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Biomedical subjects

R Schulz

Publications and source records attributed to R Schulz.

At least 91 records · Page 5Linked to original sources
PubMed2001

Linear and non-linear dynamics of heart rate variability in brain dead organ donors.

Recent studies outlined linear and non-linear dynamics in heart rate variability; however, their physiological origin is still unknown. The present study investigated the impact of cerebral function on linear and non-linear dynamics in heart rate variability. Electrocardiograms from seven brain dead organ donors and seven healthy volunteers were analyzed. Atropine was used in healthy volunteers to adjust their heart rate to that of the donors. As compared to healthy volunteers without atropine, the linear dynamics of heart rate variability, determined by time and frequency domain analyses, were significantly reduced in healthy volunteers with atropine and, to an even greater extent, in donors. Atropine tended to increase the complexity and non-linearity of heart rate variability in healthy volunteers, as determined by the correlation dimension D and the largest Lyapunov exponent L, respectively (D = 9.43 +/- 2.93 vs. 7.65 +/- 0.97 and L = 0.525 +/- 0.099 vs. 0.504 +/- 0.047 bits.beat-1; both NS), while these indices were significantly reduced in donors by 19.5 +/- 12.8% and 15.0 +/- 11.7%, respectively (D = 6.16 +/- 0.98 and L = 0.428 +/- 0.059 bits.beat-1; both p < 0.05 vs. volunteers). Thus, loss of cerebral function reduces both linear and non-linear components of heart rate variability.

Adult↗
PubMed2001

Perfusion-contraction match and mismatch.

The present article describes the concept of perfusion-contraction matching originally proposed by Ross, goes on to critically discuss the available techniques to measure both regional myocardial blood flow and function in the experimental and clinical setting, and finally analyzes the available evidence for perfusion-contraction match and mismatch during normoperfusion and various scenarios of myocardial ischemia/reperfusion, including acute and subacute ischemia, coronary microembolization, stunning and hibernation.

Animals↗
PubMed2001

Rainfall-induced sediment and pesticide input from orchards into the Lourens River, Western Cape, South Africa: importance of a single event.

Rainfall-induced runoff transported sediments and pesticides into the Lourens River and its tributaries during a 28.8-mm rainstorm in mid-December 1998. Average 1-h peak levels of current-use insecticides applied to adjacent orchard plots were 1.5 micrograms l-1 azinphos-methyl, 0.2 microgram l-1 chlorpyrifos and 2.9 micrograms l-1 total endosulfan (alpha, beta, S) in the river itself. Respective average 1-h pesticide levels associated with suspended particles were 1247, 924 and 12,082 micrograms kg-1, along with 980 micrograms kg-1 of prothiofos. Total suspended solids increased during runoff from 32 to 520 mg l-1. The contaminated edge-of-field runoff entered the river via the tributaries directly bordering the orchard-growing areas. Increased concentrations of azinphos-methyl and prothiofos associated with suspended sediments were demonstrated to persist for about 3.5 months without any further input in one of the tributaries. This illustrates that the short-term exposure has the potential to result in long-term contamination of surface waters. In terms of chemical load during the 1-h peak discharge period, the single rainfall event caused a loss of 173 g h-1 azinphosmethyl, 55 g h-1 chlorpyrifos, 740 g h-1 total endosulfan (alpha, beta, S) and 41 g h-1 prothiofos. Levels of contamination were extremely high; they exceed the national water quality standards and those established by the US EPA. A comparison with standard toxicity data and 24-h LC50 s for the local amphipod species Paramelita nigroculus, obtained during this study, indicates that the concentrations found in the river may result in acute toxic effects on aquatic invertebrates and fishes. A probability analysis of 10-y rainfall data revealed that the frequency of a similar storm event occurring within the main spraying season is 1.7 y-1.

Agriculture↗
PubMed2001

Effects of chronic ammonium and nitrite contamination on the macroinvertebrate community in running water microcosms.

In the present study, during a three-month exposure lethal and sublethal effects of ammonium and its products on typical brook organisms (Gammarus pulex, Amphipoda; Radix ovata, Gastropoda; Limnephilus lunatus Trichoptera) were monitored in microcosms approximating field conditions. Every 24 h during this period the microcosms were contaminated with ammonium at five different nominal concentrations, which by chemical reactions produced a mixture of the toxic products ammonia and nitrite. G. pulex proved the most sensitive to the ammonia and nitrite contamination resulting from the ammonium load. In contrast. L. lunatus and R. ovota exhibited clearly effects only at concentrations 10 times higher. It is appropriate to investigate ammonium pollution with its reaction products as a mixture, because in natural bodies of water receiving ammonium input (e.g., from sewage-treatment plants) the substances ammonium/ammonia and nitrite are likewise present simultaneously.

Animals↗
PubMed2001

Comparison of spray drift- and runoff-related input of azinphos-methyl and endosulfan from fruit orchards into the Lourens River, South Africa.

Spray drift and edge-of-field runoff are regarded as important routes of nonpoint-source pesticide input into aquatic surface waters, with current regulatory risk assessment in Europe focussing largely on spray drift. However, the two routes of entry had rarely been compared directly in the same catchment. To this end, the concentrations and loads of the current-use insecticides azinphos-methyl (AZP) and endosulfan (END) were monitored in the Lourens River, South Africa downstream of a 400-ha fruit orchard area during normal farming practice. Spray drift-related peak pesticide levels in the tributaries were in the range of 95th-percentiles of standard drift values according to regulatory risk assessment procedures. Resulting concentrations in Lourens River water samples (n = 3) at a discharge of 0.28 m3/s were as high as 0.04 +/- 0.01 microg/l AZP and 0.07 +/- 0.02 microg/l END. Pesticide levels at the same site during runoff following 3 storm events varying in rainfall between 6.8 and 18.4 mm/d (discharge: 7.5-22.4 m3/s) were considerably higher: by factors between 6 and 37 for AZP (0.26-1.5 microg/l) and between 2 and 41 for END (0.13-2.9 microg/l). Levels of pesticides associated with suspended particles were increased during runoff only up to 1247 microg/kg AZP and 12082 microg/kg END. A possible reason for the relative importance of runoff is that runoff largely integrates potential pesticide input over both time and space, because the prerequisites for the occurrence of runoff in terms of application and plot characteristics as well as meteorological conditions are far less specific than for spray drift. A probability analysis based on pesticide application patterns and 10-yr rainfall data indicates that the frequencies of rainfall events > or = 10 and > or = 15 mm/d are 3.4 and 1.7 per spraying season, respectively.

Agriculture↗
PubMed2001

Lack of aura experience correlates with bitemporal dysfunction in mesial temporal lobe epilepsy.

UNLABELLED: The diagnostic value of lack of aura experience in patients with temporal lobe epilepsy (TLE) is unclear. PURPOSE: To evaluate possible factors of bitemporal dysfunction in patients with mesial TLE who did not experience an aura in electroencephalography EEG/video monitoring for epilepsy surgery. METHODS: Ictal scalp EEG propagation patterns of 347 seizures of 58 patients with mesial temporal lobe sclerosis or non-lesional mesial TLE, interictal epileptiform discharges (IED), presence of unilateral mesial temporal lobe sclerosis in visual magnetic resonance imaging (MRI) analysis, prose memory performance, history or not of an aura, and postictal memory or absence of an aura were analyzed. The ictal EEG was categorized as follows. EEG seizure: (a) remaining regionalized, (b) non-lateralized, (c) showing later switch of lateralization or bitemporal asynchronous ictal patterns. RESULTS: Absent aura in monitoring was significantly correlated with absence of unitemporal MRI sclerosis (P=0.004), bitemporal IED (P=0.008), and propagation of the ictal EEG to the contralateral temporal lobe (P=0.001). Other historical data and interictal prose memory performance were not significantly correlated with absent aura. Ten of 11 patients without aura in monitoring also had absent or rare auras in their history. CONCLUSIONS: Lack of aura experience strongly correlates with indicators of bitemporal dysfunction such as bitemporal interictal sharp waves and bitemporal ictal propagation in scalp EEG, and absence of lateralized MRI sclerosis in patients with mesial TLE. The fact that absent auras are not correlated with episodic memory suggests a transient memory deficit, probably because of rapid propagation to the contralateral mesial temporal lobe.

Adolescent↗
PubMed2001

Spatiotemporal relationship between seizure activity and interictal spikes in temporal lobe epilepsy.

PURPOSE: To analyze the spatio-temporal relationship between seizure propagation and interictal epileptiform discharges (IEDs) in patients with bitemporal epilepsy. METHODS: We investigated 18 adult patients with intractable temporal lobe epilepsy (TLE) who had undergone continuous video-EEG monitoring during presurgical evaluation. Only those patients were selected who had independent IEDs over both temporal lobes. Two authors evaluated the ictal and interictal EEG data independently. RESULTS: We analyzed 52 lateralized seizures of 18 patients. Thirty-one seizures showed ipsilateral seizure spread exclusively, whereas in 21 seizures the contralateral hemisphere was also involved. In lateralized seizures without contralateral propagation, we found that spikes ipsilateral to the seizure onset occurred postictally in a greater ratio than preictally (P<0.001). In lateralized seizures with contralateral propagation, we found no significant changes in the postictal spike distribution. CONCLUSIONS: Our findings showed that the lateralization of IEDs may depend on the brain areas involved by the preceding seizures, suggesting that spikes can be influenced by the seizure activity, and are not independent signs of epileptogenicity.

Electroencephalography↗
PubMed2001

Area characteristics and individual-level socioeconomic position indicators in three population-based epidemiologic studies.

PURPOSE: There is growing interest in incorporating area indicators into epidemiologic analyses. Using data from the 1990 U.S. Census linked to individual-level data from three epidemiologic studies, we investigated how different area indicators are interrelated, how measures for different sized areas compare, and the relation between area and individual-level social position indicators. METHODS: The interrelations between 13 area indicators of wealth/income, education, occupation, and other socioenvironmental characteristics were investigated using correlation coefficients and factor analyses. The extent to which block-group measures provide information distinct from census tract measures was investigated using intraclass correlation coefficients. Loglinear models were used to investigate associations between area and individual-level indicators. RESULTS: Correlations between area measures were generally in the 0.5--0.8 range. In factor analyses, six indicators of income/wealth, education, and occupation loaded on one factor in most geographic sites. Correlations between block-group and census tract measures were high (correlation coefficients 0.85--0.96). Most of the variability in block-group indicators was between census tracts (intraclass correlation coefficients 0.72--0.92). Although individual-level and area indicators were associated, there was evidence of important heterogeneity in area of residence within individual-level income or education categories. The strength of the association between individual and area measures was similar in the three studies and in whites and blacks, but blacks were much more likely to live in more disadvantaged areas than whites. CONCLUSIONS: Area measures of wealth/income, education, and occupation are moderately to highly correlated. Differences between using census tract or block-group measures in contextual investigations are likely to be relatively small. Area and individual-level indicators are far from perfectly correlated and provide complementary information on living circumstances. Differences in the residential environments of blacks and whites may need to be taken into account in interpreting race differences in epidemiologic studies.

Adult↗
PubMed2001

Long-term effects of educational and peer discussion group interventions on adjustment to breast cancer.

The authors report a 3-year follow-up of the effects of 8-week support group interventions on the quality of life of women with early stage breast cancer. Shortly after diagnosis, women were randomly assigned to 1 of 4 conditions: control, education, peer discussion, and education plus peer discussion. The education group intervention focused on providing information to enhance control over the illness experience, whereas the peer discussion group intervention focused on providing emotional support through the expression of feelings. Consistent with the results that emerged 6 months after the interventions (V. S. Helgeson, S. Cohen, R. Schulz, & J. Yasko, 1999), the authors found that the benefits of the education intervention were maintained over a 3-year period (N=252), although effects dissipated with time. The authors continued to find no benefits of the peer discussion intervention, either alone or in combination with education.

Adaptation, Psychological↗
PubMed2001

Elimination of doxepin isomers from the horse following intravenous application.

The tricyclic antidepressant doxepin, representing a 5:1 mixture of trans- and cis-isomers, owns tranquilizing properties. This compound has been associated with illicit medication of racing horses, and therefore should be considered in doping control. Because analysis of doxepin in equine body fluids has not been documented in the literature, a highly sensitive analytical method was developed to individually monitor the doxepin isomers in blood and urine of horses by the use of gas chromatography/mass spectrometry. Following a dose of 1 mg doxepin-HCl/kg intravenously (i.v.), both the isomers were quantified for up to 24 h in serum of horses (n=4). The beta-half-lives of the trans- and cis-isomers were 3.5 and 3.1 h, respectively. The ratio of the trans/cis-isomers was found to be constant (4.7:1) during drug elimination and thus corresponded to the original composition of the antidepressant. Up to 12 h following administration low trans-isomer concentrations in an average range of 2-6 ng/mL were detected in urine of each of the horses, while the cis-isomer was only present in two of four horses for up to 8 and 12 h, respectively. In serum, mean trans-isomer concentrations exceeded urine levels maximally 120-fold after 3 h and at least sixfold after 12 h. As serum exhibits considerably higher concentrations of the doxepin isomers as compared with urine, blood of horses is the recommended body fluid when screening for the antidepressant.

Animals↗
PubMed2001

Illness representations according to age and effects on health behaviors following coronary artery bypass graft surgery.

OBJECTIVES: To determine if illness representations differ as a function of age and how these representations, in conjunction with age, predict postoperative health behaviors. DESIGN: Prospective study of patients undergoing coronary artery bypass graft (CABG) surgery. SETTING: A large metropolitan hospital providing regional cardiac care for patients in a tri-state area, located in Pittsburgh, Pennsylvania. PARTICIPANTS: All consenting patients (N = 309) from a consecutive series of patients scheduled for CABG surgery between January 1992 and January 1994. To be eligible for participation, patients could not be scheduled for any other coincidental surgery (e.g., valve replacement), and could not be in cardiac intensive care or experiencing angina at the time of the referral. Participants were predominantly male (70%) and married (80%), and averaged 62.8 years of age. MEASUREMENTS: Postoperative self-reported health behaviors. RESULTS: Older participants awaiting CABG surgery were significantly more likely to believe old age to be the cause of their coronary heart disease (CHD) and significantly less likely to believe genetics, health-damaging behaviors, health-protective behaviors, and emotions to be the cause of their CHD than were younger participants awaiting surgery. Furthermore, the older participants were significantly more likely to believe they had no control over the disease and that the disease would be gone after surgery, and reported fewer postoperative health behavior changes than did younger participants. CONCLUSION: These findings demonstrate significant differences in illness representations as a function of age. Furthermore, differences in postoperative health behaviors were consistent with differing illness representations.

Adult↗
PubMed2001

Cellular pathophysiology and therapy of pulmonary hypertension.

The identification of several mutations of the bone morphogenetic protein receptor 2 (BMPR2) gene, a member of the transforming growth factor beta receptor family, gives hope for new insights into the pathophysiology of pulmonary hypertension. Genetic predisposition might dictate the responses of pulmonary artery fibroblasts, smooth muscle cells, and endothelial cells, as well as platelets and leukocytes, or their specific interactions with different extrinsic factors. These cells possess distinct subtypes and interact with each other. Pulmonary hypertension is associated with vasoconstriction, remodeling, and in situ thrombosis of the pulmonary arteries, but the initial events and their relationship to the genetic background are presently unknown. Current therapeutic approaches are based on our knowledge of the physiologic regulation of pulmonary artery tone, pathophysiologic changes, and our clinical experience with different treatment strategies. Beyond diuretics and anticoagulants, prostaglandins are generally accepted therapeutic agents for primary pulmonary hypertension and related diseases, whereas high-dose calcium-channel blockers are reserved for a small subset of patients, those who respond favorably to vasodilators in an acute test. Long-term intravenous prostacyclin infusion has become the most important specific therapy for primary pulmonary hypertension and associated diseases. However, this therapy is hampered by catheter complications and systemic side effects. Alternative application routes of prostacyclin or its stable analogs may avoid these problems. Inhaled application of the prostacyclin analog iloprost results in predominant pulmonary vasodilation with few systemic side effects and may possess clinical efficacy similar to that of intravenous prostacyclin. Inhaled nitric oxide is widely accepted as a screening agent for active responders to vasodilators and has a similar hemodynamic profile as inhaled iloprost, although the percentage of responders is considerably lower. However, there are unsolved toxicologic questions and practical difficulties concerning the safe long-term application of nitric oxide. Combining inhaled vasodilators with phosphodiesterase inhibitors may prolong the duration of the effects and improve the convenience of inhaled therapy for pulmonary hypertension. Therapeutic approaches in the future may aim at the transforming growth factor beta pathway and at the identification of early stages of the disease to prevent further disease progression.

Animals↗
PubMed2001

Inhibition of peroxynitrite-induced dityrosine formation with oxidized and reduced thiols, nitric oxide donors, and purine derivatives.

Peroxynitrite, formed by the combination of superoxide anion and nitric oxide, is a powerful oxidant at physiological pH and is apparently involved in the pathogenesis of several human diseases. Therefore, inhibitors of peroxynitrite-induced oxidation are important targets for pharmaceutical development. The reaction of peroxynitrite with L-tyrosine, one of its biological targets, yields stable products, including nitrotyrosine and dityrosine. Here we test the ability of thiols, nitric oxide donors, and purine derivatives to inhibit peroxynitrite-induced dityrosine formation in a physiological buffer containing bicarbonate/CO2. We show that both reduced and oxidized thiols, nitric oxide donors, and urate, but not other purine derivatives, reduce peroxynitrite-induced dityrosine formation.

Molecular Structure↗
PubMed2001

Judging outcomes in psychosocial interventions for dementia caregivers: the problem of treatment implementation.

PURPOSE: In published dementia caregiver intervention research, there is widespread failure to measure the level at which treatment was implemented as intended, thereby introducing threats to internal and external validity. The purpose of this article is to discuss the importance of inducing and assessing treatment implementation (TI) strategies in caregiving trials and to propose Lichstein's TI model as a potential guide. DESIGN AND METHODS: The efforts of a large cooperative research study of caregiving interventions, Resources for Enhancing Alzheimer's Caregiver Health (REACH), illustrates induction and assessment of the three components of TI: delivery, receipt, and enactment. RESULTS: The approaches taken in REACH vary with the intervention protocols and include using treatment manuals, training and certification of interventionists, and continuous monitoring of actual implementation. IMPLICATIONS: Investigation and description of treatment process variables allows researchers to understand which aspects of the intervention are responsible for therapeutic change, potentially resulting in development of more efficacious and efficient interventions.

Adaptation, Psychological↗