No abstract

Assessment of precision errors in bone mineral densitometry is important for characterization of a technique's ability to detect longitudinal skeletal changes. Short-term and long-term precision errors should be calculated as root-mean-square (RMS) averages of standard deviations of repeated measurements (SD) and standard errors of the estimate of changes in bone density with time (SEE), respectively. Inadequate adjustment for degrees of freedom and use of arithmetic means instead of RMS averages may cause underestimation of true imprecision by up to 41% and 25% (for duplicate measurements), respectively. Calculation of confidence intervals of precision errors based on the number of repeated measurements and the number of subjects assessed serves to characterize limitations of precision error assessments. Provided that precision error are comparable across subjects, examinations with a total of 27 degrees of freedom result in an upper 90% confidence limit of +30% of the mean precision error, a level considered sufficient for characterizing technique imprecision. We recommend three (or four) repeated measurements per individual in a subject group of at least 14 individuals to characterize short-term (or long-term) precision of a technique.

In order to define the role of intracranial and extracranial complications in determining outcome from severe head injury, 734 patients from the Traumatic Coma Data Bank were analyzed. Nine classes of intracranial and 13 classes of extracranial complications occurring within the first 14 days after admission were analyzed, while controlling for age, admission Glasgow Coma Scale motor score, early hypoxia or hypotension, and severe extracranial trauma. Outcome for survivors was based on the last recorded Glasgow Outcome Scale score, obtained a median of 521 days after injury. Intracranial complications did not significantly alter outcome for the study group. Of the extracranial complications, pulmonary, cardiovascular, coagulation, and electrolyte disorders occurred most frequently at 2 to 4 days. Infections developed later, peaking at 5 to 11 days. Gastrointestinal, renal, and hepatic complications followed no specific time course. Electrolyte abnormalities were the most frequent occurrence (59% of patients) but did not alter outcome. Pulmonary infections (41%), shock (29%, systemic blood pressure < or = 90 mm Hg for 30 minutes or more), coagulopathy (19%), and septicemia (10%) were significant independent predictors of an unfavorable outcome. Backward-elimination, stepwise logistic regression modeling indicated that the estimated reduction of unfavorable outcome was 2.9% for the elimination of pneumonia, 3.1% for coagulation disturbances, 1.5% for septicemia, and 9.3% for shock. These data suggest that extracranial complications are highly influential in determining the outcome from severe head injury and that significant improvements in outcome in a sizeable proportion of patients could be accomplished by improving the ability to prevent or reverse pneumonia, hypotension, coagulopathy, and sepsis.

No abstract

Changing body composition has been suggested as a pathway to explain age-related functional decline. No data are available on the expected changes in body composition as measured by dual-energy X-ray absorptiometry (DXA) in a population-based cohort of older persons. Body composition data at baseline, 1-yr follow-up, and 2-yr follow-up was measured by DXA in 2,040 well-functioning black and white men and women aged 70-79 yr, participants of the Health, Aging, and Body Composition Study. After 2 yr, a small decline in total body mass was observed (men: -0.3%, women: -0.4%). Among men, fat-free mass and appendicular lean soft tissue mass (ALST) decreased by -1.1 and -0.8%, respectively, which was masked by a simultaneous increase in total fat mass (+2.0%). Among women, a decline in fat-free mass was observed after 2 yr only (-0.6%) with no change in ALST and body fat mass. After 2 yr, the decline in ALST was greater in blacks than whites. Change in total body mass was associated with change in ALST (r = +0.58 to +0.70; P < 0.0001). Among participants who lost total body mass, men lost relatively more ALST than women, and blacks lost relatively more ALST than whites. In conclusion, the mean change in body composition after a 1- to 2-yr follow-up was 1-2% with a high interindividual variability. Loss of ALST was greater in men compared with women, and greater in blacks compared with whites, suggesting that men and blacks may be more prone to muscle loss.