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PubMed2001

Pentagonal dodecahedranes: polyfunctionalization and MS fragmentation.

With the use of four- to eight-fold functionalized dodecahedranes (1-3), opportunities to arrive at highly strained dodecahedranes with two to four pairs of vicinal, eclipsed bromine substituents through front-side substitution and addition reactions have been explored. In standard processes, the interception of beta-OCH(3) radical/cationic intermediates was not problematic (9-12, 37, 50). The interception of beta-CO(2)R radicals was possible for Cl(*) (18) but not for Br(*) (17). The interception of beta-chloro radicals was possible for Cl(*) (27) but not for Br(*) (26), and the interception of beta-Br cations ("bromonium ions") with Br(-) was modest (45) to highly inefficient (24, 26). Two X-ray structural analyses (dimethoxy dibromide 9 and tetramethoxy tetrabromide 53) indicated the structural consequences of the molecular strain introduced by the two (four) vicinal CH(3)O/Br pairs. A systematic analysis of the MS spectra confirms that, in virtually all cases studied, the elimination of the substituents occurs without significant carbon-cage disruption, leading ultimately to multiply unsaturated dodecahedral ions for dodecahedrahexa(C(20)H(8))enes, -hepta(C(20)H(6))enes, and -octa(C(20)H(4))enes.

Journal Article↗
PubMed2007

Separating bias and sensitivity in judgments of associative memory.

Ratings of the degree of association between words are linearly related to normed associative strengths, but the intercept is high, and the slope is shallow (the judgments of associative memory [JAM] function). Two experiments included manipulations intended to decrease the intercept and increase the slope. Discrimination training on many pairs of words and constraining ratings to sum to a constant both reduced the intercept but failed to change the slope. The intercept of the JAM function appears to contain a bias component that can be manipulated independently of the slope, which reflects sensitivity to associative strengths.

Association↗
PubMed1993

6-[18F]fluoro-L-dopa metabolism in living human brain: a comparison of six analytical methods.

In 11 normal volunteers and six patients with Parkinson's disease, we compared six different analyses of dopaminergic function with L-3,4-dihydroxy-6-[18F]fluorophenylalanine (FDOPA) and positron emission tomography (PET). The caudate nucleus, putamen, and several reference regions were identified in PET images, using magnetic resonance imaging (MRI). The six analyses included two direct determinations of DOPA decarboxylase activity (k3D, k3*), the slope-intercept plot based on plasma concentration (K), two slope-intercept plots based on tissue content (k3r, k3s), and the striato-occipital ratio [R(T)]. For all analyses, the difference between two groups of subjects (normal volunteers and patients with Parkinson's disease) was larger in the putamen than in the caudate. For the caudate nucleus, the DOPA decarboxylase activity (k3D, k3*), tissue slope-intercept plots (kr3, ks3); and striato-occipital ratio [R(T)] analyses significantly discriminated between the normal volunteers and the patients with Parkinson's disease (p < 0.005) [with least significance for k3* (p < 0.05)], while the plasma slope-intercept plot (K) failed to do so. For the putamen, the values for k3D, k3*, K, k3r, k3s, and R(T) of normal volunteers were significantly higher than those of patients (p < 0.005) [with least significance for K (p < 0.025)]. Linear correlations were significant between k3D and k3s; k3D and k3r; k3D and R(T); and k3D and k3*, in this order of significance. We found no correlation between k3D and K values in the caudate nucleus.

Adult↗
PubMed2006

n-alkanes on Pt(111) and on C(0001)Pt(111): chain length dependence of kinetic desorption parameters.

We have measured the desorption of seven small n-alkanes (C(N)H(2N+2), N=1-4,6,8,10) from the Pt(111) and C(0001) surfaces by temperature programed desorption. We compare these results to our recent study of the desorption kinetics of these molecules on MgO(100) [J. Chem. Phys. 122, 164708 (2005)]. There we showed an increase in the desorption preexponential factor by several orders of magnitude with increasing n-alkane chain length and a linear desorption energy scaling with a small y-intercept value. We suggest that the significant increase in desorption prefactor with chain length is not particular to the MgO(100) surface, but is a general effect for desorption of the small n-alkanes. This argument is supported by statistical mechanical arguments for the increase in the entropy gain of the molecules upon desorption. In this work, we demonstrate that this hypothesis holds true on both a metal surface and a graphite surface. We observe an increase in prefactor by five orders of magnitude over the range of n-alkane chain lengths studied here. On each surface, the desorption energies of the n-alkanes are found to increase linearly with the molecule chain length and have a small y-intercept value. Prior results of other groups have yielded a linear desorption energy scaling with chain length that has unphysically large y-intercept values. We demonstrate that by allowing the prefactor to increase according to our model, a reanalysis of their data resolves this y-intercept problem to some degree.

Journal Article↗
PubMed2002

Maternal plasma corticotropin-releasing hormone trajectories vary depending on the cause of preterm delivery.

OBJECTIVE: Although second trimester maternal plasma corticotropin-releasing hormone concentrations are elevated in women who are destined to deliver preterm, the sensitivity and positive predictive value of an individual test of corticotropin-releasing hormone concentration is low. This poor screening performance may be due in part to the observation that the causes of preterm delivery are heterogenous, with potentially different effects on corticotropin-releasing hormone production. We have reanalyzed data from a previous cohort of women with multiple samplings to determine whether the trajectory of increase of placental corticotropin-releasing hormone provided more information than did a single sample. STUDY DESIGN: In this cohort, where 2 to 4 samples that had been assayed for corticotropin-releasing hormone were available on 305 women, the general form of the exponential equation y = ae(bt) was fitted to the corticotropin-releasing hormone data of each individual by the Gauss-Newton nonlinear least squares method, which generated the parameters, y-intercept and rate of rise, in corticotropin-releasing hormone concentration for each woman. Nonparametric statistical techniques, including bootstrapping, were applied to compare the results for the group of women who delivered at term with the group of women who delivered spontaneously preterm and the group of women who were delivered preterm by induction or cesarean delivery because of obstetric indication. RESULTS: The 3 clinically defined groups have significantly different parameters, y-intercept and rate of rise, which describe the corticotropin-releasing hormone trajectory. The group that delivered preterm because of obstetric indications had a similar mean y-intercept but significantly greater mean rate of rise in corticotropin-releasing hormone concentration than the term group (0.3491 vs 0.1788; 95% CI, 0.2331-0.4615 vs 0.1394-0.2330). The group that delivered spontaneously preterm had a significantly greater mean y-intercept than the group that delivered preterm because of obstetric indication (17.08 vs 1.83; 95% CI, 5.89-28.43 vs 0.03-5.19) but a similar mean rate of rise to the group that delivered at term. CONCLUSION: These data suggest that spontaneous preterm delivery is associated with an abnormal setting of the production of corticotropin-releasing hormone that is present from very early in pregnancy, although women who experience an induced preterm delivery are characterized by rapidly rising placental corticotropin-releasing hormone concentrations. These data further suggest that clinical abnormalities that are associated with preterm delivery by induction or cesarean delivery are associated with abnormalities that lead to a rapidly increasing corticotropin-releasing hormone concentrations. Trajectories for corticotropin-releasing hormone provide information beyond that obtained from a single sample.

Cesarean Section↗
PubMed1993

Age determination of experimental venous thrombi by ultrasonic tissue characterization.

PURPOSE: The ability of ultrasonic tissue characterization based on radiofrequency signal processing to detect compositional differences in thrombi of varying ages was evaluated in vivo. METHODS: Thrombi were produced in 49 jugular veins of 26 anesthetized 18 to 20 kg pigs by partial ligation and application of direct electric current. Thrombi were imaged 30 minutes after formation and 1, 7, and 14 days later with a color Doppler ultrasound scanner that identified the thrombi, and acquired radio frequency data for ultrasonic tissue characterization analysis. Ultrasonic tissue characterization used two parameters from the normalized power spectrum, slope, and intercept, which are related to scatterer size, scatterer concentration, and acoustic-impedance differences between scatterers and surrounding medium. Previous in vitro studies demonstrated that lower slope and higher intercept values correlated with greater cellularity and more-dense fibrin mesh. Histologic examination was performed for each time period. The values of slope and intercept for each timed observation were compared by a multilinear discriminant analysis. RESULTS: There were no statistical differences between day 0 and day 1. Statistically-significant differences in ultrasonic tissue characterization parameters were seen between all other time intervals with p values < 0.01. Older thrombi tended to demonstrate higher slope and lower intercept values. These ultrasonic tissue characterization changes correlated with a red cell and fibrin-mesh density reduction, which was confirmed by histologic findings and was indicative of partial spontaneous thrombolysis. The degree of spontaneous thrombolysis provides an estimate of the age of thrombi. CONCLUSION: Ultrasonic tissue characterization is capable of distinguishing age differences in thrombi in an animal model and has the potential for noninvasive application in clinical diagnosis.

Animals↗
PubMed2006

An alternative approach to evaluation of poolability for stability studies.

The current method for pooling the data from different batches or factors, suggested by ICH Q1E guidance, is to use analysis of covariance (ANCOVA) for test interaction between slopes and intercepts and factors. Failure to reject the null hypothesis of equality of slopes and equality of intercepts, however, does not prove that slopes and intercepts from different levels of factors are the same, and the data can be pooled for estimation of shelf life. In addition, the ANCOVA approach uses indirect parameters of intercepts and slopes in the regression model for assessment of poolability. The hypothesis for poolability is then formulated on the basis of the concept of equivalence for the means among the distributions of the quantitative attributes at a particular time point. Methods based on the intersection-union procedure are proposed to test the hypothesis of equivalence. A large simulation study was conducted to empirically investigate the size and power of the proposed method for the bracketing and matrixing designs given in the ICH Q1D guidance. Simulation results show that the proposed method can adequately control the size and provides sufficient power when the number of factors considered is fewer than three. A numerical example using the published data illustrates the proposed method.

Computer Simulation↗
PubMed2003

Comparison of methods for analyzing longitudinal binary outcomes: cognitive status as an example.

Longitudinal data generate correlated observations. Ignoring correlation can lead to incorrect estimation of standard errors, resulting in incorrect inferences of parameters. In the example used here, standard logistic regression, a population-averaged (PA) model fit using generalized estimating equations (GEE), and random-intercept models are used to model binary outcomes at baseline, three and six years later. The outcomes indicate cognitive impairment versus no cognitive impairment in a sample of community dwelling elders. The models include both time-invariant (age, gender) and time-varying (time, interactions with time) covariates. The absolute estimates from random-intercept models are larger than those of both standard logistic and GEE models. Compared to the model fit using GEE that accounts for time dependency, standard logistic regression models overestimate standard errors of time-varying covariates (such as time, and time by problems with activities of daily living), and underestimate the standard errors of time-invariant covariates (such as age and gender). The standard errors from the random-intercept model are larger than those from logistic regression and GEE models. The choice of models, GEE or random-intercept, depends on the research question and the nature of the covariates. Population-averaged methods are appropriate when between-subjects effects are of interest, and random-effects are useful when subject-specific effects are important.

Aged↗
PubMed1988

Effect of packed cell volume on diastolic coronary artery pressure-flow relations in the dog.

To elucidate the role of the haemorheological properties of the perfusate in the coronary circulation, the diastolic pressure-flow relation was studied in nine open chest heart blocked dogs with minimal vasomotor tone when blood with various packed cell volumes (12-67%) was used as perfusate. An electrical analogue model with proximal resistance R1, capacitance C, distal resistance R2, and the zero flow pressure intercept Pint was derived from the observation of the pressure-flow relation to support the data analysis. The diastolic pressure decay was then determined after the perfusion line had been clamped to calculate stop flow coronary artery pressure (Psf). The stop flow coronary artery pressure decreased in relation to packed cell volume (r = 0.45, p less than 0.01), and the value for the lowest packed cell volume (10-29%) was slightly higher than the great cardiac vein pressure (about 3 mmHg). The zero flow pressure intercept of the steady state pressure-flow relation showed a close correlation with the stop flow coronary artery pressure (r = 0.87, p less than 0.001). The value of R1 + R2, which reflects the inverse of the steady state pressure-flow slope, decreased simultaneously with the packed cell volume (r = 0.62, p less than 0.001). The resistance ratio R2/(R1 + R2) by our model prediction decreased in relation to packed cell volume (r = 0.5, p less than 0.001). The values of stop flow coronary artery pressure, zero flow pressure intercept, and R1 + R2 for the highest packed cell volume (50-69%) were 17.8(1.1) mmHg, 25.1(1.3) mmHg, and 0.48(0.05) mmHg.ml-1.min.100 g-1 respectively, whereas those for the lowest packed cell volume (10-29%) were 13.4(0.8) mmHg, 19.7(1.0) mmHg, and 0.24(0.02) mmHg.ml-1.min.100 g-1. The pressure difference between the stop flow coronary artery pressure and the zero flow pressure intercept may be due to the non-linearity in the pressure-flow relation at a low perfusion pressure. The left ventricular end diastolic pressure and great cardiac vein pressure did not change in relation to the packed cell volume of the coronary perfusate. Thus it is concluded that packed cell volume is one factor determining the high zero flow pressure.

Animals↗
PubMed1997

Mechanisms of adenosine-induced epicardial coronary artery dilatation.

BACKGROUND: In order to ascertain whether human adenosine-induced dilatation of epicardial arteries is direct or flow-mediated, we compared the effects of intracoronary adenosine infusion on epicardial coronary arteries with those produced by dipiridamole, a selective arteriolar vasodilator. METHODS AND RESULTS: In 24 patients with angiographically normal coronary arteries, coronary blood flow velocity was measured by a Doppler wire during intracoronary infusion of adenosine or dipyridamole, which is known to increase intramyocardial adenosine concentration. Coronary angiograms were obtained at baseline and immediately after the end of each infusion period; coronary diameters 5 mm distal to the wire tip were measured by computer-assisted quantitative coronary angiography. Peak coronary blood flow velocities during adenosine or dipyridamole infusions were similar (52.0 +/- 15.5 and 47.9 +/- 24.2 cm.s-1, P = ns). Coronary diameters immediately after adenosine and dipyridamole infusions were similar and both higher than that at baseline (2.80 +/- 0.63 and 2.86 +/- 0.64 vs 2.44 +/- 0.69 mm, P < 0.05). The absolute and percentage increases of coronary artery diameters in response to adenosine were highly correlated to coronary blood flow velocity (R = 0.622, intercept -0.10 +/- 0.14, P = 0.002 and R = 0.617, intercept -15.2 +/- 9.9, P = 0.001, respectively); similar correlations were found in response to dipyridamole (R = 0.708, intercept -0.44 +/- 0.19, P < 0.001 and R = 0.649, intercept -13.5 +/- 8.7, P < 0.001, respectively). Finally the absolute and percentage changes of coronary artery diameters caused by adenosine were highly correlated to those caused by dipyridamole (R = 0.840 P < 0.001 and R = 0.836, P < 0.001 respectively). CONCLUSIONS: A significant correlation exists between epicardial coronary vasodilation and coronary blood flow velocity during intracoronary adenosine infusion, thus suggesting that epicardial coronary vasodilation induced by adenosine is predominantly flow-mediated rather than direct. This conclusion is supported by the observation that similar findings were obtained using dipyridamole, which can only dilate epicardial coronary arteries indirectly, through the increase in coronary blood flow velocity caused by the inhibition of intramyocardial adenosine re-uptake.

Adenosine↗
PubMed1995

The chronotropic response of the sinus node to exercise: a new method of analysis and a study of pacemaker patients.

In this study, the intercepts and slopes of the regression lines of sinus heart rate response to exercise were examined as a possible means of assessing normal and abnormal chronotropic responses. The regressions were plotted for 223 normal subjects and 93 pacemaker patients during progressive bicycle exercise. The 93 pacemaker patients consisted of two groups, (a) 46 with symptomatic sick sinus syndrome (daytime sinus or nodal bradycardia of < 45.min-1 or atrial asystole > 1.5 s together with other features of the syndrome) and (b) 47 with second- or third-degree AV block (in whom a one-to-one AV relationship was either restored by dual chamber pacing or in whom normal AV conduction was present at the time of exercise). Examination of the regression lines showed them to be sufficiently linear in both normal subjects and pacemaker patients to allow calculation of the intercept and slope values. Multiple regression analysis of these values showed that the AV block group did not differ significantly from the normal individuals. However, in the patients with sick sinus syndrome, the intercept but not the slope values were significantly lower than in the normal subjects (P < 0.01). The patients with sick sinus syndrome appeared to have an abnormality of sinus node function, where the basic rate setting is too low at all levels of exercise, although the acceleration with exercise is normal. Among the sick sinus syndrome patients, only four (9%) had intercept values lying more than 2 standard deviations below that of the normal control group and were deemed to be chronotropically incompetent. Finally, the problems with the various methods used to investigate chronotropic incompetence are reviewed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2000

Radiation-use efficiency and dry matter partitioning of a young olive (Olea europaea) orchard.

Radiation-use efficiency (RUE) relates biomass production to the photosynthetically active radiation (PAR) intercepted by a plant or crop. We determined RUE and biomass partitioning coefficients of young olive (Olea europaea) trees for use in a general growth model. In 1995, 1-year-old olive trees var. 'Picual' were planted at a density of either 0.5 or 2.0 trees m(-2) near Córdoba, Spain, at a site providing favorable growth conditions. During the experiment (1995-1997), both PAR interception by the canopy and plant area index (PAI) were measured with radiation sensors. Regular harvests were performed to determine leaf area and biomass accumulation in roots, wood (stem, branches and trunk) and leaves. Leaf, wood and root biomass partitioning coefficients were calculated. The leaf area partitioning coefficients were also estimated. Dry matter production was linearly related to cumulative intercepted PAR. Seasonal RUE, calculated as the slope of the regression of aboveground biomass and cumulative intercepted PAR, was 1.35 g (MJ PAR)(-1). Radiation-use efficiency appeared to respond to environmental conditions, but was independent of planting density and PAI. The young olive trees allocated 0.26 of their total biomass to roots. Partitioning of aboveground dry matter was 0.60 to wood and 0.37 to leaves. As competition increased, dry matter partitioning to wood increased to 0.70.

Journal Article↗
PubMed2001

Shoot structure and photosynthetic efficiency along the light gradient in a Scots pine canopy.

We examined the effects of structural and physiological acclimation on the photosynthetic efficiency of Scots pine (Pinus sylvestris L.) shoots. We estimated daily light interception (DLI) and photosynthesis (DPHOT) of a number of sample shoots situated at different positions in the canopy. Photosynthetic efficiency (epsilon) was defined as the ratio of DPHOT to the potential daily light interception (DLI(ref)) defined as the photosynthetically active radiation (PAR) intercepted per unit area of a sphere at the shoot location. To calculate DLI(ref), DLI and DPHOT, the radiation field surrounding a shoot in the canopy was first modeled using simulated directional distributions of incoming PAR on a clear and an overcast day, and estimates of canopy gap fraction in different directions provided by hemispherical photographs. A model of shoot geometry and measured data on shoot structure and photosynthetic parameters were used to simulate the distribution of PAR irradiance on the needle surface area of the shoot. Photosynthetic efficiency (epsilon) was separated into light-interception efficiency (epsilon(I) = DLI/DLI(ref)) and conversion efficiency (epsilon(PHOT) = DPHOT/DLI). This allowed us to quantify separately the effect of structural acclimation on the efficiency of photosynthetic light capture (epsilon(l)), and the effect of physiological acclimation on conversion efficiency (epsilon(PHOT)). The value of epsilon increased from the top to the bottom of the canopy. The increase was largely explained by structural acclimation (higher epsilon(I)) of the shade shoots. The value of epsilon(PHOT) of shade foliage was similar to that of sun foliage. Given these efficiencies, the clear-day value of DPHOT for a sun shoot transferred to shade was only half that of a shade shoot at its original position. The method presented here provides a tool for quantitatively estimating the role of acclimation in total canopy photosynthesis.

Light↗
PubMed2003

Three-dimensional lamina architecture alters light-harvesting efficiency in Fagus: a leaf-scale analysis.

Modification of foliage exposition and morphology by seasonal average integrated quantum flux density (Qint) was investigated in the canopies of the shade-tolerant late-successional deciduous tree species Fagus orientalis Lipsky and Fagus sylvatica L. Because the leaves were not entirely flat anywhere in the canopy, the leaf lamina was considered to be three-dimensional and characterized by the cross-sectional angle between the leaf halves (theta). Both branch and lamina inclination angles with respect to the horizontal scaled positively with irradiance in the canopy, allowing light to penetrate to deeper canopy horizons. Lamina cross-sectional angle varied from 170 degrees in the most shaded leaves to 90-100 degrees in leaves in the top of the canopy. Thus, the degree of leaf rolling increased with increasing Qint, further reducing the light-interception efficiency of the upper-canopy leaves. Simulations of the dependence of foliage light-interception efficiency on theta demonstrated that decreases in theta primarily reduce the interception efficiency of direct irradiance, but that diffuse irradiance was equally efficiently intercepted over the entire range of theta values in our study. Despite strong alteration in foliage light-harvesting capacity within the canopy and greater transmittance of the upper crown compared with the lower canopy, mean incident irradiances varied more than 20-fold within the canopy, indicating inherent limitations in light partitioning within the canopy. This extensive canopy light gradient was paralleled by plastic changes in foliar structure and chemistry. Leaf dry mass per unit area varied 3-4-fold between the canopy top and bottom, providing an important means of scaling foliage nitrogen contents and photosynthetic capacity per unit area with Qint. Although leaf structure versus light relationships were qualitatively similar in all cases, there were important tree-to-tree and species-to-species variations, as well as evidence of differences in investments in structural compounds within the leaf lamina, possibly in response to contrasting leaf water availability in different trees.

Fagus↗
PubMed2004

Small-area incidence trends in breast cancer.

BACKGROUND: During the past 2 decades, the observed incidence of in situ and early-stage invasive breast cancer has increased substantially as a result of increased use of mammography. Geographic variability in the increase in breast cancer incidence has been observed among large areas. Examining the variability among small areas in the incidence over time will facilitate appropriate geographic allocation of resources aimed at increasing screening. METHODS: We examined county-specific increases in breast cancer incidence over time, specifically the variability and spatial correlation in the increase in breast cancer incidence. The analyses were based on county-level data (1973-1997) from the Iowa Surveillance, Epidemiology, and End Results program. A spatiotemporal hierarchical Bayesian model was used to examine variability in county-specific rates (intercepts, slopes, and spatial correlations) among white women at least 40 years of age. RESULTS: Posterior values indicate there was little variability among counties in the change in breast cancer incidence over time (slope) but substantial variation among intercepts. There was considerable spatial correlation among the county-specific intercepts but a lack of a spatial correlation among the county-specific slopes. There was no correlation between the county-specific intercept and slope. CONCLUSIONS: Breast cancer incidence increased over time, but county-specific rates increased independently relative to their neighboring counties or their initial rate.

Adult↗
PubMed2002

The evolution of trade-offs: testing predictions on response to selection and environmental variation.

The concept of phenotypic trade-offs is a central element in evolutionary theory. In general, phenotypic models assume a fixed trade-off function, whereas quantitative genetic theory predicts that the trade-off function will change as a result of selection. For a linear trade-off function selection will readily change the intercept but will have to be relatively stronger to change the slope. We test these predictions by examining the trade-off between fecundity and flight capability, as measured by dorso-longitudinal muscle mass, in four different populations of the sand cricket, Gryllus firmus. Three populations were recently derived from the wild, and the fourth had been in the laboratory for 19 years. We hypothesized that the laboratory population had most likely undergone more and different selection from the three wild populations and therefore should differ from these in respect to both slope and intercept. Because of geographic variation in selection, we predicted a general difference in intercept among the four populations. We further tested the hypothesis that this intercept will be correlated with proportion macropterous and that this relationship will itself vary with environmental conditions experienced during both the nymphal and adult period. Observed variation in the phenotypic trade-off was consistent with the predictions of the quantitative genetic model. These results point to the importance of modeling trade-offs as dynamic rather than static relationships. We discuss how phenotypic models can incorporate such variation. The phenotypic trade-off between fecundity and dorso-longitudinal muscle mass is determined in part by variation in body size, illustrating the necessity of considering trade-offs to be multi factorial rather than simply bivariate relationships.

Animals↗
PubMed2006

Heritability of P300 amplitude development from adolescence to adulthood.

Early adulthood is a period of late brain development corresponding to the age of onset for psychopathology associated with P300 amplitude reductions. Although amplitude from a single occasion is heritable, little is known about genetic influences on change during this period. This is the first study of P300 change to combine latent growth and twin models. P300 at Pz was measured up to three times at approximately ages 17, 20, and 23 in monozygotic and dizygotic male twins using a visual task. P300 decreased with age. Correlations indexing the stability of amplitude over time were high (median r=.72) and almost 90% of the stable variance (i.e., the model intercept) was attributable to genetic influences. The rate of decrease was heritable, and the genes influencing intercept may be the same ones influencing change. Finally, intercept was more heritable than amplitude at any single time point. Intercept may be a more useful aid in the search for genes associated with relevant psychopathology than single measures of P300. Over a broader age range growth indices may be useful "developmental" endophenotypes.

Adolescent↗
PubMed2006

Is ventilatory efficiency dependent on the speed of the exercise test protocol in healthy men and women?

Indices of ventilatory efficiency have proven useful in assessing patients with heart and lung disease. One of these indices is the slope of the ventilation (V(E)) versus carbon dioxide output (VCO(2)) relationship during cardiopulmonary exercise testing (CPET) for work rates where the relationship is linear. However, this relationship is defined not only by the slope but also by the y-intercept. To examine whether this relationship is dependent on the speed of the CPET protocol, 30 healthy subjects (16 males) were administered a rapid CPET with 1-min increment duration (1-min CPET) to the limit of tolerance and a slow CPET with 4-min increment duration (4-min CPET) to the lactate threshold. Ventilation and the gas fractions for oxygen and CO(2) were measured with a Vacumed metabolic cart. The average increment size of both protocols for both sexes was not significantly different (P>0.05). For the males, the mean (SD) slope for the 1- and 4-min CPET was 20.12 (2.61) and 20.37 (2.41), respectively. The corresponding values for the y-intercept were 4..89 (2.08) and 5..10 (2.00) l min(-1). For the females, the mean (SD) slope for the 1- and 4-min CPET was 23.90 (2.38) and 24.16 (2.55), respectively. The corresponding values for the y-intercept were 3.93 (0.39) and 3.77 (0.71) l min(-1). Paired t-test analysis demonstrated for both sexes that the slopes and y-intercepts were not different for the two protocols (P>0.05). The results of this study demonstrate that the V(E) versus VCO(2) relationship is not dependent on the speed of the CPET protocol.

Adult↗