Miguel Vargas-Luna

Effects of occupational stress on the gastrointestinal tract.

The aim of this review is to provide a general overview of the relationship between occupational stress and gastrointestinal alterations. The International Labour Organization suggests occupational health includes psychological aspects to achieve mental well-being. However, the definition of health risks for an occupation includes biological, chemical, physical and ergonomic factors but does not address psychological stress or other affective disorders. Nevertheless, multiple investigations have studied occupational stress and its physiological consequences, focusing on specific risk groups and occupations considered stressful. Among the physiological effects of stress, gastrointestinal tract (GIT) alterations are highly prevalent. The relationship between occupational stress and GIT diseases is evident in everyday clinical practice; however, the usual strategy is to attack the effects but not the root of the problem. That is, in clinics, occupational stress is recognized as a source of GIT problems, but employers do not ascribe it enough importance as a risk factor, in general, and for gastrointestinal health, in particular. The identification, stratification, measurement and evaluation of stress and its associated corrective strategies, particularly for occupational stress, are important topics to address in the near future to establish the basis for considering stress as an important risk factor in occupational health.

Gastric activity studies using a magnetic tracer

A magnetic pulse generator has been set up in order to study gastric activity. Two coils 1.05 m in diameter, arranged in a Helmholtz configuration, were used. The system generated magnetic field pulses higher than 15 mT, of duration 17.3+/-1.2 ms. Measurements were performed in 11 male volunteers, with average age 29.3+/-6.4 years and body mass index 26.0+/-4.8 kg m(-2). Magnetite (Fe3O4) particles with diameters from 75 to 125 microm were used as magnetic tracers, which were mixed in 250 ml of yogurt in concentrations from 2 to 5 g. Signals were registered by using a high speed 3 axis fluxgate digital magnetometer and processed to determine the relaxation of the magnetic tracers by fitting a first-order exponential function to the data, a mean relaxation constant K = 116+/-40 s(-1) was obtained. Also, an average gastric peristaltic frequency was measured; a value of 3.2+/-0.3 cpm was determined.

Use of short-term bio-impedance for gastric motility assessment

Gastric motility (GM) has been assessed using bio-impedance (BI) techniques in the time domain using short term recordings and analyzing mainly the median of the area under the fast Fourier transform (FFT) spectra. The BI technique has been applied to the gastric system mainly for gastric emptying (GE) studies. However, gastric motility evaluation using BI has not been fully implemented. In this study, we propose the use of the BI technique for the evaluation of gastric motility considering global features of the fast FFT spectra. The study was performed in eleven healthy subjects who were evaluated in fasting and postprandial conditions. The results indicate that the use of the median of the area under the FFT spectra is equivalent to the use of the main peak of the spectra to determine the changes in gastric motility from the fasting to the postprandial state. This demonstrates that BI is a valid technique for gastric motility evaluation in short time recordings.

In vivo measurement of human skin absorption of topically applied substances by a photoacoustic technique

A photoacoustic technique is used for studying topically applied substance absorption in human skin. The proposed method utilizes a double-chamber PA cell. The absorption determination was obtained through the measurement of the thermal effusivity of the binary system substance-skin. The theoretical model assumes that the effective thermal effusivity of the binary system corresponds to that of a two-phase system. Experimental applications of the method employed different substances of topical application in different parts of the body of a volunteer. The method is demonstrated to be an easily used non-invasive technique for dermatology research. The relative concentrations as a function of time of substances such as ketoconazol and sunscreen were determined by fitting a sigmoidal function to the data, while an exponential function corresponds to the best fit for the set of data for nitrofurazona, vaseline and vaporub. The time constants associated with the rates of absorption, were found to vary in the range between 10 and 58 min, depending on the substance and the part of the body.

Effect of psychological stress on gastric motility assessed by electrical bio-impedance.

AIM To evaluate gastric motility using electrical bio-impedance (EBI) and gastric changes as a result of stress induced by psychological tests. METHODS A group of 57 healthy women, aged 40-60 years, was recruited, and a clinical history and physical examination were performed. The women were free from severe anxiety, chronic or acute stress, severe depression, mental diseases and conditions that affect gastric activity. The women were evaluated under fasting conditions, and using a four-electrode configuration, the gastric signals were obtained through a BIOPAC MP-150 system. The volunteers were evaluated using the following paradigm: basal state, recording during the Stroop Test, intermediate resting period, recording during the Raven Test, and a final resting period. We analyzed the relative areas of the frequency spectrum: A1 (1-2 cpm), A2 (2-4 cpm), A3 (4-8 cpm), and A4 (8-12 cpm), as well as the median of area A2 + A3. The data were analyzed by an autoregressive method using a Butterworth filter with MatLab and Origin. Analysis of variance (ANOVA) and Friedman ANOVA (for nonparametric variables) were performed; in addition, pairs of groups were compared using the T dependent and Wilcoxon T tests. RESULTS The results of the main values of area A2 were not significantly different comparing the five steps of the experimental paradigm. Nevertheless, there was a tendency of this A2 region to decrease during the stress tests, with recuperation at the final resting step. When an extended gastric region was considered (1-4 cpm), significant differences with the psychological stress tests were present (F = 3.85, P = 0.005). The A3 region also showed significant changes when the stress psychological tests were administered (F = 7.25, P < 0.001). These differences were influenced by the changes in the adjacent gastric region of A2. The parameter that we proposed in previous studies for the evaluation of gastric motility by electrical bio-impedance (EBI) was the median of the area under the region from 2 to 8 cpm (A2 + A3). The mean values of these frequencies (median of the A2 + A3 area) with the stress test showed significant changes (F = 5.5, P < 0.001). The results of the Wilcoxon T test for the A4 area parameter, which is influenced by the breathing response, changed significantly during the Raven stress test (P < 0.05). CONCLUSION We confirm that the gastric response to acute psychological stress can be evaluated by short-term EBI.

Electrical bioimpedance and other techniques for gastric emptying and motility evaluation.

The aim of this article is to identify non-invasive, inexpensive, highly sensitive and accurate techniques for evaluating and diagnosing gastric diseases. In the case of the stomach, there are highly sensitive and specific methods for assessing gastric motility and emptying (GME). However, these methods are invasive, expensive and/or not technically feasible for all clinicians and patients. We present a summary of the most relevant international information on non-invasive methods and techniques for clinically evaluating GME. We particularly emphasize the potential of gastric electrical bioimpedance (EBI). EBI was initially used mainly in gastric emptying studies and was essentially abandoned in favor of techniques such as electrogastrography and the gold standard, scintigraphy. The current research evaluating the utility of gastric EBI either combines this technique with other frequently used techniques or uses new methods for gastric EBI signal analysis. In this context, we discuss our results and those of other researchers who have worked with gastric EBI. In this review article, we present the following topics: (1) a description of the oldest methods and procedures for evaluating GME; (2) an explanation of the methods currently used to evaluate gastric activity; and (3) a perspective on the newest trends and techniques in clinical and research GME methods. We conclude that gastric EBI is a highly effective non-invasive, easy to use and inexpensive technique for assessing GME.

Utility of the short time bioelectrical impedance for the gastric motility assessment: Preliminary Results

In the usual technique for gastric motility as- sessment, electrical potential variation of gastric mioelectrical activity is recorded. Electrical bio-impedance (EBI) is useful mainly for gastric emptying studies using long time recordings. In this study we evaluated the gastric motility of 11 subjects being in fasting and postprandial conditions. Experiments using drugs to increase the gastric motility and to change the gastric acidity were performed in three of these subjects. With Fourier analysis of short time recordings made during differ- ent steps of the experiments (using four electrodes) we found the dominant peaks at frequencies around 2-3 cpm. These peaks had relative variations in heights and widths. Also the intensity of the gastric EBI spectra at higher frequencies in- creases in the postprandial state and after the use of drugs to increase the gastric motility. These results were similar than those reported using epigastrography. In this study short time bioelectrical impedance assessment for the evaluation of gas- tric motility is proposed.

Erythrocyte Sedimentation Rate Study by Photopyroelectric Technique

Preliminary studies of erythrocyte sedimentation rate in real time, using the inverse photopyroelectric method, are presented. The advantages of this methodology is that the sample is not illuminated directly and that the process can be monitored through the measurement of the thermal contact between a pyroelectric sensor and the blood. The thermal effusivity was determined using a one‐dimensional heat diffusion model, where the pyroelectric sensor is thermally thin and the blood is thermally thick. It was demonstrated that during the process, the thermal effusivity decreases in the region of the contact between the blood and the pyroelectric sensor. The usefulness of these results in real time monitoring using photothermal techniques is discussed.

Skin absorption studied by photoacoustic techniques

In this work we propose for the particular problem of penetration of substance into skin, a setup which is based on the conventional photoacoustic cell. In order to avoid some problems, intrinsic to the material under study and the sensibility of the technique, we use the thermal effusivity of the skin-substance system to monitor this phenomenon, in vivo and in situ. We measure the changes of thermal effusivity due to the absorption of some topical medicaments. These values are compared with those from an adjacent sample of clean skin (without medicament, natural fats or transpiration). This experiment was performed on a volunteer in different parts of the human skin. We use stainless steel (250 mm thickness) as the thermally thin light absorbance surface. The values for this parameter are in agreement with some reported in the literature. Besides the measurements described above.

Explorative geometrical RUS study of bone phantoms considering load variations

In this work we employ the resonant ultrasound spectroscopy technique in time-domain to perform an explorative geometrical study of bone phantoms. We measured a set of acrylic tubes of equal length but with different internal diameters in order to make a first step study related to the decrease in wall thickness due to osteoporosis process in human bones. We considered the spectra obtained with the sample subjected to pressure and their development to the free body resonance frequency spectra.