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At least 1,603 records · Page 89Linked to original sources
PubMed1995

Determinants of transmitral inflow pattern 10-14 days after acute myocardial infarction.

AIM: The administration of thrombolytic therapy after an acute myocardial infarction can reduce the size of the infarct and improve left ventricular function. We used pulsed Doppler to assess left ventricular diastolic function after an acute myocardial infarction in patients treated with recombinant tissue plasminogen activator (rTPA). PATIENTS AND METHODS: We studied 104 patients after an acute myocardial infarction, 48 treated with a placebo and 56 with rTPA. They were compared with 36 age-matched controls. The Doppler parameters measured included the early peak in diastolic flow velocity, the peak during atrial contraction, the atrial: early ratio, mean deceleration, deceleration time, and half-filling fraction. Doppler parameters for large and small infarct sizes were compared. RESULTS: The Doppler parameters did not differ between treatment groups. Compared with the normal controls, significant differences were observed in both treatment groups for the early peak (placebo P < 0.05; rTPA P < 0.001), the atrial: early ratio (placebo P < 0.05; rTPA P < 0.01), and the half-filling fraction (P < 0.001 for both). In patients with large infarcts, the atrial peak was depressed (P = 0.008). Multivariate analysis showed that end-diastolic pressure, age, end-systolic volume, and regional wall motion parameters were major predictors of Doppler parameters.

Adult↗
PubMed2005

Prophylactic ephedrine and combined spinal epidural: maternal blood pressure and fetal heart rate patterns.

OBJECTIVE: Labor analgesia with the combined spinal epidural approach has been associated with maternal hypotension and fetal heart rate (FHR) changes. The purpose of this study was to estimate whether prophylactic intramuscular ephedrine before combined spinal epidural prevents these complications. METHODS: In a prospective double blind trial, 100 healthy patients with term singletons received intramuscular ephedrine 25 mg or placebo by random allocation before combined spinal epidural. During the first hour after analgesia, maternal heart rate, blood pressure, and need for treatment of significant hypotension were recorded. Fetal heart rate tracings for 1 hour before and for 1 hour after administration of anesthetic were evaluated. Categorical variables were compared with Fisher exact test. Continuous variables were compared with one way analysis of variance for repeated measures. P < .05 was considered significant. RESULTS: Prophylactic ephedrine reduced the incidence of maternal hypotension after combined spinal epidural (P < .007). In controls, there was a significant increase in the incidence and frequency of late decelerations in the hour following combined spinal epidural compared with the previous hour (P < .005 and P < .01). Compared with controls, there was an increased incidence of fetal tachycardia in patients who received prophylactic ephedrine (P < .006), which was associated with increased FHR reactivity (P < .03). CONCLUSION: Although prophylactic ephedrine prevents maternal hypotension and fetal late decelerations, it is associated with fetal tachycardia. The value of prophylactic ephedrine at combined spinal epidural should be weighed against potential changes in fetal heart rate patterns. LEVEL OF EVIDENCE: I.

Adrenergic Agents↗
PubMed2005

Effect of environmental temperature on shock absorption properties of running shoes.

OBJECTIVE: To determine the effect of temperature changes on the shock attenuation of 4 running shoe shock absorption systems. DESIGN: Prospective. SETTING: Motion analysis laboratory. INTERVENTIONS: The shock attenuation of 4 different running shoes representing common shock absorption systems (Nike Air Triax, Asics Gel Nimbus IV, Adidas a3 cushioning, Adidas Supernova cushion) was measured at ambient temperatures of -20 degrees C, -10 degrees C, 0 degrees C, +10 degrees C, +20 degrees C, +30 degrees C, +40 degrees C, and +50 degrees C. Repeated-measures analysis of variance was used to determine differences between shoes. OUTCOME MEASURES: Shock attenuation as indicated by peak deceleration (g) measured by a mechanical impactor following ASTM Standard F1614-99. RESULTS: Shock attenuation decreased significantly with reduced temperature for each shoe tested. The Adidas a3 shoe exhibited significantly higher peak decelerations (lower shock attenuation) at cold temperatures compared with the other shoes. CONCLUSIONS: Cold ambient temperatures significantly reduce the shock attenuation of commonly used running shoes. These findings have important clinical implications for individuals training in extreme weather environments, particularly those with a history of lower limb overuse injuries.

Athletic Injuries↗
PubMed2005

Left ventricular hypertrophy and preclinical impaired glucose tolerance and diabetes mellitus contribute to abnormal left ventricular diastolic function in hypertensive patients.

BACKGROUND: Impaired left ventricular diastolic function is not uncommon in patients with either diabetes mellitus or hypertension. This study was carried out to assess the contribution of left ventricular hypertrophy, high blood pressure, preclinical impaired glucose tolerance and diabetes mellitus to left ventricular diastolic function in patients attending a hypertension clinic. METHODS: Echocardiography, 24-h ambulatory blood pressure monitoring and oral glucose tolerance tests were carried out in 152 consecutive hypertensive patients who had no evidence of ischaemic heart disease and were not known to be diabetic. From echocardiography, E/A (peak velocity of early/atrial filling waves of the transmitral flow) at rest and at peak standardized isometric exercise using handgrip, left ventricular mass index and deceleration time of the E wave were derived. RESULTS: Patients with impaired glucose tolerance and diabetes mellitus had lower E/A than the euglycaemic subjects both at rest (P=0.0073) and during isometric exercise (P<0.0001). E/A significantly reduced during isometric exercise in patients with impaired glucose tolerance and diabetes but not in euglycaemic patients. Deceleration time was shortened with a worsening degree of glucose intolerance in all the patients (P=0.0005), in those with left ventricular hypertrophy (P=0.0006) and in those without left ventricular hypertrophy (P=0.033). When adjusted for age, gender, race, body mass index, smoking history, ambulatory blood pressure findings, cholesterol and triglyceride levels and antihypertensive medications taken, E/A at isometric exercise was related to results of glucose tolerance tests and was inversely proportional to left ventricular mass index (P<0.0001). No significant differences were found whether patients were taking antihypertensive medications or not. CONCLUSION: In hypertensive patients, left ventricular diastolic function is determined by left ventricular mass index and the status of preclinical glucose intolerance, independent of age, gender, race, body mass index, blood pressure level, nocturnal drop in blood pressure or lipid level. These findings were not prejudiced by antihypertensive medications.

Adult↗
PubMed1997

Optimal killing for obligate killers: the evolution of life histories and virulence of semelparous parasites.

Many viral, bacterial and protozoan parasites of invertebrates first propagate inside their host without releasing any transmission stages and then kill their host to release all transmission stages at once. Life history and the evolution of virulence of these obligately killing parasites are modelled, assuming that within-host growth is density dependent. We find that the parasite should kill the host when its per capita growth rate falls to the level of the host mortality rate. The parasite should kill its host later when the carrying capacity, K, is higher, but should kill it earlier when the parasite-independent host mortality increases or when the parasite has a higher birth rate. When K(t), for parasite growth, is not constant over the duration of an infection, but increases with time, the parasite should kill the host around the stage when the growth rate of the carrying capacity decelerates strongly. In case that K(t) relates to host body size, this deceleration in growth is around host maturation.

Animals↗
PubMed2003

Wake field in dielectric acceleration structures.

In this study we present a general approach for the analysis of the wake field of a point charge moving in a vacuum tunnel bored in dielectric material that is uniform in the direction parallel to the motion of the bunch. In the transverse direction the structure surrounding the dielectric may have arbitrary geometry. A quasianalytic expression that relates the decelerating force with the first dielectric layer, the radius of the vacuum tunnel where the charge moves, and the reflection characteristics of the structure has been developed. Simulation results for a simple structure indicate that, if the effective location where the reflection occurs in the dielectric is sufficiently apart from the edge of the vacuum tunnel, it has no effect on the point charge. In fact, the decelerating field converges exponentially as this distance increases, to the asymptotic value determined by the first dielectric layer. An estimate of the trailing wake when the structure supports a specific mode is also provided.

Journal Article↗
PubMed2004

Electron acceleration by a self-diverging intense laser pulse.

Electron acceleration by a laser pulse having a Gaussian radial and temporal profile of intensity has been studied. The interaction region is vacuum followed by a gas. The starting point of the gas region has been chosen around the point at which the peak of the pulse interacts with the electron. The tunnel ionization of the gas causes a defocusing of the laser pulse and the electron experiences the action of a ponderomotive deceleration at the trailing part of the pulse with a lower intensity rather than an acceleration at the rising part of the laser pulse with a high intensity, and thus gains net energy. The initial density of the neutral gas atoms should be high enough to properly defocus the pulse; otherwise the electron experiences some deceleration during the trailing part of the pulse and the net energy gain is reduced. The rate of tunnel ionization increases with the increase in the laser intensity and the initial density of neutral gas atoms, and with the decreases in the laser spot size, which causes more defocusing of the laser pulse. The required initial density of neutral gas atoms decreases with the increase in the laser intensity and also with the decrease in the laser spot size.

Journal Article↗
PubMed2003

Asymmetric self-phase modulation and compression of short laser pulses in plasma channels.

A relativistically intense femtosecond laser pulse propagating in a plasma channel undergoes dramatic photon deceleration while propagating a distance on the order of a dephasing length. The deceleration of photons is localized to the back of the pulse and is accompanied by compression and explosive growth of the ponderomotive potential. Fully explicit particle-in-cell simulations are applied to the problem and are compared with ponderomotive guiding center simulations. A numerical Wigner transform is used to examine local frequency shifts within the pulse and to suggest an experimental diagnostic of plasma waves inside a capillary.

Journal Article↗
PubMed2003

Direct measurement of transition frequencies in isolated pHe+ atoms, and new CPT-violation limits on the antiproton charge and mass.

A radio frequency quadrupole decelerator and achromatic momentum analyzer were used to decelerate antiprotons and produce p4He+ and p3He+ atoms in ultra-low-density targets, where collision-induced shifts of the atomic transition frequencies were negligible. The frequencies at near-vacuo conditions were measured by laser spectroscopy to fractional precisions of (6-19) x 10(-8). By comparing these with QED calculations and the antiproton cyclotron frequency, we set a new limit of 1 x 10(-8) on possible differences between the antiproton and proton charges and masses.

Journal Article↗
PubMed2006

Scalar-field-dominated cosmology with a transient acceleration phase.

A new cosmological scenario driven by a slow rolling homogeneous scalar field whose exponential potential V(Phi) has a quadratic dependence on the field Phi in addition to the standard linear term is discussed. The derived equation of state for the field predicts a transient accelerating phase, in which the Universe was decelerated in the past, began to accelerate at redshift z approximately 1, is currently accelerated, but, finally, will return to a decelerating phase in the future. This overall dynamic behavior is profoundly different from the standard evolution of the cold dark matter model with a cosmological constant, and may alleviate some conflicts in reconciling the idea of a dark-energy-dominated universe with observables in String or M theory. Some theoretical predictions for the present scalar field plus dark matter dominated stage are confronted with cosmological observations in order to test the viability of the scenario.

Journal Article↗
PubMed1987

Rapid phytochrome regulation of wheat seedling extension: light pretreatment extends coupling time, increases response lag, and decreases light sensitivity.

Rapid effects of light on wheat seedling extension growth were monitored by sensitive transducer techniques. Seedlings grown in complete darkness responded to light by a marked deceleration of extension growth after a mean latent period of 10.4 minutes. Pulses (5 minutes) of red (660 nanometers), green (530 nanometers), and far-red (730 nanometers) light caused marked extension rate depression, and the red effect could not be reversed by 730 nanometers far-red. Pulses of 1 second red (72 micromoles per square meter) were effective, and were reversible by immediate long wavelength (759 nanometers) far-red. Seedlings pretreated with 2 minute broadband green light (0.6 micromole per square meter), 28 hours prior to the experimental light treatments, displayed similar extension rate decelerations in response to red light, but after a longer mean lag of 23.75 minutes. No response was observed with red light treatments of less than 1 minute, and the effects of 5 minutes of red light were fully reversible by 5 minutes of 730 nanometers far-red. Fluence-response curves showed that nonpretreated seedlings were approximately 100 times more sensitive to far-red-absorbing form of phytochrome than were those given prior light treatment. Although the fluence-response relationship for nonpretreated seedlings matched the photoconversion kinetics of phytochrome reasonably well, that for the pretreated seedlings indicated a requirement for repeated photoconversions for maximum action. The results are discussed in relation to the possibility that phytochrome may regulate the availability, or the activity, of a component of its own transduction chain.

Journal Article↗
PubMed2006

Toward quantitative fetal heart rate monitoring.

Continuous electronic fetal heart rate (FHR) monitoring during labor is motivated by the clinical experience that fetal distress causes loss of FHR variation and the occurrence of decelerations late during uterine contraction. This practice is of uncertain clinical benefit, perhaps because the interpretation is qualitative. We have developed new quantitative measures and analyzed cardiotocograph records from 148 consecutive patients, 44 of whom had at least one "nonreassuring" epoch. In multivariate regression models, measures of deceleration and variability were significantly associated with the obstetrician's diagnosis (receiver operating characteristic area 0.84, p < 0.05). This approach may be useful clinically.

Algorithms↗
PubMed2003

Preattentive processing of alcohol stimuli.

An experiment was conducted to test the automatic analysis of briefly presented alcohol stimuli in alcohol-dependent individuals. Alcoholics and controls were exposed to four different conditions: two brief (30 ms) and two long (130 ms) exposure conditions, each containing alcoholic and non-alcoholic pictures. Heart rate (HR) interbeat intervals were recorded and phasic cardiac responses assessed. Alcoholics had a stronger initial HR deceleration after exposure to masked alcohol slides compared with masked control slides, indicating a preattentive analysis of alcohol stimuli. This initial HR deceleration in the masked condition suggests an automatic attentional focusing to degraded alcohol cues. No such attentional effect was found when the pictures were presented unmasked and were clearly perceived. The implication of these results for the understanding of relapse in addictive behavior is discussed.

Alcohol Drinking↗
PubMed2005

Maternal position during non-stress test and fetal heart rate patterns.

OBJECTIVE: The aim of the study was to determinate whether maternal position during the non-stress test (NST) in different weeks of pregnancy influences fetal heart rate patterns. MATERIALS AND METHODS: A total of 1055 NST lasting 30 min were performed in 368 autochthonous mothers with low-risk pregnancies. On the basis of maternal position during the test we divided into three groups: reclining, sitting, and walking. The cardiotocographic parameters considered were: number of minutes of reactive NST with minimum length, number of fetal movements, fetal heart rate baseline, number of large accelerations, number of dubious NST, and number of variable decelerations. RESULTS: Fetal heart rate patterns in low-risk pregnancies were studied using NST in different gestational ages and in different maternal positions. Differences in heart rate were found in relationship to both gestational age and maternal position. The minimum length of NST necessary to record at least three large accelerations was significantly different in relationship to both gestational age and maternal position. The number of fetal movements perceived by the mother was greater in the reclining position than in sitting or walking. Together with the progression of pregnancy, the number of dubious NST decreased in all subgroups, especially in the sitting position. The greatest number of variable decelerations was observed in the reclining position and it was increased with pregnancy progression. The NST duration did not vary greatly in the reclining position, but in the sitting position or during walking, the time taken to record the three large accelerations required to define the trace as reactive, decreased significantly with the progression of pregnancy CONCLUSIONS: Non-stress test in sitting position or during walking should be encouraged because fetal reactivity is more quickly observed.

Adult↗
PubMed2003

The adaptive dynamics of altruism in spatially heterogeneous populations.

We study the spatial adaptive dynamics of a continuous trait that measures individual investment in altruism. Our study is based on an ecological model of a spatially heterogeneous population from which we derive an appropriate measure of fitness. The analysis of this fitness measure uncovers three different selective processes controlling the evolution of altruism: the direct physiological cost, the indirect genetic benefits of cooperative interactions, and the indirect genetic costs of competition for space. In our model, habitat structure and a continuous life cycle makes the cost of competing for space with relatives negligible. Our study yields a classification of adaptive patterns of altruism according to the shape of the costs of altruism (with decelerating, linear, or accelerating dependence on the investment in altruism). The invasion of altruism occurs readily in species with accelerating costs, but large mutations are critical for altruism to evolve in selfish species with decelerating costs. Strict selfishness is maintained by natural selection only under very restricted conditions. In species with rapidly accelerating costs, adaptation leads to an evolutionarily stable rate of investment in altruism that decreases smoothly with the level of mobility. A rather different adaptive pattern emerges in species with slowly accelerating costs: high altruism evolves at low mobility, whereas a quasi-selfish state is promoted in more mobile species. The high adaptive level of altruism can be predicted solely from habitat connectedness and physiological parameters that characterize the pattern of cost. We also show that environmental changes that cause increased mobility in those highly altruistic species can beget selection-driven self-extinction, which may contribute to the rarity of social species.

Adaptation, Physiological↗
PubMedDate not supplied

Left ventricular diastolic function in the elderly.

Previous studies using pulsed Doppler echocardiography have demonstrated a pattern of abnormal left ventricular relaxation associated with increasing age. Specifically, aging is associated with decreased peak velocity of early diastolic mitral inflow, increased peak velocity of late diastolic inflow, increased isovolumic relaxation time, and early diastolic deceleration time. Abnormal relaxation can progress to significantly elevated left atrial pressure--characterized by increased early peak velocity and shortened isovolumic relaxation time and deceleration time--as part of the disease processes. Left ventricular diastolic dysfunction is highly prevalent, occurring in one half to two thirds of elderly patients with congestive heart failure, in association with normal systolic function. Left ventricular hypertrophy, which is commonly related to systemic arterial hypertension, and ischemic heart disease are the two major causes of abnormal left ventricular diastolic function in the elderly. Recently, newer echocardiographic techniques have been described that allow more accurate evaluation of left ventricular diastolic function. Treatments for left ventricular diastolic dysfunction should focus on the underlying disease etiology as well as on the derangement in left ventricular diastolic function. Although calcium channel blockers and angiotensin-converting enzyme inhibitors have been used clinically to treat diastolic dysfunction, their effects on prognosis remain unproven.

Aged↗
PubMed1982

The effect of puberty and short-term oral administration of testosterone undecanoate on GH tests and sex-steroid related plasma compounds in GH deficient patients.

In twelve boys and two girls, with idiopathic (partial) growth hormone deficiency diagnosed at prepubertal age, we studied the effect of spontaneous puberty (six patients) as well as the effect of sex-steroid priming (eight patients). Six boys received testosterone undecanoate and two girls ethinyloestradiol for 5 days. Two pubertal patients showed a normal GH response, the patients primed with testosterone or oestrogen did not, despite a distinct effect on sex-steroid related plasma compounds. Reevaluation of GH status appears to be worthwhile in GH deficient patients presenting with short stature, growth deceleration at an early pubertal age and delayed sexual maturation. Sex-steroid priming is unlikely to alter the outcome of GH testing, whenever marked growth deceleration is evident at prepubertal age.

Adolescent↗
PubMed2005

Left ventricular and cardiac autonomic function in survivors of testicular cancer.

BACKGROUND: Following cisplatin-based chemotherapy, survivors of testicular cancer have a high prevalence of cardiovascular risk factors and an increased risk of cardiovascular disease. Cardiac function has not been extensively studied and no comparisons have been made with men from the general population. DESIGN: Left ventricular and cardiac autonomic function were evaluated in chemotherapy-treated testicular cancer patients, in stage I patients after orchidectomy only, and in healthy men using Doppler echocardiography [wall motion score index, peak early (E) and atrial filling (A) velocities across the mitral valve, E/A-ratio, isovolumetric relaxation time, and deceleration time of the early peak flow] and measurements of N-terminal pro-brain natriuretic peptide and baroreflex sensitivity. Furthermore, 24-h ambulatory blood pressure was measured. RESULTS: Ninety chemotherapy-treated patients (median age 37 years, range 20-65; median follow up of 7 years, range 3-13) were compared with 44 stage I patients (median age 36 years, range 24-63) and 47 healthy controls (median age 37 years, range 22-55). Wall motion score index was less than 1.5 in all participants. Chemotherapy-treated patients had a higher peak A-wave and a lower E/A-ratio than stage I patients and controls. Isovolumetric relaxation and deceleration times did not differ between groups. Age, 24-h diastolic blood pressure and treatment with chemotherapy were significantly associated with E/A-ratio. Natriuretic peptide levels were normal. Baroreflex sensitivity was similar in the three groups. CONCLUSIONS: Chemotherapy-treated testicular cancer survivors have a lower E/A-ratio than healthy subjects from the general population, which may indicate impaired relaxation of the left ventricle and reflect the high prevalence of cardiovascular risk factors previously reported in these men.

Adult↗