RESUMO
Near-infrared spectroscopy is a noninvasive optical method used primarily to monitor tissue oxygenation due to the absorption properties of hemoglobin. Accurate estimation of hemoglobin concentrations and other light absorbers requires techniques that can separate the effect of absorption from the much greater effect of light scattering. One of the most advanced methods is time-resolved near-infrared spectroscopy (TR-NIRS), which measures the absorption and scattering coefficients of a turbid medium by modeling the recorded distribution time of flight of photons. A challenge with TR-NIRS is that it requires accurate characterization of the dispersion caused by the system. In this study, we present a method for circumventing this problem by applying statistical moment analysis to two time-of-flight distributions measured at separated source-detector distances. Simulations based on analytical models and Monte Carlo code, and tissue-mimicking phantoms, were used to demonstrate its accuracy for source-detector distances typically used in neuroimaging applications. The simplicity of the approach is well suited to real-time applications requiring accurate quantification of the optical properties of a turbid medium.
Assuntos
Nefelometria e Turbidimetria/métodos , Fenômenos Ópticos , Algoritmos , Método de Monte Carlo , Imagens de Fantasmas , Fótons , Espectroscopia de Luz Próxima ao Infravermelho , Fatores de TempoRESUMO
BACKGROUND: The effective screening of myocardial infarction (MI) patients threatened by ventricular tachycardia (VT) is an important issue in clinical practice, especially in the process of implantable cardioverter-defibrillator (ICD) therapy recommendation. This study proposes new parameters describing depolarization and repolarization inhomogeneity in high resolution body surface potential maps (HR BSPM) to identify MI patients threatened by VT. MATERIAL/METHODS: High resolution ECGs were recorded from 64 surface leads. Time-averaged HR BSPMs were used. Several parameters for arrhythmia risk assessment were calculated in 2 groups of MI patients: those with and without documented VT. Additionally, a control group of healthy subjects was studied. To assess the risk of VT, the following parameters were proposed: correlation coefficient between STT and QRST integral maps (STT_QRST_CORR), departure index of absolute value of STT integral map (STT_DI), and departure index of absolute value of T-wave shape index (TSI_DI). These new parameters were compared to known parameters: QRS width, QT interval, QT dispersion, Tpeak-Tend interval, total cosines between QRS complex and T wave, and non-dipolar content of QRST integral maps. RESULTS: STT_DI, TSI_DI, STT_QRST_CORR, QRS width, and QT interval parameters were statistically significant (p ≤ 0.05) in arrhythmia risk assessment. The highest sensitivity was found for the STT_DI parameter (0.77) and the highest specificity for TSI_DI (0.79). CONCLUSIONS: Arrhythmia risk is demonstrated by both abnormal spatial distribution of the repolarization phase and changed relationship between depolarization and repolarization phases, as well as their prolongation. The proposed new parameters might be applied for risk stratification of cardiac arrhythmia.
Assuntos
Mapeamento Potencial de Superfície Corporal/métodos , Taquicardia Ventricular/fisiopatologia , Idoso , Eletrocardiografia , Humanos , Pessoa de Meia-Idade , Medição de Risco , Sensibilidade e Especificidade , Taquicardia Ventricular/diagnóstico por imagem , UltrassonografiaRESUMO
In this work, we propose an integrated self-powered sensing system, driven by a hybrid biofuel cell (HBFC) with carbon paper discs coated with multiwalled carbon nanotubes. The sensing system has a biocathode made from laccase or bilirubin oxidase, and the anode is made from a zinc plate. The system includes a dedicated custom-built electronic control unit for the detection of oxygen and catechol analytes, which are central to medical and environmental applications. Both the HBFC and sensors, operate in a mediatorless direct electron transfer mode. The measured characteristics of the HBFC with externally applied resistance included the power-time dependencies under flow cell conditions, the sensors performance (evaluated by cyclic voltammetry), and chronoamperometry. The HBFC is integrated with analytical devices and operating in a pulse mode form long-run monitoring experiments. The HBFC generated sufficient power for wireless data transmission to a local computer.
Assuntos
Biocombustíveis , Técnicas Biossensoriais , Enzimas Imobilizadas/química , Nanotubos de Carbono/química , Lacase/química , Oxigênio/químicaRESUMO
BACKGROUND: Magnetic resonance imaging (MRI) changes in tick-borne encephalitis (TBE) are non-specific and the pathophysiological mechanisms leading to their formation remain unclear. This study investigated brain perfusion in TBE patients using dynamic susceptibility-weighted contrast-enhanced magnetic resonance perfusion imaging (DSC-MRI perfusion). METHODS: MRI scans were performed for 12 patients in the acute phase, 3-5days after the diagnosis of TBE. Conventional MRI and DSC-MRI perfusion studies were performed. Cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and time to peak (TTP) parametric maps were created. The bilateral frontal, parietal, and temporal subcortical regions and thalamus were selected as regions of interest. Perfusion parameters of TBE patients were compared to those of a control group. RESULTS: There was a slight increase in CBF and CBV, with significant prolongation of TTP in subcortical areas in the study subjects, while MTT values were comparable to those of the control group. A significant increase in thalamic CBF (p<0.001) and increased CBV (p<0.05) were observed. Increased TTP and a slight reduction in MTT were also observed within this area. CONCLUSIONS: The DSC-MRI perfusion study showed that TBE patients had brain perfusion disturbances, expressed mainly in the thalami. These results suggest that DSC-MRI perfusion may provide important information regarding the areas affected in TBE patients.
Assuntos
Encéfalo/diagnóstico por imagem , Encefalite Transmitida por Carrapatos/diagnóstico por imagem , Doença Aguda , Adulto , Anticorpos Antivirais/sangue , Anticorpos Antivirais/líquido cefalorraquidiano , Encéfalo/patologia , Estudos de Casos e Controles , Circulação Cerebrovascular , Encefalite Transmitida por Carrapatos/patologia , Feminino , Humanos , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Tamanho da AmostraRESUMO
We aimed to determine whether optical methods based on bolus tracking of an optical contrast agent are useful for the confirmation of cerebral circulation cessation in patients being evaluated for brain death. Different stages of cerebral perfusion disturbance were compared in three groups of subjects: controls, patients with posttraumatic cerebral edema, and patients with brain death. We used a time-resolved near-infrared spectroscopy setup and indocyanine green (ICG) as an intravascular flow tracer. Orthogonal partial least squares-discriminant analysis (OPLS-DA) was carried out to build statistical models allowing for group separation. Thirty of 37 subjects (81.1%) were classified correctly (8 of 9 control subjects, 88.9%; 13 of 15 patients with edema, 86.7%; and 9 of 13 patients with brain death, 69.2%; p < 0.0001). Depending on the combination of variables used in the OPLS-DA model, sensitivity, specificity, and accuracy were 66.7-92.9%, 81.8-92.9%, and 77.3-89.3%, respectively. The method was feasible and promising in the demanding intensive care unit environment. However, its accuracy did not reach the level required for brain death confirmation. The potential usefulness of the method may be improved by increasing the depth of light penetration, confirming its accuracy against other methods evaluating cerebral flow cessation, and developing absolute parameters for cerebral perfusion.
Assuntos
Morte Encefálica/diagnóstico por imagem , Morte Encefálica/diagnóstico , Adulto , Idoso , Idoso de 80 Anos ou mais , Encéfalo , Edema Encefálico/diagnóstico por imagem , Circulação Cerebrovascular/fisiologia , Meios de Contraste/farmacologia , Análise Discriminante , Estudos de Viabilidade , Feminino , Humanos , Verde de Indocianina , Análise dos Mínimos Quadrados , Masculino , Pessoa de Meia-Idade , Modelos Estatísticos , Perfusão , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Espectroscopia de Luz Próxima ao Infravermelho/métodosRESUMO
OBJECTIVE: The aim of this study was to evaluate influence of noise, T-wave jitter and electrocardiographic (ECG) signal parameters on sensitivity of T-wave alternans (TWA) detection methods. METHODS: Methods of the TWA detection were tested: correlation (CM), spectral (FFTM), spectral with coherent averaging (CFFTM), complex demodulation (CDM), Karhunen-Loeve transform (KLT) and KLT realized by adaptive filtering. The TWA amplitude and duration time were estimated on simulated ECG signals. Gaussian and physiological noises at different level were added. Influence of sampling frequency and amplitude resolution of the ECG signal was tested. Detection sensitivity was calculated. RESULTS: The TWA episodes in presence of white noise with signal to noise ratio (SNR) greater then 15 dB were reliably detected. For signals with high noise level better sensitivity was received with the CM. For the spectral methods, the best parameters were obtained with the CFFTM but for physiological noises all the methods were unable to detect the TWA episodes when SNR was lower then 10 dB. Analysis done using the CM and the CDM strongly depended on sampling frequency if the TWA episodes were short and had low amplitude. CONCLUSIONS: All spectral methods are sensitive to physiological interference. Changes of the sampling frequency should be very carefully applied.
Assuntos
Arritmias Cardíacas/diagnóstico , Eletrocardiografia , Processamento de Sinais Assistido por Computador , Arritmias Cardíacas/fisiopatologia , Simulação por Computador , Humanos , Valor Preditivo dos TestesRESUMO
A relationship between the brain rhythmic activity and the hemodynamic response was studied using the simultaneous measurement of electroencephalogram (EEG) and the functional near-infrared spectroscopy (fNIRS) during a motor task (self-paced right finger movements) for 10 subjects. An EEG recording with a 32-electrode (10-10) system was made and the hemodynamic response was obtained using 8 optodes placed over the sensorimotor cortex on both hemispheres. During the task an increase in oxyhemoglobine (HbO) was accompanied by a decrease in deoxyhemoglobine (HbR) concentration and a decrease in amplitudes (desynchronisation) of alpha (8-13 Hz) and beta (13-30 Hz) EEG rhythms. These phenomena were prominent in the hemisphere contralateral to the moving finger. The delays between the hemodynamic and electrophysiological variables were on average 2.8 s. Highly significant (p < 0.0001) negative Pearson correlations were found between HbO and alpha (r2 = -0.69) and HbO and beta (r2 = -0.54) rhythms. Positive correlations r2 = 0.5 between these rhythms and HbR were found.
Assuntos
Ondas Encefálicas/fisiologia , Movimento/fisiologia , Acoplamento Neurovascular/fisiologia , Córtex Sensório-Motor/fisiologia , Adulto , Feminino , Dedos , Hemoglobinas/análise , Humanos , Masculino , Oxiemoglobinas/análise , Espectroscopia de Luz Próxima ao InfravermelhoRESUMO
We present an overview of the wide range of potential applications of optical methods for monitoring traumatic brain injury. The MEDLINE database was electronically searched with the following search terms: "traumatic brain injury," "head injury," or "head trauma," and "optical methods," "NIRS," "near-infrared spectroscopy," "cerebral oxygenation," or "cerebral oximetry." Original reports concerning human subjects published from January 1980 to June 2015 in English were analyzed. Fifty-four studies met our inclusion criteria. Optical methods have been tested for detection of intracranial lesions, monitoring brain oxygenation, assessment of brain perfusion, and evaluation of cerebral autoregulation or intracellular metabolic processes in the brain. Some studies have also examined the applicability of optical methods during the recovery phase of traumatic brain injury . The limitations of currently available optical methods and promising directions of future development are described in this review. Considering the outstanding technical challenges, the limited number of patients studied, and the mixed results and opinions gathered from other reviews on this subject, we believe that optical methods must remain primarily research tools for the present. More studies are needed to gain confidence in the use of these techniques for neuromonitoring of traumatic brain injury patients.
Assuntos
Lesões Encefálicas Traumáticas/diagnóstico por imagem , Circulação Cerebrovascular/fisiologia , Hemorragia Intracraniana Traumática/diagnóstico por imagem , Neuroimagem/métodos , Imagem Óptica/métodos , Lesões Encefálicas Traumáticas/metabolismo , Lesões Encefálicas Traumáticas/patologia , Lesões Encefálicas Traumáticas/fisiopatologia , Humanos , Hemorragia Intracraniana Traumática/metabolismo , Hemorragia Intracraniana Traumática/patologia , Oximetria/métodos , Consumo de Oxigênio/fisiologia , Espectroscopia de Luz Próxima ao Infravermelho/métodosRESUMO
BACKGROUND: Experimental studies documented the relationship between T wave alternans (TWA) and duration of refractoriness. To date, association between TWA and QT interval on standard ECG has not been examined. Aim. To assess the relationship between TWA and QT interval. METHODS: The study group consisted of 70 patients (57 males, mean age 56+/-16 years) with implantable cardioverterdefibrillator (ICD). TWA was measured using a high-resolution ECG obtained from surface orthogonal bipolar XYZ leads and analysed using a Fast Fourier transform. All recordings were performed during ventricular pacing at 100 betas/min. Correlation between T wave amplitude (T max) and QT interval (measured from R wave to T max) was calculated. RESULTS: TWA was found in 18 patients. In this group of patients, there was a significant positive correlation between Tmax and QT (r = 0.766), whereas in patients with negative TWA no such correlation was detected. CONCLUSIONS: (1) Positive correlation between QT and T max probably depicts the relationship between T wave amplitude and duration of repolarisation, which is associated with TWA; (2) methods used for T wave localisation, based on the identification of Q wave (with possible QT-RR correction) overestimate TWA due to periodic changes (with TWA frequency) in location of T wave in the analysed window; and (3) these results provide new insights in the genesis of TWA.
Assuntos
Eletrocardiografia , Sistema de Condução Cardíaco/fisiopatologia , Adulto , Idoso , Desfibriladores Implantáveis , Feminino , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
INTRODUCTION: Recent studies point to analysis of T-wave alternans as a promising indicator of an increased risk of life-threatening ventricular arrhythmias. In this study the occurrence of T-wave alternans in the high-resolution ECGs recorded during the exercise stress test and scintigraphic tests (SPECT) in patients with ischemic heart disease was examined. MATERIAL AND METHODS: The study group consisted of 33 patients after myocardial infarction. In the group of patients after myocardial infarction and with low left ventricular ejection fraction correlations of 70% between the test results of T-wave alternans and SPECT and 60% between the test results of T-wave alternans and stress test were found. RESULTS: In the group of patients after myocardial infarction but with high left ventricular ejection fraction correlations were respectively 39% and 48%. The analysis of the electrocardiographic maps showed a strong dependence of this correlation on the T-wave alternans amplitude and location of the ECG measuring electrode on the chest. The results might suggest that in patients after myocardial infarction and at increased risk for sudden cardiac death T-wave alternans may also provide information about cardiac electrical instability associated with ischemia. CONCLUSIONS: It can also be assumed that the position of the electrode where the highest level of the T-wave alternans was detected can indicate the location of the ischemic region of the heart.
RESUMO
The aim of the study was to determine optimal measurement conditions for assessment of brain perfusion with the use of optical contrast agent and time-resolved diffuse reflectometry in the near-infrared wavelength range. The source-detector separation at which the distribution of time of flights (DTOF) of photons provided useful information on the inflow of the contrast agent to the intracerebral brain tissue compartments was determined. Series of Monte Carlo simulations was performed in which the inflow and washout of the dye in extra- and intracerebral tissue compartments was modeled and the DTOFs were obtained at different source-detector separations. Furthermore, tests on diffuse phantoms were carried out using a time-resolved setup allowing the measurement of DTOFs at 16 source-detector separations. Finally, the setup was applied in experiments carried out on the heads of adult volunteers during intravenous injection of indocyanine green. Analysis of statistical moments of the measured DTOFs showed that the source-detector separation of 6 cm is recommended for monitoring of inflow of optical contrast to the intracerebral brain tissue compartments with the use of continuous wave reflectometry, whereas the separation of 4 cm is enough when the higher-order moments of DTOFs are available.
Assuntos
Meios de Contraste/farmacocinética , Aumento da Imagem/métodos , Imagem de Perfusão/métodos , Espectroscopia de Luz Próxima ao Infravermelho/métodos , Adulto , Velocidade do Fluxo Sanguíneo , Encéfalo , Circulação Cerebrovascular , Desenho de Equipamento , Análise de Falha de Equipamento , Feminino , Humanos , Masculino , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
Inaccurate electrode placement and differences in inter-individual human anatomies can lead to misinterpretation of ECG examination. The aim of the study was to investigate the effect of precordial electrodes displacement on morphology of the ECG signal in a group of 60 patients with diagnosed cardiac disease. Shapes of ECG signals recorded from precordial leads were compared with signals interpolated at the points located at a distance up to 5 cm from lead location. Shape differences of the QRS and ST-T-U complexes were quantified using the distribution function method, correlation coefficient, root-mean-square error (RMSE), and normalized RMSE. The relative variability (RV) index was calculated to quantify inter-individual variability. ECG morphology changes were prominent in all shape parameters beyond 2 cm distance to precordial leads. Lead V2 was the most sensitive to displacement errors, followed by leads V3, V1, and V4, for which the direction of electrodes displacement plays a key role. No visible changes in ECG morphology were observed in leads V5 and V6, only scaling effect of signal amplitude. The RV ranged from 0.639 to 0.989. Distortions in ECG tracings increase with the distance from precordial lead, which are specific to chosen electrode, direction of displacement, and for ECG segment selected for calculations.
Assuntos
Eletrocardiografia/métodos , Coração/anatomia & histologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Eletrodos , Humanos , Masculino , Pessoa de Meia-Idade , Reprodutibilidade dos TestesRESUMO
INTRODUCTION: The aim of the study was to assess myocardial ischemia by analysis of ST-segment changes in high-resolution body surface potential maps (HR-BSPM) measured at rest and during an exercise stress test. MATERIAL AND METHODS: The study was carried out on a group of 28 patients with stable coronary artery disease and 15 healthy volunteers. The HR-BSPM were measured at rest and during the exercise stress test on a supine ergometer. The workload was increased in stages by 25 W every 2 min, beginning at 50 W. The maps of ST-segment depression (ST60) were calculated from time averaged recordings at rest and at maximal workload. RESULTS: The efficiency in detection of myocardial ischemia was higher for HR-BSPM than for standard 12-lead electrocardiography (ECG) when both methods were evaluated by outcomes of coronarography. The sensitivity of HR-BSPM was 82.4% while for the standard 12-lead ECG exercise stress test it was 58.8%. For some patients significant changes in the ST segment were observed at stress HR-BSPM but were not visible in standard 12-lead ECG recorded under the same conditions. CONCLUSIONS: Obtained high values of sensitivity and specificity in myocardial ischemia detection suggest that maps of ST60 calculated from HR-BSPM can improve detection of patients with ischemic heart disease in comparison to the standard electrocardiographic exercise stress test examinations.