COLD-INDUCED INCREASES IN ERYTHROCYTE COUNT, PLASMA-CHOLESTEROL AND PLASMA-FIBRINOGEN OF ELDERLY PEOPLE WITHOUT A COMPARABLE RISE IN PROTEIN-C OR FACTOR-X

1. Six elderly (66-71 years) and six young (20-23 years) subjects (hal f of each group women) were cooled for 2 h in moving air at 18 degrees C to investigate possible causes of increased mortality from arterial thrombosis among elderly people in cold weather. Compared with thermo neutral control experiments, skin temperature (trunk) fell from 35.5 t o 29.5 degrees C, with little change in core temperature. 2. Erythrocy te count rose in the cold from 4.29 to 4.69 x 10(12)/l, without a chan ge in mean corpuscular volume, indicating a 14% or 438 ml decline in p lasma volume; increased excretion of water, Na+ and K+ accounted for l oss of only 179 ml of extracellular water. 3. Plasma cholesterol and f ibrinogen concentrations rose in the elderly subjects from 4.90 mmol/l and 2.97 g/l (control) to 5.45 mmol/l and 3.39 g/l in the cold, and i n the young subjects from 3.33 mmol/l and 1.84 g/l (control) to 3.77 m mol/l and 2.07 g/l in the cold. Increases were significant for the eld erly subjects, the young subjects and the group as a whole, except for cholesterol in the young subjects, and all were close to those expect ed from the fall in plasma volume. 4. Plasma levels of Protein C and f actor X did not increase significantly in the cold in the elderly subj ects, young subjects, or the group as a whole. 5. The results suggest that loss of plasma fluid in the cold concentrates major risk factors for arterial thrombosis, while small molecules, including protective P rotein C, redistribute to interstitial fluid.