Hyponatremia in the elderly patients was characterized by the difficulties in its diagnosis and treatment. The purpose of this study was to classify the hyponatremia in the elderly patients. A total of 78 cases of hyponatremia was obsurbed in 525 consecutive aged autopsied (14.6%). Among these hyponatremia 25 cases (32%) had an apparent cause of hyponatremia, such as heart failure, renal failure or suction of body fluids. On the other hands, the cause of hyponatremia in the remainder (41 cases) was obscure and wasting diseases such as cerebrovascular accident (39.0%), malignancy (31.4%) and pneumonia (51.2%) were frequently observed as a underlying disorders. Subsequently, the group with hyponatremia of unknown etiology was examined. According to their urinary sodium concentration, they could be devided into two subgroups, one with urinary sodium concentration over 50mEq/L and the other with that below 50mEq/L. The first group of hyponatremia with urinary sodium concentration over 50mEq/L was characterized as follows. 1. excessive sodium loss to urine in spite of hyponatremia (108.0±5.22mEq/day) 2. high urinary Na/K ratio (4.0±0.57) 3. increased total plasma volume (65.0±2.0ml/Kg) 4. low plasma renin activity (PRA) (1.3±0.21/ngml/hr.) The other group of hyponatremia with urinary sodium concentration below 50mEq/L was characterized as follows. 1. high serum BUN levels (32.0±5.09mg/dl) 2. high amount of daily urinary potassium excretion (35.7±5.38mEq/day) 3. low urinary Na/K ratio (1.6±0.22) 4. heigh level of PRA (3.7±0.65ng/ml/hr.) The supressed PRA and low serum sodium concentration in the first group might be explained by the increased plasma volume. Therefore, the first group of hyponatremia with urinary sodium concentration over 50mEq/L showed the characteristics compatible with dilutional hyponatremia. In the patients of hyponatremia, with urinary sodium concentration below 50mEq/L, the systolic blood pressure during hyponatremia (135±13.0mmHg) was significantly lower than that before developing hyponatremia (175±6.5mmHg). (P<0.02) This significant fall of systolic blood pressure posibly induced by the decreased plasma volume or by the loss of sodium from the body fluids might be related to the increased PRA. Therefore the latter group of hyponatremia with urinary sodium concentration below 50mEq/L showed the characteristics compatible with volume depletion. In conclution, the measurement of the urinary sodium concentration is a simple and helpful tool for the evaluation of the hyponatremia.
Osteoporosis characterized by the loss of bone mass is quite common in the elderly people. However the quantitative study of the loss of bone mass with aging in Japanese has not been reported so far. Therefore, the purpose of this study is to clarify the effect of aging on the loss of bone mineral content in Japanese. Radial mineral content (RMC) in 381 Japanese patients was measured by the photon absorption method developed by Nowland-Cameron. The coefficient of variance of this method was 1.9±1.09% in 100 times of scanning. In the male subjects, the mean RMC was at its muximum around the age of thirties (0.68±0.016g/cm2) and then gradually decreased with aging showing its lowest value (0.52±0.040g/cm2) around the age of eighties. In the female subjects, RMC was at its maximum around the age of forties (0.61±0.012g/cm2) and then fell rapidly after the age of fifties showing its lowest value around the age of eighties (0.42±0.024g/cm2). The loss of RMC with aging in the female subjects without fracture was significantly greater than that in the age matched male subjects. RMC was significantly smaller in the females with fractures than that in the females without fracture. The longitudinal study revealed that the mean rate of bone mineral loss with aging was significantly greater in the females with fractures (-20.4%/3 years) than that in the females without fracture (-8.9%/3 years). In an attempt to clarify the influence of physical parameters such as body weight, body height and age on the RMC in the elderly patients, we have subsequently studied the correlation between the RMC and these three physical factors, respectively. Body weight and body height had a significant positive correlation with RMC in both sexes respectively, while age had a significant negative correlation with RMC in both sexses. Subsequently, we have calculated the partial correlation coefficient between RMC and these three parameters, respectively. Among three factors examined, the most intimately correlated factor with RMC was body weight in the males and age in the females, respectively. Subsequently, correlation between RMC and these three parameters was studied by using multiple regression analysis. It was found that RMC was expressed by the following formula. Male: RMC(g/cm2)=0.443-0.04x+0.05y-0.07z Female: RMC(g/cm2)=0.641-0.12x+0.001y+0.45z x: age x 0.1 (year), y: body weight x 0.1 (Kg) z: body height x 0.01 (cm) The validity of this experimental formula was checked by the distribution pattern of the residuals obtained by reducing the theoretical RMC calculated by this formula from the actual value in the females. It was found that the distribution pattern of the residuals in the females without fracture was of normal distribution at the centre in zero, thus showing the validity of this experimental formula. The frequency distribution of the residuals in the females with fractures was found to be significantly shifted to the negative side compared with that of the females without fracture. In conclusion, it was clearly demonstrated that RMC in the aged females with fractures can be distinguished statistically from that in the aged females without fracture using by this experimental formula.