Alexandre Visintainer Pino

Positive end-expiratory pressure at minimal respiratory elastance represents the best compromise between mechanical stress and lung aeration in oleic acid induced lung injury.

IntroductionProtective ventilatory strategies have been applied to prevent ventilator-induced lung injury in patients with acute lung injury (ALI). However, adjustment of positive end-expiratory pressure (PEEP) to avoid alveolar de-recruitment and hyperinflation remains difficult. An alternative is to set the PEEP based on minimizing respiratory system elastance (Ers) by titrating PEEP. In the present study we evaluate the distribution of lung aeration (assessed using computed tomography scanning) and the behaviour of Ers in a porcine model of ALI, during a descending PEEP titration manoeuvre with a protective low tidal volume.MethodsPEEP titration (from 26 to 0 cmH2O, with a tidal volume of 6 to 7 ml/kg) was performed, following a recruitment manoeuvre. At each PEEP, helical computed tomography scans of juxta-diaphragmatic parts of the lower lobes were obtained during end-expiratory and end-inspiratory pauses in six piglets with ALI induced by oleic acid. The distribution of the lung compartments (hyperinflated, normally aerated, poorly aerated and non-aerated areas) was determined and the Ers was estimated on a breath-by-breath basis from the equation of motion of the respiratory system using the least-squares method.ResultsProgressive reduction in PEEP from 26 cmH2O to the PEEP at which the minimum Ers was observed improved poorly aerated areas, with a proportional reduction in hyperinflated areas. Also, the distribution of normally aerated areas remained steady over this interval, with no changes in non-aerated areas. The PEEP at which minimal Ers occurred corresponded to the greatest amount of normally aerated areas, with lesser hyperinflated, and poorly and non-aerated areas. Levels of PEEP below that at which minimal Ers was observed increased poorly and non-aerated areas, with concomitant reductions in normally inflated and hyperinflated areas.ConclusionThe PEEP at which minimal Ers occurred, obtained by descending PEEP titration with a protective low tidal volume, corresponded to the greatest amount of normally aerated areas, with lesser collapsed and hyperinflated areas. The institution of high levels of PEEP reduced poorly aerated areas but enlarged hyperinflated ones. Reduction in PEEP consistently enhanced poorly or non-aerated areas as well as tidal re-aeration. Hence, monitoring respiratory mechanics during a PEEP titration procedure may be a useful adjunct to optimize lung aeration.

Comparative effects of vaporized perfluorohexane and partial liquid ventilation in oleic acid-induced lung injury

Background:It is currently not known whether vaporized perfluorohexane is superior to partial liquid ventilation (PLV) for therapy of acute lung injury. In this study, the authors compared the effects of both therapies in oleic acid–induced lung injury. Methods:Lung injury was induced in 30 anesthetized and mechanically ventilated pigs by means of central venous infusion of oleic acid. Animals were assigned to one of the following groups: (1) control or gas ventilation (GV), (2) 2.5% perfluorohexane vapor, (3) 5% perfluorohexane vapor, (4) 10% perfluorohexane vapor, or (5) PLV with perfluorooctane (30 ml/kg). Two hours after randomization, lungs were recruited and positive end-expiratory pressure was adjusted to obtain minimal elastance. Ventilation was continued during 4 additional hours, when animals were killed for lung histologic examination. Results:Gas exchange and elastance were comparable among vaporized perfluorohexane, PLV, and GV before the open lung approach was used and improved in a similar fashion in all groups after positive end-expiratory pressure was adjusted to optimal elastance (P < 0.05). A similar behavior was observed in functional residual capacity (FRC) in animals treated with vaporized perfluorohexane and GV. Lung resistance improved after recruitment (P < 0.05), but values were higher in the 10% perfluorohexane and PLV groups as compared with GV (P < 0.05). Interestingly, positive end-expiratory pressure values required to obtain minimal elastance were lower with 5% perfluorohexane than with PLV and GV (P < 0.05). In addition, diffuse alveolar damage was significantly lower in the 5% and 10% perfluorohexane vapor groups as compared with PLV and GV (P < 0.05). Conclusions:Although the use of 5% vaporized perfluorohexane permitted the authors to reduce pressures needed to stabilize the lungs and was associated with better histologic findings than were PLV and GV, none of these perfluorocarbon therapies improved gas exchange or lung mechanics as compared with GV.

A closed-loop mechanical ventilation controller with explicit objective functions

A closed-loop lung ventilation controller was designed, aiming to: 1) track a desired end-tidal CO/sub 2/ pressure (P/sub et/CO/sub 2/), 2) find the positive end-expiratory pressure (PEEP) of minimum estimated respiratory system elastance (E/sub rs,e/), and 3) follow objective functions conjectured to reduce lung injury. After numerical simulations, tests were performed in six paralyzed piglets. Respiratory mechanics parameters were estimated by the recursive least squares (RLS) method. The controller incorporated a modified PI controller for P/sub et/CO/sub 2/ and a gradient descent method for PEEP. In each animal, three automated PEEP control runs were performed, as well as a manual PEEP titration of E/sub rs,e/ and a multiple P/sub et/CO/sub 2/ step change trial. Overall performance indexes were obtained from PEEP control, such as minimum E/sub rs,e/ (37.0/spl plusmn/4.5cmH/sub 2/O.L/sup -1/), time to reach the minimum E/sub rs,e/ (235/spl plusmn/182 s) and associated PEEP (6.5/spl plusmn/1.0 cmH/sub 2/O), and from P/sub et/CO/sub 2/ control, such as rise time (53 /spl plusmn/ 22 s), absolute overshoot/undershoot of P/sub et/CO/sub 2/ (3/spl plusmn/1 mmHg), and settling time (145 /spl plusmn/ 72 s). The resulting CO/sub 2/ controller dynamics approximate physiological responses, and results from PEEP control were similar to those obtained by manual titration. Multiple dependencies linking the involved variables are discussed. The present controller can help to implement and evaluate objective functions that meet clinical goals.

Knee bioelectric impedance assessment in healthy/with osteoarthritis subjects

The present study analyzes parameters estimated by bioelectric impedance spectroscopy (BIS) in subjects with healthy and with osteoarthritis (OA) knees. Thirty-two male volunteers, members of the Parachute Military Infantry Brigade of Rio de Janeiro, Brazil, participated in the study (62 knee joints). Clinical specialists used the Dejour scale for OA classification and divided the subjects into a control (without OA) and a pathological group (with different degrees of OA). BIS data were obtained in a standing position using a BIS technique based on the current response to a step voltage excitation. Differences between groups were measured by means of a Wilcoxon-Mann-Whitney test. Results indicate that raw bioimpedance parameters seem to be sensitive to the physiological changes associated with OA. Thus, data indicate that extra-cellular resistance (Re) and reactance of the equivalent capacitance (Xcx) increase according to the disease intensity (p < 0.001). In conclusion, the BIS technique seems to be able to provide the objective and non-invasive basis for helping the diagnosis of knee OA.

Objective assessment of knee osteroarthritis in parachuters by bioimpedance spectroscopy

The aim of the present study was to derive an objective and noninvasive assessment of osteoarthritis of the knee joint by bioimpedance spectrocopy (BIS). The study was performed in Brazilian Military Parachuters and intends to contribute to the improvement of the early diagnosis of joint degeneration. Twelve male volunteers (24 knee joints) participated in the study. A novel index (ID) to assess the disease was proposed from the raw bioimpedance parameter. This index was compared with a subjective rating (Dejour scale) performed by 3 therapists. The results indicated that the values of ID were significantly different (p<0.001) between the control group (class 1 of Dejour) and the pathological group (class 2 or higher). A Spearman correlation of −0.81 between the values of ID and the therapists rating was detected. Despite the need of increasing the sample size, the novel technique seems to be capable of supplying an objective and non-invasive tool for helping the diagnosis of the knee osteoarthritis.

A fractional electrical impedance model in detection of occlusal non-cavitated carious

Identification of occlusal caries remains a major concern for the diagnosis, which is still highly subjective and presents a considerable variability among clinicians. Dentists have been observed an increase of a specifically type of caries lesion, the hidden caries. Among the available techniques to assess the hidden caries, the measurement of electrical impedance has been shown to be one of the most promising. This paper presents a fractional electrical model for the tooth and uses such a model associated to a BioImpedance Spectroscopy (BIS) method based on the current response to a step voltage excitation. An analytical solution for the current response is presented based on a fractional calculus approach. Estimate parameters of the proposed model achieved using an in vitro data acquired in a protocol performed to collect bioimpedance data showed that it seems possible to detect occlusal non-cavitated caries, and that the principal confounding factor in the diagnosis of the incipient occlusal caries, the pigmented areas, can also be differentiated.

Comparison of two bioimpedance spectroscopy techniques in the assessment of body fluid volumes

The present study aimed to compare the estimates of body liquid volumes performed by two bioimpedance spectrometry techniques. One based on a step response technique (BIS-PEB) and second one based on multifrequency Xitron Hydra 4200 equipment (Xitron Technologies, San Diego, CA, USA). The convenience sample was initially composed of 422 students from a military parachuting course of the Brazilian Army. From such sample 42 male students were randomly selected to be evaluated during three weeks. The anthropometrical characteristics of the sample can be summarized as: 25.18 ± 4.10 years old; weight equals of 76.77 ± 7.84 kg; height equals to 174.96 ± 5.67 cm; body mass index (BMI) equal to 25.05 ± 2.11 kg m-2. Bland-Altman graphics were used to compare the two methods in what concerns to estimate of extracellular fluid (ECF), intracellular fluid (ICF), and total body water (TBW). One can observe that the estimates of the two techniques present a good correlation, especially in the case of ECF (r = 0.975). The present study indicates that BIS-PEB technique associated with De Lorenzo equation can supply noninvasive estimates of body fluid volumes comparable to Xitron Hydra 4200 equipment.

Time-scaling based sliding mode control for Neuromuscular Electrical Stimulation under uncertain relative degrees

This paper addresses the application of the sliding mode approach to control the arm movements by artificial recruitment of muscles using Neuromuscular Electrical Stimulation (NMES). Such a technique allows the activation of motor nerves using surface electrodes. The goal of the proposed control system is to move the upper limbs of subjects through electrical stimulation to achieve a desired elbow angular displacement. Since the human neuro-motor system has individual characteristics, being time-varying, nonlinear and subject to uncertainties, the use of advanced robust control schemes may represent a better solution than classical Proportional-Integral (PI) controllers and model-based approaches, being simpler than more sophisticated strategies using fuzzy logic or neural networks usually applied in this control problem. The objective is the introduction of a new time-scaling base sliding mode control (SMC) strategy for NMES and its experimental evaluation. The main qualitative advantages of the proposed controller via time-scaling procedure are its independence of the knowledge of the plant relative degree and the design/tuning simplicity. The developed sliding mode strategy allows for chattering alleviation due to the impact of the integrator in smoothing the control signal. In addition, no differentiator is applied to construct the sliding surface. The stability analysis of the closed-loop system is also carried out by using singular perturbation methods. Experimental results are conducted with healthy volunteers as well as stroke patients. Quantitative results show a reduction of 45% in terms of root mean square (RMS) error (from 5.9° to [Formula: see text] ) in comparison with PI control scheme, which is similar to that obtained in the literature.

Assessment of Tooth Structure using an Alternative Electrical Bioimpedance Spectroscopy Method

In the past few years bioimpedance has been used in many applications in dentistry, such as estimating the length of root canals and the physical properties of enamel. Despite the significant number of studies using bioimpedance to investigate the dental structure, many of them use only the real component of bioimpedance, i.e., the resistance, disregarding the information provided by the imaginary one, i.e., the reactance. Moreover, in different studies that investigate both parts of bioimpedance, the data are obtained by using single frequency or multifrequency methods based on sinusoidal sweep. The aim of this study was to investigate the use of an alternative bioimpedance spectroscopy (BIS) method based on step response in the assessment of tooth structure. To test the feasibility of the studied method we performed in vitro experiments that considered the successive removal of enamel layers of 22 healthy teeth, the accomplishment of the BIS method, and the estimate of bioimpedance parameter that were associated with the changes in the tooth structure. To deal with the variability of bioimpedance parameters a dental health index (DHI) is proposed. The findings include the behavior of bioimpedance parameters of intact teeth, as well as those associated with the successive removal of the enamel layer, and indicate that DHI is sensitive enough to detect changes of the enamel layer. The results point to the feasibility of the studied BIS method in evaluating tooth structure and that it might be used to assess dental health.

Real-Time Monitoring of Yeasts Growth Based on Bioimpedance Spectroscopy

Industrial bioprocesses usually occur in bioreactors, where the stages of a microorganism growth must be monitored to optimize the whole process. Off-line analytical methods are considered gold standard for such monitoring, but they are time consuming and may postpone important decisions making. Thus, there is always demand for the development of real time (on-line) monitoring methods for bioprocesses. Despite the existence of some real time methods used to measure the concentration of biomass in real time, such as optical density or turbidimetry, many of them are not able to distinguish living microorganisms from other materials, including dead microorganisms. This work proposes an on-line method for monitoring of total biomass, as well as the amount of viable cells, using a bioimpedance spectroscopy based on the current response to a step voltage excitation. To evaluate the proposed method, we performed an experiment of growth with yeast strain Saccharomyces cerevisiae species with initial inoculum of 0.1 and 0.5 g/L. The total amount of microorganism (using Neubauer chamber), the number of viable ones (using dyeing with methylene blue), and bioimpedance data were collected every hour during a period of 12 h. For each initial inoculum, series of data were collected. The results indicate the proposed technique presents good prediction of the total amount of microorganism (\( r = 0.918 \)) and of the number of viable ones (\( r = 0.858 \)).