Thoracic Impedance Research Articles

A Comparison of Cardiac Output by Thoracic Impedance and Direct Fick in Children With Congenital Heart Disease Undergoing Diagnostic Cardiac Catheterization

To evaluate the measurement of cardiac output (CO) using continuous electrical bioimpedance cardiography (Physioflow; Neumedx, Philadelphia, PA) (CO(PF)) with a simultaneous direct Fick measurement (CO(FICK)) in children with congenital heart disease. A prospective cohort study comparing 2 methods of measurement of CO. A quaternary university-affiliated pediatric hospital. Children undergoing cardiac catheterization for clinical care. The Physioflow measured continuous real time CO in 15-second epochs and simultaneous measurement of cardiac output by direct Fick (with mass spectrometry to assess VO(2)) were acquired. Sixty-five patients were recruited, and data from 56 (25 males) were adequate for analysis. The median age at study was 3.5 years (range, 0.4-16.6 years), and the median body surface area was 0.62 m(2) (range, 0.31-1.71). There were 25 of 56 (45%) with univentricular physiology. A total of 19,228 Physioflow data points were available for the analysis of which 14,569 (76%) were valid; 96% of the invalid measurements were identified as artifacts by the device. The average cardiac index of valid measurements was 3.09 ± 0.72 L/min/m(2). Compared with the Fick CO, the mean bias was -0.09 L/min, but the 95% limits of agreement were -3.20 to +3.01 L/min/m(2). Consequently, only 20 of 56 (36%) of measurements were within 20%, and 31 of 56 (55%) of measurements were within 30% of each other. Compared with measurements made by direct Fick, CO measured using the Physioflow device was unreliable in anesthetized children with congenital heart disease.

Studies on separating the impedance change components of blood vessels and ventricles in thorax from mixed impedance signals on chest surface

The aim of the present study is to separate the impedance change components of the blood vessels and ventricles in thorax from the mixed impedance signals detected on the chest surface. The mixed impedance signals on the chest surface are measured with a 15 electrode lead system. The thoracic impedance equations are established and solved iteratively with the algebraic reconstructed technique. Experiments were performed on 80 healthy, otherwise normal, adults. Five impedance change components for the aorta (AO), blood vessel in left lung (PL), blood vessel in right lung (PR), left ventricle (LV), and right ventricle (RV) are separated from the mixed impedance signals. The experiments show that the main waveform of the ventricular components LV and RV is contrary to that of the vascular components AO, PL, and PR, and the negative peak point of the waveform graphs of LV and RV are in phase with the second cardiac sound (S2). The waveform graphs of various components correspond with the physiological activities of the heart and blood vessels in a cardiac cycle. The statistical results for 80 normal adults show that the amplitude of AO is the largest and that of PL and PR is the next, while that of LV and RV is the smallest. There are significant differences between them (P < 0.01). The mathematical model and the measurement method for the separation in the present paper are feasible.

Poor Sleep and Cardiovascular Function in Children

We investigated whether sleep quantity and quality were related to 24-hour ambulatory blood pressure and cardiovascular reactivity in children. We studied term-born, healthy 8.0-year olds (SD: 1.4 years) without sleep-disordered breathing (231 and 265 children provided valid data for analyses of ambulatory blood pressure and cardiovascular reactivity, respectively). Sleep was registered with an actigraph for 6 nights on average (SD: 1.2; range: 3 to 13 nights). Ambulatory blood pressure was measured for 24-hours (41% nonschool days) with an oscillometric device. The children underwent the Trier Social Stress Test for Children, during which blood pressure, electrocardiography, and thoracic impedance were recorded and processed offline to give measures of cardiovascular and autonomic function. Neither quantity nor quality of sleep was related to 24-hour ambulatory blood pressure or cardiovascular reactivity after accounting for major covariates (sex, age, height, body mass index, and parental education). Although lower sympathetic nervous system activation and higher cardiac activation under stress were found in the group of children who slept for short duration when they were compared with the average sleep duration group, these associations were not significant after correction for multiple testing and were not seen in linear regression models of the effects of sleep duration. These findings do not support the mainstream of epidemiological findings, derived from samples more heterogeneous in age, sociodemographic characteristics, and health, suggesting that poor sleep is associated with an unhealthy cardiovascular phenotype.

Evaluation of central hemodynamics by means of independent component analysis of thoracic impedance signal

Evaluation of central hemodynamics by means of independent component analysis of thoracic impedance signal

Usefulness of Hemodynamic Sensors for Physiologic Cardiac Pacing in Heart Failure Patients

The rate adaptive sensors applied to cardiac pacing should respond as promptly as the normal sinus node with an highly specific and sensitive detection of the need of increasing heart rate. Sensors operating alone may not provide optimal heart responsiveness: central venous pH sensing, variations in the oxygen content of mixed venous blood, QT interval, breathing rate and pulmonary minute ventilation monitored by thoracic impedance variations, activity sensors. Using sensors that have different attributes but that work in a complementary manners offers distinct advantages. However, complicated sensors interactions may occur. Hemodynamic sensors detect changes in the hemodynamic performances of the heart, which partially depends on the autonomic nervous system-induced inotropic regulation of myocardial fibers. Specific hemodynamic sensors have been designed to measure different expression of the cardiac contraction strength: Peak Endocardial Acceleration (PEA), Closed Loop Stimulation (CLS) and TransValvular Impedance (TVI), guided by intraventricular impedance variations. Rate-responsive pacing is just one of the potential applications of hemodynamic sensors in implantable pacemakers. Other issues discussed in the paper include: hemodynamic monitoring for the optimal programmation and follow up of patients with cardiac resynchronization therapy; hemodynamic deterioration impact of tachyarrhythmias; hemodynamic upper rate limit control; monitoring and prevention of vasovagal malignant syncopes.

Esophageal Electrical Cardioversion of Atrial Fibrillation: When Esophagus Gives a Help to Cardiologists

Atrial fibrillation is a common clinical disease especially in the elderly and in patients with organic heart disease. Electrical cardioversion is the first choice therapeutic approach for patients in which sinus rhythm could improve the quality of life and where the maintenance of sinus rhythm is considered likely. There are different techniques to perform an electrical cardioversion, each with specific indications, advantages, and limitations. The method most frequently used to restore sinus rhythm is external direct current cardioversion; however, this technique has some disadvantages, since it requires a high energy and usually general anesthesia. Esophageal cardioversion is an alternative method to obtain restoration of sinus rhythm, warranting acute and long-term results absolutely comparable with those obtained by the conventional transthoracic technique, especially in obese and COPD patients with high thoracic impedance for whom the standard technique may be less effective.

A 3.9 mW 25-Electrode Reconfigured Sensor for Wearable Cardiac Monitoring System

A low power highly sensitive Thoracic Impedance Variance (TIV) and Electrocardiogram (ECG) monitoring SoC is designed and implemented into a poultice-like plaster sensor for wearable cardiac monitoring. 0.1 Ω TIV detection is possible with a sensitivity of 3.17 V/Ω and SNR > 40 dB. This is achieved with the help of a high quality (Q-factor > 30) balanced sinusoidal current source and low noise reconfigurable readout electronics. A cm-range 13.56 MHz fabric inductor coupling is adopted to start/stop the SoC remotely. Moreover, a 5% duty-cycled Body Channel Communication (BCC) is exploited for 0.2 nJ/b 1 Mbps energy efficient external data communication. The proposed SoC occupies 5 mm × 5 mm including pads in a standard 0.18 μm 1P6M CMOS technology. It dissipates a peak power of 3.9 mW when operating in body channel receiver mode, and consumes 2.4 mW when operating in TIV and ECG detection mode. The SoC is integrated on a 15 cm × 15 cm fabric circuit board together with a flexible battery to form a compact wearable sensor. With 25 adhesive screen-printed fabric electrodes, detection of TIV and ECG at 16 different sites of the heart is possible, allowing optimal detection sites to be configured to accommodate different user dependencies.

Implantable Sensors for Heart Failure

Heart failure (HF) affects more than 5 million Americans, and acute decompensated heart failure (ADHF) has emerged as the leading cause of hospitalization among people over the age of 65 years.1 Importantly, HF is a leading public health concern, and hospitalization expenses related to management of ADHF impose a substantial financial burden on the health care system. Additionally, readmission rates after hospitalization for ADHF may be as high as 50% at 6 months,2 and insights from the ADHERE registry suggest that a majority of patients admitted with ADHF have a history of heart failure.1 These data demonstrate that the majority of patients admitted with ADHF are known to the medical system and to medical providers, thereby creating an opportunity for upstream strategies that may be capable of detecting early HF destabilization and implementing therapies to restabilize the patient and avert hospitalization. The anticipated changes in the health care system—with a focus on bundled payments for disease management—will necessitate robust disease management programs to optimize therapy and minimize recurrent admissions once patients have been diagnosed with HF. Perhaps even more importantly, averting repeat episodes of ADHF is likely to have a stabilizing effect on the progression of HF and may improve long-term morbidity and mortality. The transition from chronic HF to ADHF involves perturbations in multiple intersecting processes including neurohormonal circuits, inflammatory mediators, cardiorenal interactions, and myocardial performance. Concurrently, derangements in comorbid illnesses such as coronary disease, atrial and ventricular arrhythmias, and hypertension also contribute to the pathophysiology of ADHF.3 Ultimately, these multiple pathways lead to an elevation in ventricular filling pressures and signs of vascular congestion, which, in concert with symptoms from impaired cardiac output, lead to the clinical constellation of ADHF. This pathophysiologic paradigm highlights multiple opportunities for detecting early changes in the processes that …

Influence of training and maturity status on the cardiopulmonary responses to ramp incremental cycle and upper body exercise in girls

It has been suggested that the potential for training to alter the physiological responses to exercise in children is related to a "maturational threshold". To address this, we investigated the interaction of swim-training status and maturity on cardiovascular and metabolic responses to lower and upper body exercise. Twenty-one prepubertal [Pre: 11 trained (T), 10 untrained (UT)], 30 pubertal (Pub: 14 T, 16 UT), and 18 postpubertal (Post: 8 T, 10 UT) girls completed ramp incremental exercise on a cycle and an upper body ergometer. In addition to pulmonary gas exchange measurements, stroke volume and cardiac output were estimated by thoracic bioelectrical impedance, and muscle oxygenation status was assessed using near-infrared spectroscopy. All T girls had a higher peak O(2) uptake during cycle (Pre: T 49 ± 5 vs. UT 40 ± 4; Pub: T 46 ± 5 vs. UT 36 ± 4; Post: T 48 ± 5 vs. UT 39 ± 8 ml·kg(-1)·min(-1); all P < 0.05) and upper body exercise (Pre: T 37 ± 6 vs. UT 32 ± 5; Pub: T 36 ± 5 vs. UT 28 ± 5; Post: T 39 ± 3 vs. UT 28 ± 7 ml·kg(-1)·min(-1); all P < 0.05). T girls also had a higher peak cardiac output during both modalities, and this reached significance in Pub (cycle: T 21 ± 3 vs. UT 18 ± 3; upper body: T 20 ± 4 vs. UT 15 ± 4 l/min; all P < 0.05) and Post girls (cycle: T 21 ± 4 vs. UT 17 ± 2; upper body: T 22 ± 3 vs. UT 18 ± 2 l/min; all P < 0.05). None of the measured pulmonary, cardiovascular, or metabolic parameters interacted with maturity, and the magnitude of the difference between T and UT girls was similar, irrespective of maturity stage. These results challenge the notion that differences in training status in young people are only evident once a maturational threshold has been exceeded.

End-tidal CO2 and invasive cardiac output measurements versus thoracic impedance measurements during mechanical CPR as an indicator of effective CPR in a porcine model of cardiac arrest

Purpose of the study: A number of physiological indicators were explored to determine if ICG amplitude could be used as a determinant of effective CPR to guide lay responders in administering optimized cardiac massage thereby improving survival rates from out of hospital cardiac arrest.Materials and methods: A total of seven porcine models around 52.8 ± 9 kg were used. End-tidal CO2 (ETCO2), Cardiac Output (CO), Carotid Flow and the Impedance Cardiogram (non-invasive measure of cardiac output) were utilized as a basis for detecting the presence of effective CPR. Ethical approval was granted by the Northern Ireland Home Office. Models were anaesthetised using Propofol and Isoflurane and connected to a Datex Ohmeda® monitor. Carotid flow and coronary perfusion pressure were measured via the carotid and thermodilution via the jugular. Recordings from each experiment were acquired using HEM® Notocord software for analysis.Results: ETCO2 levels averaged 23.3 mmHg during CPR compared to the models who did not receive CPR producing values close to of 3 ± 1 mmHg. Cardiac Output values of >22% of the normal CO were achieved which, reported as adequate for ROSC. Carotid Flow increased with depth of CPR. ICG amplitude increased with CO as did ETCO2. The results show that the physiological parameters used were good indicators of CPR efficacy.Conclusions: These findings are potentially significant in the field of resuscitation. An algorithm will incorporate the results from this study, providing feedback to the operator on the quality of CPR by measuring the ICG amplitude which can be correlated to the basic physiological parameters recorded during this study. Purpose of the study: A number of physiological indicators were explored to determine if ICG amplitude could be used as a determinant of effective CPR to guide lay responders in administering optimized cardiac massage thereby improving survival rates from out of hospital cardiac arrest. Materials and methods: A total of seven porcine models around 52.8 ± 9 kg were used. End-tidal CO2 (ETCO2), Cardiac Output (CO), Carotid Flow and the Impedance Cardiogram (non-invasive measure of cardiac output) were utilized as a basis for detecting the presence of effective CPR. Ethical approval was granted by the Northern Ireland Home Office. Models were anaesthetised using Propofol and Isoflurane and connected to a Datex Ohmeda® monitor. Carotid flow and coronary perfusion pressure were measured via the carotid and thermodilution via the jugular. Recordings from each experiment were acquired using HEM® Notocord software for analysis. Results: ETCO2 levels averaged 23.3 mmHg during CPR compared to the models who did not receive CPR producing values close to of 3 ± 1 mmHg. Cardiac Output values of >22% of the normal CO were achieved which, reported as adequate for ROSC. Carotid Flow increased with depth of CPR. ICG amplitude increased with CO as did ETCO2. The results show that the physiological parameters used were good indicators of CPR efficacy. Conclusions: These findings are potentially significant in the field of resuscitation. An algorithm will incorporate the results from this study, providing feedback to the operator on the quality of CPR by measuring the ICG amplitude which can be correlated to the basic physiological parameters recorded during this study.

Part 5: Adult Basic Life Support

Part 8 : Advanced life support : 2010 International Consensus on Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Science With Treatment Recommendations

Modulation of plasma adrenomedullin by epinephrine infusion during head up tilt

We investigated whether head up tilt (HUT) with and without simultaneous epinephrine infusion modulate plasma adrenomedullin. We studied eight healthy male volunteers, using two 5 min 70° HUT trials: control (saline infusion) and intervention (epinephrine infusion, titrated to a dose which increased supine systolic pressure by 20% above resting values). Protocols were randomized and separated by 2 weeks. Cardiac function and systolic time intervals, recorded using a phonocardiograph microphone, included left ventricular ejection time (LVET), pre-ejection period (PEP), PEP/LVET and electromechanical systole (QS2). Compared to saline infusion, epinephrine increased supine adrenomedullin (3.2 ± 0.8 pmol/l, i.e., mean ± SEM, respectively), heart rate (HR) (+11.3 ± 2.6 bpm), systolic pressure (+18.4 ± 2.6 mmHg) but decreased supine LVET, LVET corrected for HR (LVETi) and QS2-time (all p = 0.004). Despite similar HUT induced thoracic fluid shifts, reflected by similar thoracic impedance changes, HUT-induced adrenomedullin increases were minimal in epinephrine-supplemented men in comparison to controls (+8% vs. 42%). During HUT, epinephrine infusion decreased only the LVET (p = 0.039). Our findings confirm that short-term HUT increases plasma adrenomedullin. They further suggest that with increased supine epinephrine levels (epinephrine infusion clamping systolic arterial pressure at 120% control level), supine cardiac performance rises to a level similar to that during HUT, while adrenomedullin is still elevated with HUT. This might be in accordance with a 'dampening' role of adrenomedullin during catecholaminergic cardiovascular stimulation. As epinephrine is used as a drug to treat cardiac arrest and ventricular arrhythmias, our results may have important clinical/emergency resuscitation applications.

Part 5: Adult basic life support: 2010 International consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations

Part 5: Adult basic life support: 2010 International consensus on cardiopulmonary resuscitation and emergency cardiovascular care science with treatment recommendations

3D modelling of the human thorax for ventilation distribution measured through electrical impedance tomography

Thoracic electrical impedance tomography (EIT) aims to reconstruct a cross-sectional image of the internal spatial distribution of conductivity from electrical measurements made by injecting small alternating currents via an electrode array placed on the surface of the thorax. It is a non-invasive, radiation-free monitoring technique. In this paper, true 3D thorax models with conductivity distribution or complex conductivity distribution under different ARDS conditions are built up in comparison with the 2.5D ones, and EIT-derived numeric indices are also employed for evaluation of the lung ventilation. The purpose of this paper is to study different effects of different thorax models with either conductivity or complex conductivity on the reconstructed images and ventilation indices.

Chest Pulse-Wave Velocity: A Novel Approach to Assess Arterial Stiffness

Pulse-wave velocity (PWV) is considered as the gold-standard method to assess arterial stiffness, an independent predictor of cardiovascular morbidity and mortality. Current available devices that measure PWV need to be operated by skilled medical staff, thus, reducing the potential use of PWV in the ambulatory setting. In this paper, we present a new technique allowing continuous, unsupervised measurements of pulse transit times (PTT) in central arteries by means of a chest sensor. This technique relies on measuring the propagation time of pressure pulses from their genesis in the left ventricle to their later arrival at the cutaneous vasculature on the sternum. Combined thoracic impedance cardiography and phonocardiography are used to detect the opening of the aortic valve, from which a pre-ejection period (PEP) value is estimated. Multichannel reflective photoplethysmography at the sternum is used to detect the distal pulse-arrival time (PAT). A PTT value is then calculated as PTT = PAT - PEP. After optimizing the parameters of the chest PTT calculation algorithm on a nine-subject cohort, a prospective validation study involving 31 normo- and hypertensive subjects was performed. 1/chest PTT correlated very well with the COMPLIOR carotid to femoral PWV (r = 0.88, p < 10 (-9)). Finally, an empirical method to map chest PTT values onto chest PWV values is explored.

Does change in thoracic impedance measured via defibrillator electrode pads accurately detect ventilation breaths in children?

Introduction Resuscitation guidelines recommend rescue ventilations consist of tidal volumes 7–10 ml/kg. Changes in thoracic impedance (ΔTI) measured using defibrillator electrode pads to detect and guide rescue ventilations have not been studied in children. Aim We hypothesized that ΔTI measured via standard anterior–apical (AA) position can accurately detect ventilations with volume >7 ml/kg in children. We also compared standard AA position with alternative anterior–posterior (AP) position. Methods IRB-approved, prospective, observational study of sedated, subjects (6 months to 17 years) on conventional mechanical ventilation. Thoracic impedance (TI) was obtained via Philips MRx defibrillator with standard electrode pads for 5 min each in AA and AP positions. Ventilations were simultaneously measured by pneumotachometer (Novametrix CO 2SMO Plus). Results Twenty-eight subjects (median 4 years, IQR 1.7–9 years; median 16.3 kg, IQR 10.5–39 kg) were enrolled. Data were available for 21 episodes in AA position and 22 episodes in AP position, with paired AA and AP data available for 18. For ventilations with volume <7 ml/kg, the defibrillator algorithm detected 80.0% for both AA and AP ( p = 0.99). For ventilations ≥7 ml/kg, detection was 95.1% for AA and 95.7% for AP ( p = 0.38). Conclusions Changes in thoracic impedance obtained via defibrillator pads can accurately detect ventilations above 7 ml/kg in stable, mechanically ventilated children, corresponding to rescue ventilations recommended during CPR. Both AA and AP pad positions were less sensitive to detect smaller volumes (<7 ml/kg) than higher volumes (≥7 ml/kg), suggesting that shallow ventilations during CPR might be missed. There were no differences in impedance measurements between standard AA pad position and commonly used alternative AP pad position.

The influence of priming exercise on oxygen uptake, cardiac output, and muscle oxygenation kinetics during very heavy-intensity exercise in 9- to 13-yr-old boys

The present study examined the effect of priming exercise on O(2) uptake (Vo(2)) kinetics during subsequent very heavy exercise in eight 9- to 13-yr-old boys. We hypothesised that priming exercise would 1) elevate muscle O(2) delivery prior to the subsequent bout of very heavy exercise, 2) have no effect on the phase II Vo(2) tau, 3) elevate the phase II Vo(2) total amplitude, and 4) reduce the magnitude of the Vo(2) slow component. Each participant completed repeat 6-min bouts of very heavy-intensity cycling exercise separated by 6 min of light pedaling. During the tests Vo(2), muscle oxygenation (near infrared spectroscopy), and cardiac output (Q) (thoracic impedance) were determined. Priming exercise increased baseline muscle oxygenation and elevated Q at baseline and throughout the second exercise bout. The phase II Vo(2) tau was not altered by priming exercise (bout 1: 22 + or - 7 s vs. bout 2: 20 + or - 4 s; P = 0.30). However, the time constant describing the entire Vo(2) response from start to end of exercise was accelerated (bout 1: 43 + or - 8 s vs. bout 2: 36 + or - 5 s; P = 0.002) due to an increased total phase II Vo(2) amplitude (bout 1: 1.73 + or - 0.33 l/min vs. bout 2: 1.80 + or - 0.59 l/min; P = 0.002) and a reduced Vo(2) slow component amplitude (bout 1: 0.18 + or - 0.08 l/min vs. bout 2: 0.12 + or - 0.09 l/min; P = 0.048). These results suggest that phase II Vo(2) kinetics in young boys is principally limited by intrinsic muscle metabolic factors, whereas the Vo(2) total phase II and slow component amplitudes may be O(2) delivery sensitive.

SHORT-TERM EFFECTS OF LOSARTAN THERAPY ON HAEMODYNAMIC PARAMETERS IN HYPERTENSIVE PATIENTS: PP.5.223

Objectives: The aim of this study was to assess the short-term effects of antihypertensive therapy with losartan, alone or combined with hydrochlorthiaside, on blood pressure and hemodynamics parameters of hypertensive patients. Design and Methods: The study comprised 76 patients (36 men and 40 women) with arterial hypertension (grade I or II), aged 60.93 ± 10.51 years. Ambulatory 24-hour blood pressure monitoring (ABPM, using Space Labs 90202) and thoracic bioelectric impedance (TBI, using Task-Force monitor) were performed to estimate haemodynamic parameters (peripheral vascular resistance, PVR, and blood volume, BV). The subjects who had increased PVR [32 patients (12 men and 20 women)] were treated with 50 mg losartan per day. Those with increased both PVR and BV [44 patients (21 men and 23 women)] were treated with 50 mg losartan and 12.5 mg hydrochlorthiaside per day. Short-term effects of therapy were assessed after 30 and 60 days. Results: After a two months therapy both groups experienced a significant decrease of blood pressure. Patients with increased PVR responded to losartan therapy with significant decrease of PVR after 30 and 60 days (PVRbeginning=68.5 ± 14.0; PVR30days=36.0 ± 11.5; PVR60days=9.5 ± 9.0; p < 0.001). The group treated with losartan and hydrochlorthiaside showed significant decrease of PVR (PVRbeginning=42.5 ± 11.0; PVR30days=26.5 ± 10.0; PVR60days=15.5 ± 9.0; p < 0.001) and blood volume (BVbeginning=39.0 ± 12.0; BV30days=22.0 ± 9.5; BV60days=11.0 ± 8.5; p < 0.001). Heart rate remained unchanged during the treatment in both groups. Conclusion: Short-term therapy of losartan in patients with arterial hypertension was efficient in reducing blood pressure and peripheral vascular resistance. The combination of losartan and hydrochlorthiaside could in addition reduce patient's blood volume.

Wavelet-based correlations of impedance cardiography signals and heart rate variability

The wavelet-based correlation analysis is employed to study impedance cardiography signals (variation in the impedance of the thorax z(t) and time derivative of the thoracic impedance (- dz/dt)) and heart rate variability (HRV). A method of computer thoracic tetrapolar polyrheocardiography is used for hemodynamic registrations. The modulus of wavelet-correlation function shows the level of correlation, and the phase indicates the mean phase shift of oscillations at the given scale (frequency). Significant correlations essentially exceeding the values obtained for noise signals are defined within two spectral ranges, which correspond to respiratory activity (0.14-0.5 Hz), endothelial related metabolic activity and neuroendocrine rhythms (0.0095-0.02 Hz). Probably, the phase shift of oscillations in all frequency ranges is related to the peculiarities of parasympathetic and neuro-humoral regulation of a cardiovascular system.

Cardiovascular responses to standing and walking in earth and simulated moon and mars gravities

IntroductionHuman cardiovascular responses to standing and walking in simulated reduced gravity were measured using a treadmill enclosed in a lower‐body positive pressure (LBPP) chamber (AlterG device).MethodsHeart rate, HR, continuous blood pressure, BP, (Portapres), segmental fluid shift (THRIM), diastolic function and stroke volume (Biosounds) were recorded on 7 subjects (4 males, 3 females) at supine and while standing and walking under 100% (earth), 40% (mars), and 20% (moon) body weights (BW).ResultsSubjects standing at 20% and 40% BW had reduced HR (p&lt;0.01), increased systolic BP (p&lt;0.05) and increased thoracic impedance (p&lt;0.001) compared to standing. Reduced BW was associated with increased upper and lower leg impedance (loss of fluid volume, p&lt;0.05). Stroke volume was greatest while supine, at 20%, 40% BW and walking compared to standing (p&lt;0.01). Mitral E to A ratio was reduced for 20%, 40%, and 100% BW compared to supine (p&lt;0.01). The number of blood pressure ramps and baroreflex sequences decreased as body weight was reduced.ConclusionFluid redistribution in the body and short‐term cardiovascular changes induced by Alter‐G unloading are compatible with those resulting from exposure to microgravity. Supported by KY NASA EPSCoR 52611.