Dynamics of Auditory Plasticity after Cochlear Implantation: A Longitudinal Study

Human representational cortex may fundamentally alter its organization and (re)gain the capacity for auditory processing even when it is deprived of its input for more than two decades. Stimulus-evoked brain activity was recorded in post-lingual deaf patients after implantation of a cochlear prosthesis, which partly restored their hearing. During a 2 year follow-up study this activity revealed almost normal component configuration and was localized in the auditory cortex, demonstrating adequacy of the cochlear implant stimulation. Evoked brain activity increased over several months after the cochlear implant was turned on. This is taken as a measure of the temporal dynamics of plasticity of the human auditory system after implantation of cochlear prosthesis.

Right Hemispheric Laterality of Human 40 Hz Auditory Steady-state Responses

Hemispheric asymmetries during auditory sensory processing were examined using whole-head magnetoencephalographic recordings of auditory evoked responses to monaurally and binaurally presented amplitude-modulated sounds. Laterality indices were calculated for the transient onset responses (P1m and N1m), the transient gamma-band response, the sustained field (SF) and the 40 Hz auditory steady-state response (ASSR). All response components showed laterality toward the hemisphere contralateral to the stimulated ear. In addition, the SF and ASSR showed right hemispheric (RH) dominance. Thus, laterality of sustained response components (SF and ASSR) was distinct from that of transient responses. ASSR and SF are sensitive to stimulus periodicity. Consequently, ASSR and SF likely reflect periodic stimulus attributes and might be relevant for pitch processing based on temporal stimulus regularities. In summary, the results of the present studies demonstrate that asymmetric organization in the cerebral auditory cortex is already established on the level of sensory processing.

N1m recovery from decline after exposure to noise with strong spectral contrasts

Comb-filtered noise (CFN, derived from white noise by suppressing regularly spaced frequency regions) was presented for 3 s followed by two types of test stimuli. One test stimulus (SB) was comprised of spectra centered in the stop-band regions of the CFN and the other test stimulus (PB) of spectra centered in the band pass regions of the CFN. Magnetoencephalographically recorded N1m responses evoked by SB stimuli were decreased relative to the N1m response evoked by PB stimuli. This effect was maximal when the interval between the CFN and test stimuli was short (0.5 s) but was detected at intervals up to 2 s. The results suggest lateral inhibition in the auditory cortex and point to a decay of inhibition lasting on the order of seconds.

The effect of attention on the auditory steady-state response

40-Hz auditory steady state responses to amplitude modulated tones were recorded with magnetoencephalography to investigate the effect of focused attention. A modulation discrimination task and a destructive visual task established the attended and the non-attended experimental conditions. A strong contrast between these conditions was demonstrated by largely enhanced sustained responses under the attention condition. A significant attentional effect on the ASSR amplitude was observed mostly in the left hemisphere between 200 to 500 ms after stimulus onset. In contrast, transient gamma-band and N1 responses were not affected by the different states of attention.

Cortical oscillations modulated by congruent and incongruent audiovisual stimuli

Congruent or incongruent grapheme-phoneme stimuli are easily perceived as one or two linguistic objects. The main objective of this study was to investigate the changes in cortical oscillations that reflect the processing of congruent and incongruent audiovisual stimuli. Graphemes were Japanese Hiragana characters for four different vowels (/a/, /o/, /u/, and /i/). They were presented simultaneously with their corresponding phonemes (congruent) or non-corresponding phonemes (incongruent) to native-speaking Japanese participants. Participants' reaction times to the congruent audiovisual stimuli were significantly faster by 57 ms as compared to reaction times to incongruent stimuli. We recorded the brain responses for each condition using a whole-head magnetoencephalograph (MEG). A novel approach to analysing MEG data, called synthetic aperture magnetometry (SAM), was used to identify event-related changes in cortical oscillations involved in audiovisual processing. The SAM contrast between congruent and incongruent responses revealed greater event-related desynchonization (8-16 Hz) bilaterally in the occipital lobes and greater event-related synchronization (4-8 Hz) in the left transverse temporal gyrus. Results from this study further support the concept of interactions between the auditory and visual sensory cortices in multi-sensory processing of audiovisual objects.

Stimulus induced reset of 40-Hz auditory steady-state responses

Auditory steady-state responses (ASSR) were evoked with 40-Hz amplitude modulated 500-Hz tones. An additional impulse-like noise stimulus (2,000 +/- 500 Hz) with spectrum clearly distinct from the one of the AM sound, induced pronounced perturbations in the ASSR. The effect of the interfering noise was interpreted as (1) reset of the ASSR because of a sudden loss in phase coherence, (2) a decrease in signal power immediately after presentation of the noise impulse, and (3) a modulation of ASSR amplitude and phase resembling the time course of the ASSR onset. The time-course of the ASSR onset was interpreted as reflecting temporal integration over several 100 ms. The reset of the ASSR was discussed as a powerful mechanism, which allows for fast reaction to a short stimulus change that overcomes the disadvantage of the ASSR's long integration time constant.

Auditory cortex responses to the transition from monophonic to pseudo-stereo sound

Human cortical responses to the change in spaciousness of sound were recorded with the method of magnetoencephalography (MEG). The phases of dichotically presented 500-Hz tones were shifted so that the sound was perceived as originating either from a point-like source centered in the head or from separated sources in space. The phase shift was embedded in 40-Hz amplitude modulation. Thus, the phase shift could not be detected from a monaural signal. The transition between 'mono' and 'pseudo-stereo' quality of the sound elicited a P1-N1-P2 response similar to the onset response as well as a decrement in the steady-state response. The responses were discussed as reflecting binaural processing in the central auditory system.

Lateral inhibition and habituation of the human auditory cortex

The goal of this study was to compare the lateral inhibition and the habituation in the human auditory cortex, two important physiological effects during auditory processing that can be reliably measured by means of magnetoencephalography when recording auditory evoked fields. Applying 40-Hz amplitude-modulated stimuli allowed us to record simultaneously the slow transient evoked and the steady-state fields and thus to characterize the lateral inhibition and the habituation effect in primary and non-primary auditory cortical structures. The main finding of the study is that the lateral inhibition effect of non-primary auditory areas as measured on the major component of the slow transient auditory evoked field (N1) is significantly stronger than the corresponding habituation effect. By contrast, this effect was not observed for the 40-Hz steady-state fields, characterizing the activation of the primary auditory cortex in humans. The results might be interpreted as (i) evidence that the inhibition mediated by lateral connections is stronger than the habituation of excitatory neurons in the non-primary auditory cortex and (ii) the processing hierarchy in the human auditory cortex is demonstrated by the different behaviour of lateral inhibition and habituation in primary and non-primary auditory cortical structures.

Cardiovascular risk factors and probability for cardiovascular events in HIV-infected patients. Part II: gender differences

OBJECTIVE

Due to the side effects of antiretroviral therapy and long term survival there is an increasing concern of an elevated rate of cardiovascular diseases in HIV-infected patients. The present study analysed the cardiovascular risk profile and the probability of cardiovascular events in HIV-infected patients, due to differences of gender.

METHODS

Cardiovascular risk factors of 309 HIV-infected adults, including 240 males were analysed. Overall 10-years probability for cardiovascular events was evaluated by the Framingham algorithm.

RESULTS

Gender differences were detected in cardiovascular risk factors such as lipid values, blood pressure and the rate of smoking. Tobacco use was much more common in HIV-infected males compared with HIV-infected females (67.5% vs. 49.3%; p<0.001). Although no significant difference was noticed in total cholesterol (5.49 +/- 0.09 vs. 5.53 +/- 0.19 mmol/L, p = 0.84), the HDL-cholesterol concentration was significantly lower (1.09 +/- 0.03 vs. 1.36 +/- 0.06 mmol/L, p < 0.001) and the triglyceride concentration higher (3.01 +/- 0.21 vs. 2.06 +/- 0.26 mmol/L, p = 0.02) in HIV-infected males compared to HIV-infected females. Additionally, systolic blood pressure was higher in HIV-infected males compared with HIV-infected females (123.1 +/- 1.1 vs. 115.4 +/- 2.1 mmHg, p < 0.01). No significant differences were detected in HbA1c concentrations between both groups (5.15 +/- 0.07 vs. 5.31 +/- 0.11, p = 0.26). The overall 10-years probability for cardiovascular events was 8.7% (median) in HIV-infected males and 1.7% in HIV-infected females (p < 0.0001).

CONCLUSIONS

In the present study, we observed gender differences in the cardiovascular risk profile of HIV-infected individuals. The risk of premature atherosclerosis and associated cardiovascular events was significantly higher in HIV-infected males.

Cardiovascular risk factors and probability for cardiovascular events in HIV-infected patients: part I. Differences due to the acquisition of HIV-infection

OBJECTIVE

Due to side effects, such as hyperlipidaemia and insulin resistance, there is an increasing concern that antiretroviral drugs lead to an epidemic of cardiovascular diseases in HIV-infected patients. The present study characterizes the cardiovascular risk profile of HIV-infected individuals, due to the acquisition of HIV-infection.

METHODS

Cardiovascular risk factors of 309 HIV-infected adults (HIV-acquisition: 59.2% by homosexual contact (group 1), 28.5% by heterosexual contact (group 2), 9.1% by intravenous drug abuse (group 3) and 3.2% by blood transfusion (group 4)) were analysed. Overall 10-years probability for cardiovascular events was analysed by the Framingham algorithm.

RESULTS

Tobacco use was more common in group 1 subjects compared with group 2 subjects (67% vs. 52%; p<0.05). Additionally, group 1 subjects exhibited elevated total cholesterol (5.6 +/- 0.1 mmol/L vs. 4.8 +/- 0.3), LDL-cholesterol (3.6 +/- 0.1 mmol/L vs. 2.8 +/- 0.2) and triglyceride concentrations (3.2 +/- 0.3 mmol/L vs. 1.7 +/- 0.2) compared with group 3 (all p<0.05). No significant differences between the groups were detected in glucose metabolism. The overall 10-years probability for cardiovascular events was significantly higher in group 1 compared with group 2 and group 3 (12.2 +/- 0.8% vs. 6.6 +/- 0.9% and 7.9 +/- 1.6%, p<0.05).

CONCLUSIONS

The cardiovascular risk profile differs between subgroups of HIV-infected individuals, leading to significant higher probability of cardiovascular events in group 1 subjects. The risk of premature atherosclerosis by HIV-infected individuals and therapeutic options remains to be established.

Electro-magnetic base technology for estremely sensitive immunosensors and DNA-chips

We report on the development of an innovative electro-magnetic base technology for estremely sensitive sensors allowing the electrical detection of biological analytes like antigenes or DNA as well as a simple multiple detection of binding forces occurring at specific bonds between proteins. The technology is based on the strong impact of specifically captured magnetic microbeads on an electrical current generated in a fluid by a small sensor chip with an array of activated microelectrodes. The new technological principle with the on-chip detection of analytes will be suitable for large scale applications due to its mass production compatible technologies and allow an alternative way to monitor relevant substances without the consumption of critical additional solutions and reagents.

Chemical and biochemical microsensors in silicon for the clinical on-line monitoring

Miniaturised chemosensors and biosensors for applications in clinical diagnostics and biomedical fields can be fabricated in silicon with high reproducibility using the containment technology. They are characterised by excellent durability of the sensitive membranes. Meanwhile, there are sensors available for a variety of relevant medically parameters such as pH, the blood electrolytes sodium, calcium, potassium, and the blood metabolites glucose and lactate. The miniaturised sensors provide the opportunity to develop product solutions with minimal sampling volume requirements for the "Point of Care (POC)" sector through the combination of innovative microtechnical components. Two examples are presented, such microsystems have been implemented for the medical applications of "Blood Monitoring" and "Glucose Monitoring".

Use of an augmented reality display of patient monitoring data to enhance anesthesiologists' response to abnormal clinical events

One obstacle to safety in the operating room is anesthesiologist distraction having to shift attention back and forth from the patient to a vital sign monitor while performing either routine or emergency procedures. The purpose of this study was to measure the decrease in anesthesiologist distraction made possible by using a head-worn, see-through personal display (HWD) using retinal scanning technology. With the head-up display, they were able to focus their attention exclusively on the patient and the task at hand. The Nomad reduced the number of times the anesthesiologist had to shift their attention by a more than a third (17 times versus 58 times). This allowed them to spend more time focused on the patient.

Renal enlargement as primary presentation of acute lymphoblastic leukaemia

Renal enlargement in acute lymphoblastic leukaemia is well reported in literature from Western Countries. However there are very few reports from developing countries. Bilateral symmetrical enlargement of kidneys as a primary presentation of acute lymphoblastic leukaemia is rare. We report a child who had acute lymphoblastic leukaemia presenting with bilateral renal mass.

A pilot scheme for the development of evidence-based practice

This article presents an evaluative account of a pilot scheme that aimed to introduce evidence-based practice in one NHS trust. The scheme was based on collaboration between staff in the quality assurance department and a nurse researcher based in a university. This collaboration enabled three designated staff to develop skills required for evidence-based practice and guide the production of information that could be disseminated to nurses throughout the trust. Evaluation demonstrated that participants had examined eight practice-based topics and devised protocols that could be applied to practice in a range of hospital and community settings throughout the trust. Evaluation also highlighted the importance of ensuring that members of other disciplines are aware of, and feel involved in, new developments even if they are not directly concerned with them.

Acoustically and electrically evoked responses of the human cortex before and after cochlear implantation

Multi-channel auditory evoked potentials (AEP) were recorded before and after cochlear implantation (CI) from a patient suffering from severe high frequency hearing loss with residual, but highly fluctuating hearing around 250 Hz. Immediately after CI activation early components of the N1 were present. Later N1 components developed during the use of CI. The unique result of this single case study is the concordance of the cortical AEP pattern obtained by native and artificial peripheral stimulation, which can be regarded as an indicator for the adequate function of the CI.

Metabolism of rabbit plasma-derived factor VII in relation to prothrombin in rabbits

In the human circulation, factor VII is present in relatively low plasma concentration (0.01 microM) and has been reported to have a short half-life (t(1/2); 6 h). In contrast, prothrombin is present in a relatively high plasma concentration (2 microM) and has a relatively long catabolic half-life (t(1/2) = approximately 2-3 days). This report examines the metabolic characteristics of purified rabbit plasma factor VII and prothrombin, radiolabeled with (125)I and (131)I, respectively, in healthy young rabbits. From the plasma clearance curves of protein-bound radioactivities, fractional catabolic rates and compartmental distributions were calculated using a three-compartment model. Turnover of factor VII within the intravascular space (2.95 days) exceeded that of prothrombin (1.9 days). However, the whole body fractional catabolic rate of factor VII (0.34 days(-1); catabolic t(1/2) = 2.04 days) was significantly slower than that of prothrombin (0.53 days(-1); t(1/2) = 1.31 days). Furthermore, the fractional distributions of factor VII in the intravascular (0.14) and extravascular compartments (0.76) differed from those of prothrombin (0.29 and 0.53). Absolute quantities of factor VII and prothrombin catabolized by a 3-kg rabbit amounted to 0.18 and 24.0 mg/day, respectively (molar ratio of prothrombin to factor VII = 100). The molar ratio of catabolism was compared with the release rates of factor VII and prothrombin from rabbit livers perfused ex vivo. After correction for uptake of factor VII and prothrombin by the liver, the molar ratio of released prothrombin to factor VII in the perfusate was approximately 293:1 over a 0.25- to 3-h interval. These results indicate that, compared with prothrombin, factor VII in the healthy rabbit circulates as a relatively long-lived protein. This behavior does not reflect that reported for factor VII in the human circulation.

Human auditory middle latency responses: influence of stimulus type and intensity

Human auditory middle latency responses (MLR) to click and tone pip stimuli of different intensities were recorded by means of magnetoencephalography (MEG) and electroencephalography (EEG). Clicks elicited larger responses with significantly shorter latencies than the tone pips at the same intensity in dB sensation level (SL). Most MLR amplitudes increased and their latencies decreased with increasing stimulus intensity for both types of stimulation. Pa and Nb amplitudes saturated at intensities of 60 dB SL in the case of click stimulation. The shorter latencies of MLR evoked by the click were explained by its short rise time and the high frequency content of its spectrum. MEG source analysis yielded MLR sources which were clearly different from those of the slow cortical wave N1. They seem to be located in primary auditory areas along Heschl's gyrus.

Reliability of the Sunnybrook Facial Grading System by novice users

OBJECTIVES

To evaluate the intrarater and inter-rater reliability of the Sunnybrook Facial Grading System (SFGS) by novice users.

DESIGN

Prospective interval study using one measurement instrument.

SETTING

Tertiary teaching hospital (Sunnybrook & Women's College Health Science Centre).

METHODS

Twenty-two patients with a wide spectrum of facial dysfunction recorded on videotapes were rated using the SFGS by eight novice observers independently in two different sittings separated by 3 weeks. The order of patients was randomized for the second sitting. Intraclass correlation coefficients were calculated for component scores and for total scores within and between raters.

RESULTS

The intrarater reliability coefficients for the eight raters ranged from .838 to .929. This largely overlaps with the data obtained in previous studies with expert raters. The inter-rater reliability for all eight raters at time 1 was .982 and for time 2 was .970. This is higher than what was previously obtained with expert raters.

CONCLUSION

The SFGS is as reliable when applied by novice users as by expert users.

Metabolism of rabbit angiostatin glycoforms I and II in rabbits: angiostatin-I leaves the intravascular space faster and appears to have greater anti-angiogenic activity than angiostatin-II

Plasminogen (PLG) exists in the circulation as two glycoforms, I and II. Angiostatin (AST) is a polypeptide that has been cleaved from the kringle region of PLG and has strong anti-angiogenic properties. AST-I and AST-II, which consisted only of kringles 1 through 3, were prepared by the action of urokinase on purified rabbit PLG-I and PLG-II, respectively, in the presence of N-acetyl cysteine, followed by affinity chromatography on lysine-Sepharose. Purified AST-I and AST-II were tested for functional activity with a chick chorioallantoic membrane (CAM) model; when similar amounts were applied to a 6-day CAM, AST-I was substantially more effective than AST-II in decreasing vascular supply to the CAM over a 72-hour period; this activity correlated with a loss of capillaries, probably through apoptosis of endothelial cells. Radiolabeled AST-I and AST-II (iodine 125 and iodine 131) were co-injected intravenously into healthy rabbits to determine their clearances from plasma measured over 3 days. Over a dose range of 0.08 to 2.7 microg/kg, the fractional catabolic rate within the intravascular space (j(3)) indicated that AST-I was cleared 3-fold to 4-fold more rapidly than AST-II (P < .001). The catabolic half-life of AST-I (2.01 +/- 0.19 days) was significantly less than that of AST-II (2.62 +/- 0.20 days). The faster clearance of AST-I from the intravascular space was matched by its more rapid passage than AST-II to the extravascular space of various organs over 60 minutes in vivo. This property of AST-I as compared with AST-II may partially explain its greater anti-angiogenic potential. From the plasma concentrations of PLG-I and PLG-II and their relative behaviors toward rabbit VX-2 lung tumors in vivo, we predict that substantially greater quantities of AST-II than AST-I may be released into the extravascular space of tumors.

Magnetic resonance spectroscopy of the human brain

Magnetic resonance (MR; synonymous with NMR = nuclear magnetic resonance) is a universal physical technique best known for non-invasive detection and anatomical mapping of water protons (H). MR-spectroscopy (MRS) records protons from tissue chemicals other than water, intrinsic phosphorus containing metabolites, sodium, potassium, carbon, nitrogen, and fluorine. MRS is therefore an imaging technique with the potential to record human and animal biochemistry in vivo. As a result of wide availability of MRI equipment in research laboratories and hospitals, MRS is a serious competitor with PET to define normal body composition and its perturbation by pharmacological and pathological events. This article describes practical aspects of in vivo MRS with particular emphasis on the brain, where novel metabolites have been described. A survey of these new aspects of neurochemistry emphasize their practical utility as neuronal and axonal markers, measures of energy status, membrane constituents, and osmolytes, as well as some xenobiotics, such as alcohol. The concept of multinuclear in vivo MRS is illustrated by diagnosis and therapeutic monitoring of several human brain disorders. Although these methods are currently most frequently encountered in human studies, as well as with transgenic and knockout mouse models, MRS adds a new dimension to anatomic and histopathologic descriptions.

[AIDS and non-Hodgkin's lymphoma: initial cardiac manifestations of highly malignant B-cell lymphoma 18 years after HIV infection]

HISTORY AND FINDINGS

A 35-year-old man who, as a result of intravenous drug abuse, had become infected with HIV 18 years previously, was admitted with signs of right-heart failure. Three months earlier a systolic murmur had first been heard in the 5th intercostal space parasternally.

INVESTIGATIONS

Transesophageal echocardiography (TEE) demonstrated a 3 x 2 cm right atrial tumour, moderate to severe tricuspid regurgitation and pulmonary hypertension. Blood cultures grew Streptococcus.

DIAGNOSIS, TREATMENT AND COURSE

Endocarditis with atrial thrombi and recurrent pulmonary emboli was diagnosed and treated with antibiotics and anticoagulants. Three weeks later the TEE showed an increase in the atrial tumour. Computed tomography of skull, thorax and abdomen did not demonstrate any significantly enlarged lymph nodes. Exploratory thoracotomy revealed an infiltrating highly malignant centroblastic non-Hodgkin's lymphoma (NHL) of almost the entire free wall of the right atrium. After two courses of chemotherapy (CHOP protocol) the size of the tumour had significantly decreased.

CONCLUSION

The differential diagnosis of a right atrial tumour can be difficult in patients with HIV or AIDS. Even if the site is atypical and there is no lymphadenopathy, a lymphoma should be considered. In case of doubt a histological diagnosis via an exploratory thoracotomy should be performed.

Pharmacokinetics and pharmacodynamics of sotalol in a pediatric population with supraventricular and ventricular tachyarrhythmia

OBJECTIVE

This pharmacokinetic-pharmacodynamic study was designed to define the steady-state relationship between pharmacologic response and dose or concentration of sotalol in children with cardiac arrhythmias, with an emphasis on neonates and infants.

METHODS

The treatment consisted of an upward titration with unit doses of 10, 30, and 70 mg of sotalol per square meter of body surface area. The patients received 3 doses at each dose level. The dosing interval was 8 hours. The Class III and beta-blocking activities of sotalol were derived from the QT and R-R intervals, respectively, of the surface electrocardiogram, which was recorded at 6 scheduled times before and after the third, sixth, and ninth doses. During these three dose intervals, 4 scheduled blood samples were also collected. Drug concentrations were measured with a validated nonstereoselective liquid chromatographic tandem mass spectrometric detection assay. Pharmacokinetic and pharmacodynamic parameters were obtained with standard methods.

RESULTS

Twenty-one centers enrolled 25 patients in the study: 7 were neonates, 9 were infants, and 11 were children between the ages of 2 years and 12 years. The area under the drug concentration-time curve increased proportionately with dose. The apparent oral clearance of sotalol was linearly correlated with body surface area and creatinine clearance. The smallest children (body surface area <0.33 m2) displayed greater drug exposure than the larger children. The increase of QTc and R-R intervals was dose dependent. At the 70-mg/m(2) dose level, the mean (+/- standard deviation) maximum increase for the QTc interval was 14% +/- 7% and the average Class III effect during a dose interval was 7% +/- 5%. At the same dose level, the mean maximum increase of the R-R interval was 25% +/- 15% and the average beta-blocking effect during a dose interval was 12% +/- 13%. The effects tended to be larger in the smallest children. The Class III response and the plasma concentrations of sotalol were linearly related. The treatment was well tolerated.

CONCLUSIONS

The steady-state pharmacokinetics of sotalol were dose proportionate. Pharmacologically important beta-blocking effects were observed at the 30-mg/m2 and 70-mg/m2 dose levels. Important Class III effects were seen at the 70-mg/m2 dose level. The Class III effect was linearly related to the drug concentration.