Multi-response deconvolution of auditory evoked potentials in a reduced representation space.

The estimation of auditory evoked potentials requires deconvolution when the duration of the responses to be recovered exceeds the inter-stimulus interval. Based on least squares deconvolution, in this article we extend the procedure to the case of a multi-response convolutional model, that is, a model in which different categories of stimulus are expected to evoke different responses. The computational cost of the multi-response deconvolution significantly increases with the number of responses to be deconvolved, which restricts its applicability in practical situations. In order to alleviate this restriction, we propose to perform the multi-response deconvolution in a reduced representation space associated with a latency-dependent filtering of auditory responses, which provides a significant dimensionality reduction. We demonstrate the practical viability of the multi-response deconvolution with auditory responses evoked by clicks presented at different levels and categorized according to their stimulation level. The multi-response deconvolution applied in a reduced representation space provides the least squares estimation of the responses with a reasonable computational load. matlab/Octave code implementing the proposed procedure is included as supplementary material.

Auditory brainstem responses obtained with randomised stimulation level.

OBJECTIVE: To present randomised stimulation level (RSL) - a stimulation paradigm in which the level of the stimuli is randomised, rather than presented sequentially as in the conventional paradigm. DESIGN: The value of RSL was evaluated by (i) comparing the morphology of auditory brainstem responses (ABRs) elicited by the conventional and RSL paradigms, and by (ii) an online survey investigating the hearing comfort of the stimulus sequence. STUDY SAMPLE: ABRs were obtained from 11 normal-hearing adults (8 females, 25-29 years). The online survey was administered to 238 adults from the general community. RESULTS: Results showed that (i) both stimulation paradigms elicit ABR signals of similar morphology, (ii) RSL provides a faster comprehensive representation of the ABR session, and that (iii) the general population found RSL stimuli to be more comfortable. CONCLUSIONS: The simultaneous evaluation of all ABR traces of the session provided by RSL has potential to improve the identification of ABR components by enabling clinicians to make use of the response tracking strategy from the start of the test, which is critical in situations where ABRs present an abnormal morphology. New research opportunities and the clinical potential of RSL are discussed.

Auditory brainstem and middle latency responses recorded at fast rates with randomized stimulation.

Randomized stimulation and averaging (RSA) allows auditory evoked potentials (AEPs) to be recorded at high stimulation rates. This method does not perform deconvolution and must therefore deal with interference derived from overlapping transient evoked responses. This paper analyzes the effects of this interference on auditory brainstem responses (ABRs) and middle latency responses (MLRs) recorded at rates of up to 300 and 125 Hz, respectively, with randomized stimulation sequences of a jitter both greater and shorter than the dominant period of the ABR/MLR components. Additionally, this paper presents an advanced approach for RSA [iterative-randomized stimulation and averaging (I-RSA)], which includes the removal of the interference associated with overlapping responses through an iterative process in the time domain. Experimental results show that (a) RSA can be efficiently used in the recording of AEPs when the jitter of the stimulation sequence is greater than the dominant period of the AEP components, and (b) I-RSA maintains all the advantages of RSA and is not constrained by the restriction of a minimum jitter. The significance of the results of this study is discussed.

Anemia, overhydration, and lower muscle strength in hemodialysis patients with protein-energy wasting.

INTRODUCTION: The protein-energy wasting (PEW) syndrome is a common complication in hemodialysis (HD) patients associated to morbidity and mortality. Our objective was to assess the prevalence of PEW and its association with erythropoietin resistance index (ERI) score, body composition by impedance, health-related quality of life, and muscle strength. METHODS: In this cross-sectional, observational, multicenter study, we included data from 191 HD patients from three HD clinics located in Mexico City, Mexico. Clinical and biochemistry variables, body composition, handgrip strength, and the KDQOL-SF36 questionnaire were collected for each patient. FINDINGS: Prevalence of PEW was 22% (n = 41/191), with a higher frequency in those with diabetes mellitus (59% vs. 49%, p = 0.04). Subjects with PEW had lower hemoglobin levels (9.5 + 1.6 g/dl vs. 10.3 + 1.7 g/dl; p = 0.005) and higher ERI scores (19.2 ± 11.2 vs. 15.6 ± 8.2; p = 0.04) compared with the non-PEW group. In analysis of body composition, PEW was associated to higher overhydration status (42.2 vs. 24.9 OH/kg; p = 0.009), higher extracellular water (263 ± 40 vs. 246 ± 32 ml/kg; p = 0.019), lower lean tissue index (12.2 ± 3.2 vs. 14.1 ± 3.7 ml/m2 ; p = 0.021), and lower fat tissue index (9.6 ± 5.7 vs. 12.3 ± 6.2 ml/m2 ; p = 0.043). Handgrip strength was lower in PEW patients (22.5 vs. 28.1 kg; p = 0.002). Finally, no significant differences were observed between groups in quality-of-life assessment. DISCUSSION: In this study, PEW was associated to poor responsiveness to erythropoiesis-stimulating agents, lower muscle strength, and higher overhydration status due to the increase in extracellular water which replaced the loss of tissue. Nevertheless, quality-of-life assessment was not different in patients with PEW compared with those without this complication.

Chronic potentiation of cardiac L-type Ca(2+) channels by pirfenidone.

AIMS: On the basis of its ability to inhibit fibrosis, pirfenidone has drawn the attention as an intriguing candidate for treating cardiac disease. However, its precise electrophysiological effects have yet to be elucidated. Here, we have investigated its potential to modulate ion channels. METHODS AND RESULTS: Adult rat cardiac myocytes were investigated using whole-cell patch-clamp, western-blot and qRT-PCR techniques. Pirfenidone increased the density of L-type Ca(2+) current (I(CaL,) 50-100%), without significantly altering Na(+), K(+), or T-type Ca(2+) currents. The effect was dose-dependent, with an EC(50) of 2.8 µM. Its onset was slow, with a lag period larger than 1 h and time to maximum of 24-48 h. Concomitant changes were observed in the voltage-dependent activation of I(CaL) (-5 mV shift in both V(1/2) and k). In contrast, the following properties of I(CaL) remained normal: steady-state inactivation, Ca(V)1.2 levels (mRNA and protein), and intramembrane charge movement. Indeed, the conductance-to-charge ratio, or G(max)/Q(max), was increased by 80%. The effect on I(CaL) was mimicked by an inhibitor of nitric oxide (NO) synthase (NOS), and attenuated by both cyclic adenosine monophosphate (cAMP) and cAMP-dependent protein kinase (PKA) inhibitors. Conversely, cytokines, reactive oxygen species, and Ca(2+) were all ruled out as possible intermediaries. Additional experiments suggest that pirfenidone increases action potential duration by ∼50%. CONCLUSION: Pirfenidone augments I(CaL), not through higher expression of L-type channels, but through promoting their Ca(2+)-conducting activity. A possible inhibition of NOS expression is likely involved, with subsequent reduced NO production and stimulated cAMP/PKA signalling. These findings may be relevant to the cardioprotective effect of pirfenidone.

Analysis of programming maps and its application for balancing multichannel cochlear implants.

Channel balancing is important for correct perception when using multichannel cochlear implants. In this paper we analyse the effect of channel imbalance on hearing perception in cochlear-implanted patients. Based on warble tone audiometry measured for 10 implanted patients, we evaluate how hearing sensitivity is affected by an imbalance. We also study the distribution along the cochlea of the programming parameters for 146 patients. The parameters are compared for different groups of patients (defined taking into account the age at implantation, the stimulation mode, and the presence of severe cochlear damage). The aim of this study is to obtain information that can be useful for balancing the channels for the patients in the different groups, as well as to evaluate the effect of an imbalance on perception. These results provide some complementary information that can be applied to the correct fitting of the cochlear implant processor.