G. Donald Whedon

Immobilization and bone.

The major advances of the past several years in bone measurement have direct applicat ions for manned space missions, for paraplegics, for patients confined to bed by disease and for the large population of relatively hypodynamic elderly individuals. A meeting held in San Francisco (June 16, 1982) focussed on newer measurement methods and on major results obtained by both histological and noninvasive approaches. The specific aim was to provide the National Aeronautics and Space Administration (NASA) with information to help implement appropriate programs of research. G. Donald Whedon, National Institute of Health, summarized the history of research on bone loss in immobilization and space flight. Negative calcium balance of 150-200 mg/day continued for up to 20 -30 weeks in young bed rest subjects; in the Skylab astronauts, the pattern and degree of calcium loss was similar to that in bed rest but with much inter-individual variation. Calcium losses in patients with spinal cord injuries appeared somewhat higher than in bed rest subjects, and higher losses were found in subjects with complete versus incomplete spinal cord lesions. Calciuria usually declined to the normal range by 30 weeks, but in some patients, a modest elevation was evident even after one year (N. Eric Naftchi, New York University). Losses in paraplegic patients were evidenced h i s t o m o r p h o m e t r i c a l l y by a 33% reduc t i on of trabecular bone volume in iliac crest biopsy over 25 weeks (P. Minaire and C. Alexandre, Hospital Regional, St. Etienne, France). There was both an in-

Disuse osteoporosis: Physiological aspects

SummaryImmobilization in plaster, bed rest, and the weightless state all result in calcium loss which if continued for a few months will result in detectable demineralization of the lower extremities. The upper extremities are “different” bones (presumably differently programed genetically), for they have not been seen to develop X-ray-detectable demineralization except after several months of severe paralysis. The substantial losses of calcium in inactivity are accompanied by sizeable losses of nitrogren, reflective of muscle atrophy. Hence, we do not know how much of the bone loss in disuse is mediated by diminished direct physical forces on bone, how much by decreased muscle pull on periosteum, and how much perhaps by circulatory or other changes.Immobilization in plaster, bed rest, and the weightless state all result in calcium loss which if continued for a few months will result in detectable demineralization of the lower extremities. The upper extremities are “different” bones (presumably differently programed genetically), for they have not been seen to develop X-ray-detectable demineralization except after several months of severe paralysis. The substantial losses of calcium in inactivity are accompanied by sizeable losses of nitrogren, reflective of muscle atrophy. Hence, we do not know how much of the bone loss in disuse is mediated by diminished direct physical forces on bone, how much by decreased muscle pull on periosteum, and how much perhaps by circulatory or other changes.

Effects of High Dietary Calcium and Phosphorus on Calcium, Phosphorus, Nitrogen and Fat Metabolism in Children

effects of high dietary phosphate on dental caries,’0 a group of children became available who presumably had been receiving diets high in calcium and phosphorus for periods of from one to two years. The present report is concerned with the effects of these diets on metabolic balances of minerals and nitrogen in eighteen children from this study. EXPERIMENTAL METHODS

Recent Advances in Management of Osteoporosis

Osteoporosis is defined as a condition of decreased total bone mass, that is, a decrease in amount of essentially normal bone tissue within an undiminished outer bone volume or envelope. The suggestion in recent years of a substitute term, “osteopenia,” came from a desire to give a better indication of decreased bone mass. The degree of bone loss has not been specifically determined, but in concept it is that beyond which bones under stress are especially susceptible to fracture. Although the key word in the title of this paper is “management,” some comments on etiology are important, because out of a broadening of our ideas of cause and development over the past 35 years have come suggestions for more intelligent management overall and even for potential treatment for milder or earlier forms.Osteoporosis is defined as a condition of decreased total bone mass, that is, a decrease in amount of essentially normal bone tissue within an undiminished outer bone volume or envelope. The suggestion in recent years of a substitute term, “osteopenia,” came from a desire to give a better indication of decreased bone mass. The degree of bone loss has not been specifically determined, but in concept it is that beyond which bones under stress are especially susceptible to fracture. Although the key word in the title of this paper is “management,” some comments on etiology are important, because out of a broadening of our ideas of cause and development over the past 35 years have come suggestions for more intelligent management overall and even for potential treatment for milder or earlier forms.