Waist circumference as an indicator of adiposity and the relevance of body height.

Waist circumference (WC) is an obvious indicator of adiposity, but there is a confusing diversity of approaches to its quantitative use. Because taller people of any given relative fat content tend to have bigger WCs, indices of adiposity commonly take the form WC/height(q), where q is 1 or less. Sometimes the influence of height is regarded as insignificant, so that q is taken as zero. More attention has been given to such indices than to establishing how to use them for predicting adiposity. The usual approach has been empirical and statistical, but many published findings can be integrated using a more analytical approach. This leads to several hypotheses that are supported by published evidence, but which remain to be fully tested. Testing mainly requires data sets of the kind that have already been used for related purposes. The main hypotheses are as follow. For adults, the preferred index is WC/height(0.5), while for adolescents and children it is WC/height. However, to obtain equations for the prediction of percentage body fat, the latter should be regressed on the reciprocals of the squares of these indices, namely 1/(WC(2)/height) and 1/(WC/height)(2) respectively. These expressions decrease with increasing percentage body fat, but should do so in a linear manner. Two other hypotheses are that the non-fat content of the abdomen tends to increase with percentage body fat and that the ratio WC(2)/height is approximately proportional to the body mass index. The analysis is based mainly on the following ideas: firstly, that the area of fat or adipose tissue in a transverse computed tomogram of the abdomen equals the total area less the fat-free area, the former being the main determinant of WC and the latter being partly determined by fat-free body size as represented by height; secondly, that guidance can be usefully be sought in simple, dimensionally-correct models of body form, but that parameters in the resulting equations may become attenuated by the necessary use of regression analysis or the maximizing of correlations. There may be a better measure of fat-free body size with which to replace height in these indices, but the waist-to-hip ratio is unhelpful. It is hoped that this analysis can be usefully extended to the problem of estimating intra-abdominal (visceral) fat from waist circumference.

Up the Tower of Psychobabel: does lexical anarchy impede research into 'psychological stress'?

The terminology relating to 'psychological stress' is so confused and ambiguous that research in this field - and application of its results - must surely be hampered. Relevant words with conflicting usages and scientific definitions include 'stress' itself, 'stressor', 'strain', 'challenge', 'demand', 'threat', 'resource', 'coping' and 'mental load'. 'Stress' and 'anxiety' are often confounded. Because of this confusion it can be hard to decide how closely one view of stress matches another and to integrate the variety of published conceptual frameworks. The word 'stress' is therefore useful only as a deliberately vague umbrella term. Nevertheless there is moderate consensus in the literature that the mental state characterizing 'stress' (which, to avoid ambiguity, we call 'psystress') results from awareness that one is not coping with something, a perceived stressor, that relates to a need that is deemed personally important. Other definitions and models of 'stress' are compared. 'Stress' is often applied to situations that actually cause pleasurable excitement. We propose the unambiguous term 'euchallenge' for such enjoyable demands, because 'eustress' and 'challenge' also have other meanings. Supposedly adverse stress responses are sometimes studied using tasks or situations, which are assumed to be stressors, but which for some individuals might be euchallenges or in others produce apathy through perceived irrelevance to personal needs. Much research utilizes self-report stress questionnaires and many of these are composed with poor regard to theory. Some, for example, mix psystress causation with a variety of response factors or pay inadequate attention to 'chronic' and 'acute' time scales. Testees may even be required to interpret words on which psychologists themselves disagree - notably 'stress' itself. It is important, therefore, to evaluate carefully every test in the context of its purpose, but, most importantly for scientific advance, to relate it to a comprehensive testable theoretical model.

Why is the body mass index calculated as mass/height2, not as mass/height3?

BACKGROUND: The body mass index or BMI, mass/height(2), is used to predict fatness and health. It is an approximation to the Benn index, mass/height(p), where p (typically 1.1-2.5 for adult populations) makes the index uncorrelated with height. Mass/height(3) is an index of body build that is independent of scale and statistics. AIM: To explain why p varies and is less than three, show how statistical methods can distort perceptions of mass-height relationships, and clarify the nature of the BMI. METHODS: A hypothetical adult population is modelled statistically, with mass being approximately proportional to height(3) and with neither variable determining the other. Values of p are calculated both for the model and for real adults. RESULTS: In both cases p increases with the correlation between mass and height. Both p and that correlation are usually lower for women than for men. CONCLUSIONS: In adult populations mass must vary more nearly with height(3) than with height(2), although, for reasons explained, conventional statistical techniques suggest otherwise. Nevertheless the BMI is a valid predictor of fatness from mass and height in adults and is properly divisible into fat mass and fat-free mass indices. The validity of the latter three indices for children is questionable.

Differences in pH between interstitial fluid and arterial blood in water-breathing and air-breathing vertebrates.

Most cells are bathed by interstitial fluid, but extracellular pH measurements are mostly for arterial plasma. Whole-body mean pH differences between the two fluids have been estimated in terms of a simple model. This relates to the diffusive exchange of carbon dioxide and oxygen and utilizes literature data, for 22 vertebrate species, on arterial and mixed-venous tensions of both gases. Uncertainties arise because the carbon dioxide reaction in blood may sometimes be in disequilibrium and because carbon dioxide diffusion is facilitated to unknown degrees in the presence of buffers. Nevertheless, the model suggests that the pH difference should tend to vary inversely with arterial carbon dioxide tension. In some species, this may aid interstitial pH homeostasis, but a clearer implication is that the difference should be generally greater in water breathers than in air breathers. It has previously been found that arterial pH in water-breathing teleosts also tends to be higher than in air-breathing tetrapods (when allowance is made for temperature and plasma sodium concentration) and to a comparable extent. Thus, mean interstitial pH may be more nearly similar in the two groups than is arterial pH. Direct measurements of interstitial pH do not yet suffice to test the model.

Concentrations of sodium, potassium and cortisol in saliva, and self-reported chronic work stress factors.

One hundred and fifteen electronics factory employees completed questionnaires relevant to work stress, and gave unstimulated saliva samples. As previously found, Perceived Coping Incapacity correlated very significantly with self-reported emotional upset and psychosomatic complaints. Salivary [Na+] correlated significantly with Perceived Coping Incapacity (rho = -0.30, p < 0.01), and also with emotional upset (rho = -0.19, p < 0.05). Raised [K+] tended to be associated with reduced fatigue (rho = -0.21, p < 0.05) and lower self-medication (rho = -0.21, p < 0.05) together with a greater perceived personal work responsibility (rho = 0.19, p < 0.05)-all consistent with the perception of work demands as positive challenges rather than stressors. Self-reported fatigue and emotional upset at work gave higher correlations with [K+] and [Na+] than either did on its own. Salivary [cortisol] was uncorrelated with self-reported work stress indices, and with [K+] and [Na+].

The dependence of normal plasma pH on sodium concentration in amphibians, reptiles and man.

Normal plasma pH at a given temperature is typically higher in freshwater turtles than in other reptiles, but lower than in amphibians. Normal pH in the different species at a given temperature shows a negative correlation with sodium concentration. Human plasma fits this pattern. What may be more nearly constant from species to species than plasma pH is the pH at particular sites on cell surfaces, and therefore the ionization of proteins located there.

The roles of intracellular buffers and bone mineral in the regulation of acid-base balance in mammals.

1. Regulation of intracellular and extracellular pH may conflict in their requirements for movement of acid or base. 2. Cells make a positive or a negative contribution to 'tissue buffering' of extracellular fluid (ECF), depending on their internal buffer value, on the tightness of their internal pH control by membrane mechanisms, and on the nature of the acid-base disturbance. 3. A role is suggested for electrogenic Na-HCO3 co-transport in some of the ion shifts that occur in acid-base disturbances. 4. The time course of 'tissue buffering' in nephrectomized mammals in hypercapnia is variable, and it is far from clear in intact, unanaesthetized mammals. 5. Buffering of ECF by Ca salts of bone mineral in acidosis can only be substantial if accompanied by Ca excretion; the release of HCO3 with Na and K is more significant. 6. The relative importance of cells and of bone mineral in the buffering of ECF is unclear.

Relative changes in salivary Na+ and K+ concentrations relating to stress induction.

Three independent studies are reported in which periods of "relaxation" (A) and presumed stressors (B) were given to female students in an ABA design. The "stressors" were: (1) obligatory time-wasting activity; (2) a mental "IQ" test; and (3) delivering a speech. Saliva was collected immediately after "relaxation" and "stress" periods. "Stress" and "arousal" state were retrospectively assessed in experiments (1) and (2) by subject self-rating and in experiment 1 also by trained observers for the periods A and B. The molar [K+/Na+] ratio was determined for each saliva sample. The prediction that [K+/Na+] would increase with stress induction was supported by statistically significant results with stressors 1 and 2 (p less than 0.01), but speech delivery (3) resulted in a significant rise of [K+/Na+] after the stressor period. Correlations between [K+/Na+] and "stress" and "arousal" ratings also substantiated the prediction.

Clarification of the concept of psychological stress ("psystress").

The concept of "stress" in the current academic literature is unstandardized, and therefore confusing. The theoretical approach of regarding stress as an intervening variable seems most generally agreed on by researchers; the unambiguous term "Psystress" proposal to denote the mental state involved. Aspects of vocabulary concerning psystress production and response are also discussed.

The protein content of extracellular fluids and its relevance to the study of ionic regulation: net charge and colloid osmotic pressure.

1. Protein net charge in blood plasma and haemolymph is relevant to overall anion-cation balance, Donnan equilibria, colloid osmotic pressures (COPs), buffering and liquid junction potentials, but its definition and measurement are not always straightforward. 2. Normal values of protein net charge in man and other animals are discussed, as is their dependence on pH. 3. Although it is clear that charge on a protein augments COP, the theory of COP is still incomplete. 4. The dependence of COP on protein and salt concentrations and on pH are therefore considered empirically. 5. Normal values for COP in various animals are given and the regulation of COP is discussed.

On calculating concentrations of "HCO3" from pH and PCO2.

1. As used in the Henderson-Hasselbalch equation, [HCO3], [CO2] and pH may all be variously defined; values of pK'1 must be chosen accordingly. 2. In common usage, "HCO3" may include CO3, carbamate, various ion pairs and possibly other bound CO2, as well as free HCO3 ions. 3. pH measurements may be systematically affected by the choice of standard buffers and by proteins and blood cells, and the errors in pH may be pH-dependent. 4. According to how it is expressed, the solubility coefficient for CO2 (S) may be influenced by sample water content, proteins and lipids. However, it need not feature in the calculation. 5. pK'1 is often found to decrease with increasing pH. This may be partly due to inclusion of CO3 and carbamate, but not of H2CO3.HCO3-, in "HCO3" and partly, perhaps, to errors in pH measurement. 6. To the extent that pH measurements are reliable, concentrations or activities of true HCO3 are calculable from pH and PCO2, but, if pH measurements are likely to be systematically erroneous, it may be preferable to define "HCO3" as "total bound CO2" and to base pK'1 on gasometric or titrimetric determinations of that.

Internal reference standards in ionic regulation and the predictability of ionic concentrations in animals.

The regulation of ions at similar concentrations in most individuals of a species suggests the existence of internal reference standards. Few have been identified, but many probably relate to cell membrane properties, including potentials, surface charge densities and equilibrium constants of receptor molecules. Solubility may sometimes determine the product [Ca2+] [CO2-3]. Reference standards must generally each relate to more than one ionic species. For some concentrations, including osmolality, there may be no direct reference standard.

Ionic regulation in fish: the influence of acclimation temperature on plasma composition and apparent set points.

Published data on the influence of acclimation temperature on normal ionic concentrations in fish plasma are summarized. Although osmolality rises near 0 degree C in many marine fish, there is otherwise no general tendency in marine species for osmolality, Na and Cl to fall with increasing temperature. The suggestion that osmolality, Na and Cl in freshwater fish typically fall with decreasing temperature is not supported. K and Ca generally rise with increasing temperature, or stay constant. Mg generally falls with increasing temperature, or stays constant. Evidence on concomitant variations in set points is sparse, but apparent set points for osmolality/Na/Cl, except near 0 degree C, usually vary by less than +/- 2% degrees C-1.

The role of imidazole ionization in the control of breathing.

Interacting effects of pH and temperature on ventilation in turtles and alligators have suggested that pH is monitored in terms of imidazole ionization, but the view that this is true in alligators and ectotherms generally has been attacked. Published evidence re-interpreted here indicates that this "alphastat control" could indeed operate in turtles, alligators, chickens (i.e. intrapulmonary chemoreceptors) and perhaps cats. Nevertheless, studies on temperature effects cannot distinguish with certainty between imidazole and some amino groups in this context.

Inorganic ion pairs in physiology: significance and quantitation.

1. Body fluids contain ion pairs such as NaC10, CaCl+, CaHCO+3 and MgSO04. 2. Ion pairs must often be considered in the quantitation of acid-base, solubility, Donnan and other equilibria. 3. Fluxes of ion pairs, such as NaCO-3 and perhaps NaSO-4 and NaCl0, may sometimes contribute significantly to total ion fluxes across cell membranes. 4. Dissociation constants for ion pairs are discussed, but values appropriate to body fluids are often uncertain.

Cell composition as assessed from osmolality and concentrations of sodium, potassium and chloride: total contributions of other substances to osmolality and charge balance.

From published data for various tissues on intracellular Na, K and Cl were calculated the net anionic charge on all other substances present and also the total contribution of these to osmolality, assuming osmotic equilibrium with extracellular fluid. These parameters were compared for muscle and nerve of animals differing widely in osmolality and also for other mammalian cells. Cell volume regulation in some euryhaline species was considered; it is only partly due to ninhydrin-positive materials. In sheep mammary glands K seems to be sequestered with lactose and anion. Changes in mammalian muscle due to adrenalectomy, hypophysectomy, K deficiency, myotonia, acid-base imbalance and treatment with deoxycorticosterone or insulin were discussed.

The composition of animal cells: solutes contributing to osmotic pressure and charge balance.

The cytoplasmic solutes of vertebrates and invertebrates, other than Na, K and Cl, are surveyed in relation to their influence on ionic regulation through osmolality and charge balance. The most abundant include MgATP, phosphagens, amino acids, various other nitrogen and phosphorus compounds and sometimes anaerobic end products and antifreeze agents. Differences in muscle osmolality, e.g. between marine and non-marine animals, affect mainly nitrogenous solutes of no net charge, such as certain amino acids, taurine, betaine, trimethylamine oxide and urea. The high osmolality of axoplasm in marine invertebrates is due more to anions such as aspartate, glutamate and isethionate.