Caryl Magnus Boyden

BODY CELL MASS AND LIMITS OF HYDRATION OF THE FAT‐FREE BODY: THEIR RELATION TO ESTIMATED SKELETAL WEIGHT*

The identification and definition of a central, energy-exchanging mass of working tissue has long been sought as a standard for body composition, and to provide a reference basis for the measurement and expression of such rates as oxygen consumption, caloric requirement, carbon dioxide production, basal metabolism, basal metabolic expenditure, and work performance. Such a “core” reference for the central tissues of the body has, in the past, been identified with such concepts as the “lean body mass” and the “fat-free body.” As reference standards for energy turnover or work performance the “lean body mass” and the “fat-free body” suffer both anatomically and conceptually from the fact that they include such compositional elements as the plasma volume, the extracellular fluids, the skeleton, cartilage, tendons, dermis, hair, teeth, fascia, collagen, elastin, and pathological water accumulations. These are components of the body identified with the extracellular tissues, concerned largely with support and transport but with no direct or intrinsic significance as regards oxidative energy turnover. All body cells contain potassium at concentrations ranging in the vicinity of 150 mEq. per kg. of cell water. Although there is little evidence from man to indicate that the intracellular potassium concentration is the same in all cellular tissues, there is strong persumptive evidence from osmotic considerations and acid base equilibria that most of the cells of the body contain this ion at concentrations very similar to each other, if not identical. In sharp contrast, potassium is not present to any extent in those other fluids and matrices of the body that are extracellular in site, concerned with support and transport and which we identify as the extracellular tissues. These ( as mentioned above ) included the intercellular matrix substances of fascia, tendon, dermis, and skeleton together with that very large fluid component of the body that is outside of cells. One might raise the objection here that there are cells in bone and cells in tendon for example. For the clarity of this concept i t should be emphasized that these cells, however sparse in population, contain potassium at normal intracellular concentrations and are included in the “body cell

Circadian variation in response to potassium infusion.

The response of 5 normal men to an intravenous infusion of potassium chloride was compared at midday and midnight. Each subject was maintained on strict supine bedrest with oral intake limited to 100 ml distilled waterlhr for the 9 hr before and after each infusion. Potassium chloride, 37 mEq, (with an added label of 200 µCi 42KCl) in iso‐osmolar solution was administered via a central venous catheter over 1 hr starting either at midday or midnight. Plasma potassium concentration was elevated by 40% more at midnight than at midday, and plasma 42K activity also rose to a higher level at midnight. These differences were reflected by greater T wave elevations of the electrocardiogram at midnight than at midday, although urinary potassium excretion (total and 42K labeled) was higher at midday than at midnight, indicating that there was reduced renal excretory responsiveness to elevations in plasma potassium concentration at midnight compared with midday. Plasma aldosterone concentration rose during the potassium infusions at both midday and midnight by a similar amount, which suggests that the induced increments in aldosterone secretion were not a major determinant of the differing renal response. These findings indicate that circadian modulations in the physiologic mechanisms which regulate potassium homeostasis profoundly influence the response to exogenous potassium loads. Special caution must therefore be taken in administering potassium infusions at night.

Body composition in the dog. I. Findings in the normal animal.

Summary o 1. A technique is presented for the simultaneous measurement of total body water, extracellular fluid, red cell volume, plasma volume, exchangeable sodium, exchangeable chloride and exchangeable potassium in the dog. The method requires five venipunctures and 60 to 80 ml. of blood for sampling. 2. The reproducibility of the technique has been examined by means of five repeated measurements in three dogs at weekly intervals. The errors of the method are small, and approximate the expected statistical errors due to counting and chemistry. 3. The body compositional findings in the normal dog are contrasted briefly with those found in man. These dogs had less body fat than is seen in the normal adult female human subject; within the aqueous phase of body composition a larger fraction of water is occupied by cellular tissue than in the human being; body tonicity as exemplified in the ratio Na e +K e /TBW is approximately 10 mEq./L. higher in the dog than in man; this latter fact is correlated with the higher concentration of sodium in the serum found in the dog. 4. For long-term observation of changes in the animals body composition as a result of disease, the isotope dilution technique for body composition appears preferable to the metabolic balance method.

Body composition in the dog. II. The effect of progressive congestive heart failure.

Summary o 1. The multiple simultaneous dilution technique has been employed to measure alterations in body composition occurring in dogs with surgically produced cardiac valvular lesions. Control studies in the normal state were followed by repeated estimations in the same animals with mild valvular damage (tricuspid insufficiency), and subsequently in the state of florid congestive heart failure (tricuspid insufficiency plus pulmonary stenosis). 2. The pattern of change has in general corresponded to that emerging from previous studies in the human. Total body water (TBW), exchangeable sodium (Nae) and exchangeable chloride (Cle) were found to be significantly elevated even in the earliest stage of valvular damage (TI), and grossly elevated in the stage of congestive failure (TI and PS). Exchangeable potassium (Ke) and red cell volume (RV) on the other hand were elevated in the stage of mild valvular damage but subsequently returned to control values in the stage of gross heart failure. 3. In a few details the response of the dog appears to differ from that in man. Hyponatremia is not a regular result of congestive heart failure; the expansion of body water is even greater than is seen in man and the ratio Nae+Ke/TBW is maintained at a higher level in the dog than in man in congestive heart failure. 4. The significance of these variations is discussed in the light of current knowledge.