Petr Kudrna

Models of PaO2 response to the continuous distending pressure maneuver during high frequency oscillatory ventilation in healthy and ARDS lung model pigs

ABSTRACT Purpose/Aim: High-frequency oscillatory ventilation (HFOV) is a method of ventilation that theoretically achieves the goals of lung protective ventilation in acute respiratory distress syndrome (ARDS) patients. It is characterized by a rapid delivery of small tidal volumes at high frequencies oscillating around a continuous distending pressure (CDP). Optimization of CDP is not an easy task and it is titrated empirically in the clinical practice. The aim of this study is to investigate whether the level of CDP consistently affects the shape of the partial pressure of oxygen (PaO2) response to stepwise changes in CDP during HFOV of healthy and ARDS-induced pigs. Materials and Methods: We performed two stepwise maneuvers of CDP in 14 pigs: one before and one after the lung lavage, inducing ARDS. For each CDP step performed, we fitted a segment of PaO2 curve with a one-term power model. Results: PaO2 course follows shapes modeled by root, linear, quadratic, and cubic functions for values of PaO2 ≤ 110 mmHg and PaO2 ≤ 200 mmHg, before and after the lung lavage, respectively. PaO2 course follows a shape modeled exclusively by a root function for values of PaO2 > 110 mmHg and PaO2 > 200 mmHg, before and after the lung lavage, respectively. It is not possible to describe a relationship between the shape of the PaO2 course and the values of CDP. Conclusions: The PaO2 curve may give information about the level of recruitment of alveoli, but cannot be used for optimization of CDP level during HFOV in healthy and ARDS lung model pigs.

Design and Demonstration of a Complex Neonatal Physiological Model for Testing of Novel Closed-Loop Inspired Oxygen Fraction Controllers

Recently published clinical trials document that manual control of oxygen fraction in the inspiratory gas in neonates is not prompt enough to react to the rapidly changing physiological status of a neonate. As a result, the arterial blood oxygen saturation exhibits significantly long periods when the actual oxygen saturation level goes outside the desired safe range. Simple closed-loop systems are able to optimize the inspiratory oxygen fraction in steady-state situations, but they do not perform well in the context of rapidly changing physiological parameters. As a consequence, new algorithms for the closed-loop control of the inspired oxygen fraction are being developed and are becoming available. The aim of our study was to create a physiologically-realistic model of a neonatal organism allowing more extensive bench testing of newly developed algorithms for oxygen control in neonates. The design of the model is based both on the theoretical and up-to-date knowledge of the physiological principles, as well as on the well-documented observations by the authors in the neonatal intensive care units. The simulated outputs of the model correlate well with the real situations observed in the clinical environment.

Variability of vital signs in simulations with mannequin in education of bioengineers

We are using life-size mannequins within an education subjects, e.g. “Medical devices” for a demonstration of basic principles of modern clinical devices such as mechanical lung ventilator. Limitation of many simulators is uniformity of its outputs for same input parameters. This paper describes variability of the vital signs of the mannequin when the same scenario was used for different base patients available at human patient simulator.

Electronic hand grip dynamometer

Main purpose of this paper is to describe a propose and compile a dynamometric measurement system which would measure the isometric force of a handgrip. Although, in the practice, there have already been the mechanic hand dynamometers which could evaluate only a limited amount of information, precisely the maximum strength of a handgrip, our aim is to compile the full electronic hand dynamometer. This work is focused on a design of an appropriate hardware and software for processing and evaluating of the measured data. By the software is able to display the dynamometric graph and also the actual and the maximal strength. It is possible to count maximal gradient of the strength and all these data could be stored in a file. The created dynamometric system might be used in the clinical practice, more accurately on the rehabilitation department where it could replace the current mechanical hand dynamometers or for patients with Parkinsons disease where is possible to evaluate a tremor.

Response time of indirectly accessed gas exchange depends on measurement method

Abstract Noninvasive techniques are routinely used for assessment of tissue effects of lung ventilation. However, comprehensive studies of the response time of the methods are scarce. The aim of this study was to compare the response time of noninvasive methods for monitoring of gas exchange to sudden changes in the composition of the inspired gas. A prospective experimental study with 16 healthy volunteers was conducted. A ventilation circuit was designed that enabled a fast change in the composition of the inspiratory gas mixture while allowing spontaneous breathing. The volunteers inhaled a hypoxic mixture, then a hypercapnic mixture, a hyperoxic mixture and finally a 0.3% CO mixture. The parameters with the fastest response to the sudden change of O2 in inhaled gas were peripheral capillary oxygen saturation (SpO2) and regional tissue oxygenation (rSO2). Transcutaneous oxygen partial pressure (tcpO2) had almost the same time of reaction, but its time of relaxation was 2–3 times longer. End-tidal carbon dioxide (EtCO2) response time to change of CO2 concentration in inhaled gas was less than half in comparison with transcutaneous carbon dioxide partial pressure (tcpCO2). All the examined parameters and devices reacted adequately to changes in gas concentration in the inspiratory gas mixture.

Models of a PaO2 Course during a Stepwise Change of Continuous Distending Pressure in HFOV

Acute respiratory distress syndrome (ARDS) is an acute severe lung disease commonly encountered in intensive care units. High-frequency oscillatory ventilation (HFOV) could offer effective lung protective ventilation by delivering very low tidal volumes around constant relatively higher continuous distending pressure (CDP) at frequencies of 3 to 15 Hz. Optimization of CDP is not an easy task and it is titrated empirically in the clinical practice. The aim of this study is to investigate if the level of CDP affects the shape of the partial pressure of oxygen (PaO2) response of the organism to the CDP stepwise changes. Ten pigs were used in this study. In order to mimic ARDS, surfactant deficiency was induced by a double or triple lung lavage. Every 10 minutes, CDP was stepwise increased by 2 cmH2O. Increase in CDP was stopped when severe signs of hemodynamics deterioration were observed and then, CDP was stepwise decreased by 2 cmH2O to its initial value. For each CDP step performed, we fitted PaO2 with a one-term power model as follows: y=a·x b, where x is the time, a is the amplitude of the model and exponent b reflects the shape of the model. For values of PaO2200mmHg, PaO2 course follows a shape modelled exclusively by a root function. It is not possible to describe a relationship between the shape of the PaO2 course and the values of CDP. When alveoli are not recruited at all, oxygenation is more sensitive to changes in lung volume and aeration and thus, PaO2 grows or drops rapidly following linear and/or quadratic functions. Instead of, when alveoli are open and recruited changes in PaO2 are less sensitive to minor changes in lung aeration and thus, PaO2 grows and drops slower following only root function. The CDP level does not affect the response of organism in terms of shape change of PaO2, probably due to the fact that the recruitment occurs at different values in each pig.

Identification of the model of the respiratory system in high-frequency oscillatory ventilation

Mechanical ventilation is used during respiratory failure in many patients. High-frequency oscillatory ventilation is used as a rescue therapy at adult patients. High-frequency ventilation has minimum monitoring and even tidal volume is not routinely measured. Models of the respiratory system can contribute to better understanding about principle of high-frequency oscillatory ventilation. The identification of simple RLC model is described in the study and effect of lung compliance upon tidal volume and alveolar pressure is discussed. It was shown that reduced lung compliance has a minimal effect upon tidal volume whereas it significantly affects an amplitude of alveolar pressure.

Software monitor of vital functions for a mannequin realized on tablet PC

This Study deals with a development of a virtual patient monitor for a mannequin. We have included the virtual patient simulator into the education and we have developed the application of software monitor to increase the interest of the students about the exercises. The application is developed for a PC tablet and the data of vital functions, such as heart rate, saturation of blood by oxygen, partial pressure of oxygen and carbon dioxide in the arterial blood, are transferred from the simulator into the mobile patient monitor. Application is developed in LabVIEW environment and Data Dashboard application from National Instruments is used for displaying the data. Transfer of data between control computer with model and tablet is realized by Shared Variables Engine.