PubMed Health⌕ Search

Biomedical subjects

P Cordero

Publications and source records attributed to P Cordero.

15 recordsLinked to original sources
PubMed2001

Clustering and fluidization in a one-dimensional granular system: molecular dynamics and direct-simulation Monte Carlo method.

We study a one-dimensional granular gas of pointlike particles not subject to gravity between two walls at temperatures T(left) and T(right). The system exhibits two distinct regimes, depending on the normalized temperature difference Delta=(T(right)-T(left))/(T(right)+T(left)): one completely fluidized and one in which a cluster coexists with the fluidized gas. When Delta is above a certain threshold, cluster formation is fully inhibited, obtaining a completely fluidized state. The mechanism that produces these two phases is explained. In the fluidized state the velocity distribution function exhibits peculiar non-Gaussian features. For this state, comparison between integration of the Boltzmann equation using the direct-simulation Monte Carlo method and results stemming from microscopic Newtonian molecular dynamics gives good coincidence, establishing that the non-Gaussian features observed do not arise from the onset of correlations.

Journal Article↗
PubMed2000

Thermal convection in fluidized granular systems

Thermal convection is observed in molecular dynamic simulations of a fluidized granular system of nearly elastic hard disks moving under gravity, inside a square box. Boundaries introduce no shearing or time dependence, but the energy injection comes from a slip (shear-free) thermalizing base. The top wall is perfectly elastic and lateral boundaries are either elastic or periodic. The spontaneous temperature gradient appearing in the system due to the inelastic collisions, combined with gravity, produces a buoyancy force that, when dissipation is large enough, triggers convection.

Journal Article↗
PubMed2000

Hydrodynamic theory for granular gases

A granular gas subjected to a permanent injection of energy is described by means of hydrodynamic equations derived from a moment expansion method. The method uses as reference function not a Maxwellian distribution f(M) but a distribution f(0)=Phif(M), such that Phi adds a fourth cumulant kappa to the velocity distribution. The formalism is applied to a stationary conductive case showing that the theory fits extraordinarily well the results coming from our Newtonian molecular dynamic simulations once we determine kappa as a function of the inelasticity of the particle-particle collisions. The shape of kappa is independent of the size N of the system.

Journal Article↗
PubMed1996

Evaluation of intercostal cryoanalgesia versus conventional analgesia in postthoracotomy pain.

The objective of the study was to evaluate the effects of cryoanalgesia in patients undergoing posterolateral thoracotomy. A double-blind randomized and prospective study was performed in 100 patients undergoing thoracotomy. They were randomized into two groups: Group A, 55 patients, who had undergone an intercostal cryoanalgesia and group B, control, 45 patients treated only with pharmacological analgesia ad libitum. In both groups we assessed pain in the first 7 postsurgical days, the amount of analgesia required, electromyography of the intercostal muscles involved and recording of maximal static respiratory pressures. Postsurgical pain was significantly lower (p < 0.001) in group A. No patient in group A needed major analgesia and the amount of aminopyrines required was significantly lower (p < 0.001) than those used in group B. Maximal static inspiratory pressure (PImax) showed no significant changes and no significant differences were found between the two groups. Maximal static expiratory pressure (PEmax) significantly decreased (p < 0.001) in the 1st and 2nd week and it was not related to the type of analgesia used. We advocate the use of cryoanalgesia since it significantly reduces pain as well as the doses of analgesia.

Adult↗
PubMed1995

[Pleural thickening in tuberculous pleural effusion. The associated factors].

We aimed to determine which factors were related to the development of residual pleural thickening (RPT) after completion of prescribed treatment. Sixty-two patients with pleural tuberculosis (PTB) were assigned to 2 groups according to the presence or absence of RPT > 2 mm in the side and lower portion of a chest film after completion of prescribed treatment. No patient had been given corticoids. Thickening developed in 72.6%, more often in men (OR, 4.06; p = 0.034), in older patients (36 +/- 21 versus 27 +/- 12 years; p = 0.05). Smoking, size of effusion, duration of symptoms, encapsulation, PPD, pleural biopsy, bacteriology and pH, glucose, proteins and cholesterol in pleural fluids, as well as their respective pleura/serum coefficients, were similar in both groups. Pleural LDH (LDHp) and its pleura/serum coefficient (LDHp/LDHs) were 454.3 +/- 234.6 U/l and 3.21 +/- 1.67 U/l in the group with RPT and 306.0 +/- 137.2 U/l and 2.00 +/- 1.16 in the group with no sequelae (p = 0.004 and p = 0.016, respectively). Using 2.10 as the cutoff for LDHp/LDHs, sensitivity was 78.9% and specificity was 71.4%, giving a positive predictive value of 88.2% and a negative predictive value of 55.5%. We conclude that RPT a) is a frequent complication, b) is mainly found in men, c) is age-related and d) can be fairly safely predicted using 2.10 as the cutoff for LDHp/LDHs.

Adolescent↗
PubMed1995

[Bronchiolitis obliterans organizing pneumonia (Ardystil syndrome) and chronic demyelinating disease of the central nervous system].

A 19-years-old woman with bronchiolitis obliterans organizing pneumonia (BOOP) secondary to inhalation of toxins in the workplace (Ardystil syndrome) and chronic demyelinating disease of the central nervous system is described. The clinical and radiological picture led to suspicion of BOOP and the diagnosis was confirmed by transbronchial biopsy. The diagnosis of chronic demyelinating disease of the central nervous system was based on the presence of signs of transitory neurological dysfunction along with nuclear magnetic resonance images of the brain that were consistent with the clinical evaluation. The temporal and spatial concurrence of the two diseases in our patient suggests that we may be observing either a new syndrome associated with the inhalation of toxic substances or a coincidence of two diseases that are rare in the population we serve.

Adult↗
PubMed1995

Ventilatory pattern at rest and response to hypercapnic stimulation in patients with obstructive sleep apnea syndrome.

We studied the ventilatory pattern and mouth occlusion pressure (P0.1) at rest and the response to awake hypercapnic stimulation in 27 patients with obstructive sleep apnea syndrome (OSAS). The respiratory pattern was characterized by both increased P0.1 and VT/Ti (p < 0.05), with a higher VE (p < 0.01) due to a slight increase in VT. Ventilatory response to hypercapnic stimulation showed no significant differences with respect to the control group. Our findings reveal that OSAS patients show an increased minute output secondary to a mild degree of hyperstimulation on the baseline central ventilatory control and that there is a subgroup of patients with a decreased ventilatory response to CO2.

Adult↗
PubMed1994

[Ventilation pattern at rest and respiratory response to hypercapnic stimulation after lung transplantation].

We aimed to assess breathing pattern at rest by studying occlusion pressure after the first 100 miliseconds (P0.1) and ventilatory response to hypercapnia after lung transplantation. Seven transplanted patients were compared with a control group of 7 healthy subjects. The breathing pattern at rest after transplantation included a significant increase in minute volume (VE) at the expense of an increase in tidal volume (VT) and above all of mean inspiratory flow (VT/Ti). There were no significant differences in ventilatory response to hypercapnia between the 2 groups, although the response curves of both VE and VT to CO2 tended to slope downward. These results can be explained by the mechanics of ventilation in some subjects studied and by the effect of pulmonary denervation on ventilatory control.

Adult↗
PubMed1994

Stenting of proximal venous obstructions to maintain hemodialysis access.

PURPOSE: The purpose of the study was to evaluate the efficacy of stenting central venous obstructions in patients dependent on hemodialysis to preserve or restore central venous patency and allow for continued hemodialysis from the affected side. METHODS: Twenty-five self-expanding (17) and balloon-expandable (8) stainless steel stents were deployed in 19 patients with end-stage renal disease and central venous stenosis or occlusion. Nineteen lesions were treated: 11 subclavian and eight innominate. Twenty-two stents were initially implanted. RESULTS: Stent deployment was successful in all cases and immediately remedied the underlying cause of venous hypertension. Follow-up at up to 17 months revealed three deaths from unrelated causes, one occlusion at 3.25 months, and three restenoses at 16 days, 2.5 and 5 months, respectively, with successful implantation of three additional stents for a primary central patency rate of 68% (+/- 14%) and secondary central patency rate of 93% (+/- 7%). CONCLUSIONS: Stenting of subclavian and innominate venous stenoses and occlusions effectively corrected the underlying lesions responsible for disturbed hemodynamics and, in most cases, prolonged available hemodialysis access from the affected side. Stents seem to be valuable adjuncts in the management of failing hemodialysis access due to central venous stenosis or occlusion.

Adult↗
PubMed1991

Renal and endocrine responses to a renin inhibitor, enalkiren, in normal humans.

Interpretation of renin-angiotensin blockade with angiotensin converting enzyme inhibitors is potentially confounded by their multiple effects. We used a selective renin inhibitor (enalkiren, A-64662) to explore the renal and endocrine effects of angiotensin II in healthy men. Each received 90-minute enalkiren infusions at 2-day intervals, on a low (10 mmol, 16 subjects) and high (200 mmol, 12 subjects) salt diet. Plasma renin activity, immunoreactive plasma angiotensin II and aldosterone concentrations, inulin, and p-aminohippurate clearance were measured by standard methods. Plasma renin activity fell at 0.1 micrograms/kg, but the threshold for biologic effect was 256 micrograms/kg, where plasma immunoreactive angiotensin II and aldosterone concentration fell, and renal plasma flow rose (p less than 0.01). The maximal renal vascular response (+152 +/- 23 ml/min/1.73 m2) occurred at 512 micrograms/kg (p less than 0.01). Diastolic and mean blood pressure fell modestly but significantly (p less than 0.05). Responses were limited on a high salt diet. We confirm that conventional plasma renin activity measurement is misleading in humans receiving a renin inhibitor. The renal vascular response to renin inhibition in this study appeared to substantially exceed reported responses to angiotensin converting enzyme inhibition, perhaps reflecting a crucial and relatively inaccessible intrarenal locus.

Adult↗
PubMedDate not supplied

[Adenoid cystic carcinoma of the trachea and bronchi. Presentation of 2 cases and review of the literature].

Adenoid cystic carcinoma is a rare but insidious tumor of the trachea and bronchi. It is infiltrative and tends to recur at the same site. Diagnosis is often late, generally when a large part of the bronchial opening is occluded and with extensive invasion of submucosal tissue, making elective surgery difficult and complementary radiotherapy necessary in most cases. The prognosis, however, is fairly good, with survival after 5 years in 75% of patients. We present cases diagnosed recently at our hospital, one with a large longitudinal tracheal tumor and the other with a located in the carina. The literature is reviewed.

Adult↗