Biomedical subjects

Mesut Sahin

Publications and source records attributed to Mesut Sahin.

8 recordsLinked to original sources

PubMed2006

Organization in the descending tracts of the dorsolateral funiculus in the cat.

Organization of the fibers in the descending tracts of the dorsolateral funiculus of the cervical spinal cord was investigated in cats. The spinal cord was penetrated with microelectrodes at 400 mum intervals in the medio-lateral direction at the c5/c6 and c6/c7 segmental borders. Silicon substrate microelectrodes with a linear arrangement of activated iridium contacts were used. The stimulus consisted of a 20 ms train of charge balanced biphasic current pulses at 330 Hz. The evoked activities from selected forelimb muscles were acquired into computer. Only the data points with an activation threshold of less than 35 muA were considered in the analysis. Muscle contractions were mostly in the form of short twitches. In both spinal segments, an area of high threshold was found in the middle of the dorsolateral funiculus. Majority of the muscles studied had a dorsal or ventral concentration of activation points. The distal muscles were mostly activated in the ventro-lateral aspect of the funiculus, while the elbow muscle maps spread to both dorsal and ventral sides. These results show a functional organization in both cervical segments studied, with overlapping regions between the areas dedicated for each forelimb muscle.

Animals↗

PubMed2006

Extraction of motor activity from the cervical spinal cord of behaving rats.

Injury at the cervical region of the spinal cord results in the loss of the skeletal muscle control from below the shoulders and hence causes quadriplegia. The brain-computer interface technique is one way of generating a substitute for the lost command signals in these severely paralyzed individuals using the neural signals from the brain. In this study, we are investigating the feasibility of an alternative method where the volitional signals are extracted from the cervical spinal cord above the point of injury. A microelectrode array assembly was implanted chronically at the C5-C6 level of the spinal cord in rats. Neural recordings were made during the face cleaning behavior with forelimbs as this task involves cyclic forelimb movements and does not require any training. The correlation between the volitional motor signals and the elbow movements was studied. Linear regression technique was used to reconstruct the arm movement from the rectified-integrated version of the principal neural components. The results of this study demonstrate the feasibility of extracting the motor signals from the cervical spinal cord and using them for reconstruction of the elbow movements.

Animals↗

PubMed2006

Performing only one cardiovascular reflex test has a high positive predictive value for diagnosing autonomic neuropathy in patients with chronic renal failure on hemodialysis.

BACKGROUND: Autonomic neuropathy is an important cause of morbidity and mortality in patients with chronic renal failure (CRF) on hemodialysis. Generally, cardiovascular reflex tests are used to determine autonomic neuropathy. Our purpose in this study was to determine the frequency of autonomic neuropathy in patients with CRF on hemodialysis by using cardiovascular reflex tests and compare the sensitivity of each test. METHODS: The authors performed five tests: heart rate response to the Valsalva maneuver, heart rate variation during deep breathing, heart rate response to standing up, blood pressure response to standing up, and blood pressure response to hand grip exercise in order to determine autonomic neuropathy. Each test subject was evaluated as normal, borderline, and abnormal and scored as 0, 1, and 2, respectively. Subjects with a total score > or = 5 were considered to have autonomic neuropathy. Forty subjects with CRF on hemodialysis were included in this study. None of the subjects had diabetes mellitus or any other etiology that could cause autonomic neuropathy. RESULTS: Thirty-five of 40 subjects (87.5%) had abnormal autonomic tests. In 35 subjects, the relationship between autonomic neuropathy and biochemical parameters, effects of treatment with vitamin D and erythropoietin, and urea reduction rate were studied. No relationship was found between autonomic neuropathy and age, time on hemodialysis, urea reduction rate, albumin, ferritin, calcium, inorganic phosphorus, intact parathyroid hormone, hemoglobin levels, and treatment with vitamin D and erythropoietin. The abnormal test results were as follows: 20 subjects (50%) in the heart rate response to the Valsalva Maneuver, 31 (77.5%) in the heart rate variation during deep breathing, 28 (70%) in the heart rate response to standing up, 6 (15%) in the blood pressure response to standing up, and 31 subjects (77.5%) in the blood pressure response to hand grip exercise tests. Among these five tests, the two most abnormal tests were the heart rate variation during deep breathing and the blood pressure response to hand grip exercise. CONCLUSION: Patients with CRF on hemodialysis frequently have autonomic neuropathy. For the diagnosis and follow-up of patients, five cardiovascular autonomic reflex tests are generally used. In this study, it was determined that performing only one test instead of all five tests has a high sensitivity and is more practicable in terms of determining autonomic neuropathy.

Adult↗

PubMed2005

Separation of spinal cord motor signals using the FastICA method.

Evoked motor signals descending down the corticospinal tract can be recorded selectively with multi-contact electrodes from the spinal cord surface. This method of extracting motor signals from the spinal cord may provide a means of communication for people with spinal cord injury. The information rate obtained with such an interface will improve if the separation of neural channels can be increased. In this study, the feasibility of increasing the channel separation was investigated using the blind source separation (BSS) technique. Neural signals recorded with multi-contact surface electrodes were treated as a linear mixture of independent neural sources located inside the spinal cord. Principal component analysis (PCA) was applied to estimate the dimensionality of the raw signals, and then the fixed-point FastICA algorithm was used to separate the primary neural sources from the secondary (smaller) ones. In all trials but one, the separation between the neural channels has increased by eliminating the secondary sources. These results suggest that the information rate of a spinal cord interface can be improved by separating the neural recordings into their independent components and selecting the ones with the largest distance between them. Comparison of independent component analysis (ICA) and PCA reveals that ICA performs better in this application.

Action Potentials↗

PubMed2005

Dilation of the oropharynx via selective stimulation of the hypoglossal nerve.

The functional effects of selective hypoglossal nerve (HG) stimulation with a multi-contact peripheral nerve electrode were assessed using images of the upper airways and the tongue in anesthetized beagles. A biphasic pulse train of 50 Hz frequency and 2 s duration was applied through each one of the tripolar contact sets of the nerve electrode while the pharyngeal images were acquired into a computer. The stimulation current was limited to 20% above the activation threshold for maximum selectivity. The images showed that various contact sets could generate several different activation patterns of the tongue muscles resulting in medial and/or lateral dilation and closing of the airways at the tongue root. Some of these patterns translated into an increase in the oropharyngeal size while others did not have any effect. The pharyngeal sizes were not statistically different during stimulation either between the two different positions of the head (30 degrees and 60 degrees), or when the lateral contacts were compared with the medial ones. The contacts that had the least effect generated an average of 53 +/- 15% pharyngeal dilation relative to the best contacts, indicating that the results are marginally sensitive to the contact position around the HG nerve trunk. These results suggest that selective HG nerve stimulation can be a useful technique to produce multiple tongue activation patterns that can dilate the pharynx. This may in turn increase the size of the patient population who can benefit from HG nerve stimulation as a treatment method for obstructive sleep apnea.

Animals↗

PubMed2005

A low-noise preamplifier for nerve cuff electrodes.

A single-stage, low-noise preamplifier is designed using the concept of noise matching for recordings of neural signal with cuff electrodes. The signal-to-noise ratio is approximately 1.6 times higher than that of a low-noise integrated amplifier (AMP-01) for a cuff impedance of 1.5 komega. The bandwidth is 230 Hz-8.25 kHz (Rs=2 komega), and the common-mode-rejection-ratio is 91.2 dB at 1 kHz.

Action Potentials↗

PubMed2004

Selective stimulation of the canine hypoglossal nerve using a multi-contact cuff electrode.

Electrical activation of the tongue protrusor muscle has been demonstrated as an effective technique for alleviating upper airway (UAW) obstructions and is considered a potential treatment for obstructive sleep apnea (OSA). Recent studies, however, have shown marked improvements in UAW patency by coactivating the tongue protrudor and retractor muscles. As such, selective stimulation of the hypoglossal nerve (XII) using a single implantable device presents an attractive approach for treating OSA. In order to demonstrate the feasibility of such a device, the maximum achievable stimulation selectivity of the Flat Interface Nerve Electrode (FINE) was investigated. The XII nerve of beagles was stimulated with an acutely implanted FINE, while the corresponding neural and muscular responses were recorded and analyzed. The overall performance of the FINE, as depicted by the average of the maximum target-specific selectivity values, S(i), confirmed that high degrees of selectivity can be achieved at both the fascicular and muscular levels: 0.93 +/- 0.03 (n = 5) and 0.88 +/- 0.03 (n = 4), respectively. The results of this study demonstrate the feasibility of the FINE for selective stimulation of the XII nerve branches and the innervated tongue muscles.

Airway Obstruction↗

PubMed2004

Information capacity of the corticospinal tract recordings as a neural interface.

Recording the motor output of the central nervous system from the cervical spinal cord was investigated as a method of generating voluntary command signals, potentially to be used in quadriplegic individuals. Corticospinal volleys evoked by motor cortex stimulation were recorded from the spinal cord surface with multicontact electrodes in anesthetized cats. The multicontact recordings were analyzed for their information-carrying capacity as a neural interface. Neural signals resulting from the stimulation of various points in the motor cortex were considered as symbols of an alphabet that were sent through a discrete information channel. The information capacity of this channel at the thermal noise level of the electrode contacts was calculated. The maximum information rate was 1.57 bits in a trial for a 4-symbol alphabet. The background noise that reduces the information rate to 50% of its maximum theoretical value was defined as the half-bitrate-noise-tolerance (HBR-NoiseTol) and used as a measure of symbol distinguishability. The HBR-NoiseTol for all trials on average was 24 +/- 12%, 18 +/- 10%, and 15 +/- 9% for interfaces with 2-, 3-, and 4-symbol alphabets (n = 11 trials). The average peak-to-peak amplitude of the neural volleys was 13.5 +/- 6.7 microV (n = 11). These results suggest that the corticospinal signals can be recorded with spatial selectivity from the spinal cord surface and thus warrant further investigation of their potential use for a spinal cord-computer interface.

Action Potentials↗