Body mass variation

Body mass variation for solids The variation in body mass due to food intake and subsequent excretion, in kg. 

Body mass variation for water The body mass variation due to intake of water and excretion of urine, in kg. 

A recent variation on the prediction of human VD using allometric scaling involves the use of what has been termed "fractal volume of distribution (vf) [7], This refers to the VD value corrected to within the bounds of actual volumes within the body - in the case of human the upper and lower bounds would be 70 1 and plasma volume, respectively. Thus, even if a compound were to have a VDSS of 1000 1, its Vf would be 69.8 1. The authors of this approach have shown that Vf scales allometrically across species better than VD [8], with the explanation that body volume and body mass are exactly scaleable across species. Animal values for Vf are calculated from VD obtained from pharmacokinetic studies using the relationship ... 

Fig. 6. (A) Variation of total daily metabolic rate for 18 weeks after initiating caloric restriction in male F344 rats at 6 weeks of age. The metabolic rate is normalized to the unit lean mass. Adapted from reference 21. (B) Metabolic rate x unit lean body mass-1 x 24hr-1 for both ad libitum-isd and calorically restricted male F344 rats from 6 weeks to 24 months of age. Adapted from reference 21.

Figure 7.35. Variation in phospholipid composition of mitochondrial membranes in relation to body mass. The mole percent of 22 6 (w-3) fatty acids in the identified fatty acid pool of mitochondrial membrane phospholipids is plotted against body mass of nine mammals (see legend to figure 7.34 for identification of species). (Figure modified after Porter et al., 1996.)...

Despite the burgeoning of obesity world-wide, it is still only a minority who become clinically obese (see above). Thus there is individual variation with a secular trend . Genetic factors are believed to play a major role in such variation, according to twin, family and adoption studies (Damcott et al. 2003). It has been calculated that up to 80% of the variance in body mass can be attributed to genetic factors. 

Aberle J, Fedderwitz I, Klages N et al (2007) Genetic variation in two proteins of the endocannabinoid system and their influence on body mass index and metabolism under low fat diet. Horm Metab Res 39 395-397... 

This constancy is not a human privilege but extends to all mammals, Thus, a remarkable constancy is observed in the mean corpuscular volume in mammals, which varies between 20-120 compared to a body mass ranging from 2 g for the shrew to 4 x 10 g for the elephant. Similarly, little variation is seen in the hematocrit and the hemoglobin concentration in all mammals, resulting in a variation of no more than 20% of the O2 capacity. 

Prescribing, dispensing and administration of medicines for children pose a unique set of risks, predominantly because of the wide variation in body mass, which requires doses to be calculated individually based on patient age, weight or body surface area, and their clinical condition. This increases the likelihood of errors, and tenfold errors, as... 

Otabe S, Clement K, Dina C, et al. A genetic variation in the 5 flanking region of the UCP3 gene is associated with body mass index in humans in interaction with physical activity. Diabetologia. 2000 43 245-249. 

FIGURE 7.4.15 Variation of pulmonary resistance (excluding upper airway resistance) with body mass. (From Johnson, A.T., Biomechanics and Exercise Physiology Quantitative Modeling, CRC Press/Taylor Francis, Boca Raton, FL, 2007. With permission.)... 

In mammals, there are characteristic variations in cardiac function with heart size. In the power law relation for heart rate as a function of body mass (analogous to Equation 54.3), the coefficient k is 241 beats.min and the power a is —0.25 [5]. In the smallest mammals, hke soricine shrews that weigh only a few grams, maximum heart rates exceeding 1000 beats.min have been measured [ 57]. Ventricular cavity volume scales linearly with heart weight, and ejection fraction and blood pressure are reasonably invariant from rats to horses. Hence, stroke work also scales directly with heart size [58], and thus work rate and energy consumption would be expected to increase with decreased body size in the same manner as heart rate. However, careful studies have demonstrated only a twofold increase in myocardial heat production as body mass decreases in mammals ranging from humans to rats, despite a 4.6-fold increase in heart... 

Krieger JW, et al. Effects of variation in protein and carbohydrate intake on body mass and composition during energy restriction a meta-regression 1. Am J Clin Nutr. 2006 83(2) 26 -74. 

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