrations were determined in 60 donors undergoing discontinuous plasmapheresis. Samples were taken before the start of the procedure and when maximum ECV (ECV(max)) was reached at the end of the last withdrawal. Donors were randomly selected after stratification for sex and BV. In a control investigation, the same donors were kept in a reclined position for the duration of a plasmapheresis session without plasma withdrawal. ANP plasma concentration changes were correlated with changes of hemodynamic variables, which were recorded noninvasively with bioelectrical impedance cardiography.

RESULTS

Median ANP concentration decreased from 13.0 to 8.4 pg per mL during donation and from 11.6 to 10.5 pg per mL during the control session. The mean control-adjusted ANP change due to plasma withdrawal was -2.62 pg per mL (p = 0.006). This decrease was not attributable to a dilution effect. ANP change did not correlate with changes of recorded hemodynamic variables.

CONCLUSION

The decrease of the ANP serum concentration during plasmapheresis demonstrates that the ECV(max) constitutes a hypovolemic challenge of the donors, which elicits a neurohormonal regulatory mechanism aimed at maintaining cardiovascular homeostasis.

Evaluation of a noninvasive continuous cardiac output monitoring system based on thoracic bioreactance

Noninvasive cardiac output (CO) measurement can be useful in many clinical settings where invasive monitoring is not desired. Bioimpedance (intrabeat measurement of changes in transthoracic voltage amplitude in response to an injected high-frequency current) has been explored for this purpose but is limited in some clinical settings because of inherently low signal-to-noise ratio. Since changes in fluid content also induce changes in thoracic capacitive and inductive properties, we tested whether a noninvasive CO measurement could be obtained through measurement of the relative phase shift of an injected current (i.e., bioreactance). We constructed a prototype device that applies a 75-kHz current and determines the relative phase shift (dΦ/d t) of the recorded transthoracic voltage. CO was related to the product of peak dΦ/d t, heart rate, and ventricular ejection time. The preclinical study was done in nine open-chest pigs put on right heart bypass so that CO could be varied at known values. This was followed by a feasibility study in 27 postoperative patients who had a Swan-Ganz catheter (SGC). The measurements of noninvasive CO measurement and cardiopulmonary bypass pump correlated to each other ( r = 0.84) despite the large variation in CO and temperatures. Similarly, in patients, mean CO values were 5.18 and 5.17 l/min as measured by SGC and the noninvasive CO measurement system, respectively, and were highly correlated over the range of values studied ( r = 0.90). Preclinical and clinical data demonstrate the feasibility of using blood flow-related phase shifts of transthoracic electric signals to perform noninvasive continuous CO monitoring.

Noninvasive Hemodynamic Monitoring in the Intensive Care Unit

This article reviews the clinically available devices that have been approved for noninvasive hemodynamic monitoring in critically ill patients. In addition this article reviews some of the surrogate markers that can be used to assess adequacy of cardiac output.

Hemodynamic Response to Exercise as Measured by the Solar IKG Impedance Cardiography Module and Correlation with Metabolic Variables

OBJECTIVE

Impedance Cardiography (ICG) has been shown to be a feasible and accurate method for non-invasive measurement of cardiac index (CI). Aim of this investigation was the correlation of hemodynamic variables under exercise as measured by a specific ICG-monitor (Solar IKG-Modul, Version 3.0, GE-Healthcare, Freiburg, Germany) with metabolic variables.

METHODS

Ten healthy volunteers were included in the investigation doing ergometer exercise (5 min equilibration followed by 5 min each at 50, 75, 100 and 125 W). Hemodynamic parameters were obtained by ICG. Metabolic variables were assessed by indirect calorimetry with the Deltatrac II Metabolic monitor using a helmet system for spontaneous respiration.

RESULTS

CI increased throughout exercise (baseline: 3.0 +/- 0.4 l/min/m(2); 125 W: 4.8 +/- 0.5 l/min/m(2)). Heart rate (baseline: 87.2 +/- 13.4 bpm; 125 W: 152.7 +/- 22.4 bpm) and contractility (velocity index) (baseline: 48.9 +/- 9.3/1000 s; 125 W: 70.5 +/- 10.0/1000 s) showed a continuous rise while the stroke index decreased after an initial rise (baseline: 35.0 +/- 4.6 ml/m(2); 50 W: 37.6 +/- 4.9 ml/m(2); 75 W: 41.2 +/- 5.9 ml/m(2); 125 W: 32.3 +/- 6.1 ml/m(2)). VO(2) (baseline: 335.2 +/- 84.1 ml/min; 125 W: 1298.9 +/- 282.3 ml/min) and VCO(2)(baseline: 255.4 +/- 74.5 ml/min; 125 W: 1342.5 +/- 282.5 ml/min) increased throughout exercise. There was a good correlation in the individual fits between hemodynamic and metabolic variables.

CONCLUSION

CI in healthy volunteers, as measured by the Solar IKG-Modul, correlates well with O(2)-consumption and CO(2)-production in individual subjects, thus indicating the metabolic needs under exercise conditions in healthy individuals.

Noninvasive assessment of cardiac output using thoracic electrical bioimpedance in hemodynamically stable and unstable patients after cardiac surgery: a comparison with pulmonary artery thermodilution

OBJECTIVE

To compare noninvasive cardiac output (CO)measurement obtained with a new thoracic electrical bioimpedance (TEB) device, using a proprietary modification of the impedance equation, with invasive measurement obtained via pulmonary artery thermodilution.

DESIGN

Prospective, observational study.

SETTING

Surgical intensive care unit (ICU) of a university-affiliated community hospital.

PATIENTS AND PARTICIPANTS

Seventy-four adult patients undergoing elective cardiac surgery with routine pulmonary artery catheter placement.

INTERVENTIONS

None.

MEASUREMENTS AND RESULTS

Simultaneous paired CO and cardiac index (CI) measurements by TEB and thermodilution were obtained in mechanically ventilated patients upon admission to the ICU. For analysis of CI data the patients were subdivided into a hemodynamically stable group and a hemodynamically unstable group. The groups were analyzed using linear regression and tests of bias and precision. We found a significant correlation between thermodilution and TEB (r = 0.83; n < 0.001), accompanied by a bias of -0.01 l/min/m(2) and a precision of +/-0.57 l/min/m(2) for all CI data pairs. Correlation, bias, and precision were not influenced by stratification of the data. The correlation coefficient, bias, and precision for CI were 0.86 (n< 0.001), 0.03 l/min/m(2), and +/-0.47 l/min/m(2) in hemodynamically stable patients and 0.79 (n< 0.001), 0.06 l/min/m(2), and +/-0.68 l/min/m(2) in hemodynamically unstable patients.

CONCLUSIONS

Our results demonstrate a close correlation and clinically acceptable agreement and precision between CO measurements obtained with impedance cardiography using a new algorithm to calculate CO from variations in TEB, and those obtained with the clinical standard of care, pulmonary artery thermodilution, in hemodynamically stable and unstable patients after cardiac surgery.

Impedance cardiography for cardiac output estimation: reliability of wrist-to-ankle electrode configuration

BACKGROUND

Non-invasive measurement of cardiac output (CO) may become an important modality for the treatment of heart failure. Among the several methods proposed, impedance cardiography (ICG) has gained particular attention. There are 2 basic technologies of ICG: thoracic and whole-body ICG whereby the electrodes are applied either to the chest or to the limbs. The present study is aimed to test the effectiveness of the Non-Invasive Cardiac System (NICaS), a new ICG device working with a wrist-to-ankle configuration.

METHODS AND RESULTS

To evaluate the reliability of NICaS derived CO (NI-CO), 50 CO measurements were taken simultaneously with thermodilution (TD-CO) and modified Fick (Fick-CO) in 35 cardiac patients, with the TD-CO serving as the gold-standard for the evaluation. Overall, 2-tailed Pearson's correlation and Bland-Altman limits of agreement between NI-CO and TD-CO were r=0.91 and -1.06 and 0.68 L/min and between Fick-CO and TD-CO, r=0.80 and -1.52 and 0.88 L/min, respectively. Good correlation was observed in patients with loading conditions altered by nitroglycerin and also in patients with moderate valvular diseases.

CONCLUSION

Agreement between NI-CO and TD-CO is within the boundaries of the FDA guidelines of bio-equivalence. NI-CO is applicable for non-invasive assessment of cardiac function.

Blood volume regulation in donors undergoing intermittent-flow plasmapheresis involving a high extracorporeal blood volume

BACKGROUND

Intermittent-flow plasmapheresis (IFP) often involves a large extracorporeal blood volume (ECV) of donors during donation. Depending on equipment and donor characteristics, ECV can exceed 20 percent of a donor's blood volume (BV). It was the aim of this study to delineate mechanisms of BV regulation associated with these volume shifts.

STUDY DESIGN AND METHODS

Parameters of BV regulation were recorded in 60 donors (30 men, 30 women) undergoing IFP, who were randomly selected after stratification for sex and BV. Shock index (SI), stroke volume (SV), cardiac index (CI), and thoracic fluid content (TFC) were determined at the beginning of the procedure and when maximum ECV (ECV(max)) was reached with noninvasive techniques. In a control investigation, donors were kept in reclined position for the duration of an IFP session without actually donating.

RESULTS

SI increased significantly during IFP (+0.18; p < 0.0001). SV decreased significantly (-14.3 mL/stroke; p < 0.0001). CI did not decrease significantly (-0.07 L/min/m(2) body surface area; p = 0.33). Preservation of CI was due to a significant rise in heart rate (+13.4 beats/min; p < 0.0001). TFC decreased significantly during IFP (-0.77 kOmega(-1); p < 0.0001), indicating the development of an intravascular volume deficit. The changes of SI, heart rate, and TFC weakly correlated with ECV(max).

CONCLUSION

The hemodynamic response during IFP is consistent with a hypovolemic challenge of the donors and is sufficient to maintain cardiac function. ECV(max) during donation does not reliably predict the degree of hypovolemic stress, as long as it remains below 20 percent. This might warrant reevaluation of collection limits based on ECV(max).