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Biomedical subjects

Francisco Ortega

Publications and source records attributed to Francisco Ortega.

At least 19 recordsLinked to original sources
PubMed2006

New evidence of shared dinosaur across Upper Jurassic Proto-North Atlantic: Stegosaurus from Portugal.

More than one century after its original description by Marsh in 1877, we report in this paper the first uncontroversial evidence of a member of the genus Stegosaurus out of North America. The specimen consists of a partial skeleton from the Upper Jurassic of Portugal, herein considered as Stegosaurus cf. ungulatus. The presence of this plated dinosaur in the upper Kimmeridgian-lower Tithonian Portuguese record and synchronic levels of the Morrison Formation of North America reinforces previous hypothesis of a close relationship between these two areas during the Late Jurassic. This relationship is also supported by geotectonic evidences indicating high probability of an episodic corridor between the Newfoundland and Iberian landmasses. Together, Portuguese Stegosaurus discovery and geotectonic inferences could provide a scenario with episodical faunal contact among North Atlantic landmasses during the uppermost Kimmeridgian-lowermost Tithonian (ca. 148-153 Ma ago).

Animals↗
PubMed2006

Mental health at the third month of haemodialysis as a predictor of short-term survival.

BACKGROUND: The aim of this study was to evaluate the survival of patients initiating haemodialysis (HD), and to analyse whether low health-related quality of life (HRQoL) levels are predictors of mortality in the short-term, controlling certain variables that had been shown in other studies to have a bearing on survival, and using scores, standardized for age and sex, of the HRQoL measurement tool employed. METHODS: This is a multicentric prospective study of all patients on HD in all the dialysis units in Asturias, a region with a little over one million inhabitants, from 1 January 2001 to 30 September 2002. A total of 199 patients initiated HD in our region and survived the first 3 months. Of these, 137 patients who remained on HD for at least 3 months had complete responses on HRQoL measures. RESULTS: It was observed that adjusted relative risk (RR) of death increased by 5% for each year of age increase (RR=1.05, 95% CI 1.01-1.09: P=0.006); in the same way, for each increase in the Mental Component Summary (MCS) score, the adjusted RR of death diminished by 4% (RR=0.96, 95% CI 0.94-0.99; P=0.006). CONCLUSION: Mental health has been shown to be a factor independently associated with mortality; as the MCS score worsens the adjusted RR of death of a patient on HD increases.

Adult↗
PubMed2006

Equilibrium and dynamics of Langmuir monolayers when the interface is a selective solvent: Polystyrene-b-poly(t-butyl acrylate) block copolymers.

The surface pressure of monolayers of insoluble diblock copolymers has been measured. One of the blocks is made of poly(t-butyl acrylate) (PtBA), and the other one by polystyrene (PS). The interface is a good solvent for PtBA, while it is a poor solvent for PS. For the sake of comparison, monolayers of a PtBA homopolymer (good solvent conditions) and of poly(4-hydroxy styrene) (P4HS) (poor solvent conditions) have been also measured. It has been found that the relative length of the blocks plays an important role on the shape of the surface pressure Pi versus surface concentration Gamma curves and also on the shape of the equilibrium compressibility versus Gamma curves. However, it does not affect the maximum value of Pi reached at high Gamma's. Surprisingly, the ellipsometric thickness of the copolymer monolayers is almost independent of the relative length of the blocks. The dynamics of the monolayers has been studied by step compression and by surface-light scattering techniques. When M(w,PtBA) >> M(w,PS) single exponential relaxations are observed. However, stretched exponentials are obtained for M(w,PS) > or = M(w,PtBA). The relaxation times decrease with increasing Gamma for all the copolymers studied. This is the behavior usually found for poor solvent conditions (P4HS) and opposite to that found for homopolymers under good solvent conditions [PtBA, poly(vinylacetate)]. This means that the solvent quality of the interface does not determine the pressure dependence of tau. The elasticity modulus of the monolayers in the kilohertz range takes values that are similar to those of the high-frequency limit of the relaxation experiments. This means that the relaxation processes have characteristic frequencies below 1 Hz.

Journal Article↗
PubMed2006

Fourier-transform rheology of polymer Langmuir monolayers: analysis of the non-linear and plastic behaviors.

The linear regime (LR) of viscoelastic behavior has been found to be limited to rather small values of strain, well below the strains found in many technological processes. A Fourier-transform method is described for analyzing the surface rheology data obtained in insoluble Langmuir polymer monolayers beyond the LR. In the concentrate regime, the monolayers show a transition from elastic to plastic behavior, which is characterized by high irreversibility. A simple 2-D rubber model is presented that describes the behavior of the monolayers in the non-linear region not too far from the end of the LR.

Elasticity↗
PubMed2006

[Phenomenology of viscerality: the impact of medical imaging technologies on corporeality].

This article deals with the phenomenological dimension of the inner body in light of the success of new medical imaging technologies outside the biomedical field itself. The new technologies contribute not only to the disembodiment of subjectivity, but also to the virtualization and objectification of corporeality. They neglect the constitutive subjective dimension of the living body. The article investigates this fundamental dimension of corporeality, ungraspable through medical imaging.

Anthropology, Cultural↗
PubMed2006

[The transparent body: medical imaging and popular culture in the twentieth century].

In today's societies, successful new medical imaging technologies have focused unprecedented attention on the inside of the human body. These techniques have jumped the walls of the biomedical field per se, penetrating the fields of culture and law. The article traces a genealogy of twentieth-century medical techniques used to visualize the human body and brain, from X-rays to the more sophisticated CTs, MRIs, and PET scans. It explores the changes that these ever more numerous visualization techniques have occasioned in our corporality and examines how these technologies have been received in the courtroom and in popular culture, especially in literature, movies, and magazines.

Culture↗
PubMed2005

Equilibrium behavior and dilational rheology of polyelectrolyte/insoluble surfactant adsorption films: didodecyldimethylammonium bromide and sodium poly(styrenesulfonate).

The surface pressure of monolayers of an insoluble surfactant, didodecyldimethylammonium bromide (DODAB), has been measured onto subphases with different concentrations of poly(styrenesulfonate) (PSS) and at different temperatures. The presence of PSS in the subphase shifts the surface-pressure (Pi) curves to larger areas per DODAB molecule, A, and shifts the surface phase transition to higher Pi's. The presence of PSS chains decreases the surface electric potential; the decrease is higher than expected from the formation of a double layer between the DODAB molecules and the PSS segments. Increasing the temperature shifts the surface-pressure curves to higher areas and also increases the values of Pi of the surface phase transition. The effect of the PSS chains on the Pi versus A curves is contrary to the one induced by the presence of inert electrolytes in the subphase. The behavior is consistent with the existence of a dense layer of PSS segments beneath the DODAB monolayer at low PSS concentrations, c. Two PSS layers exist at higher concentrations, a dense layer immediately below the DODAB and a less-dense layer, below the first one, that protrudes deep into the subphase. The surface-pressure relaxation curves have been found to be bimodal through the whole range of surface pressures and at all the values of polymer concentration studied. These results point out that the adsorption layers behave mainly as elastic bodies, with zero-frequency elasticity, epsilon(omega = 0), which agrees with the equilibrium compressibility modulus. The increase [epsilon(omega = 1) - epsilon(omega = 0)] has been found to be independent of both polymer concentration and molecular weight. The zero-frequency-dilational viscosity, kappa(omega = 0), strongly increases with Pi in the two-dimensional condensed-liquid region. The surface viscosity strongly decreases with increasing frequency; the decreasing rate is higher than the one found for the monolayers of nonionic insoluble polymers. kappa(omega = 0) has also been found to be independent of both polymer concentration and molecular weight. These results seem to indicate that it is the film formed by the DODAB molecules and the first dense polymer layer that determines the surface viscoelastic moduli of this system.

Journal Article↗
PubMed2005

Surface rheology of two-dimensional percolating networks: Langmuir films of polymer pancakes.

We report surface rheological measurements on Langmuir films of submicron-sized polymer coils (pancakes). The dynamics of the sol phase is found to be governed by free volume as in the simplest percolation problem. The observed rheology of the percolated phase (gel-like) is compatible with predictions for compressed arrangements of highly deformed soft particles interacting through their contact interfaces.

Journal Article↗
PubMed2005

Surface light-scattering at the air-liquid interface: from newtonian to viscoelastic polymer solutions.

The dynamics of the liquid-air interface of aqueous solutions of a tensioactive triblock copolymer (Pluronic F-68) has been studied using surface quasielastic light scattering over a broad range of concentrations and temperatures. Ancillary surface tension and bulk rheometry data have been obtained for the same system. The results show that the classical theoretical spectrum for monolayers on a Newtonian fluid can be applied only for concentrations below 4.10(-2) mM. For concentrations above c = 14 mM a clear peak centered at zero frequency appears in the spectrum. This feature is incompatible with the classical theoretical spectrum. The SQELS spectra have been described in terms of the theory of Wang and Huang [Wang, C. H.; Huang, Q. R. J. Chem. Phys. 1997, 107, 5898] considering that the loss modulus of the concentrated solutions shows the existence of two relaxation modes even at low frequencies. The theory is able to explain the existence of a peak centered at zero frequency in the spectra, and the theoretical spectra point out the existence of an elastic peak together with the capillary one. There is a reasonable agreement between the relaxation times and the product Gtau obtained from the fits of the SQELS spectra to the theory of Wang and Huang and those obtained from bulk rheology.

Journal Article↗
PubMed2005

Collective and self-diffusion coefficients in an ionic critical mixture: 3-methylpyridine+water+NaBr.

The dynamics of concentration fluctuations of three critical samples of the 3-methylpyridine (3MP)+water+NaBr system have been measured by photon correlation spectroscopy. The collective-diffusion coefficient D shows the usual Ising behavior near the critical temperature T(c). However, as |T-T(c)| increases, the dynamic correlation length calculated from D, xi, takes values higher than the correlation length of the critical fluctuations calculated from static light scattering, xi(s). At the largest |T-T(c)| measured, xi approaches the value, xi(0,d) approximately equal to 1.13 nm, while the amplitude of xi(s) is xi(0,s)=0.38 nm. Pulsed-gradient NMR spectroscopy points out the existence of two dynamic contributions. One of them is consistent with the existence of molecular entities of hydrodynamic radius 0.31 nm, while the other one indicates the existence of aggregates rich in 3MP of radius 1.16 nm. The existence of the aggregates may explain the apparent anomalous behavior of the dynamic light scattering experiments for this system far from the critical point.

Journal Article↗
PubMed2005

Langmuir monolayers of the zwitterionic surfactant hexadecyl 1-N-L-tryptophan glycerol ether.

We report the formation of Langmuir monolayers of pure zwitterionic hexadecyl 1-N-L-tryptophan glycerol ether (C(16)-TGE) surfactant and mixed monolayers of cationic-zwitterionic surfactant obtained modifying the pH of the subphase. The pressure-area and surface potential-area isotherms and fluorescence microscopy measurements have been used to characterize the surface phase transitions in the monolayers. These transitions appeared at larger areas as the pH decreased from 6.0 to 2.0 and almost disappeared as the pH decreased further. The analysis of the surface potential and the infrared reflection-absorption spectroscopy data suggests that the phase transition is associated with a change of orientation of both the hydrocarbon chain and the aromatic group of the surfactant with respect to the air-water surface. The surface rheology of the monolayers was studied by quasielastic light scattering and by the oscillatory barrier technique. The results indicate that there is at least one relaxation process in the monolayer.

Journal Article↗
PubMed2005

The timely construction of arteriovenous fistulae: a key to reducing morbidity and mortality and to improving cost management.

BACKGROUND: Some investigators have shown that the initial placement of a catheter or graft, instead of the timely construction of an arteriovenous fistula (AVF), late referral to nephrology services and unplanned dialysis increase morbidity and mortality in chronic haemodialysis (CHD) patients. Furthermore, a delay in providing an adequate AVF entails significant increases in treatment-related costs. This study was limited to the analysis of the effects of the lack of an adequate vascular access for CHD on morbidity and mortality. METHODS: According to the vascular access they had in the first 3 months of CHD treatment 96 patients were divided into three groups (VA group): Group 1 (G1), having an adequate AVF in the first 3 months; Group 2 (G2), starting with a catheter but finishing with an AVF; and Group 3 (G3) starting and finishing with a catheter. Time-dependent Cox regression analysis was performed to identify variables associated with survival, and the standardized mortality index (SMI) was calculated. Finally, we studied cost-effectiveness. RESULTS: Time-dependent Cox regression and logistic regression analyses showed the statistically significant variable to be the VA group. To ensure that mortality was comparable between VA groups, eliminating age bias, the findings were adjusted applying SMI. G1 patients appear to have a lesser risk of death (relative risk, 0.39) than G2 and G3 patients, as do G2 relative to G3 patients. Also, after adjustment with SMI, patients over 65 years, presumably at greater risk of death, have a lower mortality than the <or=65 age group. Patients with an adequate and functioning AVF lived longer than the others, and the cost of each 'death prevented' was lower (3318/patient). CONCLUSIONS: The lack of an adequate AVF at the start of haemodialysis decreases survival significantly-even if patients are not diabetic, are referred to a nephrologist early and planned haemodialysis is initiated. It also increases the cost of each prevented death.

Adult↗
PubMed2005

Exercise training in mitochondrial myopathy: a randomized controlled trial.

Patients with mitochondrial myopathies (MM) usually suffer from exercise intolerance due to their impaired oxidative capacity and physical deconditioning. We evaluated the effects of a 12-week supervised randomized rehabilitation program involving endurance training in patients with MM. Twenty MM patients were assigned to a training or control group. For three nonconsecutive days each week, patients combined cycle exercise at 70% of their peak work rate with three upper-body weight-lifting exercises performed at 50% of maximum capacity. Training increased maximal oxygen uptake (28.5%), work output (15.5%), and minute ventilation (40%), endurance performance (62%), walking distance in shuttle walking test (+95 m), and peripheral muscle strength (32%-62%), and improved Nottingham Health Profile scores (21.47%) and clinical symptoms. Control MM patients did not change from baseline. Results show that our exercise program is an adequate training strategy for patients with mitochondrial myopathy.

Adolescent↗
PubMed2004

Long-time relaxation dynamics of langmuir films of a glass-forming polymer: evidence of glasslike dynamics in two dimensions.

We have carried out an experimental study on the mechanical relaxation of Langmuir films of a glass-forming polymer, poly-(4-hydroxystyrene), a good example of a two-dimensional system made of condensed polymer coils (at poor-solvent conditions). This study allows us to explore the response functions of the film and the temperature and density dependencies of the relaxation time. The dynamical properties show glasslike features (non-Debye mechanical response and non-Arrhenius relaxation times) reconcilable within the frame of the mode-coupling model.

Journal Article↗
PubMed2004

The contribution of the arrector pili muscle and sebaceous glands to the follicular unit structure.

BACKGROUND: The evidence of hairs grouped into well-defined follicular units has given a new vision of hair anatomy and pathology. The sebaceous glands and the arrector pili muscle, as part of the pilosebaceous unit, should be viewed as important parts of this organized follicular unit structure. OBJECTIVE: This study was performed to define the morphology and the relationships between the sebaceous glands, muscles, and follicles within the context of the follicular unit structure. METHODS: This study analyzes horizontal, microscopic serial sections of large areas of normal human scalp skin stained with hematoxylin and eosin, Masson's trichrome, and desmin. The course of the arrector pili muscles from their superficial origins to their follicular attachments was followed in each section, which enabled us to match each muscle with its corresponding follicular unit. RESULTS: Serial, horizontal sections show that, at the upper isthmus, the arrector pili muscle is arranged as a muscular unit structure at the periphery of each follicular unit. Then, at a lower level, the muscle divides and encircles the sebaceous gland, and penetrates between the sebaceous lobules towards the follicular attachment zone. CONCLUSION: Microphotographic evaluation of large areas of scalp is important for assessing the anatomical relationships between the sebaceous glands, arrector pili muscles, and hair follicles as components of the follicular unit. We introduce the anatomical concept of a follicular unit served by a muscular unit, which can be identified in horizontal sections made at the upper level of the isthmus. This muscular unit results from the merging of the arrector pili muscles that originate from the hair follicles contained in that particular follicular unit. This anatomical disposition suggests that the arrector pili muscles could play an important role in the integrity of the follicular unit as well as in the secretion of the sebum contents.

Adult↗
PubMed2004

Recipient age as a determinant factor of patient and graft survival.

BACKGROUND: Age of renal transplants has been related to death, alloimmune response and graft outcome. We reviewed the influence of patient age on transplant outcome in three cohorts of patients transplanted in Spain during the 1990 s. METHODS: Patient age was categorized into four groups (I, 18-40; II, 41-50; III, 51-60; and IV, > 60 years). Risks factors for acute rejection were evaluated by logistic regression adjusting for transplant centre and transplantation year, while a Cox proportional hazard model was employed for analysing patient and graft survival. RESULTS: Older patients had a higher death rate (I, 3.5%; II, 7.7%; III, 13.2%; and IV, 16.9%; P<0.001), but a lower standardized mortality index (I, 7.6; II, 7.0; III, 5.8; and IV, 4.1; P = 0.0019). Older patients had the lowest risk of acute rejection [odds ratio (OR) 0.79 and 95% confidence interval (CI) 0.66-0.97 for group II; OR 0.75 and 95% CI 0.62-0.91 for group III; OR 0.43 and 95% CI 0.33-0.56 for group IV). Death-censored graft survival was poorer in patients older than 60 years (relative risk 1.40; 95% CI 1.09-1.80), but this result was not explained by any combination of patient age with donor age, delayed graft function or immunosuppression. CONCLUSIONS: Patient age is a main determinant of transplant outcome. Although death rate is higher for older patients, standardized mortality was not. Thus, the efforts to reduce mortality should be also implemented in younger patients. Old patients have a low risk of acute rejection but a poorer death-censored graft survival. This last result was not explained by any controlled variable in our study.

Adolescent↗
PubMed2003

Relaxation dynamics of langmuir polymer films: a power-law analysis.

We report an experimental study on the mechanical relaxation of Langmuir films of a flexible polymer: polyvinylacetate, a good example of a two-dimensional polymeric system at good-solvent conditions. This study allows us to explore the dependence of the relaxation times and the surface viscosity on the concentration. In the semidilute regime, both dynamical properties follow well-defined power laws, which are in quantitative agreement with 2D reptation.

Biopolymers↗