Nested Bloch waves in elastic structures with configurational forces.

Small axial and flexural oscillations are analysed for a periodic and infinite structure, constrained by sliding sleeves and composed of elastic beams. A nested Bloch-Floquet technique is introduced to treat the nonlinear coupling between longitudinal and transverse displacements induced by the configurational forces generated at the sliding sleeve ends. The action of configurational forces is shown to play an important role from two perspectives. First, the band gap structure for purely longitudinal vibration is broken so that axial propagation may occur at frequencies that are forbidden in the absence of a transverse oscillation and, second, a flexural oscillation may induce axial resonance, a situation in which the longitudinal vibrations tend to become unbounded. The presented results disclose the possibility of exploiting configurational forces in the design of mechanical devices towards longitudinal actuation from flexural vibrations of small amplitude at given frequency. This article is part of the theme issue 'Modelling of dynamic phenomena and localization in structured media (part 1)'.

Tacticity in chiral phononic crystals.

The study of vibrational properties in engineered periodic structures relies on the early intuitions of Haüy and Boscovich, who regarded crystals as ensembles of periodically arranged point masses interacting via attractive and repulsive forces. Contrary to electromagnetism, where mechanical properties do not couple to the wave propagation mechanism, in elasticity this paradigm inevitably leads to low stiffness and high-density materials. Recent works transcend the Haüy-Boscovich perception, proposing shaped atoms with finite size, which relaxes the link between their mass and inertia, to achieve unusual dynamic behavior at lower frequencies, leaving the stiffness unaltered. Here, we introduce the concept of tacticity in spin-spin-coupled chiral phononic crystals. This additional layer of architecture has a remarkable effect on their dispersive behavior and allows to successfully realize material variants with equal mass density and stiffness but radically different dynamic properties.

Influence of aging and other cardiovascular risk factors on baroreflex sensitivity.

OBJECTIVES: To examine the influence of known cardiovascular risk factors (cholesterol, blood glucose levels, arterial pressures, heart rate, and aging) on baroreflex sensitivity. DESIGN: An observational epidemiological study. SETTING: Geriatric Division at the Policlinico Umberto Primo, University of Rome La Sapienza. PARTICIPANTS: Two hundred three subjects whose ages ranged from 9 to 94 years, apparently healthy and free of detectable clinical evidence of atherosclerosis. MEASUREMENTS: All subjects underwent determination of baroreflex sensitivity by phenylephrine infusion (BSphe), and by a noninvasive method derived from spectral analysis of R-R interval and arterial pressure variabilities (alpha index). RESULTS: The population, subdivided into tertiles for each variable studied, had lower BSphe values and lower alpha indexes as a function of age, plasma low-density lipoprotein (LDL) cholesterol, and systolic blood pressure. The alpha index was significantly lower in both groups with elevated LDL cholesterol levels than in those with lower levels (II and III vs I tertile, P <.001), whereas BSphe differed significantly only in the two groups who had extreme levels of LDL (I vs III tertile, P <.001). Multiple regression analysis identified a negative association of the alpha index with age (P <.001), heart rate (P <.01), area under the glucose-response curve (P <.001), and LDL cholesterol (P <.01), but of BSphe only with age (P <.001) and heart rate (P <.01). CONCLUSION: These findings indicate that some risk factors for coronary heart disease adversely influence baroreflex sensitivity.

Noninvasive assessment of mitoxantrone cardiotoxicity in relapsing remitting multiple sclerosis.

Multiple sclerosis is the most common cause of neurologic disability in young adults. Recent reports have suggested that Mitoxantrone might be a candidate for clinical trials in multiple sclerosis patients. The authors studied 20 patients with relapsing remitting multiple sclerosis to evaluate cardiac toxicity during a one-year follow-up period. Patients were divided into 2 groups: group A, mitoxantrone treated patients (cumulative dose of 96 mg/m2); group B, placebo patients. The clinical course of multiple sclerosis was assessed using the Expanded Disability Status Scale and the number of relapses during the follow-up. Each patient had an electrocardiogram and a spectral and color flow Doppler echocardiographic examination at enrollment, and 6 and 12 months later, to investigate cardiac toxicity. The mean exacerbation rate was reduced significantly in group A patients. No significant differences in the electrocardiograms or the echocardiographic parameters of systolic and diastolic function were noted between the two groups or in group A during the follow-up. Mitoxantrone treatment seems able to improve the clinical course of relapsing remitting multiple sclerosis patients. It does not show any cardiac toxicity in selected patients at this dosage.

Spectral analysis of heart rate variability in elderly non-dipper hypertensive patients.

To assess by autoregressive model the frequency domain heart rate variability (HRV) during clinostatism and after passive orthostatic load (head-up tilt), 81 hypertensive and normotensive subjects (42 men and 39 women) were subdivided into four groups: 20 adult normotensive subjects (Group 1); 21 elderly normotensive subjects (Group 2); 20 elderly hypertensive subjects with nocturnal blood pressure (BP) falls (Group 3); and 20 elderly hypertensive subjects without nocturnal BP falls (Group 4). They were chosen to assess the influence of aging and arterial hypertension on sympathetic-parasympathetic balance. The age-related decrease observed in nearly all HRV spectral frequency components (normalised units [NUs], high frequency [HF] and low frequency [LF]) was reported in elderly patients in rest conditions. LF indexes resulted in decreases in Group 3 and these data seemed to be emphasised in Group 4. After passive tilt, spectral data were recorded as follows: 25.3+/-1.8 vs 17.8+/-2.2 HF, Group 2 vs Group 1, P<0.001; 72.5+/-0.8 vs 75.6+/-1.8 LF, P< 0.001, Group 2 vs Group 1. Both sympathetic and parasympathetic indexes were lower in Group 3 (44.6+/-1.1 vs 72.5+/-0.8 LF, P< 0.001, Group 3 vs Group 2; 9.9+/-1.8 vs 25.3+/-1.8 HF, P < 0.001, Group 3 vs Group 2) and data became clearer in Group 4 (8.5 2.1 vs 9.9+/-1.8 HF, P< 0.001; 40.4+/-1.5 vs 44.6+/-1.1 LF, Group 4 vs Group 3). The established influence of aging on autonomic nervous system activity appears to be increased by arterial hypertension due to worsening of the sympathetic-parasympathetic response to standardised stimulation. The loss of nocturnal BP declines in arterial hypertension was found to occur in association with a decrease in autonomic nervous system activity.

Effects of cardiac rehabilitation on atrial wave in patients after myocardial infarction.

Cardiac rehabilitation (CR) can improve cardiac hemodynamic performance in patients after myocardial infarction (MI). Little evidence is provided concerning the consequences of CR on atrial wave duration, and less is known about the link between pre-arrhythmogenic patterns and the cardiovascular performance improvement in these subjects. Twenty-six patients, post-MI 0 to 7 days, underwent a complete CR cycle and a signal-averaged electrocardiogram (SAECG) for the evaluation of atrial activation parameters (group 1) to appreciate if physical training can promote parallel improvement in cardiovascular and intra-atrial conduction parameters. A control group of 24 well-matched nonischemic subjects (group 2) was chosen for data comparison. Resting heart rate (p < 0.01) and resting double product (p < 0.01) decreased after CR in groups 1 and 2, while diastolic blood pressure at maximal stress was decreased in group 1 (p < 0.01) with a parallel increase in the time of physical training (p < 0.05). SAECG parameters of atrial activation were unchanged in group 1 after the comparison and only total atrial duration activation (dA) reached statistical significance (113.3 +/- 17.2 msec vs 120.8 +/- 14.2 msec, subjects after CR vs before CR, p < 0.01). CR could improve intra-atrial activation in subjects after MI, but the consequences of hemodynamic adjustment of the trained heart must undergo a more accurate evaluation to verify if CR can prevent adverse arrhythmogenic complications of MI through cardiovascular performance improvement.

Growth and surface characterization of TiNbZr thin films deposited by magnetron sputtering for biomedical applications.

Low modulus of elasticity and the presence of non-toxic elements are important criteria for the development of materials for implant applications. Low modulus Ti alloys can be developed by designing ß-Ti alloys containing non-toxic alloying elements such as Nb and Zr. Actually, most of the metallic implants are produced with stainless steel (SS) because it has adequate bulk properties to be used as biomaterials for orthopedic or dental implants and is less expensive than Ti and its alloys, but it is less biocompatible than them. The coating of this SS implants with Ti alloy thin films may be one alternative to improve the biomaterial properties at a relatively low cost. Sputtering is a physical deposition technique that allows the formation of nanostructured thin films. Nanostructured surfaces are interesting when it comes to the bone/implant interface due to the fact that both the surface and the bone have nanoscale particle sizes and similar mechanical properties. TiNbZr thin films were deposited on both Si(111) and stainless steel (SS) substrates. The TiNbZr/Si(111) film was used as a model system, while the TiNbZr/SS film might improve the biocompatibility and extend the life time of stainless steel implants. The morphology, chemical composition, Young's modulus, and hardness of the films were analyzed by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), and nanoindentation.

Short-term effect of exercise on platelet factor 4 in normal subjects and in patients with coronary artery disease.

BACKGROUND: The aim of this study was to evaluate the plasma concentration of a platelet-derived protein, platelet factor 4 (PF4), before and after exercise in coronary artery disease. METHODS: We enrolled 60 patients with documented ischemic heart disease. The subjects were divided into two groups: Group 1 patients with previous myocardial infarction (n = 20, 13 males, 7 females, mean age 51.6 +/- 7.5 years, range 38-62 years); Group 2 patients with exercise-induced angina (n = 40, 22 males, 18 females, mean age 52.6 +/- 8.0 years, range 38-65 years). Patients with hypertension, hyperlipidemia and diabetes were excluded. Patients with angina or ST segment depression during the stress test were included in a subgroup (n = 33, 21 males, 12 females, mean age 50.3 +/- 6.3 years, range 40-65 years). Twenty healthy subjects without coronary risk factors (13 males, 7 females, mean age 53.2 +/- 7.1 years, range 38-65 years) served as controls. PF4 was measured in all patients at baseline and 5 min after a bicycle exercise test. Plasma PF4 levels were measured performed by radioimmunoassay (ng/ml, normal range 0-10). RESULTS: Patients with ischemic heart disease showed a high basal concentration of PF4 compared with controls. PF4 levels at baseline vs after stress test were 4.1 +/- 2.5 vs 5.3 +/- 2.6 ng/ml in healthy subjects; 33.4 +/- 15.8 vs 56.2 +/- 28.2 ng/ml (p < 0.001) in Group 1; 22.4 +/- 15.8 vs 44.6 +/- 28.4 ng/ml (p < 0.001) in Group 2; 29.9 +/- 15.5 vs 67.7 +/- 26.1 ng/ml in the subgroup with angina or ST segment depression (p < 0.001), and 23.1 +/- 16.5 vs 26.0 +/- 18.1 ng/ml in those without angina or ST segment depression (NS). CONCLUSIONS: These findings support the hypothesis that a significant increase in PF4 levels after exercise is associated with clinically significant coronary artery disease.

Left ventricular function, cardiac dysrhythmias, atrial activation, and volumes in nondipper hypertensive individuals with left ventricular hypertrophy.

BACKGROUND: Arrhythmic patterns and left ventricular geometric adaptations to pressure overload were investigated in 76 patients with untreated borderline-to-moderate sustained essential hypertension studied by 2-dimensional and M-mode echocardiography, 12-lead, Holter, and signal-averaged electrocardiography, and ambulatory blood pressure monitoring. METHODS AND RESULTS: Sixty-two age- and sex-matched normal adults were chosen for data comparison. Hypertrophic hypertensive patients were subdivided into 2 subgroups: 44 patients with nocturnal blood pressure reduction (dippers) and 32 patients without it (nondippers). Common afterload and diastolic function indexes were found to be lower in combined nondipper and dipper groups, but only fractional shortening decreased in nondippers. The number of premature atrial and ventricular contractions per hour was high in dippers and nondippers, with no statistically significant differences between them; atrial and ventricular complex dysrhythmias were similar. Signal-averaged electrocardiography showed a prolonged P-wave duration in dipper and nondipper patients with high atrial volumes but no late ventricular potentials and no difference in quantitative P-wave analysis. Left atrial volumes, P-wave duration, and premature atrial contractions were found to be positively linked to left ventricular hypertrophy. In nondipper patients a linear correlation was observed between left atrial volume and P-wave duration, although supraventricular ectopic activity was connected to left atrial volume enlargement both in dipper and nondipper patients. CONCLUSIONS: These data suggest that the nondipper pattern is not linked to a worse arrhythmogenic substrate; only atrial volume increase may be related to significant supraventricular activity and prolonged atrial activation in nondipper patients, but late ventricular potentials are uncommon in hypertrophic hypertensive patients.