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Biomedical subjects

K Held

Publications and source records attributed to K Held.

At least 19 recordsLinked to original sources
PubMed2006

Nocturnal ghrelin, ACTH, GH and cortisol secretion after sleep deprivation in humans.

Ghrelin is an endogenous ligand of the growth hormone (GH) secretagogue (GHS) receptor. It is hypothesised to play a key role in energy balance stimulating food intake and body weight. Besides GH-releasing hormone (GHRH) and somatostatin, it is thought to be a regulating factor of GH release. Ghrelin also appears to be involved in sleep regulation. We showed recently that ghrelin promotes slow-wave sleep and the nocturnal release of GH, cortisol and prolactin in humans. Similarly, promotion of non-rapid-eye-movement (NREM) sleep was reported in mice after systemic ghrelin. If ghrelin is a factor that induces and/or maintains sleep, it should be enhanced after a period of sleep deprivation (SD). To clarify this issue, nocturnal ghrelin, GH, ACTH and cortisol plasma concentrations were determined and simultaneously sleep electroencephalogram (EEG) was recorded (2300-0700 h) during sleep before and after 1 night of total SD in 8 healthy subjects. Compared to baseline, ghrelin levels increased earlier by a non-significant trend, already before the beginning of recovery sleep. Further a non-significant trend occurred, suggesting higher ghrelin secretion in the first half of the night. The ghrelin maximum was found significantly earlier after SD than at baseline. GH secretion during the first half of the night and total night after SD were elevated. ACTH and cortisol were also elevated, which was most pronounced during the second half of the night. No effects of SD on the time of the maximum were found for GH, ACTH and cortisol. The increase in ACTH after SD is a novel finding. Whereas the effects of SD on ghrelin levels were relatively weak, our findings are in line with the hypothesis that ghrelin is a sleep-promoting factor in humans. Ghrelin may be involved in sleep promotion after SD.

Adrenocorticotropic Hormone↗
PubMed2006

Pressure-induced metal-insulator transition in LaMnO3 is not of Mott-Hubbard type.

Calculations employing the local density approximation combined with static and dynamical mean field theories (LDA+U and LDA+DMFT) indicate that the metal-insulator transition observed at 32 GPa in paramagnetic LaMnO3 at room temperature is not a Mott-Hubbard transition, but is caused by orbital splitting of the majority-spin eg bands. For LaMnO3 to be insulating at pressures below 32 GPa, both on-site Coulomb repulsion and Jahn-Teller distortion are needed.

Journal Article↗
PubMed2006

Renin-angiotensin-aldosterone system, HPA-axis and sleep-EEG changes in unmedicated patients with depression after total sleep deprivation.

BACKGROUND: Changes in the activity of the renin-angiontensin-aldosterone system (RAAS) in depression have recently been reported. Renin and aldosterone secretion are coupled to sleep in healthy subjects. As total sleep deprivation (TSD) leads to a rapid mood improvement in patients with depression, it is of interest to investigate its effect on the response of the RAAS in the recovery night in this population as a possible probe for the neurobiological effects of TSD and potentially other rapid acting antidepressive interventions. Additionally we explored the HPA-system and the sleep-EEG-changes. METHODS: We compared the sleep related activity of the RAAS before and after TSD in seven depressed patients. After an accommodation night, a polysomnographic examination was performed between 23.00 h and 7.00 h. This was followed by 40 h of TSD and a second polysomnography. During the examination blood samples were taken in the night every 20 min for analysis of renin, aldosterone, ACTH and cortisol. RESULTS: During recovery-sleep renin was significantly increased (p < 0.05). Aldosterone showed no change. ACTH and cortisol were decreased by trend in the first half of the night. REM-density and intermittent wakefulness was significantly decreased (p < 0.05), whereas slow wave sleep increased by trend in the first half of the night. CONCLUSION: TSD in patients with depression leads to an increase in renin secretion and a concomitant trend for a decrease in HPA axis activity in the recovery night. These changes could be a "fingerprint" of a rapidly antidepressive treatment.

Adrenocorticotropic Hormone↗
PubMed2004

Mutual experimental and theoretical validation of bulk photoemission spectra of Sr1-xCaxVO3.

We report high-resolution high-energy photoemission spectra together with parameter-free LDA + DMFT (local density approximation + dynamical mean-field theory) results for Sr1-xCaxVO3, a prototype 3d(1) system. In contrast to earlier investigations the bulk spectra are found to be insensitive to x. The good agreement between experiment and theory confirms the bulk sensitivity of the high-energy photoemission spectra.

Journal Article↗
PubMed2004

Projective quantum monte carlo method for the anderson impurity model and its application to dynamical mean field theory.

We develop a projective quantum Monte Carlo algorithm of the Hirsch-Fye type for obtaining ground state properties of the Anderson impurity model. This method is employed to solve the self-consistency equations of dynamical mean field theory. It is shown that the approach converges rapidly to the ground state so that reliable zero-temperature results are obtained. As a first application, we study the Mott-Hubbard metal-insulator transition of the frustrated one-band Hubbard model, reconfirming the numerical renormalization group results.

Journal Article↗
PubMed2004

Filling of the mott-hubbard gap in the high temperature photoemission spectrum of (V0.972Cr0.028)2O3.

Photoemission spectra of the paramagnetic insulating phase of (V0.972Cr0.028)2O3, taken in ultrahigh vacuum up to the unusually high temperature (T) of 800 K, reveal a property unique to the Mott-Hubbard (MH) insulator that has not been observed previously. With increasing T the MH gap is filled by spectral weight transfer, in qualitative agreement with high-T theoretical calculations combining dynamical mean field theory and band theory in the local density approximation.

Journal Article↗
PubMed2004

The somatostatin analogue octreotide impairs sleep and decreases EEG sigma power in young male subjects.

The long-acting somatostatin (SRIF) analogue octreotide decreased nonrapid eye movement sleep (NREMS) in the rat. This effect is opposite to the promotion of sleep after growth hormone (GH)-releasing hormone (GHRH) in various species including humans. Therefore, it appears likely that GHRH and SRIF, besides their opposite action on pituitary GH release, interact reciprocally in sleep regulation. In previous studies, SRIF impaired sleep in elderly subjects, although sleep in young men remained unchanged. We hypothesized that octreotide is a useful tool to study the role of SRIF in human sleep regulation. We examined the effect of subcutaneous administration of 0.1 mg octreotide at 2245 on the sleep EEG of seven young male controls (age, mean+/-SD, 22.3+/-3.0 years). In comparison to placebo, octreotide administration prompted decreases of sleep stage 4 during the total night and of rapid eye movement sleep (REMS) density during the first half of the night. Intermittent wakefulness increased during the second half of the night. The spectral analysis of total night NREMS revealed a significant decrease of sigma power. Similar to the effect of the short-acting SRIF in the elderly, the long-acting SRIF analogue octreotide impaired sleep in young healthy subjects. Obviously, the influence of octreotide on sleep is superior to that of short-acting SRIF, which did not affect sleep in young men. We suggest a reciprocal interaction of GHRH and SRIF in sleep regulation.

Adolescent↗
PubMed2004

Reboxetine induces similar sleep-EEG changes like SSRI's in patients with depression.

BACKGROUND: Reboxetine is a novel selective noradrenaline reuptake inhibitor. The antidepressive properties of the substance are established. METHODS: The influence of reboxetine on the sleep-EEG of eight patients with depression HAMD (mean +/- SD) 19.7 +/- 1.5 (5 women, 3 men; age range 31 to 75 years) was investigated. Sleep EEG was examined twice. The first examination was performed before starting active medication. The second examination was subsequently performed when patients received 8 to 10 mg reboxetine per day. RESULTS: Conventional sleep-EEG analysis showed a significant increase in intermittent wakefulness and sleep stage 2 and a decrease in sleep efficiency and REM time. Under reboxetine no significant changes were observed in sleep-EEG spectral analysis. CONCLUSION: Our results indicate, that reboxetine induces sleep-EEG changes similar to those after selective serotonin reuptake inhibitors (SSRI's) by increasing intermittent wakefulness and decreasing REM time.

Adrenergic Uptake Inhibitors↗
PubMed2003

Prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3.

We present the first observation of a prominent quasiparticle peak in the photoemission spectrum of the metallic phase of V2O3 and report new spectral calculations that combine the local-density approximation with the dynamical mean-field theory (using quantum Monte Carlo simulations) to show the development of such a distinct peak with decreasing temperature. The experimental peak width and weight are significantly larger than in the theory.

Journal Article↗
PubMed2003

Random matrix theory for closed quantum dots with weak spin-orbit coupling.

To lowest order in the coupling strength, the spin-orbit coupling in quantum dots results in a spin-dependent Aharonov-Bohm flux. This flux decouples the spin-up and spin-down random matrix theory ensembles of the quantum dot. We employ this ensemble and find significant changes in the distribution of the Coulomb blockade peak height, in particular, a decrease of the width of the distribution. The puzzling disagreement between standard random matrix theory and the experimental distributions by Patel et al. [Phys. Rev. Lett. 81, 5900 (1998)]] might possibly be attributed to these spin-orbit effects.

Journal Article↗
PubMed2003

[Cardiovascular diseases and the subspecialties cardiology and angiology in "Schlichtungs"- Proceedings].

A: The Schlichtungsstelle (expert panel for alternative dispute resolution) of Northern Germany, in 2001, decided on 2620 malpractice claims; 233 of these were related to the treatment of cardiovascular disorders, coronary and venous diseases being the most common. The physicians involved in these disputes represented 18 (sub-)specialities. Complaints related to procedures were the ones most frequently submitted by the patients, followed by those concerning diagnostics. Negligence was found to be present in 37% of the cases, the highest proportion being due to mistakes of diagnosis, followed by organisational and system-related mistakes. Medical negligence as the cause of injury was assumed in 46/233 (20%) of the cases, the injuries being serious in 18 and fatal in 6 of the 46 patients. Negligent and non-negligent iatrogenic injuries combined, amounted to 132/233 (57%) of the "cardiovascular" panel cases. B: From 1992 to 2001, we collected 165 panel cases involving cardiologists and 3 involving angiologists. In most of these the underlying disease was coronary, but in 14 cases the underlying disorder was psychosomatic. 35% of the complaints submittted by the patients were about invasive procedures. 12% of the instances of negligence determined in the panel proceedings were due to procedural mistakes, whereas 47% were due to mistakes related to indication and to the monitoring of the patients after procedures. Negligent iatrogenic injury was assumed in 27%, non-negligent iatrogenic injury in another 53% of the cases, so that the total of iatrogenic injuries amounted to 80% of the "cardio-angiologists" panel cases. 19/168 (11%) patients died from iatrogenic injuries. Organization and coordination among medical persons and institutions treating patients need improvement. A considerable number of disputes and claims seems to be initiated and caused by deficits in doctor-patient-communication. Attempts at reducing negligence and adverse events should center around those professionals actually involved in patient care, where the decisions on diagnostics, indication and therapy are made. Processes promoting patient safety should be based and depend on the groups cooperating in their daily work (department, practice). External influences and directives tend to be less effective.

Aftercare↗
PubMed2002

Ghrelin promotes slow-wave sleep in humans.

Ghrelin, an endogenous ligand of the growth hormone (GH) secretagogue (GHS) receptor, stimulates GH release, appetite, and weight gain in humans and rodents. Synthetic GHSs modulate sleep electroencephalogram (EEG) and nocturnal hormone secretion. We studied the effect of 4 x 50 microg of ghrelin administered hourly as intravenous boluses between 2200 and 0100 on sleep EEG and the secretion of plasma GH, ACTH, cortisol, prolactin, and leptin in humans (n = 7). After ghrelin administration, slow-wave sleep was increased during the total night and accumulated delta-wave activity was enhanced during the second half of the night. Rapid-eye-movement (REM) sleep was reduced during the second third of the night, whereas all other sleep EEG variables remained unchanged. Furthermore, GH and prolactin plasma levels were enhanced throughout the night, and cortisol levels increased during the first part of the night (2200-0300). The response of GH to ghrelin was most distinct after the first injection and lowest after the fourth injection. In contrast, cortisol showed an inverse pattern of response. Leptin levels did not differ between groups. Our data show a distinct action of exogenous ghrelin on sleep EEG and nocturnal hormone secretion. We suggest that ghrelin is an endogenous sleep-promoting factor. This role appears to be complementary to the already described effects of the peptide in the regulation of energy balance. Furthermore, ghrelin appears to be a common stimulus of the somatotropic and hypothalamo-pituitary-adrenocortical systems. It appears that ghrelin is a sleep-promoting factor in humans.

Adrenocorticotropic Hormone↗
PubMed2002

[Results of 903 settlement proceedings in internal medicine].

BACKGROUND AND OBJECTIVE: Physicians - as others in their activities - err and may cause injuries to patients. The case material of Schlichtungsstellen and Gutachterkommissionen (expert panels for extrajudicial claims resolution) may provide suggestions as to the nature and gravity of negligent adverse events in medical care. METHODS: Cases are decided by members of the panel, one physician and one lawyer being responsible for each case. They assess, aided by external expert opinion, records for evidence of negligence and, in case of negligence, for a causal relation to injury. Given that relation, they recommend compensation in favor of the patient. Data on complaints, mistakes and injuries are filed. RESULTS: We assumed negligence in 40 % of our 903 panel cases (most frequently due to mistakes in diagnosis, indication and monitoring after procedures), and negligent injury, resulting in recommendations for the patient in 26 %. In the 363 cases concerning invasive procedures (diagnostic, interventional, and injections) mistakes of indication outnumbered those in performing the procedure. Negligent injuries resulted in severe lesions or even permanent disability in 111 patients, in 30 patients in death. Even in the cases without evidence of negligence, many of the patients had suffered iatrogenic injuries. CONCLUSIONS: Physicians must make decisions about complex problems, under very difficult circumstances (Eddy); diagnosis is mistaken frequently, and indication also. According to patients' complaints and to the relevant literature, communication is of crucial importance regarding the doctor-patient-relationship and the prevention of disputes. The number of treatment-caused lesions made visible by claims constitutes only a fraction of the total of iatrogenic injuries actually suffered by patients. The analysis of adverse events in medical care should include system-based sources of errors and untoward outcomes.

Aged↗
PubMed2002

[Long-term effects of rehabilitation of an outpatient "heart group". A case control study].

The effects of an outhospital cardiac rehabilitation program in "heart groups" (HG) are studied in a case-control design. The control group (KG) was collected by match-pairing from 12,560 cases of a rehabilitation clinic fitting in the relevant criteria to those of members of the HG. Patients of both groups (n = 75/group) after myocardial infarction and CABG were followed up over 7.5 years. There was no significant difference in risk factor modification. Exercise tolerance improved significantly in the HG by increasing maximum work capacity by 50% in spite of a mean age of 60 years at the beginning. Members of HG had significantly lesser cardiac complaints and lower need for cardiac medication. Cardiac morbidity was reduced by 54% and costs for medical care were lowered by 47% in HG. Although effects of secondary prevention on reducing risk factors were still insufficient, exercise tolerance in higher age and quality of life were improved, reduction in medication and in the morbidity saved costs for the health system.

Case-Control Studies↗
PubMed2001

Cerium volume collapse: results from the merger of dynamical mean-field theory and local density approximation.

The merger of density-functional theory in the local density approximation and many-body dynamical mean-field theory allows for an ab initio calculation of Ce including the inherent 4f electronic correlations. We solve the equations by the quantum Monte Carlo technique and calculate the Ce energy, spectrum, and double occupancy as a function of volume. At low temperatures, the correlation energy exhibits an anomalous region of negative curvature which drives the system towards a thermodynamic instability, i.e., the gamma-to- alpha volume collapse, consistent with experiment. The connection of the energetic with the spectral evolution shows that the physical origin of the energy anomaly and, thus, the volume collapse is the appearance of a quasiparticle resonance in the 4f-spectrum which is accompanied by a rapid growth in the double occupancy.

Journal Article↗
PubMed2001

Mott-hubbard metal-insulator transition in paramagnetic V2O3: an LDA+DMFT(QMC) study.

The electronic properties of paramagnetic V2O3 are investigated by the computational scheme LDA+DMFT(QMC). This approach merges the local density approximation (LDA) with dynamical mean-field theory (DMFT) and uses quantum Monte Carlo simulations (QMC) to solve the effective Anderson impurity model of DMFT. Starting with the crystal structure of metallic V2O3 and insulating (V0.962Cr0.038)2O3 we find a Mott-Hubbard transition at a Coulomb interaction U approximately 5 eV. The calculated spectrum is in very good agreement with experiment. Furthermore, the orbital occupation and the spin state S = 1 determined by us agree with recent polarization dependent x-ray-absorption experiments.

Journal Article↗
PubMed2000

Similarities between the hubbard and periodic anderson models at finite temperatures

The single band Hubbard and the two band periodic Anderson Hamiltonians have traditionally been applied to rather different physical problems-the Mott transition and itinerant magnetism, and Kondo singlet formation and scattering off localized magnetic states, respectively. In this paper, we compare the magnetic and charge correlations, and spectral functions, of the two systems. We show quantitatively that they exhibit remarkably similar behavior, including a nearly identical topology of the finite temperature phase diagrams at half filling. We address potential implications of this for theories of the rare earth "volume collapse" transition.

Journal Article↗