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A Requena

Publications and source records attributed to A Requena.

15 recordsLinked to original sources
PubMed2001

Variational Calculations of Rovibrational Energies for CO(2).

Vibrational-rotational energy levels for the CO(2) molecule are computed variationally using an empirical potential energy surface previously determined. The calculations are carried out using a set of generalized internal coordinates properly optimized to describe the internuclear motions of the molecule. The rovibrational energies are used to determine the vibrational terms G(v) and the inertia constants B(v) for states with l = 0 to l = 6, and the values of these molecular constants are compared to those derived from the observed spectra. There exists excellent agreement between the calculated and the observed constants, which confirms the good quality of the potential energy surface used. Copyright 2001 Academic Press.

Journal Article↗
PubMed2001

Size evolution of the vibrational predissociation process in Br2...Nen clusters: simulation and kinetic study.

A hybrid quantum-classical simulation of the vibrational predissociation of Br2...Nen, (n = 2-11) clusters in the B electronic state is carried out. The time-evolution of the reactants, products, and intermediates is analyzed by a kinetic mechanism consisting of three elementary steps: direct vibrational predissociation (VP), intramolecular vibrational redistribution (IVR), and evaporative cooling (EC). The importance of intramolecular vibrational redistribution followed by evaporative cooling relative to direct vibrational predissociation is shown to increase rapidly with increasing cluster size. Final product state distributions reveal that only one or less Br2 stretching quantum per neon atom is required in order to achieve complete dissociation (n quanta for n < or = 9 and n - 1 for n = 10 and 11). The proportion of available energy going into translation is proposed as a parameter to study the statistical behavior of the Van der Waals clusters. It is shown to depend only on the number of remaining degrees of freedom, a characteristic of a statistical behavior, for n > or = 3.

Journal Article↗
PubMed2001

Endocrinological and ultrasonographic variations after immature oocyte retrieval in a natural cycle.

BACKGROUND: In-vitro oocyte maturation is an appealing alternative in reproductive medicine but the results obtained are still poor. The aim of our prospective and observational investigation was to study the hormonal modifications that immature follicular aspiration might induce in a natural cycle as well as the implications that these alterations may have in the endometrium. METHODS: Eleven patients (13 cycles) were included in our in-vitro oocyte maturation programme. Ovaries were scanned with transvaginal probes every day and follicular aspiration was performed when a follicle of 9 mm was visualized. Blood was also drawn for hormonal analysis. Endometrial thickness was recorded every day after oocyte retrieval. Two endometrial biopsies were taken on days 6 and 8 after oocyte retrieval. RESULTS: We observed a significant drop in serum oestradiol concentrations after immature oocyte retrieval previous to follicle dominance. Immediately after, rises in both FSH and LH were detected. Also, a new dominant follicle started to grow 3-4 days later. Steroid hormones secreted by this newly recruited follicle were significantly lower than in controls, inducing inadequate endometrial thickness. CONCLUSIONS: These studies show that exogenous hormonal administration might be necessary to achieve a correct endometrial growth when in-vitro oocyte maturation is employed in IVF.

Adult↗
PubMed2000

Conditions that affect acquisition of developmental competence by mouse oocytes in vitro: FSH, insulin, glucose and ascorbic acid.

The simplest unit required for the support of oocyte growth and development is the oocyte-granulosa cell complex. Therefore, a culture system was established that utilizes these complexes to assess mechanisms promoting nuclear, cytoplasmic and genomic maturation in mammalian oocytes. Deletion of serum from the culture, results in increased apoptosis in oocyte-associated granulosa cells (OAGCs), however, addition of ascorbic acid (0.5 mM) significantly reduced the level of apoptosis in the OAGCs, although no improvement of oocyte developmental competence was detected. The effects of reducing glucose during oocyte growth were studied since, under some culture conditions, glucose has deleterious effects on early preimplantation development. Reducing the glucose concentration to 1 mM resulted in the production of oocytes with greatly reduced developmental competence. Deleterious effects of FSH plus insulin during oocyte growth in vitro on preimplantation development are reviewed and discussed in terms of the communication of oocytes with inappropriately developing granulosa cells. Evidence that oocytes promote the appropriate differentiation of OAGCs in intact follicles in vivo is also discussed. It is hypothesized that oocytes control the differentiation of these cells, in order to promote intercellular signaling essential for the acquisition of competence to undergo normal embryogenesis.

Animals↗
PubMed2000

The potential use of maturation in vitro of human oocytes in low responder patients.

PURPOSE: To assess whether maturation in vitro of human oocytes (MIVHO) could be an alternative treatment in low responders to ovarian stimulation for in vitro fertilization (IVF). METHODS: Prospective case-control study. Spontaneously ovulatory women who volunteered were included in our program of MIVHO at the Instituto Valenciano de Infertilidad. Rates of oocyte retrieval, in vitro maturation, fertilization, and development up to the blastocyst stage were studied. RESULTS: A significantly increased rate of oocyte retrieval was found when the pickup was performed before follicular selection. No differences were found when MIVHO was used in a low responder patient with an ovarian content of early antral follicles > 5 as compared to normal responders. CONCLUSIONS: MIVHO could be a successful choice in low responder patients with an acceptable number of early antral follicles. Oocyte retrieval should be performed before follicular selection in order to obtain more oocytes.

Adult↗
PubMed2000

High doses of gonadotrophins combined with stop versus non-stop protocol of GnRH analogue administration in low responder IVF patients: a prospective, randomized, controlled trial.

Recent evidence suggests that early cessation of gonadotrophin releasing hormone analogue (GnRHa) administration may offer some benefit to low responder patients undergoing IVF. A prospective, randomized controlled trial was designed to evaluate whether early cessation of GnRHa in an ovarian stimulation regimen is more beneficial than just increasing the doses of gonadotrophins. Seventy low responder patients (less than three mature follicles in a previous cycle) with normal basal follicle stimulating hormone concentrations and a previous cancelled IVF cycle were randomly allocated into two protocols: (i) non-stop protocol: long GnRHa suppression with high doses of gonadotrophins, and (ii) stop protocol, in which GnRHa administration is stopped with the onset of menses, while gonadotrophin doses remained similar to the non-stop protocol. A significantly higher number of mature oocytes were obtained in the study group (stop protocol) compared to the control group (non-stop protocol) (8.7 +/- 0.9 versus 6.2 +/- 0.7, P: = 0. 027). The stop protocol reduced the number of ampoules of gonadotrophins required (56.6 +/- 2.7 versus 68.0 +/- 3.5, P: = 0. 013). Both protocols resulted in a similar cancellation rate (2.7 versus 5.8%) (with no cycles cancelled due to ovulation), pregnancy rate (14.3 versus 18.7%), and implantation rate (12.1 versus 8.8%). The early cessation of GnRHa combined with high doses of gonadotrophins permitted the retrieval of a significantly higher number of oocytes.

Adult↗
PubMed1999

Determination of a Potential Energy Surface for CO2 Using Generalized Internal Vibrational Coordinates.

A potential energy surface for CO2 is determined from experimental data using generalized internal vibrational coordinates. These coordinates are defined as two arbitrary distances and the angle between them and depend on two external parameters, which can be properly optimized. An optimal generalized internal coordinate system is obtained for CO2 by minimizing unconverged vibrational energies with respect to the external parameters. The optimal coordinates are shown to be superior to previously derived normal hyperspherical coordinates for this molecule. A nonlinear least-squares fit of the potential energy surface of CO2 to observed vibrational frequencies is made by using the optimal internal coordinates and fully variational calculations. The potential function is represented by a fourth-order Morse-cosine expansion and its quality is checked by computing highly excited vibrational transition frequencies which were not included in the fit. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Maturation in vitro of human oocytes from unstimulated cycles: selection of the optimal day for ovum retrieval based on follicular size.

The potential use of immature oocytes for in-vitro fertilization (IVF) requires the conditions for successful maturation to be defined. This study focused on the day of oocyte retrieval. The selection of a dominant follicle may induce endocrine changes in the remaining cohort that may be detrimental to their subsequent fertilization and embryonic development. Natural cycles in volunteer donors were followed by measurement of serum oestradiol and by vaginal ultrasound, starting on day 3 of the cycle. Cycles were randomly allocated to one of two groups: group 1 (n = 10), in which follicles were aspirated before the leading follicle was 10 mm in diameter; and group 2 (n = 9), in which follicles were aspirated when a dominant follicle was clearly visible with diameter >10 mm. Oocytes were cultured in vitro to metaphase II (MII) stage, donated, and inseminated by intracytoplasmic sperm injection (ICSI) with husband's spermatozoa. Those that became fertilized within 24 h were further co-cultured in autologous endometrial epithelial cells up to the blastocyst stage, and cryopreserved. There was a significantly (P < 0.05) increased rate of oocyte retrieval in group 1 (70.8% of aspirated follicles) compared with group 2 (50.5%). Maturation to MII and fertilization were similar between the groups. However, development to blastocyst stage was significantly (P < 0.05) higher in group 1 embryos (56.5%) compared with group 2 (35.7%). There was a positive correlation (r2 = 0.1978) between the appearance of the cumulus cells and the ability to develop to blastocyst stage when both parameters were analysed in group 1, whereas no such correlation was found in group 2. In conclusion, our data suggest the importance of retrieving immature oocytes before follicular selection, and define the conditions for the first stage in the use of immature oocytes. Further stages must be defined before this technique can be used clinically.

Adult↗
PubMed1995

Acute leukemia during pregnancy: obstetric management and perinatal outcome of two cases.

The coexistence of leukemia and pregnancy is extremely rare. This paper describes two cases of acute promyelocytic leukemia diagnosed during the second trimester of pregnancy and the most suitable approach to the management of this situation is analyzed. Possible teratogenic effects of mono- or polychemotherapy during pregnancy, depending upon the gestational age at which chemotherapy is given, are discussed.

Abnormalities, Drug-Induced↗