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Biomedical subjects

R B Harrist

Publications and source records attributed to R B Harrist.

At least 37 records · Page 2Linked to original sources
PubMed1987

Administration-time-dependency of the pharmacokinetic behavior and therapeutic effect of a once-a-day theophylline in asthmatic children.

Using a double-blind, placebo-control, crossover study design, 8 asthmatic children (8-15 years) were evaluated for temporal patterns in airways function throughout separate study periods when treatment was placebo or Theo-24 once-daily on separate occasions at 0600, 1500 or 2100 hr. During 39-hr in-hospital observations, pulmonary function and serum theophylline concentrations (STC) were assessed every 3 hr under all treatments. The pharmacokinetics of Theo-24 varied greatly depending on the dosing time. For the afternoon and evening dosings, the Cmax, Tmax, AUC, % swing, % fluctuation, % AUC fluctuation, % nocturnal excess and Cav(2-6 hr) were all statistically significantly greater than for the morning dosing. Compared with the placebo regimen, dosing patients with Theo-24 at 1500 hr disrupted circadian patterns of airways function, especially airways patency, while dosing at 2100 hr, reduced the amplitude and shifted the acrophase of several spirometric measures to a slightly earlier time. Theo-24 treatment irrespective of dosing time resulted in comparable enhancement of the group 24-hr mean, minimum and maximum values of airways patency with reference to placebo baselines. Theo-24 dosing at 1500 or 2100 hr, however, resulted in the best effect on the airways as assessed by the 24-hr mean FEV 1.0 level in 7 of the 8 asthmatic children. When the drug was given at 1500 hr, the time of lowest FEV 1.0 was shifted from the nighttime hours in 5 of 8 patients. These findings suggest that clinicians need to individualize the theophylline dosing schedule of patients to best control the symptoms of asthma.

Asthma↗
PubMed1986

Mathematic modeling of fetal growth: development of individual growth curve standards.

To provide a more precise means for monitoring individual fetal growth and to improve the detection of growth abnormalities, the Rossavik growth model [P = c(t)k + s(t)] has been used to establish individual growth curve standards. A longitudinal study of the growth of one-dimensional (biparietal diameter, head, and abdominal circumferences), two-dimensional (head and abdominal profile areas), and three-dimensional (head and abdominal volumes) parameters in 18 normal fetuses has revealed that the growth of all parameters can be well-described by the Rossavik model (R2: 97.2 to 99.5%). Strong statistical evidence was obtained indicating that the coefficient k is principally a geometric coefficient having a value determined primarily by the dimension of the parameter being studied. It was also found that the coefficients c and s can be estimated from the data obtained before 28 weeks' conceptual age. Individual growth curve models derived from data obtained before 28 weeks were capable of predicting growth beyond 28 weeks. These models provide growth curve standards for evaluating individual fetal growth beyond 28 weeks.

Embryonic and Fetal Development↗
PubMed1985

Estimation of fetal weight with the use of head, body, and femur measurements--a prospective study.

In utero estimates of fetal weight were evaluated prospectively in 109 fetuses with the use of sonographic models developed in a previous study. This report confirms that the best in utero weight estimates result from the use of models based on measurements of head size, abdominal size, and femur length. Since the accuracy of these models (1 SD = 7.5%) is significantly better than those based on measurements of head and body (e.g., biparietal diameter, abdominal circumference), we recommend routine use of such models in obstetric sonography.

Abdomen↗
PubMed1985

Primary irritant contact dermatitis from synthetic pyrethroid insecticide exposure.

Synthetic pyrethroids are widely used insecticides with numerous applications, varying from food protection to general pest control. Humans are capable of tolerating greater acute and chronic exposures to the pyrethroids than to many other insecticides. An abnormal cutaneous sensation (paresthesia) is known to occur after dermal contact with the pyrethroids. Recent field studies have indicated that a primary irritant contact dermatitis may also develop. This investigation evaluated dermal irritancy from cutaneous synthetic pyrethroid application to albino rabbits. Through repeated daily applications of either fenvalerate or permethrin, a slight erythema was noted visually which correlated with increased cutaneous blood flow measured by laser Doppler velocimetry. Histopathological changes were also documented, but no significant differences were detected in edema or thermal variation.

Animals↗
PubMed1985

Effect of subchronic formaldehyde inhalation on minute volume and nasal deposition in Sprague-Dawley rats.

Since respiratory depression during formaldehyde (HCHO) inhalation is an important mechanism in reducing the dose received and potentially the toxicity in the nasal passages of exposed animals, this study was conducted to determine if changes in the pattern of minute volume response and nasal deposition occurred in nosepiece challenges to rats after long-term repeated exposures to HCHO. Male Sprague-Dawley rats were exposed to 0, 0.5, 3, or 15 ppm HCHO for 6 h/d, 5 d/wk, for 8 or 16 wk. The preexposed animals and age-specific controls were then submitted to a HCHO nosepiece challenge at the same concentration that was received in the subchronic exposure. Very high nasal deposition was demonstrated in all measurements. There was a diminished maximum minute volume depression in the 16-wk group relative to the 8-wk group. The difference in response was not statistically associated with the subchronic preexposure concentration. The substantial recovery of all initially depressed responses that occurred during the challenges probably diminished the impact of the decreased maximum responses on the resulting nasal deposition over the course of the long-term exposures.

Absorption↗
PubMed1985

Synthetic pyrethroid insecticides: a dermatological evaluation.

Synthetic pyrethroids are lipophilic insecticides whose biological activity seems to be directly related to their chemical structure. In this investigation differences in cutaneous sensation were detected by human participants between synthetic pyrethroids with a cyano group in the (S)-configuration of the 3-phenoxybenzyl alcohol of their molecular structure (fenvalerate) and those that do not (permethrin). A strong relation was noted between insecticidal potency and degree of induced cutaneous sensation for the alpha-cyano and non-cyano pyrethroids, with a prominent difference between the two. No sensation was observed by any of the same participants on topical exposure to the inert ingredients of these agents. A linear correlation between concentration and degree of induced dysaethesia was observed for both pyrethroids. Regressing the cutaneous sensation on the common logarithm of concentration resulted in a regression equation of Y = 84.0 + 31.0X1 for fenvalerate and Y = 27.5 + 15.8X1 for permethrin. A highly efficacious therapeutic agent for pyrethroid exposure was noted to be dl-alpha tocopherol acetate. An impressive degree of inhibition of paraesthesia resulted from the topical application of vitamin E acetate, with a therapeutic index of almost 100%.

Dose-Response Relationship, Drug↗
PubMed1985

Use of femur length/abdominal circumference ratio in detecting the macrosomic fetus.

The femur length/abdominal circumference ratio, expressed as FL/AC X 100, was determined in 156 fetuses and evaluated as a predictor of fetal macrosomia within one week prior to delivery. The normal range (mean +/- 2 SD) in the 105 normal-weight fetuses was 22.0 +/- 2, while the normal range in the 51 macrosomic fetuses was 20.5 +/- 2; these differences were highly significant (P = less than .0001). The predictive power of a positive ratio was 68%, with a sensitivity of 63%. This ratio was particularly useful in the subset (n = 9) of macrosomic fetuses whose mothers were diabetic, correctly identifying 89% of this group. Because it is age independent, this ratio should prove most helpful in identifying fetuses at risk for macrosomia in patients whose dates are not known, since it may become abnormal before the fetal weight falls above the 90th percentile at term (3,900 g). In patients whose dates are known, early fetal macrosomia is best predicted by evaluating the abdominal circumference against normal standards for age.

Abdomen↗
PubMed1984

Sonographic estimation of fetal weight. The value of femur length in addition to head and abdomen measurements.

Sonographic estimation of fetal weight in utero was performed in 167 live-born fetuses examined within one week of delivery. Regression models were based on measurements of abdominal circumference, head circumference, biparietal diameter, and femur length, both alone and in combination. The best results (1 S.D. = 7.5% of actual weight) were obtained by combining measurements of the fetal head, abdomen, and femur, most likely due to the strong linear relationship between femur length and crown-heel length.

Abdomen↗
PubMed1984

Estimating fetal age: computer-assisted analysis of multiple fetal growth parameters.

Regression models for predicting menstrual age based on real-time sonographic measurements of four fetal parameters (biparietal diameter, head circumference, abdominal circumference, and femur length), used alone and in combination, were developed in a cross-sectional study of 361 fetuses between 14 and 42 menstrual weeks. The head circumference and femur length were the strongest individual predictors of age. A number of combinations of fetal parameters, including the combination of head circumference and femur length, provided age estimates that were significantly better (p = 0.05) than those using any single parameter alone. It was also demonstrated that simply averaging individual age estimates in a given case could provide results that were not significantly different from those obtained by using the same parameters in a complex regression equation. The advantages and potential pitfalls of this system of fetal dating are discussed.

Abdomen↗
PubMed1984

Relation of fetal femur length to neonatal crown-heel length.

Sonographically measured femur lengths in 102 fetuses were compared with neonatal crown-heel lengths within 72 hours of delivery. The optimal model for describing crown-heel length as a function of femur length was a linear model, with a coefficient of determination (r2) of 66 per cent; the standard deviation in predicting crown-heel length from femur length was 2.4 cm. These data were compared with autopsy data from the literature, which showed an even stronger correlation between femur length and crown-heel length. Because of the strong correlation between these two dimensions, the femur length should prove useful in the detection of intrauterine growth retardation when crown-heel length is compromised. It should also be useful as a variable in the prediction of fetal weight in utero, since crown-heel lengths at the extremes of normal can significantly affect in utero weight estimates using ultrasound.

Body Height↗
PubMed1984

The femur length/head circumference relation in obstetric sonography.

The relationship of sonographic femur length to biparietal diameter (BPD) in utero may be useful in detecting short-limb dwarfism, hydrocephaly, microcephaly, and measurement errors. Because BPD can be adversely affected by head shape changes (e.g., dolichocephaly), falsely high or low values of femur length/BPD could result. Because head circumference is less affected by head shape changes than is BPD, it should be a better standard of head size against which to judge limb length. The authors report normal values for the relationship between femur length and head circumference, based on a cross-sectional analysis of 361 normal fetuses (15-42 weeks) using real-time ultrasound.

Cephalometry↗
PubMed1983

Computer assisted analysis of fetal age in the third trimester using multiple fetal growth parameters.

A new technique is described for predicting menstrual age in the third trimester of pregnancy (28-42 weeks) using multiple fetal growth parameters (biparietal diameter, head circumference, abdominal circumference, femur length). Evaluation of this technique in 177 normal third trimester pregnancies demonstrated that significant improvement in the variability in predicting menstrual age can be achieved when two or more parameters are used collectively instead of a single parameter used individually. The optimal combination prior to 36 weeks was biparietal diameter, abdominal circumference, and femur length, while after 36 weeks the optimal combination was head circumference, abdominal circumference, and femur length. The use of these combinations resulted in smaller mean errors, standard deviations, and maximum errors. Regression equations and tables of normal values are provided to facilitate the use of this dating method.

Diagnosis, Computer-Assisted↗
PubMed1983

A date-independent predictor of intrauterine growth retardation: femur length/abdominal circumference ratio.

The relation between sonographically measured fetal femur length and abdominal circumference (expressed as femur length/abdominal circumference X 100) was studied in 361 normal pregnancies between 15 and 42 weeks. This ratio was found to be independent of menstrual age, with a normal range after 21 weeks (mean +/- 2 SD) of 22 +/- 2. This ratio also was evaluated as a predictor of intrauterine growth retardation in 30 cases using the 90th percentile (23.5) as the upper limit of normal, which resulted in identification of 63% of the growth-retarded fetuses. Because it is independent of menstrual age, this ratio should prove most useful in evaluating high-risk patients who present in the third trimester of pregnancy with no dates. It is also of value in detecting growth retardation in patients with good menstrual history, since it was shown to become abnormal in asymmetrically growth-retarded fetuses before the estimated weight fell below the 10th percentile.

Abdomen↗
PubMed1983

A prospective evaluation of fetal femur length as a predictor of gestational age.

Variability (+/- 2 SD) in prediction of fetal gestational age from ultrasonographic measurements of fetal femur length was evaluated prospectively in 287 fetuses between 18 and 42 weeks' gestation. Variability increased throughout pregnancy, ranging from +/- 11.6 days between 18 and 24 weeks to +/- 22.7 days in the last six weeks of pregnancy. These findings are comparable with variability in prediction of gestational age from biparietal diameter measurement between 18 and 42 weeks, which indicates that the femur length may serve as an adequate alternative for prediction of gestational age in cases in which the biparietal diameter cannot, for technical reasons, be obtained.

Female↗
PubMed1982

Longitudinal studies of fetal growth with the use of dynamic image ultrasonography.

To characterize the growth of individual fetuses, serial measurements of the crown-rump length (CRL), biparietal diameter (BPD), head circumference (HC), and abdominal circumference (AC) were made at specified intervals of 2 to 3 weeks (between 6 to 8 weeks [conceptual age] and delivery) in 20 normal fetuses with known dates of conception. Values for the HC-AC ratio and the estimated fetal weight were also obtained from these data. Measurements of CRL were similar to those reported previously, except in those cases in which the follicular phase was prolonged or the fetal growth potential was reduced. Mathematical modeling demonstrated that the linear-cubic model was optimal for the BPD and HC growth curves, the linear model for the AC, and the linear-quadratic model for fetal weight. The HC-AC ratio could not be modeled adequately because of significant individual variability. Optimal models for average longitudinal growth curves were determined for the BPD, HC, AC, and fetal weight from individual growth curves. These average longitudinal curves were similar in shape, mean values, and variability to those obtained in previous cross-sectional studies. Statistical analysis indicated that the coefficients of the average longitudinal curves are not likely to change by more than 5% to 15% if the size of the sample is increased very significantly. These results indicate that the average longitudinal growth curves are good estimators of the true population growth curves.

Adult↗
PubMed1982

Fetal head and abdominal circumferences: I. Evaluation of measurement errors.

Several sources of error associated with the measurement of fetal head and abdominal circumferences (HC, AC) were examined using dynamic image ultrasound. Statistically significant systematic intraobserver errors were not seen unless technical differences in the images were present (HC only) and the range for random errors was 4-5% (2 SD) for both measurements. Although differences in the procedures used to acquire images for measurement had some effect on accuracy (HC only), the primary source of variations in measurements made by different investigators was the measurement methods. Different measuring devices gave different results and different investigators used the same devices differently. Under optimal measuring conditions, the interobserver error for experienced investigators was 1.2 (+/-4.3 SD)% for HC and 2.4 (+/-1.6 SD)% for AC. Comparison of prenatal and postnatal measurements indicated that there were no systematic differences for HC but for AC, the prenatal measurements were 6% greater. Random differences were +/-6% (2 SD) for HC and +/-13% (2 SD) for AC.

Abdomen↗