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Biomedical subjects

L Kaplan

Publications and source records attributed to L Kaplan.

At least 19 recordsLinked to original sources
PubMed2001

Eigenstate structure in graphs and disordered lattices.

We study wave function structure for quantum graphs in the chaotic and disordered regime, using measures such as the wave function intensity distribution and the inverse participation ratio. The result is much less ergodicity than expected from random matrix theory, even though the spectral statistics are in agreement with random matrix predictions. Instead, analytical calculations based on short-time semiclassical behavior correctly describe the eigenstate structure.

Journal Article↗
PubMed2001

Scarring effects on tunneling in chaotic double-well potentials.

The connection between scarring and tunneling in chaotic double-well potentials is studied in detail through the distribution of level splittings. The mean level splitting is found to have oscillations as a function of energy, as expected if scarring plays a role in determining the size of the splittings, and the spacing between peaks is observed to be periodic of period 2 pi Planck's over 2 pi in action. Moreover, the size of the oscillations is directly correlated with the strength of scarring. These results are interpreted within the theoretical framework of Creagh and Whelan. The semiclassical limit and finite-Planck's over 2 pi effects are discussed, and connections are made with reaction rates and resonance widths in metastable wells.

Journal Article↗
PubMed2001

Localization of eigenfunctions in the stadium billiard.

We present a systematic survey of scarring and symmetry effects in the stadium billiard. The localization of individual eigenfunctions in Husimi phase space is studied first, and it is demonstrated that on average there is more localization than can be accounted for by random-matrix theory, even after removal of bouncing-ball states and visible scars. A major point of the paper is that symmetry considerations, including parity and time-reversal symmetries, enter to influence the total amount of localization. The properties of the local density of states are also investigated, as a function of phase space location. Aside from the bouncing-ball region of phase space, excess localization is found on short periodic orbits and along certain symmetry-related lines; the origin of all these sources of localization is discussed quantitatively and comparison is made with analytical predictions. Scarring is observed to be present in all the energy ranges considered. In light of our results, the excess localization in individual eigenstates is interpreted as being primarily due to symmetry effects.

Journal Article↗
PubMed2001

Chemotherapy for human immunodeficiency virus-associated non-Hodgkin's lymphoma in combination with highly active antiretroviral therapy.

PURPOSE: This study investigated the efficacy, toxicity, and pharmacokinetic interactions resulting from simultaneous combination chemotherapy and highly active antiretroviral therapy (HAART) for patients with human immunodeficiency virus (HIV)-associated non-Hodgkin's lymphoma (NHL). In addition, the effects on viral load, CD4 counts, and opportunistic infections were examined with the use of combination chemotherapy combined with HAART. PATIENTS AND METHODS: Sixty-five patients with previously untreated and measurable disease at any stage of HIV-associated NHL of intermediate or high grade were entered onto this study at 17 different centers. The first 40 patients entered onto the study received reduced doses of cyclophosphamide and doxorubicin, combined with vincristine and prednisone (modified CHOP [mCHOP]), whereas the subsequent 25 patients entered onto the study received full doses of CHOP combined with granulocyte colony-stimulating factor (G-CSF). All patients also received stavudine, lamivudine, and indinavir. RESULTS: The complete response rates were 30% and 48% among patients who received mCHOP and full-dose CHOP combined with HAART, respectively. Grade 3 or 4 neutropenia occurred in 25% of patients receiving mCHOP and 12% of those receiving full-dose CHOP combined with G-CSF (25% v 12%). There were similar numbers of patients with grade 3 or 4 hyperbilirubinemia (12% and 17%), constipation and abdominal pain (18% and 17%), and transaminase elevation (48% and 52%) on the modified and full-dose arms of the study, respectively. Doxorubicin clearance and indinavir concentration curves were similar among patients on this study and historical controls, whereas cyclophosphamide clearance was 1.5-fold reduced as compared with control values. Human immunodeficiency virus (HIV) load declined from a median baseline value of 29,000 copies/mL to a median minimum value on therapy of 500 copies/mL. CONCLUSION: Either modified-dose or full-dose CHOP chemotherapy for HIV-NHL, delivered with HAART, is effective and tolerable.

Adult↗
PubMed2001

Disability as a function of social networks and support in elderly African Americans and Whites: the Duke EPESE 1986--1992.

OBJECTIVES: We examined the association of structural and functional aspects of social relationships with change in disability, and the degree to which race modifies these associations. METHODS: Data are from a population-based sample of 4,136 African Americans and Whites aged > or = 65 living in North CAROLINA: Disability data were collected during seven consecutive yearly interviews and summarized in two outcome measures. Measures of social relationships included five measures representing network size, extent of social interaction, and specific type of relationships, as well as instrumental and emotional support. Weighted proportional odds models were fitted to model disability as a function of baseline social network and support variables, and the interaction of each variable with follow-up time. RESULTS: Network size and social interaction showed significant negative associations with disability risks, which did not vary by race, or as a function of time. Social interaction with friends was associated with a reduced risk for disability, but social interaction with children or relatives was not related to disability. Instrumental support was associated with a significantly increased disability risk, with a greater adverse effect among Whites than African AMERICANS: Emotional support was not associated with disability, but a protective effect for ADL disability was found after controlling for its intercorrelation with instrumental support. DISCUSSION: The findings provide further evidence for the role of social relationships in the disablement process, although not all types of social relationships may be equally beneficial. Furthermore, these associations may be more complex than simple causal effects. There were few racial differences in the association of social relationships with disability, with the possible exception of instrumental support, which may allude to possible sociocultural differences in the experience of instrumental support exchanges.

Activities of Daily Living↗
PubMed2000

Wave function structure in two-body random matrix ensembles

We study the structure of eigenstates in two-body interaction random matrix ensembles and find significant deviations from random matrix theory expectations. The deviations are most prominent in the tails of the spectral density and indicate localization of the eigenstates in Fock space. Using ideas related to scar theory we derive an analytical formula that relates fluctuations in wave function intensities to fluctuations of the two-body interaction matrix elements. Numerical results for many-body fermion systems agree well with the theoretical predictions.

Journal Article↗
PubMed2000

Differential leptin responses to acute and chronic biliary obstruction in rats.

BACKGROUND/AIMS: Recently leptin, a protein released from adipocytes, has been identified as a potent circulating satiety factor. We therefore undertook this series of experiments to examine leptin's role in the anorexia associated with biliary obstruction. METHODS: Rats underwent either surgical bile duct resection (BDR) or sham resection (sham). Body weight, and food and water intake were measured during a baseline period and for 8 days after surgery. At 4, 8 and 16 h as well as on days 2, 4, 6, and 8 postsurgery, sham and BDR rats were sacrificed and sera collected for subsequent measurement of leptin hormone concentration by RIA. White adipose tissue was collected on days 2, 4, 6 and 8 for leptin mRNA determination by Northern blot. RESULTS: Obstructive cholestasis in BDR rats caused significant anorexia for up to 7 days post-surgery, whereas in sham rats, a significant decrease in food intake was only observed in the first 24-h period following surgery. In both sham and BDR rats, water intake was significantly decreased during the first 24-h period after surgery, but had recovered to baseline levels by day 2 in both groups. Fat pad mass corrected to body weight was not significantly different between the two experimental groups. Serum leptin levels were significantly increased 4 and 8 h after surgery, had normalized by 16 h post-surgery, and were then decreased in BDR rats on days 2, 4, 6 and 8 compared with controls. Leptin mRNA levels in epididymal fat pads were decreased by approximately 2-fold in BDR rats compared with sham rats on days 2, 4, 6 and 8. Furthermore, day 5 BDR and sham rats demonstrated similar anorectic responses to centrally administered leptin. CONCLUSIONS: Leptin production is significantly increased early after biliary obstruction but is reduced after prolonged biliary obstruction. Increased circulating leptin levels may contribute to the profound anorexia observed early after biliary obstruction but appear not to mediate the anorexia observed during more chronic biliary obstruction.

Acute Disease↗
PubMed2000

Quality Enhancement Research Initiative in stroke: prevention, treatment, and rehabilitation.

Stroke is the third leading cause of death and a leading cause of adult disability in the United States. Both within and outside of the Veterans Health Administration (VHA), the lack of a systematic approach to stroke prevention and treatment may have contributed to reduced rates of compliance with recommended practices and increased rates of stroke. Gaps in the knowledge base inhibit a systematic approach to high-quality care within the veteran population. Initial recommendations for closing those gaps are proposed. In some cases (eg, systematic anticoagulation management), the VHA is perceived as a leader in applied research; therefore, a systematic national policy for implementing these clinics may significantly reduce stroke rates. In other areas (eg, carotid endarterectomy), databases exist that would help advance quality and outcomes, but short-term studies are necessary to establish their utility. To promote strategic improvement in prevention, treatment, and rehabilitation for veterans who may be at risk or have had a stroke, specific objectives are proposed to (1) identify best practices for the effective delivery of long-term anticoagulation and enhance veterans' access to these services, (2) develop risk-adjusted models for the surgical preventive procedure carotid endarterectomy to understand facility variation in outcomes so practices can be improved, (3) define a systematic acute stroke management system so that high-quality stroke-related care can be generalizable to a variety of VHA settings, and (4) assess the impact of poststroke rehabilitation on risk adjustment and the location of outcomes so as to facilitate the implementation of best rehabilitation practices.

Adult↗
PubMed2000

Periodic orbit effects on conductance peak heights in a chaotic quantum dot

We study the effects of short-time classical dynamics on the distribution of Coulomb blockade peak heights in a chaotic quantum dot. The location of one or both leads relative to the short unstable orbits, as well as relative to the symmetry lines, can have large effects on the moments and on the head and tail of the conductance distribution. We study these effects analytically as a function of the stability exponent of the orbits involved, and also numerically using the stadium billiard as a model. The predicted behavior is robust, depending only on the short-time behavior of the many-body quantum system, and consequently insensitive to moderate-sized perturbations and interactions.

Journal Article↗
PubMed2000

Short-time effects on eigenstate structure in sinai billiards and related systems

There is much latitude between the requirements of Schnirelman's theorem regarding the ergodicity of individual high-energy eigenstates of classically chaotic systems on the one hand, and the extreme requirements of random matrix theory on the other. It seems likely that some eigenstate statistics and long-time transport behavior bear nonrandom imprints of the underlying classical dynamics while simultaneously obeying Schnirelman's theorem. Indeed this was shown earlier in the case of systems that approach classical ergodicity slowly, and is also realized in the scarring of eigenstates, even in the Planck's over 2pi-->0 limit, along unstable periodic orbits and their manifolds. Here we demonstrate the nonrandom character of eigenstates of Sinai-like systems. We show that mixing between channels in Sinai systems is dramatically deficient compared to random matrix theory predictions. The deficit increases as |ln Planck's over 2pi| for Planck's over 2pi-->0, and is due to the vicinity of the measure zero set of orbits that never collide with the Sinai obstruction. Coarse graining to macroscopic scales recovers the Schnirelman result. Three systems are investigated here: a Sinai-type billiard, a quantum map that possesses the essential properties of the Sinai billiard, and a unitary map corresponding to a quasirandom Hamiltonian. Various wave function and long-time transport statistics are defined, theoretically investigated, and compared to numerical data.

Journal Article↗
PubMed1999

Pulse oximetry plethysmographic waveform during changes in blood volume.

Systolic pressure variation (SPV) and its dDown component have been shown to be sensitive factors in estimating intravascular volume in patients undergoing mechanical ventilation. In this study, ventilation-induced changes in pulse oximeter plethysmographic waveform were evaluated after removal and after reinfusion of 10% estimated blood volume. The plethysmographic waveform variation (SPVplet) was measured as the difference between maximal and minimal peaks of waveform during the ventilatory cycle, and expressed as a percentage of the signal amplitude during apnoea. dUp(plet) and dDown(plet) were measured as the distance between the apnoeic plateau and the maximal or minimal plethysmographic systolic waveform, respectively. Intravascular volume was changed by removal of 10% of estimated blood volume and followed by equal volume replacement with Haemaccel. A 10% decrease in blood volume increased SPVplet from mean 17.0 (SD 11.8)% to 31.6 (28.0)% (P = 0.005) and dDown(plet) from 8.7 (5.1)% to 20.5 (12.9)% (P = 0.0005) compared with baseline. Changes in plethysmographic waveform correlated with changes in arterial SPV and dDown (r = 0.85; P = 0.0009). In the absence of invasive arterial pressure monitoring, ventilation-induced waveform variability of the plethysmographic signal measured from pulse oximetry is a useful tool in the detection of mild hypovolaemia.

Adolescent↗
PubMed1999

Scar and antiscar quantum effects in open chaotic systems.

We predict and numerically observe strong periodic orbit effects in the properties of weakly open quantum systems with a chaotic classical limit. Antiscars lead to a large number of exponentially narrow isolated resonances when the single-channel (or tunneling) opening is located on a short unstable orbit of the closed system; the probability to remain in the system at long times is thus exponentially enhanced over the random matrix theory prediction. The distribution of resonance widths and the probability to remain are quantitatively given in terms of only the stability matrix of the orbit on which the opening is placed. The long-time remaining probability density is nontrivially distributed over the available phase space; it can be enhanced or suppressed near orbits other than the one on which the lead is located, depending on the periods and classical actions of these other orbits. These effects of the short periodic orbits on quantum decay rates have no classical counterpart, and first appear on times scales much larger than the Heisenberg time of the system. All the predictions are quantitatively compared with numerical data.

Journal Article↗
PubMed1999

Measuring scars of periodic orbits.

The phenomenon of periodic orbit scarring of eigenstates of classically chaotic systems is attracting increasing attention. Scarring is one of the most important "corrections" to the ideal random eigenstates suggested by random matrix theory. This paper discusses measures of scars and in so doing also tries to clarify the concepts and effects of eigenfunction scarring. We propose a universal scar measure which takes into account an entire periodic orbit and the linearized dynamics in its vicinity. This measure is tuned to pick out those structures which are induced in quantum eigenstates by unstable periodic orbits and their manifolds. It gives enhanced scarring strength as measured by eigenstate overlaps and inverse participation ratios, especially for longer orbits. We also discuss off-resonance scars which appear naturally on either side of an unstable periodic orbit.

Journal Article↗
PubMed1999

Depressive symptoms among spousal caregivers of institutionalized mates with Alzheimer's: boundary ambiguity and mastery as predictors.

The goal of this study was to identify factors that predict whether or not community-dwelling spouses experience depressive symptoms upon institutionalization of a mate with Alzheimer's disease. Eighty-four community-dwelling spouses (50 wives/34 husbands) completed questionnaires. Boundary ambiguity alone accounted for 51% of the variability in the depressive symptoms score, while mastery alone was found to account for 32%. The total explained variance, when controlling for demographic variables, was 68%. In the stepwise regression analysis, it was observed that mastery did not add significantly to the explanation of the depressive symptom score over and above boundary ambiguity. However, boundary ambiguity and mastery were somehow linked together and were powerful in explaining caregiver symptoms of depression. If a goal is to keep caregivers healthy, then interventions and education about how to live with ambiguity and how to be masterful in spite of the ambiguous status of one's mate seem necessary. Clinical implications are discussed. Future research might build upon this study's limitations for an even better understanding of factors that relate to caregiver depressive symptoms.

Adaptation, Psychological↗
PubMed1998

Expression of AP-2 transcription factors in human breast cancer correlates with the regulation of multiple growth factor signalling pathways.

The AP-2 transcription factors are required for normal growth and morphogenesis during mammalian development. Previous in vitro studies have also indicated that the AP-2 family of proteins may be involved in the etiology of human breast cancer. The AP-2 genes are expressed in many human breast cancer cell lines, and critical AP-2-binding sites are present in both the ERBB-2 (HER2/neu) and estrogen receptor promoters. We have now characterized immunological reagents that enable specific AP-2 family members, including AP-2alpha and AP-2gamma, to be detected in human breast cancer epithelium. Data obtained with these reagents demonstrate that whereas AP-2alpha and AP-2gamma are both present in benign breast epithelia, there is a significant up-regulation of AP-2gamma expression in breast cancer specimens (P = 0.01). There was also a significant correlation between the presence of the AP-2alpha protein and estrogen receptor expression (P = 0.018) and between specimens containing both AP-2alpha/AP-2gamma proteins and ERBB-2 expression (P = 0.003). Furthermore, we detected an association (P = 0.04) between the expression of AP-2gamma and the presence of an additional signal transduction molecule implicated in breast cancer, the insulin-like growth factor I receptor. Analysis of the proximal promoter of the insulin-like growth factor I receptor revealed a novel AP-2-binding site. Thus, AP-2 proteins may directly regulate the transcription of this growth factor receptor. Taken together, these data strongly support a role for the AP-2 gene family in the control of cell growth and differentiation in breast cancer.

Binding Sites↗
PubMed1998

Sequential or simultaneous, same-day anterior decompression and posterior stabilization in the management of vertebral osteomyelitis of the lumbar spine.

STUDY DESIGN: A retrospective clinical study of patients with vertebral osteomyelitis of the lumbar spine necessitating surgical treatment. All patients underwent sequential (same-day) or simultaneous anterior decompression and posterior stabilization of the involved vertebrae. OBJECTIVE: To evaluate the efficacy and clinical out-come of sequential or simultaneous anterior and posterior surgical approaches in the management of vertebral osteomyelitis of the lumbar spine. SUMMARY OF BACKGROUND DATA: Anterior approach alone and staged anterior decompression and posterior stabilization have been advocated as the surgical treatment methods of choice for patients with vertebral osteomyelitis of the lumbar spine. The drawbacks of the latter management plan are the necessity to use external support or the delayed patient mobilization and the need for additional anesthesia and surgical trauma. Sequential (same-day) anterior and posterior approaches are used regularly in the surgical management of scoliosis and other spinal deformities. It would appear advantageous to also use the same strategy (i.e., combined same-day double approaches) in the management of vertebral osteomyelitis of the lumbar spine. METHODS: Ten consecutive patients who had a diagnosis of vertebral osteomyelitis of the lumbar spine underwent combined (same-day) anterior and posterior approaches either in a sequential or simultaneous manner. Indications for surgery included neurologic deficit, abscess formation, instability with localized kyphosis formation, and failure of nonoperative treatment. Patients were evaluated clinically and radiographically after surgery. RESULTS: All 10 patients had uneventful surgery. Only one patient required a second surgical procedure because of expulsion of the anterior bone graft and pull-out of instrumentation. All patients were mobilized within the 2 days immediately after surgery. At the mean follow-up examination 30 months after surgery, all patients had regained their motor function and prior ambulatory status. CONCLUSIONS: Patients with lumbar osteomyelitis necessitating surgery can undergo combined, same-day surgery either in a sequential or simultaneous manner. This is a safe and efficient way to control the infection and stabilize the affected segments, allowing for early mobilization of these sick elderly patients.

Aged↗