RESUMO
Hyperarid Atacama soils are reported to contain significantly reduced numbers of microbes per gram of soil relative to soils from other environments. Molecular methods have been used to evaluate microbial populations in hyperarid Atacama soils; however, conflicting results across the various studies, possibly caused by this low number of microorganisms and consequent biomass, suggest that knowledge of expected DNA concentrations in these soils becomes important to interpreting data from any method regarding microbial concentrations and diversity. In this paper we compare the number of bacteria per gram of Atacama Desert soils determined by real-time quantitative polymerase chain reaction with the number of bacteria estimated by the standard methods of phospholipids fatty acid analysis, adenine composition (determined by liquid chromatography - time-of-flight mass spectrometry), and SYBR-green microscopy. The number determined by real-time quantitative polymerase chain reaction as implemented in this study was several orders of magnitude lower than that determined by the other three methods and probably underestimates the concentrations of soil bacteria, most likely because of soil binding during the DNA extraction methods. However, the other methods very possibly overestimate the bacteria concentrations owing to desiccated, intact organisms, which would stain positive in microscopy and preserve both adenine and phospholipid fatty acid for the other methods.
Assuntos
Carga Bacteriana/métodos , Fenômenos Fisiológicos Bacterianos , Bioquímica , Monitoramento Ambiental/métodos , Microscopia , Reação em Cadeia da Polimerase em Tempo Real , Microbiologia do Solo , Bactérias/química , Bactérias/genética , Biomassa , Clima Desértico , Ácidos Graxos/análise , Fosfolipídeos/análise , Solo/químicaRESUMO
Up-converting phosphors promise simpler readout systems with less background at a given signal level than many other popular approaches. (To listen to a podcast about this feature, please go to the Analytical Chemistry website at pubs.acs.org/journal/ancham.).
Assuntos
Química Clínica/métodos , Química Clínica/tendências , Sondas Moleculares , Sistemas Automatizados de Assistência Junto ao Leito/tendências , Citocinas/análise , Citocinas/metabolismo , Humanos , Imunoensaio , Interferon gama/análise , Interferon gama/metabolismo , Técnicas Analíticas Microfluídicas , Sondas Moleculares/metabolismoRESUMO
We investigate the signaling mechanisms that induce retinal ganglion cell (RGC) axon elongation by asking whether surviving neurons extend axons by default. We show that bcl-2 overexpression is sufficient to keep purified RGCs alive in the absence of any glial or trophic support. The bcl-2-expressing RGCs do not extend axons or dendrites unless signaled to do so by single peptide trophic factors. Axon growth stimulated by peptide trophic factors is remarkably slow but is profoundly potentiated by physiological levels of electrical activity spontaneously generated within embryonic explants or mimicked on a multielectrode silicon chip. These findings demonstrate that these surviving neurons do not constitutively extend axons and provide insight into the signals that may be necessary to promote CNS regeneration.
Assuntos
Axônios/fisiologia , Sobrevivência Celular/efeitos dos fármacos , Substâncias de Crescimento/farmacologia , Peptídeos/farmacologia , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Células Ganglionares da Retina/fisiologia , Transdução de Sinais/fisiologia , Animais , Técnicas de Cultura de Células/métodos , Sobrevivência Celular/fisiologia , Células Cultivadas , Colforsina/farmacologia , Meios de Cultivo Condicionados , Eletrofisiologia/métodos , Inibidores Enzimáticos/farmacologia , Matriz Extracelular/química , Matriz Extracelular/metabolismo , Corantes Fluorescentes/metabolismo , Humanos , Ratos , Ratos Sprague-Dawley , Células Ganglionares da Retina/citologia , Vias Visuais/citologia , Vias Visuais/metabolismoRESUMO
Electrical stimulation represents a useful tool for electrophysiologic investigation of electrically excitable cells such as cardiomyocytes. The stimulation threshold and electrophysiologic response to precisely timed pulses yields valuable information regarding physiologic processes. However, determining these parameters accurately, while simultaneously resolving time-dependent or transient effects has been difficult or impossible with previous methods. This paper presents a discrete-time algorithmic controller used for closed-loop electrical stimulation of HL-1 clonal cardiomyocytes cultured on, and stimulated using, a planar microelectrode array. We introduce the temporal error-controlled algorithm (TECA), that is well-suited to control using capture fraction, a low data rate, highly quantized feedback parameter describing stimulation efficacy. HL-1 cardiomyocytes were electrically stimulated and resulting parameters were used to develop a representative model of partial capture, enabling extensive analysis of the algorithm. The performance of this approach is compared via computer simulation to a previously introduced conditional convergence algorithm to quantify its performance and relative advantages. Operation of the TECA is demonstrated by tracking the real-time biological response of stimulation threshold to a rapid increase in extracellular potassium concentration in four independent cell cultures. This work enables the use of stimulation threshold as a real-time, continuously monitored parameter with considerable utility in cardiac pharmacology, electrophysiology, and cell-based biosensing.
Assuntos
Potenciais de Ação/fisiologia , Algoritmos , Relógios Biológicos/fisiologia , Estimulação Cardíaca Artificial/métodos , Miócitos Cardíacos/fisiologia , Processamento de Sinais Assistido por Computador , Terapia Assistida por Computador/métodos , Animais , Linhagem Celular , Retroalimentação , Sistema de Condução Cardíaco/fisiologia , Camundongos , Terapia Assistida por Computador/instrumentaçãoRESUMO
A 2-D optical scanner was developed for the imaging and quantification of up-converting phosphor (UCP) labels in immunoassays. With resolution better than 500 microm, a scan rate of 0.4 mm/s, and a 1-2% coefficient of variation for repeatability, this scanner achieved a detection limit of fewer than 100 UCP particles in an 8.8. x 10(4) microm(2) area and a dynamic range that covered more than three orders of magnitude. Utilizing this scanner, a microfluidic chip immunoassay for the cytokine interferon-gamma (IFN-gamma) was developed: concentrations as low as 3 pM (50 pg/mL) were detected from 100 microL samples with a total assay time of under an hour, including the 8 min readout. For this UCP-based assay, 2-D images of the capture antibody lines were scanned, image processing techniques were employed to extract the UCP emission signals, a response curve that spanned 3-600 pM IFN-gamma was generated, and a five-parameter logistic mathematical model was fitted to the data for determination of unknown IFN-gamma concentrations. Relative to common single-point or 1-D scanning optical measurements, our results suggest that a simple 2-D imaging system can speed assay development, reduce errors, and improve accuracy by characterizing the spatial distribution and uniformity of surface-captured optical labels as a function of assay conditions and device parameters.
Assuntos
Imunoensaio/instrumentação , Lasers , Medições Luminescentes/instrumentação , Óptica e Fotônica/instrumentação , Desenho de Equipamento , Análise de Falha de Equipamento , Imunoensaio/métodos , Medições Luminescentes/métodos , Coloração e Rotulagem/métodosRESUMO
Impedance cardiography is the most common clinically validated, noninvasive method for determining the timing of the opening of the aortic valve, an important event used for measuring preejection period, which reflects sympathetic beta-adrenergic influences on the heart. Automatic detection of the exact time of the opening of the aortic valve (B point on the impedance cardiogram) has proven to be challenging as its appearance varies between and within individuals and may manifest as a reversal, inflection, or rapid slope change of the thoracic impedance derivative's (dZ/dt) rapid rise. Here, a novel automatic algorithm is proposed for the detection of the B point by finding the main rapid rise of the dZ/dt signal, which is due to blood ejection. Several conditions based on zero crossings, minima, and maxima of the dZ/dt signal and its derivatives are considered to reject any unwanted noise and artifacts and select the true B-point location. The detected B-point locations are then corrected by modeling the B-point time data using forward and reverse autoregressive models. The proposed algorithm is validated against expert-detected B points and is compared with different conventional methods; it significantly outperforms them by at least 54% in mean error, 30% in mean absolute error, and 27% in standard deviation of error. This algorithm can be adopted in ambulatory studies requiring beat-to-beat evaluation of cardiac hemodynamic parameters over extended time periods where expert scoring is not feasible.
Assuntos
Valva Aórtica/fisiologia , Cardiografia de Impedância/métodos , Processamento de Sinais Assistido por Computador , Adulto , Algoritmos , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Reprodutibilidade dos Testes , Adulto JovemRESUMO
NASA's periodic selection of astronauts is a highly selective process accepting applications from the general population, wherein the mechanics of selection are not made public. This research was an effort to determine if biases (specifically age) exist in the process and, if so, at which points they might manifest. Two sets of analyses were conducted. The first utilized data requested via the Freedom of Information Act (FOIA) on NASA astronaut applicants for the 2009 and 2013 selection years. Using a series of multinomial and logistic regressions, the data were analyzed to uncover whether age of the applicants linearly or nonlinearly affected their likelihood of receiving an invitation, as well as their likelihood of being selected into the astronaut program. The second used public data on age at selection and age at other career milestones for every astronaut selected from 1959 to 2013 to analyze trends in age over time using ordinary least-squares (OLS) regression and Pearson's correlation. The results for the FOIA data revealed a nonlinear relationship between age and receiving an interview, as well as age and selection into the astronaut program, but the most striking observation was the loss of age diversity at each stage of selection. Applicants younger or older than approximately 40 years were significantly less likely to receive invitations for interviews and were significantly less likely to be selected as an astronaut. Analysis of the public-source data for all selections since the beginning of the astronaut program revealed significant age trends over time including a gradual increase in selectee age and decreased tenure at NASA after last flight, with average age at retirement steady over the entire history of the astronaut program at approximately 48 years.
Assuntos
Astronautas , Mobilidade Ocupacional , Seleção de Pessoal , United States National Aeronautics and Space Administration , Fatores Etários , Distribuição de Qui-Quadrado , Feminino , Humanos , Modelos Logísticos , Masculino , Probabilidade , Voo Espacial , Estados UnidosRESUMO
Automatic electrocardiogram (ECG) beat classification is essential to timely diagnosis of dangerous heart conditions. Specifically, accurate detection of premature ventricular contractions (PVCs) is imperative to prepare for the possible onset of life-threatening arrhythmias. Although many groups have developed highly accurate algorithms for detecting PVC beats, results have generally been limited to relatively small data sets. Additionally, many of the highest classification accuracies (> 90%) have been achieved in experiments where training and testing sets overlapped significantly. Expanding the overall data set greatly reduces overall accuracy due to significant variation in ECG morphology among different patients. As a result, we believe that morphological information must be coupled with timing information, which is more constant among patients, in order to achieve high classification accuracy for larger data sets. With this approach, we combined wavelet-transformed ECG waves with timing information as our feature set for classification. We used select waveforms of 18 files of the MIT/BIH arrhythmia database, which provides an annotated collection of normal and arrhythmic beats, for training our neural-network classifier. We then tested the classifier on these 18 training files as well as 22 other files from the database. The accuracy was 95.16% over 93,281 beats from all 40 files, and 96.82% over the 22 files outside the training set in differentiating normal, PVC, and other beats.
Assuntos
Algoritmos , Diagnóstico por Computador/métodos , Eletrocardiografia/métodos , Frequência Cardíaca , Redes Neurais de Computação , Complexos Ventriculares Prematuros/diagnóstico , Complexos Ventriculares Prematuros/fisiopatologia , Humanos , Reprodutibilidade dos Testes , Estudos Retrospectivos , Sensibilidade e Especificidade , Fatores de TempoRESUMO
Electrically active living cells cultured on extracellular electrode arrays are utilized to detect biologically active agents. Because cells are highly sensitive to environmental conditions, environmental fluctuations can elicit cellular responses that contribute to the noise in a cell-based biosensor system. Therefore, the characterization and control of environmental factors such as temperature, pH, and osmolarity is critical in such a system. The cell-based biosensor platform described here utilizes the measurement of action potentials from cardiac cells cultured on electrode arrays. A recirculating fluid flow system is presented for use in dose-response experiments that regulates temperature within +/-0.2 degrees C, pH to within +/-0.05 units, and allows no significant change in osmolarity. Using this system, the relationship between the sensor output parameters and environmental variation was quantified. Under typical experimental conditions, beat rate varied approximately 10% per degree change in temperature or per 0.1 unit change in pH. Similar relationships were measured for action potential amplitude, duration, and conduction velocity. For the specific flow system used in this work, the measured environmental sensitivity resulted in an overall beat rate variation of +/-4.7% and an overall amplitude variation of +/-3.3%. The magnitude of the noise due to environmental sensitivity has a large impact on the detection capability of the cell-based system. The significant responses to temperature, pH, and osmolarity have important implications for the use of living cells in detection systems and should be considered in the design and evaluation of such systems.
Assuntos
Técnicas Biossensoriais/instrumentação , Eletrodos , Concentração de Íons de Hidrogênio , Temperatura , Fatores de TempoRESUMO
An integrated electrical stimulation and recording system was designed for closed-loop control and analysis of cardiac cultures on planar microelectrode arrays. Stimulated action potentials from HL-1 clonal myocyte cultures were digitized, stimulation artifacts were removed using nulling and filtering methods, and analysis was performed to determine stimulation efficacy in real time. Results of this analysis were used to determine future stimulation waveform parameters such as polarity, amplitude, pulse duration, and rate or pattern. Algorithms were designed utilizing real-time analysis and control to maintain a desired electrophysiological response of the culture, such as an arbitrary capture fraction value. This paper presents the hardware and software design of the stimulus pulse circuitry, artifact extraction, analysis, and control components of the system. Applications of this technology include the study of cardiac cell physiology, improving the speed and accuracy of traditional open-loop stimulation protocols, pharmacological screening, and improving the performance of biosensors based on sensing electrical activity in cardiac cultures.
Assuntos
Potenciais de Ação/fisiologia , Técnicas de Cultura de Células/instrumentação , Estimulação Elétrica/instrumentação , Eletrocardiografia/instrumentação , Contração Miocárdica/fisiologia , Miócitos Cardíacos/fisiologia , Marca-Passo Artificial , Animais , Estimulação Cardíaca Artificial/métodos , Técnicas de Cultura de Células/métodos , Células Cultivadas , Estimulação Elétrica/métodos , Eletrocardiografia/métodos , Desenho de Equipamento , Análise de Falha de Equipamento , Retroalimentação/fisiologia , CamundongosRESUMO
A novel, unobtrusive and wearable, multiparameter ambulatory physiologic monitoring system for space and terrestrial applications, termed LifeGuard, is presented. The core element is a wearable monitor, the crew physiologic observation device (CPOD), that provides the capability to continuously record two standard electrocardiogram leads, respiration rate via impedance plethysmography, heart rate, hemoglobin oxygen saturation, ambient or body temperature, three axes of acceleration, and blood pressure. These parameters can be digitally recorded with high fidelity over a 9-h period with precise time stamps and user-defined event markers. Data can be continuously streamed to a base station using a built-in Bluetooth RF link or stored in 32 MB of on-board flash memory and downloaded to a personal computer using a serial port. The device is powered by two AAA batteries. The design, laboratory, and field testing of the wearable monitors are described.
Assuntos
Medicina Aeroespacial/instrumentação , Vestuário , Armazenamento e Recuperação da Informação/métodos , Monitorização Ambulatorial/instrumentação , Telecomunicações/instrumentação , Telemedicina/instrumentação , Transdutores , Medicina Aeroespacial/métodos , Desenho de Equipamento , Análise de Falha de Equipamento , Monitorização Ambulatorial/métodos , Projetos Piloto , Telemedicina/métodosRESUMO
The use of a noninvasive hemodynamic monitor to estimate arterial stiffness, by measurement of pulse transit time (PTT), was demonstrated in microgravity. The monitor's utility for space applications was shown by establishing the correlation between ground-based and microgravity-based measurements. The system consists of a scale-based ballistocardiogram (BCG) and a toe-mounted photoplethysmogram (PPG). PTT was measured from the BCG I-wave to the intersecting tangents of the first trough and maximum first derivative of the PPG waveforms of each subject. The system was tested on a recent series of parabolic flights in which the PTT of nine subjects was measured on the ground and in microgravity. An average of 60.2 ms PTT increase from ground to microgravity environments was shown, and was consistent across all test subjects (standard deviation = 32.9 ms). This increase in PTT could be explained by a number of factors associated with microgravity and reported in previous research, including elimination of hydrostatic pressure, reduction of intrathoracic pressure, and reduction of mean arterial pressure induced by vasodilation.
Assuntos
Monitorização Fisiológica , Rigidez Vascular/fisiologia , Adulto , Pressão Arterial , Balistocardiografia , Feminino , Hemodinâmica , Humanos , Masculino , Pessoa de Meia-Idade , Fotopletismografia , Análise de Onda de Pulso , Ausência de Peso , Adulto JovemRESUMO
The performance and practicality of a scale-based ballistocardiogram (BCG) system for hemodynamic monitoring of astronauts on extended space missions was demonstrated. The system consists of a modified electronic weighing scale fitted with foot bindings to mechanically couple the subject to the scale. This system was tested on a recent series of parabolic flights in which scale-based and accelerometry-based free-floating BCG of 10 subjects was measured in microgravity. The signal-to-noise ratio (SNR) of the scale-based BCG was, on average, a factor of 2.1 (6.3 dB) higher than the free-floating method, suggesting that the tethered scale approach might be more robust in terms of signal quality. Additionally, this approach enables practical BCG-based hemodynamic monitoring in fractional-g environments, and on small space vehicles such as NASA's upcoming Orion capsule. The scale-based results in microgravity were also compared to ground measurements (1 g), where there was an average 38.7 ms RJ interval reduction from ground to microgravity environments that is consistent across 9 of 10 subjects. This phenomenon is likely due to the transient increase in venous return, and consequent decrease in pre-ejection period, experienced during the microgravity time intervals.
Assuntos
Balistocardiografia/métodos , Postura , Ausência de Peso , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Razão Sinal-Ruído , Adulto JovemRESUMO
The seismocardiogram (SCG) signal traditionally measured using a chest-mounted accelerometer contains low-frequency (0-100 Hz) cardiac vibrations that can be used to derive diagnostically relevant information about cardiovascular and cardiopulmonary health. This work is aimed at investigating the effects of respiration on the frequency domain characteristics of SCG signals measured from 18 healthy subjects. Toward this end, the 0-100 Hz SCG signal bandwidth of interest was sub-divided into 5 Hz and 10 Hz frequency bins to compare the spectral energy in corresponding frequency bins of the SCG signal measured during three key conditions of respiration--inspiration, expiration, and apnea. Statistically significant differences were observed between the power in ensemble averaged inspiratory and expiratory SCG beats and between ensemble averaged inspiratory and apneaic beats across the 18 subjects for multiple frequency bins in the 10-40 Hz frequency range. Accordingly, the spectral analysis methods described in this paper could provide complementary and improved classification of respiratory modulations in the SCG signal over and above time-domain SCG analysis methods.
Assuntos
Acelerometria/instrumentação , Testes de Função Cardíaca , Respiração , Processamento de Sinais Assistido por Computador/instrumentação , Adulto , Apneia/fisiopatologia , Feminino , Testes de Função Cardíaca/instrumentação , Testes de Função Cardíaca/métodos , Humanos , Masculino , Análise Espectral , Adulto JovemRESUMO
Ballistocardiography and seismocardiography are both non-invasive mechanical measurements of the vibrations of the body in response to the heartbeat. The ballistocardiogram (BCG) signal represents the movements of the whole body in response to cardiac ejection of blood into the vasculature; the seismocardiogram (SCG) corresponds to local vibrations of the chest wall associated with sub-audible tissue and blood movement and audio frequency heart-valve closure dynamics. This paper focuses on methods for quantifying "signal consistency"--a quantitative measure of how morphologically similar each heartbeat in a patient's recording is compared to the ensemble average taken over the recording. Before comparing each beat to the average, known physiological sources of inconsistency--such as respiratory amplitude and timing variability--are removed, then the remaining inconsistency is quantified. Previously described methods for BCG signals are expanded to fit the high-frequency (> 20 Hz) components of the SCG. The use of this method in future work could help enable proactive management of heart disease in extra-clinical settings.
Assuntos
Eletrocardiografia/métodos , Frequência Cardíaca/fisiologia , Processamento de Sinais Assistido por Computador , Balistocardiografia , HumanosRESUMO
We report on the feasibility of standing ballistocardiogram (BCG) measurements recorded in a microgravity environment. A clinically-tested BCG monitoring scale was adapted for parabolic flight for the microgravity measurements. Upon completion of this flight campaign, the BCG scale was shown to make measurements in micro-g and one-g environments--which is a first demonstration for a standing BCG system. This screening experiment demonstrated proof-of-concept attributes of the hardware design necessary for future characterization studies with multiple subjects. This scale-based BCG system is proposed as a practical device for hemodynamic monitoring for astronauts in Earth, Lunar, Martian, orbital, and interplanetary environments.
Assuntos
Balistocardiografia/métodos , Postura/fisiologia , Ausência de Peso , Aceleração , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
Cardiac arrhythmias are disturbances of the electrical conduction pattern in the heart with severe clinical implications. The damage of existing cells or the transplantation of foreign cells may disturb functional conduction pathways and may increase the risk of arrhythmias. Although these conduction disturbances are easily accessible with the human eye, there is no algorithmic method to extract quantitative features that quickly portray the conduction pattern. Here, we show that co-occurrence analysis, a well-established method for feature recognition in texture analysis, provides insightful quantitative information about the uniformity and the homogeneity of an excitation wave. As a first proof-of-principle, we illustrate the potential of co-occurrence analysis by means of conduction patterns of cardiomyocyte-fibroblast co-cultures, generated both in vitro and in silico. To characterise signal propagation in vitro, we perform a conduction analysis of co-cultured murine HL-1 cardiomyocytes and murine 3T3 fibroblasts using microelectrode arrays. To characterise signal propagation in silico, we establish a conduction analysis of co-cultured electrically active, conductive cardiomyocytes and non-conductive fibroblasts using the finite element method. Our results demonstrate that co-occurrence analysis is a powerful tool to create purity-conduction relationships and to quickly quantify conduction patterns in terms of co-occurrence energy and contrast. We anticipate this first preliminary study to be a starting point for more sophisticated analyses of different co-culture systems. In particular, in view of stem cell therapies, we expect co-occurrence analysis to provide valuable quantitative insight into the integration of foreign cells into a functional host system.
Assuntos
Miócitos Cardíacos/fisiologia , Algoritmos , Animais , Arritmias Cardíacas/fisiopatologia , Linhagem Celular , Técnicas de Cocultura , Análise de Elementos Finitos , Humanos , Camundongos , MicroeletrodosRESUMO
We present the design and performance characteristics of a platelet analysis platform based on a microfluidic impedance cytometer. Dielectrophoretic focusing is used to centre cells in a fluid stream, which then forms the core of a two-phase flow (dielectric focusing). This flow then passes between electrodes for analysis by differential impedance spectroscopy at multiple frequencies from 280 kHz to 4 MHz. This approach increases the signal-to-noise ratio relative to a single-phase, unfocused stream, while minimising the shear forces to which the cells are subjected. The percentage of activated platelets before and after passage through the chip was measured using flow cytometry, and no significant change was measured. Measuring the in-phase amplitude at a single frequency is sufficient to distinguish platelets from erythrocytes. Using multi-frequency impedance measurements and discriminant analysis, resting platelets can be discriminated from activated platelets. This multifrequency impedance cytometer therefore allows ready determination of the degree of platelet activation in blood samples.
Assuntos
Plaquetas/química , Citometria de Fluxo/métodos , Técnicas Analíticas Microfluídicas/métodos , Eletrodos , Citometria de Fluxo/instrumentação , Humanos , Técnicas Analíticas Microfluídicas/instrumentaçãoRESUMO
BACKGROUND: Methods for the electrical inhibition of cardiac excitation have long been sought to control excitability and conduction, but to date remain largely impractical. High-amplitude alternating current (AC) stimulation has been known to extend cardiac action potentials (APs), and has been recently exploited to terminate reentrant arrhythmias by producing reversible conduction blocks. Yet, low-amplitude currents at similar frequencies have been shown to entrain cardiac tissues by generation of repetitive APs, leading in some cases to ventricular fibrillation and hemodynamic collapse in vivo. Therefore, an inhibition method that does not lead to entrainment - irrespective of the stimulation amplitude (bound to fluctuate in an in vivo setting) - is highly desirable. METHODOLOGY/PRINCIPAL FINDINGS: We investigated the effects of broader amplitude and frequency ranges on the inhibitory effects of extracellular AC stimulation on HL-1 cardiomyocytes cultured on microelectrode arrays, using both sinusoidal and square waveforms. Our results indicate that, at sufficiently high frequencies, cardiac tissue exhibits a binary response to stimulus amplitude with either prolonged APs or no effect, thereby effectively avoiding the risks of entrainment by repetitive firing observed at lower frequencies. We further demonstrate the ability to precisely define reversible local conduction blocks in beating cultures without influencing the propagation activity in non-blocked areas. The conduction blocks were spatiotemporally controlled by electrode geometry and stimuli duration, respectively, and sustainable for long durations (300 s). CONCLUSION/SIGNIFICANCE: Inhibition of cardiac excitation induced by high-frequency AC stimulation exhibits a binary response to amplitude above a threshold frequency, enabling the generation of reversible conduction blocks without the risks of entrainment. This inhibition method could yield novel approaches for arrhythmia modeling in vitro, as well as safer and more efficacious tools for in vivo cardiac mapping and radio-frequency ablation guidance applications.
Assuntos
Estimulação Elétrica/métodos , Sistema de Condução Cardíaco/citologia , Potenciais de Ação , Animais , Linhagem Celular , Estimulação Elétrica/instrumentação , Eletrodos , Espaço Extracelular/metabolismo , Camundongos , Miócitos Cardíacos/citologia , Fatores de TempoRESUMO
We report on the preliminary deployment of a bathroom scale-based ballistocardiogram (BCG) system for the in-hospital monitoring of patients with heart failure. These early trials provided valuable insights into the challenges and opportunities for such monitoring. In particular, the need for robust algorithms and adapted BCG metric is suggested. The system was designed to be robust and user-friendly, with dual ballistocardiogram (BCG) and electrocardiogram (ECG) capabilities. The BCG was measured from a modified bathroom scale, while the ECG (used as timing reference) was measured using dry handlebar electrodes. The signal conditioning and digitization circuits were USB-powered, and data acquisition performed using a netbook. Four patients with a NYHA class III at admission were measured daily for the duration of their treatment at Stanford hospital. A measure of BCG quality, in essence a quantitative implementation of the BCG classes originally defined in the 1950s, is proposed as a practical parameter.