OptiVol for Volume Assessment in Patients With Continuous Flow Left Ventricular Assist Device.

OptiVol (Medtronic PLC, Minneapolis, MN) is a diagnostic feature of some cardiac implantable electronic devices (CIEDs) based on changes in thoracic impedance (TI) over time. Changes in TI can predict heart failure (HF) hospitalizations and mortality in HF populations. However, the utility of this feature is unknown in patients with a left ventricular assist device (LVAD). To determine if OptiVol and TI correlate with clinical HF events in a population of LVAD patients, hospitalization outcomes were collected retrospectively from the electronic health records at a single academic medical center in 80 LVAD patients with an OptiVol-capable CIED. Demographics, medical history, and available clinical data were reviewed and reported. The primary outcomes of interest were TI and OptiVol trends before and after hospitalization, and association of trends before and after these events was evaluated. Most patients had a HeartMate II LVAD and most CIEDs were defibrillators, and 23 (29%) had at least one HF hospitalization during the study period. HF hospitalizations were preceded by signs of volume overload in Optivol (60%) and TI (78%) with recovery of these measures post hospitalization in 33% and 25% of patients, respectively. Monitoring of TI and OptiVol may be one effective component of HF management in LVAD patients as part of a comprehensive program.

Dual impedance cardiography: An inexpensive and reliable method to assess arterial stiffness.

Pulse wave velocity (PWV) is a common measure of arterial stiffness. Non-invasive methods to measure PWV are widely used in biomedical studies of aging and cardiovascular disease, but they are rarely used in psychophysiology. Barriers to wider use include the prohibitive costs of specialized equipment and need for trained technicians (e.g., ultrasonographers). Here, we describe an impedance cardiography method to measure PWV. By this method, impedance signals are dually collected from the thorax and calf. Combined with ensemble averaging of vascular signals, this dual impedance cardiography (d-ICG) method allows for the measurement of aortic flow onset and the arrival time of peripheral pulse waveforms to compute PWV. In a community sample of adults (aged 19-78 years), PWV measured with d-ICG exhibited a strong positive correlation with age. Moreover, age-specific mean PWV values were within the normative reference intervals established by large scale studies using other techniques. PWV derived from d-ICG exhibited high test-retest reliability across several days, as well as excellent inter-rater reliability. Last, PWV exhibited expected associations with known cardiovascular disease risk factors and indicators of autonomic cardiovascular control. d-ICG is an inexpensive and reliable method to assess arterial stiffness.

Can bioimpedance cardiography assess hemodynamic response to passive leg raising in critically ill patients: A STROBE-compliant study.

ABSTRACT: Passive leg raising (PLR) is a convenient and reliable test to predict fluid responsiveness. The ability of thoracic electrical bioimpedance cardiography (TEB) to monitor changes of cardiac output (CO) during PLR is unknown.In the present study, we measured CO in 61 patients with shock or dyspnea by TEB and transthoracic echocardiography (TTE) during PLR procedure. Positive PLR responsiveness was defined as the velocity-time integral (VTI) ≥10% after PLR. TTE measured VTI in the left ventricular output tract. The predictive value of TEB parameters in PLR responders was tested. Furthermore, the agreement of absolute CO values between TEB and TTE measurements was assessed.Among the 61 patients, there were 28 PLR-responders and 33 non-responders. Twenty-seven patients were diagnosed with shock and 34 patients with dyspnea, with 55.6% (15/27) and 54.6% (18/34) non-responders, respectively. A change in TEB measured CO (ΔCO) ≥9.8% predicted PLR responders with 75.0% sensitivity and 78.8% specificity, the area under the receiver operating characteristic curve (AUROC) was 0.79. The Δd2Z/dt2 (a secondary derivative of the impedance wave) showed the best predictive value with AUROC of 0.90, the optimal cut point was -7.1% with 85.7% sensitivity and 87.9% specificity. Bias between TEB and TTE measured CO was 0.12 L/min, and the percentage error was 65.8%.TEB parameters had promising performance in predicting PLR responders, and the Δd2Z/dt2 had the best predictive value. The CO values measured by TEB were not interchangeable with TTE in critically ill settings.

Modified electrode placements for measurement of hemodynamic parameters using impedance cardiography.

Measuring and monitoring hemodynamic parameters has brought many benefits in supporting diagnosis and treatment for cardiovascular patients. There are many advantages to measuring hemodynamic parameters by non-invasive technique based on impedance cardiography (ICG) such as simplicity, real-time and low cost. However, the electrode positions of this method are very difficult to implement in cases where the patient has to use multiple medical devices at the same time, especially for patients on active treatment and resuscitation. This paper presents the results of the study proposing new three locations of ICG electrodes to overcome the above limitation. Accordingly, we measured and evaluated 10 volunteers on the Niccomo device. The results show that all three positions of proposed electrode can be used to replace standard electrode position. In particular, the 1st proposed position, can be used to measure all five hemodynamic parameters HR, SV, LVET, Zo, CO and ICG waveforms, expressed by the average correlation and the relative average difference of five parameters, R 2 ¯ = 0.9641 and Mean ¯ = 3.31%. The 2nd proposed position can be used to measure four parameters HR, SV, LVET, CO and ICG waveforms shown by R 2 ¯ = 0.9091 and Mean ¯ = 8.67%. The 3rd proposed position can be used to measure three parameters HR, Zo and LVET, expressed by R 2 ¯ = 0.8485 and Mean ¯ = 9.26%.

Increased respiratory disturbance index measured using an advanced device algorithm is associated with heart failure development.

Previous studies suggested that sleep-disordered breathing was associated with cardiovascular diseases such as heart failure (HF). Recently, algorithms of cardiac implantable electronic devices (CIEDs) have been developed to detect advanced sleep apnea (SA); the Apnea Scan (AP Scan) being an example. The purpose of this study was to investigate the association between respiratory disturbance index (RDI) measured using the AP Scan algorithm and HF development. We retrospectively studied consecutive patients with CIEDs equipped with the AP Scan algorithm which were implanted between December 1, 2011 and March 31, 2019. These patients were divided into 2 groups according to the trends of RDI: patients with a continually high RDI > 30 (severe SA group) and those without a continually high RDI (non-severe SA group). There were 16 and 46 patients in the severe and non-severe SA groups, respectively. Increased left ventricular end-diastolic and end-systolic dimensions were observed in the severe SA group. Regarding cardiovascular events, HF was observed in 8 patients (50.0%) in the severe SA group and 1 patient (2.2%) in the non-severe SA group; thus, there was a significantly higher proportion of patients with HF in the severe SA group. In conclusion, continually high RDI was associated with HF development in patients with CIEDs equipped with the AP Scan algorithm. Therefore, an elevated RDI may be a risk factor for the development of HF in patients with CIEDs.

Validity analysis of respiratory events of polysomnography using a plethysmography chest and abdominal belt.

PURPOSE: Respiratory inductive plethysmography (RIP) is recommended as an alternative respiratory sensor for the identification of each apnea and hypopnea event in polysomnography. Using this sensor, the cumulative RIP results from the chest and abdomen (RIP sum) and time-derived results of the RIP sum (RIP flow) are calculated to track respiratory flow. However, the effectiveness of this sensor and the calculated respiratory results is still unclear, and validation studies for the scoring of respiratory events in polysomnography are rare. METHODS: Two hundred subjects were selected according to the severity of obstructive sleep apnea. A sleep specialist re-evaluated the respiratory events based on RIP flow data in a single-blind study. Statistical analysis was conducted with paired respiratory events scored in each of the RIP flow and polysomnography datasets. RESULTS: All respiratory events scored from the RIP flow were strongly correlated with those identified with standard sensors of polysomnography, regardless of disease severity. Most of the respiratory parameters from RIP flow trended toward underestimation. The RIP flow obtained from the alternative RIP sensor was appropriate for the diagnosis of obstructive sleep apnea based on a receiver operating characteristic curve. CONCLUSIONS: Scored respiratory events from RIP flow data effectively reflected the respiratory flow and statistically correlated with the results from standard polysomnography sensors. Therefore, analyzing RIP flow utilizing an RIP sensor is considered a reliable method for respiratory event scoring.

Evaluation of thoracic impedance trends for implant-based remote monitoring in heart failure patients - Results from the (J-)HomeCARE-II Study.

AIMS: Remote monitoring by implantable devices substantially improves management of heart failure (HF) patients by providing diagnostic day-to-day data. The use of thoracic impedance (TI) as a surrogate measure of fluid accumulation is still strongly debated. The multicenter HomeCARE-II study evaluated clinically apparent HF events in the context of remote device diagnostics, focusing on the controversial role of TI. METHODS AND RESULTS: We followed 497 patients (66.6 ±â€¯10.1 years, 77% male, QRS 139.8 ±â€¯36.0 ms, ejection fraction 26.8 ±â€¯7.0%) implanted with a CRT-D (67%) or an ICD (33%) for 21.4 ±â€¯8.1 months. An independent event committee confirmed 171 HF events of which 82 were used to develop a TI-based algorithm for the prediction of imminent cardiac decompensation. Highly inter-individual variations in patterns of TI trends were observed. The algorithm resulted in a sensitivity of 41.5% (50.0%) with 0.95 (1.34) false alerts per patient year, and a positive predictive value of 7.9% overall and 27.9% in the HF event group of patients. Averaged ratio statistics showed a significant pre-hospital decrease and a highly significant in-hospital increase in TI after intensified diuresis. Recurrent decompensations turned out to be preceded by a significantly stronger decrease of TI compared to first events with a higher chance for detection (63.6% sensitivity, p < 0.05). CONCLUSIONS: Overall performance in predicting imminent decompensation by monitoring TI alone is limited due to its high inter-patient variability. TI stand-alone applications should be redirected towards a target population with more advanced symptoms where post-hospital observation aimed to maintain the patient's discharge status might be the most valuable approach. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov Identifier NCT00711360 (HomeCARE-II) and NCT01221649 (J-HomeCARE-II).

A novel technique to assess the quality of ventilation during pre-hospital cardiopulmonary resuscitation.

BACKGROUND: Devices that measure ventilation in the pre-hospital setting are deficient especially during early cardiopulmonary resuscitation (CPR) before placement of an advanced airway. Consequently, evidence is limited regarding the role of ventilation during early CPR and its effect on outcomes. OBJECTIVE: To develop software that automatically identifies ventilation waveforms recorded by defibrillators based on changes in transthoracic impedance during standard CPR. METHODS: This was an observational, retrospective analysis of non-traumatic pre-hospital cardiac arrest patients who received 30:2 CPR by emergency medical service rescuers. Data was collected from 550 cases recorded by the bioimpedance channel of defibrillators. Two expert clinicians independently assessed all episodes from the time of initial CPR until placement of an advanced airway, defined acceptable ventilation waveforms, and annotated the pauses between compressions with ventilation waveforms. We then developed software that incorporated the expert criteria and automatically annotated pauses with acceptable ventilations. RESULTS: A total of 7396 pauses were analyzed, mean(SD) duration of 30:2 CPR was 13 (8) min, with 13 (10) pauses/patient, and mean pause duration of 6 (3) s. Reviewer 1 and reviewer 2 identified 2375 and 2249 pauses with any acceptable ventilation, respectively, with an inter-rater reliability of 0.94. The novel software program reproduced expert annotation with excellent agreement (>0.8) and high accuracy, both sensitivity and specificity above 90%, compared to two reviewers. The software presented a substantial agreement with the reviewers (κ > 0.73) for ventilation counts in the pauses. CONCLUSION: We developed a novel and reliable strategy that enables investigation of ventilation quality during standard CPR using thoracic bioimpedance. This strategy would allow a timely and reliable automatic annotation of large scale resuscitation datasets.

Full Impedance Cardiography measurement device using Raspberry PI3 and System-on-Chip biomedical Instrumentation Solutions.

Impedance Cardiography (ICG) is a non-invasive method for monitoring cardiac dynamics using Electrical Bioimpedance (EBI) measurements. Since its appearance more than 40 years ago, ICG has been used for assessing hemodynamic parameters. This paper present a measurement system based on two System on Chip (SoC) solutions and Raspberry PI, implementing both a full 3-lead ECG recorder and an impedance cardiographer, for educational and research development purposes. Raspberry PI is a platform supporting Do-It-Yourself project and education applications across the world. The development is part of Biosignal PI, an open hardware platform focusing in quick prototyping of physiological measurement instrumentation. The SoC used for sensing cardiac biopotential is the ADAS1000, and for the EBI measurement is the AD5933. The recording were wirelessly transmitted through Bluetooth to a PC, where the waveforms were displayed, and hemodynamic parameters such as heart rate, stroke volume, ejection time and cardiac output were extracted from the ICG and ECG recordings. These results show how Raspberry PI can be used for quick prototyping using relatively widely available and affordable components, for supporting developers in research and engineering education. The design and development documents, will be available on www.BiosignalPI.com, for open access under a Non Commercial-Share A like 4.0 International License.

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.

Estado actual de la hemodinamia no invasiva en hipertensión arterial / Current status of noninvasive hemodynamics in hypertension

La hipertensión arterial es un trastorno hemodinámico que resulta de un desajuste persistente entre el volumen minuto cardíaco y la resistencia periférica. La hipertensión arterial experimenta una progresión hemodinámica durante su historia natural. La cardiografía por impedancia es un método de evaluación del aparato cardiovascular que obtiene información hemodinámica latido a latido a través del análisis de las variaciones de la impedancia del tórax al paso de una corriente eléctrica. La cardiografía de impedancia desenmascara el deterioro hemodinámico subyacente al incremento de la presión arterial conforme aumenta la edad y la presión arterial sistólica. Este método puede ayudar a mejorar el control tensional a través del tratamiento individualizado con reducción de la resistencia periférica, el mantenimiento del volumen minuto cardíaco o su aumento, de encontrarse bajo, la mejoría de la complacencia arterial y la preservación de la perfusión órgano-tisular. Es útil en el manejo de los pacientes con hipertensión resistente, dado que se logra un mayor porcentaje de pacientes controlados con cambios en el tratamiento con relación a las mediciones hemodinámicas. La cardiografía por impedancia tiene importancia y utilidad pronóstica en relación con el patrón de deterioro hemodinámico y el incremento de eventos cardiovasculares (AU)

Hypertension is a haemodynamic disorder resulting from a persistent mismatch between cardiac output and peripheral resistance. Hypertension undergoes haemodynamic progression during its natural history. Impedance cardiography is a method of evaluating the cardiovascular system that obtains haemodynamic information from beat to beat through the analysis of variations in the impedance of the thorax on the passage of an electric current. Impedance cardiography unmasks the haemodynamic deterioration underlying the increase in blood pressure as age and systolic blood pressure increases. This method may help to improve blood pressure control through individualized treatment with reduction of peripheral resistance, maintenance of cardiac output or its increase, improvement of arterial compliance and preservation of organ-tissue perfusion. It is useful in the management of patients with resistant hypertension, since a greater percentage of patients controlled with changes in the treatment in relation to the haemodynamic measurements are obtained. Impedance cardiography is important and has prognostic utility in relation to a haemodynamic deterioration pattern and increased cardiovascular events (AU)

Validation of non-invasive haemodynamic methods in patients with liver disease: the Finometer and the Task Force Monitor.

Patients with advanced cirrhosis often present a hyperdynamic circulation characterized by a decrease in systolic and diastolic blood pressure (SBP and DBP), and an increase in heart rate (HR) and cardiac output (CO). Accurate assessment of the altered circulation can be performed invasively; however, due to the disadvantages of this approach, non-invasive methods are warranted. The purpose of this study was to compare continuous non-invasive measurements of haemodynamic variables by the Finometer and the Task Force Monitor with simultaneous invasive measurements. In 25 patients with cirrhosis, SBP, DBP and HR were measured non-invasively and by femoral artery catheterization. CO was measured non-invasively and by indicator dilution technique. The non-invasive pressure monitoring was considered acceptable with a bias (accuracy) and a SD (precision) not exceeding 5 and 8 mmHg, respectively, as recommended by the Association for the Advancement of Medical Instrumentation. The accuracy and precision of the Finometer and the Task Force Monitor were as follows: SBP: -3·6 ± 17·9 and -8·9 ± 17·5 mmHg, respectively; DBP: 4·2 ± 9·6 and 1·9 ± 8·6 mmHg, respectively; HR: 2·0 ± 6·9 and 2·2 ± 6·2 bpm, respectively; and CO: 0·1 ± 1·6 and -1·0 ± 2·0 L min-1 , respectively. The study demonstrates that the overall performances of the Finometer and the Task Force Monitor in estimating absolute values of SBP, DBP, HR and CO in patients with cirrhosis are not equivalent to the gold standard, but may have an acceptable performance with repeated measurements.

Refined heart failure detection algorithm for improved clinical reliability of OptiVol alerts in CRT-D recipients.

BACKGROUND: The reliability of intrathoracic impedance monitoring for prediction of heart failure (HF) by implantable cardiac devices is controversial. Despite using additional device-based parameters described in the PARTNERS HF study, such as new onset of arrhythmias, abnormal autonomics, low biventricular pacing rate or patient activity level, the predictive power of device diagnostic algorithm is still in doubt. The objective of this study was to compare the device diagnostic algorithm described in the PARTNERS HF study to a newly developed algorithm applying refined diagnostic criteria. METHODS: Fourty two patients were prospectively enrolled who had been implanted with an intrathoracic impedance and remote monitoring capable implantable cardiac defibrillator with a cardiac resychroniza-tion therapy (CRT-D) device in this observational study. If a remote OptiVolTM alert occurred, patients were checked for presence of HF symptoms. A new algorithm was derived from the original PARTNERS HF criteria, considering more sensitive cut-offs and changes of patterns of the device-based parameters. RESULTS: During an average follow-up of 38 months, 722 remote transmissions were received. From the total of 128 transmissions with OptiVol alerts, 32 (25%) corresponded to true HF events. Upon multivariate discriminant analysis, low patient activity, high nocturnal heart rate, and low CRT pacing (< 90%) proved to be independent predictors of true HF events (all p < 0.01). Incorporating these three refined criteria in a new algorithm, the diagnostic yield of OptiVol was improved by increasing specific-ity from 37.5% to 86.5%, positive predictive value from 34.1% to 69.8% and area under the curve from 0.787 to 0.922 (p < 0.01), without a relevant loss in sensitivity (96.9% vs. 93.8%). CONCLUSIONS: A refined device diagnostic algorithm based on the parameters of low activity level, high nocturnal heart rate, and suboptimal biventricular pacing might improve the clinical reliability of OptiVol alerts.

Diagnostic power and healthcare resource consumption of a dedicated workflow algorithm designed to manage thoracic impedance alerts in heart failure patients by remote monitoring.

PURPOSE: Modern cardiac implantable devices provide diagnostic information on several physiological variables which are associated with worsening heart failure, creating an opportunity for early intervention to prevent heart failure symptoms and hospitalizations. We evaluated diagnostic accuracy and workload of a remote monitoring (RM) workflow algorithm which leverages intrathoracic impedance and other device diagnostics. METHODS: In our RM workflow a team of expert nurses was responsible for continuity of care, direct relationship with patients and implementation of a specific protocol to evaluate RM alerts and to limit unnecessary resource consumption. Each patient was univocally assigned to a reference nurse. End points were diagnostic accuracy, healthcare utilization, defined as any hospital admission, and actionability of alerts, defined as medication change or other clinical action. RESULTS: One-hundred twenty-six consecutive patients with implantable cardioverter defibrillator/cardiac resynchronization therapy defibrillator were followed for a median time of 23 months. Out of 2176 remote transmissions, 893 (41%) in 111 patients (88.1%) showed clinically relevant events triggered by 574 alerts [2.2 (95% confidence interval = 2.0-2.4) per patient per year]. Among 309 alerts with intrathoracic impedance crossing, heart failure deterioration was confirmed in 116 (37.5%). Clinical actions followed 76/116 (65.5%) true heart failure alerts and 17/193 (8.8%) false-positive alerts (P < 0.001). In particular, drug therapy change followed 72/116 (62.1%) true heart failure alerts and 15/193 (7.8%) false-positive alerts (P < 0.001). Healthcare utilization occurred in 65.5% true heart failure alerts and in 24.9% false-positive alerts (P < 0.001). CONCLUSION: A dedicated workflow algorithm results in more focused clinical surveillance leading to prompt detection and treatment of acute heart failure events without wasting healthcare resource.

Pacemaker-detected severe sleep apnea predicts new-onset atrial fibrillation.

AIMS: Sleep apnea (SA) diagnosed on overnight polysomnography is a risk factor for atrial fibrillation (AF). Advanced pacemakers are now able to monitor intrathoracic impedance for automatic detection of SA events. METHODS AND RESULTS: We enrolled 160 consecutive recipients of a dual-chamber pacemaker endowed with the ApneaScan algorithm (Boston Scientific). If the pacemaker-measured Respiratory Disturbance Index was ≥30 episodes per hour for at least one night during the first week after implantation, SA was defined as severe. Patients were considered to have experienced AF episodes if the device detected a cumulative AF burden ≥6 h in a day. Sixteen patients in AF at the time of implantation were excluded from our analysis. During follow-up, AF burden ≥6 h/day was documented in 35 (24%) of the patients included in the analysis and in 12 (13%) of the 96 patients with no history of AF. Severe SA was detected in 89 patients during the first week after implantation; 58 of these had no history of AF. Severe SA at the baseline was associated with a higher risk of AF both in the whole population (log-rank test, hazard ratio: 2.38; 95% CI: 1.21-4.66; P = 0.025) and among patients with no previous history of AF (log-rank test, hazard ratio: 2.80; 95% CI: 1.10-7.10; P = 0.047). Moreover, severe SA at the time of follow-up device interrogation predicted AF occurrence within the next 3 months (log-rank test, hazard ration: 2.13; 95% CI: 1.11-4.08; P = 0.036). CONCLUSIONS: In pacemaker patients, device-diagnosed severe SA was independently associated with a higher risk of AF (≥6 h/day) and new-onset AF. In particular, severe SA on follow-up data review identified patients who were ∼2-fold more likely to experience an AF episode in the next 3 months.

Blood Pressure Estimation Using Pulse Transit Time From Bioimpedance and Continuous Wave Radar.

OBJECTIVE: We have developed and tested a new architecture for pulse transit time (PTT) estimation at the central arteries using electrical bioimpedance, electrocardiogram, and continuous wave radar to estimate cuffless blood pressure. METHODS: A transmitter and receiver antenna are placed at the sternum to acquire the arterial pulsation at the aortic arch. A four-electrode arrangement across the shoulders acquires arterial pulse across the carotid and subclavian arteries from bioimpedance as well as a bipolar lead I electrocardiogram. The PTT and pulse arrival times (PATs) are measured on six healthy male subjects during exercise on a bicycle ergometer. Using linear regression, the estimated PAT and PTT values are calibrated to the systolic and mean as well as diastolic blood pressure from an oscillometric device. RESULTS: For all subjects, the Pearson correlation coefficients for PAT-SBP and PTT-SBP are -0.66 (p = 0.001) and -0.48 (p = 0.0029), respectively. Correlation coefficients for individual subjects ranged from -0.54 to -0.9 and -0.37 to -0.95, respectively. CONCLUSION: The proposed system architecture is promising in estimating cuffless arterial blood pressure at the central, proximal arteries, which obey the Moens-Korteweg equation more closely when compared to peripheral arteries. SIGNIFICANCE: An important advantage of PTT from the carotid and subclavian arteries is that the PTT over the central elastic arteries is measured instead of the peripheral arteries, which potentially reduces the changes in PTT due to vasomotion. Furthermore, the sensors can be completely hidden under a patients clothes, making them more acceptable by the patient for ambulatory monitoring.

Non-invasive measurement of cardiac output using AESCULON® mini after Fontan operation.

BACKGROUND: Electrical velocimetry correlates well with established methods of measuring cardiac output (CO) such as thermodilution and echocardiography. In this study, we compared the cardiac function of children with single right ventricle (SRV) and single left ventricle (SLV) on non-invasive postoperative measurement of hemodynamic parameters using AESCULON® mini. METHODS: Demographic, preoperative, and perioperative data were obtained from medical records. We retrospectively reviewed the AESCULON mini data of 21 patients with single ventricle who underwent Fontan operation. The patients were divided into two groups according to morphologic diagnosis: SRV (n = 9) and SLV (n = 12). The following hemodynamic parameters were analyzed: stroke volume (SV); CO; cardiac index (CI); stroke volume variation (SVV); and ventricular ejection time (VET). RESULTS: Hemodynamic parameters were as follows (SRV vs SLV): heart rate (HR), 140.5 beats/min versus 121 beats/min; SV, 14.5 mL vs 19.9 mL; CO, 2 L/min vs 2.3 L/min; CI, 4.3 L/min/m2 versus 4.4 L/min/m2 ; SVV, 15.5% versus 13.9%; and VET, 167.7 s versus 197.7 s. HR and VET were statistically different between the two groups. CONCLUSIONS: CI does not differ with laterality of the single ventricle. SRV VET, however, was significantly shorter than SLV VET in the acute postoperative period. Conversely, SRV HR was higher than SLV HR, which may mean that SRV compensates for lower VET by increasing HR.

Monitoring of Daily Body Weight and Intrathoracic Impedance in Heart Failure Patients With a High Risk of Volume Overload Decompensation.

BACKGROUND: Decompensation is frequent in heart failure (HF) patients and predicts poor prognosis. HYPOTHESIS: Volume-overload events in HF patients are preceded by changes in intrathoracic impedance (Z) and body weight (BW); monitoring these parameters may be useful to predict decompensation. METHODS: Forty-three HF patients (LVEF 25% ± 12%) with a recent HF event and an implantable cardioverter-defibrillator providing daily Z were equipped with telemonitoring scales submitting daily BW. Changes in BW and Z 30 days prior to major (HF hospitalization) and minor (ambulatory adjustment of diuretics) were analyzed. RESULTS: During median of 427 days follow-up 25 major and 41 minor events occurred. Z decreased by -4.8 (95% confidence interval [CI]: CI -6.7 to -3.0) and -4.3 (95% CI: -5.5 to -3.2) within 30 days prior to major and minor events respectively (P < 0.001). BW increased before major events by 2.3 kg (95% CI: 1.0 to 3.5, P < 0.01) and minor events 1 kg (95% CI: 0.5 to 1.4, P < 0.001). Sensitivity of Z for major/minor HF events was 83.3% (95% CI: 71.7 to 91.0) and for BW 43.9% (95% CI: 31.9 to 56.7). The unexplained detection rate per patient-year was 1.6 (interquartile range [IQR], 0-3.1) for Z and 4.8 (IQR 1.6-11.1) for BW. Combined Z and BW sensitivity was 42.4% (95% CI: 30.6 to 55.2) and unexplained detection rate was 0.8 (IQR, 0-1.5) per patient-year. CONCLUSIONS: Decompensation is marked by a decrease in Z and increase in BW the preceding 30 days. Monitoring of Z predicts HF decompensations with better sensitivity and lower unexplained detection rate than BW.

Evaluating the clinical value of oscillatory cardiopulmonary coupling in patients with obstructive sleep apnea hypopnea syndrome by impedance cardiogram.

OBJECTIVES: For patients with obstructive sleep apnea hypopnea syndrome (OSAHS), chronic inflammation and hemodynamic oscillations caused by respiratory events contribute to cardiovascular disease (CVD). In this study, a physiological marker named oscillatory coupling factor (OCF) exacted from cardiac output (CO) was introduced. This study aimed to evaluate the clinical value of OCF and tentatively explore its predictive value of cardiovascular prognosis in OSAHS patients. METHODS: An impedance cardiogram (ICG) was used to continuously obtain the participants' CO with simultaneous polysomnography. Participants were divided into three groups: an OSAHS-CVD- group (n = 19); an OSAHS + CVD- group (n = 34); and an OSAHS + CVD + group (n = 36). The OCF was exacted from the CO by using empirical mode decompensation-based detrended fluctuation analysis (EMD-DFA). RESULTS: The OCF values were: OSAHS + CVD + group [1.20 (0.98-1.78)] > OSAHS + CVD- group [1.14 (1.02-1.94)] > OSAHS-CVD- group [0.95 (0.56-1.16)], (p = 0.001). A Spearman test showed that OCF was positively correlated with age, apnea/hypopnea index (AHI), microarousal index (MAI), oxygen desaturation index (ODI), and negatively correlated with the lowest SpO2. Ten participants were treated by one-night continuous positive airway pressure (CPAP): their AHI decreased from 44.9 (18.0-72.9)/hour to 1.25 (0.0-7.5)/hour, and their OCF fell from 1.17 (1.10-1.69) to 1.08 (0.96-1.23) (p = 0.038). Seventy-seven participants were effectively followed up. Seven participants developed CVD events or newly diagnosed CVD; their OCFs were distributed on a relatively high level [1.18 (1.01-1.56)]. CONCLUSION: The OSAHS participants had higher OCFs than those without OSAHS, while CVD made the OCFs even higher; CPAP could rectify this change. Oscillatory coupling factor may be a physiological marker of cardiopulmonary coupling and have potential cardiovascular prognostic value for people with OSAHS.

Evaluation of a method utilizing PhysioFlow®, a novel signal morphology-based form of impedance cardiography, to measure cardiac output in the conscious beagle.

INTRODUCTION: Currently, standard methods for measuring cardiac output are either invasive (i.e. flow probe) or are limited in terms of short measurement intervals and measurement variability (i.e. echocardiography). The ability to reliably measure cardiac output in a non-invasive manner in large animals would provide a valuable tool to expand functional cardiovascular endpoints in preclinical safety studies. PhysioFlow® is a novel method that uses waveform analysis of an impedance signal to measure cardiac output non-invasively. Unlike cardiac impedance techniques in the past, PhysioFlow® is not dependant on thoracic structure or basal thoracic impedance (Z0) and therefore this methodology is transferrable from human to animal models. METHODS: Three tool compounds with known effects on cardiac output were administered to conscious beagle dogs to determine if the non-invasive PhysioFlow® system could detect the expected changes in stroke volume and cardiac output as determined by literature references using the current standard methodologies (e.g. aortic blood flow and thermodilution). RESULTS: The PhysioFlow® system was able to detect increases in cardiac output when dosed with 20µg/kg of Dobutamine, a decrease in cardiac output when dosed with 0.1mg/kg of Acepromazine, and no significant change in cardiac output when dosed with 2mg/kg of Minoxidil. These results are within expected ranges based on published literature (Stepien et al., 1995; Taylor et al., 2007). DISCUSSION: PhysioFlow®, a signal morphology-based impedance cardiography, can be utilized to reliably and non-invasively measure cardiac output in beagle dogs.