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Biomedical subjects

E Cerda

Publications and source records attributed to E Cerda.

13 recordsLinked to original sources
PubMed2005

Mechanics of scars.

When a wound heals, as everyone has observed, it contracts, thickens and wrinkles the neighbouring skin, forming a scar. The morphology of the scar depends on the type of wound; an urgent tracheotomy leads to a very different scar than a carefully planned face lift. The surgical challenges of intrusive procedures such as removal of skin lesions, skin transplantation or grafting, and scar removal are complicated by the complex geometry and stress states in different parts of the body. We show that, for relatively general conditions, the nature of the localisation of the scar is determined by the background tension of the skin which can arrest the formation of wrinkles around a scar. Our physical experiments to simulate this procedure indicate that the region deformed by the defect has a characteristic length scale r* approximately 1 square root of tau, where tau is the natural tension of the skin.

Biomechanical Phenomena↗
PubMed2004

The elements of draping.

We consider the gravity-induced draping of a 3D object with a naturally flat, isotropic elastic sheet. As the size of the sheet increases, we observe the appearance of new folded structures of increasing complexity that arise because of the competition between elasticity and gravity. We analyze some of the simpler 3D structures by determining their shape and analyzing their response and stability and show that these structures can easily switch between a number of metastable configurations. For more complex draperies, we derive scaling laws for the appearance and disappearance of new length scales. Our results are consistent with commonplace observations of drapes and complement large-scale computations of draping by providing benchmarks. They also yield a qualitative guide to fashion design and virtual reality animation.

Body Constitution↗
PubMed2003

Geometry and physics of wrinkling.

The wrinkling of thin elastic sheets occurs over a range of length scales, from the fine scale patterns in substrates on which cells crawl to the coarse wrinkles seen in clothes. Motivated by the wrinkling of a stretched elastic sheet, we deduce a general theory of wrinkling, valid far from the onset of the instability, using elementary geometry and the physics of bending and stretching. Our main result is a set of simple scaling laws; the wavelength of the wrinkles lambda approximately K(-1/4), where K is the stiffness due to an "elastic substrate" effect with a multitude of origins, and the amplitude of the wrinkle A approximately lambda. These could form the basis of a highly sensitive quantitative wrinkling assay for the mechanical characterization of thin solid membranes.

Elasticity↗
PubMed2001

[Cefotaxime, twenty years later. Observational study in critically ill patients].

OBJECTIVE: Afer twenty years of commercial availability of cefotaxime, the objective of this study was to know the reasons and modes of use, administration dosage as well as its effectiveness and tolerance in critically ill patients admitted to Intensive Care Units (ICU) in our country. DESIGN: Open, prospective, observational, multicenter study. SUBJECTS: All patients who had cefotaxime administered in monotherapy or in combination with other antibiotics were included as cases in this study. RESULTS: A total of 624 patients were included in 44 ICUs (average 14 cases). Cefotaxime was indicated for therapy of 274 community-acquired infections (43.9%), 194 prophylaxis (31.1%), and 156 nosocomial infections (25.0%). Both community-acquired pneumonia (149, 34.7%) and mechanical ventilation associated pneumonia (62, 14.4%) predominated, followed by trachebronchitis (60, 13.9%) and central nervous system infections (42, 9.8%). Over half of infections (222, 51.6%) presented as systemic inflammatory response syndrome (SIRS), 133 (30.9%) as severe sepsis, and 75 (17.4%) as septic shock. In 374 (87.0%) out of the 430 cases of infection treatment, cefotaxime wan prescribed on an empirical basis and in 150 of them (40.1%) a further confirmation of the causative agent was obtained. In 120 (27.9%) cases, cefotaxime was administered as monotherapy and in the remaining cases in association with one or more antibiotics.The use of cefotaxime as prophylaxis was evaluated as failure in 31 (16.0%) of the cases, whereas in treatment it was considered as failure in 98 (22.8%) of the 430 cases, 51 community-acquired infections, 27 (27.3%) of ICU-acquired infections, and 20 (35.1%) nosocomial infections acquired outside the ICU. In 127 (29.5%) of the 430 infection treatments the initial treatment was changed. The reasons for the change included clinical failure (36, 28.3%), recovery of an uncovered pathogen with the antibiotic (40, 31.5%), emergence of multi-resistant pathogens (28, 22.0%), to decrease the therapeutic spectrum (7, 5.5%), and other reasons (16). Cefotoxime was also changed in 21 (6.0%) of the 194 cases in which it was used as prophylaxis. In 32 (5.1%) patients 37 adverse effects were noted which were associated with a possible or likely use of cefotaxime. Most notably, diarrhoea in 15 (2.4%) occasions and skin rash in 6 cases (1.0%). CONCLUSIONS: Cefotaxime is still one of the therapies of choice for community-acquired and nosocomial infections as well as in different prophylactic modes. It is mostly used on an empirical basis and associated with other antibiotics. Clinical and microbiological efficiency is high whereas adverse effects related to its use have been scarce.

Antibiotic Prophylaxis↗
PubMed1993

Hemodynamic effects of oxygen therapy in patients with acute exacerbations of chronic obstructive pulmonary disease.

The effects of oxygen therapy in patients with stable COPD have been previously reported; however, the hemodynamic changes induced by oxygen therapy in patients during acute exacerbations of COPD are less well known. To investigate the hemodynamic effects of controlled oxygen therapy in patients with acute exacerbations of COPD shortly after arriving at the hospital, we studied 15 consecutive patients who came to the emergency room with acutely decompensated COPD that did not require mechanical ventilation. Patients were monitored with a pulmonary artery catheter and a radial artery catheter. Oxygen uptake was calculated by the modified Fick equation. Arterial and venous blood gas levels and hemodynamic parameters were measured while breathing room air (baseline) and after 30 min on oxygen therapy via face mask. Measurements were repeated after 24 and 48 h. The fractional concentration of oxygen in the inspired gas (FIO2) administered was adjusted to keep the PaO2 above 55 mm Hg. All patients had a PaO2 below 45 mm Hg at the beginning of the study. After 30 min of oxygen therapy, there was a significant (p < 0.05) increase in arterial oxygen saturation (from 62 +/- 16 to 87 +/- 9 percent), mixed-venous oxygen pressure (from 25 +/- 5 to 43 +/- 11 mm Hg), and oxygen delivery (from 11.1 +/- 3.7 to 19.3 +/- 8.9 ml/kg.min). Oxygen uptake did not change significantly (from 4.1 +/- 1.2 to 4.3 +/- 1.6 ml/kg.min). The oxygen extraction ratio decreased from 37.5 +/- 10.1 to 25.3 +/- 9.6 percent. These changes were maintained during the following 48 h. There were no significant changes in cardiac output and systemic vascular resistance. A trend toward lower values of pulmonary vascular resistance did not reach statistical significance. We conclude that oxygen therapy in patients with acute exacerbations of COPD that do not require mechanical ventilation increases oxygen delivery without changes in cardiac output or oxygen uptake.

Acute Disease↗
PubMed1990

Bronchodilators in patients with chronic obstructive pulmonary disease on mechanical ventilation. Utilization of metered-dose inhalers.

Bronchodilators are used widely in the acute exacerbations of chronic obstructive pulmonary disease (COPD), although their effectiveness is not clearly established. We used three bronchodilators in 20 patients with COPD who were being mechanically ventilated. Two of the bronchodilators, ipratropium bromide and salbutamol, were administered from metered-dose inhalers (MDI) through an adapter to the endotracheal tube, and the third, aminophylline, was administered in the form of intravenous infusion. Before administering each drug, peak airway pressure, end-inspiratory pressure, resistive pressure, and auto positive end-expiratory pressure (auto-PEEP) were measured, and inspiratory resistance (Rins) and compliance were calculated. Heart rate (HR) and blood pressure were also recorded, and arterial pH and blood gas determinations were made. These measurements were repeated 60 min after the administration of aminophylline, 15 and 60 min after administering salbutamol, and 30 and 60 min after administering ipratropium bromide. With these three drugs, airway pressures were reduced, as well as auto-PEEP and Rins, with respect to basal values (p less than 0.05). The changes in compliance were only significant with salbutamol (p less than 0.05). HR was only significantly modified with aminophylline (p less than 0.05). No blood gas change was observed with any of the three drugs. It can be concluded that: (1) the three drugs used in this study were equally effective in producing significant bronchodilation in patients on mechanical ventilation for severe acute exacerbation of COPD; (2) the administration of bronchodilators by MDI in intubated patients through a special adapter was as effective as the intravenous administration of aminophylline.

Aged↗