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Selected AbstractsNew York's nature: a review of the status and trends in species richness across the metropolitan regionDIVERSITY AND DISTRIBUTIONS, Issue 1 2009Linda M. Puth ABSTRACT Aim, The world's population is urbanizing, yet relatively little is known about the ecology of urban areas. As the largest metropolitan area in the USA, New York City is an ideal location to study the effects of urbanization. Here, we aim to produce a better understanding of the state of the research for species richness of flora and fauna across the New York metropolitan region. Location, New York metropolitan region, USA. Methods, We conducted a review of the published and grey literature, in which we targeted studies of species richness, and categorized each study by habitat, location and taxonomic group. Results, We found 79 studies reporting location-specific species richness data, resulting in 261 location-taxonomic group records. Of these, 26 records had data from multiple time periods; 17 showed decreases in species richness, six reported increases and three showed stable species richness. Of these 26 records, most declines were attributed to anthropogenic causes, such as habitat loss/degradation and invasive species, while most increases reflected recovery from major habitat loss or increases in exotic species. Overall, most records (84) were terrestrial, followed by those in freshwater (72) and mixed habitats (61). When parsed by taxonomic group, the most commonly studied groups were plants (76) and mammals (48). Main conclusions, In general, we discovered fewer studies than expected reporting species richness, especially studies reporting species richness for more than one point in time. Most studies that did contain data over time reported declines in species richness, while several studies reporting increasing or stable species richness reflected increases in exotic species. This survey provides a crucial first step in establishing baseline ecological knowledge for the New York metropolitan region that should help prioritize areas for protection, research and development. Furthermore, this research provides insights into the impacts of urbanization across the USA and beyond and should help establish similar frameworks for ecological understanding for other metropolitan regions throughout the world. [source] Empirical design of computer support and staffing in concurrent engineeringHUMAN FACTORS AND ERGONOMICS IN MANUFACTURING & SERVICE INDUSTRIES, Issue 2 2006Joe W. Meredith Manufacturing environments are characterized by underlying operational approaches and assumptions. One such assumption is that concurrent engineering (CE) is superior to traditional sequential processing. A laboratory experiment was conducted using 180 engineering and building construction students as subjects. The engineering methodology variable was sequential and concurrent engineering. There were large teams, consisting of six students, and small teams, consisting of three students. The computer support variable was using and not using groupware. Each team was given a set of requirements to design a transportation system that moved a payload from one point to another. Each team was asked to (a) develop a design concept, (b) develop a detail design in the form of engineering drawings, (c) manufacture the system based on their design products (e.g., drawings and specifications) using toy plastic LEGOS, and (d) test the system to determine if it met the design requirements. There was no significant difference in performance between concurrent engineering groups and sequential engineering processes. Small groups significantly outperformed large groups in all conditions. Computer support did not significantly improve the performance of large or small groups. Participants in the experiment were equally satisfied with all conditions. An external survey strongly endorsed the superiority of CE as compared to sequential engineering. Results are discussed in terms of why practitioners believe in the effectiveness of CE, yet an empirical test failed to demonstrate better performance. © 2006 Wiley Periodicals, Inc. Hum Factors Man 16: 177,193, 2006. [source] Analysis of single rock blocks for general failure modes under conservative and non-conservative forcesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2007F. Tonon Abstract After describing the kinematics of a generic rigid block subjected to large rotations and displacements, the Udwadia's General Principle of Mechanics is applied to the dynamics of a rigid block with frictional constraints to show that the reaction forces and moments are indeterminate. Thus, the paper presents an incremental-iterative algorithm for analysing general failure modes of rock blocks subject to generic forces, including non-conservative forces such as water forces. Consistent stiffness matrices have been developed that fully exploit the quadratic convergence of the adopted Newton,Raphson iterative scheme. The algorithm takes into account large block displacements and rotations, which together with non-conservative forces make the stiffness matrix non-symmetric. Also included in the algorithm are in situ stress and fracture dilatancy, which introduces non-symmetric rank-one modifications to the stiffness matrix. Progressive failure is captured by the algorithm, which has proven capable of detecting numerically challenging failure modes, such as rotations about only one point. Failure modes may originate from a limit point or from dynamic instability (divergence or flutter); equilibrium paths emanating from bifurcation points are followed by the algorithm. The algorithm identifies both static and dynamic failure modes. The calculation of the factor of safety comes with no overhead. Examples show the equilibrium path of a rock block that undergoes slumping failure must first pass through a bifurcation point, unless the block is laterally constrained. Rock blocks subjected to water forces (or other non-conservative forces) may undergo flutter failure before reaching a limit point. Copyright © 2007 John Wiley & Sons, Ltd. [source] Optimization of tree-shaped flow distribution structures over a disc-shaped areaINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2003S. Lorente Abstract In this paper, we review the fundamental problem of how to design a flow path with minimum overall resistance between one point (O) and many points situated equidistantly on a circle centred at O. This is a fundamental problem in energy engineering: the distribution of fluid, energy, electric power, etc., from points to surrounding areas. This problem is also fundamental in heat transfer and electronics cooling: how to bathe and cool with a single stream of coolant a disc-shaped area or volume that generates heat at every point. This paper outlines, first, a direct route to the construction of effective tree-shaped flow structures. The starting point is the optimization of the shape of each elemental area, such that the length of the flow path housed by the element is minimized. Proceeding towards larger and more complex structures,from elements to first constructs, second constructs, etc.,the paper develops tree-shaped flow structures between one point and a straight line, as an elemental problem, and a circle and its centre. We also consider the equivalent tree-shaped networks obtained by minimizing the pressure drop at every step of the construction, in accordance with geometric constraints. The construction method is applied to a fluid flow configuration with laminar fully developed flow. It is shown that there is little difference between the two methods. The minimal-length structures perform very close to the fully optimized designs. These results emphasize the robustness of optimized tree-shaped flows. Copyright © 2003 John Wiley & Sons, Ltd. [source] Constructal tree-shaped paths for conduction and convectionINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2003Adrian Bejan Abstract This lecture reviews a series of recent results based on the geometric minimization of the resistance to flow between one point (source, sink) and a volume or an area (an infinity of points). Optimization is achieved by varying the geometric features of the flow path subject to volume constraints. The method is outlined by using the problem of steady volume-point conduction. Optimized first is the smallest elemental volume, which is characterized by volumetric heat generation in a low-conductivity medium, and one-dimensional conduction through a high-conductivity ,channel'. Progressively larger volumes are covered by assemblies of previously optimized constructs. Tree-shaped flow structures spring out of this objective and constraints principle. Analogous problems of fluid flow, and combined heat and fluid flow (convection, trees of fins) are also discussed. The occurrence of similar tree structures in nature may be reasoned based on the same principle (constructal theory) (Bejan, 2000). Copyright © 2003 John Wiley & Sons, Ltd. [source] Studying the relation between temporal reward discounting tasks used in populations with ADHD: A factor analysisINTERNATIONAL JOURNAL OF METHODS IN PSYCHIATRIC RESEARCH, Issue 3 2010Anouk Scheres Abstract Background: This study aimed at investigating the relationship between tasks that have been used in attention deficit hyperactivity disorder (ADHD) to measure choices between smaller immediate and larger delayed rewards: real and hypothetical temporal discounting tasks, and single-choice paradigms. Methods: Participants were 55 undergraduate psychology students. Tasks included a real and hypothetical version of a temporal discounting (TD) task with choices between a large reward (10 cents) after delays up to 60 seconds, and smaller immediate rewards (2,8 cents); two versions of a hypothetical temporal discounting task with choices between a large reward ($100) after delays up to 120 months, and smaller immediate rewards ($1,$95); a Choice Delay Task with choices between one point now and two points after 30 seconds (one point is worth five cents). Results: Correlation analyses showed that the real and the hypothetical TD tasks with 10 cents were very strongly associated. However, the hypothetical TD tasks with $100 did not correlate with either the real or the hypothetical TD task with 10 cents. Principal component analysis extracted two components: one for small amounts and short delays, and a second one for large rewards and long delays. Conclusions: Temporal reward discounting is not a uniform construct. Functional brain imaging research could shed more light on unique brain activation patterns associated with different forms of temporal reward discounting. Copyright © 2010 John Wiley & Sons, Ltd. [source] Lower urinary tract symptoms in relation to lifestyle and medical conditions in Japanese workersINTERNATIONAL JOURNAL OF UROLOGY, Issue 5 2009Kentaro Tomita Objectives: To examine the association of medical conditions and lifestyle with lower urinary tract symptoms (LUTS) in a population of Japanese male workers. Methods: A questionnaire survey on LUTS was conducted at the time of a periodic health examination among workers of a group of engineering and shipbuilding companies in Southern Kanto, Japan. A total of 1278 (85%) men responded. LUTS were assessed by using a modified International Prostate Symptom Score questionnaire. Men having at least one point of the score were regarded as positive. Logistic regression analysis was used to examine the relation of the LUTS to age, smoking, drinking, body mass index, and medical treatment of diabetes mellitus, hypertension, and dyslipidemia. Results: Age was a strong determinant of LUTS. Men undergoing medical treatment for diabetes mellitus were significantly more likely to have LUTS than men without treatment (multivariate-adjusted odds ratio, 1.8; 95% confidence interval, 1.0,3.2). Increased odds of LUTS were also observed in men undergoing medical treatment for hypertension or dyslipidemia. Smoking, drinking alcohol, and obesity were not related to LUTS. Conclusions: Our present findings, together with previous epidemiological and experimental evidence, suggest that LUTS might share common etiological factors with diabetes mellitus, hypertension, and dyslipidemia. [source] Accuracy of patient recall of preoperative symptom severity (angina and breathlessness) at one year following aorta-coronary artery bypass graftingJOURNAL OF CLINICAL NURSING, Issue 3 2009Grace M Lindsay Aim and objective., The accuracy with which patients recall their cardiac symptoms prior to aorta-coronary artery bypass grafting is assessed approximately one year after surgery together with patient-related factors potentially influencing accuracy of recall. Background., This is a novel investigation of patient's rating of preoperative symptom severity before and approximately one year following aorta-coronary artery bypass grafting. Design., Patients undergoing aorta-coronary artery bypass grafting (n = 208) were recruited preoperatively and 177 of these were successfully followed up at 16·4 (SD 2·1) months after surgery and asked to describe current and recalled preoperative symptoms using a 15-point numerical scale. Method., Accuracy of recall was measured and correlated (Pearson's correlation) with current and past symptoms, health-related quality of life and coronary artery disease risk factors. Hypothesis tests used Student's t -test and the chi-squared test. Results., Respective angina and breathlessness scores were recalled accurately by 16·9% and 14·1% while 59% and 58% were inaccurate by more than one point. Although the mean preoperative and recalled scores for severity of both angina and breathlessness and were not statistically different, patients who recalled most accurately their preoperative scores had, on average, significantly higher preoperative scores than those with less accurate recall. Patients whose angina and breathlessness symptoms were relieved by operation had significantly better accuracy of recall than patients with greater levels of symptoms postoperatively. Conclusion., Patient's rating of preoperative symptom severity before and one year following aorta-coronary artery bypass grafting was completely accurate in approximately one sixth of patients with similar proportions of the remaining patients overestimating and underestimating symptoms. The extent to which angina and breathlessness was relieved by operation was a significant factor in improving accuracy of recall. Relevance to clinical practice., Factors associated with accuracy of recall of symptoms provide useful insights for clinicians when interpreting patients' views of the effectiveness of aorta-coronary artery bypass grafting for the relief of symptoms associated with coronary heart disease. [source] Phase imaging using highly coherent X-rays: radiography, tomography, diffraction topographyJOURNAL OF SYNCHROTRON RADIATION, Issue 3 2000José Baruchel Several hard X-rays imaging techniques greatly benefit from the coherence of the beams delivered by the modern synchrotron radiation sources. This is illustrated with examples recorded on the `long' (145,m) ID19 `imaging' beamline of the ESRF. Phase imaging is directly related to the small angular size of the source as seen from one point of the sample (`effective divergence' , microradians). When using the `propagation' technique, phase radiography and tomography are instrumentally very simple. They are often used in the `edge detection' regime, where the jumps of density are clearly observed. The in situ damage assessment of micro-heterogeneous materials is one example of the many applications. Recently a more quantitative approach has been developed, which provides a three-dimensional density mapping of the sample (`holotomography'). The combination of diffraction topography and phase-contrast imaging constitutes a powerful tool. The observation of holes of discrete sizes in quasicrystals, and the investigation of poled ferroelectric materials, result from this combination [source] Delayed reflection of the energy flow at a potential step for dispersive wave packetsMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 10 2004F. Ali Mehmeti Abstract We study Klein,Gordon equations with constant coefficients and different dispersion relations on two one-dimensional semi-infinite media coupled with transmission conditions. We obtain lower and upper bounds of the reflected part of the energy flow at the connecting point when the frequency band involved in the initial signal is sufficiently narrow. We detect a phenomenon of delayed reflection for low frequency wave packets, which is in accordance with the recent experiments of Haibel and Nimtz. The result is then generalized for a star-shaped network of n semi-infinite branches connected at one point. Copyright © 2004 John Wiley & Sons, Ltd. [source] Botulinum neurotoxin type A injections reduce spasticity in mild to moderate hereditary spastic paraplegia, Report of 19 casesMOVEMENT DISORDERS, Issue 2 2008Martin J. Hecht MD Abstract Hereditary spastic paraplegia (HSP) is characterized by lower extremity spasticity. Symptomatic therapy generally includes physical therapy and oral antispastic agents, in selected cases intrathecal baclofen. Because of the positive results in other treatments of spasticity, the use of botulinum neurotoxin type A (BoNT-A) might also be considered for patients with HSP. We report the effect of BoNT-A injections in 19 unselected patients with HSP treated by the members of the German Spasticity Education Group. In 17 patients, the modified Ashworth scale had improved by one point. In one patient, it improved by three points. Most of the patients reported reduction of spasticity. BoNT-A injections were continued in 11 of 19 patients (57.9%). All of the patients with continued injections had a good or very good global subjective improvement. Patients with less pronounced spasticity and patients with accompanying physical therapy tended to exhibit a better effect. Only four patients reported adverse effects which were increased weakness in three patients and pain in one patient. BoNT-A injections appear to reduce spasticity effectively and safely, especially in patients with mild to moderate spasticity. The preliminary results of our case series should encourage larger studies of BoNT-A injections in HSP. © 2007 Movement Disorder Society [source] Motor patterns and propulsion in the rat intestine in vivo recorded by spatio-temporal mapsNEUROGASTROENTEROLOGY & MOTILITY, Issue 5 2005D. M. Ferens Abstract, We have used spatio-temporal maps derived from video images to investigate propagated contractions of the rat small intestine in vivo. The abdomen, including an exteriorized segment of jejunum, was housed in a humid chamber with a viewing window. Video records were converted to spatio-temporal maps of jejunal diameter changes. Intraluminal pressure and fluid outflow were measured. Contractions occupied 3.8 ± 0.2 cm of intestine and propagated anally at 3.1 ± 0.2 mm s,1 when baseline pressure was 4 mmHg. Contractions at any one point lasted 8.7 ± 0.6 s. Contractions often occurred in clusters; within cluster frequencies were 2.28 ± 0.04 min,1. Pressure waves, with amplitudes greater than about 9 mmHg, expelled fluid when the baseline pressure was 4 mmHg. In the presence ofl -NAME, circular muscle contractions occurred at a high frequency, but they were not propagated. We conclude that video recording methods give good spatio-temporal resolution of intestinal movement when applied in vivo. They reveal neurally-mediated propulsive contractions, similar to those previously recorded from intestinal segments in vitro. The propagated contractions had speeds of propagation that were slower and frequencies of occurrence that were less than speeds and frequencies of slow waves in the rat small intestine. [source] Subjective pain experience of people with chronic back painPHYSIOTHERAPY RESEARCH INTERNATIONAL, Issue 4 2000Professor Lorraine H De Souza Chair of Rehabilitation Abstract Background and Purpose Studies into the effect of pain experience on those who have it have largely focused on the views and interpretations of researchers gained by the use of assessment tools aimed at measuring pain. The purpose of this study was to explore and describe pain, as experienced by those with chronic back pain, and to document ,insider' accounts of how pain is perceived and understood by those who have it. Method Unstructured interviews using the framework approach. Subjects were sampled for age, sex, ethnicity and occupation, from new referrals with back pain to a rheumatology outpatient clinic. Eleven subjects (5 M; 6 F) agreed to be interviewed. Interviews were unstructured, but followed a topic guide. Subjects were interviewed in English (nine) or their preferred language (two). Tape-recordings of interviews were transcribed verbatim and read in depth twice to identify the topics or concepts. Data were extracted in the form of words and phrases by use of thematic content analysis. The themes were pain description and amount of pain. An independent researcher reviewed the data and confirmed or contended the analysis. Results All subjects, except one, provided descriptors of the quality of their pain. The use of simile was common to emphasize both what the pain was, and what it was not. Five subjects expressed a loss of words in trying to describe their pain. Only 13 of 29 different pain descriptors used were commensurate with those in the McGill Pain Questionnaire (Melzack, 1983). Subjects had great difficulty quantifying their pain intensity. Several explained how the pain fluctuated, thus, quantifying pain at one point in time was problematic. Only one subject offered a numerical description of pain intensity. Conclusions Subjects provided graphic and in-depth descriptions of their pain experience, but these bore little resemblance to commonly used assessment tools. The findings challenge the appropriateness of such formal instruments. Copyright © 2000 Whurr Publishers Ltd. [source] Effectiveness of the Kampo kami-shoyo-san (TJ-24) for tremor of antipsychotic-induced parkinsonismPSYCHIATRY AND CLINICAL NEUROSCIENCES, Issue 5 2000Toshihiro Ishikawa MD Abstract The aim of the present study was to evaluate the effectiveness of the Kampo medication kami-shoyo-san against tremor due to antipsychotic-induced parkinsonism. Kami-shoyo-san consists of several medicinal herbs that are known in traditional Chinese medicine to be effective in treating Parkinson's disease and convulsions. We gave kami-shoyo-san to eight patients at Higashiowari National Hospital who were exhibiting tremor, a symptom of antipsychotic-induced parkinsonism. The tremor was evaluated on a five-point scale before and after the administration of kami-shoyo-san, and the findings were compared statistically. The results showed a stastistically significant reduction in the tremor after the administration of kami-shoyo-san (P < 0.01), with 62.5% of patients showing an improvement of one point or more. The tremor did not worsen in any of the patients, and none complained of side-effects. Thus, kami-shoyo-san appears to be effective against the tremor from parkinsonism. Kami-shoyo-san consists of 10 medicinal herbs, including Radix Bulpleuri, Radix Paeoniae, Radix Angelicae Sinensis, and Radix Glycyrrhizae, which are effective in treating disturbances in muscular movement according to TCM theory. Of the 10 herbs contained in kami-shoyo-san, we believe the abovementioned ones are particularly effective in helping to reduce the tremor associated with parkinsonism. [source] Hans Kelsen's Doctrine of ImputationRATIO JURIS, Issue 1 2001Stanley L. Paulson First, the author examines the traditional doctrine of imputation. A look at the traditional doctrine is useful for establishing a point of departure in comparing Kelsen's doctrines of central and peripheral imputation. Second, the author turns to central imputation. Here Kelsen's doctrine follows the traditional doctrine in attributing liability or responsibility to the subject. Kelsen's legal subject, however, has been depersonalized and thus requires radical qualification. Third, the author takes up peripheral imputation, which is the main focus of the paper. It is argued that with respect to the basic form of the law, exhibited by the linking of legal condition with legal consequence, peripheral imputation counts as an austere doctrine, shorn as it is of all references to legal personality or the legal subject. If Kelsen's reconstructed legal norms are empowerments, then the austere doctrine of peripheral imputation captures the rudiments of their form, exactly what would be expected if peripheral imputation does indeed serve as the category of legal cognition. Finally, the author develops the puzzle surrounding the legal "ought" in this context. Although Kelsen talks at one point as though the legal "ought" were the peculiarly legal category, the author submits that this is not the best reading of Kelsen's texts. [source] Measuring function in rheumatoid arthritis: Identifying reversible and irreversible componentsARTHRITIS & RHEUMATISM, Issue 9 2006Daniel Aletaha Objective Measurement of physical function at one point in time cannot distinguish impairment caused by the active disease process from chronic irreversible impairment. We aimed to dissect these two components of functional limitation in rheumatoid arthritis (RA) by using the disability index of the Health Assessment Questionnaire (HAQ) as the measure of function. Methods We performed a secondary analysis of data from 6 contemporary clinical trials of RA (2,763 patients). Patients in whom remission was achieved in the trials, based on a simplified disease activity index, were identified. In an individual patient, HAQ scores at trial entry represented both reversible and irreversible impairments, while HAQ scores at the time of RA remission represented the mostly irreversible component, and the difference between these corresponded to the component related to disease activity. We tested the concept that the HAQ has a reversible and an irreversible component by associating the HAQ score during remission with 2 measures associated with the degree of accrued damage: duration of RA and radiographic severity. Results Among patients in whom clinical remission was achieved (n = 295), average HAQ scores despite clinical remission increased progressively with the duration of RA, from 0.19 (<2 years of RA) to 0.36 (2,<5 years) to 0.38 (5,<10 years) to 0.55 (,10 years) (P < 0.001). The reversibility of HAQ scores decreased with the duration of RA (median 100%, 83.3%, 81.9%, and 66.7%, respectively; P < 0.001). Findings were similar in patients subgrouped by quartile of radiographic scores. Conclusion Differences in the sources of functional limitations should be considered in the interpretation of functional measures, and in their use for prediction and in cost analyses. [source] The optimal extraction of water along an arbitrarily configured river systemAUSTRALIAN JOURNAL OF AGRICULTURAL & RESOURCE ECONOMICS, Issue 2 2009Alex Coram The fundamental problem for any scheme of water management that tries to maximise welfare across a river system is that of determining the optimal allocation at every point. The problem cannot, in general, be avoided by trading water rights because the price will not account for the effect of extraction at any one point on all other points. This article interprets the problem in terms of the indeterminacy that results from missing information on the value of water at internal junctions between rivers. It is then solved in an optimal control theory framework. [source] Principle of adaptive opticsACTA OPHTHALMOLOGICA, Issue 2009PG SÖDERBERG Purpose To provide an overview of adaptive optics imaging of the retina. Methods In ophthalmoscopical imaging, the two dimensional spatial radiance variation of the back scattered light from the retinal surface is measured. Perfect imaging would require that light backscattered from one point on the retina examined is refocused to one point on the detector. Due to diffraction, light scattering and aberrations, some of the light, injected into the eye examined and some of the light back scatted from the retina examined, are deviated. This leads to loss of contrast. Aberrations induced are, for each individual, specific to the optics of the eye examined. In AOSLO, in addition to confocal illumination and light detection, aberrations induced by the optics of the eye examined are individually measured by wave front sensing and corrected for. Results In the AOSLO, a wave front sensor is introduced between the light source and the eye examined. The information from the wave front sensor is fed back to a deformable mirror, also placed in between the light source and the eye examined. The deformable mirror corrects the wave front aberrations induced by the optics of the eye examined. This allows the injected light to form a point on the retinal surface and simultaneously, the backscattered light from the retina of the eye examined to be focused to a point on a detector. An x-y scanner in front of the eye allows sequential illumination and capturing of aberration minimized back scattered light from an x-y matrix of the retinal surface of the eye examined. The relative radiances measured in the x-y matrix represent the image. Conclusion Adaptive optics in ophthalmoscopy improves contrast in the image of the retina examined by correcting for aberrations induced by the optics of the eye examined. [source] Growth hormone, acromegaly, and heart failure: an intricate triangulationCLINICAL ENDOCRINOLOGY, Issue 6 2003Luigi Saccà Summary Short-term GH or IGF-I excess provides a model of physiological cardiac growth associated with functional advantage. The physiological nature of cardiac growth is accounted for by the following: (i) the increment in cardiomyocyte size occurs prevalently at expense of the short axis. This is the basis for the concentric pattern of left ventricular (LV) hypertrophy, with consequent fall in LV wall stress and functional improvement; (ii) cardiomyocyte growth is associated with improved contractility and relaxation, and a favourable energetic setting; (iii) the capillary density of the myocardial tissue is not affected; (iv) there is a balanced growth of cardiomyocytes and nonmyocyte elements, which accounts for the lack of interstitial fibrosis; (v) myocardial energetics and mechanics are not perturbed; and (vi) the growth response is not associated with the gene re-programming that characterizes pathologic cardiac hypertrophy and heart failure. Overall, the mechanisms activated by GH or IGF-I appear to be entirely different from those of chronic heart failure. Not to be neglected is also the fact that GH, through its nitric oxide (NO)-releasing action, contributes to the maintenance of normal vascular reactivity and peripheral vascular resistance. This particular kind of interaction of GH with the cardiovascular system accounts for: (i) the lack of cardiac impairment in short-term acromegaly; (ii) the beneficial effects of GH and IGF-I in various models of heart failure; (iii) the protective effect of GH and IGF-I against post-infarction ventricular remodelling; (iv) the reversal of endothelial dysfunction in patients with heart failure treated with GH; and (v) the cardiac abnormalities associated with GH deficiency and their correction after GH therapy. If it is clear that GH and IGF-I exert favourable effects on the heart in the short term, it is equally undeniable that GH excess with time causes pathologic cardiac hypertrophy and, if it is not corrected, eventually leads to cardiac failure. Why then, at one point in time in the natural history of acromegaly, does physiological cardiac growth become maladaptive and translate into heart failure? Before this transition takes places, the acromegalic heart shares very few features with other models of chronic heart failure. None of the mechanisms involved in the progression of heart failure is clearly operative in acromegaly, save for the presence of insulin-resistance and mild alterations of lipoproteins and clot factors. Is this enough to account for the development of heart failure? Probably not. On the other hand, it must be stressed that GH and IGF-I activate several mechanisms that play a protective role against the development of heart failure. These include ventricular unloading, deactivation of neurohormonal components, antiapoptotic effect and enhanced vascular reactivity. Ultimately, all data available concur to hypothesize that acromegalic cardiomyopathy represents a progressive model of cardiac hypertrophy in which the cardiotoxic and pro-remodelling effect is intrinsic to the excessive and unrestrained myocardial growth. [source] | ||||||||||||||||