PubMed Health⌕ Search

Biomedical subjects

B Quintana

Publications and source records attributed to B Quintana.

10 recordsLinked to original sources
PubMed2001

Coincidence summing corrections for the natural decay series in gamma-ray spectrometry.

Using a Monte Carlo code and a Markov formalism to describe the decay schemes, coincidence-summing correction factors can be calculated with a suitable accuracy. For two different measuring geometries and an HPGe detector, calculated and experimental correction factors have been shown to closely agree for 152Eu. The simulation method has subsequently been applied in assessing the need for coincidence-summing corrections for members of the uranium, thorium and actinium series measurable by gamma-spectrometry. Correction factors were calculated for predominant gamma emissions significantly affected by coincidence-summing effects and the correctness of our calculations tested for environmental samples. The test makes it evident that in order to obtain reliable and unbiased activity values for some natural radionuclides coincidence summing cannot be neglected in environmental measurements at small source-detector distances.

Journal Article↗
PubMed2000

Towards a proper modeling of detector and source characteristics in Monte Carlo simulations

We performed a systematic study on the influence of different source configurations on the reliability of Monte Carlo calculations for the response of Ge detectors. Calculated full-energy peak efficiencies are compared to experimental values in the energy range 46-1800 keV. Setups with different characteristics are considered, from point-like to volume sources. Among the latter there are filters and aqueous matrices and sediments in Petri boxes or Marinelli beakers. The analysis of the deviations between experimental and calculated results for the different configurations enables us to detect inaccuracies in the description of detector and source characteristics and to improve them. By means of this procedure satisfactory results of the efficiencies were obtained in the whole energy range. For all setups, the deviations average 1.5%, except for the sediment sources where they are up to 3.3%.

Journal Article↗
PubMed1999

Arterial oxygenation during one-lung ventilation: combined versus general anesthesia.

UNLABELLED: The optimal anesthetic management of patients undergoing thoracotomy for pulmonary resection has not been definitely determined. We evaluated whether general i.v. anesthesia (propofol-fentanyl) provides superior PaO2 during one-lung ventilation (OLV) compared with thoracic epidural anesthesia (TEA) with supplemental local and general anesthetics. We studied 60 patients who had prolonged periods of OLV for elective thoracic surgery for lung cancer and who were prospectively randomized into two groups. In 30 patients (GA group), fentanyl/propofol/rocuronium anesthesia was used. Another 30 patients (TEA group) were anesthetized with propofol/rocuronium/epidural thoracic bupivacaine 0.5%. A double-lumen endotracheal tube was inserted, and mechanical ventilation with 100% oxygen was used during the entire study. Arterial and venous blood gases were recorded before surgery in a lateral position with two-lung ventilation, 15 and 30 min after OLV (OLV + 15 and OLV + 30, respectively) in all patients. We measured PaO2, venous central oxygen tension, arterial and central venous oxygen saturation, venous admixture percentage (Qs/Qt%), and arterial and central venous oxygen content. The mean values for PaO2 during OLV in the GA group after 15 min (175 mm Hg) and 30 min (182 mm Hg) were significantly (P < 0.05) higher compared with the TEA group (120 and 118 mm Hg, respectively). Furthermore, Qs/Qt% was significantly (P < 0.05) increased in the TEA group during OLV. There were no other significant differences. We conclude that using the TEA regimen is associated with a lower PaO2 and a larger intrapulmonary shunt during OLV than with total i.v. anesthesia alone. IMPLICATIONS: Sixty patients undergoing elective lung surgery during a prolonged period of intraoperative one-lung ventilation were studied and randomized to receive general i.v. anesthesia or general i.v. anesthesia combined with thoracic epidural anesthesia. The arterial oxygenation in the first group was better than that in the second group during one-lung ventilation.

Aged↗
PubMed1996

Plasma concentrations of vigabatrin in epileptic patients.

OBJECTIVE: To measure plasma concentrations of vigabatrin in a group of 30 adult epileptic patients with complex partial seizures (CPS) refractory to conventional antiepileptic drugs. With a view to better defining the drug's dose-response relationships in the presence of concomitant alternative antiepileptic drugs. METHODS: High-performance liquid chromatographic analysis of blood samples drawn at steady-state trough levels from patients receiving vigabatrin. RESULTS: The steady-state plasma concentrations of vigabatrin showed marked interpatient variability (CV = 59.5%). The mean concentration was 42 +/- 25 micrograms/ml (range 11.5-102.7 micrograms/ml). Nineteen patients (63%) had plasma levels between 20 and 60 micrograms/ml. The plasma clearance of vigabatrin ranged from 0.24 to 1.37 ml/min/kg (mean +/- SD = 0.74 +/- 0.40 ml/min/kg), with a median value of 0.64 ml/min/kg. Concomitant treatment with carbamazepine increased the plasma clearance of vigabatrin from 0.59 ml/min/kg (monotherapy), 0.54 ml/min/kg (co-treated with phenobarbital) and 0.41 ml/min/kg (co-treated with valproic acid) to 0.92 ml/min/kg. CONCLUSION: Vigabatrin plasma levels show wide interpatient variability, and co-administration with carbamazepine increases vigabatrin's clearance. While there is no relationship between plasma level and anti-epileptic effect, abnormally high levels of the drug may increase toxicity.

Adult↗
PubMed1996

The insulin-sensitizing agent troglitazone improves metabolic and reproductive abnormalities in the polycystic ovary syndrome.

We performed this study to investigate the hypothesis that insulin resistance plays a role in the pathogenesis of reproductive abnormalities in women with the polycystic ovary syndrome (PCOS). Twenty-five women with PCOS were enrolled in a double-blind randomized 3-month trial of two doses of the insulin-sensitizing agent, troglitazone, 21 of whom completed the study: 200 mg, n = 10; 400 mg, n = 11. Baseline hormonal parameters and glucose tolerance were compared with 12 age- and weight-matched ovulatory control women. There were no significant changes in body mass index during the study. Fasting (P < 0.01) and 2-h post-75-g glucose load insulin levels (P < 0.05), as well as integrated insulin responses to the glucose load, decreased (P < 0.05), and insulin sensitivity assessed by a frequently sampled iv glucose tolerance test increased significantly (P < 0.001) during troglitazone treatment. This was accompanied by significant decreases in the levels of nonsex hormone-binding globulin-bound testosterone (P < 0.01), dehydroepiandrosterone sulfate (P < 0.001), estradiol (P < 0.01), and estrone (P < 0.001). Stepwise regression analysis indicated that decreases in nonsex hormone-binding globulin testosterone levels were significantly correlated with decreases in integrated insulin responses to the glucose load (r2 0.44, P < 0.01). The only significant changes at the 200-mg troglitazone dose were an increase in insulin sensitivity (P < 0.05) and decreases in dehydro-epiandrosterone sulfate (P < 0.01) and estrone (P < 0.05) levels. At the 400-mg dose, in addition to the changes noted in the entire troglitazone treatment group, increases in the disposition index (the product of insulin sensitivity and secretion) achieved significance, as did decreases in androstenedione (P < 0.01) and LH (P < 0.05) levels and increases in sex hormone-binding globulin levels (P < 0.01). Two PCOS women had ovulatory menses. We conclude that 1) troglitazone improves total body insulin action in PCOS, resulting in lower circulating insulin levels; 2) insulin resistance, probably via hyperinsulinemia, results in a general augmentation of steroidogenesis and LH release in PCOS; and 3) insulin-sensitizing agents, such as troglitazone, may provide a novel therapy for PCOS.

Adult↗
PubMed1991

Pharmacokinetics of intravenous midazolam during epidural anaesthesia.

Midazolam concentration curves versus time were analysed in 10 otherwise healthy patients (ASA I-II) with inferior limb pathologies. The benzodiazepine was used as an adjuvant agent to epidural anaesthesia in view of its lower residual effect compared with other intravenous benzodiazepines. Midazolam pharmacokinetics in these patients fitted an open two-compartment model. The plasma levels versus time corresponded to a biexponential process with a very rapid distribution phase (t1/2a = 5.7 +/- 2.4 min) and an elimination phase (t1/2 beta = 66 +/- 37 min). Mean values for distribution volumes in the central compartment and extrapolated values were Vc = 0.12 +/- 0.04 l/kg and V beta = 1.28 +/- 0.92 l/kg. This kinetic behaviour explains the rapid but short duration of midazolam action. The induction time, estimated from the start of hypnosis (eye closure), was from 60 to 120 s with i.v. injection. The duration of action for the dose administered was from 15 to 60 min, with plasma levels below 90 ng/ml upon eye opening.

Adult↗
PubMed1990

Estrogen receptor gene amplification is found in some estrogen receptor-positive human breast tumors.

The genomic organization of the estrogen receptor (ER) gene has been analyzed in 21 primary human breast cancers and 1 axillary metastasis. No evidence of rearrangements of the ER gene was found in the analyzed tumors. In 6/14 ER-positive tumors a certain degree of amplification of the ER gene, ranging from 1.6 to 3-fold, was detected. No correlation was observed between the level of gene amplification and the amount of ER in the tumors. In the 8 ER-negative tumors analyzed no amplification could be detected. It is concluded that ER gene amplification may be one of the mechanisms underlying the increased ER expression in some breast tumors.

Adult↗
PubMedDate not supplied

[Premedication with clonidine in the neurosurgical patient: sedation, anesthetic requirements and hemodynamic perfusion].

OBJECTIVES: To analyze the effect of premedication with clonidine on postoperative sedation, anesthetic requirements and hemodynamic repercussions in patients undergoing craniotomy due to supratentorial intracranial pathology. PATIENTS AND METHODS: Twenty ASA I/II patients in a double-blind prospective study were assigned randomly to receive lorazepam (0.03 mg/kg/po, n = 10) or clonidine (0.005 mg/kg/po, n = 10) the night before and 90 minutes before surgery. Arterial pressure and heart rate were monitored continuously during and immediately after surgery (first 24 hours). Anesthetic induction was achieved with thiopental (maximum 6 mg/kg) and maintained with O2/N2O and an infusion of alfentanyl (1 microgram/kg/min). Hemodynamic response to surgical stimulus was treated with additional boluses of alfentanyl up to a maximum dose of 0.1 mg/kg and with an increase in infusion dosage to 2 micrograms/kg/min. When these were ineffective, isoflurane was given. All patients were extubated in the operating room. RESULTS: No differences in level of sedation were found between the two groups. The infusion dose and total amount of alfentanyl given were smaller for patients treated with clonidine (0.8 +/- 0.04 vs 0.6 +/- 0.01 microgram/kg/min and 22.4 +/- 5.3 vs 17.5 +/- 4.9 mg, respectively) (p < 0.05). No differences were found in isoflurane requirements (5/5 vs 2/8). Mean arterial pressure and heart rate were lower with clonidine from 3 minutes after intubation until the patient's arrival in the recovery room (p < 0.05), with marked bradycardia (49 +/- 5 vs 73 +/- 7 bpm) (p < 0.05) upon intubation. CONCLUSIONS: Premedication of neurosurgical patients with clonidine offers no advantages over lorazepam with respect to sedation. Nevertheless, clonidine may offer advantages with respect to the amount of alfentanyl required and attenuation of perioperative adrenergic response.

Adult↗