Terapia por láser de baja potencia: consideraciones óptico-físicas y biológicas determinantes en su aplicación clínica / Low power laser therapy: opto-physical and biological considerations underlying its clinical application

ObjetivosAnalizar la distribución de energía en un tejido cuando se emplea terapia por láser de baja potencia y estudiar las especificaciones mínimas de equipos de terapia láser para estimar la dosis.Material y métodosSe ha empleado el método de Monte Carlo para obtener la distribución de energía absorbida por la piel para dos tipos de láser y la teoría de la difusión para estimar la longitud de penetración y el recorrido libre medio. Se ha estudiado la variación de esa distribución en función de la raza (caucásico, asiático, afroamericano) y para dos localizaciones anatómicas distintas. Se ha analizado la información facilitada por diversos fabricantes de equipos comerciales para determinar si es necesario adaptar la dosimetría recomendada.ResultadosLa radiación láser infrarroja (810nm) se absorbe mayoritariamente en un espesor de piel de 1,9±0,2mm para caucásicos, entre 1,73±0,08mm (volar del antebrazo) y 1,80±0,11mm (palma) para asiáticos y entre 1,25±0,09mm (volar del antebrazo) y 1,65±0,2mm (palma) para afroamericanos. El recorrido libre medio de la luz siempre es menor que 0,69±0,09mm. Para los equipos comerciales analizados la única característica geométrica del haz láser que se menciona es la superficie que oscila entre 0,08 y 1cm2, pero no se especifica cómo es la distribución de energía, la divergencia del haz, forma de la sección transversal, etc.ConclusionesDependiendo del equipo de terapia por láser de baja potencia utilizado, el tipo de paciente y la zona a tratar, el clínico debe adaptar las dosis recomendadas (AU)

ObjectivesTo analyze the distribution of energy deposited in a tissue when this is irradiated with a low power laser and to study the minimum characteristics that manufacturers of low power laser therapy equipments should include to estimate the dosage.Material and methodsMonte Carlo simulation was performed to determine the absorption location of the laser energy. The diffusion theory was used to estimate penetration depth and mean free path. Variation of this distribution was studied based on three different skin types (Caucasians, Asians and Afroamericans) and for two different anatomic locations: palm and volar forearm. Information given by several manufactures of low power laser therapy equipments has been analyzed.ResultsInfrared (810nm) laser radiation is mainly absorbed in a skin layer of thickness 1.9±0.2mm for Caucasians, from 1.73±0.08mm (volar forearm) to 1.80±0.11mm (palm) for Asians, and from 1.25±0.09mm (volar forearm) to 1.65±0.2mm (palm) for Afroamericans. The light mean free path is lower than 0.69±0.09mm for all cases. The laser beam characteristics (beam shape, energy distribution on a transversal section, divergence, incidence angle, etc.) are not usually specified by the manufacturers. Only beam size (ranging from 0.08 to 1cm2) is given in some cases.Discussion and conclusionsDepending on the low power laser therapy equipment, on the patient and on the anatomic area to be treated, the staff should adapt the recommended dosage for each individual case (AU)

HIV/AIDS and maternity care in Kenya: how fears of stigma and discrimination affect uptake and provision of labor and delivery services.

Although policies and programs exist to promote safe motherhood in sub-Saharan Africa, maternal health has not improved and may be deteriorating in some countries. Part of the explanation may be the adverse effects of HIV/AIDS on maternity care. We conducted a study in Kisumu, Kenya to explore how fears related to HIV/AIDS affect women's uptake and health workers' provision of labor and delivery services. In-depth qualitative interviews with 17 maternity workers, 14 pregnant or postpartum women, four male partners and two traditional birth attendants; as well as structured observations of 22 births; were conducted at four health facilities. Participants reported that fears of HIV testing; fears of involuntary disclosure of HIV status to others, including spouses; and HIV/AIDS stigma are among the reasons that women avoid delivering in health facilities. Maternity workers now have to take into account the HIV status of the women they serve (as well as their own fears of becoming infected and stigmatized) but do not seem to be adequately prepared to handle issues related to consent, confidentiality and disclosure. Importantly, it appeared that women of unknown HIV status during labor and delivery were likely to be targets of stigma and discriminatory practices and that these women were not receiving needed counseling services. The findings suggest that increasing infection control precautions will not be enough to address the challenges faced by maternity care providers in caring for women in high-HIV-prevalence settings. Maternity workers need enhanced culturally sensitive training regarding consent, confidentiality and disclosure. Furthermore, this study points to the necessity of paying more attention to the care of women of unknown HIV-serostatus during labor and delivery. Such interventions may improve the quality of maternity care, increase utilization and contribute to overall improvements in maternal health, while also enhancing prevention of mother-to-child-transmission and HIV care.

Complexes of (dG-dC)20 with Mn2+ ions: a study by vibrational circular dichroism and infrared absorption spectroscopy.

The B-Z transition of the synthetic oligonucleotide, (dG-dC)20, induced by Mn2+ ions at room temperature, was investigated by absorption and Vibrational Circular Dichroism (VCD) spectroscopy in the range of 1800-800 cm(-1). Metal ion concentration was varied from 0 to 0.73 M Mn2+ (0 to 8.5 moles of Mn2+ per mole of oligonucleotide phosphate, [Mn]/[P]). While both types of spectra showed considerable changes as the Mn2+ concentrations were raised, differences between the two were often complementary in their expression and extent, those displayed by VCD being more clearly evident due to the inversion of the opposite helical sense from the right-handed to the left-handed conformation. The main phase of the transition occurred in the metal ion concentration between 0.8-1.1 [Mn]/[P]. Gradual changes that took place in the spectra were interpreted in terms of simultaneous processes that depended on metal ion concentration, namely B-Z transformation, binding of Mn2+ to phosphates and to nitrogen bases, and partial denaturation. Below approximately 0.6 [Mn]/[P], only a small portion of the oligonucleotide adopted the Z conformation within a 3 hour period, whereas conversion was completed in the same time interval for concentrations between 0.9-1.2 [Mn]/[P]. At [Mn]/[P] >1.7, complete transition to the Z-form took place immediately on adding Mn2+. Applying VCD spectroscopy in combination with conventional infrared absorption proved most useful for corroborating changes in the absorption spectra, and for detecting in an unique manner, not attainable by absorption methods, conformational changes that lead to the inversion of the helical sense of the oligonucleotide.

Autonomy in endemic goiter.

The occurrence of hyperthyroidism in many individuals after introduction of iodine prophylaxis in endemic goiter areas can have dramatic consequences for the affected individuals. It indicates that in such individuals the increase of serum thyroid hormone level in response to iodine supplementation does not exert its normal negative feedback on thyroid activity, ie, that in such individuals some thyroid tissue has become autonomous. In this short review we summarize what is known about the possible mechanisms, cause, diagnosis, and consequences of thyroid autonomy.

Response of brain metastases from breast cancer to systemic chemotherapy.

In a prospective, nonrandomized study, the response of brain metastases (BM) from breast cancer to a standard systemic chemotherapy regimen was measured by clinical follow-up and serial computed tomography (CT) scans. Treatment consisted of 4-week courses of cyclophosphamide, methotrexate, and 5-fluorouracil (CMF) in 20 patients or 3-week courses of cyclophosphamide, doxorubicin, and 5-fluorouracil (CAF) in 2 patients. Seven patients had previously received CMF or CAF as adjuvant treatment or for progressive systemic disease. Another seven patients had been previously treated for BM with the use of surgery and/or radiation therapy (RT). Based on the results of clinical follow-up and CT scan, a response that lasted at least 6 weeks was seen in 13 patients (59%; 95% confidence interval, 37% to 80%), including 4 of the 7 patients with recurrent BM. Objective tumor regression occurred after two courses of chemotherapy in 76% of the patients who could be examined and after six courses in 47%. The median duration of neurologic remission in the 13 patients was 30 weeks (range, 15 to 66 weeks). The median overall survival time was 25 weeks (range, 2 to 83 weeks). The response rate of systemic disease paralleled the neurologic response. When compared with a matched group of historical control subjects treated with RT alone, chemotherapy induced a higher rate of neurologic response and led to a longer survival time. These results warrant further studies on the use of chemotherapy in BM from breast cancer.

Neurological disorders in the Roman Empire, as reported by A. Cornelius Celsus.

The first author on medical history and compiler of medical knowledge was, in all probability, A. Cornelius Celsus. Uncertainties about his real profession and background are discussed. Some details of his treatise on history, anatomy, general symptoms and signs, and treatment of medical disorders, as far as these might be of interest to a neurologist, are presented.

The role of calcium and guanosine 3':5'-monophosphate in the action of acetylcholine on thyroid metabolism.

The role of calcium and guanosine 3':5'-monophosphate (cyclic GMP) in the regulation of thyroid metabolism has been investigated in dog thyroid slices. Carbamoylcholine enhanced glucose carbon-1 oxidation, protein iodination, cyclic GMP accumulation and decreased thyrotropin-induced adenosine 3':5'-monophosphate (cyclic AMP) accumulation and iodine secretion; it did not affect protein synthesis. The effects of carbamoylcholine were reproduced under various experimental conditions by supplementary calcium in the medium, ouabain, and in media in which Na+ had been replaced by choline chloride. They were inhibited by lanthanum. These results further support the hypothesis that free intracellular Ca2+ is the intracellular signal for carbamoylcholine effects and suggest that a Na+ -gradient-driven Ca2+ extrusion mechanism operates in the thyroid cell. Mn2+ reproduced the effect of Ca2+ on glucose oxidation, protein iodination and cyclic GMP accumulation in Ca2+ -depleted slices and medium, and thus mimicked some intracellular effects of Ca2+. On the other hand Mn2+ inhibited the carbamoylcholine effect on thyrotropin-induced thyroid secretion and cyclic AMP accumulation, and Ca2+ inhibited the Mn2+-induced cyclic GMP accumulation. This suggests that the two ions compete for the same channel. Similarly Mn2+ inhibited calcium effects in the presence of ionophore A23187. Procaine inhibited protein iodination under all conditions suggesting a primary effect; it also inhibited all carbamoylcholine and ouabain actions. However the drug did not inhibit the effects of choline chloride and its action was reversed by raising carbamoylcholine but not Ca2+ concentration; it is therefore doubtful that procaine acts by blocking Ca2+ channels. In media without added Ca2+, Mn2+ increased cyclic GMP accumulation but did not decrease thyrotropin-induced cyclic AMP accumulation or iodine secretion, which suggests that cyclic GMP cannot be the sole mediator of the latter two effects of carbamoylcholine.

[Calcium, cGMP and cAMP roles in thyroid regulation (author's transl)]. / Calcium, cGMP et cAMP dans la régulation thyroïdienne.

Cholinergic agents induce an accumulation of cGMP in thyroid tissue and inhibit cAMP accumulation and thyroid hormone secretion resulting from TSH action. The aim of the present work was to determine the respective roles of Ca++ and/or cGMP in these actions. The results show that two complementary mechanisms may be demonstrated: 1) cGMP activates phosphodiesterase activity and cAMP hydrolysis. 2) Independently of cyclic nucleotide concentrations, increased intracytoplasmic Ca++ directly inhibits TSH induced stimulated hormone secretion.