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S Calvin

Publications and source records attributed to S Calvin.

18 recordsLinked to original sources
PubMed2005

Limiting the recruitment of degrees of freedom reduces the stability of perception-action patterns.

The goal of the present study was to examine how recruiting/suppressing degrees of freedom affects the (differential) stability of two rhythmic perception-action patterns. In particular, participants synchronized either adduction-on-the-beat or abduction-on-the-beat movements of the right index finger with an auditory metronome. The stability of both patterns as performed in the horizontal plane was predicted to depend on the utilization, or recruitment, of the vertical plane of motion. Movements of the index finger were either free or physically restricted to the horizontal plane. The results showed that in the free condition, the vertical plane was recruited more in the more stable pattern (abduction-on-the-beat) than in the less stable pattern (adduction-on-the-beat). In the constrained condition, abduction-on-the-beat pattern was destabilized, whereas the stability of the adduction-on-the-beat pattern was preserved. These results suggest that the recruitment of the vertical plane of motion in the abduction-on-the-beat movements brought about an increase in the stability of this pattern. More generally, the trade-off between the stability of coordination patterns in the horizontal plane is based on a self-organizing process of recruitment in which neuromuscular factors are an intrinsic aspect.

Adult↗
PubMed2002

A dynamic pattern analysis of coordination between breathing and rhythmic arm movements in humans.

We investigated the behavioral dynamics of human breathing-wrist movement coordination in a 1:1 frequency locking task. A pronation-supination wrist movement and a short trial duration were chosen to limit both mechanical and metabolic constraints on the respiratory system. Subjects voluntarily controlled their breathing rhythm to follow the metronome. We found that pronation-expiration and pronation-inspiration patterns coexisted as the (sole) stable fixed-point attractors of the coordination system. The pronation-expiration pattern was more stable than the pronation-inspiration pattern. Depending on the oscillation frequency, this differential stability gave rise to both absolute and relative coordination. These results show that simple behavioral laws of coordination encapsulate neural coupling dynamics evidenced from experimental research in human beings and animals. They challenge the classical view that such a coupling is not present for all imposed movement frequencies. Rather, relative coordination emerges as a result of the modification of coupling strength with frequency. These results can be accommodated by the asymmetric version of the HKB model of coordination dynamics. Thus, our data suggest that the principles and models of coordination dynamics may be taken as a reference to study the coupling of the motor and physiological subsystems involved in breathing-movement coordination.

Arm↗
PubMed2001

Nonviral transfection of intact pancreatic islets.

Ex vivo gene transfer offers a potential means to introduce genes into cells, which may play an important role in preventing graft rejection and inducing graft tolerance. This study examined the efficiency and toxicity of several lipid-based transfection reagents (LipofectAMINE, DOTAP, and DOSPER) in intact pancreatic islets. Isolated islets were transfected with a pCMV-beta-galactosidase plasmid using several DNA/liposome ratios (1:12) of liposomes (3-72 microl) and DNA (3 and 6 microg). Transfection efficiency was quantified by microscopic evaluation of beta-galactosidase gene expression in whole intact islets. Functionality of the transfected islets was measured by insulin response to glucose solutions. All transfection reagents evaluated in this study transfected cells within the islets. As expected, untransfected controls and transfected islets with DNA alone did not express beta-gal. The highest transfection efficiency and functional viability were obtained following a 48-h incubation after exposure to the transfection mixtures as follows: 3 microl DNA and 18 microl DOTAP/ml (1:6 ratio), 6 microg DNA and 12 microl DOSPER/ml (1:2 ratio), or 6 microg DNA and 12 microl Lipofect-AMINE/ml (1:2 ratio). The highest rate of transfected cells per islet was obtained using DOTAP. In vitro functionality was not significantly different between DOTAP and nontreated controls. However, optimal transfection efficiency doses of LipofectAMINE and DOSPER significantly reduced the stimulated insulin response of the transfected islets (p < 0.05, ANOVA). The calculated stimulation index (SI) was 7.8+/-0.6 (mean +/- SEM) for DOTAP-transfected islets compared with 8.4+/-0.5 for nontransfected control islets (p = ns). The SI of DOSPER- and LipofectAMINE-transfected islets was significantly lower (6.1+/-0.5 and 3.4+/-0.5, respectively, p < 0.05). Lipid-based transfection using DOTAP at a DNA/lipid ratio of 1:6 provides an effective means of ex vivo gene delivery without compromising in vitro functionality of the transfected islets.

Animals↗
PubMed1999

Cortical event-related potentials show the structure of hypnotic suggestions is crucial.

Electroencephalographic cortical event-related potentials (ERPs) are affected by information processing strategies and are particularly appropriate for the examination of hypnotic alterations in perception. The effects of positive obstructive and negative obliterating instructions on visual and auditory P300 ERPs were tested. Twenty participants, stringently selected for hypnotizability, were requested to perform identical tasks during waking and alert hypnotic conditions. High hypnotizables showed greater ERP amplitudes while experiencing negative hallucinations and lower ERP amplitudes while experiencing positive obstructive hallucinations, in contrast to low hypnotizables and their own waking imagination-only conditions. The data show that when participants are carefully selected for hypnotizability and responses are time locked to events, rather robust physiological markers of hypnosis emerge. These reflect alterations in consciousness that correspond to participants' subjective experiences of perceptual alteration. Accounting for suggestion type reveals remarkable consistency of findings among dozens of researchers.

Cerebral Cortex↗
PubMed1991

Is pulsed Doppler velocimetry useful in the management of multiple-gestation pregnancies?

Few studies have addressed the significance of umbilical artery pulsed Doppler velocimetry in multiple gestation. Level II ultrasonography and pulsed Doppler studies were performed in 94 twin pairs and seven sets of triplets, which yielded data on 207 fetuses. A systolic/diastolic ratio was calculated for each fetus; abnormal pulsed Doppler velocimetry showed high correlation with adverse pregnancy events. Those with abnormal Doppler findings tended to be born 3 to 4 weeks earlier and to exhibit a greater number of stillbirths and structural malformations, as well as greater morbidity, when compared with fetuses without abnormal Doppler results. Fifteen of 17 infants with abnormal antenatal waveforms suffered serious morbidity. Seven were small for gestational age, and two were borderline for small for gestational age. An additional five infants with abnormal waveforms were appropriate for gestational age but were either recipient or donor in the twin transfusion syndrome. Eleven fetuses with this syndrome are described. Donor twins tended to be severely small for gestational age, with 7 of the 11 infants showing elevated systolic/diastolic ratios. Amniotic fluid volume tended to be diminished in the donor's sac but normal or increased in the recipient's sac. The observations in the study correlate with suspected physiologic changes of this syndrome. Because present findings suggest that fetuses with abnormal velocimetry suffer increased morbidity and mortality, a more rational method of management that uses Doppler data is suggested for multiple gestations.

Blood Circulation↗
PubMed1991

Characterization of ascites present at cesarean section.

Ascites has been reported at cesarean section delivery in pregnancies complicated by preeclampsia. The frequency and composition of peritoneal fluid collections in pregnancy have not previously been described. This descriptive study evaluated presence, composition, and characteristics of ascites present in 41 women undergoing cesarean delivery for a variety of indications. Twenty-six women had sufficient quantities of peritoneal fluid to be collected immediately after opening the parietal peritoneum. The protein content of the fluid was analyzed. The presence of fluid was not related to labor preceding delivery. All preeclamptic women in this study had fluid obtainable at cesarean section. Large volume ascites was noted in five preeclamptic women whose fluid had low total protein content, consistent with a transudate. Intrahepatic portal hypertension is one possible explanation of the large volume and low protein ascites in some preeclamptic patients. Ultrasonic measurements in preeclamptic patients and normotensive pregnant women showed uniform portal vein diameters and Doppler-derived portal vein flow velocities in all patients. The physiology of peritoneal fluid production in complicated and normal pregnancy remains unexplained.

Adult↗
PubMed1990

Plasma levels of fibronectin and prostacyclin metabolite in peripartum preeclamptic women.

Plasma fibronectin and prostacyclin levels have been reported to vary in preeclamptic women when compared with pregnant control women. Elevation of fibronectin and deficiency of prostacyclin have been postulated to be due to endothelial cell disruption or dysfunction. Eighteen preeclamptic women and 19 normal pregnant controls were evaluated for plasma levels of fibronectin and the prostacyclin metabolite 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). 6-keto-PGF1 alpha and fibronectin plasma levels in patients were significantly different from control patients, with preeclamptic patients exceeding control subjects. Five patients had serial samples of 6-keto-PGF1 alpha prior to, during, and after intravenous magnesium sulfate therapy and no consistent effect was noted. No correlation existed between fibronectin and 6-keto-PGF1 alpha levels or between either compound and platelet count or liver function tests. Despite an overall elevation of fibronectin in preeclamptic patients, two patients with the hemolysis, elevated liver tests, and low platelet count syndrome showed low normal fibronectin levels coinciding with thrombocytopenia, hemolysis, and liver dysfunction. The magnitude of fibronectin elevation may therefore not predict the severity of preeclampsia. The significance of these findings is discussed.

Adolescent↗
PubMed1988

Factor VIII: von Willebrand factor patterns in the plasma of patients with pre-eclampsia.

Elevation of the factor VIII protein to coagulant ratio previously has been reported to predict the severity of pre-eclampsia. Abnormal levels and patterns of factor VIII: von Willebrand factor (VIII/vWF) have been reported in thrombotic thrombocytopenia purpura (TTP). Severe pre-eclampsia shares many features with this syndrome. Nine primigravid patients with pre-eclampsia were evaluated by assays for factor VIII/vWF protein and coagulant activity and were compared to nine normal primigravid (controls). The patients and controls were indistinguishable by factor VIII antigen/coagulant activity ratios. Pre-eclamptic patients also had unremarkable factor VIII patterns on crossed immunoelectrophoresis. The evaluation of factor VIII/vWF multimeric patterns showed four patients with abnormal patterns in the pre-eclamptic patients and three abnormal patterns in the controls. These patterns were not analogous to the factor VIII abnormalities found in TTP.

Adolescent↗
PubMed1988

Oxygen saturation in the supine hypotensive syndrome.

This study used recently available, continuous noninvasive monitoring techniques to evaluate positional variations in pulse, blood pressure, and maternal oxygen saturation in 42 women undergoing fetal nonstress testing in the third trimester. Ten nonpregnant women were similarly evaluated with the automatic sphymomanometer and pulse oximeter. Six of 42 pregnant women (14.3%) developed the supine hypotensive syndrome (defined as a mean blood pressure decrease of 15 mmHg and a sustained increase in pulse of 20 beats per minute) when in the supine position. Nine of them (21.4%) met at least one of the criteria, but the majority (27 of 42, 64.3%) met neither criterion. None of the ten nonpregnant subjects had hypotension or tachycardia, although nine demonstrated blood pressure elevation after assuming the supine position. Significant oxygen desaturation did not occur in any patient, although three of six hypotensive patients had a transient 3-5% desaturation after supine rest. This study confirms that a significant percentage of patients in the third trimester are affected to some degree by supine hypotension. However, significant oxygen desaturation does not appear to occur.

Adolescent↗
PubMed1987

Tissue-specific expression of cell-surface Qa-2 antigen from a transfected Q7b gene of C57BL/10 mice.

We screened a cDNA library prepared from a BALB.B10 CTL clone that expresses Qa-2 antigen, and isolated four clones derived from Q7b, a Qa region gene of C57BL/10. One of these Q7b cDNAs and the Q7b chromosomal gene were subcloned into expression vectors and transfected into L cells and R1.1 thymoma cells. We found that the chromosomal Q7b gene expresses Qa-2 on the surface of R1.1 cells, but not on L cells while the Q7b cDNA expresses protein on the surface of both cell types. The levels of Qa-2 expression do not correlate with the total levels of Q7b mRNA in these transfectants. Our results suggest that the tissue-specific expression of Qa-2 may be controlled, in part, by mechanisms of alternate RNA splicing. By using hybrid gene constructs, we have mapped the tissue-specific element to the 3' part of the gene, downstream of a site near the middle of exon 4. The hybrid polypeptides differ significantly in their transmembrane and cytoplasmic regions. These portions of the protein also may play a role in the tissue-specific expression of Qa-2.

Animals↗
PubMed1986

Beta 2-microglobulin is not required for cell surface expression of the murine class I histocompatibility antigen H-2Db or of a truncated H-2Db.

beta 2-Microglobulin (beta 2m) has been thought essential for transport of all major histocompatibility complex class I antigens to the cell surface. Here, we show that the mouse class I antigen H-2Db is expressed at the cell surface even when there is no beta 2m present within the cell. This was established by transfecting the H-2Db gene into the R1E cell line, which lacks beta 2m. The conformation of the Db antigen expressed by the R1E transfectant is very different from that of the native molecule. This Db antigen is not recognized by Db-allospecific and Db-restricted cytotoxic T lymphocytes or by most monoclonal antibodies to the native Db. We show further that a deletion construct of the Db gene, which consists of exon 1 linked to exons 4-8, expresses a truncated Db antigen lacking domains 1 and 2 [Db-(1 + 2)] at the cell surface after transfection into the R1E line. Previous biochemical and crystallographic data have indicated that domain 3 is associated with beta 2m; unexpectedly, Db-(1 + 2) does not associate with beta 2m when the mouse beta 2mb gene is transfected into the R1E transfectant expressing the truncated Db. This suggests that interactions with domains 1 and 2 are important for the paired association of domain 3 and beta 2m in the native Db antigen.

Animals↗
PubMed1985

Peritonitis in children undergoing continuous ambulatory peritoneal dialysis.

During a four-year period there were 77 episodes and 15 recurrences of peritonitis in 30 children treated with continuous ambulatory peritoneal dialysis for periods of one to 39 months (mean, 15.3 months). The incidence was one episode per 6.0 patient-months. Organisms cultured included Staphylococcus epidermidis (17 episodes), Staphylococcus aureus (15 episodes), and fungi (four episodes). Special culture techniques were needed to ensure a high yield of positive cultures. Peritonitis was usually treated with intraperitoneal administration of cefazolin sodium, and 61% of the episodes were treated at home. There was one death, from Candida peritonitis, and catheters were removed in 11 children because of resistant or recurrent peritonitis (eight cases) or fungal peritonitis (three cases). Peritonitis rates were highest in children who had difficulty performing bag changes aseptically but who could not be transferred to hemodialysis and in hospitalized patients.

Adolescent↗
PubMed1982

Continuous ambulatory peritoneal dialysis in children: comparison with hemodialysis.

The clinical and biochemical effects of continuous ambulatory peritoneal dialysis in 20 children and of hemodialysis in 16 children were compared over a 2 1/2-year period. Statistically significant differences between the treatment groups included higher hematocrit, higher serum carbon dioxide and cholesterol levels, large intake of calories and protein, and lower systolic blood pressure and rates of transfusion in the patients receiving continuous ambulatory peritoneal dialysis. These patients had more complications than the patients receiving hemodialysis, but hospitalization rates in the two groups were similar. The cost of continuous ambulatory peritoneal dialysis was +19,600 per patient-year; the cost of hemodialysis was +54,300 per patient-year; the cost of hemodialysis was +54,300 per patient-year. There were four treatment failures with continuous ambulatory peritoneal dialysis and one with hemodialysis. Patients treated with both forms of dialysis preferred continuous ambulatory peritoneal dialysis. We conclude that continuous ambulatory peritoneal dialysis is an important alternative to hemodialysis in children.

Blood Pressure↗