Changes in ventilatory mechanics caused by variations in PEEP and pressure support : study in healthy subjects under non-invasive mechanical ventilation

RESUMEN: Introducción. Por lo general, la mecánica ventilatoria se ha estimado en modo controlado con el uso de aproximaciones no adecuadas para ventilación espontánea. Objetivo. Medir los cambios de la mecánica ventilatoria ante variaciones de la presión positiva al final de la expiración (PEEP, por su sigla en inglés) y la presión soporte (PS) en ventilación mecánica no invasiva. Materiales y métodos. A través de una estrategia no invasiva, se estimó la mecánica ventilatoria bajo diferentes niveles de PEEP y PS. Para tal fin, se utilizó un simulador mecánico y se registró una base de datos de 14 sujetos sanos conectados de manera no invasiva a un ventilador mecánico. Resultados. Se obtuvieron valores medianos de resistencia y compliancia de 91.2[77.8-135.9]mL/cmH2O y 8.3[6.1-10.4]cmH2O/L/s para los 14 sujetos sanos con PEEP y PS de 0 cmH2O, respectivamente. En los incrementos de PEEP, los sujetos presentaron aumento estadísticamente significativo en la compliancia. Por el contrario, en el incremento de presión soporte, no se observaron cambios de ningún parámetro. Conclusiones. Se encontraron valores de compliancia y resistencia, acordes con los configurados en el simulador mecánico y coherentes con los reportados en la literatura en el caso de sujetos sanos. Esto resulta de gran utilidad al tomar decisiones en unidades de cuidados intensivos.ABSTRACT: Introduction: Traditionally, ventilatory mechanics has been delivered in controlled modes through the use of inappropriate approaches for spontaneous ventilation. Objective: To measure the changes of ventilatory mechanics caused by PEEP and pressure support (PS) variations in non-invasive mechanical ventilation. Materials and methods: The ventilatory mechanics was evaluated through a non-invasive strategy, under different PEEP and pressure support levels. For this purpose, a mechanical simulator was used, and a database of 14 healthy subjects non-invasively connected to a mechanical ventilator was recorded. Results: For the 14 healthy subjects under PEEP and pressure support conditions of 0 cmH2O, the median resistance and compliance values were 91.2 [77.8-135.9] mL/cmH2O and 8.3[6.1-10.4]cmH2O/L/s, respectively. PEEP compliance showed a statistically significant increase in all subjects. On the other hand, no changes in any of the parameters were observed regarding pressure support increase. Conclusions: The proposed technique allowed to find compliance and resistance values consistent with those set in the mechanical simulator, which, in turn, coincide with those reported in the literature for healthy subjects. This information is useful for decision-making in intensive care units

Laboratorio virtual para prácticas de control por computador

Aquest treball descriu un laboratori virtual desenvolupat per a donar suport a les pràctiques de Control per Computador de l'ETSEIB (Escola Tècnica Superior d'Enginyers Industrials de Barcelona). El laboratori està totalment desenvolupat mitjançant Easy Java Simulations (EJS).Peer Reviewe

Optimization techniques in respiratory control system models

One of the most complex physiological systems whose modeling is still an open study is the respiratory control system where different models have been proposed based on the criterion of minimizing the work of breathing (WOB). The aim of this study is twofold: to compare two known models of the respiratory control system which set the breathing pattern based on quantifying the respiratory work; and to assess the influence of using direct-search or evolutionary optimization algorithms on adjustment of model parameters. This study was carried out using experimental data from a group of healthy volunteers under CO2 incremental inhalation, which were used to adjust the model parameters and to evaluate how much the equations of WOB follow a real breathing pattern. This breathing pattern was characterized by the following variables: tidal volume, inspiratory and expiratory time duration and total minute ventilation. Different optimization algorithms were considered to determine the most appropriate model from physiological viewpoint. Algorithms were used for a double optimization: firstly, to minimize the WOB and secondly to adjust model parameters. The performance of optimization algorithms was also evaluated in terms of convergence rate, solution accuracy and precision. Results showed strong differences in the performance of optimization algorithms according to constraints and topological features of the function to be optimized. In breathing pattern optimization, the sequential quadratic programming technique (SQP) showed the best performance and convergence speed when respiratory work was low. In addition, SQP allowed to implement multiple non-linear constraints through mathematical expressions in the easiest way. Regarding parameter adjustment of the model to experimental data, the evolutionary strategy with covariance matrix and adaptation (CMA-ES) provided the best quality solutions with fast convergence and the best accuracy and precision in both models. CMAES reached the best adjustment because of its good performance on noise and multi-peaked fitness functions. Although one of the studied models has been much more commonly used to simulate respiratory response to CO2 inhalation, results showed that an alternative model has a more appropriate cost function to minimize WOB from a physiological viewpoint according to experimental data.Postprint (author's final draft

Cambios en la articulación de la palabra en pacientes con oclusión clase III o mordida abierta anterior sometidos a cirugía ortognática

ABSTRACT: This study analyzed the changes that occurred in the articulation of oral phonemes (AP), the levels of stridence and hissing in patients with class III malocclusion and / or anterior open bite and that were subjected to orthognathic surgery. The sample consisted of 16 patients (12 females and 4 males), 12 of them were treated at the Stomatological and Maxillofacial Surgery Unit of the Hospital Universitario San Vicente de Paul, the other 4 were selected from private practice during the period of March and December 2001. The age range was between 16 and 37 years of age, with an average of 23,8 years. The sample included patients with class III malocclusion and / or anterior open bite that underwent orthognathic surgery. A Sound Forge 5.0® software, property of the radio station of University of Antioquia was used to look for changes in the articulation of various phonemes that imply dentoalveolar pronunciation. The results suggest that after the surgical correction of the skeletal discrepancies there is a positive change of the phonemes for the majority of patients.RESUMEN: La presente investigación analizó los cambios en la articulación de la palabra (AP), los niveles de estridencia y sibilancia en pacientes con maloclusiones clase III o mordida abierta anterior sometidos a cirugía ortognática, con el fin de aportar e integrar conocimientos a la profesión odontológica en el manejo integral y multidisciplinario de dichas alteraciones. La muestra incluyó dieciséis pacientes (doce mujeres y cuatro hombres), doce de ellos fueron atendidos en la Unidad de Cirugía Maxilofacial y Estomatología del Hospital Universitario San Vicente de Paúl, Medellín (Colombia), y los cuatro restantes fueron seleccionados en la consulta privada durante el periodo comprendido entre marzo y diciembre de 2001. La edad osciló entre los 16 y 37 años de edad, con un promedio de 23,8 años. Se incluyeron pacientes con oclusión clase III o mordida abierta anterior que fueron sometidos a procedimientos de cirugía ortognática. Para la evaluación de la AP se utilizó un software Sound Forge 5.0® de propiedad y licencia de la Emisora Cultural de la Universidad de Antioquia, en la búsqueda de cambios en la articulación de diversos fonemas que implican pronunciación dento alveolar. Los resultados sugieren que luego de la corrección quirúrgica de las discrepancias esqueléticas se obtiene un cambio positivo en la articulación de la palabra para la mayoría de los pacientes

Closed loop system prototype for intravenous anesthesia administration

RESUMEN: En este artículo se presenta el desarrollo de un sistema en lazo cerrado de administración de anestesia intravenosa. Para lograr esto se implementan diferentes subsistemas: un modelo multicompartimental de distribución de fármacos en el cuerpo humano, un algoritmo para determinar la curva de velocidades a las que debe infundirse el anestésico Propofol para obtener el efecto de anestesia general, un protocolo de comunicación para enviar el vector de velocidades a una bomba de infusión convencional y un lazo de realimentación para controlar todo el sistema a partir del índice bi-espectral que se utiliza como indicador de la profundidad de anestesia. El resultado final es un instrumento versátil, con prestaciones similares a las de equipos comerciales y con una interfaz interactiva, que facilita la operación por parte del anestesiólogo desde un computador convencional.ABSTRACT: This paper presents the development of a closed-loop system for intravenous administration. Therefore, several sub-systems have been developed independently. A multi-compartment drug distribution model for the human body, an algorithm for determining the infusion rate of Propofol to achieve the desired anesthesia effect, a communication protocol for sending the infusion rate array to a conventional infusion pump. Finally, a feedback to control the whole system based on a bi-spectral index signal (BIS) as an anesthetic deepness measure. The final result is a useful instrument, similar to commercially available systems, with a friendly interface that can be controlled by the anesthesiologist from a personal computer

Designing of a portable and wireless device for ambulatory monitoring of non-invasive blood pressure

En países en vía de desarrollo, la medición de los signos vitales es realizada en hospitales o laboratorios especializados donde los pacientes permanecen bajo observación médica. La integración de sistemas de adquisición de datos biomédicos con las tecnologías de la información, permite un monitoreo continuo de variables fisiológicas sin que el paciente deba desplazarse a centros especializados, lo que mejora la calidad de la atención médica y ofrece posibilidades únicas para la investigación. Este artículo presenta un monitor de presión arterial no invasiva, automático, portátil y de control inalámbrico mediante el uso del protocolo ZigBee, diseñado para ser usado en lugares fuera de la cobertura presencial de instituciones médicas. Además del diseño y la implementación de un prototipo del sistema de monitoreo usando una red inalámbrica de área personal, se presentan resultados satisfactorios de su uso.In developing countries, the measurement of vital signs is performed at hospitals or specialized laboratorieswhere patients remain under medical observation. The integration of biomedical data acquisition systems andinformation technologies allow a continuous monitoring of patient’s physiological variables (parameters)without moving himself to remote medical centers, which improves medical care quality and offers uniqueopportunities for research. This paper presents anautomatic and portable non-invasive blood pressuremonitor, which incorporates a module for wireless communication using the ZigBee protocol, designed tobeused outside the coverage area of health care centers. Additionally to the designing and building of theprototype, the preliminary results of its use are presente

A novel strategy to fit and validate physiological models: a case study of acardiorespiratory model for simulation of incremental aerobic exercise

Applying complex mathematical models of physiological systems is challenging due to the large number of parameters. Identifying these parameters through experimentation is difficult, and although procedures for fitting and validating models are reported, no integrated strategy exists. Additionally, the complexity of optimization is generally neglected when the number of experimental observations is restricted, obtaining multiple solutions or results without physiological justification. This work proposes a fitting and validation strategy for physiological models with many parameters under various populations, stimuli, and experimental conditions. A cardiorespiratory system model is used as a case study, and the strategy, model, computational implementation, and data analysis are described. Using optimized parameter values, model simulations are compared to those obtained using nominal values, with experimental data as a reference. Overall, a reduction in prediction error is achieved compared to that reported for model building. Furthermore, the behavior and accuracy of all the predictions in the steady state were improved. The results validate the fitted model and provide evidence of the proposed strategy’s usefulness.Peer ReviewedPostprint (published version

Modeling of cardiovascular system for evaluation of vascular reactivity estimation techniques based on reactive hyperemia

RESUMEN: La evaluación de la reactividad vascular (RV) se hace mediante la respuesta hiperémica después de una isquemia producida por oclusión arterial. Existen técnicas de medición de RV que permiten evaluar la función vascular con menor costo y sin dependencia del operador, pero se encuentran en desarrollo y requieren validación y aceptación clínica. Objetivo: Modelar computacionalmente la mecánica vascular con el fin de evaluar el desempeño de una técnica de RV. Materiales y métodos: Se modificó el modelo eléctrico de la vasculatura del brazo, obteniendo el volumen periférico con y sin oclusión de la arteria braquial. Se realizó una identificación computacional que relaciona el volumen periférico con los resultados de una técnica de evaluación de RV que presenta cambios de color en la mano ocluida durante hiperemia reactiva. El software utilizado fue Matlab®. Resultados: El modelo modificado permitió obtener el volumen periférico con y sin oclusión representando la perfusión en la microvascultura. El modelo no lineal Hammerstein-Weiner fue el mejor descriptor de los cambios de color en función de la dinámica del sistema vascular y presentó porcentaje de ajuste promedio de 95,69%. Conclusiones: Es posible modelar computacionalmente la técnica de evaluación de la función vascular utilizando identificación no lineal.ABSTRACT: The evaluation of vascular reactivity (VR) is done by the hyperemic response after ischemia produced by arterial occlusion. There are VR measurement techniques that allow the evaluation of vascular function at lower cost and without dependence on the operator, but they are in development and require validation and clinical acceptance. Objective: To model vascular mechanics computationally in order to evaluate the performance of a VR technique. Materials and methods: The electrical model of the vasculature of the arm was modified, obtaining the peripheral volume with and without brachial artery occlusion. A computational identification, which relates the peripheral volume to the results of a VR evaluation technique and presents color changes in the occluded hand during reactive hyperemia, was performed. The software used was Matlab®. Results: The modified model allowed to obtain the peripheral volume with and without occlusion, representing the perfusion in the microvasculature. The Hammerstein-Weiner non-linear model was the best descriptor of color changes depending on the dynamics of the vascular system and it presented an average adjustment percentage of 95.69%. Conclusions: It is possible to model computationally the technique of evaluation of vascular function using nonlinear identification

Potencial aplicação clínica da eletromiografia de superfície como indicador de recuperação neuromuscular durante testes de desmame após envenenamento por organofosforados

ABSTRACT: This study aimed to explore the usefulness of measuring respiratory muscle activity in mechanically ventilated patients suffering from acute organophosphate poisoning, with a view towards providing complementary information to determine the best time to suspend ventilatory support. Surface electromyography in respiratory muscles (diaphragm, external intercostal and sternocleidomastoid muscles) was recorded in a young man affected by selfpoisoning with an unknown amount of parathion to determine the muscle activity level during several weaning attempts from mechanical ventilation. The energy distribution of each surface electromyography signal frequency, the synchronization between machine and patient and between muscles, acetylcholinesterase enzyme activity, and work of breathing and rapid shallow breathing indices were calculated in each weaning attempt. The work of breathing and rapid shallow breathing indices were not correlated with the failure/success of the weaning attempt. The diaphragm gradually increased its engagement with ventilation, achieving a maximal response that correlated with successful weaning and maximal acetylcholinesterase enzyme activity; in contrast, the activity of accessory respiratory muscles showed an opposite trend

Dispositivo para simulación de patologías restrictivas en sujetos sanos ventilados mecánicamente de manera no invasiva

RESUMEN: La evaluación de la mecánica ventilatoria en pacientes ventilados mecánicamente permite ajustar su tratamiento en las unidades de cuidados intensivos en términos del ajuste del modo ventilatorio y sus parámetros asociados. Sin embargo, solo con maniobras obstructivas es posible estimar parámetros como la compliancia y la resistencia respiratorias en ventilación espontánea. Una de las limitaciones más importantes en el desarrollo de técnicas de estimación no obstructivas de la mecánica ventilatoria es que se trata de un sistema no estacionario y la variación de sus parámetros está sujeta a la variabilidad del patrón ventilatorio. Este artículo tiene como objetivo presentar y evaluar un dispositivo que permita modificar artificialmente la distensibilidad torácica de un sujeto sano, lo cual permitirá registrar en un futuro una base de datos útil para el desarrollo de técnicas de estimación de la mecánica ventilatoria. El dispositivo se conformó por una coraza, una bomba y un controlador que permite variar la presión al interior de la coraza, la cual fue ubicada en el pecho y abdomen de los voluntarios para cambiar la distensibilidad de manera controlada. 5 voluntarios participaron en la avaluación del dispositivo, consiguiendo cambios porcentuales de 34,5 ± 9,4% respecto a su valor en reposo para una presión de 10 cmH2O y cambios de 46,8 ± 5,7% para la máxima presión de 20 cmH2O. Se logró diseñar un dispositivo que permitiera modificar artificialmente la distensibilidad torácica de manera comparable para cualquier sujeto sano. Palabras claves: Mecánica ventilatoria, compliancia torácica, enfermedades restrictivas, sistemas de control.ABSTRACT: The respiratory mechanics assessment in patients with mechanical ventilation allows to adjust the treatment in intensive care units related to the ventilatory mode and parameters of mechanical ventilator settings. However, to estimate the compliance and respiratory resistance in spontaneous ventilation is only possible with obstructive maneuvers or invasive techniques. One of the most important limitations to develop new techniques for respiratory mechanics estimation is the non-stationary characteristic of the system and the variability of parameters according to the variability of the breathing pattern. The aim of this article is to present and evaluate a device that allows artificially modify the thoracic compliance of a healthy subject, which will make possible to register in the future a useful database for the development of techniques for estimating ventilatory mechanics. The device was formed by a cuirass, a pump and a controller that allows to vary the pressure inside the cuirass, which was placed in the chest and abdomen of the volunteers to change compliance in a controlled manner. 5 volunteers participated in the performance test of the device, achieving percentage changes of 34.5 ± 9.4% respecting their resting value for a pressure of 10 cmH2O and changes of 46.8 ± 5.7% for the maximum pressure of 20 cmH2O. It was possible to design a device that allowed to artificially modify thoracic compliance in a comparable way for any healthy subject. KEYWORDS: Respiratory mechanics, thoracic compliance, restrictive diseases, control systems