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PubMedDate not supplied

A simple two-component model of the electrically evoked compound action potential in the human cochlea.

Neural response telemetry (NRT) permits in situ intracochlear recordings of the electrically evoked compound action potential from the auditory nerves using scala tympani electrodes. The recorded NRT waveforms can generally be categorized under either single positive peak or double positive peak waveforms. This is similar to the observations from Stypulkowski and van den Honert, who suggested that the double peak complex arises from two components that could be axonal and dendritic in origin, respectively. Using a simple mathematical model which linearly combines two separate waveforms similar in shape but differing in amplitude and latencies, it was possible to simulate the various NRT waveform categories. The simulation results support the view that the two waveform components originate from dendritic or axonal processes and implies that the shape of the response waveform may provide information about the degree of neural survival in the stimulated cochlea. This information could be useful for determining optimal speech coding parameters for cochlear implant users on an individual basis.

Cochlea↗
PubMed2000

Telemetric assessment of intracranial pressure changes consequent to manipulations of the Codman-Medos programmable shunt valve.

INTRODUCTION: Noninvasive manipulation of programmable shunt valves may allow customization of intracranial pressure (ICP) dynamics in individual shunted patients. Manipulations of the recently FDA-approved Codman-Medos variable pressure valve (VPV) are monitored by radiographic changes in the valve mechanism, necessitating a skull radiograph with each pressure change. We wished to assess the in vivo impact of VPV manipulations on ICP changes using a noninvasive telemonitor as an alternative to radiographic confirmation and as a method for validating the ICP changes. METHODS: TeleSensor devices (Radionics) were implanted in-line with 12 VPV shunt systems. ICP was assessed telemetrically in the supine position whenever the valve pressure was adjusted (both before and 2-5 min after the manipulation). RESULTS: Valve manipulation was confirmed by radiograph for the initial manipulations only and matched the telemetric pressure changes observed in all cases. Confirmed manipulations of the valve were generally followed by a near equivalent relative change in ICP (</=2 cm difference 74% of the time); however, the absolute value of the supine ICP was dependent on the entire shunting system and was equivalent to the valve setting only 11% of the time. Supine ICP and ICP dynamics were also dependent more on the shunt system than simply on the valve setting and were different for each of the shunt systems tested. CONCLUSIONS: We have confirmed that the VPV does cause ICP changes in shunted hydrocephalic patients that are essentially equivalent to programmed relative changes in the valve settings. These changes can be as easily monitored by noninvasive telemetry as by repeated radiography. However, our observations demonstrate that additional factors in the shunting system render the ICP absolutely equivalent to the VPV setting only rarely, implying that a programmable shunt valve is not necessarily equivalent to programmable ICP.

Adolescent↗
PubMedDate not supplied

Telemetric small intestinal motility recording in awake rats: a novel approach.

INTRODUCTION: Ideally, gastrointestinal motility recording should be done in freely moving, stress-free animals. However, no such method is currently available for rats. METHODS: Two NiCr electrodes were sutured to the jejunum and connected to an implantable electromyographic (EMG) transmitter in rats. EMG signals were radio-transmitted to a receiver placed at the bottom of the rats' home cages. RESULTS: Fasting and postprandial jejunal EMG signals could be detected by telemetry. Phase III contractions of the MMC were easy to identify visually and occurred at a rate of about 4.8 per hour. Feeding disrupted the phasic contraction pattern 15 min after the start of food intake and lasted for 2 h. The motility index (MI, area under the curve) was calculated and increased postprandially. CONCLUSION: Telemetric transmission of rat gastrointestinal EMG signals is feasible and results are comparable to those given in the literature.

Animals↗
PubMed2002

Asymmetry and symmetry in brain waves from dolphin left and right hemispheres: some observations after anesthesia, during quiescent hanging behavior, and during visual obstruction.

Studies of sleep in cetaceans (whales, dolphins, and porpoises), substantiated by electrophysiological data, are rare with the great majority of observations having been made by one group from Russia. This group employed hard-wired recording with low-noise cables for their EEG observations, whereas our report describes behavioral and EEG observations of dolphin sleep using telemetry. Marked asymmetry of the EEG was observed during behavioral sleep posture. At different times synchronized slow waves appeared in both left and right brain hemispheres concurrently with lower voltage, faster, desynchronized EEG activity in the opposite hemisphere. On the other hand, during one brief period of sleep behavior, sleep-like EEG activity appeared on leads from both hemispheres. When the animal was exposed to a loud sound, it woke with lower voltage, faster, relatively symmetrical, desynchronized EEG activity appearing from both hemispheres. Additionally, the EEG appeared relatively desynchronized and symmetrical between the two hemispheres when the animal was awake during recovery from pentothal-halothane anesthesia as well as during waking periods when one or both of the animal's eyes were covered by an opaque rubber suction cup.

Animals↗
PubMedDate not supplied

Auditory brainstem implant in posttraumatic cochlear nerve avulsion.

Patients aged over 12 years with neurofibromatosis type 2 are considered candidates for an auditory brainstem implant (ABI). This study extends the indication criteria of ABI to subjects with profound hearing loss due to damaged cochleas and/or cochlear nerves (CNs) following head injuries. In our department, over the period from April 1997 to November 2002, 32 patients, 23 adults and 9 children, were fitted with ABIs. Their ages ranged from 14 months to 70 years. These patients were suffering from a variety of tumor (13 subjects) and nontumor CN or cochlear diseases (19 subjects). Six patients, 5 adults and 1 child, had profound hearing loss following head injury. Their mean age was 25 years (range: 16-48 years). Five were male and 1 female. The retrosigmoid approach was used in all 6 patients. The electrode array was inserted into the lateral recess of the fourth ventricle and correct electrode positioning was monitored with the aid of electrically evoked auditory brainstem responses and neural response telemetry. Correct implantation was achieved in all patients. No complications were observed due to implantation surgery or related to ABI activation and stimulation of the cochlear nuclei. At activation, an average of 9.8 electrodes (range 5-13) were switched on without side effects. One to 6 electrodes were activated in the following sessions after time periods ranging from 2 to 16 months. All patients achieved auditory-alone-mode closed-set word recognition scores ranging from 40 to 100%; 3 had auditory-alone-mode open-set sentence recognition scores of 60-100%; 2 of these even had speech-tracking performance scores of 38 and 43 words, respectively, showing an ability to engage in normal conversation and converse over the phone. The present study demonstrates that the ABI is a useful rehabilitation instrument in subjects with damaged cochleas and/or CN avulsion following head injury who are unamenable or poorly responsive to auditory rehabilitation using cochlear implants.

Adolescent↗
PubMed2006

The role of the selective serotonin reuptake inhibitor fluoxetine in temperature regulation in ovariectomized rat models.

Thermoregulation is an integrated network of neuroendocrine, autonomic and somatosensory responses. Thermoregulatory dysfunction occurs during fluctuations or decline of gonadal hormone levels and results in vasomotor symptoms such as hot flushes and/or night-time sweating. The neurotransmitter serotonin (5-HT), has been reported to play a role in thermoregulation via changes in extracellular 5-HT levels and/or activation of various 5-HT receptors. The purpose of this study was to evaluate the role of the selective 5-HT reuptake inhibitor (SSRI), fluoxetine (FLX), on temperature regulation using ovariectomized (OVX) rodent models of thermoregulation. Single, subcutaneous (s.c.) administration of FLX (3, 10, 30 and 60 mg/kg) dose-dependently reduced core body temperature (CBT). FLX at 3 and 10 mg/kg s.c. showed no statistically significant decrease on tail-skin temperature (TST), whereas at higher doses (30 and 60 mg/kg) a significant decrease in TST was noted in the telemetry model. To mimic chronic SSRI treatment, a 5-HT(1A) antagonist (WAY-100635; 0.3 mg/kg) was administered 20 min prior to FLX (10 mg/kg). This combination showed no significant improvement on temperature dysfunction compared to FLX alone. Similarly, in a morphine-dependent model of temperature dysfunction FLX, was inactive at 10 mg/kg whereas the 30 and 60 mg/kg s.c. dose abated the naloxone-induced increase in TST by 55 and 81%, respectively. In summary, FLX affected CBT at all doses, but alleviated thermoregulatory dysfunction only at higher doses that are non-selective for the 5-HT system.

Animals↗
PubMedDate not supplied

Instrumentation, working hypotheses, and clinical aspects of neurostimulation.

The paper describes instrumentation developed in our laboratory for the therapy of neurological disorders, including (a) hybrid stimulator for chronic use which retains constant current characteristics, providing a low resistance path during the quiescent phase between pulses to minimize the postpulse charge; (b) brain radio stimulators, crystal controlled, with digital logic section and an optoelectric sensor for telemetry of the intensity used; (c) external stimoceiver for experimental and clinical use, combining multichannel stimulator and EEG telemetric instrument; (d) transdermal stimoceivers, totally implantable for two-way communication with the brain through the intact skin; and (e) implantable microprocessor for detection of EEG signals which are used to trigger contingent brain stimulation. Our working hypotheses for chronic brain stimulation include (a) electrical modification of the functional set point of specific cerebral areas; (b) feedback-controlled stimulation; and (c) establishment of artificial neuronal links with the aide of the computer. The paper concludes with a discussion of the indications for therapeutic use of brain stimulation and criteria for patient selection.

Animals↗
PubMed1976

Telemetric estimation of the descending colon pressure changes on dogs before and after total and selective vagotomy.

This experimental study describes the pressure changes of the descending colon before and after total and selective vagotomy combined with Finney's pyloroplasty as estimated by telemetry. The results obtained from the study of 20 dogs show that the motility of the descending colon is extremely reduced after total vagotomy with no change after selective vagotomy.

Animals↗
PubMed1995

Cardiovascular and antilipolytic effects of the adenosine agonist GR79236.

Adenosine is known to produce cardiovascular effects such as bradycardia and hypotension via activation of myocardial (A1) and vascular (A2) receptors and antilipolytic effects through activation of adipocyte (A1) receptors. We established the cardiovascular and antilipolytic profile of the adenosine A1 agonist GR79236 (N6-[(1S,trans)-2-hydroxycyclopentyl]-adenosine) and compared it with CPA (N6-cyclopentyl-adenosine). GR79236 was approximately 3-fold less potent than CPA in inhibiting in vitro lipolysis. In conscious rats, both agents were shown to have antilipolytic and glucose-lowering properties. In rats instrumented with telemetry transmitters, orally administered CPA was one log unit more potent than GR79236 as a hypotensive and bradycardiac agent. In summary, GR79236 is an A1-selective adenosine agonist which reduces heart rate and mean arterial pressure and produces decreased plasma lipids and glucose levels.

Adenosine↗
PubMed1990

Effect of dental plaque age and bacterial composition on the pH of artificial fissures in human volunteers.

Changes in sucrose-induced plaque pH profiles and the microbial composition of occlusal tooth surface fissures were analyzed using wire telemetry and bacterial culturing techniques. Four human volunteers wore appliances containing artificial fissures constructed with ion-sensitive field-effect transistor (ISFET) electrodes for 1, 2 and 4 days; 1 subject kept the electrode for 3 weeks. After monitoring the plaque pH response at the base of the fissure to a 10% (w/v) sucrose rinse the plaque was removed and analyzed for total viable bacteria, total and specific streptococci, lactobacilli and Actinomyces spp. One-day-old plaque showed a rapid drop in plaque pH to a minimum of 4.8 +/- 0.2, with 2-day-old plaque showing the most acidogenic pH profile (minimum pH 4.6 +/- 0.2). The 4-day-old plaque response was less acidogenic (minimum pH 5.0 +/- 0.3) than the results from days 1 and 2. Responses from 13- and 21-day-old fissure plaques showed greatly decreased acidogenic responses (day 21 minimum pH 5.7). Viable bacteria recovered from the fissure increased from approximately 4 x 10(6) colony-forming units on day 1 to 1.2 x 10(7) on days 2 and 4 and 1.7 x 10(7) on day 21. Streptococci (greater than 50%) and Actinomyces (greater than 10%) dominated in the fissure plaques and their levels were related to minimum pH. Since fissure plaque of all ages tested contained high concentrations of acidogenic bacteria, the decreased acidogenic response at the base of fissures with increasing plaque age suggests that maturing fissure plaques provide an increasingly greater diffusion barrier to fermentable carbohydrates.

Actinomyces↗
PubMed1996

Acidogenic potential and total salivary carbohydrate content of expectorants following the consumption of some cereal-based foods and fruits.

The acidogenic potential of a group of popular cereal-based foods and fruits and total carbohydrate content of salivary expectorants following their consumption were assessed using an indwelling electrode with telemetry and the anthrone method. Paired t tests indicated that sorbitol did not cause the plaque pH to fall as low as any of the test foods (p <0.05) but there was no significant difference between sucrose and the test foods. Only the fruits produced less acid than sucrose. The breakfast cereals tended to yield the highest levels of total carbohydrate in the salivary expectorants although a greater percentage of original carbohydrate was retained after rice and bread. These results suggest the important effect of carbohydrate retention on plaque pH response.

Acids↗
PubMed1980

Telemetric urodynamic investigations in normal males.

To study the applicability of telemetry in urodynamics, 10 healthy males were evaluated by both standard and telemetric urodynamic techniques. TV observation made correlation of the data with the actual situation possible. During bladder filling, intravesical pressure could be registrated in a lying, sitting and standing position. Stress conditions such as walking, running, climbing steps, kneebends, push-ups and even handstands were tested. Detrusor instability was detected with telemetric techniques in 6 volunteers, while regular cystometry showed evidence of instability in only 2 cases. Desire to void occurred in telemetric studies at lower bladder volume than in regular cystometry. A normal voiding phase was registered in all telemetric investigations, while 3/10 men displayed an abnormal micturition pattern in regular sitting cystometry. The advantages of telemetric urodynamic investigations are: (1) simulation of several stress conditions because of the patient's independence of stationary laboratory equipment; (2) lowered psychogenic stress as the patient is left undisturbed and can urinate in a normal position and (3) 24-hour investigations. It is indicated in (1) incontinence if no urine loss can be detected by regular cystometry; (2) micturition disorders in psychogenic inhibition of micturition is suspected, and (3) enuresis if 24-hour investigations are desired.

Adult↗
PubMed2003

Phosphodiesterase type 5 as a target for the treatment of hypoxia-induced pulmonary hypertension.

BACKGROUND: Phosphodiesterase type 5 (PDE5) is a novel therapeutic target for the treatment of pulmonary hypertension. This study examined the distribution of PDE5 in normal and hypoxic lung and the effect of chronic PDE5 inhibition with sildenafil, initiated before and during exposure to hypoxia, on pulmonary artery pressure (PAP) and structure. METHODS AND RESULTS: Sprague-Dawley rats were exposed to hypoxia (10% O2) for up to 42 days. PAP, measured continuously by telemetry, increased gradually by 20 to 40 mm Hg, reaching a plateau between 10 and 14 days, and declined to normal levels on return to normoxia. PDE5 immunoreactivity was localized to smooth muscle cells in the medial layer of pulmonary arteries and veins in the normal lung and in distal muscularized arteries (<25 microm diameter) after hypoxia-induced pulmonary hypertension. Sildenafil (25 or 75 mg x kg(-1) x d(-1)) given before hypoxia produced marked dose-dependent inhibition in the rise of PAP (60% to 90% reduction; P<0.0001) and vascular muscularization (28.4+/-5.0% reduction; P<0.001). When begun after 14 days of hypoxia, sildenafil significantly reduced PAP (30% reduction; P<0.0001) and partially reversed pulmonary artery muscularization (39.9+/-4.9% reduction; P<0.001). CONCLUSIONS: PDE5 is found throughout the muscularized pulmonary vascular tree, including in newly muscularized distal pulmonary arteries exposed to hypoxia. PDE5 inhibition attenuates the rise in PAP and vascular remodeling when given before chronic exposure to hypoxia and when administered as a treatment during ongoing hypoxia-induced pulmonary hypertension.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2004

Plasma B-type natriuretic peptide levels predict postoperative atrial fibrillation in patients undergoing cardiac surgery.

BACKGROUND: Postoperative (postop) atrial fibrillation (AF) occurs in up to 60% of patients after cardiac surgery, leading to longer hospital stays and increased healthcare costs. Recently, B-type natriuretic peptide (BNP) has been reported to predict occurrence of nonpostoperative AF. This study evaluates whether elevated preoperative (preop) plasma BNP levels predict the occurrence of postop AF. METHODS AND RESULTS: One hundred eighty-seven patients with no history of atrial arrhythmia who had a preoperative BNP level and had undergone cardiac surgery were identified. Their records were reviewed, and postoperative ECG and telemetry strips were analyzed for AF until the time of discharge. Postop AF was documented in 80 patients (42.8%). AF patients were older (68+/-11 versus 64+/-14 years, P=0.04), but there was no difference in sex distribution, hypertension, left ventricular (LV) function, LV hypertrophy (LVH), left atrial size, history of coronary artery disease (CAD), or beta-blocker use. Preop plasma BNP levels were higher in the postop AF patients (615 versus 444 pg/mL, P=0.005). After adjustment for age, sex, type of surgery, hypertension, LV function, LVH, left atrial size, CAD, and beta-blocker use, the odds ratios of postop AF according to increasing quartiles, compared with patients with lowest quartile, were 1.8, 2.5, and 3.7 (P(trend)=0.03). CONCLUSIONS: An elevated preop plasma BNP level is a strong and independent predictor of postop AF. This finding has important implications for identifying patients at higher risk of postop AF who could be considered for prophylactic antiarrhythmic or beta-blocker therapy.

Aged↗
PubMed1995

Arrhythmias and death after coronary artery occlusion in the rat. Continuous telemetric ECG monitoring in conscious, untethered rats.

BACKGROUND: The onset of acute myocardial infarction (MI) is accompanied by a rapid increase in electrical instability and often fatal ventricular arrhythmias. The aim of this study was to assess the continuous arrhythmia profile during the initial 48 hours after coronary artery ligation in the rat in relation to time course, mortality, and infarct size. METHODS AND RESULTS: Continuous ECG recording were obtained in 26 conscious, untethered rats for 24 hours before and 48 hours after coronary ligation by use of an implantable telemetry system. All episodes of ventricular tachycardia and fibrillation were counted and their durations summed. Infarct size was measured at 48 hours after MI or after spontaneous death. After ligation, two distinctly active arrhythmogenic periods developed (A1, 0 to 0.5 hours; A2, 1.5 to 9 hours), each followed by a quiescent phase of low ectopy (Q1, 0.5 to 1.5 hours; Q2, 10 to 48 hours). The total mortality rate of 65% was found within the two active periods, with 13 of 15 deaths occurring in A2. Rats with larger infarcts (> or = 50%) and nonsurvivors tended to have increased arrhythmia frequency and duration compared with both animals with smaller MIs (< 50%) and survivors. CONCLUSIONS: Two distinct arrhythmogenic periods occur in rats with acute MI that may be caused by different mechanisms and correspond to the bimodal arrhythmia time course seen in dogs and humans after acute MI. Telemetric monitoring of the ECG in the conscious rat after infarction will be useful in assessment of the differential effects of therapeutic interventions on these two arrhythmogenic periods and in the study of potential mechanisms for the spontaneous resolution of ventricular ectopy and risk of sudden death.

Animals↗
PubMed2003

Comprehensive congenic coverage revealing multiple blood pressure quantitative trait loci on Dahl rat chromosome 10.

Chromosome mapping based on congenic strains can restrict quantitative trait loci (QTLs) for blood pressure (BP) into small intervals that are otherwise indistinguishable in linkage analysis. Also, congenic strains can be created to test a candidate gene to be a BP QTL. Taking full advantage of these features, we produced 10 congenic strains by replacing various segments of chromosome (Chr) 10 of the Dahl salt-sensitive (DSS) rat with those of the Lewis (LEW) rat. These strains were made to systematically cover an entire section of Chr 10. Three of the strains were designed to narrow the intervals that harbor previously mapped QTL1 and QTL2. Two of the strains were designed for the express purpose of testing the QTL candidacy of loci for inducible nitric oxide synthase (Nos2) and angiotensin-converting enzyme (Ace) genes. BPs of these strains were measured by telemetry and compared with those of the DSS rat. Consequently, QTL1 and QTL2 were narrowed to segments of 53.5 and 100.4 centiRays, respectively. A new QTL, QTL3, was found between QTL1 and QTL2. Both Nos2 and Ace have been disqualified as QTLs in the DSS and LEW comparison. Therefore, there are no obvious candidate genes in the segments that harbor these 3 QTLs, which represent genes previously not thought to be involved in BP regulation. These QTLs will likely have an influence on studies of human hypertension because of their homology with the human CHR 17 region in which QTLs for BP have been found.

Animals↗
PubMed2004

Clonidine improves spontaneous baroreflex sensitivity in conscious mice through parasympathetic activation.

Alpha-2 adrenoceptors are important in baroreflex regulation. We tested the impact of alpha-2 adrenoceptors on heart rate variability (HRV) and spontaneous baroreflex sensitivity (BRS) in conscious mice with telemetry (TA11PA-C20). Baseline beat-to-beat measurements (2 hours between 8:00 am to 12:00 pm) were compared with measurements after intraperitoneal alpha-2 adrenoceptor blockade (yohimbine 2 mg/kg) and alpha-2 adrenoceptor stimulation (clonidine 1, 10, and 50 mg/kg). Blood pressure (BP) was 128+/-6/87+/-6 mm Hg and heart rate (HR) was 548+/-18 bpm at baseline. BRS, calculated with the cross-spectral method, was 1.2+/-0.1 ms/mm Hg at baseline. BP increased 20+/-2/13+/-2 mm Hg with yohimbine. HR increased by 158+/-23 bpm. BRS did not change. BP decreased 16+/-7/5+/-4 mm Hg with 1 mg/kg of clonidine and did not change with a higher dose. HR decreased with clonidine (176+/-28, 351+/-21, 310+/-29 bpm during 1, 10, and 50 mg/kg of clonidine, P<0.01). HRV (total power=4629+/-465, 7002+/-440, and 6452+/-341 ms2 during 1, 10, and 50 mg/kg of clonidine, P<0.01) and BRS were profoundly increased with clonidine (14+/-1, 13+/-1, and 10+/-1 ms/mm Hg, P<0.01). The effects of clonidine were abolished with atropine (2 mg/kg plus 50 mg/kg of clonidine) but not with metoprolol (4 mg/kg plus 50 mg/kg of clonidine). These data suggest that alpha-2 adrenoceptors exert a regulatory influence on autonomic cardiovascular control and baroreflex function. The effect of clonidine on baroreflex HR regulation is mediated by the parasympathetic nervous system. These murine data fit well with recent human observations regarding parasympathetic activation via alpha-2 adrenoceptors.

Adrenergic alpha-2 Receptor Agonists↗