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At least 73 records · Page 4Linked to original sources
PubMed1987

Acute hypothalamic-pituitary-adrenal responses to the stress of treadmill exercise. Physiologic adaptations to physical training.

To study the effects of physical conditioning on the hypothalamic-pituitary-adrenal axis, we examined the plasma ACTH, cortisol, and lactate responses in sedentary subjects, moderately trained runners, and highly trained runners to graded levels of treadmill exercise (50, 70, and 90 percent of maximal oxygen uptake) and to intravenous ovine corticotropin-releasing hormone (1 microgram per kilogram of body weight). Basal evening concentrations of ACTH and cortisol, but not of lactate, were elevated in highly trained runners as compared with sedentary subjects and moderately trained runners. Exercise-stimulated ACTH, cortisol, and lactate responses were similar in all groups and were proportional to the exercise intensity employed. These responses, however, were attenuated in the trained subjects when plotted against applied absolute workload. Only the highly trained group had diminished responses of ACTH and cortisol to ovine corticotropin-releasing hormone, consistent with sustained hypercortisolism. We conclude that physical conditioning is associated with a reduction in pituitary-adrenal activation in response to a given workload. Alterations of the hypothalamic-pituitary-adrenal axis consistent with mild hypercortisolism and similar to findings in depression and anorexia nervosa were found only in highly trained runners. Whether these alterations represent an adaptive change to the daily stress of strenuous exercise or a marker of a specific personality profile in highly trained athletes is unknown.

Adaptation, Physiological↗
PubMedDate not supplied

A physiological adaptation to undernutrition.

A total of 432 children under the age of 10 years were measured for height and weight, and the morbidity and mortality indices were studied in six counties of the maize region of the state of Yucatán, Mexico. Undernutrition, because of its relationship to morbidity and mortality, was considered an important selection factor operating between the ages of 6 and 24 months. It was also observed that short stature was an adaptive response to the first years of undernutrition, that allowed children to maintain an adequate body weight under conditions of nutritional stress during the first 10 years of life.

Acute Disease↗
PubMed1979

Effect of a low protein diet during pregnancy of the rhesus monkey. II. Physiological adaptation of the infant.

Heart rate, respiratory rate, and ability to maintain body temperature were evaluated in six infants born to rhesus monkeys that had been fed a low protein diet throughout pregnancy. All infants were kept in incubations equipped with a "servo" control thermal unit that maintained the infants' skin temperature at 37.0 C (98.6 F). The thermal units were disconnected and the infants were exposed to room temperature (approximately 27 C) for 6-hr periods each day after 24 hr of age in order to determine the efficiency of thermal control mechanism. The thermal servo control units were "on" for a longer period of time in experimental animals than in control animals during the first 24 hr of life. Infants from mothers fed the low protein diets were also less able to maintain their own body temperatures after exposure to room temperature. This function was seriously compromised in two of the six experimental infants. The compromised temperature control mechanism seen in these infant monkeys is a serious and potentially lethal side-effect of protein-calorie malnutrition during pregnancy. The possible relationship of inadequate maternal nutrition to the inefficient thermal mechanism of certain "high risk" human newborns should be reevaluated.

Adaptation, Physiological↗
PubMed1977

Human physiological adaptability through the life sequence.

Changes in organ function from birth to old age were investigated from published data. In essence, the observations of Shock and colleagues on maximal breathing capacity, vital capacity, glomerular filtration rate, renal plasma flow, basal metabolic rate (BMR), ulnar nerve conduction velocity, cardiac index, and intracellular water (ICW) for the age period 30 to 85 years were extended to the time of birth. There were two principal findings. First, with the exception of BMR and ICW, these functional indices increased from a low point at birth to a maximum between 3 and 20 years of age and then after 30 years declined progressively to 85 years; BMR declined from a maximum in infancy and ICW peaked at about 30 years and then declinded. Second, the coefficient of variation increased regularly from birth to old age. Because the peak of organ function coincided with the period of minimal mortality, the curve of organ function across the life sequence was considered to represent changes in adaptive capacity. Supporting evidence from studies of physical fitness, thermoregulation, and seasonal change of mortality was considered. It was concluded that these shifts in adaptive capacity between birth and old age were fundamental baselines for investigations of the epidemiology of health.

Adaptation, Physiological↗
PubMed2002

Endothelial response to hypoxia: physiologic adaptation and pathologic dysfunction.

When subjected to a period of oxygen deprivation, endothelial cells exhibit a characteristic pattern of responses that can be considered either adaptive or pathologic, depending on the circumstances. In this review, the molecular basis for these responses is detailed. Hypoxia shifts the endothelial phenotype towards one in which anticoagulant properties are diminished, permeability and leukoadhesivity are increased, and proinflammatory features dominate the endovascular milieu. Of all the different points of intersection between the coagulation and inflammatory axes in the vasculature, perhaps most fundamentally, hypoxia alters several key transcriptional factors, including early growth response gene 1 (Egr1) and hypoxia-inducible factor (HIF) 1, which coordinate separate programs of gene activation. The preponderance of forces in the hypoxic endovascular environment, perhaps designed as an evolutionary adaptation to oxygen deprivation, can trigger severe, pathologic, clinical consequences in the setting of tissue ischemia.

Adaptation, Physiological↗
PubMed1986

Physiological adaptation to physical conditioning. Old problems revisited.

Three classical problems in the field of man's adaptive response to exercise are reviewed. A case is made for the pump capacity of the heart limiting maximal oxygen uptake in man. This conclusion is based on findings that the capacity of skeletal muscle of man markedly surpasses that of the heart supplying it with a flow and thereby oxygen. It is suggested that only one third of the muscle mass of man can fully tax the capacity of the heart and consume the oxygen delivered by the heart. If a larger muscle mass is intensely engaged in the exercise, vasoconstriction must occur in the arterioles of the exercising limbs to avoid a reduction in blood pressure. Evidence is presented that a decrease in heart rate at submaximal exercise-observed after a period of physical conditioning, is caused by an altered autonomic chronotropic activity to heart, which most likely is due to a less potent feed back reflex from exercising muscles. The enlarged stroke volume is secondary to a larger diastolic filling, which via a Frank-Starling mechanism results in an elevation in the stroke volume. Last, it is argued that the altered metabolic response to exercise after physical conditioning, i.e. the larger lipid oxidation and reduced lactate production, results from local regulatory mechanisms rather than from changes in supply of oxygen, substrates, or hormones. Further, the muscle metabolic response to exercise is thought to play a major role in modulating systemic cardiovascular regulation in exercise.

Adaptation, Physiological↗
PubMed1991

Lack of physiological adaptation of the atrioventricular interval to heart rate in patients chronically paced in the AAIR mode.

Seventeen consecutive patients, aged 56 +/- 12, were chronically paced in the AAIR mode for a symptomatic sinus node disease with atrial chronotropic incompetence defined by a peak exercise heart rate (HR) less than 75% of the maximal predicted heart rate (MPHR) mean = 65 +/- 10%). Sensors used were activity sensing (n = 7), minute ventilation (n = 6), or respiratory rate (n = 4). Basic pacing rate was programmed at 71 +/- 5 beats/min and the maximal sensor rate at approximately 85% MPHR (143 +/- 10); other sensor parameters were programmed individually. Six months after implant, two standardized and symptom limited exercise tests were performed in random order, AAI and AAIR modes, respectively. AAIR pacing significantly improved peak exercise HR (139 +/- 14 vs 112 +/- 30 beats/min; P less than 0.01), maximal sustained workload (132 +/- 42 vs 110 +/- 38 watts; P less than 0.02), and total exercise duration (724 +/- 299 vs 594 +/- 245 sec; p less than 0.02) compared to the AAI mode. In all 17 patients, HR was continuously sensor driven in the AAIR mode, making it possible to precisely study the adaptation of the stimulus-R interval and of the stimulus-R:RR ratio during exercise. Six patients normally adapted with a progressive shortening. Six others did not adapt at all without any variation of interval. Five patients paradoxically increased their stimulus-R interval (286 +/- 10 msec at peak E vs 220 +/- 19 msec at rest) and their stimulus-R:RR ratio (67 +/- 20% vs 29 +/- 4%), producing P waves occurring immediately after, or even within the R wave of the preceding cycle; two patients complained of severe exercise related symptoms corresponding to the so-called "AAIR pacemaker syndrome." The principal factors involved in the nonadaptation of AV interval to HR were related to the patient (organic heart disease, with the particular problem of the denervated heart; the bradytachy syndrome; and the use of drugs, especially beta blockers and Class I antiarrhythmic drugs) or to the pacemaker ("overstimulation" phenomenon). These observations constitute an additional argument for wider indications of implanting DDDR units in these patients.

Adaptation, Physiological↗