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At least 37 records · Page 2Linked to original sources
PubMed1979

Age-dependent pattern of autonomic heart rate control during hypoxia in fetal and newborn lambs.

Autonomic nervous control of heart rate (HR) during hypoxia was studied longitudinally using 9 chronically catheterized fetal lambs (109 day to term) and 10 newborn lambs (2--28 days old). Changes in heart rate (deltaHR) during hypoxia were age-dependent. Before 120 days of gestation deltaHR was insignificant, but between 120 days to term bradycardia occurred. The newborn response was marked tachycardia. Autonomic influences on HR were quantified using atropine and propranolol blockade. In fetal lambs, antagonistic increases in parasympathetic and sympathetic outflows were evident during hypoxia. In hypoxic lambs 120 days to term, net bradycardia reflected predominant parasympathetic cardio-deceleration; before 120 days of gestation both the parasympathetic and sympathetic outflows increased, but no net deltaHR occurred. In hypoxic newborn lambs, sympathetic and parasympathetic changes contributed synergistically to the net tachycardia. Thus the pattern of autonomic control of HR during hypoxia differs in fetal and newborn lambs. Changes in sympathetic and parasympathetic influences are antagonistic in the fetus, but synergistic in the newborn.

Age Factors↗
PubMed1975

Learned heart-rate control by a patient with a ventricular parasystolic rhythm.

A 31-year-old woman with a ventricular parasystolic rhythm is described. The arrhythmia was always absent below a rate of 72 per minute, and always present over a rate of 106 per minute. Voluntary heart-rate control was learned using a biofeedback techinque, as a result of which she could increase her rate by 25 per minute and decrease it by 1-2 per minute. Both voluntary speeding and exercise brought on the arrhythmia, but later in the training she could reach a higher heart-rate before the arrhythmia appeared. Propranolol inhibited the arrhythmia only to the extent that is slowed the heart.

Adult↗
PubMed1991

A simplified method for cryopreservation of peripheral blood stem cells at -80 degrees C without rate-controlled freezing.

A simplified method was established for cryopreservation of peripheral blood stem cells (PBSCs) using hydroxyethyl starch (HES) and dimethylsulfoxide (DMSO) as a cryoprotective agent at -80 degrees C without rate-controlled freezing. The data indicate that a cryoprotective solution consisting of 6% HES and 5% DMSO produced the highest recovery rates for nucleated cells (92.0 +/- 3.5%), CFU-GM (73.8 +/- 4.1%) and BFU-E (82.2 +/- 6.9%), and the highest trypan blue viability (88.4 +/- 3.6%). For long-term cryopreservation of PBSCs, CFU-GM recovery rates remained almost unchanged during 5-18 months; the mean CFU-GM recovery rate after 18 months of cryopreservation was 70 +/- 11%. When large-scale samples of PBSCs in 100-ml freezing bags were cryopreserved for clinical use, cell and CFU-GM recoveries were similar. Using this method, 10 patients with hematological malignancy received PBSC transplants after marrow-ablative chemotherapy. All demonstrated early engraftment; seven are now alive in unmaintained complete remission for 3.5-15 months after PBSC transplant. This simple and inexpensive method will be useful for the wider application of PBSC transplant as a therapeutic alternative in the treatment of malignant diseases.

Acute Disease↗
PubMed1975

Effect of rotation on the diffusion-controlled rate of ligand-protein association.

The rate of binding a fairly large ligand molecule to a protein is reduced below the usual diffusion-controlled rate by the requirement of a certain rotational orientation. A simple, approximate treatment of this effect is given for special cases of spherical and ellipsoidal ligands. As the center of an ellipsoidal ligand approaches a protein surface, there is an effective repulsive potential between ligand and surface owning to restricted rotation of the ligand. The frequency factor kT/h of the Eyring rate theory is replaced in these reactions involving diffusion in solution by D/Rlambda, where D = diffusion coefficient of ligand, lambda = thermal deBroglie wavelength of ligand, and R = "capture" distance around the binding site on the protein.

Adsorption↗
PubMed1978

Multicentric origin of the atrial depolarization wave: the pacemaker complex. Relation to dynamics of atrial conduction, P-wave changes and heart rate control.

In studies to ascertain the basis of dynamic changes in the P wave, bipolar epicardial potentials were recorded from multiple atrial electrodes in dogs. One hundred to 120 activation times were displayed by a digital computer and used to construct atrial isotemporal activation sequence maps. Changes in heart rate or beat-to-beat cycle length were induced by vagal stimulation or infusion of autonomic mediating drugs. Changes in cycle length were associated with dynamic changes in the atrial activation sequence and surface P-wave. A conspicuous finding was that epicardial atrial depolarization began at three widely separated locations. These three points were consistently present in all animals and were generally located at the 12, 3, and 6 o'clock positions of the superior vena cava-right atrial junction. The dynamic changes in P waves and atrial activation sequence which accompanied the changes in cycle length were due to sudden shifts in the point of earliest activity between the three early sites. Asymmetric atrial depolarization with more rapid conduction along the crista terminalis, superior interatrial band, and pectinate muscles was present in all dogs. Although the anisotropic atrial geometry played an important role in the asymmetric conduction, the widely distributed onset of activity contributed significantly to the uneven spread. The multiple points of origin of the atrial wavefront might be explained by either a trifocal, distributed pacemaker or the epicardial exits of three specialized pathways conducting an impulse emanating from a single focus. These data explain the dynamic variation in P-wave morphology in normal hearts and also imply a relationship between the altered origin of atrial depolarization, atypical P waves, brady- or tachyarrhythmias, and heart rate control.

Action Potentials↗
PubMed1976

The effects of controlled muscle tension on performance and learning of heart-rate control.

Thirty female subjects were divided in three groups and instructed in group I to increase their HRs with the aid of continuous feedback of performance, while they tensed their right forearm muscles 20% of maximal voluntary contraction. In the last session only feedback was used, Group II were trained with feedback only. Group III for the first two sessions tensed their muscles only, and in the last session trained HR increases with feedback only. Group I was superior in HR performance in the first two sessions. In the third session they deteriorated significantly and could not be distinguished from the other two groups. The results were interpreted in terms of relations between somatic and autonomic events and transfer between different states of somatic involvement during learning. Electrodermal activity and respiration were included as control variables.

Adult↗
PubMed1991

A placebo-controlled trial of continuous intravenous diltiazem infusion for 24-hour heart rate control during atrial fibrillation and atrial flutter: a multicenter study.

The safety and efficacy of a 10- to 15-mg/h continuous infusion of intravenous diltiazem were evaluated in 47 patients with atrial fibrillation or flutter who first responded to 20 mg or 20 mg followed by one or more 25-mg bolus doses of open label intravenous diltiazem. Of the 47 patients, 44 responded to the bolus injection and were randomized under double-blind conditions to receive either a continuous infusion of intravenous diltiazem (10 to 15 mg/h) (23 patients) or placebo (21 patients) for up to 24 h. Seventeen (74%) of the 23 patients receiving diltiazem infusion and none of the 21 with placebo infusion maintained a therapeutic response for 24 h (p less than 0.001). Over 24 h, patients receiving diltiazem infusion lost response significantly more slowly than did those receiving placebo infusion (p less than 0.001). Nonresponders to the double-blind infusion were given an additional bolus injection of open label intravenous diltiazem and administered an open label 24-h intravenous diltiazem infusion. The overall proportion of patients maintaining a response to a 24-h infusion of intravenous diltiazem under double-blind or open label conditions combined was 83% (34 of 41). Efficacy of the 24-h infusion of intravenous diltiazem was similar in elderly versus young patients, those who did versus those who did not receive digoxin and those weighing less than 84 versus greater than or equal to 84 kg. However, intravenous diltiazem appeared to be more effective in atrial fibrillation than in atrial flutter. No significant untoward effects were noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed2026

Family-Wise Error Rate Control in Clinical Trials With Overlapping Populations.

We consider clinical trials with multiple, overlapping patient populations that test multiple treatment policies specifically tailored to these populations. Such designs may lead to multiplicity issues, as false statements will affect several populations. For type I error control, often the family-wise error rate (FWER) is controlled, which is the probability to reject at least one true null hypothesis. If the joint distribution of the test statistics is known, the FWER level can be exhausted by determining critical values or adjusted-levels. The adjustment is typically done under the common ANOVA assumptions. However, the performed tests are then only valid under the rather strong assumption of homogeneous null effects, that is, when the null hypothesis applies to all subpopulations and their intersections. We show that under cancelling null effects, when heterogeneous effects cancel out in some or all subpopulations, this procedure does not provide FWER control. We also suggest different alternatives and compare them in terms of FWER control and their power.

Humans↗
PubMed1976

System analysis of heart rate control in man.

The dynamic property of the heart rate response to exercise was determined and expressed in the frequency domain to establish a method of examining cardiovascular control function. The response of heart rate to a stimulus was measured at 5-s intervals in nine healthy young volunteers. The stimulus consisted of several runs of two-step exercise practiced in semirandom sequence for 19 min. The weight function of the system was estimated from autocorrelation function of the input signal and cross-correlation function between the input and output signals. The weight function was transformed into a transfer function and its Bode plot diagram was drawn. From the diagram, four dynamic parameters were determined. These parameters are as follows: K is a constant showing the theoretical steady-state increment of heart rate, and T1, T2, T3 are time constants. The values obtained in the present experiment with the healthy young males were: K 46.0 +/- 14.6 beats, T1, 2.12 +/- 0.44, T2, 1.12 +/- 0.16, and T3 0.70 +/- 0.07 min.

Adult↗
PubMed1992

Heart rate control in awake dog after selective SA-nodal parasympathectomy.

Selective surgical sinoatrial (SA)-nodal parasympathectomy (PSX) was used to distinguish the role of the cardiac autonomic nerves in heart rate (HR) control in awake dogs (n = 8) during rest and behavioral arousal. Resting HR increased from 85 +/- 9 beats (mean +/- SE) before surgery to 114 +/- 6 beats after denervation (P less than 0.05). Atrioventricular (AV)-nodal block occurred during the first 1-3 wk post-PSX, but subsequently resolved. Dogs were behaviorally conditioned by following a 30-s tone (CS+) by a 0.5-s shock. Before denervation the CS+ evoked an initial, rapidly developing tachycardia (phase 1), which was followed by a more slowly developing, but larger, phase 2 tachycardia. The selective SA-nodal parasympathectomy essentially abolished the phase 1 conditional HR response (magnitude: 23 +/- 5 vs. 5 +/- 2 beats, pre- vs. postdenervation, respectively). The phase 2 HR increase was similar before and after the denervation (magnitude: 44 +/- 6 vs. 33 +/- 6 beats; rate of increase: 5 +/- 1 vs. 6 +/- 1 beats/s, pre- vs. post-PSX). Beta-Blockade (propranolol, 1 mg/kg) after PSX decreased phase 2 (magnitude: 7 +/- 3 beats; rate of increase: 1 +/- 0.3 beats/s). These data reveal a sterotypic pattern of change in cardiac autonomic nervous drive during a sudden arousal from rest. Phases 1 and 2 appear to be selective and specific indexes of changes in SA-nodal parasympathetic and sympathetic tone, respectively. The selective denervation unmasks during stress a component of HR control that occurs in the absence of adrenergic or cholinergic mechanisms. These data suggest that multiple interactions occur within the intrinsic ganglion plexuses of the heart with respect to HR control.

Animals↗
PubMed1990

Guanosine tetraphosphate (ppGpp) dependence of the growth rate control of rrnB P1 promoter activity in Escherichia coli.

We have fused the ribosomal RNA promoter P1 from the rrnB gene of Escherichia coli to lacZ and examined its guanosine tetraphosphate (ppGpp)-dependent expression at different growth rates. The rrnB P1-lacZ fusion was constructed on plasmid vectors and then recombined into the chromosome of a delta lac relA1 strain close to the normal location of the rrnB locus and in the normal orientation, coincident with the direction of replication. A series of spoT strains differing in the severity of their SpoT defect were analyzed with respect to their growth characteristics and ppGpp metabolism. The spoT203 allele was introduced into the rrnB P1-lacZ fusion containing strain and used to manipulate the ppGpp concentration independently of the growth medium. 1) The levels of ppGpp during exponential growth are decreased in rich media due to a decreased activity of (p)ppGpp synthetase II (PSII). 2) The specific activity of rrn P1-directed beta-galactosidase was increased in a parabolic fashion with increasing growth rate. A theoretical analysis showed that this was to be expected since enzyme expression from a stringently controlled promoter is affected by changes in the growth rate both via the control of the promoter, and indirectly via the control of bulk mRNA synthesis. 3) The observer specific enzyme activities were converted into rrnB P1 promoter activities, given as lacZ transcription relative to the total rate of transcription. The rrn P1 promoter activity decreased exponentially with increasing cytoplasmic concentration of ppGpp, independent of whether a given level of ppGpp was achieved by using different growth media or by using a spoT allele. These results support two hypotheses: (i) that RNA polymerase is partitioned by ppGpp into two fractions with different abilities to initiate transcription at rrn P1 promoters; and (ii) that during exponential growth ppGpp is derived from ppGpp synthetase II (PSII). Together these hypotheses predict that the growth rate control of rRNA synthesis reflects a control of PSII activity which is regulated by the composition of the growth medium.

Chloramphenicol↗
PubMed1992

Functional capacity of patients with atrial fibrillation and controlled heart rate before and after cardioversion.

OBJECTIVE: To measure exercise duration (which frequently is diminished by atrial fibrillation) and to compare the gain in exercise duration achieved by heart rate control with the gain after cardioversion. METHODS AND RESULTS: Eighteen patients (10 with structural heart condition and eight with lone atrial fibrillation) did the treadmill exercise stress test using the Bruce protocol. Resting supine heart rate was lowered below 100 beats/min by verapamil (initial exercise stress test). An exercise stress test was then repeated as often as needed to achieve 'heart rate control' (less than 130 beats/min at the end of a 3 min walk at 10 degrees elevation and 2.74 km/h speed). This heart rate control was obtained by gradual increases in verapamil dose. Subsequently, the patients were converted to normal sinus rhythm chemically (seven patients) or electrically (11 patients) and an exercise stress test was repeated. At cardioversion, patients were on antiarrhythmic therapy and verapamil was discontinued in most. All patients had left atrial size measured by echocardiogram before and after cardioversion, and all were followed for four months. Upon achieving controlled heart rate, exercise duration increased in 16 patients (average gain was 164 s). After cardioversion to normal sinus rhythm, exercise duration further increased in 13 cases with an average additional gain of 90 s. The total increase in exercise duration after cardioversion was 254 s. Post cardioversion, all patients with lone atrial fibrillation improved. A decline in exercise performance occurred in four patients with fixed cardiac output. Average gain in exercise duration was independent of drugs used. Left atrial size remained increased post cardioversion (50.4 mm before and 52 mm after). During four months of follow-up, only eight patients could continue on the same medication given for cardioversion. Three patients did not maintain normal sinus rhythm. CONCLUSIONS: Conversion to normal sinus rhythm in patients with atrial fibrillation is associated with improved exercise tolerance except in cases with fixed cardiac output. Restoration of mechanical atrial function appears to be responsible for improved exercise performance following cardioversion.

Aged↗
PubMed1977

Effects of instructions, biofeedback, and cognitive activities on heart rate control.

In a factorial experiment, 90 male and 90 female subjects were given (a) either instructions to increase heart rate (HR), decrease HR, or no instructions to change their HR; (b) either true biofeedback, false biofeedback, or no biofeedback; and (c) either instructions concerning cognitions to help them change HR or no instructions concerning cognitions. The results indicated that (a) for increasing HR, instructions to increase HR were as effective as the combination of instructions and true biofeedback; (b) for decreasing HR, neither instructions nor biofeedback nor the combination of instructions and biofeedback was more effective than simply sitting quietly; (c) although subjects instructed to increase HR showed higher HRs at the end of training than subjects instructed to decrease, the increase subjects showed a decline in HR from the initial period; (d) almost all subjects reported using cognitions to influence HR, and instructions concerning the use of cognitions did not facilitate changes in HR; and (e) women showed higher HRs, which declined more slowly than those of men, but sex did not interact with any treatment variable. It was concluded that increases (or retarded decreases) in HR were due to instructions, and decreases were due to simple adaptation, thus raising serious questions concerning the effectiveness of the biofeedback component of "biofeedback training" for altering HR.

Biofeedback, Psychology↗
PubMed1990

Alpha-amylase (EC 3.2.1.1) susceptibility rather than viscosity or gastric emptying rate controls plasma responses to starch in healthy humans.

The relationship between starch alpha-amylase (EC 3.2.1.1) susceptibility, plasma responses and gastric emptying rates has been investigated in humans. Nine randomly chosen healthy subjects were given three carbohydrate test meals (25 g starch or equivalent glucose units): two maize starch pastes with (a) 240 (S24) or (b) 500 (S50) g amylose/kg, and a glucose solution (GS). At 30 min, in vitro starch alpha-amylolysis was 48 (SD 4)% for S24 and 35 (SD 4)% for S50. Test meals differed in viscosity (mPa x s: S24, 54,000; S50, 190; GS, 4). Carbohydrates were labelled with 99mTechnetium and isotope gastric emptying was measured by external gamma counting. Carbohydrate isotopic gastric emptying patterns were exponential. Half gastric emptying time (min) was significantly (P less than 0.05) shorter for S50 (19(SD 2] than for GS (26(SD 2] or S24 (29(SD 2]. No correlation was found between half gastric emptying time and plasma response values. Values for peak insulin (pmol/l) above fasting were significantly (P less than 0.05) different: GS, 306 (SD 11); S24, 227 (SD 11); S50, 187 (SD 11). It is concluded that alpha-amylase susceptibility of the test carbohydrates is a determining factor in the insulin response of healthy subjects, while viscosity of the test meals and gastric emptying rate have no effect.

Adult↗