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Whole body protein breakdown using 15N and skeletal muscle protein breakdown from urinary 3-methylhistidine were measured simultaneously in seven skeletal trauma and eight normal subjects on a standard hypocaloric, protein free diet. The trauma group had a 31% greater resting metabolic energy expenditure than controls. The control males lost 3.73 mumol/kg/day of 3-methylhistidine which suggested a protein breakdown rate of 0.89 g P/kg/day. The control females lost 2.46 mumol/kg/day of 3-methylhistidine or a breakdown rate of 0.58 g P/kg/day. These parameters were 187% greater for males and 163% greater for females in the trauma group. The measured whole body protein breakdown rates were 3.64 g P/kg/day for the control males and 2.69 for females. Skeletal trauma increased both by 73%. Skeletal trauma raised the muscle contribution to the whole body breakdown rate from 24.4 to 40.4% for men and from 21.6 to 33.0% for women. This disproportionate increase in muscle protein breakdown is consistent with muscle protein metabolism being most seriously affected by severe injury.

The development of a three-compartment model for glucose metabolism in man is discussed. A nonlinear regression method was used to determine the parameters of the model by simultaneously fitting typical blood glucose and breath COs specific activity data obtained after intravenous administration of C14-tagged glucose. The three-compartment model is compared with a two-compartment model on the basis of ability to fit the data, confidence limits on the best parameter values, strength of parameter correlation, and sensitivity to changes in certain fixed parameters. The three-compartment model fits the data better than the two-compartment model, and in most but not all cases has reasonably well-determined parameter values.The human body can be viewed as a chemical reactor closely linked to a control system. Its over-all behavior is governed by interacting processes involving chemical reactions, transport of mass and energy, fluid flow, and a variety of electrical and mechanical phenomena. The complexity of this system is so great that a quantitative treatment of the whole body is very difficult. In addition, it is often impossible to isolate subsystems which can be studied independently. Nevertheless, recent developments in many areas, and especially in mathematics and computers, have made the com-