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Biomedical subjects

R Burr

Publications and source records attributed to R Burr.

At least 37 records · Page 2Linked to original sources
PubMed1994

Nycthemeral profile of nonspectral heart rate variability measures in women and men. Description of a normal sample and two sudden cardiac arrest subsamples.

Heart rate variability (HRV), a noninvasive systemic index of the central autonomic nervous system, demonstrates considerable within-subject variability, including a strong systematic 24-hour nycthemeral (or less precisely, circadian) component. Recent interest in the timing of sudden cardiac arrest (SCA), especially the pronounced morning rise in sudden deaths, has motivated research into coincident dynamic phenomena in HRV indices of central autonomic nervous system activity. In this study, statistical (nonspectral) HRV measures (SD and %RR50) were summarized for consecutive 15-minute blocks from 24-hour Holter electrocardiogram tapes. Six subgroups were scrutinized: women and men respectively in three clinical strata (normal subjects [n = 85 women and 40 men], SCA with no current or prior myocardial infarction [MI] [n = 9 women and 31 men], SCA with old MI [n = 7 women and 48 men]). Significant nycthemeral effects were observable for all HRV measures in five of the six groups, with a dramatic fall in HRV during the hours of the morning with the highest phenomenologic incidence of SCA. Both strata of SCA subjects had much lower HRV than the normal subjects. This effect was strongest during the night-time hours, particularly for a purported index of vagal tone (%RR50). For reasons that are not known, the nine female SCA survivors who had no current or previous MI presented very distinct 24-hour patterns for the HRV measures studied. Twenty-four-hour profiles of short-term statistical HRV provide a rich field for the observation of within-subject adaptations of the central autonomic nervous system inputs to the heart in both normal and clinical subgroups.

Circadian Rhythm↗
PubMed1994

Day of injury CT scan as an index to pre-injury brain morphology.

This study compared the ventricle-to-brain ratio (VBR) of the day-of-injury (DOI) computerized tomogram (CT) in traumatic brain-injured (TBI) patients with post-injury (2 months or greater) magnetic resonance (MR) VBRs in the same patients and in medical control subjects. The DOI VBR did not differ significantly from the medical controls, but both (DOI and medical control VBR) differed significantly from post-injury VBR. Additionally, a case study is presented wherein MR imaging studies were obtained prior to TBI so that a direct comparison of pre-injury to DOI to post-injury changes could be made. In this case the pre-injury and DOI VBRs were within approximately 9% of each other. In contrast, the post-injury VBR demonstrated over a 100% increase in comparison to either the pre-injury or DOI scan. This case and another case are illustrated using three-dimensional image analysis to represent ventricular change over time. These cases, along with the similarity of the DOI VBR with the medical controls, suggests that the DOI VBR can be utilized as an estimate or index of pre-injury ventricle/brain morphology. This will permit the use of DOI CT data for within-subject designs in TBI research that examines the course of degenerative changes over time.

Adolescent↗
PubMed1993

Circadian rhythms and nursing research: methodological considerations.

The role circadian rhythms play in mental health, sleep, human development and aging, pharmacologic efficacy, immune function, and cardiovascular health makes them a natural focus of nursing research. Integration of chronobiologic concepts into nursing care demands sound empirical support. Nevertheless, issues such as detection of linear trends, the fit of circadian data to a cosinor model and circular distributions, add complexity to the collection, analysis and interpretation of circadian rhythm data. The purpose of this paper is to convey an informed understanding of ways in which to deal with this intricate assembly of issues.

Circadian Rhythm↗
PubMed1991

Cigarette smoking: risk factor for premature facial wrinkling.

OBJECTIVE: To determine if cigarette smoking is a risk factor for the development of premature facial wrinkling. DESIGN: Cross-sectional study. SETTING: Smoking cessation clinic and community. PATIENTS: Convenience sample of 132 adult smokers and non-smokers in 1988. MEASUREMENTS: A questionnaire was administered to quantify cigarette smoking and to obtain information about possibly confounding factors such as skin pigmentation, sun exposure, age, and sex. Wrinkling was assessed using photographs of the temple region, and a severity score based on predetermined criteria was assigned. A logistic regression model, which controlled for confounding variables, was developed to assess the risk for premature wrinkling in response to pack-years of smoking. MAIN RESULTS: The prevalence of premature wrinkling was independently associated with sun exposure and pack-years of smoking. After controlling for age, sex, and sun exposure, premature wrinkling increased with increased pack-years of smoking. Heavy cigarette smokers (greater than 50 pack-years) were 4.7 times more likely to be wrinkled than nonsmokers (95% CI, 1.0 to 22.6; P value for trend = 0.05). Sun exposure of more than 50,000 lifetime hours also increased the risk of being excessively wrinkled 3.1-fold (CI, 1.2 to 7.1). When excessive sun exposure and cigarette smoking occurred together, the risk for developing excessive wrinkling was multiplicative (prevalence ratio of 12.0; CI, 1.5 to 530). CONCLUSION: Cigarette smoking is an independent risk factor for the development of premature wrinkling.

Adult↗
PubMed1990

Power spectral analysis of heart rate variability after biofeedback training.

This study investigated the effects of biofeedback/self-management training on heart rate variability (HRV) in six sudden cardiac arrest survivors. The physiological-theoretical basis of the training was cognitively inducing respiratory sinus arrhythmia. Power spectral analyses and nonspectral analyses (Kleiger, Magid, SCANN, BB50 measures) of HRV measured before and after 5 weeks of biofeedback training are described. The posttraining Kleiger measure of mean HRV increased compared to the pretraining mean HRV (159 +/- 37 ms vs 147 +/- 38 ms). After training, the high frequency components (0.27-0.30 Hz) of the power density spectra were markedly increased, suggesting an increase of respiratory-driven parasympathetic activity. After training, the low frequency components (0.05 Hz) were slightly decreased, suggesting a decrease in sympathetic activity. The increases noted in the high frequency components were more striking during 9 hours at night than during the day. These data indicate that subjects who have had sudden cardiac arrest can, through biofeedback/self-management, cognitively increase their HRV over a 5-week period, consequently increasing parasympathetic activity.

Arrhythmia, Sinus↗
PubMed1980

[The effect of etomidate on the activity of human pseudocholinesterase. In vivo-in vitro-enzymekinetics (author's transl)].

Etomidate (Hypnomidate), a safe and effective short-acting hypnotic drug of special value for induction of anesthesia, seems to be a noncompetitive activator, as well as a competitive inhibitor, of pseudocholinesterase E.C. 3.1.1.8). This is analogous to the effects of morphine and its derivatives with which etomidate has a structural similarity. The analysis of enzyme kinetics in vitro gave a Km of 10.4 (+/- 1.1) microM and a Vmax of 2.4 (+/- 0.3) mmoles/1 min for the hydrolysis of S-butyrylthiocholine by human pseudocholinesterase. Etomidate does not show any influence on the reaction rate of pseudocholinesterase on S-butyrylthiocholine in the standard test. From the experimental results it is derived that even under in vivo conditions of induction of anesthesia by etomidate, no influence is to be expected on the turnover of succinylcholine by the normal pseudocholinesterase. There is no explanation for the occasionally prolonged postnarcotic apnea following administration of etomidate as far as competition of etomidate with succinylcholine for the pseudocholinesterase is concerned and as long as enzyme variants of higher affinity for etomidate can be excluded.

Anesthesia, General↗
PubMed1979

Effects of hypercaloric glucose infusion on lipid metabolism in injury and sepsis.

UNLABELLED: Lipolysis was studied by measuring glycerol turnover (GTO) in injured and infected patients. GTO was elevated two to three times the normal values in five injured and four infected patients during D5W infusion. No correlation was found between GTO and plasma glycerol concentration in the two patient groups. GTO showed similar levels when measured during TPN in five injured and three infected patients. During TPN, plasma FFA levels remained unchanged in injured but decreased by 48% in septic patients. B-OH butyrate concentrations were high during D5W and dropped in both groups during TPN. Norepinephrine urinary output was high in both groups during D5W and TPN. CONCLUSIONS: 1) GTO was elevated two to three times the normal range in injury and infection; plasma glycerol concentration was not related to GTO. 2) In face of high catecholamine output, the insulin response to TPN did not inhibit TG breakdown but did decrease plasma ketone body concentrations.

Adult↗
PubMed1976

Influence of viability on bromosulfophthalein uptake by isolated hepatocytes.

The initial rates of BSP uptake by isolated hepatocytes were compared in cells of good and poor viability. Cells with impaired viability were obtained by ageing or by accident also in fresh preparations. Viability was judged by trypan blue stainability, membrane potential and respiratory parameters indicative for energy state, substrate supply and plasma membrane permeability changes. It was found that concomitant with impaired viability there was a decline of uptake rates at low and an increase at high BSP concentrations with a crossover point at 10 muM as manifest in an increase of Km and V. Simultaneously, the affinity and size of the membrane bound fraction decreases. The results give kinetic support to the supposition that it is the decreased uptake from plasma to liver that is responsible for the prolonged plasma retention times in the liver function test of patients with impaired hepatobiliary function.

Cell Membrane Permeability↗
PubMed1975

Uptake of taurocholic acid into isolated rat-liver cells.

Binding and transport characteristics for uptake of taurocholic acid by isolated rat liver cells were studied. 1. An adsorption of taurocholate to the cell surface is terminated in less than 15 s. A Ks of 0.55 mM and a total binding capacity of 3.8 nmol/mg cell protein is determined. 2. The rate of uptake of taurocholate follows Michaelis-Menten kinetics with Km = 19 muM and V = 1.7 nmol/mg protein min. 3. There is a broad pH optimum for uptake between pH 6.5 -- 8.0. 4. The activation energy amounts to 29 kcal/mol. At high taurocholate concentration an unusual upward bend is observed in the Arrhenius plot. 5. Taurocholate uptake is competitively inhibited by taurochenodeoxycholate (Ki = 9 muM). It is noncompetitively inhibited by bromosulfophthalein (Ki = 3 muM). 6. At physiological taurocholate concentrations a 200-fold intracellular accumulation of taurocholate is observed. 7. Uptake is inhibited by about 75% by either antimycin A, carbonylcyanide m-chlorophenyl-hydrazone, ouabain. 8. Replacement of extracellular Na+ by either K+ or sucrose results in a 75% decrease of uptake. 9. It is concluded that taurocholate uptake is a carrier-mediated process, and suggested that the energy for intracellular accumulation is made available by cotransport of Na+.

Animals↗