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Biomedical subjects

F Stahl

Publications and source records attributed to F Stahl.

At least 19 recordsLinked to original sources
PubMed2003

Malocclusion and caries prevalence: is there a connection in the primary and mixed dentitions?

The purpose of this epidemiological cross-sectional study was to determine the prevalence of malocclusion and caries in children and to investigate whether a relationship exists between prevalence of caries and studied malocclusion. The study consisted of 8,864 preschool and schoolchildren with primary dentitions (mean age 4.5 years) and mixed dentitions (mean age 8.9 years). 1997 WHO dental caries criteria were applied to both groups. The existence of an increased caries risk was deducted from the dmft and DMFT indices related to age. Malocclusion in primary and mixed dentitions was classified into seven types. Fifty-seven percent of all children had some form of malocclusion. Prevalence of malocclusion increased and was significantly greater in the mixed dentition sample (p < 0.001) than in the primary dentition sample. Seventy-four percent of children with primary dentitions and 23% of children with mixed dentitions had zero dmft and DMFT scores. Mean dmft indices in subjects with primary and mixed dentitions were 1.02 and 1.53, respectively. No positive correlation between prevalence of caries and malocclusion could be established in the sub sample with primary teeth only. However, statistically significant parallelism in prevalence of malocclusion and caries were found for posterior cross-bite (p= 0.050) and mandibular overjet (p= 0.013) in children with mixed dentitions.

Child↗
PubMed2003

Alterations of myocardial presynaptic sympathetic innervation in patients with multi-vessel coronary artery disease but without history of myocardial infarction.

In patients with myocardial infarction, left ventricular sympathetic denervation exceeds the size of the scar tissue. However, little is known about the regional innervation in patients with coronary artery disease (CAD) but no myocardial infarction. Using positron emission tomography (PET) with N-ammonia and C-hydroxyephedrine (HED), resting perfusion and presynaptic sympathetic innervation were studied in eight patients (seven males, one female; 58+/-9 years) with multi-vessel CAD and no history of myocardial infarction. Using polar map analysis of the PET data, the results were regionally compared with normal databases. The mean HED retention was 8.0%+/-2.0% x min(-1). Myocardial resting perfusion was normal in 23 of 24 vascular territories. Despite normal resting perfusion, significantly reduced HED retention, indicating dysinnervation, was found in 14 of 23 (61%) vascular territories (six of eight patients). Of the dysinnervated territories, 11 (79%) showed angiographically severe stenosis (>or=90% of native vessel/coronary artery bypass graft), eight (57%) showed ischaemia (myocardial perfusion scintigraphy/stress-electrocardiogram) and 12 (86%) had been revascularized. Of the nine segments with normal innervation, two (22%) revealed severe stenosis, two (22%) showed ischaemia and seven (78%) had been revascularized. It can be concluded that, in patients with advanced CAD and normal left ventricular function, dysinnervation can occur in the absence of myocardial infarction. This is consistent with the hypothesis that sympathetic neurones are more susceptible than myocytes to ischaemic damage.

Aged↗
PubMed2001

The acenes: is there a relationship between aromatic stabilization and reactivity?

[reaction--see text] Despite the increasing reactivity from benzene to heptacene, the acene resonance energies per pi electron are nearly constant. The reactivities (computed activation energies) of the individual acene rings correlate with the reaction energies and depend on the product stabilities. Nucleus-independent chemical shifts (NICS; note the sizes of the red dots, above) indicate that the more reactive inner rings actually are more aromatic than the less reactive outer rings and even more aromatic than benzene itself.

Journal Article↗
PubMed2001

Growth and recombination of phage lambda in the presence of exonuclease V from Bacillus subtilis.

When expressed in Escherichia coli, the AddAB exonuclease/recombinase from Bacillus subtilis blocks the growth of phage lambda. Mutants of lambda that are deleted for ea47, a gene of unknown function which is expressed early in the lytic cycle, are not blocked for growth. The blocked-growth phenotype of lambda ea47+ in the presence of AddAB is expressed only when phage DNA replication is permitted.

Bacillus subtilis↗
PubMed2001

A combined crossed molecular beam and ab initio investigation of C2 and C3 elementary reactions with unsaturated hydrocarbons--pathways to hydrogen deficient hydrocarbon radicals in combustion flames.

Crossed molecular beam experiments on dicarbon and tricarbon reactions with unsaturated hydrocarbons acetylene, methylacetylene, and ethylene were performed to investigate the dynamics of channels leading to hydrogen-deficient hydrocarbon radicals. In the light of the results of new ab initio calculations, the experimental data suggest that these reactions are governed by an initial addition of C2/C3 to the pi molecular orbitals forming highly unsaturated cyclic structures. These intermediates are connected via various transition states and are suggested to ring open to chain isomers which decompose predominantly by displacement of atomic hydrogen, forming C4H, C5H, HCCCCCH2, HCCCCCCH3, H2CCCCH and H2CCCCCH. The C2(1 sigma g+) + C2H4 reaction has no entrance barrier and the channel leading to the H2CCCCH product is strongly exothermic. This is in strong contrast with the C3(1 sigma g+) + C2H4 reaction as this is characterized by a 26.4 kJ mol-1 threshold to form a HCCCCCH2 isomer. Analogous to the behavior with ethylene, preliminary results on the reactions of C2 and C3 with C2H2 and CH3CCH showed the H-displacement channels of these systems to share many similarities such as the absence/presence of an entrance barrier and the reaction mechanism. The explicit identification of the C2/C3 vs. hydrogen displacement demonstrates that hydrogen-deficient hydrocarbon radicals can be formed easily in environments like those of combustion processes. Our work is a first step towards a systematic database of the intermediates and the reaction products which are involved in this important class of reactions. These findings should be included in future models of PAH and soot formation in combustion flames.

Journal Article↗
PubMed2001

Mouse chromosome 19 and distal rat chromosome 1: a chromosome segment conserved in evolution.

Through a combination of radiation hybrid mapping and studies by FISH and zoo-FISH we have made a comparative investigation of the distal portion of rat chromosome 1 (RNO1) and the entire mouse chromosome 19 (MMU19). It was found that homologous segments of RNO1 and MMU19 are similar in banding morphology and in length as determined by several different methods, and that the gene order of the 46 genes studied appears to be conserved across the homologous segments in the two species. High-resolution zoo-FISH techniques showed that MMU19 probes highlight only a continuous segment on RNO1 (1q43-qter), with no detectable signals on other rat chromosomes. We conclude that these data suggest the evolutionary conservation of a chromosomal segment from a common rodent ancestor. This segment now constitutes the entire MMU19 and a large segment distally on RNO1q in the mouse and rat, respectively.

Animals↗
PubMed2000

[Percutaneous myocardial laser revascularization. A new therapy technique for patients with coronary disease and severe angina pectoris without conventional therapy options].

BACKGROUND AND OBJECTIVES: In patients with intractable angina because of end-stage coronary artery disease, transmyocardial laser revascularization (TMR) leads to improvement of angina pectoris and increased exercise capacity. However, surgical thoracotomy is required for TMR with considerable morbidity and mortality. Therefore, a catheter-based laser system has been developed which allows to create laser channels into the myocardium from the left ventricular cavity. PATIENTS AND METHODS: 46 patients (38 m, 8 f) with refractory angina pectoris due to severe coronary artery disease were treated with "percutaneous myocardial laser revascularisation" (PMR). Clinical parameters (severity of angina pectoris, use of additional nitroglycerin) and results of non-invasive tests (exercise-ECG, echocardiography, thallium-scintigraphy) were analysed at baseline and 3, 6 and 12 months after PMR. RESULTS: The PMR procedure was successfully completed in all patients. In 30 patients, one region (anterior, lateral, inferior) of the left ventricle was treated and in 16 patients, 2 or 3 regions were treated. Clinical follow-up demonstrated significant improvement of angina pectoris (CCS-class at baseline: 3.1 +/- 0.2, 3 months after PMR: 1.8 +/- 0.7, 12 months after PMR: 1.5 +/- 0.9) (p < 0.001) and increased exercise capacity (exercise time on standard bicycle ergometry at baseline: 383 +/- 151 s, 3 months after PMR: 494 +/- 140 s, 12 months after PMR: 480 +/- 151 s) (p < 0.05), but thallium scintigraphy failed to show improved perfusion of the laser treated regions. CONCLUSIONS: PMR is a new safe and feasible therapeutic option in patients with refractory angina pectoris due to end-stage coronary artery disease. Initial results show significant improvement of clinical symptoms and an increased exercise capacity but thallium scintigraphy failed to show improved perfusion after PMR.

Aged↗
PubMed2000

[Percutaneous myocardial laser revascularization (PMR)].

In patients with severe angina pectoris due to coronary artery disease, who are not candidates for either percutaneous coronary angioplasty or coronary artery bypass surgery, transmyocardial laser revascularization (TMR) often leads to improvement of clinical symptoms and increased exercise capacity. One drawback of TMR is the need for surgical thoracotomy in order to gain access to the epicardial surface of the heart. Therefore, a catheter-based system has been developed, which allows creation of laser channels into the myocardium from the left ventricular cavity. Between January 1997 and November 1999, this "percutaneous myocardial laser revascularization" (PMR) has been performed in 101 patients at the Herzzentrum Leipzig. In 63 patients, only 1 region of the heart (anterior, lateral, inferior or septal) was treated with PMR, in 38 patients 2 or 3 regions were treated in 1 session. There were 12.3 +/- 4.5 (range 4 to 22) channels/region created into the myocardium. After 3 months, the majority of patients reported significant improvement of clinical symptoms (CCS class at baseline: 3.3 +/- 0.4, after 6 months: 1.6 +/- 0.8) (p < 0.001) and an increased exercise capacity (baseline: 397 +/- 125 s, after 6 months: 540 +/- 190 s) (p < 0.05). After 2 years, the majority of patients had experienced sustained clinical benefit after PMR, the CCS class after 2 years was 1.3 +/- 0.7, exercise capacity was 500 +/- 193 s. However, thallium scintigraphy failed to show increased perfusion in the PMR treated regions. The pathophysiologic mechanisms of myocardial laser revascularization is not yet understood. Most of the laser channels are found occluded after various time intervals after intervention. Other possible mechanisms include myocardial denervation or angioneogenesis after laser revascularization, however, unequivocal evidence for these theories is not yet available. In conclusion, PMR seems to be a safe and feasible new therapeutic option for patients with refractory angina pectoris due to end-stage coronary artery disease. The first results indicate improvement of clinical symptoms and increased exercise capacity, whereas evidence of increased perfusion after laser revascularization in the laser-treated regions is still lacking.

Adult↗
PubMed2000

Changes in myocardial perfusion after catheter-based percutaneous laser revascularisation.

This study investigated the effect of percutaneous laser revascularisation (PMR) on regional myocardial blood flow. PMR is a new therapeutic modality for patients suffering from angina pectoris due to coronary artery disease (CAD) that is not amenable to revascularisation. Initial clinical studies discovered reduced angina pectoris and increased exercise capacity after PMR. There are no previous clinical studies reporting the impact of PMR on perfusion. Thirty-six patients with end-stage CAD underwent thallium-201 single-photon emission tomography studies on four different occasions: immediately before PMR and 3, 6 and 12 months following PMR. Each study consisted of pharmacological stress and rest scintigraphy. Semiquantitative evaluation was performed by use of 14 standardised wall segments which were classified (a) according to the localisation of the PMR target region into treated segments, segments adjacent to the treated area and non-treated segments and (b) according to the pre-therapeutic local perfusion into four groups: no (0), slight (I), moderate (II) or severe (III) perfusion deficit. At stress in treated segments of groups II and III local scintigraphic count densities increased from 60.1% and 34.7% at baseline to 65.3% and 48.3% after 12 months (P<0.05) while they decreased in segments of group 0 from 94.2% to 85.7% (P<0.05). In rest studies no changes occurred. Thus, the local rest-stress differences within the target areas become smaller after PMR. In the PMR target area but not in the nontreated area an improvement in regional myocardial flow reserve occurs in wall segments with initially severely or moderately reduced stress perfusion. This effect is consistent with the clinical improvement after PMR.

Aged↗
PubMed2000

Light-emitting diode (LED) polymerisation of dental composites: flexural properties and polymerisation potential.

The clinical performance of light polymerised dental composites is greatly influenced by the quality of the light-curing unit (LCU) used. Commonly used halogen LCUs have some specific drawbacks such as decreasing of the light output with time. This may result in low degree of monomer conversion of the composites with negative clinical implications. Previous studies have shown that blue-light-emitting diode (LED) LCUs have the potential to polymerise dental composites without having the drawbacks of halogen LCUs. Despite the relatively low irradiance of current LED LCUs, their efficiency is close to that of conventional halogen LCUs with more than twice the irradiance. This phenomenon has not been explained fully yet. Hence, more tests of the LED LCU's effectiveness and of the mechanical properties of oral biomaterials processed with LED LCUs need to be carried out. This study investigates the flexural properties of three different composites with three different shades, which were polymerised with either a commercial halogen LCU or an LED LCU, respectively. In most cases no significant differences in flexural strength and modulus between composites polymerised with a halogen LCU or an LED LCU, respectively, were found. A simple model for the curing effectiveness based on the convolution absorption spectrum of the camphorquinone photoinitiator present in composites and the emission spectra of the LCUs is presented.

Composite Resins↗
PubMed2000

[Percutaneous myocardial laser revascularization (PMR), a new therapeutic procedure for patients with refractory angina pectoris].

In patients with severe angina pectoris due to coronary artery disease, who are not candidates for either percutaneous coronary angioplasty or coronary artery bypass surgery, transmyocardial laser revascularization (TMR) often leads to improvement of clinical symptoms and increased exercise capacity. One drawback of TMR is the need for surgical thoracotomy in order to gain access to the epicardial surface of the heart. Therefore, a catheter-based system has been developed, which allows creation of laser channels into the myocardium from the left ventricular cavity. Between January 1997 and November 1999, this "percutaneous myocardial laser-revascularization" (PMR) was performed in 85 patients at the Herzzentrum Leipzig. In 43 patients, only one region of the heart (anterior, lateral, inferior or septal) was treated with PMR; in 42 patients two or three regions were treated in one session. 12.3 +/- 4.3 (range 4-22) channels/region were created into the myocardium. Six months after PMR, the majority of patients reported significant improvement of clinical symptoms (CCS class at baseline: 3.3 +/- 0.4; after 6 months: 1.6 +/- 0.9) (p < 0.001) and an increased exercise capacity (baseline: 349 +/- 138 s; after 6 months: 470 +/- 193 s) (p < 0.05); however, thallium scintigraphy failed to show increased perfusion in the PMR treated regions. PMR seems to be a safe and feasible new therapeutic option for patients with refractory angina pectoris due to end-stage coronary artery disease. The first results indicate improvement of clinical symptoms and increased exercise capacity; evidence of increased perfusion in the laser-treated regions is still lacking.

Adult↗
PubMed1999

Catheter-based percutaneous myocardial laser revascularization in patients with end-stage coronary artery disease.

OBJECTIVES: This study evaluates the feasibility and safety of a catheter-based laser system for percutaneous myocardial revascularization and analyses the first clinical acute and long-term results in patients with end-stage coronary artery disease (CAD) and severe angina pectoris. BACKGROUND: In patients with CAD and intractable angina who are not candidates for either coronary artery bypass grafting (CABG) or percutaneous transluminal coronary angioplasty (PTCA), transmyocardial laser revascularization (TMR) has been developed as a new treatment that results in reduced angina pectoris and increased exercise capacity. However, surgical thoracotomy is required for TMR with considerable morbidity and mortality. METHODS: A catheter-based system has been developed that allows creation of laser channels in the myocardium from within the left ventricular cavity. Laser energy generated by a Holmium: YAG (Cardiogenesis Corporation, Sunnyvale, California) laser was transmitted to the myocardium via a flexible optical fiber capped by an optic lens. The optical fiber was maneuvered to the target area under biplane fluoroscopy through a coaxial catheter system permitting movement in three dimensions. RESULTS: Thirty-four patients with severe CAD not amenable to either CABG or PTCA and refractory angina pectoris (Canadian Cardiologic Society [CCS] Angina Scale Class III-IV) were included in the study. Ischemic regions were identified by coronary angiography and confirmed by thallium scintigraphy. The percutaneous myocardial revascularization (PMR) procedure was successfully completed in all patients. In 29 patients, one vascular territory of the left ventricle and in 5 patients, two vascular territories were treated. Eight to fifteen channels were created in each ischemic region. Major periprocedural complications were limited to an episode of arterial bleeding requiring surgical repair. There was one death early after PMR, due to a myocardial infarction (MI) in a nontreated region. Clinical follow-up at 6 months (17 patients) demonstrated significant improvement of angina pectoris (CCS class before PMR: 3.0+/-0.0, six months after PMR: 1.3+/-0.8, p<0.0001) and increased exercise capacity (exercise time on standard bicycle ergometry before PMR: 384+/-141 s, six months after PMR: 514+/-158 s, p<0.05), but thallium scintigraphy failed to show improved perfusion of the laser treated regions. CONCLUSIONS: Percutaneous myocardial revascularization is a new safe and feasible therapeutic option in patients with CAD and severe angina pectoris not amenable to either CABG or PTCA. Initial results show immediate and significant improvement of symptoms and exercise capacity but evidence of improved myocardial perfusion is still lacking.

Aged↗
PubMed1999

Diagnosis of Cushing's syndrome: re-evaluation of midnight plasma cortisol vs urinary free cortisol and low-dose dexamethasone suppression test in a large patient group.

We studied plasma cortisol levels at 00:00 h and 08:00 h in 103 patients with Cushing's syndrome and 144 patients in whom this diagnosis had been excluded. These patients were hospitalized in our department from 1975 to 1996. Additionally, we measured these parameters in 20 healthy volunteers and in 5 patients with nonendocrine disease. Corresponding data of urinary free cortisol and low-dose dexamethasone suppression testing were included in the evaluation. Values (mean+/-SD) from patients with Cushing's syndrome: 510+/-232 nmol/l (range 165-1488) for plasma cortisol 00:00 h, 574+/-242 nmol/l (range 236-1612) for plasma cortisol 08:00 h, 991+/-885 nmol/24 h (range 154-4866) for urinary free cortisol and 479+/-304 nmol/l (range 34 - 1,393) for plasma cortisol after 1.5 mg dexamethasone. Values from the patients excluded from Cushing's syndrome: 99+/-76 nmol/l (range 5-371) for plasma cortisol 00:00 h, 393+/-136 nmol/l (range 119-812) for plasma cortisol 08:00 h, 126+/-84 nmol/24 h (range 30-485) for urinary free cortisol, and 64+/-82 nmol/l (range 5-395) for plasma cortisol after 1.5 mg dexamethasone. Values of the healthy volunteers respectively patients with non-endocrine disease: 59+/-30 nmol/l (range 25-130) respectively 127+/-80 nmol/l (range 62-265) for plasma cortisol 00:00 h and 388+/-144 nmol/l (range 157-651) respectively 498+/-113 nmol/l (range 302-581) for plasma cortisol 08:00 h. None of the Cushing patients exhibited a 00:00 h plasma cortisol below 140 nmol/l and only one had a urinary free cortisol below 200 nmol/24 h, whereas 4 were complete dexamethasone suppressors. The diagnostic value of these parameters was examined based on various cutoffs. We recommend determination of midnight plasma cortisol as an efficient and simple additional procedure for the diagnosis of Cushing's syndrome. The sensitivity and specificity of this procedure is similar to urinary free cortisol and slightly above the low-dose dexamethasone suppression testing in our hospitalized patients.

Adult↗
PubMed1998

Intra- vs intersubunit communication in the homodimeric restriction enzyme EcoRV: Thr 37 and Lys 38 involved in indirect readout are only important for the catalytic activity of their own subunit.

EcoRV is a dimer of two identical subunits which together form one binding site for the double-stranded DNA substrate. Concerted cleavage of both strands of the duplex requires intersubunit communication to synchronize the two catalytic centers of EcoRV. Here we address the question of how contacts to the DNA backbone trigger conformational changes which lead to the activation of both catalytic centers. The structure of the specific EcoRV-DNA complex shows that a region including amino acids Thr 37 and Lys 38 is involved in interactions with the DNA backbone and is a candidate for intersubunit communication. Homodimeric EcoRV T37A and K38A variants have a 1000-fold reduced catalytic activity. To examine whether Thr 37 and Lys 38 of one subunit affect the catalytic center in the same subunit and/or in the other subunit, we have produced heterodimeric variants containing a Thr 37 --> Ala or Lys 38 --> Ala substitution in one subunit combined with a wild type (wt) subunit (wt/T37A and wt/K38A) or with a subunit which contains an amino acid substitution (Asp 90 --> Ala) in the active site (D90A/T37A and D90A/K38A). Cleavage experiments with supercoiled pAT153 show that wt/T37A and wt/K38A preferentially nick the DNA. A steady-state kinetic analysis of the cleavage of an oligodeoxynucleotide substrate shows that the activity of wt/T37A and wt/K38A is half of that of wild type EcoRV, whereas D90A/T37A and D90A/K38A are almost inactive. These results demonstrate that Thr 37 and Lys 38 affect primarily the catalytic center in their own subunit and that both subunits of EcoRV can be activated independently of each other. We suggest that Thr 37 and Lys 38 control the catalytic activity of the active site in their own subunit by positioning alpha-helix B.

Catalysis↗
PubMed1998

Free plasma catecholamines in spinal cord injured persons with different injury levels at rest and during exercise.

Spinal cord lesion leads to an interruption of pathways from brain to the peripheral sympathetic nervous system, which results in pathological changes in sympathetic innervation. Free epinephrine (E), norepinephrine (NE) and dopamine (DA) were measured in 30 tetraplegics (TETRA), 15 high-lesion paraplegics (T1 and T4, HPARA), 15 paraplegics with injuries between T5 and T10 (MPARA), 15 low-lesion paraplegics (below T10, LPARA) and 16 non-handicapped control persons (C) at rest, at 60 and 100% of maximal oxygen consumption during graded wheelchair ergometry (WCE). The TETRA showed significant lower E and NE levels at rest and only slight increases during physical exercise. The E and NE concentrations of the paraplegics with a lesion below T5 were significantly higher than those of the high-lesion paraplegics, as well as those of the control persons at every point in the study. All paraplegics and the control persons showed, at submaximal and maximal exercise, a significant increase in NE. Only a slight increase in E in HAPRA was shown. No differences were found at rest and during exercise in E and NE levels in the MPARA and LPARA. No significant differences were found in the dopamine concentration at rest or during exercise for any of the groups. In summary, different levels of lesion and the resulting interruption to sympathetic pathways in the spinal cord are decisive factors in the degree of impairment of sympathetic innervation in SCI persons. Tetraplegics show less preganglionic resting activity because of interruption of impulses from central centers and no considerable stimulation of the sympathetic nervous system during maximal exercise. Individuals with high paraplegia have a partial impairment of catecholamine release, especially of epinephrine, at rest and during exercise. Paraplegics with a lesion level below T5 showed an augmented basal and exercise-induced upper spinal thoracic sympathetic activity in comparison to control persons.

Adult↗
PubMed1998

Catecholamines, heart rate, and oxygen uptake during exercise in persons with spinal cord injury.

The purpose of this study was to investigate the influence of different injury levels in persons with spinal cord injury (SCI) on epinephrine (Epi) and norepinephrine (NE) at rest and during graded wheelchair exercise and the related changes in heart rate and O2 uptake (VO2). Twenty tetraplegics (Tetra), 10 high-lesion paraplegics (HLPara), 20 paraplegics with SCI below T5 (MLPara), and 18 able-bodied, nonhandicapped persons (AB) were examined. Because of the higher level of interruption of the sympathetic pathways, Tetra persons showed lower Epi and NE at rest and only slight increases during exercise compared with all other groups; the Tetra subjects' impaired cardiac sympathetic innervation caused restricted cardioacceleration and strongly reduced maximal VO2. When compared with AB persons, HLPara had comparable NE but lower Epi levels as a result of partial innervation of the noradrenergic system and denervation of the adrenal medulla. MLPara subjects showed an augmented basal and exercise-induced upper spinal thoracic sympathetic activity compared with AB subjects. The increase in heart rate in relation to VO2 was higher in HLPara because of a smaller stroke volume as a result of venous blood pooling. The different exercise response in persons with SCI is a result of the interruption of pathways in the spinal cord to the peripheral sympathetic nervous system in addition to the motor paralysis.

Adult↗