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At least 919 records · Page 51Linked to original sources
PubMed2004

Soil functional responses to excess nitrogen inputs at global scale.

There is little evidence that nitrogen (N) cycling in the highly weathered, low-phosphorus (P), acidic soils found in Southern Hemisphere continents will differ greatly from that in North America and Europe. Evidence from the 'south' shows: the similarity in forms and temporal patterns in losses of N from different land uses; that the C:N ratios of the forest floor/litter layer from different continents are strongly predictive of a range of processes on a global scale; that generalizations based on Northern Hemisphere experience of the impact of N additions to 'P-limited' ecosystems are likely to fail for southern ecosystems where anatomical and physiological adaptation of native plants to low-P soils makes questionable the concept of 'P-limitation'; that the greatest threats in the 'south' are probably changes in land use that may greatly increase N inputs and turnover; that localized increases in N inputs produce similar effects to those seen in the 'north'.

Environmental Monitoring↗
PubMed1995

Establishing the criteria for anesthesia and other precautions for surgery during pregnancy.

Surgical procedures may be undertaken in the gravida with relatively little risk to the fetus or the continuation of pregnancy. The managing physician requires a thorough knowledge of the maternal physiologic adaptations to pregnancy to minimize maternal iatrogenic risks. The potential fetal effects of the planned procedure, diagnostic tests, therapeutic drugs, and anesthesia must be considered preoperative. Any potential fetal risks must be discussed with the patient and, in some cases, maternal need may obviate undertaking some procedures that place the fetus at some jeopardy. The outcome in most situations of surgery on the gravida is good for both the mother and the fetus.

Anesthesia, General↗
PubMed1975

The role of activity in anticipating and confronting stressful situations.

This paper is an analytical review of studies comparing stress reactions in threatening situations during which the person can or cannot take action. The studies reviewed were conducted mainly in real-life situations and involved diverse forms of coping activities under various conditions of danger and distress. To achieve a better understanding of the effect of activity on stress reactions, several distinctions are made: between various types of stress reactions; between various indices and measurements of stress reactions; between activity which is directly related to the source of threat and activity which is not; and between various personality dimensions. The adaptive potential of activity in stressful situations is discussed in terms of: the sense of mastery and control provided by activity; activity as a means of attention diversion; and activity as a means of discharging energy generated by mobilization. It is suggested that taking action under stressful conditions, as opposed to remaining passive, is a powerful coping tool.

17-Hydroxycorticosteroids↗
PubMedDate not supplied

Posttraumatic stress disorder and traumatic hand injuries: a neuro-occupational view.

Using the clinical phenomenon of posttraumatic stress disorder related to traumatic hand injuries, this article conceptually explores the theoretical construct of neuro-occupation on the basis of these conditions. Neuro-occupation is an evolving concept that combines knowledge and understanding of occupation with knowledge and understanding of how the human brain functions in environmental context; thus, the concept is important to the core of occupational therapy practice. The first section of the article introduces the concept of neuro-occupation; the second provides an overview of posttraumatic stress disorder and traumatic hand injury. To help therapists better understand behavior seen in clinical settings, the third section presents key neuro-occupational processes pertaining to posttraumatic stress disorder, using clinical application examples. Finally, a query about the value of neuro-occupation as a developing theoretical construct is put forth.

Adaptation, Physiological↗
PubMed1997

Animal well-being. II. Stress and distress.

The concepts of stress and distress are integral parts of consideration of animal well-being. Generally, stress refers to a state of threatened homeostasis, but precise clinical definitions, causes, and biological measurements have been controversial and confusing. Numerous factors associated with needs, life in captivity, threatening events, or aversive stimuli may threaten homeostasis. An animal's well-being or quality of life is an individual's internal somatic and mental state that is affected by what it knows or perceives; its feelings and motivational state; the responses to internal or external stimuli or environments; interacting variables; and phylogeny and ontogeny. Threats to homeostasis activate a complex pattern of behavioral changes and responses in the central and autonomic nervous and endocrine systems. Some responses can be considered normal adaptive and coping activities, satisfactorily handling the threats and therefore contributing to well-being. Other responses may be considered abnormal, maladaptive, and affective disorders. A persistent threat may lead to prolonged hyperactivity of the neuroendocrine system, which impairs rather than contributes to well-being. Except for extremes, differentiation between normal and abnormal internal states is frequently unclear. Individual adapting and coping styles may be more important than the stimuli in determining the varied responses. In animals, perception of a stimulus or life event is as important as the actual situation or environment. As caregivers, humans may know that an event or situation is no threat, but the animal usually does not function with the same information base as humans. A principal component in controlling an animal's response to an external event is determining how the animal perceives a situation. Mental and biological well-being is more likely to exist in animals if they are familiar with their environment, including social groups, and if they can predict or anticipate changes in the environment.

Adaptation, Physiological↗
PubMed2003

The influence of various physiological challenges on permanent changes to the cardiovascular system.

The concept of fetal programming provides an intellectual framework that links physiological adaptations that occur during development to permanent changes in postnatal regulatory systems. Recent research in the area of cardiovascular programming has highlighted the mechanisms by which these changes exert their effects. The aim of this review is to integrate some of the literature on nutritional changes, exposure to excess glucocorticoids and other challenges during development as they provide support for various mechanisms of programming of the cardiovascular system.

Animals↗
PubMed1991

The changing thermal response to endurance exercise during pregnancy.

This study was designed to test the hypothesis that the thermal response to endurance exercise is altered by the thermal adaptations to pregnancy. Accordingly, rectal temperature was monitored in 18 recreational athletes before, during, and after 20 minutes of continuous exercise before conception and every 6 to 8 weeks during pregnancy. Mean exercise intensity was 64% of VO2 max before conception and did not change during pregnancy. However, the peak rectal temperature reached during exercise decreased by 0.3 degrees C at 8 weeks and then fell at a rate of 0.1 degrees C per lunar month through the thirty-seventh week. This appeared to be related to changes in resting temperature, thermal mass, sweating threshold, and venous capacitance that began early in pregnancy. These data suggest that the magnitude of any exercise-associated thermal stress for the embryo and fetus is markedly reduced by the maternal physiologic adaptations to pregnancy.

Adult↗
PubMed1985

Modulation of aversively motivated learning in rats adapted to a cold stressor.

Two experiments studied effects of adaptation to cold water stress upon learning in two aversively motivated (shock) tasks. Experiment 1 found animals previously experiencing cold water stress exhibited more tolerance to shock, having shorter latencies, in an approach-avoidance conflict situation than non-treated controls. In Experiment 2, animals with previous cold water stress experience exhibited longer response latencies than controls in an active-avoidance task. These findings provide evidence that adaptation to a noncontingent stressor can modulate behavioral responses which suggest increased tolerance.

Adaptation, Physiological↗
PubMed2003

Response to thermal stress and personality.

Tolerance to cold and heat exposure shows large variations for which there is still insufficient explanation. On the other hand the relationship between the responses to mental stress and individual personality is well documented. The aim of this study was then to find if personality traits have some influence on the responses to environmental temperature exposure. A group of 20 young adults were exposed for 90 min to cold (10 degrees C) while skin temperature (Ts), oxygen consumption and discomfort rating were recorded. In a second experiment they were exposed to heat (40 degrees C) for 90 min when the sweat rate and the discomfort rating were recorded. Prior to these tests the Big Five Personality Test was used to measure the personality traits of the subjects. The results show significant negative correlation between neuroticism and the O(2) consumed, the discomfort rating and Ts for the test in the cold, while extraversion was positively related to O(2) consumption but not to Ts and discomfort rating. In response to heat, neuroticism predominance was associated with greater discomfort, reduced tolerance and diminished sweat rate. The discomfort rating, in this case, was negatively related to extraversion. It is proposed that the reduced O(2) consumption in the cold and the lower rate of sweating in the heat observed with neuroticism, are caused by enhanced activity of the sympathetic nervous system. Further investigation is required to assess the validity of this proposal. Overall, the present investigation shows that physical environmental stresses, in common with mental stress, could be in some ways related to personality traits.

Adaptation, Physiological↗
PubMed1992

Computer-assisted diagnosis and teaching of disorders of electrolyte, acid-base, and water metabolism.

Application of the tools of graphics, animation, sound and hypertext integrated with expert knowledge may help overcome the difficulties in teaching electrolyte and acid-base metabolism and its disorders. Using the Macintosh computer and the application, Hypercard we have developed two related programs with the following characteristics. Each contains graphic maps, consisting of a nomogram for plasma pH, PCO2 and HCO3 with zones representing physiological adaptation for each acid-base disorder (the Acid-Base map), and a nomogram illustrating relationships between plasma [Na+] and osmolality in hypo- and hypernatremic and hypo- and hypertonic states (the Sodium-Osmolality map). These are incorporated graphically and mathematically into each of the two Hypercard programs: The Acid-Base Diagnostician and The Osmotic Diagnostician. In the diagnostic module of each program, a differential diagnosis is developed for each of several zones on each map and, after obtaining additional user-entered clinical information, the program applies the relevant expert algorithms and presents the most likely diagnosis and differential diagnosis on screen and in printout. Each program has a teaching module involving text, hypertext, color graphics, digitized speech, and animation which demonstrate and discuss normal physiology, pathophysiology, and diagnostic criteria. The comprehensiveness and flexibility of the programs enable use by students at all levels, residents in medical and surgical disciplines, and physicians in many specialties.

Acid-Base Imbalance↗
PubMed2003

Science and cycling: current knowledge and future directions for research.

In this holistic review of cycling science, the objectives are: (1) to identify the various human and environmental factors that influence cycling power output and velocity; (2) to discuss, with the aid of a schematic model, the often complex interrelationships between these factors; and (3) to suggest future directions for research to help clarify how cycling performance can be optimized, given different race disciplines, environments and riders. Most successful cyclists, irrespective of the race discipline, have a high maximal aerobic power output measured from an incremental test, and an ability to work at relatively high power outputs for long periods. The relationship between these characteristics and inherent physiological factors such as muscle capilliarization and muscle fibre type is complicated by inter-individual differences in selecting cadence for different race conditions. More research is needed on high-class professional riders, since they probably represent the pinnacle of natural selection for, and physiological adaptation to, endurance exercise. Recent advances in mathematical modelling and bicycle-mounted strain gauges, which can measure power directly in races, are starting to help unravel the interrelationships between the various resistive forces on the bicycle (e.g. air and rolling resistance, gravity). Interventions on rider position to optimize aerodynamics should also consider the impact on power output of the rider. All-terrain bicycle (ATB) racing is a neglected discipline in terms of the characterization of power outputs in race conditions and the modelling of the effects of the different design of bicycle frame and components on the magnitude of resistive forces. A direct application of mathematical models of cycling velocity has been in identifying optimal pacing strategies for different race conditions. Such data should, nevertheless, be considered alongside physiological optimization of power output in a race. An even distribution of power output is both physiologically and biophysically optimal for longer ( > 4 km) time-trials held in conditions of unvarying wind and gradient. For shorter races (e.g. a 1 km time-trial), an 'all out' effort from the start is advised to 'save' time during the initial phase that contributes most to total race time and to optimize the contribution of kinetic energy to race velocity. From a biophysical standpoint, the optimum pacing strategy for road time-trials may involve increasing power in headwinds and uphill sections and decreasing power in tailwinds and when travelling downhill. More research, using models and direct power measurement, is needed to elucidate fully how much such a pacing strategy might save time in a real race and how much a variable power output can be tolerated by a rider. The cyclist's diet is a multifactorial issue in itself and many researchers have tried to examine aspects of cycling nutrition (e.g. timing, amount, composition) in isolation. Only recently have researchers attempted to analyse interrelationships between dietary factors (e.g. the link between pre-race and in-race dietary effects on performance). The thermal environment is a mediating factor in choice of diet, since there may be competing interests of replacing lost fluid and depleted glycogen during and after a race. Given the prevalence of stage racing in professional cycling, more research into the influence of nutrition on repeated bouts of exercise performance and training is required.

Bicycling↗
PubMed1990

Temperature regulation of young coypus (Myocastor coypus) in air and water.

Coypus (Myocastor coypus Molina) have recently colonized temperate regions of Europe in large numbers, originating from populations indigenous to subtropical regions of South America. Observations of coypu behavior in the wild and in enclosures under a temperate climate showed a preference for close proximity to water and frequent swimming bouts. Little change was observed in the semiaquatic habit in winter, despite high mortality during this period, particularly among young and adult male coypus. Evidence for constraints on thermal adaptation was sought from measurements in a thermostatic chamber of the resting metabolic rate (RMR) of young coypus caught from wild populations in France and of the body (Tb) and skin (Tsk) temperatures as a function of ambient temperature (Ta). A light heterothermic response with deep Tb falling by 0.8 degree C and stabilizing at a new level of 36.7 degrees C was observed in water and air at Ta below the lower critical temperatures. In common with other semiaquatic mammals, RMR (2.94 W/kg) was high relative to terrestrial mammals of equivalent body mass. Minimal thermal conductance was 0.10 W.kg-1.degree C-1 in air for Ta between -10 and +20 degrees C, and conductance varied in water from 0.24 to 1.18 W.kg-1.degrees C-1 for Ta between 5 and 35 degrees C. The physiological adaptations to cold and particularly the high insulative value of the fur (80-90% of the insulation) help to explain the successful extension of the coypu's range to temperate regions. Energetic costs were nevertheless high in cold water, suggesting that social factors may be implicated in severe winter mortality, particularly dominance hierarchy regulating the persistent use of water bodies even under freezing conditions.

Air↗
PubMed1994

The Vienna implantable centrifugal blood pump.

Because of the inherent disadvantages of membrane pumps, rotary pumps have been increasingly investigated in recent years. As a result of improving biocompatibility, extended assistance with implantable devices is of special interest. Questions arise concerning shear stress, blood traumatization, design of seals, and specific control conditions. In their development of an implantable impeller pump, the Vienna group studied the minimization of hemolysis and thrombus formation by means of numerical simulation, visualization, and in vitro blood evaluation. The latter was revealed to be the most powerful tool for pump evaluation. With optimization of geometry, a hemolysis of in vitro: IH = 0.008; MIH = 0.58; and in vivo: 2.1 to 3 mg% plasma-free hemoglobin could be obtained. For proper control and physiological adaptation, a controller based on a nonlinear and a fuzzy strategy was developed. Furthermore, a method for evaluation of the contractility of the assisted heart during nonpulsatile support was tested by computer simulation. This paper summarizes the evaluation methods used and provide an overview of the results of pump and controller design.

Animals↗