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Results for “augmented feedback”

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At least 163 records · Page 9Linked to original sources

PubMed2003

Development of a gait re-education system in incomplete spinal cord injury.

OBJECTIVE: The aim of the paper is to present the development of a system for swing phase restoration in patients with incomplete spinal cord injury. METHODS: The functional electrical stimulation based gait re-education system comprises a sensory system, a system providing cognitive feedback and a motor augmentation system facilitating and correcting the movement of the swinging extremity. Mathematical algorithms estimate swing quality and classify the swing phase of walking into 3 levels, termed cognitive feedback, which is provided to the patient as an auditory signal. A single-channel peroneal functional electrical stimulation was applied as a motor augmentation system to provide the patient with the motor assistance required. The important novelty of the proposed system is that motor assistance is provided only at the level that enables the patient to perform a good swing. RESULTS: The developed system was tested in a patient with incomplete spinal cord injury, with C4-5 lesion, whilst walking on a treadmill. The results show that the automated sensory-driven functional electrical stimulation augmentation system, providing only the minimal assistance required based on the subject's performance, is a viable approach that successfully releases a therapist from the task of delivering properly timed stimulation of adequate intensity in assisting the swing phase of walking.

Adult↗

PubMed2004

Labor augmentation in an Egyptian teaching hospital.

OBJECTIVES: The study documented facility-based obstetric practices for normal labor in Egypt for the first time, to determine their relationship to evidence-based medicine. This paper describes the labor augmentation pattern observed. METHODS: 176 cases of normal labor were observed by medically-trained observers using a checklist. Ward activities were also documented. Observed women were interviewed postpartum and all findings were shared with the providers for their feedback. RESULTS: Labor was augmented in 91% (165) of the labors observed; this was inappropriate for 93% or 154 women. Reasons for inappropriateness were: oxytocin ordered at the first vaginal exam (41%); in spite of intact membranes (36%), at the time of membrane rupture (42%), in spite of good progress (24%), or a combination of these. The monitoring of oxytocin-receiving women and their babies was inadequate. CONCLUSIONS: Labor augmentation and monitoring deviated from evidence-based guidelines. Obstacles to implementing protocols need to be explored.

Egypt↗

PubMed2004

Evaluation of a prototype Minified Augmented-View device for patients with impaired night vision.

An evaluation was carried out of the first prototype (LV-3) of a new night vision device, which incorporates visual field expansion through minification (Minified Augmented-View), to provide feedback for continuing development. Six subjects with night blindness completed visual function measurements and indoor mobility assessments without a device, with the LV-3 and with a commercially available comparison device (the Multi-Vision) at light levels representative of well lit and poorly lit streets. Device performance and potential benefits in real-world situations were evaluated at four outdoor locations (well lit to very dark). Results indicate that the see-through nature and spectacle-frame mounting of the LV-3 address some of the cosmetic and ergonomic disadvantages of currently available devices; however insufficient light sensitivity of the prototype camera limited LV-3 performance. With improved camera sensitivity and full implementation of the Minified-Contours Augmented-View concept in the next prototype, patients might be able to make better use of the novel field expansion and vision multiplexing features to aid outdoor night mobility.

Adult↗

PubMed2004

A model of cerebellum stabilized and scheduled hybrid long-loop control of upright balance.

A recurrent integrator proportional integral derivative (PID) model that has been used to account for cerebrocerebellar stabilization and scaling of transcortical proprioceptive feedback in the control of horizontal planar arm movements has been augmented with long-loop force feedback and gainscheduling to describe the control of human upright balance. The cerebellar component of the controller is represented by two sets of gains that each provide linear scaling of same-joint and interjoint long-loop stretch responses between ankle, knee, and hip. The cerebral component of the model includes a single set of same-joint linear force feedback gains. Responses to platform translations of a three-segment body model operating under this hybrid proprioception and force-based long-loop control were simulated. With low-velocity platform disturbances, "ankle-strategy"-type postural recovery kinematics and electromyogram (EMG) patterns were generated using the first set of cerebeller control gains. With faster disturbances, balance was maintained by including the second set of gains cerebellar control gains that yielded "mixed ankle-hip strategy"-type kinematics and EMG patterns. The addition of small amounts of simulated muscular coactivation improved the fit to certain human datasets. It is proposed that the cerebellum switches control gainsets as a function of sensed body kinematic state. Reduction of cerebellar gains with a compensatory increase in muscular stiffness yielded posture recovery with abnormal motions consistent with those found in cerebellar disease. The model demonstrates that stabilized hybrid long-loop feedback with scheduling of linear gains may afford realistic balance control in the absence of explicit internal dynamics models and suggests that the cerebellum and cerebral cortex may contribute to balance control by such a mechanism.

Biomechanical Phenomena↗

PubMed1979

Tubuloglomerular feedback and single nephron function after converting enzyme inhibition in the rat.

Experiments were done in normal rats to assess kidney, single nephron, and tubuloglomerular feedback responses during renin-angiotensin blockade with the converting enzyme inhibitor (CEI) SQ 20881 (E. R. Squibb & Sons, Princeton, N. Y.) (3 mg/kg, per h). Converting enzyme inhibition was documented by complete blockade of vascular responses to infusions of angiotensin I (600 ng/kg). Control plasma renin activity was 12.5+/-2.7 ng angiotensin I/ml per h (mean+/-SEM) and increased sevenfold with CEI (n = 7). There were parallel increases in glomerular filtration rate from 1.08+/-0.05 to 1.26+/-0.05 ml/min and renal blood flow from 6.7+/-0.4 to 7.5+/-0.5 ml/min. During CEI infusion absolute and fractional sodium excretion were increased 10-fold. Proximal tubule and peritubular capillary pressures were unchanged. Single nephron glomerular filtration rate (SNGFR) was measured from both proximal and distal tubule collections; SNGFR based only on distal collections was significantly increased by CEI. A significant difference was observed between SNGFR values measured from proximal and distal tubule sites (6.0+/-1.6 nl/min) and this difference remained unchanged after CEI administration. Slight decreases in fractional absorption were suggested at micropuncture sites beyond the late proximal tubule, whereas early distal tubule flow rate was augmented by CEI. Tubuloglomerular feedback activity was assessed by measuring changes in proximal tubule stop-flow pressure (SFP) or SNGFR in response to alterations in orthograde microperfusion rate from late proximal tubule sites. During control periods, SFP was decreased 11.2+/-0.4 mm Hg when the perfusion rate was increased to 40 nl/min; during infusion of CEI, the same increase in perfusion rate resulted in a SFP decrement of 6.7+/-0.5 mm Hg (P<.001). When late proximal tubule perfusion rate was increased from 0 to 30 nl/min, SNGFR was decreased by 15.0+/-1.2 nl/min during control conditions, and by 11.3+/-1.3 nl/min during CEI infusion. Attenuation of feedback responsiveness during CEI was also observed at lower perfusion rates with both techniques. These results indicate that blockade of the renin-angiotensin system with CEI reduces the activity of the tubuloglomerular feedback mechanism which may mediate the observed renal vasodilation.

Angiotensin I↗

PubMed1993

Effect of human prolactin administration on gonadotropin and thyrotropin secretion in normal men.

To test the hypothesis that PRL is able to feedback negatively on its own secretion (short-loop feedback) in humans via augmentation of the turnover of tuberoinfundibular dopamine (TIDA), the effects of the administration of purified hPRL on endogenous LH, FSH and TSH were assessed. Purified hPRL, given in an i.v. loading dose of 90 micrograms followed by a continuous infusion of 1.39 micrograms/min to 4 normal male volunteers resulted in a tripling of PRL levels (10.5 +/- 1.9 micrograms/L increasing to 30.9 +/- 3.6 micrograms/L) at the end of 90 min. There were no changes in LH, FSH or TSH levels, however, during or following the infusion. Purified hPRL was also given in 1 and 8 micrograms/kg doses IM to 5 normal male volunteers. Although PRL levels did not rise significantly with the 1 microgram/kg dose, levels almost doubled with the 8 micrograms/kg dose (9.5 +/- 2.2 micrograms/L increasing to 17.4 +/- 1.5 micrograms/L). Again, LH, FSH and TSH levels did not change significantly over the three hour period of sampling with either dose. In conclusion, in this study we found that a 2-3 fold increase of circulating PRL levels maintained for 1.5-3 h exerted no apparent effects on the secretion of endogenous LH, FSH and TSH. This study provides direct evidence against the existence of a short-loop feedback occurring via TIDA activation in humans over this time interval but does not rule out the possibility that such feedback may occur with more prolonged states of hyperprolactinemia or via other mechanisms or the possibility of an effect on the hypothalamic pulse generator.

Adult↗

PubMed1976

Feedback of true heart rate during exposure in vivo. Partial replication with methodological improvement.

Ten specific phobics improved during a mean of two sessions of experimental treatment by exposure in vivo in a balanced design. Short-term results replicated those of a previous study that self-control of heart rate with the aid of biofeedback significantly reduced heart rate during treatment, but this did not hasten reduction of subjective anxiety, nor of respiratory rate or skin conductance responses. An hour's pretreatment training in self-control of heart rate with the aid of feedback did not enhance the effect. Mere instructions to lower heart rate without feedback had a significant effect during treatment, but the addition of heart rate feedback to instructions significantly augmented the decline in heart rate.

Adolescent↗

PubMed2002

Group V phospholipase A2 induces leukotriene biosynthesis in human neutrophils through the activation of group IVA phospholipase A2.

We reported previously that exogenously added human group V phospholipase A(2) (hVPLA(2)) could elicit leukotriene B(4) (LTB(4)) biosynthesis in human neutrophils (Han, S. K., Kim, K. P., Koduri, R., Bittova, L., Munoz, N. M., Leff, A. R., Wilton, D. C., Gelb, M. H., and Cho, W. (1999) J. Biol. Chem. 274, 11881-11888). To determine the mechanism of the hVPLA(2)-induced LTB(4) biosynthesis in neutrophils, we thoroughly examined the effects of hVPLA(2) and their lipid products on the activity of group IVA cytosolic PLA(2) (cPLA(2)) and LTB(4) biosynthesis under different conditions. As low as 1 nm exogenous hVPLA(2) was able to induce the release of arachidonic acid (AA) and LTB(4). Typically, AA and LTB(4) were released in two phases, which were synchronized with a rise in intracellular calcium concentration ([Ca(2+)](i)) near the perinuclear region and cPLA(2) phosphorylation. A cellular PLA(2) assay showed that hVPLA(2) acted primarily on the outer plasma membrane, liberating fatty acids and lysophosphatidylcholine (lyso-PC), whereas cPLA(2) acted on the perinuclear membrane. Lyso-PC and polyunsaturated fatty acids including AA activated cPLA(2) and 5-lipoxygenase by increasing [Ca(2+)](i) and inducing cPLA(2) phosphorylation, which then led to LTB(4) biosynthesis. The delayed phase was triggered by the binding of secreted LTB(4) to the cell surface LTB(4) receptor, which resulted in a rise in [Ca(2+)](i) and cPLA(2) phosphorylation through the activation of mitogen-activated protein kinase, extracellular signal-regulated kinase 1/2. These results indicate that a main role of exogenous hVPLA(2) in neutrophil activation and LTB(4) biosynthesis is to activate cPLA(2) and 5-lipoxygenase primarily by liberating from the outer plasma membrane lyso-PC that induces [Ca(2+)](i) increase and cPLA(2) phosphorylation and that hVPLA(2)-induced LTB(4) production is augmented by the positive feedback activation of cPLA(2) by LTB(4).

Calcium↗

PubMed1980

Short-term rhythms in the performance of a simple motor task.

Following the discovery of short-term rhythmicities In physiological processes, a study was conducted to investigate existence of similar rhythms in motor behavior. Two groups of eight subjects each were tested every 10 or 20 min respectively in the performance of a linear positioning task with augmented auditory and proprioceptive feedback, for 10 consecutive hr. Each testing sample consisted of five trials with knowledge of results (KR), followed by five trials without knowledge of results (NKR). Between tests subjects drank constant amounts of fluids and urine flow was measured. Movement accuracy in the NKR condition varied rhythmically with periodicities centered at 100 min/ cycle. No comparable rhythms were found in the KR trials or in movement time. Urine flow also varied rhythmically with similar dominant periodicities, but these rhythms were unrelated to rhythms in error. The findings are interpreted to indicate rhythmic modulations in the efficiency of short-term storage and information processing from movement execution. Significance of these results to current views of motor control is discussed.

Journal Article↗

PubMed2000

Spinal cord neuromodulation for voiding dysfunction.

A clear understanding of the pathophysiology and neurophysiologic effect of neuromodulation is lacking. Apparently there is a balance of efferent and afferent negative and positive feedback loops that are augmented by external electrical stimulation. This effect may be dramatic even in patients who have have not benefited from virtually every other form of treatment.

Electric Stimulation Therapy↗

PubMed1981

Paradoxical elevation of growth hormone by intraventricular somatostatin: possible ultrashort-loop feedback.

Somatostatin, the growth hormone-inhibiting factor, when microinjected into the third ventricle of the rat brain, paradoxically induced the release of growth hormone. A pituitary site of action having been ruled out, this result supports the concept that exogenous somatostatin within the hypothalamus acts either to suppress the release of somatostatin from somatostatin-containing neurons, possibly via an ultrashort-loop feedback mechanism, or to augment release of hypothalamic growth hormone-releasing factor, thereby inducing a release of growth hormone. Injection of somatostatin into the third ventricle also decreased plasma concentrations of luteinizing hormone, follicle-stimulating hormone, and thyroid-stimulating hormone, probably by inhibiting the release of luteinizing hormone-releasing factor and thyrotropin-releasing factor.

Animals↗

PubMed2000

Angiotensinogen concentrations and renin clearance : implications for blood pressure regulation.

Renin (REN) requires seconds to convert angiotensinogen (AGT) to angiotensin I. We tested the hypothesis that this long catalytic cycle might indicate an influence of AGT concentrations on REN clearance. We studied 2 transgenic rat (TGR) strains for human (h) AGT; one strain has hAGT values approximately 7-fold higher than the other (68+/-18 versus 10+/-4 microg angiotensin I/mL). hREN (30 000 pg) was bolus-infused into both lines and into nontransgenic controls. The terminal half-life (T1/2beta) was increased (130 versus 82 minutes) and the metabolic clearance rate (MCR) was decreased (0.83+/-0.29 versus 2.2+/-0.66 microL. min(-1). g(-1)) in the high hAGT strain compared with the low hAGT strain. The difference was not related to volume of distribution at steady state. Infused hREN blocked with remikiren resulted in T1/2beta and MCR values that were not different from control values. Infused unblocked and blocked radiolabeled hREN was distributed similarly in the hAGT TGR strains. Infused mouse REN, which cannot convert hAGT, had similar T1/2beta and MCR values in hAGT TGR. Measuring REN with direct radioimmunoassay or by enzyme kinetic assay gave similar results. We next crossed homozygous hAGT TGR from both strains with homozygous hREN TGR. Heterozygous offspring from the low hAGT TGR strain had plasma REN activity, hREN concentration, and rat AGT values that were no different from those of their parents. However, TGR offspring with high hAGT values had massively elevated plasma REN activity and hREN concentration as well as elevated blood pressure, even though both the hREN and rREN genes are downregulated. We conclude that increased AGT concentrations decrease REN MCR and increase REN T1/2beta. The REN-AGT complex may stabilize plasma REN concentration and regulate plasma REN activity independent of renal REN secretion and angiotensin II-mediated feedback. These effects could augment angiotensin I generation and influence blood pressure. The notion that AGT is merely a passive substrate reservoir for REN should be revised.

Angiotensin I↗

PubMed1989

Amplification of uteroglobin secretion by alternating prolactin-progesterone administration.

Long-term ovariectomized rabbits were given injections of progesterone and prolactin in an alternating sequence (progesterone for 5 days, prolactin for 4 days and progesterone for 5 days) to test the hypothesis that each of these hormones acts to increase the other's receptor, resulting in a positive feedback process whereby prolactin augments the progesterone-dependent increase in the mRNA for the uterine protein, uteroglobin. The results of this study support the hypothesis, in that the experimental rabbits produced exceptionally large concentrations of uteroglobin.

Animals↗

PubMed2001

Secretory process regularity monitors neuroendocrine feedback and feedforward signaling strength in humans.

The present experiments examine the neuroregulatory hypothesis that the degree of sample-by-sample regularity of hormone output by an interlinked hypothalamopituitary target-organ system monitors the strength of feedback and/or feedforward signaling. To test this postulate and assess its generality, we implemented a total of nine thematically complementary perturbation experiments. In particular, we altered feedback or feedforward signaling selectively in two distinct neuroendocrine systems; namely, the growth hormone (GH) insulin-like growth factor type I (IGF-I) and the luteinizing hormone-testosterone axes. Four experimental paradigms comprised preferential reduction vs. enhancement of IGF-I or testosterone feedback signal strength; and, conversely, five others entailed selective attenuation vs. augmentation of GH-releasing hormone and gonadotropin-releasing hormone feedforward signal intensity. In these independent interventions, quantitation of subordinate (nonpulsatile) secretory pattern reproducibility via the approximate entropy statistic unmasked salient changes (P values typically <10(-3)) in the conditional regularity of serial hormone output with high consistency (96-100%). In particular, approximate entropy quantified degradation of secretory subpattern orderliness under either muted feedback restraint or heightened feedforward drive. Assuming valid interpretation of the biological constraints imposed, these experimental observations coincide with earlier reductionist mathematical predictions, wherein increased irregularity of coupled parameter output mirrors attenuated feedback and/or augmented feedforward coupling within an integrative system.

Fasting↗

PubMed2002

Success and failure in teaching the [r]-[l] contrast to Japanese adults: tests of a Hebbian model of plasticity and stabilization in spoken language perception.

A Hebbian model of learning predicts that adults may be able to acquire a nonnative speech contrast if they are trained with stimuli that are exaggerated to make them perceptually distinct. To test these ideas, we asked Japanese adults to identify contrasting [r]-[l] stimuli (e.g., rock-lock) in two training conditions. In the adaptive condition, the [r]-[l] contrast was exaggerated at first and then adjusted to maintain accurate identification. In the fixed condition, a fixed pair of stimuli were used that were distinguishable by native English speakers but difficult for the Japanese learners to discriminate. To examine whether feedback contributes to learning, we ran separate groups with and without feedback in the fixed and the adaptive conditions. Without feedback, 3 days of adaptive training produced substantial improvements, but 3 days of fixed training produced no benefit relative to control, consistent with the Hebbian account. With feedback, both fixed and adaptive training led to robust improvements, and the benefit of training transferred to a second continuum (e.g., road-load). The results are consistent with Hebbian models that are augmented to be sensitive to feedback.

Adult↗

PubMed1995

Nitric oxide as a retrograde messenger in the nucleus tractus solitarii of rats during hypoxia.

1. We examined the role of nitric oxide (NO) in respiratory regulation in the nucleus tractus solitarii (NTS), where L-glutamate release associated with peripheral chemoreceptor activation modulates the hypoxic ventilatory response. 2. Experiments were performed in unanaesthetized freely moving rats. First, the effects on the hypoxic ventilatory response of sodium nitroprusside (SNP, a NO donor) or NG-monomethyl-L-arginine (L-NMMA, a NO synthase inhibitor), microinjected into the NTS, were investigated. Second, using in vivo microdialysis, changes in extracellular L-glutamate during hypoxia were examined in the presence of L-NMMA. Third, the effect of L-NMMA on ventilatory augmentation by exogenous L-glutamate was examined. Furthermore, we measured extracellular L-citrulline concentration changes during hypoxia in the NTS to assess NO formation indirectly and also examined the effect of MK-801 (an NMDA receptor antagonist) on L-citrulline levels during hypoxia. 3. SNP increased ventilation during both normoxia and hypoxia. L-NMMA did not alter ventilation or L-glutamate levels during normoxia but significantly attenuated the hypoxic ventilatory response and the increase in L-glutamate during hypoxia. The inhibition by L-NMMA was blocked by L-arginine. The ventilatory augmentation by exogenous L-glutamate was attenuated by L-NMMA. L-Citrulline increased during hypoxia, and this increase was inhibited by MK-801. 4. We provide the first in vivo evidence that, in the NTS, NO works as a retrograde messenger in an L-glutamate-releasing positive feedback system contributing to the augmentation of ventilation during hypoxia.

Animals↗

PubMed1987

The role of brain peptides in neuroimmunomodulation.

Since neuroimmunomodulation is brought about in part, at least, by secretion of pituitary hormones involved in stress and immune responses, we review briefly the hypothalamic control of the release of ACTH, growth hormone, and prolactin. The release of ACTH is controlled particularly by corticotropin-releasing factor (CRF), but vasopressin has intrinsic releasing activity and potentiates the action of CRF at both hypothalamic and pituitary levels. Oxytocin may even potentiate the action of CRF, but has little, if any, ACTH-releasing activity by itself. In addition, epinephrine may augment responses to the CRFs. In contrast, growth hormone is under dual control by growth-hormone-releasing factor (GRF) and somatostatin, and prolactin is under multifactorial control by a series of inhibitors and stimulators. Dopamine is accepted as a physiological prolactin-inhibiting factor (PIF), but probably GABA and possibly acetylcholine as well are PIFs. There is good evidence for a peptide PIF as well. There are a number of prolactin-releasing factors (PRFs) which include oxytocin, vasoactive intestinal polypeptide, PHI and TRH. Several other peptides can also release prolactin, including angiotensin II. In response to stress there is a complex interaction of peptides intrahypothalamically. CRF augments its own release by an ultra short-loop positive feedback, and there is negative ultra short-loop feedback of GRF and somatostatin. Vasopressin appears to augment CRF release as well as to act directly on the pituitary, and there are complex interactions of various peptides to influence prolactin and GH release.

Adjuvants, Immunologic↗

PubMed2002

Nitric oxide augments voltage-gated P/Q-type Ca(2+) channels constituting a putative positive feedback loop.

P/Q-type Ca(2+) channels, which are postulated to play major roles in synaptic transmission, are regulated in a variety of ways. Ca(2+) currents through P/Q-type Ca(2+) channels (Ca(v)2.1/beta(1a)/alpha(2)delta) heterologously expressed in mammalian cells were recorded using the whole-cell patch clamp method. The oxidant H(2)O(2) increased the current amplitude and the effect was reversed by the reducing agent dithiothreitol (DTT). The stimulatory effect of H(2)O(2) on the Ca(2+) current was mimicked by the NO donors, SNAP, and diethylamine NONOate, and reversed by the reducing agent DTT. The presence of a soluble guanylate cyclase inhibitor did not abolish the ability of SNAP to increase the Ca(2+) current. Adenovirus-mediated overexpression of nitric oxide synthase in combination with application of the Ca(2+) ionophore A23187 also increased the Ca(2+) current amplitude and the effect was again reversed by DTT. The NOS inhibitor L-NAME abolished the stimulatory effect of A23187, and A23187 did not change the Ca(2+) currents in the cells treated with control adenovirus particles. The time course of the decline of the Ca(2+) current, but not of the Ba(2+) current, in response to repeated depolarization was markedly slowed by adenovirus-mediated overexpression of nitric oxide synthase. The results demonstrate that nitric oxide enhances the channel activity by promoting oxidation and suggest that Ca(2+), nitric oxide synthase, and nitric oxide could constitute a positive feedback loop for regulation of voltage-gated P/Q-type Ca(2+) channels.

Adenoviridae↗