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Biomedical subjects

C Jessen

Publications and source records attributed to C Jessen.

At least 19 recordsLinked to original sources
PubMed1992

Evidence against brain stem cooling by face fanning in severely hyperthermic humans.

To achieve a hyperthermic state 11 subjects exercised at 35 degrees C air temperature in a water-impermeable outfit, until their oesophageal temperature (Tes) exceeded 39 degrees C. Changes of brain stem temperature were assessed by the interspike intervals of auditory evoked potentials, which depend on brain stem temperature. These were recorded at rest before exercise (condition A), after exercise during a period when heat loss from the face was prevented by covering the head with a plastic hood (condition B), and again during face fanning (condition C). An increase in Tes from 37.14 +/- 0.25 degrees C to 39.05 +/- 0.15 degrees C (A to B) produced a significant reduction in interspike intervals, indicating an increase in brain stem temperature. Changing from conditions B to C, Tes and interspike intervals remained constant, indicating no change of brain stem temperature in spite of face fanning. Thus, even in severely heat stressed humans face fanning is not able to lower brain stem temperature significantly below that of the rest of the body core.

Adult↗
PubMed1992

Effects of selective brain cooling on mechanisms of respiratory heat loss.

Experiments (n = 36) in three conscious goats were performed at 35 degrees C air temperature and low (LH) or high (HH) humidity. Prior to the experiments the animals received carotid loops and an arteriovenous shunt, which made it possible to increase the temperature of the blood flowing to head and trunk (series A), or to increase the temperature of the trunk at constant carotid blood and hypothalamic temperature (Thyp), respectively (series B). Owing to the smaller cooling power of the inspired air in HH, the slope of respiratory evaporative heat loss versus aorta blood temperature (Taor) was reduced in series A and B. In series A the slopes of respiratory minute volume (VE) and respiratory frequency (RF) versus Taor were larger in HH than in LH. The effects were caused by a reduction of selective brain cooling in HH, which resulted in higher levels of Thyp. This is concluded from the results of series B, in which Thyp was equal in LH and HH, and the slopes of VE and RF over Taor showed no differences. Thus, selective brain cooling contributes to counteract the deterioration of the gain of the respiratory heat loss mechanism, which occurs during exposure to humid air.

Animals↗
PubMed1992

No evidence for brain stem cooling during face fanning in humans.

The interpeak latencies (IPLs) of the acoustically evoked brain stem potentials depend on brain stem temperature. This was used to see whether face fanning during hyperthermia lowers brain stem temperature. In 15 subjects, three thermally stable conditions were maintained by a water bath. In each condition the IPLs were determined in 10 separate trials. In condition A esophageal temperature (Tes) was 36.9 +/- 0.3 degrees C and increased to 38.6 +/- 0.2 degrees C in condition B. In conditions A and B the head was enclosed in a ventilated hood (air temperature 38 degrees C, relative humidity 100%) to suppress any direct heat loss from the head. From conditions A to B the IPL at peaks I-V decreased by 0.146 ms/degrees C change in Tes, reflecting a change in brain stem temperature. In condition C the hood was removed and the face was fanned by a cold air-stream (8-15 degrees C, 4-10 m/s) to maximize direct heat loss from the head. Skin temperature at the sweating forehead decreased from 38 to 23 degrees C, whereas Tes in condition C was maintained at the same level as in condition B (38.5 +/- 0.2 degrees C). The IPL at peaks I-V showed no difference between conditions B and C. It is concluded that face fanning in hyperthermic subjects does not dissociate brain stem temperature from Tes.

Adult↗
PubMed1991

Threshold and slope of selective brain cooling.

Experiments (n = 50) in three conscious goats were performed in a thermoneutral environment to determine the threshold (i.e. the point at which the brain temperature is equal to the carotid blood temperature) and slope (i.e. the difference between brain and carotid blood temperatures as a function of carotid blood temperature) of selective brain cooling (SBC) and analyse the thermal inputs affecting them. Prior to the experiments the animals received carotid loops and an arteriovenous shunt to manipulate head and trunk temperatures independently of each other. The mean SBC threshold was 38.75 degrees C T(carotis) and independent of T(trunk). When body core temperature was increased from a hypo- to a moderately hyperthermic level, the SBC threshold was passed before metabolic rate had reached its minimum and before cutaneous vasodilation occurred. The mean SBC slope was 0.78 and rose with increasing Ttrunk. The degree of SBC was principally independent of respiratory heat loss: high levels of heat loss were found without SBC, and large degrees of SBC were observed at low levels of heat loss. The effect of SBC in and around normothermia is to smooth the onset of shivering or panting and to establish a range of internal temperature within which metabolic rate and respiratory heat loss are simultaneously at low levels.

Animals↗
PubMed1990

Effects of spinal cord temperature on the generation and transmission of temperature signals in the goat.

A series of 38 experiments were performed in five conscious goats at air temperatures of +20 degrees C or +30 degrees C to see whether a temperature dependence of spinal cord signal transmission affects the relationships between body temperature and metabolic rate (MR) or respiratory evaporative heat loss (REHL). Prior to the experiments the animals received peridural thermodes to clamp the spinal cord temperature by perfusion temperatures of 31 degrees C, 38 degrees C or 43 degrees C (45 degrees C), carotid loops to clamp the brain temperature at 39 degrees C or 39.5 degrees C, and arteriovenous shunts to alter the trunk temperature and to determine thresholds and slopes of MR and REHL over trunk temperature. The trunk temperature thresholds, at which MR and REHL increased, were inversely related to the spinal cord temperature, thereby confirming previous observations on the generation of specific spinal temperature signals. The slopes at which MR rose below the threshold, increased with decreasing spinal cord temperature. The slopes of REHL over trunk temperature were independent of spinal cord temperature. Both observations are at variance with previously observed temperature effects on hypothalamic signal transmission and imply that temperature-dependent signal transmission at the spinal level cannot account for nonlinear interaction of various body temperatures in the control of MR and REHL.

Animals↗
PubMed1990

Repeated exposures to cold and the relationship between skin and core temperatures in control of metabolic rate in the goat (Capra hircus).

1. After 10-12 experiments in each of three goats, in which skin or core temperatures were lowered while the other temperatures remained sufficiently high to prevent metabolic rate from increasing, the core temperature threshold of shivering was lowered by 0.35 degrees C. 2. After 10-15 experiments, in which skin and core temperatures were simultaneously lowered to induce major increases of metabolic rate, no further change of threshold was observed, while the slope of metabolic rate over core temperature was reduced. 3. It is concluded that repeated cold exposures without manifest shivering can induce tolerance adaptation to cold.

Adaptation, Physiological↗
PubMed1989

Non-cutaneous peripheral thermosensitivity in the goat (Capra hircus).

1. A 0.2 m2 area of the trunk skin was denervated and its center was externally cooled or warmed, when central body temperature was lowered. 2. When the denervated skin was cooled, the central body temperature, at which shivering occurred, was significantly higher than with warming of the denervated skin. 3. It is concluded that the difference was caused by temperature signals originating from thermoreceptors in tissue layers underneath the denervated skin.

Animals↗
PubMed1988

The metabolic response to skin temperature.

Experiments were done to assess that fraction of the metabolic response to external cold exposure, which is attributable to skin temperature. In 5 conscious and closely clipped goats the metabolic rate was determined at various stable levels of skin temperature in the range from 13 to 41 degrees C, while core temperature was kept constant at 38.8 degrees C. Skin temperature was manipulated by a rapidly circulating shower bath, while core temperature was controlled by means of heat exchangers acting on arterial blood temperature in a chronic arteriovenous shunt. The metabolic response to skin temperature fell into two clearly discernible sections: a first zone with skin temperatures above 25-30 degrees C, within which the metabolic rate rose at a rate of -0.34 +/- 0.07 W/kg.degrees C with decreasing skin temperature, and a second zone with skin temperatures below 25-30 degrees C, within which the metabolic rate either plateaued or even grew smaller with further decreasing skin temperature. It is concluded that the relationship between skin temperature and metabolic rate does not directly reproduce the temperature-response curve of cutaneous cold receptors but also reflects a complex interaction of several factors, including an unspecific temperature effect on muscle metabolism.

Animals↗
PubMed1988

Thermosensitivity of the goat's brain.

1. Experiments were done in conscious goats to estimate the gain of brain temperature sensors and to evaluate that fraction of the thermosensitivity of the entire brain which can be determined by a thermode located in the hypothalamus. 2. The animals were implanted with local thermodes, carotid loops and intravascular heat exchangers permitting independent control of hypothalamic temperature, extrahypothalamic brain temperature and trunk core temperature. 3. Small and slow ramp-like displacements of hypothalamic temperature generated continuously increasing thermoregulatory responses without any dead band, if a negative feed-back from extrahypothalamic sources was suppressed. 4. The hypothalamic sensitivity determined by the metabolic response to slow ramp-like cooling of the thermode amounted to -1.4 W/(kg degrees C) and equalled approximately 30% of what had been found for total body core sensitivity in another series of experiments. 5. Total brain thermosensitivity was -1.6 W/(kg degrees C), which implies that a large thermode centred in the hypothalamus can detect approximately 85% of the thermosensitivity of the entire brain.

Animals↗
PubMed1987

Work performance, thermoregulation and muscle metabolism in thyroidectomized goats (Capra hircus).

1. Thyroid hormone deficiency resulted in a markedly diminished work efficiency of goats exercising on a treadmill at an ambient temperature of 30 degrees C. 2. The close relationship between the exercise-induced increase in core temperature and the magnitude of evaporative heat loss, characteristic for intact animals, was nearly completely abolished after thyroidectomy. 3. Muscle glycogen utilization and lactic acid accumulation during exercise were enhanced in thyroidectomized animals in spite of the lower work rate and shorter duration of exercise in comparison with euthyroid goats.

Adenine Nucleotides↗
PubMed1987

No dynamic effector responses to fast changes of core temperature at constant skin temperature.

Experiments in conscious goats were done to see whether heat production and respiratory evaporative heat loss show dynamic responses to changing core temperature at constant skin temperature. Core temperature was altered by external heat exchangers acting on blood temperature, while skin temperature was maintained constant by immersing the animals up to the neck in a rapidly circulating water bath. Core temperature was altered at various rates up to 0.9 degrees C/min. Step deviations of core temperature from control values were always followed by a positive time derivative of effector response, but never by a negative time derivative during sustained displacement of core temperature. Ramp experiments showed that the slopes at which heat production or heat loss rose with core temperature deviating from its control level grew smaller at higher rates of change of core temperature. It is concluded that neither heat production nor respiratory evaporative heat loss respond to the rate of change of core temperature. At constant skin temperature, thermoregulatory effector responses appear to be proportional to the degree to which core temperature deviates from its set level.

Animals↗
PubMed1986

Effects of skin temperature on cold defense after cutaneous denervation of the trunk.

In intact goats the core temperature threshold below which heat production increases with falling core temperature, is inversely related to the temperature of the water bath in which they stand and is therefore assumed to be indicative of the central integration of signals from skin and core temperature receptors. The present study shows that a difference in core temperature thresholds for bath temperatures of 35 degrees C and 40 degrees C persisted after denervation of about two-thirds of the skin of the trunk and limbs. Also, for a given combination of skin and core temperatures, heat production was as great or greater after cutaneous denervation as before. It is concluded that, following denervation of the trunk and upper limbs, intact temperature receptors in the non-denervated skin of the legs and tail, and/or also in tissues between the skin and core, provide important and significant inputs to the temperature regulating system. But these inputs cannot explain fully the thermoregulatory responses observed unless it is assumed that the thermosensitivity of these tissues increased.

Acclimatization↗
PubMed1986

Skin and core temperatures as determinants of heat production and heat loss in the goat.

In 82 experiments on 10 goats body core temperature (Tcore) was altered between 35 degrees and 42 degrees C by external heat exchangers acting on blood temperature while skin temperature (Tskin) was maintained constant, by a circulating shower bath, at different levels between 32 degrees and 44 degrees C. At all skin temperatures at least fourfold increases of heat production (M) and respiratory evaporative heat loss (REHL) occurred when Tcore was lowered or raised, respectively. The lower Tskin was, the higher were the thresholds of Tcore, at which M or REHL exceeded resting levels. The lower Tskin was, the higher were the slopes, at which M or REHL changed per unit of Tcore. At a given Tskin, the slopes decreased with increasing M or REHL, and were dependent on the range of Tcore. The higher the range of Tcore, the steeper changed M and REHL with changing Tcore, if all other variables were held constant. The results support the concept that an exponential relationship between Tcore and the rate of core temperature signals is the primary cause of the effects exerted by Tskin on the slopes, at which M or REHL change per unit of Tcore.

Animals↗
PubMed1986

Effects of brain and trunk temperatures on exercise performance in goats.

In 40 experiments on seven goats head and trunk temperatures were altered independently of each other and the effects on exercise performance on a treadmill (speed: 3 km/h, slope: 16%-20%) were observed. Brain temperature between 38.5 degrees C and 42.0 degrees C and trunk temperature between 39 degrees C and 43.5 degrees C did not reduce exercise performance or running time. Blood lactate concentration increased with rising brain and trunk temperatures, but did not exceed 13.1 mmol/l-1. Blood pressure and heart rate did not show any dependence on brain or trunk temperatures. Brain temperature between 42.0 degrees C and 42.9 degrees C shortened running time in 3 out of 12 experiments and reduced performance during shortlasting upward deviations of temperature. This suggests that in this species, the thermal safety limit to exercise is very close to that range of temperature which is likely to induce heat stroke.

Animals↗
PubMed1986

Competition for cool nasal blood between trunk and brain in hyperthermic goats.

An influence of brain and trunk temperatures controlled independently of each other by means of artificial heat exchangers, on the intensity of natural selective brain cooling (SBC) was studied in 6 conscious goats. Intensity of SBC was markedly enhanced by increasing brain temperature. On the other hand, a rise of trunk temperature with the cerebral temperature clamped at 39 degrees C or 40 degrees C, reduced SBC intensity in spite of a simultaneous increase in the respiratory evaporative heat loss. When brain temperature was clamped at 41 degrees C, the magnitude of SBC was essentially independent of trunk temperature. These results suggest that during hyperthermia a competition exists between trunk and brain for cool nasal blood.

Animals↗
PubMed1985

Skin AVA and capillary dilatation and constriction induced by local skin heating.

In conscious sheep, total femoral blood flow and flow through arteriovenous anastomoses (AVAs) and capillaries (CAP) in skin of the hindleg were measured employing electromagnetic and radioactive microsphere techniques. Core temperature (Tc) was manipulated using intravascular heat exchangers and hindleg skin temperature (Tsk) was manipulated by immersion in temperature controlled water. With Tc set 1 degree C above normal, AVA flow was highest at the lowest Tsk tested (34 degrees C); AVAs progressively constricted as Tsk was increased from 34 to 40-41 degrees C, then dilated again as Tsk reached the highest levels tested (42-44 degrees C). Skin CAP flow was not altered by Tsk of 34 to 42 degrees C but was increased at a Tsk of 44 degrees C. Therefore total skin blood flow followed essentially the same pattern as AVA flow; total femoral flow also followed this pattern. When Tc was set 0.5 degrees C below normal, AVA flow was low at all levels of Tsk. It is concluded that Tc plays a dominant role in control of skin blood flow, however, once Tc is at a level requiring increased heat loss, Tsk exerts an extremely potent influence on the nature and magnitude of changes in skin blood flow. The pattern of flow changes appears to reflect principally a negative feedback mechanism aimed at maintaining Tsk at approximately 40 degrees C; this may contrast with mechanisms associated with sweating and/or active vasodilatation in other species.

Animals↗
PubMed1985

Use of fibrin glue in thoracic surgery.

The results of closure of various types of postoperative thoracic fistulas with two-component fibrin sealant in 5 patients are presented. The use of a new technique for the noninvasive closure of bronchial fistulas with fibrin sealant is also described. Implications of the management of thoracic fistulas with fibrin sealant are discussed.

Aged↗