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Biomedical subjects

W M Rand

Publications and source records attributed to W M Rand.

At least 73 records · Page 4Linked to original sources
PubMed1977

Protein metabolism in human neonates: nitrogen-balance studies, estimated obligatory losses of nitrogen and whole-body turnover of nitrogen.

1. Aspects of nitrogen metabolism in the human neonate were assessed in one full-term infant and six premature infants by means of nitrogen-balance measurements, estimates of obligatory nitrogen losses and determinations of whole-body nitrogen turnover. 2. Our data indicate that the mean protein requirement for maintenance is 1-1 g of protein day-1 kg-1 and that 3-8 g of protein day-1 kg-1 should be sufficient for adequate growth in healthy premature babies. 3. The mean obligatory urinary, faecal and total nitrogen losses were estimated to be 24, 106, 145 mg day-1 kg-1 respectively. These figures are compared with published values for older infants, and the possible metabolic basis for changes in nitrogen losses during growth and development is discussed. 4. Mean values for whole-body protein synthesis and breakdown were 26-3 +/- 7-0 and 23-8 +/- 7-4 g of protein day-1 kg-1 respectively. Dietary nitrogen intake accounted for 6--18% of the nitrogen flux through the metabolic pool; urea excretion accounted for 2% of the nitrogen flux. 5. The net protein gain, estimated from nitrogen-balanced data, accounted for 9-6% of total daily protein synthesis. 6. These results are discussed in relation to published estimates of whole-body protein synthesis and breakdown at various ages. Their possible significance in the assessment of a "maintenance" requirement for protein and amino acids during the period of rapid growth and development is also considered.

Body Weight↗
PubMed1977

Determination of protein allowances in human adults from nitrogen balance data.

The problem of predicting human protein requirements is examined in detail. Three methods from the literature are shown to represent a logical sequence wherin each takes into account more sources of variation than does the previous one. These are the single level method and two versions of the multiple level method, all of which assume a population response curve. A fourth method is proposed as the next step in this sequence. This method calculates a response curve for each individual and works with the individual requirements. Since each method makes fewer assumptions about the data and, therefore, about the biological situation of population protein needs, each method gives successively larger protein allowance values, while at the same time identifying the sources of variability and uncertainty in these estimates.

Adult↗
PubMed1976

Change of urinary nitrogen excretion in response to low-protein diets in adults.

Data from nitrogen balance studies in young men and elderly women were analyzed for the pattern of urinary nitrogen excretion after the subjects had changed from an adequate to an essentially protein-free diet. The single exponential equation: y = P1e-p2t+P3, provided an adequate fit of the data, suggesting that a single-pool model describes the adaptive decline in urinary nitrogen excretion under these dietary conditions. Comparisons of the estimated parameters showed that the fractional rate constant, P2, was the same for both the young men and elderly women, but that the other coefficients differed between the two groups depending upon whether they were expressed per day, per kg of body weight, per unit creatinine excreted, or per kg of body cell mass. The length of time between the change in diet and the attainment of a new equilibrium in urinary nitrogen excretion (ts, or time to stability) is defined as ts = 1/p2 loge(p1/s) where s is the standard error of the fit. The average time to stability was the same in both groups (4.5 days), and 95% of the subjects reached the new equilibrium in nitrogen output within 8 days.

Adult↗
PubMed1975

Protein requirements of man: comparative nitrogen balance response within the submaintenance-to-maintenance range of intakes of wheat and beef proteins.

Sixteen young male students participated in two studies designed to determine the nitrogen balance response to beef or stone-ground, whole wheat protein over the submaintenance-to-maintenance range of protein intake. The objective of the studies was to evaluate the relative capacities of these proteins to meet the minimum protein needs in young adult males. A modified Latin-square design was used to allocate subjects to the four 15-day metabolic balance diet periods in each study. The last 10 days were used for fecal nitrogen determination and the last 5 days for evaluation of urinary nitrogen excretion. The diet periods were separated by a 4-day break period and began with 1 day on a "protein-free" diet. The levels of protien (N times 6.25) intake tested were 0.2, 0.3, 0.4, and 0.5 g/kg body weight/day in the beef study. The results have been compared with those obtained in a previous similar study with egg protein. The regression of estimated "true" nitrogen balance (Y) (mg N/kg/day) on nitrogen intake (X) (mg N/kg/day) was: Y equals 0.51(plus or minus 0.08)X minus 41.9(plus or minus 4.6) for beef and Y equals 0.27(plus or minus 0.06)X minus 33.6(plus or minus 5.0) for whole wheat protein. The amounts of beef and wheat proteins estimated to be requried to support body nitrogen balance in 97.5% of the population supplied 96 and 178 mg N/kg/day, respectively. The relative protein value of beef and wheat proteins, in comparison with egg protein, was 78 plus or minus 12 and 41 plus or minus 10, respectively. It is concluded that the variations in dietary protein quality should be taken into account in assessing the protein adequacy of diets for individuals and population groups.

Adolescent↗
PubMed1973

Entrainment of the body temperature rhythm in rats: effect of color and intensity of environmental light.

The daily rhythm in body temperature in rats was continuously monitored during exposure to low-intensity environmental illumination of various colors in the visible and near-ultraviolet spectrum. The ability of phase shifts in the lighting schedule to induce concomitant changes in the rhythm was used to determine the spectral sensitivity of the retinal photoreceptor systems mediating rhythm entrainment. Green light (lambda = 530 +/- 45 nanometers) was most potent, and red (lambda = 660 +/- 19 nanometers) and ultraviolet (lambda = 360 +/- 34 nanometers) were least potent in entraining the temperature rhythm.

Animals↗
PubMedDate not supplied

Adolescent growth in height and its relation to menarche in contemporary American girls.

Height measurements at frequent intervals, from age six to adulthood, of 338 middle-class American girls are used to examine contemporary height and height velocity at specified ages, the characteristics of the adolescent growth spurt and its relation to menarche. These data, analysed by fitting to a mathematical model (Preece and Baines 1978), are presented as tables of means and standard deviations, percentiles and correlations. There is no evidence of a trend towards increased or accelerated growth in height; in the United States and Western Europe, girls have been the same height at specified ages, and have grown at the same rate, for the past 45 years, at least. Examination of the data plots and the growth statistics of all 338 girls revealed a group of 67 girls (designated E) who are different from the remaining 271 girls (designated S). Plots of the E girls show no discernible growth spurt. Compared with the S girls, they are significantly taller at specified ages; velocities are greater at ages 6 and 9 but less at age 12. During the growth spurt, and at menarche, they are taller but not older. Their adult height is greater and is reached later. Their velocity at takeoff is greater but, at peak, smaller; spurt intensity is much lower. Their adolescent growth spurt contributes less to adult height. For all 338 girls (the E as well as the S subgroup), adult height is correlated only with height during the growth spurt and is virtually independent of spurt timing, whereas menarche is strongly correlated with spurt timing and very little with height. Additional indications that menarche is unrelated to size are that E girls at menarche are significantly taller but not older than the S girls, and that 19 prematurely-born girls at menarche are shorter than girls born at full term but the same age.

Adolescent↗
PubMedDate not supplied

Adolescent growth in weight and its relation to menarche in contemporary American girls.

Weight measurements at frequent intervals, from age six to adulthood, of 248 contemporary middle-class American girls were fitted to a mathematical model (Preece and Baines 1978). The results are used to examine weight and weight velocity at specified ages, the characteristics of the weight growth spurt and the relation of this spurt to menarche. These statistics are compared with previously complied height statistics for the same girls. Although the data of all 248 girls were readily fitted, no usable spurt take-off ages were found for 41 girls. Calculations, therefore, were made separately for two subsets: principal subset A (207) and variant subset B (41). The values (subset A) for weight at specified ages and at critical points of the adolescent growth spurt agree well with comparable US and Western European data. Comparing weight spurt (subset A) with height spurt, the weight spurt takes off earlier, peaks and ends later; adult weight is reached much later. The Preece-Baines model lacks a component for analysing the mid-growth spurt. Therefore, for some children, the model makes a too-early estimate of age at adolescent spurt take-off (and other dependent variables). This may account for the unrealistic take-off ages of girls in subset B, although these girls are also significantly younger and lighter than subset A girls at spurt peak and are also younger at menarche. While certain differences between the two subsets may be mathematical distortions caused by the Preece-Baines model, others may be real.

Adolescent↗
PubMedDate not supplied

Mechanical comparison of two external fixator clamp designs.

OBJECTIVE: To compare two external fixation clamp designs for their ability to resist movement of a fixation pin in relation to the connecting rod. STUDY DESIGN: Two designs of external fixator clamps were attached to connecting rods mounted on a jig for mechanical testing. Fixator pins were placed perpendicular to the connecting rod. A mechanical testing machine was used to deflect each 3.2-mm pin at a distance that was 25 mm from the center of the clamp bolt. Both clamp designs were tightened to 4.4, 6.1, and 7.8 newton-meters (N x m) torque, and loads were applied in a position ramp through 4 mm and resisting loads were measured. Two clamp orientations were used during load application, such that the deflection of the pin tended to tighten the clamp bolt or tended to loosen the clamp bolt. The tests were videotaped to determine mode of failure. Comparisons of the load/displacement curves for the two external fixator clamp designs were made using nonlinear equational curve fitting methods. The resultant plateau and rise coefficients were compared using analysis of variance. RESULTS: Slippage of the pin in relation to the clamp occurred with the Kirschner-Ehmer clamp tightened to 4.4, 6.1, and 7.8 N x m, and slipping of the pin in relation to the clamp occurred with the experimental clamp design tightened to 4.4 and 6.1 N x m but not to 7.8 N m. At 7.8 N x m, the 3.2-mm pin deformed plastically with the experimental clamp design. Increasing the torque of the clamp bolt resulted in superior plateau coefficients for both clamp designs. At each level of tightness and in each clamp orientation to applied pin load, the experimental clamp design provided greater plateau coefficients than did the Kirschner-Ehmer clamp design. At 7.8 N x m of tightness, the Kirschner-Ehmer clamp and bolt bent, whereas only slight plastic deformation of the experimental clamp design occurred. CONCLUSIONS: The experimental external fixator clamp was more secure in resisting fixator pin movement at all levels of tightening compared with the Kirschner-Ehmer-type external fixator clamp. At 7.8 N x m of tightening, the new clamp design did not allow slippage of the pin within the clamp. CLINICAL SIGNIFICANCE: The experimental external fixator clamp should result in greater rigidity of fixator configurations, in addition to providing design features that allow addition of a clamp between two installed clamps, sleeved predrilling of pilot holes for all pins, measurement of pin depth, and placement of positive profile pins at all sites.

Animals↗