Biomedical subjects

M Vargas-Luna

Publications and source records attributed to M Vargas-Luna.

4 recordsLinked to original sources

PubMed2005

Magnetic field influence on electrical properties of human blood measured by impedance spectroscopy.

The impedance spectroscopy technique (IST) was used for studying the effect of a 0.5 T magnetic field on the electrical properties of whole human blood. A Solartron SI 1260 spectrometer was used to measure the impedance spectra of magnetic field exposed blood samples compared to non-exposed samples. An equivalent electrical circuit model, consisting in a resistance Rs in series with a parallel circuit formed by a constant phase element (CPE) and another resistance Rp, is proposed to fit the data in both cases. The experiment used 3 ml human blood samples from 160 healthy donors. A Wilcoxon matched pairs statistical test was applied to the data. The data analysis seems to show a statistically significant increase of the values of resistance Rp (Z = 5.06, P < 0.001) and capacitance CT (Z = 3.32, P < 0.001) of the blood exposed to magnetic field, by approximately 10.4% and 1.9%, respectively.

Adolescent↗

PubMed2004

The colon transit time in different phases of the menstrual cycle: assessed with biomagnetic technique.

Twenty measurements of the colon transit time (CTT) were performed by biomagnetic technique in five young women. Subjects were assessed during 12 hours a day for four phases of the menstrual cycle (MC): early follicular (EF), days 1-4 of the MC; late follicular (LF), days 9-14; early luteal (EL), days 15-18; and late luteal (LL), days 23-28 of the MC. Comparison intra and inter-subjects were made. The results of a t test for dependent samples, demonstrate that women with regular MC had higher CTT on LF (3.29 +/- 1.40 m/hr) than on LL phases of the MC (1.28 +/- 0.4 m/hr) t = 3.22, p = 0.04. Also we found differences from EL to LL phases of the MC (4.49 +/- 1.72 m/hr vs. 1.29 +/- 0.35 m/hr, t = 3.05, p = 0.05). However, in a patient with polycystic ovary syndrome (PCOS), we found a CTT of 3.1 m/hr on day 3; 2 m/hr on day 15; and 0.8 m/hr on day 30 of the MC. The time of the magnetic marker displacement was higher on days 3 of the MC, if we compared these values with those from women with regular MC (1.8 +/- 0.67 m/hr). We demonstrate that biomagnetic technique is a powerful method to assess changes in CTT presented in female subjects during the MC. Furthermore, the results found for the CTT in different phases of the MC of the females subjects, are in agreement with those reported by using other techniques.

Adult↗

PubMed2004

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.

Adult↗

PubMed2002

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.

Acoustics↗