Karel Roubik

Imposed work of breathing during high-frequency oscillatory ventilation: a bench study

IntroductionThe ventilator and the endotracheal tube impose additional workload in mechanically ventilated patients breathing spontaneously. The total work of breathing (WOB) includes elastic and resistive work. In a bench test we assessed the imposed WOB using 3100 A/3100 B SensorMedics high-frequency oscillatory ventilators.MethodsA computer-controlled piston-driven test lung was used to simulate a spontaneously breathing patient. The test lung was connected to a high-frequency oscillatory ventilation (HFOV) ventilator by an endotracheal tube. The inspiratory and expiratory airway flows and pressures at various places were sampled. The spontaneous breath rate and volume, tube size and ventilator settings were simulated as representative of the newborn to adult range. The fresh gas flow rate was set at a low and a high level. The imposed WOB was calculated using the Campbell diagram.ResultsIn the simulations for newborns (assumed body weight 3.5 kg) and infants (assumed body weight 10 kg) the imposed WOB (mean ± standard deviation) was 0.22 ± 0.07 and 0.87 ± 0.25 J/l, respectively. Comparison of the imposed WOB in low and high fresh gas flow rate measurements yielded values of 1.63 ± 0.32 and 0.96 ± 0.24 J/l (P = 0.01) in small children (assumed body weight 25 kg), of 1.81 ± 0.30 and 1.10 ± 0.27 J/l (P < 0.001) in large children (assumed body weight 40 kg), and of 1.95 ± 0.31 and 1.12 ± 0.34 J/l (P < 0.01) in adults (assumed body weight 70 kg). High peak inspiratory flow and low fresh gas flow rate significantly increased the imposed WOB. Mean airway pressure in the breathing circuit decreased dramatically during spontaneous breathing, most markedly at the low fresh gas flow rate. This led to ventilator shut-off when the inspiratory flow exceeded the fresh gas flow.ConclusionSpontaneous breathing during HFOV resulted in considerable imposed WOB in pediatric and adult simulations, explaining the discomfort seen in those patients breathing spontaneously during HFOV. The level of imposed WOB was lower in the newborn and infant simulations, explaining why these patients tolerate spontaneous breathing during HFOV well. A high fresh gas flow rate reduced the imposed WOB. These findings suggest the need for a demand flow system based on patient need allowing spontaneous breathing during HFOV.

Testing of new models of the human visual system for image quality evaluation

This article deals with evaluation of image quality by various methods and comparison of their results. Generally, there are several ways how to assess image quality. Three main approaches are: subjective testing, objective testing and image quality evaluation using a human visual system model (HVS). The subjective testing is based on human perception, the objective testing on a mathematical computing and the human vision models on mathematical modelling of the human vision with respecting the human perception properties. Then, the described methods and two novel designed HVS models are used for image quality evaluation using a set of images. The results of modelling were compared with results of the subjective and objective methods.

Spontaneous breathing during high-frequency oscillatory ventilation improves regional lung characteristics in experimental lung injury.

Background: Maintenance of spontaneous breathing is advocated in mechanical ventilation. This study evaluates the effect of spontaneous breathing on regional lung characteristics during high‐frequency oscillatory (HFO) ventilation in an animal model of mild lung injury.

Demand flow facilitates spontaneous breathing during high-frequency oscillatory ventilation in a pig model.

Objective:Maintenance breathing is advocated in mechanical ventilation, which is difficult for the high-frequency oscillatory (HFO) ventilation. To facilitate spontaneous breathing during HFO ventilation, a demand flow system (DFS) was designed. The aim of the present study was to evaluate the system. Design:Animal experiment. Setting:University animal laboratory. Subjects:Eight pigs (47–64 kg). Interventions:Lung injury was induced by lung lavage with normal saline. After spontaneous breathing was restored HFO ventilation was applied, in runs of 30 minutes, with continuous fresh gas flow (CF) or the DFS operated in two different setups. Pressure to regulate the DFS was sampled directly at the Y-piece of the ventilator circuit (DFS) or between the endotracheal tube and measurement equipment at the proximal end of the endotracheal tube. In the end, animals were paralyzed. Breathing pattern, work of breathing, and gas exchange were evaluated. Measurements and Main Results:HFO ventilation with demand flow decreased breathing frequency and increased tidal volume compared with CF. Comparing HFO modes CF, DFS, and DFSPROX, total pressure–time product (PTP) was 66 cm H2O·sec·min−1 (interquartile range 59–74), 64 cm H2O·sec·min−1 (50–72), and 51 cm H2O·sec·min−1 (41–63). Ventilator PTP was 36 cm H2O·sec·min−1 (32–42), 8.6 cm H2O·sec·min−1 (7.4–10), and 1 cm H2O·sec·min−1 (−1.0 to 2.8). Oxygenation, evaluated by Pao2, was preserved when spontaneous breathing was maintained and deteriorated when pigs were paralyzed. Ventilation, evaluated by Paco2, improved with demand flow. Paco2 increased when using continuous flow and during muscular paralysis. Conclusions:In moderately lung-injured anesthetized pigs during HFO ventilation, demand flow facilitated spontaneous breathing and augmented gas exchange. Demand flow decreased total breathing effort as quantified by PTP. Imposed work caused by the HFO ventilator appeared totally reduced by demand flow.

Design and Control of a Demand Flow System Assuring Spontaneous Breathing of a Patient Connected to an HFO Ventilator

Lung protective ventilation is intended to minimize the risk of ventilator induced lung injury and currently aimed at preservation of spontaneous breathing during mechanical ventilation. High-frequency oscillatory ventilation (HFOV) is a lung protective ventilation strategy. Commonly used high-frequency oscillatory (HFO) ventilators, SensorMedics 3100, were not designed to tolerate spontaneous breathing. Respiratory efforts in large pediatric and adult patients impose a high workload to the patient and may cause pressure swings that impede ventilator function. A Demand Flow System (DFS) was designed to facilitate spontaneous breathing during HFOV. Using a linear quadratic Gaussian state feedback controller, the DFS alters the inflow of gas into the ventilator circuit, so that it instantaneously compensates for the changes in mean airway pressure (MAP) in the ventilator circuit caused by spontaneous breathing. The undesired swings in MAP are thus eliminated. The DFS significantly reduces the imposed work of breathing and improves ventilator function. In a bench test the performance of the DFS was evaluated using a simulator ASL 5000. With the gas inflow controlled, MAP was returned to its preset value within 115 ms after the beginning of inspiration. The DFS might help to spread the use of HFOV in clinical practice.

Objective and subjective image quality evaluation for security technology

The paper is devoted to the impacts of image compression algorithms on security image data. It compares three fundamentally different evaluation techniques of image objective criteria, subjective criteria and identification. We have selected two typical security image data (a car plate and a face) with different initial quality and we applied three different compression techniques-two professional (JPEG and LuRaWave-LWF) and one implemented (Karhunen-Loeve transform, KLT). A set of compressed images differing in compression rate was derived from each original image data. Finally the MSE as an objective criterion, the subjective image quality according to the ITU-R Rec. 500 and the identification measure were evaluated and compared.

Work of Breathing into Snow in the Presence versus Absence of an Artificial Air Pocket Affects Hypoxia and Hypercapnia of a Victim Covered with Avalanche Snow: A Randomized Double Blind Crossover Study.

Presence of an air pocket and its size play an important role in survival of victims buried in the avalanche snow. Even small air pockets facilitate breathing. We hypothesize that the size of the air pocket significantly affects the airflow resistance and work of breathing. The aims of the study are (1) to investigate the effect of the presence of an air pocket on gas exchange and work of breathing in subjects breathing into the simulated avalanche snow and (2) to test whether it is possible to breathe with no air pocket. The prospective interventional double-blinded study involved 12 male volunteers, from which 10 completed the whole protocol. Each volunteer underwent two phases of the experiment in a random order: phase “AP”—breathing into the snow with a one-liter air pocket, and phase “NP”—breathing into the snow with no air pocket. Physiological parameters, fractions of oxygen and carbon dioxide in the airways and work of breathing expressed as pressure-time product were recorded continuously. The main finding of the study is that it is possible to breath in the avalanche snow even with no air pocket (0 L volume), but breathing under this condition is associated with significantly increased work of breathing. The significant differences were initially observed for end-tidal values of the respiratory gases (EtO2 and EtCO2) and peripheral oxygen saturation (SpO2) between AP and NP phases, whereas significant differences in inspiratory fractions occurred much later (for FIO2) or never (for FICO2). The limiting factor in no air pocket conditions is excessive increase in work of breathing that induces increase in metabolism accompanied by higher oxygen consumption and carbon dioxide production. The presence of even a small air pocket reduces significantly the work of breathing.

Spontaneous breathing of heliox using a semi-closed circuit: a bench study.

Introduction: The use of helium-oxygen mixture (heliox) for ventilation has an advantage in patients with obstruction of the airways. The physical properties of helium enable an easier gas flow through the airways; this enables easier breathing for the patient when compared to standard ventilation of air. A high cost of heliox falls within the factors that limit the use of heliox in clinical practice. At present, heliox is administered by use of an open circuit. The aim of this study is to propose a way of heliox administration that reduces heliox consumption but does not affect the positive heliox effects upon the airway resistance. Methods: To minimize consumption of heliox, a semi-closed circuit has been designed. The circuit is a modification of an anesthetic circuit composed of parts with the lowest possible resistances. As any circuit has its own resistance, the evaluation of its possible negative effect upon the work of breathing of patients with exacerbation of chronic obstructive pulmonary disease (COPD) has been conducted. Results: A semi-closed circuit for heliox administration has been constructed and evaluated. The intrinsic resistance of both the inspiratory and expiratory limbs of the circuit is less than 140 Pa·s/l. This resistance does not represent a significant workload for a patient with COPD exacerbation whose airway resistance is 10 to 20 fold higher. Conclusions: The designed semi-closed circuit offers a potential benefit of heliox in patients with COPD exacerbation.

Center of Ventilation—Methods of Calculation Using Electrical Impedance Tomography and the Influence of Image Segmentation

Electrical impedance tomography (EIT) is a promising non-invasive, radiation-free imaging modality. Using EIT-derived index Center of ventilation (CoV), ventral-to-dorsal shifts in distribution of lung ventilation can be assessed. The methods of CoV calculation differ among authors and so does the segmentation of EIT images from which the CoV is calculated. The aim of this study is to compare the values of CoV obtained using different algorithms, applied in variously segmented EIT images. An animal trial (n=4) with anesthetized mechanically ventilated pigs was conducted. In one animal, acute respiratory distress syndrome (ARDS) was induced by repeated whole lung lavage. Incremental steps in positive end-expiratory pressure (PEEP), each with a value of 5 cmH2O (or 4 cmH2O in the ARDS model), were performed to reach total PEEP level of 25 cmH2O (or 22 cmH2O in the ARDS model). EIT data were acquired continuously during this PEEP trial. From each PEEP level, 30 tidal variation (TV) images were used for analysis. Functional regions of interest (ROI) were defined based on the standard deviation (SD) of pixel values, using threshold 15%–35% of maximum pixel SD. The results of this study show that there might be statistically significant differences between the values obtained using different methods for calculation of CoV. The differences occured in healthy animals as well as in the ARDS model. Both investigated algorithms are relatively insensitive to the image segmentation.

Tidal Volume Dependence on the Ventilatory Frequency and Alveolar Compliance in HFOV

High frequency oscillatory ventilation has limited possibility of monitoring of intrapulmonary parameters. We have measured tidal volume during high frequency oscillatory ventilation by external monitor. The experimental circuit consisted of ventilator 3100 with its patient circuit, lung simulator 5600i and monitor Florian for measuring of tidal volume. Tidal volume was measured for different values of alveolar compliance that were set on the lung simulator. Measurement was repeated for ventilatory frequencies 3, 5, 7 and 10 Hz. Ventilatory parameters were held constant during the experiment. We have found that change of alveolar compliance has minimal effect on the delivered tidal volume.