Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.

Q: Abstract: The effects of aging on calcium and bone metabolism have not been systematically examined in men. To identify age-related alterations in vitamin D and PTH physiology and to assess their impact on skeletal health, we studied 62 normal men, aged 30-92 yr. The men were in excellent health, and none had any evidence of metabolic bone disease and/or known risk factors for osteopenia. Serum 25-hydroxyvitamin D (25OHD) concentrations declined steadily with advancing age (r = -0.47; P less than 0.001), and there was a corresponding decline in serum 24,25-dihydroxyvitamin D [24,25-(OH)2D] levels (r = -0.41; P less than 0.001). Serum 1,25-(OH)2D concentrations, however, did not vary over this age range (r = -0.07; P = NS). Plasma PTH levels increased with aging (r = -0.24; P less than 0.001), and there was a concomitant increase in urinary cAMP excretion (r = 0.38; P less than 0.001). Renal function (creatinine clearance) clearly declined with increasing age (r = -0.71; P less than 0.001). In conjunction with these changes in calcium metabolism, radial and vertebral bone mineral content declined. Whereas the fall in radial bone mineral content (single photon absorptiometry) at both proximal and distal sites was slight, there was a marked decrease in vertebral bone mineral content, as measured by quantitative computed tomography (r = -0.72; P less than 0.0001). The fall in vertebral bone mineral content correlated well with the declines in serum 25OHD and 24,25-(OH)2D concentrations (r = 0.47; P less than 0.001 and r = 0.51; P less than 0.001, respectively) and with the decline in renal function (r = 0.46; P less than 0.001). Multiple regression analysis revealed that the effects of aging on bone mineral content could be accounted for in large part by concomitant changes in mineral metabolism. Both the decline in renal function and the fall in serum 24,25-(OH)2D levels were closely associated with the fall in bone mineral content. These results indicate that a decline in renal function and alterations in vitamin D metabolism occur with aging in normal men. These changes contribute to, if not cause, the associated decline in skeletal mineral content in aging men.

A: Adenosine Cyclic Monophosphate
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Q: Abstract: When right ventricular failure prohibits separation from cardiopulmonary bypass, standard methods of increasing pulmonary blood flow should be employed, including correction of hypoxia and acidosis, volume loading, and inotropic support of the right ventricle. Infusion of pulmonary vasodilators--particularly low-dose nitroprusside--should be used if the pulmonary vascular resistance is elevated. If pulmonary blood flow remains unsatisfactory, systemic intra-aortic balloon counterpulsation should be employed. In refractory cases, right-atrial-to-pulmonary-artery bypass using the Bio-Medicus centrifugal pump is the recommended therapy for those centers that do not have the Pierce-Donachy pneumatic ventricular assist-pump available. For refractory right ventricular failure following the surgical repair of congenital cardiac defects in which the placement of right atrial and pulmonary artery cannulae is not technically feasible, use of high-frequency high-volume ventilation appears to be quite promising. Utilization of pulmonary artery counterpulsation or the creation of an atrial septal defect may also be lifesaving, but is not recommended as the therapy of choice.

A: Cardiopulmonary Bypass
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Q: Abstract: The cases of two patients in whom complete but transient quadriplegia developed after an injury that was incurred while playing football are presented. Both patients were found to have a congenitally narrow cervical vertebral canal. Critical stenosis resulting in the transient quadriplegia occurred after a presumed injury to a cervical disc. In our opinion, a myelogram should be made for patients with a history of transient quadriplegia, numbness, or a burning sensation down the back or the lower extremities, even if other radiographic studies are interpreted as negative. Patients who have stenosis of the cervical spine should be advised to discontinue participation in contact sports.

A:
Adult
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