Fear gradients as a function of the temporal interval between signal and aversive event in the rat.

The degree of response suppression was measured in 5-sec intervals during a signal that was associated with electric shock. Four groups of 6 naive male albino Norway Charles River CD rats were tested with signals of fixed or random duration and with shocks that occurred at the end of the signal or at random times during the signal. In all cases, there was a transient effect of the onset of the signal, but thereafter, the 4 groups showed qualitatively different fear gradients. The magnitude of fear was closely related to the expected time to the next shock. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recording fetal heart rate as a behavioral measure.

Employed the fetal EKG with 4 electrodes placed on the maternal abdomen 1 just above the symphysis pubis, and the other across the abdomen at the level of the fundus uteri. The relationship between maternal and fetal heart rates were explored by also recording the maternal EKG. Difficulties in measuring fetal heart rate are discussed and possible solutions presented. It is concluded that fetal heart rate is a difficult but possible measure for exploration of fetal behavior. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of dexamethasone and betamethasone on fetal heart rate variability in preterm labour: a randomised study

OBJECTIVE: To compare the effects of betamethasone and dexamethasone on fetal heart rate in appropriately grown fetuses. METHODS: Eighty-two pregnant women (97 fetuses) with preterm labour were randomly allocated to receive betamethasone (n=42) or dexamethasone (n=40) for fetal lung maturation in a nonblinded fashion. Computerised cardiotocogram (CTG) parameters were compared before, during and after treatment. RESULTS: A decrease in fetal heart rate variability was found with betamethasone but no significant changes were found with dexamethasone. Fetal heart rate variability returned to pre-treatment values within a week after cessation of treatment with betamethasone. Neonatal outcome was similar in the two groups. CONCLUSIONS: These findings might prove useful in the management of compromised fetuses with decreased fetal heart rate variability in which the CTG should be used together with other parameters to assess fetal wellbeing during corticosteroid treatment. Dexamethasone may be preferable as the drug of choice since it was associated with significantly less alteration in fetal heart rate variability compared with betamethasone.     

Renal function as a marker of human fetal maturation

Sixty clinically well infants of various gestational ages (27 to 40 weeks) were studied from 24-40 hours after birth to evaluate glomerular filtration rate and renal excretion rate of sodium at various stages of fetal maturation. Creatinine clearance was directly related to gestational as (r = 0.643). Fractional sodium excretion was inversely related to gestational age (r = -0.755). The renal functions of small for gestational age infants were similar to those of full-term infants whose birth weights were appropriate for gestational age. The data showed that the glomerular functions of an infant below 32 weeks of gestation were more predominant than the tubular function resulting in a greater fractional sodium excretion rate and higher urinary Na loss in infants of this gestational age, when compared with the more mature infants.     

Multifetal pregnancy reduction: evaluation of fetal growth in the remaining twins

OBJECTIVE: Our purpose was to study fetal growth after reduction of high-order multiple gestations to twins. STUDY DESIGN: Birth weight and gestational age data were collected for 236 triplet and greater multiple pregnancies reduced to twins (113 triplets, 89 quadruplets, and 34 quintuplets or above) and was compared with those of a control group of unreduced twins. RESULTS: Rates of intrauterine growth restriction per pregnancy were significantly different between the nonreduced and all categories of reduced multifetal pregnancies. The incidence of intrauterine growth restriction was 19.4% in the nonreduced twins, 36.3% in pregnancies reduced from triplets, 41.6% in pregnancies reduced from quadruplets, and 50% from higher-order multiple gestations. There was a statistically significant trend toward increasing frequency of intrauterine growth restriction with increasing starting fetal number (p = 0.04). The increase in intrauterine growth restriction was primarily accounted for by twin pairs with only one growth-restricted newborn. CONCLUSION: Multifetal pregnancy reduction does not reduce the incidence of intrauterine growth restriction in the remaining fetuses to that of nonreduced twins.     

Temporal search as a function of the variability of interfood intervals.

We attempted to determine whether timing theories developed primarily to explain performance in fixed-interval reinforcement schedules are also applicable to variable intervals. Groups of rats were trained in lever boxes on peak procedures with a 30-, 45-, or 6O-s interval, or a 30- to 6O-s uniform distribution (Experiment 1); a 60-s fixed and 1- to 121-s uniform distribution between and within animals (Experiment 2); and a procedure in which the interval between food and next available food gradually changed from a fixed 60 s to a uniform distribution between 0 and 120 s (Experiment 3). In uniform interval schedules rats made lever responses at particular times since food, as measured by the distribution of food-food intervals, the distribution of postreinforcement pauses, and the mean response rate as a function of time since food. Qualitative features of this performance are described by a multiple-oscillator connectionist theory of timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sonographic evaluation of the uterine cervix

Ultrasonographic evaluation of the uterine cervix has been shown to help predict patients who may be at an increased risk for preterm delivery. The use of ultrasound in at-risk patients may improve the selection of those needing obstetric intervention, which therefore, may improve outcome and lower overall health care costs. Cervical competence, once thought to be a categorical variable, should now be thought of as a continuous variable, as the shortest cervical lengths are found in those women with a history of very early preterm delivery (> 24 weeks). Adjunctive tests, such as fetal fibronectin Bishop scoring and bacterial vaginosis may help to improve the accuracy of prediction of preterm birth; therefore a multifaceted risk approach to preterm birth is suggested in this article.     

Power-law relationship of heart rate variability as a predictor of mortality in the elderly

BACKGROUND: The prognostic role of heart rate (HR) variability analyzed from 24-hour ECG recordings in the general population is not well known. We studied whether analysis of 24-hour HR behavior is able to predict mortality in a random population of elderly subjects. METHODS AND RESULTS: A random sample of 347 subjects of > or =65 years of age (mean, 73+/-6 years) underwent a comprehensive clinical evaluation, laboratory tests, and 24-hour ECG recordings and were subsequently followed up for 10 years. Various spectral and nonspectral measures of HR variability were analyzed from the baseline 24-hour ECG recordings. Risk factors for all-cause, cardiac, cerebrovascular, cancer, and other causes of death were assessed. By the end of 10-year follow-up, 184 subjects (53%) had died and 163 (47%) were still alive. Seventy-four subjects (21%) had died of cardiac disease, 37 of cancer (11%), 25 of cerebrovascular disease (7%), and 48 (14%) of various other causes. Among all analyzed variables, a steep slope of the power-law regression line of HR variability (< -1.50) was the best univariate predictor of all-cause mortality (odds ratio, 7.9; 95% confidence interval [CI], 3.7 to 17.0; P<.0001). After adjusting for age and sex and including all univariate predictors of mortality in the proportional hazards analysis, ie, measures of HR variability, history of heart disease, functional class, smoking, medication, and blood cholesterol and glucose concentrations, all-cause mortality was predicted only by the slope of HR variability (adjusted relative risk, 1.74; 95% CI, 1.42 to 2.13; P<.0001) and a history of congestive heart failure (adjusted relative risk, 1.70; P=.0002). The slope of HR variability predicted both cardiac (adjusted relative risk, 2.05; P=.0002) and cerebrovascular death (adjusted relative risk, 2.84; P=.0001) but not cancer or other causes of death. CONCLUSIONS: Power-law relationship of 24-hour HR variability is a more powerful predictor of death than the traditional risk markers in elderly subjects. Altered long-term behavior of HR implies an increased risk of vascular causes of death rather than being a marker of any disease or frailty leading to death.     

Variability in isochronous tapping: Higher order dependencies as a function of intertap interval.

Isochronous serial interval production (ISIP) data, as from unpaced finger tapping, exhibit higher order dependencies (drift). This fact has largely been ignored by the timing literature, one reason probably being that influential timing models assume random variability. Men and women, 22–36 years old, performed a synchronization–continuation task with intertap intervals (ITI) from 0.4 s to 2.2 s. ISIP variability was partitioned into components attributable to drift and 1st-order serial correlation, and the results indicate that (a) drift contributes substantially to the dispersion for longer ITIs, (b) drift and 1st-order correlation are different functions of the ITI, and (c) drift exhibits break close to 1.0 s and 1.4 s ITI. These breaks correspond to qualitative changes in performance for other temporal tasks, which suggests common timing processes across modalities and tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spectral analysis of short term R-Tapex interval variability during sinus rhythm and fixed atrial rate

Analysis of heart rate variability has been proven useful in stratifying post myocardial patients at risk and in evaluating autonomic dysfunction. Recently augmented inter-lead variability of the QT interval has been associated with increased mortality as a result of arrhythmia and proposed as a marker of dispersion of ventricular repolarization. As the duration of the QT interval is largely dependent upon the length of the preceding cardiac cycle it is tempting to analyse whether neural mechanisms might also directly exert additional modulation. Using autoregressive algorithms we therefore analysed RR and R-Tapex interval variabilities in 15 normal subjects during sinus rhythm and in six patients with a fixed atrial rate. In controls mean R-Tapex interval and variance measured on the vector magnitude were, respectively, 245 +/- 6 ms and 5.1 +/- 0.7 ms2. Spectral analysis of R-Tapex indicated the presence of two spectral components which corresponded to the low and high frequency components of heart rate variability. In R-Tapex variability, high frequency (44 +/- 4 nu) was predominant over low frequency (29 +/- 4 nu). During controlled respiration, a manoeuvre associated with enhanced vagal modulation of sinus node, there was a further increase in high frequency (58 +/- 4 nu) whereas during tilt the low frequency component of R-Tapex variability became predominant (57 +/- 6 nu). In patients with a fixed atrial rate, variance was extremely low (3 +/- 0.9 ms2) and only a respiration-related high frequency component was recognizable in spectral analysis of RR and R-Tapex variabilities. This component was likely to depend upon mechanically induced changes in cardiac vector orientation. These data indicate that during sinus rhythm short-term R-Tapex interval variability is characterized by the same rhythmical components present in RR variability. However, the presence of a very low variance and of only a high frequency component in patients in whom the physiological variability of sinus node is abolished by atrial pacing. suggests that neural modulatory mechanisms do not exert a direct effect on the length of the R-Tapex interval.     

Physiological characteristics of chemostatically grown Citrobacter freundii as a function of the specific growth rate and type of nutrient limitation

Citrobacter freundii was grown aerobically in a chemostat on a mineral medium with galactose or glucose as carbon and energy sources under limitation by carbon or nitrogen source respectively. At various specific growth rates ranging from 7 to 95% mumax the culture in steady state was analysed and growth yield, specific metabolic rate of substrate utilization, intracellular concentration of pyruvate, ATP, ADP, AMP and energy charge were determined and plotted as functions of dilution rate. In all four types of experiments the physiological state of cells remained practically independent of dilution rate up to D=0.6 mumax, and at a given specific growth rate nearly independent on mumax and type of limitation. At approximately D=0.6 mumax, which is close to the maximum output dilution rate Dm, the physiological state of the cells changed: growth yields decreased and intr cellular pyruvate and adenylates concentrations increased. Consequently, in a given medium two dilution rates exist at which growth rate dx/dt is the same but the physiology of the population is quite different.     

Heart rate variability in evaluation of the autonomic nervous system. A review

Analysis of heart rate variability is increasingly used for testing the function of the autonomic nervous system in cardiovascular disease and for the diagnosis of autonomic neuropathy. In cardiovascular disease, long-term data collection (several hours) is primarily used to describe the static activity in the different branches of the autonomic nervous system. In the diagnosis of autonomic neuropathy, short-term forced variations in heart rate are employed in order to describe the dynamic capacity of the parasympathetic nervous system. In the subsequent data-analysis several different principles may be used, and the purpose of this review is to describe these principles and their use in clinical and experimental settings.     

Individual differences in output variability as a function of job complexity.

The hypothesis was tested that the standard deviation of employee output as a percentage of mean output (SDp) increases as a function of the complexity level of the job. The data examined were adjusted for the inflationary effects of measurement error and the deflationary effects of range restriction on observed SDp figures, refinements absent from previous studies. Results indicate that SDp increases as the information-processing demands (complexity) of the job increase; the observed progression was approximately 19%, 32%, and 48%, from low to medium to high complexity nonsales jobs, respectively. SDp values for sales jobs are considerably larger. These findings have important implications for the output increases that can be produced through improved selection. They may also contribute to the development of a theory of work performance. In addition, there may be implications in labor economics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dynamics of membrane excitability determine interspike interval variability: a link between spike generation mechanisms and cortical spike train statistics

We propose a biophysical mechanism for the high interspike interval variability observed in cortical spike trains. The key lies in the nonlinear dynamics of cortical spike generation, which are consistent with type I membranes where saddle-node dynamics underlie excitability (Rinzel & Ermentrout, 1989). We present a canonical model for type I membranes, the theta-neuron. The theta-neuron is a phase model whose dynamics reflect salient features of type I membranes. This model generates spike trains with coefficient of variation (CV) above 0.6 when brought to firing by noisy inputs. This happens because the timing of spikes for a type I excitable cell is exquisitely sensitive to the amplitude of the suprathreshold stimulus pulses. A noisy input current, giving random amplitude "kicks" to the cell, evokes highly irregular firing across a wide range of firing rates; an intrinsically oscillating cell gives regular spike trains. We corroborate the results with simulations of the Morris-Lecar (M-L) neural model with random synaptic inputs: type I M-L yields high CVs. When this model is modified to have type II dynamics (periodicity arises via a Hopf bifurcation), however, it gives regular spike trains (CV below 0.3). Our results suggest that the high CV values such as those observed in cortical spike trains are an intrinsic characteristic of type I membranes driven to firing by "random" inputs. In contrast, neural oscillators or neurons exhibiting type II excitability should produce regular spike trains.     

Effects of 4 hours magnesium sulfate infusion on fetal heart rate variability and reactivity in a goat model

Effects of magnesium sulfate were investigated on fetal heart rate (FHR) baseline, variability, and reactivity in goats. Six chronically catheterized fetuses of Japanese Saanen goat at 125 to 130 days' gestation (term = 147 days) were used. Magnesium sulfate was directly infused to the fetuses. Short-term variability and long-term variability were obtained according to Huey et al. The baseline, reactivity, short-term variability and long-term variability of the FHR were compared between those receiving magnesium sulfate infusions and those receiving vehicle infusions without magnesium sulfate for 4 hr. Two-way analysis of variance (ANOVA) and Duncan's multiple range test was applied for statistical significance. Four hours magnesium sulfate infusion significantly increased fetal plasma concentration of magnesium from 2.4-6.6 mg/dL, without significant changes in fetal respiratory gases and pH values. The baseline FHR was significantly decreased by magnesium infusion compared with that receiving vehicle infusion. The incidence of acceleration, short-term variability, and long-term variability during the fourth hour of magnesium infusion was also significantly decreased compared to a controlled infusion. The time spent by high amplitude phase of short-term variability and that of long-term variability were also significantly reduced. Significant correlation was obtained between the magnesium concentration and incidence of acceleration at fourth hour of magnesium infusion. Four hours infusion of magnesium sulfate significantly decreases baseline FHR, short-term variability, long-term variability, and reactivity in fetal goats at 0.85 gestation.     

Relationships between heart rate variability and antiarrhythmic effects of hydroquinidine

We report 2 elderly patients who present with a relatively acute onset of a severe symmetrical synovitis affecting the flexor digitorum tendon sheaths and wrist joints with pitting edema of the dorsum of both hands. These patients were seronegative for rheumatoid factor and responded to treatment with low dose predonisone (10 mg daily) without relapse. These presenting features were closely linked with the RS3PE syndrome originally described by McCarty.