The Noise Transfer Function (NTF) of ΔΣ modulators is typically designed after the features of the input signal. We suggest that in many applications, and notably those involving D/D and D/A ...conversion or actuation, the NTF should instead be shaped after the properties of the output/reconstruction filter. To this aim, we propose a framework for optimal design based on the Kalman-Yakubovich-Popov (KYP) lemma and semi-definite programming. Some examples illustrate how in practical cases the proposed strategy can outperform more standard approaches.
A design flow for ΔΣ modulators is illustrated, allowing quantization noise to be shaped according to an arbitrary weighting profile. Based on finite-impulse-response noise transfer functions, ...possibly with high order, the flow is best suited for digital architectures. This work builds on a recent proposal in which the modulator is matched to the reconstruction filter, showing that this type of optimization can benefit a wide range of applications in which noise (including in-band noise) is known to have a different impact at different frequencies. The designs of a multiband modulator, a modulator avoiding dc noise, and an audio modulator capable of distributing quantization artifacts according to a psychoacoustic model are discussed as examples. A software toolbox is provided as a general design aid and to replicate the proposed results.
The extent to which atrial myocardium is remodeled in patients with persistent lone atrial fibrillation (LAF) is largely unknown.
The purpose of this study was to perform a clinicopathologic ...investigation in patients with persistent LAF.
We characterized structural and molecular remodeling in atrial biopsies from 19 patients (17 males, mean age 49 years) with persistent (>7 days; n = 8) or long-lasting persistent (>1 year; n = 11) LAF who underwent surgical ablation. Atrial tissue from 15 autopsy samples without clinicopathologic evidence of heart disease served as controls.
Morphometric analysis showed cardiomyocyte hypertrophy and greater amounts of myolytic damage and interstitial fibrosis in persistent LAF patients compared to controls (P <.0001). Atrial tissue levels of heme oxygenase-1 and 3-nitrotyrosine were increased in persistent LAF patients (P <.001), consistent with oxidative stress. Levels of superoxide dismutase-2, interleukin-8, interleukin-10, tumor necrosis factor-α, and thiobarbituric acid reactive substance were greater in controls than in persistent LAF patients. Immunoreactive signal for connexin43 was reduced more frequently in persistent LAF patients than controls. There was no correlation between features of structural or molecular remodeling and clinical parameters, including persistent LAF duration.
In persistent LAF patients, the atria are modified by structural remodeling and molecular changes of oxidative stress. Tissue changes in persistent LAF appear to occur early after its onset and are qualitatively no different than those observed in patients with atrial fibrillation related to conventional risk factors. These findings suggest that different types of atrial fibrillation are associated with the same spectrum of tissue lesions. Early intervention to restore sinus rhythm in persistent LAF patients may prevent irreversible tissue change, especially interstitial fibrosis.
Advanced age alone appears to be a risk factor for increased susceptibility to cardiac arrhythmias. We previously observed in the aged rat heart that sinus rhythm ventricular activation is delayed ...and characterized by abnormal epicardial patterns although conduction velocity is normal. While these findings relate to an advanced stage of aging, it is not yet known when and how ventricular electrical impairment originates and which is the underlying substrate. To address these points, we performed continuous telemetry ECG recordings in freely moving rats over a six-month period to monitor ECG waveform changes, heart rate variability and the incidence of cardiac arrhythmias. At the end of the study, we performed in-vivo multiple lead epicardial recordings and histopathology of cardiac tissue. We found that the duration of ECG waves and intervals gradually increased and heart rate variability gradually decreased with age. Moreover, the incidence of cardiac arrhythmias gradually increased, with atrial arrhythmias exceeding ventricular arrhythmias. Epicardial multiple lead recordings confirmed abnormalities in ventricular activation patterns, likely attributable to distal conducting system dysfunctions. Microscopic analysis of aged heart specimens revealed multifocal connective tissue deposition and perinuclear myocytolysis in the atria. Our results demonstrate that aging gradually modifies the terminal part of the specialized cardiac conducting system, creating a substrate for increased arrhythmogenesis. These findings may open new therapeutic options in the management of cardiac arrhythmias in the elderly population.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In humans, chronic stressors have long been linked to cardiac morbidity. Altered serotonergic neurotransmission may represent a crucial pathophysiological mechanism mediating stress-induced cardiac ...disturbances. Here, we evaluated the physiological role of serotonin (5-HT) 1A receptors in the autonomic regulation of cardiac function under acute and chronic stress conditions, using 5-HT(1A) receptor knockout mice (KOs). When exposed to acute stressors, KO mice displayed a higher tachycardic stress response and a larger reduction of vagal modulation of heart rate than wild type counterparts (WTs). During a protocol of chronic psychosocial stress, 6 out of 22 (27%) KOs died from cardiac arrest. Close to death, they displayed a severe bradycardia, a lengthening of cardiac interval (P wave, PQ and QRS) duration, a notched QRS complex and a profound hypothermia. In the same period, the remaining knockouts exhibited higher values of heart rate than WTs during both light and dark phases of the diurnal rhythm. At sacrifice, KO mice showed a larger expression of cardiac muscarinic receptors (M2), whereas they did not differ for gross cardiac anatomy and the amount of myocardial fibrosis compared to WTs. This study demonstrates that chronic genetic loss of 5-HT(1A) receptors is detrimental for cardiovascular health, by intensifying acute, stress-induced heart rate rises and increasing the susceptibility to sudden cardiac death in mice undergoing chronic stress.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The purpose of the present study was to evaluate the extent of the ventricular epicardial fat and its relationship with the underlying myocardium, neither of which is still completely understood.
A ...total of 117 autoptic human hearts was subdivided into four groups: normals (N), ischemics (I), hypertrophics (H) and hypertrophic–ischemics (HI). In each heart, the ventricular myocardial and epicardial fat weights were measured. On the basis of these data, the epicardial fat percentage within the ventricles was calculated.
The left, right and total ventricular fat weights were greater in H and HI than in N and I (
P<.05,
P<.05,
P<.01, respectively). No differences were detected in the epicardial fat weights in comparing H versus HI and N versus I. Moreover, the fat percentage in each ventricle did not vary between the four groups. However, if compared with the right ventricle, the left ventricle showed an epicardial fat percentage consistently lower (
P<.0001). In nonhypertrophied hearts (N and I), the body mass index and the total epicardial fat weight were correlated (
P<.05), whereas in hypertrophied hearts (H and HI), they were not.
A constant fat–muscle ratio exists in each ventricle, which is not influenced by ischemia or hypertrophy. Accordingly, during the hypertrophic process, the ventricular fat and the underlying myocardium show a parallel and correlated increase in their masses.
We show that ΔΣ modulators can be interpreted as heuristic solvers for a particular class of optimization problems. Then, we exploit this theoretical result to propose a novel technique to deal with ...very large unconstrained discrete quadratic programming (UDQP) problems characterized by quadratic forms entailing a circulant matrix. The result is a circuit-based optimization approach involving a recast of the original problem into signal processing specifications, then tackled by the systematic design of an electronic system. This is reminiscent of analog computing, where untreatable differential equations were solved by designing electronic circuits analog to them. The approach can return high quality suboptimal solutions even when many hundreds of variables are considered and proved faster than conventional empirical optimization techniques. Detailed examples taken from two different domains illustrate that the range of manageable problems is large enough to cover practical applications.
Recently, strategies based on semidefinite programming (SDP) have been proposed for the design of the noise transfer function (NTF) of ΔΣ modulators. Contrarily to conventional approaches, these ...strategies can formally deal with diverse NTF optimality criteria. However, in most cases they only deliver finite impulse response (FIR) type NTFs that may require a high order to achieve the desired features and thus are not well suited for analog modulators. With a tutorial take, this paper reviews fundamental constraints and possible merit factors to be considered in the NTF selection, as well as conventional and recent design strategies, profiling the former for critical cases. Then, it shows how preassigned pole arrangements can be plugged into SDP based design methods. With this, a hybrid between conventional strategies (limited in flexibility) and recent ones (limited in requiring high orders) can be obtained, getting the best of both realms. Furthermore, this approach provides new insight on the quality of some choices made in conventional design methods.
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•Unified review of merit factors, constraints for optimizing noise shaping features.•Profiling of different design strategies for the NTF of ΔΣ modulators.•Identification of critical cases for conventional design strategies.•New hybrid strategy combining conventional pole placement and fully optimized zeros.•New design method also used to evaluate conventional designs in non-critical cases.
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