Whole-body Balance Research Articles

Animating responsive characters with dynamic constraints in near-unactuated coordinates

This paper presents a technique to enhance a kinematically controlled virtual character with a generic class of dynamic responses to small perturbations. Given an input motion sequence, our technique can synthesize reactive motion to arbitrary external forces with a specific style customized to the input motion. Our method re-parameterizes the motion degrees of freedom based on joint actuations in the input motion. By only enforcing the equations of motion in the less actuated coordinates, our approach can create physically responsive motion based on kinematic pose control without explicitly computing the joint actuations. We demonstrate the simplicity and robustness of our technique by showing a variety of examples generated with the same set of parameters. Our formulation focuses on the type of perturbations that significantly disrupt the upper body poses and dynamics, but have limited effect on the whole-body balance state.

Disposition and metabolism of the colchicine derivative [14C]-ZD6126 in rat and dog

1. The tissue distribution, disposition and metabolism of ZD6126, a novel vascular targeting agent, were investigated in rat and dog. This paper comprises the findings of several investigations, including rat quantitative whole-body autoradiography (QWBA), rat and dog balance and metabolism (both in intact and bile-duct-cannulated animals), rat enterohepatic recirculation, and comparison of metabolism between young and mature rats.2. Following intravenous administration of [14C]-ZD6126 to rats, quantitative whole-body autoradiography showed that radioactivity was widely distributed, then rapidly eliminated from the body.3. ZD6126-related material was eliminated primarily in the faeces (approximately 86%) of both species, indicating the importance of biliary clearance.4. Metabolite profiles from intact and bile-duct-cannulated animals suggest that ZD6126 is cleared primarily by metabolism. In rat, the major metabolites were ZD6126 phenol, its glucuronide and other metabolites consistent with O-demethylation and conjugation. ZD6126 was more extensively metabolized by male than female rats, and also in young compared with mature rats. In dog, metabolism occurred primarily via direct glucuronidation of the active species, ZD6126 phenol.5. Following intraduodenal infusion of bile containing [14C]-ZD6126-related material to bile-duct-cannulated rats, 30% of the radioactivity was subsequently recovered in bile and urine, showing that one or more components in bile are reabsorbed and undergo enterohepatic recirculation.

Nutritional strategies for football: Counteracting heat, cold, high altitude, and jet lag

Environmental factors often influence the physical and mental performance of football players. Heat, cold, high altitude, and travel across time zones (i.e. leading to jet lag) act as stressors that alter normal physiological function, homeostasis, metabolism, and whole-body nutrient balance. Rather than accepting performance decrements as inevitable, well-informed coaches and players should plan strategies for training and competition that offset environmental challenges. Considering the strength of scientific evidence, this paper reviews recommendations regarding nutritional interventions that purportedly counterbalance dehydration, hyperthermia, hypothermia, hypoxia, acute or chronic substrate deficiencies, sleep loss, and desynchronization of internal biological clocks.

Restricting arm use enhances compensatory reactions of leg muscles during walking

A number of recent studies have indicated that whole-body coordinated reactions are employed to regain balance following disturbances during walking. However, it is not always the case that all body segments are available to contribute to balance corrective strategies. We hypothesize that balance corrective strategies will adapt to task and environment constraints such that greater responses are generated in the available body segments when other body segments are unable to participate. In this study, we tested the hypothesis that voluntarily restricting the arms during walking would result in an increase in the amplitude of the electromyographic responses evoked in leg muscles when subjects are perturbed at the torso during walking. To do so, subjects were asked to walk on a motorized treadmill while either crossing their arms across their front or back, or with their arms swinging normally. Periodic perturbations, forwards and backwards, were applied at the pelvis randomly throughout the step cycle. This resulted in short latency responses in leg muscles. The amplitude of these responses was increased when subjects walked with their arms crossed, as compared with normal, unrestricted walking. Facilitation of these evoked responses was restricted to the early part of the stance phase, particularly at heel-strike. The pattern of muscle activation and the latency of the responses were not affected by restricting the arms. We suggest that this finding indicates that whole-body balance corrective strategies employed during walking are selected based upon the demands of the general features of the task, but that components of the strategy are scaled according to the specific context-dependent needs of the task.

Acid production and base balance in patients on chronic haemodialysis

Acid generation and elimination processes were compared with total base (bicarbonate plus metabolizable anions) turnover in 18 anuric patients undergoing post-dilutional haemofiltration. The study was conducted during the second haemodialysis session of the week by means of a whole-body base balance technique. The results showed that the mean rates of base loss and base gain during dialysis did not differ (i.e. the dialysis base balance approximated to zero). The concurrent mean rate of intestinal base absorption was 66+/-26 mmol/2 days, as calculated from the whole-body balance of the various inorganic cation and anion differences in a metabolic steady state. This level of intestinal base absorption would be capable of neutralizing the 59+/-21 mmol of H(+) ions/2 days that is contributed by sulphuric acid, which is the most important endogenous acid produced in anuric patients. In spite of the fact that intestinal base supply was adequate to neutralize endogenous acid production completely, our patients presented with pre-dialysis non-carbonic acidosis. The depression of plasma bicarbonate levels could not, however, be explained by increased concentrations of the anion gap and organic acids, which were within normal limits both before and after dialysis. We suggest as an alternative hypothesis that this pre-dialysis acidosis may represent an isotonic dilution acidosis that is induced by the ingestion of base-free tap water in order for plasma tonicity to be protected from the accumulation of impermeant dietary solutes, which takes place during the interdialysis period in anuric patients.

Application of new methods and analytical approaches to research on polyunsaturated fatty acid homeostasis

New methods and analytical approaches are important to challenge and/or validate established beliefs in any field including the metabolism of polyunsaturated fatty acids (PUFA; polyunsaturates). Four methods that have recently been applied toward obtaining a better understanding of the homeostasis of PUFA include the following: whole-body fatty acid balance analysis, magnetic resonance imaging (MRI), 13C nuclear magnetic resonance (NMR) spectroscopy, and gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS). Whole-body balance studies permit the measurement of both the percentage of oxidation of linoleate and alpha-linolenate and their conversion to long-chain PUFA. This method has shown that beta-oxidation to CO2 is normally the predominant metabolic fate of linoleate and alpha-linolenate. Furthermore, models of experimental undernutrition in both humans and animals show that beta-oxidation of linoleate and alpha-linolenate markedly exceeds their intake, despite theoretically sufficient intake of linoleate or alpha-linolenate. Preliminary results suggest that by using MRI to measure body fat content, indirect whole-body linoleate balance can be done in living humans. 13C NMR spectroscopy provided unexpected evidence that linoleate and alpha-linolenate were metabolized into lipids synthesized de novo, an observation later quantified by tracer mass balance done using GC-C-IRMS. This latter method showed that within 48 h of dosing with 13C-alpha-linolenate, >80% underwent beta-oxidation to CO2 by suckling rats, whereas 8-9% was converted to newly synthesized lipids and <1 % to docosahexaenoate. Further application of these recently developed methods in different models should clarify the emerging importance of beta-oxidation and carbon recycling in PUFA homeostasis in mammals including humans.

Balance of non-metabolizable base in continuous peritoneal dialysis patients

Acid generation and elimination processes compared to titratable non-metabolizable base (NaOH equivalents, NB) turnover in end-stage renal disease patients are examined in the light of the Law of electroneutrality. The application over 2 days of the whole-body NB balance technique to 18 patients undergoing continuous ambulatory peritoneal dialysis is evaluated. The results show that the mean rate of NB loss with peritoneal effluent (as bicarbonate and organic acid anions) exceeded the mean rate of NB gain with the dialysis fluid (as salts of lactic acid) by 24 (27), m (SD), mmol per 2 days. In spite of this, the bicarbonate and pH of the plasma remained stable and within normal limits. The concurrent mean rate of the intestinal NB absorption was about 61 (27) mmol per 2 days, as calculated from the whole body balances of the several electrolytes in the metabolic steady-state. This intestinal absorption was more than sufficient to restore the body base consumed in neutralizing endogenous acid generation: 37 (14), 2H2SO4 mmol per 2 days, the remaining NB being eliminated as bicarbonate and organic acid anions. The ample spectrum of plasma acid-base (A-B) values appears to some extent influenced by patient-related factors, such as the rate of drinking water intake and the set point deviation for organic acid turnover.

Hemodynamics and oxygen consumption during warm heart surgery

We compared the effects of normothermic cardiopulmonary bypass (CPB) with those of hypothermic CPB in patients who underwent coronary artery bypass grafting (CABG) with respect to hemodynamics and oxygen balance. The patients in our study were divided into two groups according to temperature during CPB: systemic normothermia combined with warm blood cardioplegia (group W,n=36) and systemic hypothermia combined with cold crystalloid cardioplegia (group C,n=26). In group W, the use of directcurrent (DC) defibrillators was less frequent after release of the cross clamp, and the duration of CPB and of reperfusion was shorter. After CPB, the cardiac index and arterial pressure were higher and the dosages of dopamine were lower in group W than in group C. The serum glucose level during and after CPB was lower and the base excess during CPB was higher in group W than in group C. Oxygen consumption ([Formula: see text]) was unchanged throughout the operation in group W, while it decreased during CPB and increased at the end of surgery in group C. The oxygen extraction ratio (ERo2) increased during CPB in group W, while it was unchanged throughout the operation in group C. Mixed venous oxygen saturation ([Formula: see text]) was maintained above 65% during and after CPB in group W and group C. Our results showed that normothermia may be superior to hypothermia during CPB with respect to recovery of cardiac function and avoidance of hyperglycemia. The whole-body oxygen demand-supply balance may be preserved during normothermic as well as hypothermic CPB.

Reproductive and Overwintering Adaptations in Northern Pike (Esox lucius L.): Balancing Essential Fatty Acid Requirements with Dietary Supply

In northern pike, ovarian recrudescence and membrane lipid restructuring occur during winter and may thereby create physiological requirements for essential fatty acids (EFAs) that surpass dietary EFA intake. Seasonal changes in the fatty acid composition of pike ovary and whole-body lipids and mass balance comparisons were used to identify mechanisms that during winter help balance physiological requirements for EFAs with the dietary supply. Mature ovaries of pike exhibited a polar lipid:neutral lipid ratio (70:30; based on the weight of fatty acids) much greater than that of somatic tissues (30:70), yet the fatty acid compositions of ovarian and somatic total lipids were quite similar. This similarity resulted from an adaptive reduction in the percentage of n-3 EFAs in ovarian neutral and polar lipids to levels lower than those typical of somatic lipids. Adaptive features of ovarian fatty acid composition, combined with significant reductions in the n-3 EFA content of somatic neutral lipids during winte...

Hemodynamic Changes and Oxygen Consumption in Burned Patients during Enflurane or Isoflurane Anesthesia

The effects of enflurane or isoflurane anesthesia on the systemic circulation and whole-body oxygen (O2) uptake (VO2) of 15 burn patients undergoing wound excision and skin grafting procedures were studied. The possibility that burn wound excision might adversely affect pulmonary circulation was also investigated. The patients were preanesthetically in a hyperdynamic-hypermetabolic state, characterized by a resting cardiac index (CI) of 6.2 +/- 0.9 L.min-1.m-2 (mean +/- SD), a VO2 (calculated using the Fick principle) of 213 +/- 44 mL.min-1.m-2, a normal mean systemic arterial pressure (MAP) (92 +/- 15 mm Hg), and markedly decreased systemic vascular resistance (SVR) (570 +/- 162 dynes.sec.cm-5). Mean pulmonary arterial pressure (MPAP) preanesthetically was slightly increased (21 +/- 3 mm Hg), while pulmonary vascular resistance (PVR) was in the low-normal range (59 +/- 16 dynes.sec.cm-5). No difference among the effects of enflurane and isoflurane on systemic and pulmonary hemodynamics and metabolic rate was detected. Induction of anesthesia was associated with a decrease in VO2, CI, MAP, and MPAP (P less than 0.001), while SVR and PVR did not change. The decrease in CI paralleled the decrease in VO2, thereby maintaining whole-body O2 supply-demand balance. VO2 decreased most likely because of lessened tissue O2 requirements. When anesthesia was discontinued, all metabolic and hemodynamic variables promptly returned to preanesthetic values. No effect of burn wound excision on pulmonary circulation was detected.

Plasma Membrane Proton Pumps in Animal Cells

Proton pumping in animal cell plasma membranes is mediated by at least three distinct types of transport systems and has a variety of functions. The gastric proton pump develops chemical gradients exceeding 6 pH units, secreting acid from the gastric mucosa to help digest food. Another ATPase/H+ pump, which regulates whole-body acid and bicarbonate excretion in kidney distal tubules, can develop acid gradients of 3 pH units. And ATP-independent Na+/H+ exchange systems and multiple-ion exchangers operate both to control intracellular pH and to maintain whole-body proton-bicarbonate balance.

Weight reduction in boys with muscular dystrophy.

Many children with muscular dystrophy are overweight, and although weight control is pursued in some centres it is unusual to encourage severe dietary restriction for fear that it might lead to accelerated loss of muscle. In this study, two overweight boys with muscular dystrophy were monitored by whole-body nitrogen balance, total body potassium, strength and functional measurements during calorie restriction. Both patients were found to have a transient loss of nitrogen on commencing the low calorie intake: thereafter, weight loss was not found to have any deleterious effect on muscle bulk or function in either patient. It is suggested that controlled weight-reduction in obese children with muscular dystrophy is a safe and practical way of losing excess fat, which can improve mobility and self-esteem, and may possibly effect longevity.