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Biomedical subjects

R Krug

Publications and source records attributed to R Krug.

17 recordsLinked to original sources
PubMed2006

Fully balanced steady-state 3D-spin-echo (bSSSE) imaging at 3 Tesla.

In this work a 3D fully balanced steady-state spin-echo sequence (bSSSE) was designed and implemented on a 3-Tesla whole-body MR scanner. In contrast to previously introduced nonbalanced SSSE (nbSSSE) sequences, bSSSE features fully rewound imaging gradients. Additionally, all phase encodings and the readout prephasing are performed after the refocusing pulse. Its performance was compared with previously used gradient-echo (GE) and nbSSSE sequences. The signal response of each sequence was simulated by numerical solution of the Bloch equation. All sequences were then optimized based on these simulations for high-resolution (HR) imaging of tissues with short relaxation times and applied to in vivo HR-MRI of trabecular bone. bSSSE outperformed nbSSSE sequences in terms of SNR and SNR efficiency. Measurements of structural bone parameters revealed thinner trabeculae and a lower bone/bone-marrow fraction for the bSSSE sequence compared to the nbSSSE sequence. By applying a parallel imaging technique based on generalized autocalibrating partially parallel acquisition (GRAPPA) with a reduction factor of 2, we were able to maintain a clinically feasible scan time using bSSSE. Comparisons of structural bone parameters revealed a difference of less than 3% for all structural parameters between parallel and conventional imaging.

Algorithms↗
PubMed2004

[The biofeedback sole tested is a suitable device for avoiding overload under partial load].

During healing of fractures and after implantation of artificial joints mobilization with partial load is a widespread and well-accepted therapeutic principle. Translating our recommendations into action, however, overtaxes many of the patients. The use of the biofeedback sole tested should guarantee avoiding overload under partial weight-bearing conditions. The distribution of the strain sensors in the biofeedback sole was primarily checked with the help of an established system controlling the distribution of strain (PAROTEC) in 17 voluntary, healthy people. Afterwards the biofeedback sole was connected to a digital recording system to analyze the number of steps overloaded in different test cycles in 50 volunteers while using crutches and performing partial load with 20 kg. The distribution of the strain sensors in the biofeedback sole is correct to control partial load under weight bearing with 20 kg. The permanent use of the biofeedback sole showed highly significant advantages in avoiding overload. The number of steps overloaded was reduced by 77%. This effect is independent from body weight or age.

Adult↗
PubMed2001

Should duplex ultrasonography be performed for surveillance of femoropopliteal and femorotibial arterial prosthetic bypasses?

Duplex ultrasonography (DU) has been shown to be beneficial for surveillance of lower extremity vein bypasses. However, DU as part of surveillance program for prosthetic grafts is not widely accepted. The purpose of this report was to determine if DU could reliably detect failing prosthetic infrainguinal arterial bypasses and if there were differences in predictability between femoropopliteal (FP) and femorotibial (FT) prosthetic grafts. Between January 1992 and December 1997, 89 infrainguinal grafts in 66 patients were entered into our postoperative prosthetic graft surveillance protocol, which included clinical evaluation, segmental pressures, pulse volume recordings, and DU performed every 3 months. Patients with follow-up of less than 3 months were excluded unless the graft thrombosed. An abnormal DU considered predictive of graft failure included (1) peak systolic velocity (PSV) > 300 cms/sec at inflow or outflow arteries, in the graft or at an anastomosis (unless an adjunctive arteriovenous fistula had been performed); (2) adjacent PSV ratio > 3.0; (3) uniform PSVs < 45 cms/sec; or (4) monophasic signals throughout the graft. DU was considered to have correctly diagnosed a failing graft if a stenosis > 75% the luminal diameter of the graft, at an anastomosis, or in an inflow/outflow artery was confirmed by operative or arteriographic findings or if the graft thrombosed after an abnormal DU but before intervention. Our results support the routine use of DU as a part of a graft surveillance protocol for femorotibial, but not femoropopliteal, prosthetic grafts.

Blood Vessel Prosthesis Implantation↗
PubMed2000

Selective influence of the menstrual cycle on perception of stimuli with reproductive significance: an event-related potential study.

In this study, we examined changes in the event-related potential (ERP) to stimuli with and without reproductive significance occurring during the menstrual cycle. Eleven spontaneously cycling women were tested during three menstrual phases (menses, ovulatory phase, luteal phase) differing in plasma concentrations of gonadal hormones. ERPs were recorded while subjects were presented with slides showing pictures from four different stimulus categories (sexual stimuli, babies, people occupied with body care, ordinary people). Slides were presented randomly in the context of two tasks, requiring either affective processing (i.e., to judge the emotional content of a slide as positive, neutral, or negative) or structural processing (i.e., to estimate the number of parallel thin lines inserted in each picture). Menstrual phase primarily affected a late positive component (LPC) peaking 550-600 ms poststimulus. The effects were as follows: (i) During the ovulatory phase, amplitude of the LPC to sexual stimuli was larger than that evoked by the other stimulus categories. (ii) This relationship was not apparent during the other menstrual phases or (iii) during the ovulatory phase when the task required structural processing. The ovulatory increase in LPC positivity to sexual stimuli suggests a greater valence of these stimuli during a phase of increased sexual desire. The data indicate a specific effect of the menstrual cycle on the processing of sexual stimuli that increases with deeper emotional processing.

Adult↗
PubMed1997

Late disruption of Dacron aortic grafts.

Aneurysmal degeneration, or complete disruption of Dacron grafts (as opposed to anastomotic complications such as pseudoaneurysms), are not expected by vascular surgeons. We have noted two such cases. A 65-year-old male who had an aortobifemoral, double-velour Dacron graft in 1980, presented in 1995 with a large, pulsatile mass in the right lower quadrant, caused by disruption of the mid-portion of the right limb of the Dacron graft. In a second case, a 68-year-old man had a Dacron aortobifemoral graft placed in 1968 which developed diffuse aneurysmal defects, noted clinically in 1987. Both patients had successful graft replacement. A review of the literature indicates that this complication, although unusual, has been noted periodically. Between 1970 and 1996, we identified 11 case reports of aortic Dacron graft rupture, including knitted Dacron (4), double velour (3), woven (1), knitted thin wall (1), and unspecified Dacron grafts (2). An inquiry to the FDA disclosed another 68 cases of Dacron graft failure in addition to those reported in the surgical literature. We present these cases to alert vascular surgeons of the possibility of Dacron graft degeneration, as late as 19 years after implantation. Diagnosis of the complication is readily apparent by clinical examination and imaging studies, which display an aneurysm of the graft remote from the anastomoses.

Aged↗
PubMed1996

Event-related brain potentials during identification of tachistoscopically presented pictures.

In the present study in 20 healthy subjects, event-related potentials (ERPs) were used to investigate the identification of picture stimuli. Each of 36 landscape pictures and 36 scrambled pictures was presented by a tachistoscope repeatedly until the subject made an identification response. Presentation of one picture was finished after 12 exposures. On the average, landscapes were identified after 5.8 +/- 0.4 exposures; identification responses to scrambles were always wrong and occurred after 11.8 +/- 0.1 exposures. Latencies and amplitude measures were assessed for P2, P3, N400, and the slow wave (SW). Changes in P2 across stimulus presentations did not differ between landscapes and scrambles excluding this component from being indicative for the processing of stimulus meaning. Amplitude of P3 generally declined across presentations, but increased prior to identification for landscape pictures. N400 rapidly declined across presentations of landscapes, but less rapidly for scrambles. The SW increased across stimulus presentations. This increase was more pronounced for landscape than scrambled pictures. The pattern of ERP changes can be interpreted in a framework of a stepwise inhibition of spreading activation within semantic memory with progressing picture identification.

Adult↗
PubMed1996

Jealousy, general creativity, and coping with social frustration during the menstrual cycle.

Sensitivity to feelings of jealousy in women (n = 16) at three phases of their menstrual cycle differing in serum hormone concentrations (menses, preovulatory phase, midluteal phase) was investigated. Nonspecific electrodermal activity indicating sympathetic excitation was measured while subjects listened to stories and imagined situations inducing (i) nonsexual jealousy (the partner forms a deep emotional attachment to another woman), (ii) sexual jealousy (the partner has sexual intercourse with another woman), and (iii) no jealousy (social interaction lacking intense emotionality). Subjective ratings of the intensity of jealousy during both stories of jealousy were also assessed. In addition, changes in cognitive coping abilities, in general, and in the context of socially frustrating events, were assessed by tests of divergent thinking (creativity) and the Rosenzweig Picture Frustration Test. Frequency of nonspecific electrodermal reactions was generally enhanced during the preovulatory phase. This increase was particularly strong when the women listened to stories inducing nonsexual jealousy, i.e., a story characterized by cues of a complete loss of the partner's investment. Rated jealousy tended to be enhanced during the ovulatory phase, especially after the story of nonsexual jealousy. These changes in emotionality were paralleled by an improved divergent thinking performance and less aggressive coping with socially frustrating events around the time of ovulation.

Adaptation, Psychological↗
PubMed1996

Corticosteroid receptor mediated effects on mood in humans.

The present double-blind cross-over study aimed to discriminate effects of dexamethasone (DEX) and cortisol (CORT) on mood in ten healthy men. DEX is assumed to predominantly activate glucocorticoid receptors (GR) whereas CORT binds central nervous mineralocorticoid receptors (MR) as well as GR. Mood was assessed by an extensive adjective checklist (Eigenschaftswoerterliste) every morning during two 7-day experimental periods. During one of these periods, subjects were subchronically treated with placebo, during the other they received DEX (4 mg/day). On days 5 and 7 of these periods, (in a balanced manner) either placebo or CORT (10 mg/h) was infused during the night (9 h) before mood assessment. DEX, acutely, enhanced activation, concentration, and arousal (p < .05). During prolonged DEX administration, the energizing effect of the glucocorticoid decreased, but emotional arousability and negative feelings (anger, sadness) were significantly enhanced. CORT administered during prolonged DEX treatment, counteracted these negative feelings, and enhanced scores on a dimension of "high spirits". Sole administration of CORT also enhanced "high spirits" (p < .05) and, like DEX, activation and concentration (p < .05). Results suggest GR to mediate an energizing effect and, with prolonged activation, a dysphoric influence on mood. Predominant activation of MR appears to mediate changes towards euphoric mood.

Administration, Oral↗
PubMed1995

Influence of albumin concentration, albumin species, pH and temperature on the stereoselectively different binding of (S)-(+)- and (R)-(-)-1-methyl-5-phenyl-5-propyl-barbiturate to serum albumin.

Using normal conditions (phosphate buffer pH 7.4, room temperature) and 1% human serum albumin (HSA), (R)-(-)-1-methyl-5-phenyl-5-propyl-barbiturate = (R)-(-)-1) as compared to (S)-(+)-1 was preferentially bound to albumin: the difference in the enantioselective binding was large (factor of 2) with low substrate concentrations and much smaller (factor of 1.3) with high substrate concentrations (range 5-620 micrograms/ml); with (S)-(+)-1 the decrease of the percent binding values observed with increasing concentrations was only moderately marked. The stereoselective binding difference ((R)-(-)- being greater than (S)-(+)-1) was always present independent of the albumin concentration (range 0.5-10%), the pH value (range 5-10) and the temperature (range 5-50 degrees C). Using 20 micrograms/ml as substrate concentration the stereospecific binding difference was large in solutions with low HSA concentration, in acidic and neutral pH range, and in experiments with low temperature. In contrast to HSA, bovine as well as rabbit serum albumin bound (S)-(+)-1 to a higher percentage than (R)-(-)-1; using rat serum albumin an enantioselective binding difference was not obtained. Taking into account for each of three mammalian albumins the respective number of binding classes and sites in each class, the affinity constant and total binding constant, it becomes evident that they bind (S)-(+)- and (R)-(-)-1 quantitatively differently in a species-specific manner.

Animals↗
PubMed1994

Effects of menstrual cycle on creativity.

Seventeen healthy women (21-31 years) not taking oral contraceptives were tested at three phases of the menstrual cycle distinctly differing in hormonal patterns (menses, preovulatory phase, and midluteal phase). Phase detection was assured by determination of blood hormone concentrations. Another 17 women taking oral contraceptives (combined preparation of estrogen and progestin) served as age-matched controls, and were tested during menses and during phases corresponding to preovulatory and midluteal phase. On each test occasion, aspects of creativity were assessed by a battery of six tests measuring "semantic" and "figural" abilities of divergent thinking. Additionally, a test of motor perseveration (Mittenecker-Zeigeversuch) was presented. During the preovulatory phase, creativity was in general improved when serum concentrations of estrogen (E2) and luteinizing hormone (LH) were highest whereas motor perseveration decreased. In control women, there was no preovulatory improvement of divergent thinking and no preovulatory decrease in motor perseveration.

Adult↗
PubMed1994

Stereoselective differences in the binding of N-methylated barbiturates to human serum albumin.

The binding to human serum albumin (HSA) of a homologous series of N-methylated chiral barbiturates was studied by means of equilibrium dialysis. The length of the aliphatic side chain at C-5 of the barbiturate ring was variable, and the compounds used were: (+)-(S)- and (-)-(R)-5-methyl-(A), -5-ethyl-(B), -5-propyl-(C) and -5-butyl-(D)-1-methyl-5-phenyl-barbiturate. Binding parameters (numbers of binding classes and of binding sites in each class, affinity constant, total binding constant) were obtained from the Scatchard plot of the percent binding values. For both enantiomers of A and D as well as for (-)-(R)-B 2 classes were obtained; (+)-(S)-B and both enantiomers of C had only 1 class. The total binding constant (K) indicated a more than twofold higher binding of (-)-(R)-B (2.64 x 10(3).mol-1) and C (5.75 x 10(3).mol-1) compared with the corresponding (+)-(S)-enantiomer (1.02 and 2.00 x 10(3).mol-1, respectively); in the case of D the (+)-(S)-enantiomer was preferentially bound (K = 10.14 vs. 5.40 x 10(3).mol-1 for the (-)-(R)-enantiomer). The percent binding values of (+)-(S)-A were higher than those of (-)-(R)-A; however, the K-values of the A-enantiomers were almost identical.

Barbiturates↗
PubMed1992

[The effect of "stress hormones" on emotional sensitivity].

Stress is associated with an increased secretion of hormones from the hypothalamus-pituitary-adrenal-axis (HPA-axis). Once released into the blood stream they induce a number of adaptive changes that may also have pertinence to brain functions, resulting, for example in alterations of mood. To provide evidence for a mediation of mood changes by stress related hormone secretion, the influences of a short-term administration of hormones of the HPA-axis on mood and activation were assessed in a total of 182 healthy men (aged between 18 and 34 years in 7 experiments). Effects of intravenously administered hormones on self-perceived mood and activation were assessed by a standardized adjective checklist (Eigenschaftswörterliste) in placebo-controlled, double-blind experiments during rest. Results indicated no effects following corticotropin releasing-hormone or cholecystokinin, but specific effects resulted after vasopressin, oxytocin, ACTH-related hormones, and cortisol. Vasopressin and oxytocin increased activation and attenuated arousal and anger, ACTH-related hormones increased sensitivity and diminished extraversion, while cortisol increased activation and concentration. It is concluded that hormones of the HPA-axis specifically affect mood and activation. The pattern of hormonal changes in mood may have adaptive functions by preparing for behavioral and cognitive coping with stress.

Adult↗
PubMedDate not supplied

Stereoselective binding of the enantiomers of four closely related N-methyl-barbiturates to human, bovine, and rat serum albumin.

Albumin binding for the enantiomers of four closely related N-methyl-5-phenyl-5-alkyl-barbiturates 1-4 was investigated for three different mammalian species by means of equilibrium dialysis. Lipid solubility (n-heptane/phosphate buffer distribution coefficient) increased stepwise by a factor of 56 from 1 to 4. Bovine serum albumin: The (S)-(+)-enantiomers of 1-4 were bound in a higher percentage than the (R)-(-)-enantiomers; lengthening of the aliphatic side-chain increased the binding extent in both enantiomeric groups. Human serum albumin: Binding of (S)-(+)-1 and (S)-(+)-4 was higher than that of the (R)-(-)-enantiomers; with (S)-(+)-2 and (S)-(+)-3 it was much lower than that of the corresponding (R)-(-)-enantiomers. Lengthening of the aliphatic side chain increased the binding extent of the (S)-(+)- as well as the (R)-(-)-enantiomers, but with two exceptions: 1. The (S)-(+)-1 binding exceeded that of the (S)-(+)-2 by a factor of nearly two. 2. The binding extent of (R)-(-)-4 was not further increased in comparison to (R)-(-)-3. Rat serum albumin: (S)-(+)-1 and (S)-(+)-2 were bound in a lower percentage than the (R)-(-)-enantiomers, both 3-enantiomers showing an equal binding extent; (S)-(+)-4 was bound to a slightly greater extent than the (R)-(-)-4. In the group of the (S)-(+)-enantiomers, the binding extent increased from 1 to 4, whereas in that of the (R)-(-)-enantiomers only between 1 and 4. Structural differences between the serum albumins of three mammalian species possibly cause the enantioselective binding pattern found for the enantiomers of 1-4, and are responsible for the finding that the binding extent in some cases did not correlate with the lipid solubility of the compounds.

Animals↗
PubMedDate not supplied

Selective influence of menstrual cycle on perception of stimuli with reproductive significance.

Sixteen healthy women (20-32 years) not taking oral contraceptives were tested at three phases of their menstrual cycles (menses, preovulatory phase, and midluteal phase). Another 16 women taking oral contraceptives served as age-matched controls, and were tested during menses and during phases corresponding to the preovulatory and midluteal phase. On each test occasion, perception was assessed of visual stimuli belonging to three categories: sex (nude men), babies, and stimuli related to body care. Also, meaningless syllables were given. Stimuli were presented by a tachistoscope. Presentation of each stimulus was repeated until the subject signaled recognition. Trials to recognition and correctness of the recognition response were recorded. In spontaneously cycling women effects of the phase of the menstrual cycle depended on the stimulus meaning: During the preovulatory phase, there was an increase in the number of correctly recognized sex stimuli (p < 0.05) and of stimuli falsely recognized as sex stimuli (p < 0.05). The number of stimuli falsely recognized as body care was reduced during this phase (p < 0.05). Moreover, during the luteal phase, the number of trials to recognition of baby stimuli was diminished (p < 0.01). In women taking contraceptives, no stimulus specific changes occurred, but correct recognition was generally improved during the luteal phase. Rather than supporting a general influence of the normal menstrual cycle on perceptual functions, the present results demonstrate that the effects of the menstrual cycle depend on the meaning of the stimulus with the perception of sexual stimuli, but not of stimuli related to maternal nurture, being improved during the preovulatory phase.

Adult↗
PubMedDate not supplied

Converting from general anesthesia to cervical block anesthesia for carotid endarterectomy.

Between January 1, 1992 and June 30, 1998, vascular and general surgery residents performed 401 carotid endarterectomies (185 cervical block, 216 general anesthesia) under supervision of vascular attending surgeons. In January 1995, cervical block anesthesia was newly instituted. Initially anesthesiologists were randomly assigned to these cases and anesthetic technique was not standardized. At the surgeons' insistence later in the series, three specially trained anesthesiologists routinely administered cervical block anesthesia. As experience grew, surgeons realized that operating time greater than 2 hours and high neck dissections requiring mandibular retraction were poorly tolerated by cervical block anesthesia patients but that repeat carotid endarterectomies could be safely performed. Shunts were selectively inserted if significant electroencephalographic changes occurred or carotid stump pressures were less than 50 mm Hg systolic when general anesthesia was used; neurologic changes occurred when cervical block anesthesia was used; or there was a history of ipsilateral stroke for either anesthetic method. Despite an initial learning curve with cervical block anesthesia, the stroke-mortality rate was similar between the two groups (general anesthesia: 1.9% [four cerebrovascular accidents, two deaths]; cervical block anesthesia: 1.6% [two cerebrovascular accidents, two deaths]). Eight (12%) of the first 66 cervical block anesthesia patients were converted to general anesthesia compared to 2 (1.7%) of the most recent 119 patients with cervical block anesthesia (p = 0.03). After cervical block anesthesia was initiated, seven of the first eight repeat carotid endarterectomies were performed using general anesthesia compared to one of the most recent six repeat cases (p = 0.02). As surgeons' comfort with cervical block anesthesia increased, 94% (100) of the most recent consecutive 106 carotid endarterectomies were performed using this technique. These results suggest that carotid endarterectomy can be performed as safely using cervical block anesthesia as general anesthesia, specialized anesthesiologists are essential to achieve a successful outcome, selected repeat carotid endarterectomies can be performed using cervical block anesthesia, very cephalad lesions are best treated using general anesthesia, and surgical trainees can safely perform carotid endarterectomy under attending surgeon supervision if the operation is carried out expeditiously.

Anesthesia, General↗