Biomedical subjects

K Jacobi

Publications and source records attributed to K Jacobi.

At least 19 recordsLinked to original sources

PubMed2002

Energetics and vibrational states for hydrogen on Pt(111).

We present a combination of theoretical calculations and experiments for the low-lying vibrational excitations of H and D atoms adsorbed on the Pt(111) surface. The vibrational band states are calculated based on the full three-dimensional adiabatic potential energy surface obtained from first-principles calculations. For coverages less than three quarters of a monolayer, the observed experimental high-resolution electron peaks at 31 and 68 meV are in excellent agreement with the theoretical transitions between selected bands. Our results convincingly demonstrate the need to go beyond the local harmonic oscillator picture to understand the dynamics of this system.

Journal Article↗

PubMed2001

GaAs(2 5 11): a new stable surface within the stereographic triangle.

The atomic structure of GaAs(2 5 11), a hitherto unknown stable surface, has been determined by in situ scanning tunneling microscopy and first-principles electronic structure calculations. This orientation is located within the stereographic triangle, i.e., far away from all low-index surfaces. A low-energy ( 1x1) reconstruction containing arsenic dimers forms on the surface. The analysis of the surface structure shows that, for semiconductor surfaces, the gain in stability due to minimization of the number of dangling bonds is more important than the gain from rendering a semiconducting ground state.

Journal Article↗

PubMed2001

Atomic Structure of the Stoichiometric GaAs(114) Surface.

The stoichiometric GaAs(114) surface has been prepared using molecular beam epitaxy followed by annealing in ultrahigh vacuum. Based on in situ scanning tunneling microscopy measurements and first-principles electronic-structure calculations, we determine the surface reconstruction which we call alpha2(2x1). Contrary to what is expected for a high-index surface, it is surprisingly elementary. The (2x1) unit cell contains two As dimers and two rebonded Ga atoms. The surface energy is calculated as 53 meV/Å(2), which falls well within the range of low-index GaAs surface energies.

Journal Article↗

PubMed2001

[Hemodynamic effects of pneumoperitoneum in lithotomy position].

AIM OF STUDY: The study investigates the haemodynamic effects of the varying intraabdominal pressures and patient positions during gynecological procedures employing pneumoperitoneum in lithotomy positions. METHODS: TEE was used to determine end-diastolic and end-systolic left ventricular surface areas and ejection fractions were calculated from these data. To evaluate intraabdominal volume shifts the diameter of the internal iliac vein was measured by mean of vaginal ultrasound. RESULTS: In the horizontal lithotomy position both LVEDA and LVESA increased when intraabdominal pressure increased by 10 and 15 mmHg, respectively. LVAEF significantly decreased when intraabdominal pressure increased by 15 mmHg. Also DVII decreased. In Trendelenburg position there was no change in LVEDA, LVESA, LVAEF and DVII. In Anti-Trendelenburg position LVEDA and LVESA decreased. However, LVAEF remained constant and DVII increased. CONCLUSION: The increase of the intraabdominal pressure in the lithotomy position results in an increase in intrathoracic volume and an decrease in LVAEF via elevation of the the lower extremities and compression of the splanchnic vessels. There are no changes in Trendelenburg position. However, in Anti-Trendelenburg position, gravity results in a decrease in intrathoracic blood volume. In the decreased, dilatated heart the increase in intrathoracic volume may increase myocardial wall tension and hence oxygen demand, ultimately leading to an acute heart failure. As a result laparoscopic procedures in horizontal lithotomy position should be avoided in patients with dilatative cardiomyopathy.

Adolescent↗

PubMed2000

Comparison of succinylcholine with two doses of rocuronium using a new method of monitoring neuromuscular block at the laryngeal muscles by surface laryngeal electromyography.

We compared the onset of neuromuscular block with succinylcholine (1 mg kg-1) and two doses of rocuronium (0.6 and 0.9 mg kg-1) at the adductor pollicis muscle using electromyography (EMG) and acceleromyography (AMG), and at the adductor laryngeal muscles with a new electromyographic method using a disposable surface electrode attached to the cuff of a tracheal tube. At the larynx, the mean (+/- SD) time to 90% block and the onset time of succinylcholine (38 +/- 15 and 47 +/- 19 s, respectively) were significantly shorter (P < 0.01) than for rocuronium 0.6 mg kg-1 (92 +/- 42 and 106 +/- 38 s) and rocuronium 0.9 mg kg-1 (52 +/- 31 and 64 +/- 30 s). We found that, with comparable degrees of neuromuscular block, the onset time of succinylcholine at the adductor pollicis was significantly shorter (P < 0.01) than for rocuronium 0.6 mg kg-1 and 0.9 mg kg-1 (EMG, 80 +/- 39 vs 145 +/- 48 s and 99 +/- 31 s; AMG, 90 +/- 39 vs 124 +/- 53 s and 106 +/- 38 s). Clinical duration at the adductor pollicis (AMG) was significantly longer (P < 0.01) for both rocuronium groups than for succinylcholine (T4:T1 = 0.7, 54 +/- 18 and 77 +/- 21 vs 8 +/- 6 min). The surface laryngeal electrode proved non-invasive, easy to use and reliable in measuring onset of the neuromuscular block at the larynx.

Adult↗

PubMed2000

Plasma levels of eicosanoids after transfusion of intraoperatively salvaged blood.

BACKGROUND: The interest in autologous red blood cell salvage is increasing rapidly, but it is well known that platelets and white cells are activated during cell washing. Therefore, we aimed to determine whether or not eicosanoids transfused together with the salvaged blood are responsible for nonhemolytic immunological transfusion reactions. MATERIALS AND METHODS: In 11 patients who underwent radical prostatectomy we studied the release of eicosanoids, prostaglandin E(2) (PGE(2)) and thromboxane B(2) (TxB(2)), in association with reinfusion of intraoperatively salvaged blood. Blood samples were taken before operation, on days 1 and 3 after operation and before and after cell washing. RESULTS: There was a twofold increase in PGE(2) and a twentyfold increase in TxB(2) in the unwashed salvaged blood. Washing caused a reduction in eicosanoid plasma levels of up to 95%, but a significantly lower level in relation to its corresponding preoperative value was only found for PGE(2). After transfusion of an average of 420 ml RBC sediment from washed blood, the patients' plasma concentrations of PGE(2) and TxB(2) on the 1st and 3rd postoperative day did not significantly differ compared to baseline values. CONCLUSION: Our data support the notion that RBC sediment from 'salvaged' and washed autologous blood contains increased amounts of PGE(2) and TxB(2). It remains, however, questionable if these passively infused eicosanoids become biologically active. According to our study, the PGE(2) and TxB(2) transfused are apparently not responsible for nonhemolytic immunological transfusion reactions.

Aged↗

PubMed1999

[Prophylactic analgesia in functional endoscopic sinus surgery. Hemodynamics, surgical conditions, stress response].

OBJECTIVE: Sufficient control of intraoperative bleeding in functional endoscopic sinus surgery is essential for obtaining adequate surgical results. The necessity of hypotensive anesthetic techniques is a controversial topic among anesthesiologists and ENT-surgeons. This prospective, randomized study compared N2O-supplemented intravenous anesthesia with propofol and fentanyl or sufentanil with respect to hemodynamic reactions, endocrine stress response, blood loss and surgical conditions, and recovery. METHODS: After obtaining informed consent, 32 patients undergoing endoscopic sinus procedures were anesthetized with N2O, propofol, and fentanyl or sufentanil (dosage ratio fentanyl:sufentanil = 7:1). Arterial blood pressure was measured via an arterial line, blood samples for ACTH, AVP, and cortisol were obtained pre-, intra-, and post-operatively, and a psychomotor function test was conducted pre- and postoperatively. The ENT-surgeon estimated the dryness of the surgical field on a numeric scale ranging from 1 to 5, and intraoperative blood loss was measured. RESULTS: Hemodynamic reactions to surgical simulation were blunted more sufficiently in the sufentanil group. Surgical conditions were satisfactory in all patients, but significantly better in the sufentanil group; differences in blood loss did not prove statistically significant. The endocrine stress response was efficiently blunted without significant differences between the groups. Post-operative psychomotor testing showed better recovery in the sufentanil group. CONCLUSIONS: N2O-supplemented intravenous anesthesia is suitable for functional endoscopic sinus procedure without any further need for induced hypotension; sufentanil seems to be superior in regard to hemodynamic stability, surgical conditions, and psychomotor recovery.

Adrenocorticotropic Hormone↗

PubMed1997

[Advantages and limitations of intraoperative mechanical autotransfusion in al prostatectomies].

UNLABELLED: Intraoperative autotransfusion (MAT), preoperative autologous blood donation, and preoperative normovolaemic haemodilution are three different methods to avoid homologous blood transfusion during surgical procedures. The controversial use of MAT via cell saver in tumour surgery as well as contamination of the operative field with urine illustrate the particular difficulties of autologous blood transfusion in connection with radical prostatectomy. We investigated changes in the osmotic resistance of the retransfused red blood cells (RBC), bacterial contamination, changes in coagulation parameters, and the presence of tumour cells. PATIENTS AND METHODS: After written informed consent, 24 patients who presented for radical prostatectomy were randomly allocated to either a group that used MAT or a group that used homologous transfusion. The patients received "balanced anaesthesia" with midazolam, fentanyl, atracurium, and nitrous oxide/oxygen. The analysed parameters from the preoperative period to the 3rd postoperative day are shown in Table 1. The Haemonetics 3 Plus Cell Saver was used for autotransfusion. RESULTS: Our results showed that the haematologic parameters, coagulation factors, and serum chemistry did not differ between the two groups (Tables 2-4). However, there were significant differences during the investigated period. The osmotic resistance of the salvaged RBCs was higher than that preoperatively. Furthermore, there were no tumour cells in the autologous salvaged RBCs. CONCLUSION: Our results showed no decrease in the quality of the autotransfused RBCs, urine was not retransfused; and there were no significant differences between the groups postoperatively. Although there were no tumour cells in the salvaged blood, the possibility of blood irradiation is discussed. We concluded that because of the risk of infection of homologous blood products, MAT is a safe possibility to reduce the amount of homologous blood transfusion required in connection with radical prostatectomy.

Aged↗

PubMed1997

Comparison between three transmucosal routes of administration of midazolam in children.

Midazolam was applied transmucosally in 47 children randomly assigned to three different groups. Group N received 0.2 mg.kg-1 nasally, group R 0.5 mg.kg-1 rectally, and group S 0.2 mg.kg-1 sublingually. All groups were treated 60 min prior to a planned i.v. puncture with EMLA. Reliable and valid psychological parameters (such as emotional situation, shivering, awareness, respiratory rate and facial colour) were scored after premedication and before and after i.v. puncture, 20 min after premedication and until induction. A blood sample was drawn 10, 30 and 60 min after premedication and the levels of midazolam, alpha-hydroxy-midazolam, ACTH, glucose and cortisol were measured. In all three groups the plasma levels of midazolam 10 min after premedication were higher than 70 ng.ml-1 (accepted as a sedative level). 30 min after premedication the midazolam level in the sublingual group was statistically significantly higher than in the nasal group and the psychological parameters in all three groups were significantly changed (10 min after premedication). The psychological parameters were not significantly different between the three groups over the whole study. Sublingual premedication has some advantages (most readily accepted, highest plasma levels and lowest deviations) and could be the first choice in premedication of children. All three transmucosal applications are safe and well accepted, although nasal application was rejected by two of the children.

Administration, Intranasal↗

PubMed1996