Beamforming using subspace estimation from a diagonally averaged sample covariance.

The potential benefit of a large-aperture sonar array for high resolution target localization is often challenged by the lack of sufficient data required for adaptive beamforming. This paper introduces a Toeplitz-constrained estimator of the clairvoyant signal covariance matrix corresponding to multiple far-field targets embedded in background isotropic noise. The estimator is obtained by averaging along subdiagonals of the sample covariance matrix, followed by covariance extrapolation using the method of maximum entropy. The sample covariance is computed from limited data snapshots, a situation commonly encountered with large-aperture arrays in environments characterized by short periods of local stationarity. Eigenvectors computed from the Toeplitz-constrained covariance are used to construct signal-subspace projector matrices, which are shown to reduce background noise and improve detection of closely spaced targets when applied to subspace beamforming. Monte Carlo simulations corresponding to increasing array aperture suggest convergence of the proposed projector to the clairvoyant signal projector, thereby outperforming the classic projector obtained from the sample eigenvectors. Beamforming performance of the proposed method is analyzed using simulated data, as well as experimental data from the Shallow Water Array Performance experiment.

Geoacoustic inversion for the seabed transition layer using a Bernstein polynomial model.

This paper develops an inversion method for the seabed transition layer at the water-sediment interface, often found in muddy sediments, which provides density and sound-speed profiles that were previously not resolvable. The resolution improvements are achieved by introducing a parametrization that captures general depth-dependent gradients in geoacoustic parameters with a small number of parameters. In particular, the gradients are represented by a sum of Bernstein basis functions, weighted by unknown coefficients. Compared to previous forms found in the literature, the Bernstein-based parametrization can represent a wider range of depth-dependent geoacoustic profiles using fewer parameters which leads to reduced uncertainty and improved resolution. In addition, the Bernstein basis is the most stable polynomial representation in that small perturbations to the unknown coefficients result in small, localized perturbations to the geoacoustic profile, thereby providing an efficient exploration of the parameter space using Markov-chain methods in nonlinear inversion. Geoacoustic profiles at four mud sites on the Malta Plateau are studied with the proposed approach. Results show exceptional resolution of density profiles, estimated with low uncertainty and clear sensitivity to sediment features of centimeter scale.

Fast computation of seabed spherical-wave reflection coefficients in geoacoustic inversion.

This paper develops a fast numerical approach to computing spherical-wave reflection coefficients (SWRCs) for layered seabeds, which provides substantial savings in computation time when used as the forward model for geoacoustic inversion of broadband seabed reflectivity data. The approach exploits the Sommerfeld-integral representation of SWRCs as the Hankel transform of a function proportional to the plane-wave reflection coefficient (PWRC), and applies Levin integration to the rapidly oscillating integrand cast as the product of a (pre-computed) media-independent matrix and a vector involving PWRCs at a sparse sampling of integration angles. Compared to conventional Simpson's rule integration for computation of the SWRC, the Levin integration yields speed-up factors of an order of magnitude or more. Further, it results in reduced memory requirements for storage of pre-computed quantities, a desirable property when a graphics processing unit (GPU) is used for parallel computation of SWRCs. The paper applies trans-dimensional Bayesian inversion to investigate the impact of forward modeling in terms of PWRCs and SWRCs on the estimation of geoacoustic parameters and uncertainties. Model comparisons are quantified in simulated- and measured-data inversions by comparing the estimated geoacoustic parameters to the true parameters or core measurements, respectively, and by calculating the deviance information criterion for model selection.

Eigenvector pruning method for high resolution beamforming.

This paper introduces an eigenvector pruning algorithm for the estimation of the signal-plus-interference eigenspace, required as a preliminary step to subspace beamforming. The proposed method considers large-aperture passive array configurations operating in environments with multiple maneuvering targets in background noise, in which the available data for estimation of sample covariances and eigenvectors are limited. Based on statistical properties of scalar products between deterministic and complex random vectors, this work defines a statistically justified threshold to identify target-related features embedded in the sample eigenvectors, leading to an estimator for the signal-bearing eigenspace. It is shown that data projection into this signal subspace results in sharpening of beamforming outputs corresponding to closely spaced targets and provides better target separation compared to current subspace beamformers. In addition, the proposed threshold gives the user control over the worst-case scenario for the number of false detections by the beamformer. Simulated data are used to quantify the performance of the subspace estimator according to the distance between estimated and true signal subspaces. Beamforming resolution using the proposed method is analyzed with simulated data corresponding to a horizontal line array, as well as experimental data from the Shallow Water Array Performance experiment.

High-resolution bottom-loss estimation using the ambient-noise vertical coherence function.

The seabed reflection loss (shortly "bottom loss") is an important quantity for predicting transmission loss in the ocean. A recent passive technique for estimating the bottom loss as a function of frequency and grazing angle exploits marine ambient noise (originating at the surface from breaking waves, wind, and rain) as an acoustic source. Conventional beamforming of the noise field at a vertical line array of hydrophones is a fundamental step in this technique, and the beamformer resolution in grazing angle affects the quality of the estimated bottom loss. Implementation of this technique with short arrays can be hindered by their inherently poor angular resolution. This paper presents a derivation of the bottom reflection coefficient from the ambient-noise spatial coherence function, and a technique based on this derivation for obtaining higher angular resolution bottom-loss estimates. The technique, which exploits the (approximate) spatial stationarity of the ambient-noise spatial coherence function, is demonstrated on both simulated and experimental data.

An eigenvector-based test for local stationarity applied to array processing.

In sonar array processing, a challenging problem is the estimation of the data covariance matrix in the presence of moving targets in the water column, since the time interval of data local stationarity is limited. This work describes an eigenvector-based method for proper data segmentation into intervals that exhibit local stationarity, providing data-driven higher bounds for the number of snapshots available for computation of time-varying sample covariance matrices. Application of the test is illustrated with simulated data in a horizontal array for the detection of a quiet source in the presence of a loud interferer.

Coherence extrapolation for underwater ambient noise.

This paper considers extrapolation of the vertical coherence of surface-generated oceanic ambient noise to simulate measurements made on a longer sensor array. The extrapolation method consists of projecting the noise coherence measured with a limited aperture array into the domain spanned by prolate spheroidal wave functions, which are an orthogonal basis defined by array parameters and the noise frequency. Using simulated data corresponding to selected multi-layered seabeds as ground truth, the performance of the extrapolation method is explored. Application of the technique is also demonstrated on experimental data.

Caracterización de pacientes hipertensos mayores de 18 años del consultorio médico 3 del Policlínico Docente Ana Betancourt / Characterization of hypertensive patients older than 18 years from medical practice 3 at Ana Betancourt Polyclinic

Introducción: la hipertensión arterial es una enfermedad multifactorial que constituye un problema de salud mundial. Objetivo: caracterizar, en el orden clínico-epidemiológico, el estado actual de la hipertensión arterial en pacientes mayores de 18 años del consultorio médico de familia número 3, del Policlínico Ana Betancourt, del municipio capitalino de Playa. Métodos: 64 hipertensos integraron la muestra. Se les realizó una consulta control y aplicó un cuestionario que explora variables como: factores de riesgo individuales asociados a la enfermedad, comorbilidad, nivel de información del paciente sobre su padecimiento, esquema actual de tratamiento antihipertensivo, su cumplimiento y el nivel de control alcanzado por cada paciente. Resultados: la hipertensión arterial predominó en los ancianos, en las féminas 68,75 por ciento, en la raza negra 60,93 por ciento, en los que alcanzaron la secundaria básica 34,37 por ciento y carecen de vínculo laboral 54,69 por ciento. La obesidad constituyó el trastorno comórbido más frecuente 28,13 por ciento. El antecedente familiar de hipertensión arterial se identificó 67,19 por ciento como el factor de riesgo individual que más incidió en dicha enfermedad. El 57,81 por ciento utiliza un esquema combinado de fármacos hipotensores, siendo los diuréticos los más usados 71,88 por ciento. El 42,19 por ciento incumple con el tratamiento indicado. El nivel de información acerca de la enfermedad resultó insuficiente en el 68,75 por ciento. Solo en el 53,1 por ciento n=30 la enfermedad permanece controlada. Conclusiones: la herencia constituyó el principal factor de riesgo individual. Se demostró una relación directamente proporcional entre el control de la hipertensión, el cumplimiento del tratamiento farmacológico y el nivel de información del paciente acerca de su enfermedad(AU)

Introduction: hypertension is a multi-factorial disease that is a global health problem. Objective: to characterize the clinical and epidemiological features, the current status of hypertension in patients older than 18 years from the family medical practice number 3 at Ana Betancourt Polyclinic, in Playa municipality.Methods: 64 hypertensive patients were the sample. They underwent control queries and they answered a questionnaire exploring variables such as individual risk factors associated with the disease, co-morbidity, level of patient information about this illness, current antihypertensive treatment, its implementation and the level of control achieved by each patient. Results: hypertension was predominant in the elderly, in females 68.75 percent, in black race patients 60.93 percent, majored from junior high 34.37 percent, and no employment 54.69 percent. Obesity was the most common co-morbid disorder 28.13 percent. Family history of hypertension was identified 67,19 percent as the individual risk factor that most influenced in this disease. 57.81 percent use a combination regimen of antihypertensive drugs, diuretics were the most used 71.88 percent. 42.19 percent broke the indicated treatment. The level of information about the disease was insufficient in 68.75 percent. Only 53.1percent n = 30 keeps their disease controlled. Conclusions: heredity was the main individual risk factor. A directly proportional relationship between the control of hypertension, medication compliance and patient level information about their disease was demonstrated(AU)

Caracterización de pacientes hipertensos mayores de 18 años del consultorio médico 3 del Policlínico Docente Ana Betancourt / Characterization of hypertensive patients older than 18 years from medical practice 3 at Ana Betancourt Polyclinic

Introducción: la hipertensión arterial es una enfermedad multifactorial que constituye un problema de salud mundial. Objetivo: caracterizar, en el orden clínico-epidemiológico, el estado actual de la hipertensión arterial en pacientes mayores de 18 años del consultorio médico de familia número 3, del Policlínico Ana Betancourt, del municipio capitalino de Playa. Métodos: 64 hipertensos integraron la muestra. Se les realizó una consulta control y aplicó un cuestionario que explora variables como: factores de riesgo individuales asociados a la enfermedad, comorbilidad, nivel de información del paciente sobre su padecimiento, esquema actual de tratamiento antihipertensivo, su cumplimiento y el nivel de control alcanzado por cada paciente. Resultados: la hipertensión arterial predominó en los ancianos, en las féminas 68,75 por ciento, en la raza negra 60,93 por ciento, en los que alcanzaron la secundaria básica 34,37 por ciento y carecen de vínculo laboral 54,69 por ciento. La obesidad constituyó el trastorno comórbido más frecuente 28,13 por ciento. El antecedente familiar de hipertensión arterial se identificó 67,19 por ciento como el factor de riesgo individual que más incidió en dicha enfermedad. El 57,81 por ciento utiliza un esquema combinado de fármacos hipotensores, siendo los diuréticos los más usados 71,88 por ciento. El 42,19 por ciento incumple con el tratamiento indicado. El nivel de información acerca de la enfermedad resultó insuficiente en el 68,75 por ciento. Solo en el 53,1 por ciento n=30 la enfermedad permanece controlada. Conclusiones: la herencia constituyó el principal factor de riesgo individual. Se demostró una relación directamente proporcional entre el control de la hipertensión, el cumplimiento del tratamiento farmacológico y el nivel de información del paciente acerca de su enfermedad...

Introduction: hypertension is a multi-factorial disease that is a global health problem. Objective: to characterize the clinical and epidemiological features, the current status of hypertension in patients older than 18 years from the family medical practice number 3 at Ana Betancourt Polyclinic, in Playa municipality.Methods: 64 hypertensive patients were the sample. They underwent control queries and they answered a questionnaire exploring variables such as individual risk factors associated with the disease, co-morbidity, level of patient information about this illness, current antihypertensive treatment, its implementation and the level of control achieved by each patient. Results: hypertension was predominant in the elderly, in females 68.75 percent, in black race patients 60.93 percent, majored from junior high 34.37 percent, and no employment 54.69 percent. Obesity was the most common co-morbid disorder 28.13 percent. Family history of hypertension was identified 67,19 percent as the individual risk factor that most influenced in this disease. 57.81 percent use a combination regimen of antihypertensive drugs, diuretics were the most used 71.88 percent. 42.19 percent broke the indicated treatment. The level of information about the disease was insufficient in 68.75 percent. Only 53.1percent n = 30 keeps their disease controlled. Conclusions: heredity was the main individual risk factor. A directly proportional relationship between the control of hypertension, medication compliance and patient level information about their disease was demonstrated...

Trans-dimensional geoacoustic inversion of wind-driven ambient noise.

This letter applies trans-dimensional Bayesian geoacoustic inversion to quantify the uncertainty due to model selection when inverting bottom-loss data derived from wind-driven ambient-noise measurements. A partition model is used to represent the seabed, in which the number of layers, their thicknesses, and acoustic parameters are unknowns to be determined from the data. Exploration of the parameter space is implemented using the Metropolis-Hastings algorithm with parallel tempering, whereas jumps between parameterizations are controlled by a reversible-jump Markov chain Monte Carlo algorithm. Sediment uncertainty profiles from inversion of simulated and experimental data are presented.

Bayesian geoacoustic inversion using wind-driven ambient noise.

This paper applies Bayesian inversion to bottom-loss data derived from wind-driven ambient noise measurements from a vertical line array to quantify the information content constraining seabed geoacoustic parameters. The inversion utilizes a previously proposed ray-based representation of the ambient noise field as a forward model for fast computations of bottom loss data for a layered seabed. This model considers the effect of the array's finite aperture in the estimation of bottom loss and is extended to include the wind speed as the driving mechanism for the ambient noise field. The strength of this field relative to other unwanted noise mechanisms defines a signal-to-noise ratio, which is included in the inversion as a frequency-dependent parameter. The wind speed is found to have a strong impact on the resolution of seabed geoacoustic parameters as quantified by marginal probability distributions from Bayesian inversion of simulated data. The inversion method is also applied to experimental data collected at a moored vertical array during the MAPEX 2000 experiment, and the results are compared to those from previous active-source inversions and to core measurements at a nearby site.

Experimental observations of active invariance striations in a tank environment.

The waveguide invariant in shallow water environments has been widely studied in the context of passive sonar. The invariant provides a relationship between the frequency content of a moving broadband source and the distance to the receiver, and this relationship is not strongly affected by small perturbations in environment parameters such as sound speed or bottom features. Recent experiments in shallow water suggest that a similar range-frequency structure manifested as striations in the spectrogram exists for active sonar, and this property has the potential to enhance the performance of target tracking algorithms. Nevertheless, field experiments with active sonar have not been conclusive on how the invariant is affected by the scattering kernel of the target and the sonar configuration (monostatic vs bistatic). The experimental work presented in this paper addresses those issues by showing the active invariance for known scatterers under controlled conditions of bathymetry, sound speed profile and high SNR. Quantification of the results is achieved by introducing an automatic image processing approach inspired on the Hough transform for extraction of the invariant from spectrograms. Normal mode simulations are shown to be in agreement with the experimental results.

Radiative transfer theory applied to ocean bottom modeling.

Research on the propagation of acoustic waves in the ocean bottom sediment is of interest for active sonar applications such as target detection and remote sensing. The interaction of acoustic energy with the sea floor sublayers is usually modeled with techniques based on the full solution of the wave equation, which sometimes leads to mathematically intractable problems. An alternative way to model wave propagation in layered media containing random scatterers is the radiative transfer (RT) formulation, which is a well established technique in the electromagnetics community and is based on the principle of conservation of energy. In this paper, the RT equation is used to model the backscattering of acoustic energy from a layered elastic bottom sediment containing distributions of independent scatterers due to a constant single frequency excitation in the water column. It is shown that the RT formulation provides insight into the physical phenomena of scattering and conversion of energy between waves of different polarizations.

Mid-frequency acoustic propagation in shallow water on the New Jersey shelf: mean intensity.

Mid-frequency (1-10 kHz) sound propagation was measured at ranges 1-9 km in shallow water in order to investigate intensity statistics. Warm water near the bottom results in a sound speed minimum. Environmental measurements include sediment sound speed and water sound speed and density from a towed conductivity-temperature-depth chain. Ambient internal waves contribute to acoustic fluctuations. A simple model involving modes with random phases predicts the mean transmission loss to within a few dB. Quantitative ray theory fails due to near axial focusing. Fluctuations of the intensity field are dominated by water column variability.

Mid-frequency acoustic propagation in shallow water on the New Jersey shelf. II. Intensity fluctuation.

The scintillation index and the intensity cumulative distribution function of mid-frequency (2-10 kHz) sound propagation are presented at ranges of 1-9 km in a shallow water channel. The fluctuations are due to water column sound speed variability. It is found that intensity is only correlated over a narrow frequency band (50-200 Hz) and the bandwidth is independent of center frequency and range. Furthermore, the intensity probability distribution peaks at zero for all frequencies, and follows an exponential distribution at small values.

Índices de selección y niveles independientes de descarte para dos características productivas y reproductivas en un hato holstein (Bos taurus) / Índice de seleção e níveis independentes de abate para dois características produtivas e reprodutivas em um rebanho holstein (Bos taurus) / Selection indexes and independent culling levels for two productive and reproductive traits in a holstein (Bos taurus) dairy herd

Con la finalidad de evaluar la selección mediante índices y niveles independientes de descarte (NID), para las variables producción de leche ajustada a 305 días (PL) y periodo abierto (PA), fueron analizados 1708 y 1206 registros para PL y DA, respectivamente. Mediante el programa MTDFREML se estimaron parámetros de heredabilidad de 0.23 ± 0.065 y 0.09 ± 0.074, para PL y PA, respectivamente; y repetibilidad de 0.34 ± 0.061 y 0.18 ± 0.054, para PL y PA, respectivamente. Las correlaciones genética, ambiental, y fenotípica se estimaron entre PL y PA, con valores de 0.15 ± 0.32, 0.42 y 0.34, respectivamente. Para la elaboración de Índices y NID, y para la estimación de sus progresos genéticos, fueron analizadas diferentes relaciones entre valores económicos relativos. Los mayores progresos fueron encontrados para unos valores económicos relativos de 1 a 3 (PA:PL). Así mismo, diferentes intensidades de selección fueron evaluadas encontrando para ambos casos que los mayores progresos genéticos fueron obtenidos para la máxima intensidad de selección utilizada (fracción seleccionada del 10%). Ambos métodos de selección demostraron la obtención de progresos genéticos simultáneos para los rasgos en estudio; sin embargo, de acuerdo con la estimación de una relación comparativa entre los progresos genéticos, se encontró que mediante el método de índices se proyectó un 12.6% más progreso genético por generación respecto del progreso estimado para NID. A pesar de esto y de ser el índice un método superior para la elección de los mejores animales, este requiere una estimación precisa de las correlaciones entre las características, lo cual no fue del todo factible en el desarrollo de este trabajo, por lo que se sugiere que el uso del NID es más conveniente para un programa de selección de esta naturaleza.

With the purpose to evaluate genetic selection by using indexes and independent culling levels (ICL) for productive and reproductive traits, 305-d milk yield (MY) and days open (DO), 1707 and 1206 records for MY and DO, respectively, were analyzed. By means of the MTDFREML program genetic parameters for heritability of 0.23 ± 0.065 and 0.09 ± 0.074 for MY and DO, respectively, and for repeatability of 0.34 ± 0.061 and 0.18 ± 0.054 for MY and DO, respectively, were estimated. Also the genetic, phenotypic and environmental correlations between MY and DO were estimated, resulting in values of 0.15 ± 0.32, 0.42 and 0.34, respectively. For the indexes and ICL elaboration, and the estimation of genetic progress, different relations between relative economic values were analyzed. The highest progress was found for DO:MY economic values at 1:3 ratio. In the same way, evaluations for different selection intensities were done, where the highest genetic progress was obtained by the used of the maximum selection intensity (selected fraction of 10%) for both cases. Although with both selection methods the achievement of simultaneous genetic progress for each trait was demonstrated, by estimating a comparative relationship between both genetic progresses, a 12.6% more genetic progress by each generation was found for Index than for ICL methods. Nevertheless, despite being the Index a better method for selection of the best animals it requires a more precise estimation of correlations between traits, a process that was not feasible performed in the present study. Thereafter, ICL is proposed as the more convenient for that type of selection program.

A fim de avaliar a seleção através de índices e níveis independentes de abate (NID), para as variáveis produção de leite ajustada para 305 dias (PL) e dia aberto (DA), foram analisados os registros para 1708 e 1206 MP e DA, respectivamente. Através do programa MTDFREML parâmetros da herdabilidade de 0,23 ± 0,09 ± 0.065 e 0.074, foram estimados para PL e PA, respectivamente, e parâmetros de repetibilidade de 0.34 ± 0.061 e 0.18 ± 0.054, para PL e PA, respectivamente. Correlações genéticas, fenotípicas e ambientais foram estimados entre PL e PA, com valores de 0.15 ± 0.32, 0.42 e 0.34, respectivamente. Para o desenvolvimento de indicadores e NID, e para estimar seu progresso genético relações econômicas entre os diferentes valores foram analisados. O maior avanço foi encontrado por algum parente valores econômicos de 1 a 3 (DA:PL). Do mesmo modo, diferentes intensidades de seleção foram avaliadas para ambos os casos, constataram que os maiores progressos genéticos foram obtido para a intensidade máxima de seleção utilizada (fração selecionados a partir de 10%). Ambos os métodos de seleção mostrou obtenção de progressos simultâneos características genéticas no estudo, mas de acordo com a estimativa de uma relação entre o progresso genético comparativo, verificou-se que utilizando o índice é projetado um aumento 12.6% progresso genético uma geração de progresso em matéria estimado para NID. Apesar disto, e se o índice for superior a um método para a escolha das melhores animais, isto requer uma estimativa precisa das correlações entre as características, o que não era totalmente viável para o desenvolvimento deste trabalho, de modo a uso de NID é sugerido é mais adequado para um programa de seleção desta natureza...

Demonstration of the invariance principle for active sonar.

Active sonar systems can provide good target detection potential but are limited in shallow water environments by the high level of reverberation produced by the interaction between the acoustic signal and the ocean bottom. The nature of the reverberation is highly variable and depends critically on the ocean and seabed properties, which are typically poorly known. This has motivated interest in techniques that are invariant to the environment. In passive sonar, a scalar parameter termed the waveguide invariant, has been introduced to describe the slope of striations observed in lofargrams. In this work, an invariant for active sonar is introduced. This active invariant is shown to be present in the time-frequency structure observed in sonar data from the Malta Plateau, and the structure agrees with results produced from normal mode simulations. The application of this feature in active tracking algorithms is discussed.

Nanoporous noninvasive cellular electrical activity-based analysis devices.

In recent years, rapid advancements have been made in the biomedical applications of microtechnology and nanotechnology. While the focus of such technologies have been primarily on in vitro analytical and diagnostic tools, more recently in vivo therapeutic and sensing applications have gained attention. The long-term integration of cells with inorganic materials provides the basis for novel sensing platforms. The work presented here focuses on the ability to maintain cells long-term in nanoporous silicon-based microenvironments. This article describes the creation of nanoporous, biocompatible, alumina membranes as a platform for incorporation into a cell-based device targeted for in situ recording of cellular electrical activity variations due to the changes associated with the surrounding microenvironments. Studies described herein focus on the interaction of nanoporous alumina substrates embedded in silicon patterned with cells of interest. The fidelity of such a system is demonstrated in terms of viability, proliferation, and functionality. The capability of such microfabricated nanoporous membranes, as in vitro for cell-based assays for sensing and drug delivery applications, is also demonstrated. It has potential in vivo application for therapeutic immunoisolation.

[Mean airway pressure during pressure-controlled ventilation with static vs. dynamic positive end-expiratory pressure]. / Presión media de la vía aérea con la aplicación de presión positiva al final de la espiración estática vs. dinámica.

BACKGROUND: Positive end-expiratory pressure increases mean airway pressure (Paw) in patients with mechanical ventilation. We undertook this study to compare mean airway pressure (Paw) generated with static PEEP (sPEEP) vs. dynamic PEEP (dPEEP) at the same level of total PEEP (tPEEP) in the same patient with pressure-controlled mechanical ventilation (PC). METHODS: We conducted a prospective clinical trial at the Intensive Care Unit of a university-affiliated hospital. Consecutive patients in PC with SaO2>90%; FiO2<50%; sPEEP of 4 cm H2O and inspiration-expiration ratio (I:E ratio) 1:2 were included in the study. After a basal period of time of 15 min, Paw was registered (phase one of the study protocol). In phase 2 with the ventilator settings constant, only the I:E ratio was switched to 2:1 to generate dPEEP, and after 15 min Paw and total PEEP (tPEEP) were registered (tPEEP=sPEEP+dPEEP). In phase 3, the I:E ratio was switched back to 1:2 substituting the dPEEP generated in the second phase of the study by sPEEP to maintain the same level of tPEEP of phase 2. After 15 min, Paw was again registered. Friedman and Wilcoxon's test were used, p value<0.05 was considered statistically significant. RESULTS: Thirty eight patients were admitted to the study protocol, tPEEP was 4, 8 and 8 cm H2O and median of the Paw 8.7, 13.8, and 11.4 cm H2O, respectively, with a p value<0.05 in the first, second and third phases of the study. CONCLUSIONS: During pressure control ventilation, mean airway pressure is affected by the level of total PEEP and its composition. Paw is higher when dynamic PEEP participates in the composition of total PEEP.

Presión media de la vía aérea con la aplicación de presión positiva al final de la espiración estática vs. dinámica / Mean airway pressure during pressure-controlled ventilation with static vs. dynamic positive end-expiratory pressure

Introducción: la presión positiva al final de la espiración (PEEP) incrementa la presión media de la vía aérea (Paw) en pacientes con ventilación mecánica. Con el objetivo de comparar la presión media de la vía aérea que se obtiene en un mismo paciente con ventilación mecánica controlada por presión al aplicar presión positiva al final de la espiración estática (PEEPe) y al aplicar presión positiva al final de la espiración dinámica (PEEPd), se realizó un estudio prospectivo, longitudinal, experimental, comparativo y de grupos relacionados. Material y métodos: se incluyeron pacientes con ventilación mecánica controlada por presión con SaO2 > 90 % y FiO2 < 50%, con PEEPe de 4 cm de H2O y relación inspiraciónespiración de 1:2. Después de 15 minutos se midió la presión media de la vía aérea (fase 1). Posteriormente se modificó la relación inspiración-espiración a 2:1 por 15 minutos, con el fin de generar PEEPd (fase 2). Una vez registrada la presión media de la vía aérea, en la fase 3 se regresó de nuevo a la relación inspiración-espiración 1:2, sustituyendo la PEEPd obtenida en la fase 2 por PEEPe para mantener la misma presión positiva al final de la espiración total (PEEPt) de la fase 2 (PEEPt = PEEPe + PEEPd). Concluidos los 15 minutos de estabilización, se registró de nuevo la presión media de la vía aérea y la PEEPt. Se utilizaron las pruebas de Friedman y Wilcoxon, considerando una p < 0.05 como estadísticamente significativa. Resultados: se estudiaron 38 pacientes. La PEEPt fue de 4, 8 y 8 cm de H2O, y las medianas de la presión media de la vía aérea fueron de 8.7, 13.8 y 11.4 cm de H2O en las fases 1, 2 y 3 respectivamente (p < 0.05). Conclusiones: en un mismo paciente con ventilación mecánica controlada por presión y con los mismos niveles de PEEPt, la presión media de la vía aérea es mayor al utilizar PEEPd que PEEPe.

BACKGROUND: Positive end-expiratory pressure increases mean airway pressure (Paw) in patients with mechanical ventilation. We undertook this study to compare mean airway pressure (Paw) generated with static PEEP (sPEEP) vs. dynamic PEEP (dPEEP) at the same level of total PEEP (tPEEP) in the same patient with pressure-controlled mechanical ventilation (PC). METHODS: We conducted a prospective clinical trial at the Intensive Care Unit of a university-affiliated hospital. Consecutive patients in PC with SaO2>90%; FiO2<50%; sPEEP of 4 cm H2O and inspiration-expiration ratio (I:E ratio) 1:2 were included in the study. After a basal period of time of 15 min, Paw was registered (phase one of the study protocol). In phase 2 with the ventilator settings constant, only the I:E ratio was switched to 2:1 to generate dPEEP, and after 15 min Paw and total PEEP (tPEEP) were registered (tPEEP=sPEEP+dPEEP). In phase 3, the I:E ratio was switched back to 1:2 substituting the dPEEP generated in the second phase of the study by sPEEP to maintain the same level of tPEEP of phase 2. After 15 min, Paw was again registered. Friedman and Wilcoxon's test were used, p value<0.05 was considered statistically significant. RESULTS: Thirty eight patients were admitted to the study protocol, tPEEP was 4, 8 and 8 cm H2O and median of the Paw 8.7, 13.8, and 11.4 cm H2O, respectively, with a p value<0.05 in the first, second and third phases of the study. CONCLUSIONS: During pressure control ventilation, mean airway pressure is affected by the level of total PEEP and its composition. Paw is higher when dynamic PEEP participates in the composition of total PEEP.