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Biomedical subjects

J McDaniel

Publications and source records attributed to J McDaniel.

11 recordsLinked to original sources
PubMed2002

Determinants of metabolic cost during submaximal cycling.

The metabolic cost of producing submaximal cycling power has been reported to vary with pedaling rate. Pedaling rate, however, governs two physiological phenomena known to influence metabolic cost and efficiency: muscle shortening velocity and the frequency of muscle activation and relaxation. The purpose of this investigation was to determine the relative influence of those two phenomena on metabolic cost during submaximal cycling. Nine trained male cyclists performed submaximal cycling at power outputs intended to elicit 30, 60, and 90% of their individual lactate threshold at four pedaling rates (40, 60, 80, 100 rpm) with three different crank lengths (145, 170, and 195 mm). The combination of four pedaling rates and three crank lengths produced 12 pedal speeds ranging from 0.61 to 2.04 m/s. Metabolic cost was determined by indirect calorimetery, and power output and pedaling rate were recorded. A stepwise multiple linear regression procedure selected mechanical power output, pedal speed, and pedal speed squared as the main determinants of metabolic cost (R(2) = 0.99 +/- 0.01). Neither pedaling rate nor crank length significantly contributed to the regression model. The cost of unloaded cycling and delta efficiency were 150 metabolic watts and 24.7%, respectively, when data from all crank lengths and pedal speeds were included in a regression. Those values increased with increasing pedal speed and ranged from a low of 73 +/- 7 metabolic watts and 22.1 +/- 0.3% (145-mm cranks, 40 rpm) to a high of 297 +/- 23 metabolic watts and 26.6 +/- 0.7% (195-mm cranks, 100 rpm). These results suggest that mechanical power output and pedal speed, a marker for muscle shortening velocity, are the main determinants of metabolic cost during submaximal cycling, whereas pedaling rate (i.e., activation-relaxation rate) does not significantly contribute to metabolic cost.

Adult↗
PubMed1992

Effect of protistan grazing on the frequency of dividing cells in bacterioplankton assemblages.

Grazing by phagotrophic flagellates and ciliates is a major source of mortality for bacterioplankton in both marine and freshwater systems. Recent studies have demonstrated a positive relationship between clearance rate and prey size for bacterivorous protists. We tested the idea that, by selectively grazing the larger (more actively growing or dividing) cells in a bacterial assemblage, protists control bacterial standing stock abundances by directly cropping bacterial production. Samples of estuarine water were passed through 0.8-mum-pore-size filters (bacteria only) or 20-mum-mesh screens (bacteria and bacterivorous protists) and placed in dialysis tubing suspended in 7 liters of unfiltered water. Changes in total bacterial biovolume per milliliter (bacterial biomass), frequency of dividing cells (FDC), and average per cell biovolume were followed over a period of 24 h. In three experiments, the FDC increased more rapidly and attained higher values in water passed through 0.8-mum-pore-size filters (average, 5.1 to 8.9%; maximum, 15.5%) compared with FDC values in water passed through 20-mum-mesh screens (average, 2.7 to 5.3%; maximum, 6.7%). Increases in bacterial biomass per milliliter lagged behind increases in FDC by about 4 to 6 h. Grazed bacterial assemblages were characterized by lower total biomasses and smaller average cell sizes compared with those of cells in nongrazed assemblages. We conclude that bacterivorous protists control bacterial standing stock abundances partly by preferentially removing dividing cells. Selective grazing of the more actively growing cells may also explain, in part, the ability of slow-growing cells to persist in bacterioplankton assemblages.

Journal Article↗
PubMed1987

Fatal digoxin poisoning: an unsuccessful resuscitation with use of digoxin-immune Fab.

A 1-month-old infant suffered cardiac arrest shortly after presentation to the emergency department. The child had a history of heart disease treated with digoxin. The infant died despite intensive resuscitative efforts, including the use of digoxin-specific Fab antibodies. A brief discussion of this case and the use of digoxin-specific antibodies is presented.

Antibodies↗
PubMed1982

Psychotic features in major depression. Is mood congruence important?

We studied outcome and family history in 203 patients with psychotic depression. Patients whose psychotic features were mood-incongruent were significantly younger and had a slightly poorer outcome. Morbid risks for affective disorder and schizophrenia among relatives distinguished these mood-incongruent patients from patients with non-psychotic depression but not from patients with schizophrenia. In contrast, depressive probands with mood-congruent psychotic features resembled probands with non-psychotic depression and differed significantly from schizophrenia probands in terms of family history. While depressed patients with mood-congruent psychotic features experienced poorer short-term outcome relative to non-psychotic depressed patients, a 40-year follow-up has shown that these differences disappear over time. Moreover, these two groups are quite similar according to family history data. Both family history and short-term outcome data suggest that major depression with mood-incongruent psychotic features cannot be classified altogether with either affective disorders or schizophrenia. More definite conclusions must await the results of long-term outcome and family studies of these patients presently underway.

Adolescent↗
PubMed1982

Reversible uremia and its effect on the glomerular filtration rate.

As the nephron population diminishes and azotemia develops, each remaining nephron adapts and increases its function by as much as 80%. To determine whether this adaption is permanent or transient, a rat model utilizing one remnant kidney and one normal control kidney was used. In stage one, immediately after ligation of the ureter to the control kidney, the glomerular filtration rate in the remnant kidney was 0.185 cm3/min. 1 week after ligation of the ureter to the control kidney, the glomerular filtration rate in the remnant kidney had increased to 0.336 cm3/min (stage two), and 2 weeks later, after removal of the obstruction to the control kidney, the glomerular filtration rate in the remnant kidney was 0.155 cm3/min (stage three), p less than 0.01.

Adaptation, Physiological↗
PubMed1979

Predicint lifting capacity.

As science and technology become more sophisticated and with the rapid computation capabilities of the modern computer available, it becomes both possible and economically feasible to scientifically study man and his interaction with his working environment. It is now possible for a person seeking employment to expect and obtain a position which will not be unnecessarily hazardous to his immediate health or have detrimental effects over the long run. Manual materials handling is the contributor of over 400,000 back injuries suffered in the U.S. each year. This research is directed at determining the appropriate operator variables to measure for predicting the permissible weight of lift for three ranges of lift: floor to knuckle height, knuckle height to shoulder height, and shoulder height to reach height. A modified psychophysical procedure was used during which the subjects were instructed to adjust the weight in a tote box to the maximum weight they could lift repetitively without excessive strain or fatique. The task consisted of lifting loads under different conditions of task variables, namely, height of lift, frequency of lift, and load size. Industrial workers as well as students of both sexes were used as subjects. Based on the data obtained, the lifting capacity of the worker was determined for the different ranges of lift. In addition, predictive models were developed based on the operator variables and the task variables investigated.

Accident Prevention↗