Optimization of the use of skin expanders.

BACKGROUND: Skin expansion is a physiological process that is defined as the ability of the human skin to increase its superficial area in response to stress or to a given deformation. Skin expanders are silicon bags that are implanted underneath the skin. Because the skin presents creep or relaxation, the resulting stress decreases after a time due to the imposed deformation. Skin expansions are used to reconstruct burned areas and breasts after a mastectomy or to hide scars. PURPOSE: The question that constantly arises during skin expansion is whether it creates a sufficient amount of skin or, in other words, whether the achieved expansion is sufficient to resurface the defect. These questions are answered with information about how much new tissue is required to achieve the reconstruction in a given context and calculating the required tissue (surface area) in relationship with the volume infiltrated. METHOD: Surface formulas for round and rectangular, and finite elements method for crescent skin expanders are used to calculate the relation between infiltrated volume and surface area. Those results were corrected or validated by an experimental work using 3D scanners to calculate the relation between surface area and internal volumes for the three types of expanders in question. RESULTS: The research provides information to determine the type, number, and volume of skin expanders necessary to obtain an extra amount of skin to repair a specific medical condition and to determine the amount of skin obtained even in cases when the expansion does not come to term. SYMBOLS: fci, Correcting factor, which corrects the mathematical formulas using the experimental results, for i skin expander; i, geometry of the expander, round (c), rectangular (r), or crescent (cresc/cr); Sd , surface of the defect; Sds , surface area of the donor site; Sfi, surface area obtained using a mathematical calculation for the i skin expander; S¯fi, surface area obtained experimentally for the i skin expander; Sfi∗, corrected surface area obtained using a mathematical calculation for the i skin expander corrected by the correcting factor; S¯fi∗∗ extra flap of skin obtained by expansion for the i skin expander; Vii, internal volume infiltrated in the i skin expander; Vni, nominal internal volume of the i skin expander.

Power spectra of the natural input to the visual system.

The efficient coding hypothesis posits that sensory systems are adapted to the regularities of their signal input so as to reduce redundancy in the resulting representations. It is therefore important to characterize the regularities of natural signals to gain insight into the processing of natural stimuli. While measurements of statistical regularity in vision have focused on photographic images of natural environments it has been much less investigated, how the specific imaging process embodied by the organism's eye induces statistical dependencies on the natural input to the visual system. This has allowed using the convenient assumption that natural image data are homogeneous across the visual field. Here we give up on this assumption and show how the imaging process in a human model eye influences the local statistics of the natural input to the visual system across the entire visual field. Artificial scenes with three-dimensional edge elements were generated and the influence of the imaging projection onto the back of a spherical model eye were quantified. These distributions show a strong radial influence of the imaging process on the resulting edge statistics with increasing eccentricity from the model fovea. This influence is further quantified through computation of the second order intensity statistics as a function of eccentricity from the center of projection using samples from the dead leaves image model. Using data from a naturalistic virtual environment, which allows generation of correctly projected images onto the model eye across the entire field of view, we quantified the second order dependencies as function of the position in the visual field using a new generalized parameterization of the power spectra. Finally, we compared this analysis with a commonly used natural image database, the van Hateren database, and show good agreement within the small field of view available in these photographic images. We conclude by providing a detailed quantitative analysis of the second order statistical dependencies of the natural input to the visual system across the visual field and demonstrating the importance of considering the influence of the sensory system on the statistical regularities of the input to the visual system.

The buckling of spherical liposomes.

In the classical "first approximation" theory of thin-shell structures, the constitutive relations for a generic shell element--i.e. the elastic relations between the bending moments and membrane stresses and the corresponding changes in curvature and strain, respectively-are written as if an element of the shell is flat, although in reality it is curved. In this theory it is believed that discrepancies on account of the use of "flat" constitutive relations will be negligible provided the ratio shell-radius/thickness is of sufficiently large order. In the study of drawing of narrow, cylindrical "tethers" from liposomes it has been known for many years that it is necessary to use instead a constitutive law which explicitly describes a curved element in order to make sense of the mechanics; and indeed such tethers are generally of "thick-walled" proportions. In this paper we show that the proper constitutive relations for a curved element must also be used in the study, by means of shell equations, of the buckling of initially spherical thin-walled giant liposomes under exterior pressure: these involve the inclusion of what we call the "Mkappa" terms, which are not present in the standard "first-approximation" theory. We obtain analytical expressions for both the bifurcation buckling pressure and the slope of the post-buckling path, in terms of the dimensions and elastic constants of the lipid bi-layer, and also the initial state of bending moment in the vesicle. We explain physically how the initial bending moment can affect the bifurcation pressure, whereas it cannot in "first-approximation" theory. We use these results to map the conditions under which the vesicle buckles into an oblate, as distinct from a prolate ("rugby-ball") shape. Some of our results were obtained long ago by the use of energy methods; but our aim here has been to identify precisely what is lacking in "first-approximation" theory in relation to liposomes, and so to put the "shell equations" approach onto a firm footing in mechanics.

Antagonism of the acute hemodynamic effects of captopril in decompensated congestive heart failure by aspirin administration.

The concomitant use of angiotensin-converting enzyme inhibitors and aspirin may cause pharmacological antagonism. Hence we examined the effect of aspirin on the neurohormonal function and hemodynamic response to captopril in heart failure patients. Between April 1999 and August 2000, 40 patients were randomized into four equal groups: 1) captopril, 2) aspirin, 3) captopril-aspirin: captopril was given alone on the first day, followed by aspirin on the remaining days, and 4) aspirin-captopril: aspirin was given alone on the first day, followed by captopril on the remaining days. Hemodynamic, norepinephrine and prostaglandin measurements were performed pre- and post-medication for 4 days. Captopril (50 mg) was given orally every 8 h and 300 mg aspirin was given on the first day, and 100 mg/day thereafter. In the captopril group and only on the first day of captopril-aspirin, captopril produced increases in cardiac index (2.1 +/- 0.6 to 2.5 +/- 0.5 l min-1 m-2, P<0.0001), and reduced peripheral vascular resistance (1980 +/- 580 to 1545 +/- 506 dyn s-1 cm-5/m , P<0.0001) and pulmonary wedge pressure (20 +/- 4 to 15 +/- 4 mmHg, P<0.0001). In contrast, aspirin alone or associated with captopril showed no significant hemodynamic changes. Norepinephrine decreased (P<0.02) only in the captopril group. Prostaglandin levels did not differ significantly among groups. Thus, aspirin compromises the short-term hemodynamic and neurohormonal effects of captopril in patients with acute decompensated heart failure.

Antagonism of the acute hemodynamic effects of captopril in decompensated congestive heart failure by aspirin administration

The concomitant use of angiotensin-converting enzyme inhibitors and aspirin may cause pharmacological antagonism. Hence we examined the effect of aspirin on the neurohormonal function and hemodynamic response to captopril in heart failure patients. Between April 1999 and August 2000, 40 patients were randomized into four equal groups: 1) captopril, 2) aspirin, 3) captopril-aspirin: captopril was given alone on the first day, followed by aspirin on the remaining days, and 4) aspirin-captopril: aspirin was given alone on the first day, followed by captopril on the remaining days. Hemodynamic, norepinephrine and prostaglandin measurements were performed pre- and post-medication for 4 days. Captopril (50 mg) was given orally every 8 h and 300 mg aspirin was given on the first day, and 100 mg/day thereafter. In the captopril group and only on the first day of captopril-aspirin, captopril produced increases in cardiac index (2.1 + or - 0.6 to 2.5 + or - 0.5 l min-1 m-2, P<0.0001), and reduced peripheral vascular resistance (1980 + or - 580 to 1545 + or - 506 dyn s-1 cm-5/m2, P<0.0001) and pulmonary wedge pressure (20 + or - 4 to 15 + or - 4 mmHg, P<0.0001). In contrast, aspirin alone or associated with captopril showed no significant hemodynamic changes. Norepinephrine decreased (P<0.02) only in the captopril group. Prostaglandin levels did not differ significantly among groups. Thus, aspirin compromises the short-term hemodynamic and neurohormonal effects of captopril in patients with acute decompensated heart failure

Mechanical behavior and stability of the internal membrane of the InCor ventricular assist device.

This paper describes and analyzes the mechanical behavior of the internal membrane of the InCor VAD (Heart Institute [InCor], University of São Paulo, Brazil), applying the knowledge and tools of structural engineering analysis. This membrane plays an important role in the operation of the ventricular assist device (VAD) because it separates the blood chamber from the pneumatic one, transmitting the pneumatic load to the blood, thus making the desired blood flow possible. The loading repeats itself every time the VAD beats. Therefore the performance, reliability, and durability of the membrane are critical for the performance of the VAD. The mathematical model is based on the large deflection theory of thin shells and on the finite element method. The snap-through instability phenomenon, which is responsible for transmission of the pneumatic load to the blood, was observed in the membrane both when modeled mathematically and experimentally. Principal stresses and strain distributions were obtained with this model at certain load levels along the pre- and postbuckling paths.

Does a circadian variation occur in myocardial ischemia over 48 hours in patients with unstable angina?

OBJECTIVE: To study the incidence of and variation in myocardial ischemia over 48 hours in patients with unstable angina. METHODS: Thirty-nine patients with unstable angina underwent long-term electrocardiography for 48 hours. The number of events and the period of time of ischemia (in minutes) were analyzed for the 48 hours, in two periods of 24 hours, and in periods of 4 hours. RESULTS: We analyzed 1755.8 hours of monitoring tapes, and ischemic episodes were detected in 18 (46.2%) patients, corresponding to 173 ischemic episodes, allowing the evaluation of 1304 minutes of ischemia.only 4 of which were (2.2%) symptomatic, Considering the entire period of time of recording and the predetermined time intervals, we observed a higher number of ischemic episodes (38) and a longer duration of ischemia (315.4 minutes) between 11:00 am and 3:00 pm. However, no significant differences occurred among the values in the different intervals. CONCLUSION: Long-term electrocardiography over 48 hours showed a high incidence (97.8%) of silent ischemic episodes in patients with unstable angina. No evidence of a circadian variation of myocardial ischemia in unstable angina was observed.

Numerical modeling of facial aging.

Facial aging is a biological phenomenon. Skin properties change with time, and gravity and facial expressions exert mechanical deformation. Knowledge of these alterations may suggest ways to reverse them by identifying the corresponding distortional forces. The aim of this study was to determine a pattern of change for parameters of the face during the aging process, based on the numerical fitting of measures from a sample of patients. The first aspect of this study was to define adequate facial parameters and means of measuring them. Subsequently, each parameter was defined individually, and these data were analyzed as a set. The sample for the research was restricted to a group of 40 white female patients with a history of limited exposure to the sun, with ages ranging from 25 to 65. The reason for choosing this sample was the availability of frontal pattern photographs at different ages. The parameters for each patient were measured at two different ages. A strong correlation was found between age and behavior of the parameters. This aging model can be verified qualitatively by comparing photographs of a patient with manipulated photographs simulating aging. The quantitative verification of the model was done through the comparison of the measured and the predicted parameters.

Trombose em artérias coronárias normais causando infarto agudo do miocárdio em pacientes alcoólatra / Thrombosis in normal coronary arteries causing acute myocardial infarction in an alcoholic patient

Paciente jovem, etilista, que sofreu infarto agudo do miocárdio. Após terapêutica trombolítica sem sucesso, a cineangiocoronariografia na fase aguda evidenciava trombos em múltiplas artérias. Um 2§ CATE, realizado no 7§ dia de internação revelou coronárias normais. Não havia nenhum distúrbio do metabolismo lipídico, assim como outro fator de risco de doença arterial coronária, a não ser o fato de ser tabagista de oito a 10 cigarros ao dia, há dois anos, o que nos levou a acreditar que o abuso de álcool etílico possa ter contribuído para esse evento.

[Unstable angina due to communication between the coronary artery and the right pulmonary artery in patient with Takayasu's arteritis]. / Angina instável devida a comunicação entre artéria coronária e artéria pulmonar direita em paciente com arterite de Takayasu.

A sixty three year old woman suffering from Takayasu's arteritis with involvement of the aortic arch, subclavia arteries and occlusion of the right pulmonary artery, developed progressive precordial pain. Exercise electrocardiogram disclosed ST segment depression. Coronary arteriograms demonstrated no coronary stenosis, but collateral circulation arising from circumflex coronary artery to right pulmonary artery. The collateral blood flow was considered to be of great importance, and causing the coronary steal syndrome, leading to angina pectoris.

Angina instável devida a comunicaçäo entre artéria coronária e artéria pulmonar direita em pacientes com arterite de Takayasu / Coronary steal due to collateral circulation from circumflex coronary to right pulmonary artery leading to unstable angina in Takayasu's Arteritis

Mulher de 63 anos com arterite de Takayasu, envolvendo arco aórtico, artérias subclávias e artéria pulmonar direita, com dor precordial progressiva. O eletrocardiograma de esforço revelou depressäo do segmento ST. A cineangiocoronariografia näo mostrou lesöes estenóticas ostiais e nem epicárdicas e, sim, comunicaçäo entre a artéria coronária circunflexa e o ramo do lobo superior da artéria pulmonar direita. O fluxo sangüíneo através da comunicaçäo arterial foi considerado de grau importante, provocando, provavelmente, síndrome do roubo de fluxo coronário e, conseqüentemente, o quadro de angina de peito com caráter progressivo.

[Thrombosis in normal coronary arteries causing acute myocardial infarction in an alcoholic patient]. / Trombose em artérias coronárias normais causando infarto agudo do miocárdio em paciente alcoólatra.

A case of a young patient, heavy drinker, who suffered an acute myocardial infarction (AMI), and whose cinecoronariography, early post unsuccessful intravenous thrombolysis, showed the presence of thrombi in multiple arteries is reported. A second cinecoronariography performed on the 7th day post AMI revealed normal coronary arteries. There were no plasmatic lipid or coagulation abnormalities, nor other risk factors for coronary artery disease. We speculate about the role of the heavy alcohol ingestion in this particular case.

Aspects of the mechanics of lobed liposomes.

Hotani has studied, by means of dark-field light microscopy, morphological transformations which unilamellar liposomes undergo when their interior volume decreases steadily with time as a consequence of osmosis. In a previous paper, we made a theoretical study of the initial buckling of an originally spherical vesicle into the observed oblate spheroidal shape; and we argued that some in-plane shear elastic stiffness is required-in addition to the well-known flexural stiffness of the lipid bilayer-in order to explain the observed phenomena. In the present paper, we consider a later stage in the chain of morphological transitions observed by Hotani, when a series of cudgel-shaped lobes have sprung out of a previously axisymmetric, biconcave-shaped vesicle. Specifically, we compare the observed shapes of such lobes with half of a series of "peanut"-shaped vesicles that are an equilibrium conformation of an initially spherical liposome under reduced internal volume. We find that the shapes do not match well. On the other hand, the observed lobe forms do match satisfactorily portions of "undulating tube" shapes which evolve from a hypothetical cylindrical vesicle, according to some simple calculations. In view of this agreement, we are led to propose that the formation of cudgel-shaped lobes requires some sliding of one lipid monolayer over another. This conflicts, of course, with the Love-Kirchhoff hypothesis which is normally invoked at the outset of analyses of lipid vesicles by means of classical thin-shell theory; but it is in accord with previous suggestions in the context of more obviously severe distortion of the lipid bilayer.

[When should we stop cardiopulmonary resuscitation in patients brought to the emergency room in cardiac arrest without pre-hospital care?]. / Quando interromper, na sala de emergência, as manobras de ressuscitação cardiopulmonar na parada cardiorrespiratória sem atendimento pré-hospitalar?

PURPOSE: The decision of stopping cardiopulmonary resuscitation (CPR) in patients brought to emergency room in arrest remains a challenge. Such decision is even more difficult when someone is brought by bystanders, after an acute loss of consciousness without any out-of-hospital care. To evaluate the probability of survival of these patients we reviewed retrospectively charts in our institution, during a period of five years. METHODS: One hundred and one patients that fulfilled these characteristics came to our emergency in arrest. The time to arrival since symptoms started, cardiac rhythm at first electrocardiogram (EKG), age, gender, initial CPR success, late outcomes and previous diseases were obtained. Patients were divided in two groups regarding which cardiac rhythms they had at first EKG: A-patients arriving in asystole; and VF-patients arriving in ventricular fibrillation. To evaluate time to arrival, we arbitrarily choose 15 min as a reference point. RESULTS: In these 101 subjects the mean age was 62 +/- 13.7 years and 63 (62.3%) were men. Previous heart disease was documented in 74 [dilated cardiomyopathy in 22 (21.7%), coronary heart disease in 41 (40.6%), arterial hypertension in 25 (24.7%) and others in 6 (5.6%)]. In 66 episodes we were sure of the time patients spent before arrival (mean 2.5 +/- 11 min). Only in 63 subjects we had no doubts about the rhythm at entrance: VF in 37 (58.7%), A in 22 (34.9%) and an accelerated idioventricular rhythm (AIR) in four (6.3%). Time to arrival was 18.6 +/- 10.6 in VF vs 32.5 +/- 11.7 min in A (p = 0.012). Fourteen (13.8%) subjects resumed a supraventricular rhythm with systolic pressure > or = 90 mmHg after CPR and all of them were in VF (13) or AIR (one). Nine patients (8.9%) evolved in coma. Only five (4.9%) were discharged from the hospital without any neurological disturbance and their time to arrival ranged from one to 15 (9 +/- 5.8) min. CONCLUSION: Delayed arrival to the emergency room (> 15 min) associated with asystole were predictors of unsuccessful CPR, and both data are helpful in deciding when to stop CPR in subjects arriving at the emergency department with no out-of-hospital care.

[Comparative study between verapamil and adenosine triphosphate in the treatment of paroxysmal supraventricular tachycardia]. / Estudo comparativo entre verapamil e adenosina-trifosfato no tratamento das taquicardias paroxísticas supraventriculares.

PURPOSE: To evaluate the efficacy and safety of intravenous (IV) adenosine-triphosphate (ATP) and verapamil to convert acute episodes of paroxysmal supraventricular tachycardia (PSVT) to sinus rhythm. METHODS: Fifty patients with PSVT were randomized in two groups: A) 25 treated with IV bolus of ATP (10 or 20mg), and V) 25 treated with IV verapamil, up to 15mg, during 3min. We evaluated the time delay necessary to convert the arrhytmia, doses, and side-effects. Patients with acute ischemic syndromes (< 3 weeks), severe congestive heart failure, and treatment with dipyridamole or methylxanthine were excluded. RESULTS: There were no differences between the two groups regarding to age, sex, and success rate. The average time till reversal were respectively, 30s and 248s for ATP and verapamil. Ventricular ectopy and general discomfort were observed in 33% of patients receiving ATP, whereas no side-effects occurred in group V. CONCLUSION: ATP is a good option to convert rapidly PSVT to sinus rhythm and, probably, could be the first choice to treat PSVT patients with ventricular dysfunction.

Estudo comparativo entre Verapamil e Adenosina-Trifosfato no tratamento das taquicardias paroxísticas supraventriculares / Adenosin-three phosphate compared with Verapamil to treat paroxysmal supraventricular tachycardia

Objetivo - comparar a eficácia e segurança da adenosina-trifosfato (ATP) e verapamil endovenosos na reversäo das taquicardias paroxísticas supraventriculares (TPSV). Métodos - foram analisados 50 pacientes com diagnóstico de TPSV pelo eletrocardiograma convencional. Excluíram-se aqueles com insuficiência cardíaca, quadro isquêmico agudo, uso de dipiridamol e metilxantinas. Os pacientes foram distribuídos por sorteio em dois grupos: A) ATP em bolo de 10 ou 20 mg; V) verapamil em infusäo rápida de at15 mg. Avaliaram-se sucesso, tempo de reversäo, dose empregada e efeitos colaterais. Resultados - Ocorreu sucesso na reversão em 96% do grupo A e em 92 % do grupo V (p= 1,0). O tempo médio de reversão foi de 30s no grupo A e 248s no V. Efeitos colaterais foram encontrados em 33% no grupo A, e não ocorreram no grupo V Conclusão - O ATP é uma opção atraente para a reversão das TPSV, apresentando efeitos colaterais fugazes, podendo ser droga de escolha no tratamento desses episódios na presença de disfunção ventricul

Purpose - To evaluate the efficacy and safety of intravenous (IV) adenosine-triphosphate (ATP) and verapamil to convert acute episodes of paroxysmal supraventricular tachycardia (PSVT) to sinus rhythm. Methods - Fifty patients with PSVT were randomized in two groups: A) 25 treated with IV bolus of ATP (10 or 20mg), and V) 25 treated with IV verapamil, up to 15mg, during 3min. We evaluated the time delay necessary to convert the arrhytmia, doses, and side-effects. Patients with acute ischemic syndromes (<3 weeks), severe congestive heart failure, and treatment with dipyridamole or methylxanthine were excluded. Results - There were no differences between the two groups regarding to age, sex, and success rate. The average time till reversal were respectively, 30s and 248s for ATP and verapamil. Ventricular ectopy and general disconfort were observed in 33% of patients receiving ATP, where as no side-effects occurred in group V. Conclusion - ATP is a good option to convert rapidly PSVT to sinus rhythm and, probably, could be the first choice to treat PSVT patients with ventricular dysfunction

[Acute atrial fibrillation in the emergency room. Which is the best drug for a rapid sinus rhythm conversion?]. / Fibrilação atrial aguda na unidade de emergência. Qual a droga ideal para rápida reversão ao ritmo sinusal?

PURPOSE: To evaluate differences between amiodarone, procainamide and quinidine in the time delay necessary to convert acute atrial fibrillation (AF) to sinus rhythm. METHODS: Sixty patients with acute AF were randomized in three groups (G) and treated with: quinidine (QG)-(21 patients) i.v. digital + quinidine up to 600 mg; procainamide (PG)-(23 patients) i.v. digital + i.v. procainamide, 10 mg/kg; amiodarone (AG)-(16 patients) i.v. amiodarone, 5 mg/kg. To evaluate time delay to conversion, all patients have their rhythm recorded by Holter system during four hours. Statistics were done with x2, considering significant a p < 0.05. RESULTS: There were no differences between groups regarding to age, gender and delay from symptoms initiation and medical assistance. Conversion to sinus rhythm occurred, in QG-71.4% cases; PG-47.8% and AG-50% (p > 0.05). Time delay in minutes to conversion were, respectively (media +/- SD): QG-112 +/- 43; PG-44.1 +/- 28; AG-20 +/- 13, significantly lower in PG and AG related to QG (p = 0.001). Although not significant, side effects were observed mostly in PG. CONCLUSION: Amiodarone is a good choice to convert, very quickly, acute AF. Otherwise, quinidine has the best rate of conversion but with a longer time delay.

The mechanics of axially symmetric liposomes.

Hotani has filmed morphological transformations in unilamellar liposomes, starting from a spherical shape, when the interior volume decreases steadily. Hotani's liposomes showed no evidence of general thermal fluctuations. We use a finite-deformation theory of axisymmetric, quasi-static thin shells to analyze theoretically bifurcations and changes of shape in liposomes under decreasing volume. The main structural action in a lipid bilayer is generally agreed to be its elastic resistance to bending, and it is usual to regard surface deformation as being like that of a two-dimensional liquid. We find, however, that some in-plane shear elasticity is also needed in order to produce the observed post-bifurcation behavior. Such an elasticity would be difficult to measure directly.

[Fatal acute myocardial infarction in a young cocaine addict]. / Infarto agudo do miocárdio fatal em jovem viciado em cocaína.

A 28 year-old male cocaine abuser without coronary atherosclerosis suffered fatal myocardial infarction. Necropsy revealed several myocardial infarctions of different ages. Examination of the coronary arteries revealed fibrointimal thickening of the intimal layer of the coronary arteries.