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Biomedical subjects

K Brück

Publications and source records attributed to K Brück.

At least 19 recordsLinked to original sources
PubMed1996

Comparison of thermoregulatory characteristics of patients with intra- and suprasellar pituitary adenomas.

Thermoregulatory capabilities under physiologic cold and heat exposure of 37 patients with suprasellar pituitary adenomas (As) and 10 patients with intrasellar adenomas (Ai) were analyzed and compared to each other and to 13 controls (Ctr.) In Ai no shift of the thermoregulatory threshold temperatures was observed. In As the regulation was shifted to a 0.5 degrees C higher mean body temperature in 82% of the patients, indicating a "set-point" elevation. The accuracy of the regulation against thermal loads was maintained, the velocity was reduced. Postoperative examination of As revealed a normalisation of the "set-point". Modifications of the hypothalamic amine systems by the compressive effect of the suprasellar adenomas are discussed to be the most probable cause for the observed thermoregulatory alterations.

Adenoma↗
PubMed1995

Temperature effects on ventilatory rate, heart rate, and preferred pedal rate during cycle ergometry.

According to the most customary exercise protocols, core temperature (Tc) rises in parallel with workload (WL) and experimental time. Physiological variables, however, may be related to each of these factors. To investigate effects of WL independent of experimental time and body temperature, we employed four moderate WLs in 4-min steps between 35 and 65% peak O2 uptake (VO2 peak) in randomized order. To investigate independent effects of body temperature, the same work protocol was performed both after resting in comfortable ambient temperature [control test (Cont)] and after a double cold exposure [precooling test (Pret)], where Tc and the temperature set point are decreased by approximately 0.6 and 0.3 degrees C, respectively. Eight male subjects (24 +/- 1.9 yr, VO2 peak 4.9 +/- 0.5 l/min) worked on a cycle ergometer in a climatic chamber. Heart rate (HR) and breathing frequency (BF), but not preferred pedal rate (PR), were positively correlated to Tc, the slopes amounting to 17 and 3.75 min-1/degree C for HR and BF, respectively. The regression appeared linear over the whole temperature range, and the regression lines were not shifted by precooling. PR was increased by time, but Pret-Cont differences of PR and Tc were inversely correlated (r = -0.50, P < 0.01). The effects of WL were highly significant on HR, O2 uptake, and rate of perceived exertion but not on BF, PR, and sweat rate. The relation of rate of perceived exertion to HR was shifted by precooling.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Modifications of thermoregulation in patients with suprasellar pituitary adenomas.

Thermoregulation was investigated pre and postoperatively in 5 and only preoperatively in 7 patients with suprasellar pituitary adenomas by exposing them to external cold and heat in a climatic chamber. Five healthy subjects served as controls. Body core and skin temperatures, oxygen consumption, electromyographic activity, skin blood flow and local sweating rates were continuously measured. Threshold temperatures for activation of heat production and heat loss were calculated from these data. Hormone analysis was performed before and after stimulation with releasing factors. In the patients, core temperatures as well as threshold temperatures for heat production and heat loss were elevated by about 0.5 degrees C as compared with controls. This elevation of core and threshold temperatures was achieved, despite a reduced resting metabolic rate, by a reduction of skin blood flow indicated by a low mean skin temperature. After successful operation the thermoregulatory alterations normalized. Serum levels of growth hormone were reduced preoperatively and stimulation by GHRF did not cause an appropriate increase. Prolactin was elevated in 6 patients with prolactinomas, but there was no correlation with changes in thermoregulatory threshold temperatures. Stimulation of the other hypophyseal hormones by the combined anterior pituitary function test revealed a normal hormonal response. Apart from prolactin there were no significant hormonal changes postoperatively. It is concluded that disturbances of temperature regulation are present in patients with suprasellar adenomas, but that they are not detectable by routine clinical methods. These alterations probably depend on a disturbance of hypothalamic function and are reversible by surgery.

Adenoma↗
PubMed1990

Cardiac responses to the Valsalva manoeuvre in different body positions.

A standardized Valsalva manoeuvre (VM) with a 15-s straining period was repeated in each of four postures by six male subjects. The postures were supine (SUP), sitting leaning back (LB), sitting leaning forward (LF) and standing (ST). During straining, the increase in heart rate (fc) was different between LB and LF (+50% and +23%, respectively P less than 0.05). The decrease in stroke volume (SV), which was monitored by means of impedance cardiography, was different (63%, 68%, 39%, and 72%, P less than 0.001) as well as the decrease in cardiac output (CO) (55%, 53%, 26%, and 61%, P less than 0.001) in SUP, LB, LF, and ST, respectively. Accordingly, after pressure release the smallest changes of SV, fc and CO were found in LF. In conclusion, cardiovascular stability during straining was increased during LF. Consequently, this posture would appear to be superior to other postures during unavoidable VM (weight lifting and defaecation). To perform tests on autonomic function LB would appear to be superior to the other postures because of the large autonomic responses, combined with minimum risk for the subject. The impedance method provided simple and reproducible determinations of SV changes during VM.

Adult↗
PubMed1989

Comparison of energy expenditure by the doubly labeled water technique with energy intake, heart rate, and activity recording in man.

Average daily energy expenditure determined by the doubly labeled water technique (dlwEE) was compared in six subjects (aged 20-30 y) over 2 wk under usual living conditions; average food energy intake and energy expenditure estimated from individual diary records of physical activity. In addition, energy expenditure was estimated from 24-h heart rate recordings carried out on two randomly chosen days of the 2-wk period. The group means of the dlwEE were 1.94 +/- 0.24 (means +/- SD) times larger than resting metabolic rate (= 1.94 met) and nearly identical to the average daily energy intake (1.93 +/- 0.23 met). Energy expenditure estimated from the diaries of activity and from the 24-h heart rate recording varied between 1.67 and 2.24 met depending on the calculation procedure. The dlwEE (1.94 +/- 0.24 met) is much higher than that recently determined for sedentary people (1.25 met) and thus explains that young students may achieve body weight balance with a relatively high daily food energy intake.

Adult↗
PubMed1988

Thermoregulatory, cardiovascular, and muscular factors related to exercise after precooling.

The effect of slightly lowered body temperature on endurance time and possibly related physiological factors was studied in seven male volunteers exercising on a cycle ergometer at an ambient temperature (Ta) of 18 degrees C. Work load was increased to 40% in a stepwise manner (phase I, min 0-16) followed by a period at 80% of peak oxygen consumption (VO2) sustained to exhaustion. On one day, exercise was preceded by a double cold exposure (precooling test, PRET), resulting in a 204-kJ/m2 negative heat storage and a 4 and 0.2 degrees C lower mean skin and core temperature at the start of exercise compared with the control test (CONT). Core temperature dropped further during exercise in PRET. Endurance time at 80% of peak VO2 was increased by 12% (P less than 0.05) in PRET. Heart rate (HR) was decreased throughout PRET (P less than 0.05); oxygen pulse and arteriovenous O2 difference were significantly increased in phase I of PRET, whereas the PRET-CONT differences in stroke volume and cardiac output were not significant. In phase II of PRET (min 16-28, heavy exercise) sweat rate (SR) and heat conductivity, indicating forearm blood flow, were lower (-39%, P less than 0.001; -37%). Pedal rate (PR) was 9% lower (P less than 0.01) in phase II of PRET. At the termination of exercise, PRET-CONT differences in HR, SR, and PR had disappeared.

Adult↗
PubMed1987

Adaptive changes in thermoregulation and their neuropharmacological basis.

Adaptive changes of the thermoregulatory system include morphological and functional modifications. The morphological modifications such as changes in body shape and insulation need time periods of months to years to develop, unless they are genetically fixed and appear seasonally. In general, they are preceded by functional modifications, including changes in capacity of the effector systems and changes in regulatory characteristics, which need much less time to develop. These early changes in regulatory characteristics, which can be defined as deviations in threshold and gain of the thermoregulatory responses, have been described and subdivided into short-term (minutes) and long-term (weeks) modifications. Evidence for the participation of monoaminergic brain stem systems in these modifications has been reviewed. On the basis of recent insights into the organization of the thermoregulatory system, and of evaluation of experimental evidence from electrophysiological, neuropharmacological, and neuroanatomical studies it can be concluded that these systems are involved in adaptive modifications. Receiving information from several sensory systems they seem to deliver additional modulatory signals, which may interfere with the processing of specific thermal information at several sites. Theoretically, the central monoamines may participate in the control of thermal input, in the central integration of thermal signals, and in modification of output signals to thermoregulatory effectors. Best documented is their modulatory action on thermosensitive and thermointegrative hypothalamic neurons. There, the monoamines 5-hydroxytryptamine and noradrenaline act as antagonists, which enhance or diminish the effects of thermal afferents mediated by other transmitters. Moreover, the antagonistic monoaminergic systems are interconnected and can influence each other at the level of lower brain stem. The activity in central monoaminergic systems can also be modified by neurohumoral feedback mechanisms from the periphery. By means of these interrelations the vegetative responses of the organism can be corrected and optimized. These interrelations can explain also some cross-adaptive changes in the thermoregulatory threshold for shivering evoked by nonthermal factors such as food intake or long-distance running.

Adaptation, Physiological↗
PubMed1987

Body temperature related factors diminishing the drive to exercise.

The effects of slightly below-normal body temperatures (delta Tcore-0.5 to 1 degree C) on exercise performance were examined in four series of studies employing a standardized precooling maneuver. In both the precooling tests and the control tests the subjects exercised on a cycle ergometer at an ambient temperature of 18 degrees C with the following results. In series 1, the subjects were exercising at a heart rate of 120 beats X min-1. Work rate and oxygen pulse were significantly increased, and sweat rate was less elevated in precooling tests than in controls. In series 2, in 12 well-trained rowers subjected to an incremental performance test, maximum work rate, peak VO2, time to exhaustion, and total work were not reduced in precooling tests. Eight well-trained rowers in series 3 were requested to work as hard as possible for 1 h. The mean work rate, VO2, and oxygen pulse were increased in the precooling tests by 6.8, 9.6, and 5.6%, respectively, whereas the sweat rate was 20% lower. In series 4 after a 16-min period of easy exercise (phase 1) the subjects exercised at a work rate corresponding to 80% VO2max up to exhaustion. Endurance time at this work rate was increased in precooling tests by 12% (18.5 vs. 20.8 min, p = 0.035). Heart rate was lower throughout the exercise period in precooling tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Body Temperature↗
PubMed1986

Effects of passive heat adaptation and moderate sweatless conditioning on responses to cold and heat.

Two series of experiments were performed in physically untrained subjects. In series A (heat adaptation, HA), seven male subjects were adapted to dry heat (five consecutive days at 55 degrees C ambient air temperature (Ta) for 1 h X day-1) under resting conditions. Before and after HA, the subjects' shivering responses were determined in a cold test (Ta + 10 to 0 degrees C). In series B, eight male subjects underwent mild exercise training (five consecutive days at a heart rate, HR, of 120 b X min-1) under Ta conditions individually adjusted (Ta + 15 to +5 degrees C) to prevent both sweating and cold sensations. Before and after "sweatless training", the subjects were subjected to a combined cold and heat test. During HA the thresholds for shivering, cutaneous vasodilatation (thumb and forearm) and sweating were shifted significantly (p less than 0.05) towards lower mean body temperatures (Tb). The mean decrease in threshold Tb was 0.36 degrees C. "Sweatless training" resulted in a mean increase in work rate (at HR 120 b X min-1) and oxygen pulse of 13 and 8%, respectively. However, "sweatless training" did not change the threshold Tb for shivering or sweating. Neither HA nor "sweatless training" changed the slopes of the relationships of shivering and sweating to Tb. It is concluded that the previously reported lowering of shivering and sweating threshold Tb in long-distance runners is not due to an increased fitness level, but is essentially identical with HA. The decreased shivering threshold following HA is interpreted as "cross adaptation" produced by the stressors cold and heat.

Adaptation, Physiological↗
PubMed1985

Influence of menstrual cycle on shivering, skin blood flow, and sweating responses measured at night.

In 10 women, external cold and heat exposures were performed both in the middle of luteal phase (L) and in the early follicular phase (F) of the menstrual cycle. Serum progesterone concentrations in L and F averaged 46.0 and 0.9 nmol X l-1, respectively. The experiments took place between 3:00 and 4:30 A.M., when the L-F core temperature difference is maximal. At neutral ambient temperature, esophageal (Tes), tympanic (Tty), rectal (Tre), and mean skin (Tsk) temperatures averaged 0.59 degrees C higher in L than in F. The thresholds for shivering, chest sweating, and cutaneous vasodilation (heat clearance technique) at the thumb and forearm were increased in L by an average of 0.47 degrees C, related to mean body temperature [Tb(es) = 0.87Tes + 0.13 Tsk] and to Tes, Tty, Tre, or Tsk. The above-threshold chest sweat rate and cutaneous heat clearances at the thumb and forearm were also enhanced in L, when related to Tb(es) or time. The metabolic rate, arm blood flow, and heart rate at thermoneutral conditions were increased in L by 5.0%, 1.1 ml X 100 ml-1 X min-1, and 4.6 beats X min-1, respectively. The concomitant increase in threshold temperatures for all autonomic thermoregulatory responses in L supports the concept of a resetting of the set point underlying the basal body temperature elevation in L. The effects of the increased threshold temperatures are counteracted by enhanced heat loss responses.

Analysis of Variance↗
PubMed1985

Influence of menstrual cycle on thermoregulatory, metabolic, and heart rate responses to exercise at night.

Ten women [mean maximal O2 uptake (VO2max), 2.81 l X min-1] exercised for 15 min on a cycle ergometer in the middle of the luteal phase (L) and in the early follicular phase (F) of the menstrual cycle at the same constant work rates (mean 122 W) and an ambient temperature of 18 degrees C. Serum progesterone averaged 44.7 nmol X l-1 in L and 0.7 nmol X l-1 in F. After a 4-h resting period, exercise was performed between 3 and 4 A.M., when the L-F core temperature difference is maximal. Preexercise esophageal (Tes), tympanic (Tty), and rectal (Tre) temperatures averaged 0.6 degrees C higher in L. During exercise Tes, Tty, and Tre averaged 0.5 degrees C higher. The thresholds for chest sweating and cutaneous vasodilation (heat clearance technique) at the thumb and forearm were elevated in L by an average of 0.47 degrees C, related to mean body temperature (Tb(es) = 0.87Tes + 0.13Tskin), Tes, Tty, or Tre. The above-threshold chest sweat rate and cutaneous heat clearances were also increased in L. The mean exercise heart rate was 170.0 beats X min-1 in L and 163.8 beats X min-1 in F. The mean exercise VO2 in L (2.21 l X min-1) was 5.2% higher than in F (2.10 l X min-1), the metabolic rate was increased in L by 5.6%, but the net efficiency was 5.3% lower. No significant L-F differences in the respiratory exchange ratio and postexercise plasma lactate were demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Basal Metabolism↗
PubMed1981

Effect of a precooling maneuver on body temperature and exercise performance.

Twelve subjects exercised to exhaustion at an ambient temperature of 18 degrees C on a bicycle ergometer with the load being stepwise increased. On one day, exercise was preceded by a precooling maneuver. In the precooling tests, deep body temperature attained values of about 1 degree C lower than in the control tests. There was no indication of metabolic cold defense reactions being evoked throughout the exercise period. In the precooling tests, heart rate was significantly lower than in the controls, but the mean maximum work rate, peak oxygen uptake (VO2), time to exhaustion, and total work were not reduced, i.e., work rate and VO2 were increased for a given heart rate. In the three subjects with the lowest maximum work rates, total work and exhaustion time and, in two cases, maximum work rate were increased after precooling. The onset of sweating occurred at higher work rates but at lower core, mean skin, and mean body temperature after precooling. However, the accumulated sweat secretion was considerably smaller after precooling, indicating less thermoregulatory effort.

Body Temperature↗
PubMed1980

Thermoregulatory noradrenergic and serotonergic pathways to hypothalamic units.

1. In guinea-pigs hypothalamic single units were extracellularly tested for their response to thermal stimulation of the skin and to electrical stimulation of two different pontine areas, the nucleus raphé magnus and the dorsomedial reticular formation. Furthermore, thermoregulatory control actions were measured during the stimulations.2. Electrical stimulation of those reticular formation areas containing noradrenaline cells caused an increase of oxygen uptake, electrical muscle activity and body temperature, while stimulation of the nucleus raphé magnus, known to contain serotonin cells, brought about inhibition or had no effect.3. The recorded units could be subdivided into three groups. Cell type a. Neurones on the boundary of preoptic and anterior hypothalamic regions which increased their firing rate when the skin was cooled and decreased it when the nucleus raphé magnus was stimulated. Cell type b. Neurones in the anterior hypothalamus which did not respond to brain-stem stimulation. Cell type c. More posterior neurones which increased their firing rate when the skin was warmed or when the nucleus raphé magnus was stimulated and decreased their firing rate when the reticular formation was stimulated.4. Cell type a seems to represent interneurones which are connected to the ascending serotonergic thermoregulatory pathway. As for cell type c, it is inferred that it could represent interneurones which control the threshold for shivering and non-shivering thermogenesis.

Action Potentials↗
PubMed1980

Experimental investigations on the trigger mechanism of the generalized type of heat and cold urticaria by means of a climatic chamber.

The physical conditions of challenge were investigated in a climatic chamber on 8 patients with cholinergic urticaria and 10 patients with generalized cold urticaria. The cholinergic urticaria was induced by passive or active (physical exercise) heating and psychological stimulation; the generalized cold urticaria was induced by general cooling at rest and during physical effort. The ambient temperature was varied, and the mean body temperature was recorded continuously at different measuring points. The experiments revealed that in both types of urticaria the physical trigger mechanism seems to be strictly related to thermoregulatory processes; the crucial point is neither the actual temperature of the skin surface, the average skin temperature, nor even the "core" temperature, but a rise or fall in the weighted average body temperature. In cholinergic urticaria it was not relevant whether skin lesions were provoked by passive heating of the body at rest (sauna-like conditions) or by active heating at low ambient temperature. A basically different challenge mechanism must be assumed therefore in the generalized type of heat and cold urticaria, in contrast to their localized contact types.

Body Temperature↗
PubMed1976

Effects of electrical stimulation in the lower brainstem on temperature regulation in the unanaesthetized guinea-pig.

Electrical stimulation in lower brainstem areas presumed to be parts of the ascending noradrenergic system was carried out in the unanaesthetized guinea-pig. In the same animals noradrenaline (NA) was also injected into the anterior hypothalamus. Certain points in the lower brainstem were found, the stimulation of which resulted in a rise of oxygen uptake (more than 60% over the resting level), of body temperature and of electrical muscle activity at an ambient temperature of 29-30 degrees C. Respiratory rate also rose on stimulation, while heart rate did not show a consistent change. All these changes were found to be very similar to those obtained after an intrahypothalamic injection of NA. When the electrical stimulations at the same sites were repeated several times the extent of rise in oxygen uptake became gradually smaller, amounting to only half of the initial response after four periods of stimulation. An intrahypothalamic injection of NA restored the effectiveness of electrical stimulation in the lower brainstem to the original extent. These results suggest that the thermogenesis evoked by the electrical stimulation of these lower brainstem areas may be ascribed to the activation of ascending noradrenergic pathways terminating in the hypothalamus.

Animals↗