Trimix instead of air, decreases the effect of short-term hyperbaric exposures on platelet and fibrinolysis activation.

PURPOSE: Short-term and saturated simulated dives followed by decompression with air, cause a decrease in platelet count and increased activation of fibrinolysis. The aim of this study was to determine whether short-term dives with trimix as a breathing mixture induce the activation of platelets, and/or fibrinolysis. MATERIAL AND METHODS: 30 male divers were subjected to short-term hyperbaric exposures to 0.7 MPa. Thirty divers used air and then the same divers used trimix as a breathing mixture. RESULTS: The mean platelet count dropped significantly after decompression only in the group breathing air. The number of CD62P positive platelets and the amount of platelet-derived micro particles were statistically significant higher after decompression in both exposures. The number of CD61 positive platelets increased significantly only in the group breathing air. We observed a significant decrease of factor XII and fibrinogen concentrations after decompression only in the group breathing air. A significant increase in the concentration of plasminantiplasmin complex in both groups was detected. CONCLUSIONS: Short-term hyperbaric exposure and decompression performed according to current safety standards activates platelets and the fibrinolytic system. Trimix protects divers from a reduction in the amount of platelets, fibrinogen and factor XII in the course of these exposures.

Muscle blood flow is not reduced in humans during moderate exercise and heat stress.

The effect of heat stress on circulation in an exercising leg was determined using one-legged knee extension and two-legged bicycle exercise, both seated and upright. Subjects exercised for three successive 25-min periods wearing a water-perfused suit: control [CT, mean skin temperature (Tsk) = 35 degrees C], hot (H, Tsk = 38 degrees C), and cold (C, Tsk = 31 degrees C). During the heating period, esophageal temperature increased to a maximum of 37.91, 39.35, and 39.05 degrees C in the three types of exercise, respectively. There were no significant changes in pulmonary O2 uptake (VO2) throughout the entire exercise period with either one or two legs. Leg blood flow (LBF), measured in the femoral vein of one leg by thermodilution, remained unchanged between CT, H, and C periods. Venous plasma lactate concentration gradually declined over time, and no trend for an increased lactate release during the heating period was found. Similarly, femoral arteriovenous O2 difference and leg VO2 remained unchanged between the three exercise periods. Although cardiac output (acetylene rebreathing) was not significantly higher during H, there was a tendency for an increase of 1 and 2 l/min in one- and two-legged exercise, respectively, which could account for part of the increase in total skin blood flow during heating (gauged by changes in forearm blood flow). Because LBF was not reduced during exercise and heat stress in these experiments, the additional increase in skin blood flow must have been met by redistribution of blood away from vascular beds other than active skeletal muscle.

The highest ambient temperature tolerated by normocapnic and hypercapnic rabbits.

The highest ambient temperature tolerated by rabbits was 30 degrees C at the relative humidity of air 80-95%. During the exposure to these environmental conditions the vasomotor thermoregulatory response developed fully, while the respiratory frequency did not attain the maximum level, i.e. the rabbit's potential ability for thermal panting. Prolonged heat exposure (approx. 4 hours) had a depressive effect on the respiratory frequency. Increased concentration of carbon dioxide (3, 6 and 9%) in the inspired gas mixture did not disturb the thermoregulatory mechanisms at 30 degrees C in the rabbits.

Thermoregulation in boys at prepubertal age (7-15 years).

In 70 boys aged 7-8 and 14-15 years the temperature of the skin surface (at rest), rectal temperature, thickness of the skin-fat fold and heat loss by radiation and convection were measured. Then the mean weighted skin temperature (Ts) and body thermoinsulation (I) were calculated. The investigations were carried out stable physical conditions of the environment at the ambient temperature (Ta) of 20 degrees C. It was found that the thermoinsulatory properties of the body increased with age, while the amount of eliminated heat decreased. At the age of 7 to 15 years the value of body thermoinsulation was closely correlated to the thickness of the subcutaneous adipose tissue and significantly lower than the reported values in adult men.

Reduced hypothalamic thermosensitivity following intraventricular injection of pyrogen in conscious rabbits.

Hypothalamic temperature thresholds for vasodilatory and respiratory reactions were determined before and after i.c.v. injection of pyrogen in rabbits. During the rising phase of fever the increases in the hypothalamic thresholds for vasodilatory and respiratory reactions differed from those found in the pre-pyrogen preoptic anterior hypothalamic area (POAH) heating by 2.1 +/- 0.2 degrees C and 1.89 +/- 0.31 degrees C, respectively. During the plateau phase of fever the threshold for vasodilatory reaction was further increased (by 0.7 +/- 0.23 degrees C), whereas that for panting remained at the same level. It is concluded that pyrogen exerts a depressive action on POAH thermosensitivity.

Ambient temperature effect on changes in heat exchange and skin and coat thermoisolation induced with nembutal in guinea pigs.

The experiment was carried out on adult male guinea pigs not adapted to cold at temperatures of 29 degrees, 20 degrees and 12 degrees C. During 150 minutes after nembutal injection the following values were recorded: oxygen consumption, subcutaneous, cutaneous and hair-coat temperatures. Using Hatfield's disc heat loss from the body surface by radiation and convection was measured. Nembutal not only inhibited thermogenetic processes at low ambient temperature, but decreased also heat production in a thermoneutral environment. This effect increased with decreasing ambient temperature. At the same time, there was a reduction in heat loss, although in a lower degree. The final result was a fall of the rectal temperature (even by 10 degrees C in a cold environment). Following nembutal administration skin thermoinsulation decreased slightly but the thermoinsulating activity of the hair-coat increased (the pilomotor response was more pronounced than in waking animals). Thermoregulation disturbances induced by nembutal included mainly thermogenesis impairment. The effect of general anaesthesia on heat loss was without any greater importance for maintenance of thermic homeostasis of the organism.

Comparison of heat loss by radiation and convection from the body surface of guinea pigs determined with Hatfield's disc and undimensional probability numbers.

The experiments were carried out on 10 non-acclimatized to cold adult guinea pigs at ambient temperatures (Ta) of 29 degrees, 20 degrees and 12 degrees C. The practical heat loss (radiation and convection) from the body surface was determined with Hatfield's disc. Moreover, radiation and convection were evaluated measuring the effective temperature of the hairs. It was found that the amount of heat lost through radiation and convection approached the practical heat loss determined with Hatfield's disc. Heat elimination from the body surface occurred mainly through radiation. The participation of convection in this heat loss was never above 5% of the heat lost through radiation.

Effect of nembutal anaesthesia on the tolerance of high ambient temperature in guinea pigs.

A significantly lower rise of rectal temperature was observed in guinea pigs under nembutal general anaesthesia (2 degrees C) in comparison to the rise in this temperature in non-anaesthetised animals (2.6 degrees C) kept for 2.5 hours at an ambient temperature of 36 degrees C. Better tolerance of heat in the animals under general anaesthesia was due to reduced heat production and it was independent of a modification by nembutal of the thermoinsulating properties of the skin and coat, as it is a case at low and neutral ambient temperatures.