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Biomedical subjects

M Claessens

Publications and source records attributed to M Claessens.

15 recordsLinked to original sources
PubMed2000

Physiological or pseudophysiological ECG changes in endurance-trained athletes.

"Sudden cardiac death" in seemingly healthy, active, and asymptomatic people has always been a tragic fact and is now occurring more frequently. Thus, the preventive detection of "subjects at risk" becomes a priority. A traditional resting electrocardiogram can sometimes give useful indications. Fifty-two competitive triathletes were compared with 22 control persons with similar anthropometric parameters. All subjects underwent the same noninvasive cardiac exploration with electrocardiography, bidimensional echo-Doppler examination, and maximal spiroergometric exercise tests, on a stationary bicycle as well as on a treadmill. In the triathletes we noted manifest signs of eccentric as well as concentric left ventricular hypertrophy with arguments for a supernormal diastolic left ventricular function, with important hemodynamic adjustments and with consequences on the resting electrocardiogram. We described "ten commandments" in evaluating the resting electrocardiogram of healthy competitive athletes. We suspect that the occurrence of ventricular premature beats at peak load of a maximal exercise could be the first expression of a pathological cardiac adaptation to sports activities. The resting electrocardiogram can show interesting details in detecting the "subjects at risk" for problems such as possible lethal arrhythmias and "sudden cardiac death." The analysis of the four subgroups of triathletes compels us to feel dubious about the "athletic heart syndrome" as a physiological entity. In several cases the "athletic heart" is possibly a transitional situation to a pathological hypertrophic and dilated cardiomyopathy.

Adult↗
PubMed2000

Living and dying with chronic obstructive pulmonary disease.

OBJECTIVE: To characterize chronic obstructive pulmonary disease (COPD) over patients' last 6 months of life. STUDY DESIGN: A retrospective analysis of a prospective cohort from the Study to Understand Prognoses and Preferences for Outcomes and Risks of Treatments (SUPPORT). SETTING: Hospitalization for exacerbation of COPD at five US teaching hospitals. PARTICIPANTS: COPD patients who died within 1 year (n = 416) among 1016 enrolled. METHODS: Interview and medical record data were organized into time windows beginning with death and ending 6 months earlier. OUTCOME MEASURES: Days in hospital, prognosis, illness severity, function, symptoms, patients' preferences, and impacts on families. RESULTS: One-year survival was 59%, 39% had > or = 3 comorbidities, and 15 to 25% of the patients' last 6 months were in hospitals. Exacerbation etiologies included respiratory infection (47%) and cardiac problems (30%). Better quality of life predicted longer survival (ARR: 0.36; 95% CI, 0.19-0.87) as did heart failure etiology of exacerbation (ARR: 0.57; CI, 0.40, 0.82). Estimates of survival by physicians and by prognostic model were well calibrated, although patients with the worst prognoses survived longer than predicted. Patients' estimates of prognosis were poorly calibrated. One-quarter of patients had serious pain throughout, and two-thirds had serious dyspnea. Patients' illnesses had a major impact on more than 25% of families. Patients' preferences for Do-Not-Resuscitate orders increased from 40% at 3 to 6 months before death to 77% within 1 month of death; their decisions not to use mechanical ventilation increased from 12 to 31%, and their preferences for resuscitation decreased from 52 to 23%. CONCLUSIONS: Patients with advanced COPD often die within 1 year and have substantial comorbidities and symptoms. Adequate description anchors improved care.

Aged↗
PubMed2000

Changes in mortality of acute myocardial infarction as a function of a changing treatment during the last two decades.

Forty years ago, after the establishment of coronary care units, a significant decrease in mortality of acute myocardial infarction was noted. Twenty years ago, the break-through of thrombolysis realized once again a significant decrease in mortality. In this study we compare, in a rather small community hospital, the mortality and safety of thrombolytic therapy in acute myocardial infarction with a more conventional, conservative medical therapy. We examined all cases of acute myocardial infarction between 1978 up to 1998 inclusive, concerning treatment and mortality rate after a six month period. To be included in the study, acute myocardial infarction had to fulfill particular inclusion criteria. A total of 1863 cases of acute myocardial infarction were included. The mortality rate of patients with acute myocardial infarction treated with thrombolytic agents was strikingly lower and statistically very significantly different (p < 0.001) in comparison with the mortality rate of patients treated with heparin or coumarine derivatives. The mortality rate dropped from 10.57% in the coumarine group and from 14.95% in the heparin group to 5.41% in the alteplase group, to 4.95% in the anistreplase group and 4.00% in the streptokinase subgroup. The complications directly connected to the treatment did not seem to be different between the five groups, and they were also not more frequent by using thrombolytic agents. In the last 20 years, better preventive measures (life habits, diet, medication) and trials to better control the risk factors have not influenced greatly the average amount of cholesterol in patients with an acute myocardial infarction. Also the percentage of patients with high blood pressure has hardly decreased over the last 20 years. The mortality associated with acute myocardial infarction has decreased significantly with the use of thrombolytics. In most cases, thrombolytics are administered routinely and safely. In this way, they are the first choice therapy for myocardial infarction in smaller hospitals. To obtain excellent coronary patency, thrombolytic agents with a long half-life and with PAI-1 resistance are required in the future. The current measures and medical therapies seem to be insufficient to control the risk factors for coronary atherosclerosis.

Cholesterol↗
PubMed2000

Echocardiographic and physiological performance characteristics of triathletes.

BACKGROUND: Endurance sports require a variety of physiological adaptations. OBJECTIVE: To examine the structural and functional heart adaptations and their hemodynamic implications in triathletes. PATIENTS AND METHODS: A group of 52 male triathletes was compared with a control group of 22 healthy male nonathletes. All of the subjects were given a bidimensional cardiac Doppler echocardiography examination and administered maximal exercise tests with lactic acid determinations, on a bicycle ergometer and a treadmill. RESULTS: The triathletes showed clear structural and functional heart adaptations with concentric and eccentric hypertrophy with evidence of a supernormal diastolic left ventricular function. The performance capacity of the triathlete differed significantly from that of the control subject. The maximal oxygen consumption and the maximal oxygen consumption per kilogram on the bicycle and on the treadmill were significantly higher in the triathletes. The same results and conclusions were obtained concerning aerobic capacities and power outputs on a bicycle ergometer at blood lactate concentrations of 2, 3 and 4 mmol/L. The heart rate 6 min after the start of exercise is a significant parameter for the evaluation of the physical condition of a subject. The lactic acid determinations during the recovery phase enabled important conclusions to be drawn about the physical condition of the subjects. CONCLUSIONS: The triathletes showed evidence of important structural and functional heart adaptations with hemodynamic implications. The maximal performing capacities, on the bicycle as well as on the treadmill, were distinctly higher in the triathlete group. Furthermore, the aerobic and anaerobic capacities were significantly different between the groups. In this context, the heart rate 6 min after the start of exercise and the blood lactate concentrations 20 min after the maximal exercise test were significant parameters. It was not always the best triathletes who had the most significant structural cardiac adaptations. Thus, the 'athletic heart' syndrome as a physiological entity is questioned.

Adaptation, Physiological↗
PubMed1999

Ventricular premature beats in triathletes: still a physiological phenomenon?

UNLABELLED: Sudden death is a tragic fact, unexpectedly arising in all age groups. Ventricular arrhythmias are the main cause. At the end of a maximal exercise test more ventricular premature beats were noted in a group of well trained triathletes compared with a similar control group. The etiology is multifactorial. When these ventricular premature beats are associated with specific structural and functional heart adaptations, echocardiographically and electrocardiographically well-documented, then those 'banal' ventricular premature beats cannot longer be considered as a physiological phenomenon. In these circumstances the involved subject is a candidate for dangerous arrhythmias and 'sudden cardiac death'. PURPOSE: The principal cause of 'Sudden cardiac death' is ventricular arrhythmias. We explore the incidence of ventricular premature beats (VPB) in triathletes, who engage in enforced endurance sports. METHODS: Fifty-two triathletes were compared with twenty-two control subjects with comparable anthropometric parameters in function of structural and functional cardiac adaptations. Maximal exercise tests were conducted on a stationary bicycle and a treadmill. During the last two minutes of each test, the VPB were registered. RESULTS: Statistically significant differences emerged in the cardiac structure and function between the triathletes and the controls. There were signs of cardiac hypertrophy and arguments for a supernormally diastolic left ventricular function in the triathletes. The performance capacity was also significantly higher in the triathletes. The maximal heart rate was significantly higher in the control group. The number of VPB was significantly higher in the triathletes. The increased risk of VPB in the triathlon group is caused by several factors: the degree of cardiac hypertrophy, the increased diastolic reserve, the duration of the exercise, the existence of an aortic insufficiency jet and some specific electrocardiographic findings. CONCLUSIONS: The triathlete has an increased risk of VPB during maximal efforts. We doubt the traditionally accepted view of the physiological nature of those VPB and suspect that the limit of physiological cardiac adaptations to sport efforts is exceeded with the appearance of VPB. The triathlete with VPB and with specific electrocardiographic and echocardiographic findings is a candidate for 'sudden cardiac death'.

Adult↗
PubMed1999

Structural heart adaptations in triathletes.

OBJECTIVE: To perform a triathlon in aerobic conditions, a variety of cardiovascular, haemodynamic and metabolic adaptations are required. The heart is the central concern and also the most important limiting factor. In this study we investigate the structural and functional heart adaptations of a group of triathletes. METHODS AND RESULTS: A group of 52 male triathletes was divided into 4 subgroups in function of their athletic results and compared with a control group of 22 healthy, very active but no athletic men. The groups had comparable anthropometric and general physical characteristics. Very significant differences in cardiac structure and cardiac function were observed between the groups. In the triathletes, we registered distinct signs of significantly mixed eccentric and concentric hypertrophy. Unlike the findings in a pathological left ventricular hypertrophy, the diastolic left ventricular function in triathletes was completely normal and even better than in the control group. The late passive diastolic filling period of the triathlete, in particular, seemed to have specific characteristics. The comparison between the subgroups of triathletes shows us that genetic factors probably play an important role in the cardiac adaptations in triathletes. CONCLUSIONS: In our opinion the "athletic heart" in triathletes is not a specific "physiological entity" but is a transitional phase to a dilated hypertrophic cardiomyopathy. Our study yields some arguments for the following proposition: "People are born as elite athletes, with specific characteristics of the left ventricle and with a specifically supernormal diastolic left ventricular function."

Adaptation, Physiological↗
PubMed1992

Recurrent alpha beta loop structures in TIM barrel motifs show a distinct pattern of conserved structural features.

A systematic survey of seven parallel alpha/beta barrel protein domains, based on exhaustive structural comparisons, reveals that a sizable proportion of the alpha beta loops in these proteins--20 out of a total of 49--belong to either one of two loop types previously described by Thornton and co-workers. Six loops are of the alpha beta 1 type, with one residue between the alpha-helix and beta-strand, and 13 are of the alpha beta 3 type, with three residues between the helix and the strand. Protein fragments embedding the identified loops, and termed alpha beta connections since they contain parts of the flanking helix and strand, have been analyzed in detail revealing that each type of connection has a distinct set of conserved structural features. The orientation of the beta-strand relative to the helix and loop portions is different owing to a very localized difference in backbone conformation. In alpha beta 1 connections, the chain enters the beta-strand via a residue adopting an extended conformation, while in alpha beta 3 it does so via a residue in a near alpha-helical conformation. Other conserved structural features include distinct patterns of side chain orientation relative to the beta-sheet surface and of main chain H-bonds in the loop and the beta-strand moieties. Significant differences also occur in packing interactions of conserved hydrophobic residues situated in the last turn of the helix. Yet the alpha-helix surface of both types of connections adopts similar orientations relative to the barrel sheet surface. Our results suggest furthermore that conserved hydrophobic residues along the sequence of the connections, may be correlated more with specific patterns of interactions made with neighboring helices and sheet strands than with helix/strand packing within the connection itself. A number of intriguing observations are also made on the distribution of the identified alpha beta 1 and alpha beta 3 loops within the alpha/beta-barrel motifs. They often occur adjacent to each other; alpha beta 3 loops invariably involve even numbered beta-strands, while alpha beta 1 loops involve preferentially odd beta-strands; all the analyzed proteins contain at least one alpha beta 3 loop in the first half of the eightfold alpha/beta barrel. Possible origins of all these observations, and their relevance to the stability and folding of parallel alpha/beta barrel motifs are discussed.

Alcohol Oxidoreductases↗
PubMed1992

The treatment of reflex sympathetic dystrophy syndrome: current concepts.

Reflex sympathetic dystrophy syndrome is the currently accepted term for a disorder that has previously appeared in the literature under a confusing array of designations: causalgia, Sudeck's atrophy, algoneurodystrophy, shoulder-hand syndrome, etc. The disorder, which was first described in 1864, is characterized by pain, swelling, limited range of motion with associated signs of vasomotor instability, trophic skin changes and patchy bone demineralization. It appears as an exaggerated response of an extremity to injury: trauma, infection, phlebitis or numerous other lesions. In 35 per cent of the RSDS patients, no precipitating event can be identified. The rational treatment of these patients should be based on a thorough understanding of its pathogenesis. While the optimal management is still controversial, there is a consensus that the best results will be achieved if treatment is started early and adapted to the clinical stage of the disease. The role of physical therapy is still debatable. Sympathetic interruption, corticosteroids, calcitonin, beta-blocking agents and more recently bi-phosphonates have been advocated. Proper management may result in the prevention of crippling sequelae.

Analgesics↗
PubMed1990

Basic design features of the parallel alpha beta barrel, a ubiquitous protein-folding motif.

Basic design features of the beta-sheet portion in parallel alpha beta barrels in known protein structures are analysed in the context of a model of a regular hyperboloid. A formal description of the relationships between beta-sheet twist, number of strands in the sheet and barrel dimensions is derived, and the underlying physical principles are rationalized. Results suggest that the major constraints on the geometry of the beta-sheet portion of the barrel come from the requirements to have optimal H-bonding interactions between beta-strands and to closely pack amino acid side-chains in the barrel interior so as to exclude bulk water. In addition, we show how the hyperboloid model and the ensuing formalism can serve to derive useful geometric and graphic tools for computer-aided protein design de novo. We then illustrate how these tools are used to determine that the requirement to have a closed regular eight-stranded beta-sheet surface imposes no particular constraints on the geometry (phi, psi angles) of the polypeptide backbone. Understanding the role of the amino acid sequence in determining the observed structures remains a major challenge. Detailed comparisons of known alpha beta-barrel structures (and amino acid sequence) with each other, and with polypeptide fragments from other protein crystal structures, reveal only a limited number of common sequence-structure motifs. These belong to characteristic alpha beta 1 and alpha beta 3 loop families previously described in alpha beta proteins, and occur at least once in nearly all the alpha beta-barrel structures examined.

Amino Acid Sequence↗
PubMed1989

Modelling the polypeptide backbone with 'spare parts' from known protein structures.

An automatic procedure for building a protein polyalanine backbone from C alpha positions and 'spare parts' retrieved from a data base of 66 high-resolution protein structures is described. Protein backbones are constructed from overlapping fragments of variable length, which allows the backbone of regular secondary structure elements to be built in one block. The procedure is shown to yield backbones which compare very favourably with those from highly refined X-ray structures (r.m.s. deviation between generated and crystal structures less than 1A). The method is furthermore quite insensitive to experimental errors in C alpha positions as well as to the size of the data base, and is seen to yield valuable insight into the relationships between sequence and 3-D structure: one example on triose phosphate isomerase, a beta-barrel protein, shows that beta alpha loops can be considered as structurally more uncommon than alpha beta loops. The 'spare parts' approach is also found to be useful for general-purpose modelling of local structural changes produced by insertion or deletion of residues. It should, however, be used with caution. Crude selection criteria based solely on fragment length and geometric fit to the loop base regions yield realistic backbones in about two-thirds of the test cases (r.m.s. deviations from refined crystal structure approximately 1A). In the remaining cases, sequence information, in particular the presence of glycine residues which tend to adopt more unusual backbone conformations, must be considered to obtain comparable results.

Carboxypeptidases↗
PubMed1988

Structural analysis of the 2.8 A model of Xylose isomerase from Actinoplanes missouriensis.

The structure of Xylose isomerase (X.I.) from Actinoplanes missouriensis has been solved to 2.8 Angstroms resolution. Phases were determined from a single Eu3+ derivative and from the noncrystallographic 222 symmetry of the tetrameric molecule. An atomic model was built and subjected to restrained crystallographic refinement. The resulting model is shown to be closely similar to the recently reported X.I.'s structures from three other bacterial sources. Each monomer is found to be composed of an eight-stranded alpha/beta "T.I.M." barrel forming an N-terminal domain of 328 residues followed by a large loop of 66 residues embracing an adjacent subunit. Analysis of intersubunit packing shows that the X.I. tetramer is an assembly of two tight dimers. The beta barrel fits a simple hyperboloid model as other T.I.M. barrels do. The active site, identified as the binding site for the inhibitor xylitol, is located at the carboxyl end of the beta strands in the barrel next to a pair of binding sites for Eu3+ ions, which are assumed to be sites for the divalent ions involved in catalysis. Active sites in the tetramer are oriented towards the interface between dimers. It is suggested that subunit interfaces might stabilize the active site region and this might explain the oligomeric nature of other alpha/beta barrel enzymes.

Actinomycetales↗
PubMedDate not supplied

Importance of determining the percentage body fat in endurance-trained athletes.

A triathlete has to complete a hard endurance effort in aerobic circumstances. This requires important cardiovascular, haemodynamic and metabolic adaptations which alter the percentage body fat. This study included 52 triathletes and 22 control persons. The anthropometric data of the two groups were similar. All the subjects underwent the same extensive non-invasive cardiac exploration with two-dimensional cardiac echo-doppler examination. Maximal incremental exercise tests with determination of lactate and the ventilatory threshold were done on bicycle and on treadmill. Three different methods determined the percentage of body fat: 4 and 12 skin fold method, bioelectrical impedance analysis and dual energy X-ray absorptionmetry. The results showed important structural and functional heart changes in the triathletes. These changes caused distinct heamodynamic adaptations so that the maximal performing capacity and the aerobic capacity could be forced up largely. The haemodynamic adaptations were connected with changes in the percentage body fat in triathletes. The determination of the 12 skin fold measurements enabled us to distinguish the triathletes with better competition results from the inferior triathletes. It is concluded that the method of 12 skin fold measurements gives the most reliable results and requires only a limited instrumentarium. Moreover, this examination can be performed correctly and easily in all circumstances.

Adipose Tissue↗