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At least 163 records · Page 9Linked to original sources
PubMed2006

High-dose beta-blockers and tight heart rate control reduce myocardial ischemia and troponin T release in vascular surgery patients.

BACKGROUND: Adverse perioperative cardiac events occur frequently despite the use of beta (beta)-blockers. We examined whether higher doses of beta-blockers and tight heart rate control were associated with reduced perioperative myocardial ischemia and troponin T release and improved long-term outcome. METHODS AND RESULTS: In an observational cohort study, 272 vascular surgery patients were preoperatively screened for cardiac risk factors and beta-blocker dose. Beta-blocker dose was converted to a percentage of maximum recommended therapeutic dose. Heart rate and ischemic episodes were recorded by continuous 12-lead electrocardiography, starting 1 day before to 2 days after surgery. Serial troponin T levels were measured after surgery. All-cause mortality was noted during follow-up. Myocardial ischemia was detected in 85 of 272 (31%) patients and troponin T release in 44 of 272 (16.2%). Long-term mortality occurred in 66 of 272 (24.2%) patients. In multivariate analysis, higher beta-blocker doses (per 10% increase) were significantly associated with a lower incidence of myocardial ischemia (hazard ratio [HR], 0.62; 95% confidence interval [CI], 0.51 to 0.75), troponin T release (HR, 0.63; 95% CI, 0.49 to 0.80), and long-term mortality (HR, 0.86; 95% CI, 0.76 to 0.97). Higher heart rates during electrocardiographic monitoring (per 10-bpm increase) were significantly associated with an increased incidence of myocardial ischemia (HR, 2.49; 95% CI, 1.79 to 3.48), troponin T release (HR, 1.53; 95% CI, 1.16 to 2.03), and long-term mortality (HR, 1.42; 95% CI, 1.14 to 1.76). CONCLUSIONS: This study showed that higher doses of beta-blockers and tight heart rate control are associated with reduced perioperative myocardial ischemia and troponin T release and improved long-term outcome in vascular surgery patients.

Adrenergic beta-Antagonists↗
PubMed1994

The inefficacy of intravenous propafenone for rate control in atrial fibrillation.

The antiarrhythmic agent propafenone has been reported to prolong atrioventricular node conduction and may be suitable for rate control in atrial fibrillation (AF). To evaluate this, 10 patients (seven men and three women aged 29 to 67 years, mean +/- SD 48 +/- 14) were given intravenous propafenone during AF in both the supine and upright positions. Intracardiac catheters measured local electrograms from the high right atrium and right ventricular apex during AF. Atrial rate, ventricular rate and blood pressure were recorded in the control state and after head-up tilt with these measurements repeated after propafenone 1.5 mg/kg was infused over 5 mins. Four of 10 patients reverted to sinus rhythm. Propafenone increased the mean ventricular cycle length (496 +/- 147 versus 556 +/- 152 ms, P = 0.1), although this did not reach significance. In contrast, propafenone markedly increased the mean atrial cycle length (136 +/- 35 versus 226 +/- 39, P < 0.001). The mean ventricular cycle length reverted to baseline after tilt (447 +/- 103 ms) while the mean atrial cycle length decreased but not to baseline levels (170 +/- 21 ms). The authors conclude that intravenous propafenone is generally inadequate for rate control in AF, especially in the upright position.

Adult↗
PubMed2001

Atrial fibrillation: rate control versus maintenance of sinus rhythm.

Atrial fibrillation is a common tachyarrhythmia encountered in clinical practice. Management has become increasingly complex as the therapeutic options have multiplied. Two basic strategies are available: rhythm control with or without pharmacologic manipulation, and rate control with anticoagulation. To date, no randomized controlled trial that compares the two strategies has been completed, although the Atrial Fibrillation Follow-Up Investigation of Rhythm Management (AFFIRM) trial is underway. This review outlines the rationale for each of the two basic treatment strategies, providing an overview of the advantages and disadvantages of each. Included are clinical criteria used in selecting the appropriate treatment plan.

Anti-Arrhythmia Agents↗
PubMed1983

Control rate of response or reinforcement and amphetamine's effect on behavior.

The roles of control response rate and reinforcement frequency in producing amphetamine's effect on operant behavior were evaluated independently in rats. Two multiple schedules were arranged in which one variable, either response rate or reinforcement frequency, was held constant and the other variable manipulated. A multiple differential-reinforcement-of-low-rate seven-second yoked variable-interval schedule was used to equate reinforcement frequencies at different control response rates between multiple-schedule components. Amphetamine increased responding under the variable-interval component. In contrast, amphetamine decreased responding equivalently between components of a multiple random-ratio schedule that produced similar control response rates at different reinforcement frequencies. The results provide experimental support to the rate-dependency principle that control rate of responding is an important determinant of amphetamine's effect on operant behavior.

Animals↗
PubMed2002

The application of dynamic field shaping and dynamic dose rate control in conformal rotational treatment of the prostate.

The current philosophy of dose escalation in the treatment of prostate cancer has forced the treatment planner to re-evaluate his/her planning approach. Precise and accurate delivery of dose to the prostate while maintaining the required dose limits to the normal critical structures, such as the rectum, has become increasingly difficult in light of these escalated doses. Conformal treatment techniques allow the treatment planner to precisely shape each individual treatment field so that desired volume coverage and normal tissue sparing can be achieved. In addition to these beam-shaping advantages, adjustment of an individual beam's weighting also helps to create the desired distribution and tissue sparing. Rotational therapy "simulates" treatment with multiple beams and angles, similar to the thought process behind conformal treatment technique. With rotational therapy, however, the treatment planner's inability to provide adequate beam shaping and weighting adjustment has placed limits on its value as a viable planning option. The introduction of computer-controlled treatment machines, which allow dynamic adjustment of the field shape with the rotation of the beam, makes it possible to re-evaluate rotational therapy as a potential option. Similarly, the treatment planner's ability to change field weighting can be accomplished by the application of dynamic dose rate control, allowing a rotational beam to deliver a weighting similar to that possible with conformal fixed-field techniques. Dose-volume histogram data will be used to evaluate doses delivered to the prostate, rectum, and bladder using rotational therapy with dynamic field shape and dynamic dose rate control as a treatment planning option. The dose delivery and normal tissue-sparing potential of this technique compared to coplanar and noncoplanar conformal fixed-field techniques will also be presented.

Femur Head↗
PubMed1992

Role of calcium antagonists for heart rate control in atrial fibrillation.

Atrial fibrillation is one of the most common symptomatic sustained arrhythmias seen in clinical practice. Many patients with atrial fibrillation and a ventricular response greater than 120 beats/min will experience cardiac symptoms. In the past, control of heart rate in these patients consisted of administration of intravenous digoxin, but this often proved to be ineffective or limited by toxicity. Recently, intravenous beta blockers such as esmolol have been used to slow the ventricular rate during atrial arrhythmias, but in some studies their use has been limited by hypotension. Alternatively, a bolus of an intravenous calcium antagonist, e.g., diltiazem or verapamil, may be administered to achieve acute slowing of the ventricular response. An intravenous bolus of diltiazem or verapamil may be effective, but use of either may be limited by its short duration of action and the inability to administer repeated boluses to tightly control or "fine tune" the heart rate. However, a new bolus plus maintenance infusion technique with diltiazem has shown promise in initial studies. It appears that in the future, continuous infusion techniques with intravenous calcium antagonists will be available that provide safe and effective sustained control of the ventricular response during atrial arrhythmias.

Atrial Fibrillation↗
PubMed1991

Growth rate control in fed-batch cultures of recombinant Saccharomyces cerevisiae producing hepatitis B surface antigen (HBsAg).

A recombinant Saccharomyces cerevisiae producing hepatitis B surface antigen (HBsAg) exhibited growth-associated product formation. By controlling the medium feed rate, based on the calculated amount of medium required for 1 h, a constant specific growth rate was obtained in the range of 0.12-0.18 h-1. In order to prolong the exponential growth phase, the medium feed rate was increased exponentially. A fed-batch cultivation method based on the production kinetics of batch culture enhanced HBsAg production ten times more than in batch culture. The reason for the increase can be explained by the fact that the production of HBsAg is expressed as an exponential function of time when the specific growth rate is controlled to a constant value in growth-associated product formation kinetics. In the scale-up of this culture to 91, the specific growth rate could also be maintained constant and the HBsAg production trend was similar to that in a 1-1 culture. However, ethanol accumulation occurred at a late stage in fed-bach culture. Ethanol produced was not reutilized and inhibited further cell growth.

Cell Division↗
PubMed2004

Partial A(1) adenosine receptor agonists from a molecular perspective and their potential use as chronic ventricular rate control agents during atrial fibrillation (AF).

This review provides a molecular perspective of partial agonism at the A(1) adenosine receptor. The structure-activity relationships (SAR) for affinity and intrinsic efficacy of analogues of the full agonist N6-cyclopentyladenosine (CPA) are emphasized. Both general models of activation of G protein-coupled receptors and specific molecular models of the A(1)-adenosine receptor are used to interpret the results of efforts to synthesize and assay effects of partial agonists. The SAR of affinity and intrinsic efficacy of the 2', 3', and especially the 5'-deoxy derivatives of CPA is presented. From this analysis, the nature of the interactions of specific atoms and substituents of the CPA molecule with the A(1)-adenosine receptor are deduced and presented pictorially. As an example of the therapeutic potential of partial agonists, the design and testing of analogues of CPA to provide chronic ventricular rate control during atrial fibrillation is described. The challenges associated with designing a partial A(1)-adenosine receptor agonist for providing chronic ventricular rate control during atrial fibrillation are many. To meet these challenges, further medicinal chemistry efforts in the area of partial A(1)-adenosine receptor agonism are still needed.

Adenosine↗
PubMedDate not supplied

A custom-built controlled-rate freezer for small sample cryopreservation studies.

A custom-built controlled-rate freezing machine is described. It operates by automatically raising and lowering the sample carrier in a static column of liquid nitrogen vapour. It is controlled by a computer-assisted thermocouple feedback system that operates a stepper motor driving the sample carrier. The cooling protocol is divided into three phases: cooling from +5 to -5 C, initiation of ice nucleation, and cooling from -5 to -80 C. Experiments are described to validate the device over a range of different cooling rates. A freezing protocol is established to cool samples in plastic straws over a range of rates up to 80 C/min, with rapid and consistent absorption of the latent heat.

Animals↗
PubMed1977

A simple apparatus for controlled rate corneal freezing.

The construction and operation of an apparatus for controlled rate corneal freezing is described. The cooling is obtained by close thermal contact between a vial holding the cornea and a metal core. A predetermined cooling rate is achieved by partial immersion of the core in a fixed amount of liquid nitrogen. In a preliminary series greater than or equal to 95% endothelial survival was obtained.

Corneal Transplantation↗
PubMed2005

Evaluation of hematological reconstitution potential of autologous peripheral blood progenitor cells cryopreserved by a simple controlled-rate freezing method.

A novel and simple procedure for the controlled-rate cryopreservation of peripheral blood progenitor cells (PBPCs) was introduced. A freezing bag housed in a protective aluminum canister was placed on top of a styrene foam box in the -85 degrees C electric freezer. A second set of samples was kept in cryotubes placed in a double styrene foam box in the same electric freezer. Measurement of the freezing rate in the PB bags and cryotubes demonstrated that this simple method for PBPC cryopreservation provided optimal conditions for both large-scale and small-scale cryopreservation. Within several days after autologous peripheral blood stem cell transplantation, we thawed the cells in the small sample tubes and evaluated the cell viability, the cell recovery, and the recovery rates of hematopoietic progenitor cells (HPCs), such as CD34+ cells and colony-forming unit-granulocyte/macrophage (CFU-GM) colonies. The median duration of cryopreservation was 59 days (range, 14-365 days). According to our analysis, infusions of more than 2 x 10(6) CD34+ cells/kg body weight and 0.5 x 10(6) CFU-GM colonies/kg body weight after thawing had favorable influences on the neutrophil engraftment. We have therefore established a simple freezing method for cryopreservation of human PBPCs, which ensures the transplantability of hematopoietic progenitors even after thawing. In vitro HPC assay after thawing is important to evaluate the quality of cryopreservation procedures.

Adolescent↗
PubMed1995

Development of linear and non-linear properties of heart rate control during quiet and active sleep in healthy infants.

In this study it is analyzed by linear and non-linear methods, how the control of instantaneous heart rate (IHR) develops in infants in quiet and active sleep. Ten healthy and term newborns were studied during their first half year of life. Low (LF) and high frequency power (HF) of the spectrum, and the largest Lyapunov exponent (LLE) were calculated from IHR. By means of the surrogate-data-test, significance of LLE with respect to linear correlated gaussian noise was verified. Significant differences were determined between the original and the surrogate data sets (p < 0.001) assuming non-linear properties. LF, HF, LLE have irregular developmental patterns during the first month, whereby LLE has a distinct low value on the 21st day. HF significantly increases between the second and sixth month in quiet sleep, whereas for LF and LLE no significant correlations were found, neither for quiet nor active sleep. Using linear and non-linear methods, the study shows that the system controlling heart rate pass through mainly two different developmental periods: a period of adaptation in the first four weeks, where parameters distinctly vary, followed by a period with clear developmental courses, lasting till the sixth month.

Electrocardiography↗
PubMed1993

Breast conservation therapy for early stage breast carcinoma with outstanding 10-year locoregional control rates: a case for aggressive therapy to the tumor bearing quadrant.

PURPOSE: Between 1982 and 1988 233 American Joint Committee on Cancer Stage I and II invasive breast carcinomas were prospectively treated in 225 women with conservative tumor excision, careful assessment of histopathological margins, and dose-adjusted irradiation to maximum doses of 70 Gy to the tumor bearing quadrant of the breast. METHODS AND MATERIALS: The pathological stages at presentation were T1N0 and T1N1 in 57% and 13% and T2N0 and T2N1 in 19% and 10% of the patients, respectively. All patients were irradiated according to a policy that, beyond the 50 Gy to the whole breast and draining lymphatics, the tumor-bearing quadrant was boosted in adjustment to the histopathological margin. Normal tissue margins of < 2 mm were considered positive, margins 2-5 mm close, and margins > 5 mm negative and were boosted with 20, 15, and 10 Gy, respectively. Patients in whom the margin could not be assessed were re-excised or boosted to 20 Gy. Re-excisions with no residual carcinoma were not boosted. Most patients boosted to 20 Gy to the tumor-bearing quadrant received interstitial 192-Ir implantations. RESULTS: The actuarial local control rates in the treated breast were 97.5% at 10 years with three recurrences having occurred at a median of 4.5 years after completion of radiotherapy. An additional two patients failed regionally outside the irradiation portals. The overall and disease-free survival of the whole group is 87.5% and 77%, respectively. CONCLUSION: The approach to breast conservation therapy followed in this study has resulted in outstanding local control rates and suggests that there may be a subset of patients that could be irradiated to the tumor bearing quadrant only.

Adult↗
PubMed1977

Realtion of heart rate control to heartbeat perception.

The relation of heartbeat perception to voluntary control of heart rate (HR) and to learning of enhanced HR control during feedback was studied in three experiments. In Experiment I heartbeat perception was unrelated to voluntary control of HR but was negatively correlated with HR learning. Experiments II and III showed that heartbeat perception was unrelated to either initial voluntary control or learning and suggested that sampling error accounted for the negative correlation in Experiment I. Experiment I also demonstrated that learned increases in HR are retained for at least 10 weeks following feedback training. Autonomic Perception Questionnaire scores were not predictive of voluntary HR control or learning.

Adolescent↗
PubMed1977

Treatment and generalization effects in an experimental treatment for a stutterer using contingency management and speech rate control.

An experimental treatment program for an adult stutterer, using contingency management and rate control procedures, is described. During laboratory sessions, a combination of both procedures resulted in maintained stutter-free speech within a target speech rate range. Bidaily recordings of the subject's speech across all nonlaboratory speaking situations, preceding and throughout the laboratory treatment, revealed no correspondence between laboratory and nonlaboratory speech behavior. Some positive and negative findings from this study are considered with respect to contingency management of stuttering.

Adult↗
PubMed2005

Wavelet thresholding with bayesian false discovery rate control.

The false discovery rate (FDR) procedure has become a popular method for handling multiplicity in high-dimensional data. The definition of FDR has a natural Bayesian interpretation; it is the expected proportion of null hypotheses mistakenly rejected given a measure of evidence for their truth. In this article, we propose controlling the positive FDR using a Bayesian approach where the rejection rule is based on the posterior probabilities of the null hypotheses. Correspondence between Bayesian and frequentist measures of evidence in hypothesis testing has been studied in several contexts. Here we extend the comparison to multiple testing with control of the FDR and illustrate the procedure with an application to wavelet thresholding. The problem consists of recovering signal from noisy measurements. This involves extracting wavelet coefficients that result from true signal and can be formulated as a multiple hypotheses-testing problem. We use simulated examples to compare the performance of our approach to the Benjamini and Hochberg (1995, Journal of the Royal Statistical Society, Series B57, 289-300) procedure. We also illustrate the method with nuclear magnetic resonance spectral data from human brain.

Bayes Theorem↗
PubMed1987

Influence of nifedipine on arterial baroreflex modulation of heart rate control during dynamic increases in arterial pressure: studies in normal man.

Studies in animals have demonstrated that calcium channel blocking agents exert important influences on autonomic mechanisms in addition to their direct vascular effects. Previous studies in our laboratory showed that clinical doses of nifedipine sensitized baroreceptor-mediated control of peripheral vascular resistance in normal human subjects. However, baroreflex control of vascular tone does not necessarily imply parallel control of heart rate. A series of experiments was therefore performed to test the hypothesis that therapeutic doses of nifedipine would potentiate arterial baroreflex modulation of heart rate during ramp increases of arterial pressure in normal volunteers. Arterial baroreflex control was assessed by measuring heart interval (HI) responses to dynamic ramp elevation of systolic arterial pressure (SAP) with bolus administration of phenylephrine (PE) before and after nifedipine or placebo in 19 normal subjects. Arterial baroreflex control was calculated from the slope of the regression of SAP on succeeding HI during the first 18 cardiac cycles following onset of rise of SAP after PE bolus. In 13 subjects, bolus PE produced an increase in SAP from 125 +/- 3 mm Hg to 152 +/- 5 mm Hg (p less than 0.01), with a resultant increase in HI from 1110 +/- 57 msec to 1541 +/- 87 msec (p less than 0.01). The baroreflex response was linear (r greater than 0.80, p less than 0.025) and = 17.8 +/- 3.3 msec/mm Hg.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗