Changes in limb volume during head-out water immersion in humans

In order to investigate the contribution of fluid shift from the legs to immersion-induced diuresis, 7 normal and 2 legless (both legs disarticulated at the hip) individuals were tested to measure changes in leg volume (normal subjects) and urinary excretion of solutes and water during a 3-h head-out water immersion (HOI) in thermoneutral water (34.5 +/- 0.5 degrees C) with a 1-h control period before and after immersion. On a separate day, a 5-h time control (TC) experiment on the same subjects was carried out by having them sit in thermoneutral air (29 +/- 0.1 degrees C, relative humidity 60%). The leg volume decreased by 192 +/- 20 ml during the 3-h HOI, which accounted for 3.5% of the average leg volume of the preimmersion period. During TC, however, the leg volume increased by 110 ml in the same time course. An increase in urine volume and sodium excretion was observed during HOI in both normal (P less than 0.05) and legless subjects. Net urine volume induced by HOI (urine volume during HOI minus urine volume during corresponding TC) in normal subjects was 494 +/- 89 ml in 3 h, which was close to a calculated volume reduction of the lower extremities during HOI (508 +/- 53 ml). The average net urine volume during HOI in the legless subject was 183 +/- 48 ml/min. The above results may suggest that the increase in renal water output is largely accounted for by a fluid shift from the lower extremities during HOI, however, the fluid other than that from the extremities should be accounted for as the urine source.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of hydrostatic pressure on plasma concentrations of norepinephrine during cold water immersion

Head-out immersion of humans in cold water concurrently stimulates low-pressure receptors and cutaneous cold receptors. In theory, the low-pressure receptors inhibit sympathetic nerve activity to the extent of modifying plasma norepinephrine responses to chilling of the skin. Human plasma norepinephrine concentrations ([NE]p's) were measured when low-pressure receptors were stimulated by 6 h of head-out immersion in thermoneutral water (35 degrees C). The experimental protocol was repeated when cold receptors were activated by a separate exposure to 14.8 degrees C air. Furthermore, both types of receptors were activated by 6 h of immersion in cold water (29.8 degrees C). The control exposure maintained [NE]p close to a constant value of 0.34 ng/ml. Thermoneutral water reduced [NE]p to 0.18 ng/ml after 30 min of immersion, but the change was not statistically significant (two-way ANOVA). [NE]p increased to peak values of 1.5 ng/ml in cold air (P less than 0.05) and 1.1 ng/ml in cold water (P less than 0.5), with no significant differences observed between [NE]p's in cold air and cold water. Equal rates of body heat loss occurred during the exposures to cold air and cold water. Since [NE]p's were comparably raised by separate exposures to cold water and cold air, stimulation of low-pressure receptors by immersion did not significantly depress peripheral vasomotor nerve activity during head-out immersion in cold water.     

Fluid and electrolyte intake and loss in elite soccer players during training

This study measured fluid balance during a 90-min preseason training session in the first team squad (24 players) of an English Premier League football team. Sweat loss was assessed from changes in body mass after correction for ingested fluids and urine passed. Sweat composition was measured by collection from patches attached to the skin at 4 sites. The weather was warm (24-29 degrees C), with moderate humidity (46-64%). The mean +/- SD body mass loss over the training session was 1.10+/- 0.43 kg, equivalent to a level of dehydration of 1.37 +/- 0.54% of the pre-training body mass. Mean fluid intake was 971 +/- 303 ml. Estimated total mean sweat loss was 2033 +/- 413 ml. Mean sweat electrolyte concentrations (mmol/L) were: sodium, 49 +/- 12; potassium, 6.0 +/- 1.3; chloride, 43 +/- 10. Total sweat sodium loss of 99+/- 24 mmol corresponds to a salt (sodium chloride) loss of 5.8 +/- 1.4 g. Mean urine osmolality measured on pre-training samples provided by the players was 666 +/- 311 mosmol/kg (n = 21). These data indicate that sweat losses of water and solute in football players in training can be substantial but vary greatly between players even with the same exercise and environmental conditions. Voluntary fluid intake also shows wide inter-individual variability and is generally insufficient to match fluid losses.     

Effect of glycerol-induced hyperhydration on thermoregulation and metabolism during exercise in heat

This study examined the effect of glycerol ingestion on fluid homeostasis, thermoregulation, and metabolism during rest and exercise. Six endurance-trained men ingested either 1 g glycerol in 20 ml H2O x kg(-1) body weight (bw) (GLY) or 20 ml H2O x kg(-1) bw (CON) in a randomized double-blind fashion, 120 min prior to undertaking 90 min of steady state cycle exercise (SS) at 98% of lactate threshold in dry heat (35 degrees C, 30% RH), with ingestion of CHO-electrolyte beverage (6% CHO) at 15-min intervals. A 15-min cycle, where performance was quantified in kJ, followed (PC). Pre-exercise urine volume was lower in GLY than CON (1119 +/- 97 vs. 1503 +/- 146 ml x 120 min(-1); p < .05). Heart rate was lower (p < .05) throughout SS in GLY, while forearm blood flow was higher (17.1 +/- 1.5 vs. 13.7 +/- 3.0 ml x 100 g tissue x min(-1); p < .05) and rectal temperature lower (38.7 +/- 0.1 vs. 39.1 +/- 0.1 degrees C; p < .05) in GLY late in SS. Despite these changes, skin and muscle temperatures and circulating catecholamines were not different between trials. Accordingly, no differences were observed in muscle glycogenolysis, lactate accumulation, adenine nucleotide, and phosphocreatine degradation or inosine 5'-monophosphate accumulation when comparing GLY with CON. Of note, the work performed during PC was 5% greater in GLY (252 +/- 10 vs. 240 +/- 9 kJ; p < .05). These results demonstrate that glycerol, when ingested with a bolus of water 2 hours prior to exercise, results in fluid retention, which is capable of reducing cardiovascular strain and enhancing thermoregulation. Furthermore, this practice increases exercise performance in the heat by mechanisms other than alterations in muscle metabolism.     

Core cooling and thermal responses during whole-head, facial, and dorsal immersion in 17 degrees C water

This study isolated the effects of dorsal, facial, and whole-head immersion in 17 degrees C water on peripheral vasoconstriction and the rate of body core cooling. Seven male subjects were studied in thermoneutral air (approximately 28 degrees C). On 3 separate days, they lay prone or supine on a bed with their heads inserted through the side of an adjustable immersion tank. Following 10 min of baseline measurements, the water level was raised such that the water immersed the dorsum, face, or whole head, with the immersion period lasting 60 min. During the first 30 min, the core (esophageal) cooling rate increased from dorsum (0.29 ± 0.2 degrees C h-1) to face (0.47 ± 0.1 degrees C h-1) to whole head (0.69 ± 0.2 degrees C h(-1)) (p < 0.001); cooling rates were similar during the final 30 min (mean, 0.16 ± 0.1 degrees C h(-1)). During the first 30 min, fingertip blood flow (laser Doppler flux as percent of baseline) decreased faster in whole-head immersion (114 ± 52% h(-1)) than in either facial (51 ± 47% h-1) or dorsal (41 ± 55% h(-1)) immersion (p < 0.03); rates of flow decrease were similar during minutes 30 to 60 (mean, 22.5 ± 19% h(-1)). Total head heat loss over 60 min was significantly different between whole-head (120.5 ± 13 kJ), facial (86.8 ± 17 kJ), and dorsal (46.0 ± 11 kJ) immersion (p < 0.001). The rate of core cooling, relative to head heat loss, was similar in all conditions (mean, 0.0037 ± 0.001 degree C kJ(-1)). Although the whole head elicited a higher rate of vasoconstriction, the face did not elicit more vasoconstriction than the dorsum. Rather, the progressive increase in core cooling from dorsal to facial to whole-head immersion simply correlates with increased heat loss.     

A 4 degrees C-1 min method of cold water immersion test for peripheral circulatory function in fingers]

To assess the validity of a new simplified cold water immersion test (4 degrees C-1 min method) for peripheral circulatory function, comparison was made with the conventional method (10 degrees C-10 min method). These two different methods of cold immersion test were applied to 23 patients with vibration disease and 24 healthy men. Observation was made on finger skin temperature by a thermistor and complaints in the hand by a 5-step self-reported scale method every minute during the test. The patterns of recovery of skin temperature after cold immersion in each group were similar in both methods. Pain in the hand in the 4 degrees C-1 min method was less than that in the 10 degrees C-10 min method. The recovery rate at 5 min in the patients with Raynaud's phenomenon was lower than that in those without Raynaud's phenomenon in the 4 degrees C-1 min method (p < 0.01). However, no significant differences were noted in 10 degrees C-10 min method. The results suggest that the new method is feasible in detecting the response of vasodilation after immersion. In the recovery rate at 5 min after immersion, near values of the sensitivity and specificity were observed between 50% cut-off values in the 4 degrees C-1 min method and 30% value in the 10 degrees C-10 min method. Thus, the 4 degrees C-1 min method is considered to be more useful to evaluate the physiological response after cold immersion than the 10 degrees C-10 min method.     

Structural differences between foot-and-mouth disease and poliomyelitis viruses influence their inactivation by aziridines

Inactivation of foot-and-mouth disease virus (FMDV) and poliovirus by ethyleneimine (EI) and N-acetylethyleneimine (AEI) has been studied at 25 degrees and at 37 degrees C and in different ionic conditions. FMDV is inactivated rapidly in 100 mM Tris pH 7.6 by each reagent at both temperatures. Poliovirus is also inactivated rapidly in 100 mM Tris by EI at both temperatures and by AEI at 37 degrees C. However, it is inactivated much more slowly by AEI at 25 degrees C; but if the virus is first incubated overnight at 2 degrees C with AEI before transferring to 25 degrees C inactivation then proceeds rapidly. Moreover, the rate of inactivation at 25 degrees C is markedly increased if the virus is suspended in 1 mM Tris. We had interpreted these differences as being due to the greater penetrability of poliovirus (i) in 100 mM Tris at 37 degrees C compared with 25 degrees C and (ii) at lower ionic strength. This interpretation has been confirmed by electron microscopy of FMDV and poliovirus particles stained with phosphotungstic acid. At the elevated temperature, poliovirus had an average diameter of 34+/-0. 21 nm and the stain outlined the nucleic acid core and the individual subunits, whereas at 25 degrees C it averaged 28+/-0.13 nm and the stain did not penetrate the particle. This study also showed that the particle diameter alters with changes in buffer concentration, being 28+/-0.13 nm in 100 mM Tris, 31+/-0.16 nm in 10 mM Tris and 34+/-0.21 nm in 1 mM Tris. The changes in poliovirus are reversible as addition of 1/10 volume of 1 M Tris to the virus in 1 mM Tris resulted in the return of the diameter to 28+/-0.13 nm. FMDV, on the other hand, was less sensitive to osmotic differences as its particle diameter only varied by 7% over the 100-fold change in buffer concentration compared with the 22% change observed for poliovirus.     

Body cooling in human males by cold-water immersion after vigorous exercise

Five male subjects were immersed to neck level in a whole-body water calorimeter (water temperature 19 degrees C) on two occasions. One immersion was preceded by 30 min of exercise on a treadmill at 80% of the subjects' maximum heart rate, while the other was preceded by no exercise (control). Ventilation, oxygen consumption, hand-grip strength, and heat loss (measured by calorimetry) results showed no significant differences between resting and exercise trials. Minute ventilation and oxygen consumption increased during the immersion but the magnitude of the increase varied among subjects. There was a significant decrease is isometric hand-grip strength after 30 min of immersion. Rectal temperatures fell faster (0.031 degree C +/- 0.004 degree C/min) for exercised subjects than for controls (0.019 degree C +/- 0.005 degree C/min) between 10 and 45 min of immersion (P less than 0.01). It appears that vigorous preimmersion exercise may shorten survival time in cold water due to an increase in cooling rate.     

Drinking behavior and perception of thirst in untrained women during 6 weeks of heat acclimation and outdoor training

The purposes of this study were to characterize measures of fluid intake and perception of thirst in women over a 6-week period of exercise-heat acclimation and outdoor training and examine if this lengthy acclimation period would result in changes in fluid intake that differ from those previously reported in men utilizing a shorter acclimation protocol of 8-10 days. Voluntary water intake (11-17 degrees C) and perception of thirst were measured in a group of 5 women (21-26 yr) undergoing exercise-heat acclimation for 90 min/day, 3 days/wk (36 degrees C, rh 50-70%) and outdoor training 3 days/wk for 6 weeks. Decreased drinking during acclimation was characterized by a decrease in the number of drinks (35 +/- 10 to 17 +/- 5; p <.05), greater time to first drink (9.9 +/- 2.0 to 23.1 +/- 4.7 min; p <.05), and a decrease in total volume ingested per week (3310 +/- 810 to 1849 +/- 446 ml; p <.05) through the 6-week study. Mean perceived thirst measurements remained low and showed only slight variance (3 +/- 0.4 to 5 +/- 0.4). These observations support a psycho-physiological response pattern different than that previously observed during 8-10 day acclimation protocols in men.     

Changes in cold-induced vasodilatation, pain and cold sensation in fingers caused by repeated finger cooling in a cool environment

To examine how repeated cooling of fingers with a rest pause schedule at work affects cold-induced vasodilatation (CIVD), pain and cold sensation in fingers, six healthy men aged 21 to 23 years immersed their left index fingers six times in stirred water at 10 degrees C for 10 minutes. After each cold-water immersion of the fingers, 5-minute rest pause was taken to observe the recovery process of the indicators. This cold-water immersion/rest pause test was carried out in a range of three ambient temperature conditions: 30 degrees C (warm), 25 degrees C (thermoneutral), and 20 degrees C (cool) as experienced in daily life. At the ambient temperatures of 30 degrees C and 25 degrees C, marked CIVD response occurred and the CIVD reactivity did not significantly change upon repetition of cold-water immersion. The lowered finger skin temperature also tended to recover quickly to the pre-immersion level during each post-immersion rest period. At the ambient temperature of 20 degrees C, however, the CIVD response weakened continuously upon repetition of immersion and almost disappeared during the final immersion. The recovery of finger skin temperature during each post-immersion rest was gradually delayed upon repetition of immersion. At every ambient temperature, finger pain and cold sensation induced by each cold-water immersion significantly decreased upon repetition of immersion and completely disappeared during each post-immersion rest period. Oral temperature during the experiment showed no significant change at the ambient temperatures of 25 degrees C and 30 degrees C, but it decreased significantly at the ambient temperature of 20 degrees C. These results suggest that in a cool work environment where the body core temperature is liable to decrease, repeated finger cooling may weaken CIVD reactivity and delay the recovery of finger temperature during post-immersion rest periods. In such lower ambient temperature work conditions, subjective judgements such as the decrease in finger pain and cold sensation during repeated finger cooling and the absence of them during post-immersion rest may not be reliable indicators for monitoring the risk of progressive tissue cooling and frostbite formation.     

Effect of wearing gloves on the thermal balance of Korean women wet-suit divers in cold water

Effect of wearing neoprene gloves on the thermal exchanges of wet-suited divers was studied in 8 Korean diving women. Subjects, clad with 5-6-mm-thick neoprene wet suits (jacket, pants, and boots) either with or without wearing 3-mm-thick neoprene gloves, were immersed for 3 h in water of critical temperature (17.3 degrees +/- 0.8 degree C) while the rectal and skin (chest, leg, arm, and hand) temperatures and oxygen consumption were measured. Overall thermal insulation of the subject plus suit was calculated from the rectal-to-water temperature difference divided by the estimated rate of skin heat loss. The skin heat loss was assumed to equal metabolic heat production minus respiratory heat loss, corrected for changes in heat storage when mean body temperature changed. All measurements were carried out in a resting condition. During the 3rd h of immersion, the rectal temperature was lower with gloves (delta Tre = 0.30 degree +/- 0.04 degree C; P less than 0.05) whereas metabolic heat production was not significantly different. Consequently, the total thermal insulation was nearly 16% lower with gloves than without gloves. In both the hands and forearms, the regional heat flux determined directly using a heat flux transducer was higher and the thermal insulation index was lower with gloves than without gloves. These results indicate that in wet-suited subjects resting in cold (17 degrees C) water gloves do not provide additional protection against heat loss, but rather decrease the efficiency of thermoregulatory mechanisms. We suggest that sensory input from cold receptors in the distal extremities is particularly important in thermoregulation during immersion in cold water.     

The effect of increased environmental temperature on the behavior of physiologic parameters in bicycle ergometry within the scope of the physical endurance limit

For determination of the endurance limit range, 8 healthy male probands aged between 20 and 26 years loads had carried out for one hour on a bicycle ergometer at an ambient temperature of +20 degrees C, +28 degrees C and +35 degrees C. Staying in an ambient temperature of 35 degrees C leads to a decrease in the physical endurance limit in an order of magnitude of 10 W. At 20 degrees C, in the endurance range the following values result (mean +/- s): load 68+/- 10.3 W, heart rate 113.6 +/- 5.8 beats per min., net heart rate 31.8 +/- 2.4 beats per min., oxygen uptake 1340 +/- 170 ml per min., auditory canal temperature 36.5 +/- 0.24 degrees C, sweat rate 275 +/- 143 g. At 35 degrees C, the endurance limit is attained at the following values: 57 +/- 10.6 W, heart rate 125 +/- 11.8 beats per min., net heart rate 27.4 +/- 3.6 beats per min., oxygen uptake 1210 +/- 130 ml per min., auditory canal temperature 37.2 +/- 0.3 degrees C, sweat rate 577 +/- 96 g.     

Heat stress of helicopter aircrew wearing immersion suit

The objectives of the present study were to define the lowest ambient air and cabin temperatures at which aircrews wearing immersion protection are starting to experience thermal discomfort and heat stress during flight operations, and to characterize during a flight simulation in laboratory, the severity of the heat stress during exposure to a typical northern summer ambient condition (25 degrees C, 40% RH). Twenty male helicopter aircrews wearing immersion suits (insulation of 2.2 Clo in air) performed 26 flights within an 8-month period at ambient temperatures ranging between -15 and 25 degrees C, and cabin temperatures ranging between 3 and 28 degrees C. It was observed based on thermal comfort ratings that the aircrews were starting to experience thermal discomfort and heat stress at ambient and cabin air conditions above 18 degrees C and at a WBGT index of 16 degrees C. In a subsequent study, seven aircrews dressed with the same clothing were exposed for 140 min to 25 degrees C and 40% RH in a climatic chamber. During the exposure, the aircrews simulated pilot flight maneuvers for 80 min followed with backender/flight engineer activities for 60 min. By the end of the 140 min exposure, the skin temperature, rectal temperature and heart rate had increased significantly to 35.7 +/- 0.2 degrees C, 38.4 +/- 0.2 degrees C and between 110 and 160 beats/min depending on the level of physical activity. The body sweat rate averaged 0.58 kg/h and the relative humidity inside the clothing was at saturation by the end of the exposure. It was concluded that aircrews wearing immersion suits during the summer months in northern climates might experience thermal discomfort and heat stress at ambient or cabin air temperature as low as 18 degrees C.     

Diving bradycardia and breath-holding time in man

The hypothesis that the diving response, recorded as diving bradycardia during submersed breath holding in man, would enhance his breath-holding time was tested. Five certified scuba divers served as subjects. They performed breath holds of maximal duration while nonimmersed and during submersion in cool (32 degrees C), cold (20 degrees C), and thermoneutral (35 degrees C) water. The mean breath-holding time and heart rate during the nonimmersed (control) condition were, respectively, 111.2 +/- 14.1 (SE) s and 64.1 +/- 4.7 (SE) beats/min, the relatively long breath-holding times being due primarily to the so-called short-term training effect. Compared to the control values the breath-holding time in 20 degrees C water was 54.9% shorter and heart rate 25.9% lower, in 32 degrees C water the breath-holding time was not different and heart rate was 28.1% lower, and in 35 degrees C water the breath-holding time was longer by 25.6% while there was no difference in heart rate. In all conditions the breath-hold breaking point alveolar PCO2 was the same at about 52 mmHg. The shortening of the breath holds in cold water was ascribed to a 256% increase (over nonimmersed control) in metabolic rate as well as a respiratory drive due to stimulation of skin cold receptors. As for the prolongation of breath holds in thermoneutral water, it was hypothesized that immersion caused a delay in the build-up of chemical stimuli at the chemoreceptors.     

Circulatory functions during immersion and breath-hold dives in humans

An unusual circulatory state exists in humans immersed in water at or near 35 degrees C. This circulatory state is characterized by a persistent and elevated stroke index (SI) but heart rate (HR) changes little; hence an increased cardiac index (CI) results. In comparison of measurements in air and immersion in water up to the neck level that are based on the weighted averages of 45 subjects from 8 studies, SI increased by 29%, CI increased by 24%, and HR decreased by 6%. Evidence is presented to support the finding that the increase in stroke volume is a result of enhanced preload of the heart, and that alterations in afterload and contractility play an unimportant role in affecting cardiac performance during immersion in thermoneutral water up to the level of the neck. The circulatory state represents hyperperfusion, since there is no concurrent rise in metabolic demand or heat stress. To what extent this preexisting circulatory state affects the cardiovascular responses to breath-hold (BH) diving is in most part unknown. However, the BH bradycardiac responses are more potent in a natural setting than in the laboratory where the breath hold is performed with only face immersion in water. In contrast, in the natural setting, the divers perform BH dives while they are immersed up to the neck in cold water (much lower than 35 degrees C) and are exercising. It is desirable in future studies to compare systematically other aspects of circulatory responses to BH dives while immersed in water and while exercising.     

The effect of glycerol hyperhydration on olympic distance triathlon performance in high ambient temperatures

The purpose of this study was to examine the effect of prior glycerol loading on competitive Olympic distance triathlon performance (ODT) in high ambient temperatures. Ten (3 female and 7 male) well-trained triathletes (VO2max = 58.4 +/- 2.4ml kg(-1) min(-1); bestODTtime = 131.5 +/- 2.6 min) completed 2 ODTs (1.5-km swim, 40-km bicycle, 10-km run) in a randomly assigned (placebo/ glycerol) double-blind study conducted 2 weeks apart. The wet-bulb globe temperature (outdoors) was 30.5 +/- 0.5 degrees C (relative humidity: 46.3 +/- 1.1%; hot) and 25.4 +/- 0.2 degrees C (relative humidity: 51.7 +/- 2.4%; warm) for day 1 and day 2, respectively. The glycerol solution consisted of 1.2 g of glycerol per kilogram of body mass (BM) and 25 ml of a 0.75 g x kg(-1) BM carbohydrate solution (Gatorade) and was consumed over a 60-min period, 2 hours prior to each ODT. Measures of performance (ODT time), fluid retention, urine output, blood plasma volume changes, and sweat loss were obtained prior to and during the ODT in both the glycerol and placebo conditions. Following glycerol loading, the increase in ODT completion time between the hot and warm conditions was significantly less than the placebo group (placebo 11:40 min vs. glycerol 1:47 min; p < .05). The majority of the performance improvement occurred during the final 10-km run leg of ODT on the hot day. Hyperhydration occurred as a consequence of a reduced diuresis (p < .05) and a subsequent increase in fluid retention (p < .05). No significant differences were observed in sweat loss between the glycerol and placebo conditions. Plasma volume expansion during the loading period was significantly greater (p < .05) on the hot day when glycerol appeared to attenuate the performance decrement in the heat. The present results suggest that glycerol hyperhydration prior to ODT in high ambient temperatures may provide some protection against the negative performance effects of competing in the heat.     

Hyperbaric diuresis at a thermoneutral 31 ATA He-O2 environment

The basic pattern of body water exchange was studied in four Japanese male divers during exposure to a thermoneutral 31 ATA (He-O2) environment for 3 d (Seadragon V). The hyperbaric chamber temperature was raised from 25 degrees C +/- 0.5 degrees C at 1 ATA (air) predive to 31.5 degrees C +/- 0.3 degrees C at 31 ATA. Both rectal and mean skin temperatures were measured every hour (including during sleep) and were maintained at the same level at both pressures. The exposure to 31 ATA induced an increase in the daily urine flow and a corresponding reduction in the insensible (and evaporative) water loss without changing the total daily water output. However, the daily fluid intake decreased by 600 ml at 31 ATA, and hence the divers developed a state of negative fluid balance, as reflected by a reduction in body weight and an increase in hematocrit. All changes in the pattern of body water exchange observed at 31 ATA were gradually reversed during subsequent decompression. As observed in a previous dive to 31 ATA (Seadragon IV) in which there was a subtle cold stress (as indicated by the 1 degree C reduction in mean skin temperature at 31 ATA), the increase in daily urine flow at pressure was almost entirely due to the increase in overnight urine flow. However, the hyperbaric nocturia observed in the present dive was a water diuresis in nature whereas that in the previous dive was an osmotic diuresis. These results indicate that the hyperbaric diuresis at 31 ATA is due to an increase in overnight urine flow and that the hyperbaric nocturia is not in any way related to the subtle cold stress attendant in many hyperbaric environments.     

Decreased in vitro fluoroquinolone concentrations after admixture with an enteral feeding formulation

BACKGROUND: The purpose of this study was to determine if mixing of fluoroquinolones with a common enteral feeding formulation, Ensure (Ross Products Division, Abbott Laboratories, Columbus, OH), would alter the measured in vitro quinolone concentrations over a 24-hour period. METHODS: Tablets of ciprofloxacin (500 mg), levofloxacin (500 mg), and ofloxacin (300 mg) were crushed and mixed with 240 mL of Ensure, water and calcium chloride (500 mg/L), water and magnesium chloride (200 mg/L), water and calcium chloride and magnesium chloride, and water alone. Fluoroquinolone concentrations of the mixtures were measured, via high-performance liquid chromatography, at baseline and serially over 24 hours. Experiments were performed in duplicate, at three temperatures (5 degrees C, 25 degrees C, and 37 degrees C). RESULTS: Average decreases of 82.5% +/- 1.5% for ciprofloxacin, 61.3% +/- 5.2% for levofloxacin, and 45.7% +/- 10.1% for ofloxacin (mean +/- 95% CI) were observed in vitro for Ensure over the two experimental sets at baseline. Serial analysis revealed no further significant change in any of the quinolone concentrations over the remaining 24-hour period. No significant decrease was noted with the quinolones when mixed in water and calcium, water and magnesium, water and calcium and magnesium, or water alone. This phenomenon appears to be unaffected by time and temperature. CONCLUSIONS: These data suggest there is an immediate and significant loss of fluoroquinolone when mixed with Ensure. An explanation for the loss of fluoroquinolone remains unclear.     

A study on the effect of water intake of umpires during a baseball game in a summer-heat environment

The purpose of this study was to examine the effect of umpires' intake of water during a summertime baseball game, on serum and urinary biochemical elements, body weight and physiological factors. Twenty-eight umpires were classified into two groups. Group W was composed of 14 umpires who had water while those who did not were group C. Group W had 250 ml of water that was cooled to about 5 degrees C after the 5th inning of the game. The game was played in the following environment: atmosphere temperature was 31 degrees C; wet-bulb temperature was 26 degrees C; blackglove temperature was 40 degrees C; the velocity of the wind was 1.18 m/sec in bright sunshine on a hot and moist day. The results obtained were as follows. In group W, more body weight was lost than in group C, but statistically there was no significant difference. Urinary volume in group W became smaller than in group C, but statistically there was no significant difference. Water in blood increased in group W and decreased in group C but statistically there was significant difference. In both groups, oral temperature decreased, but only in group C was there a statistically significant difference. Although the intake of water increased the volume of perspiration, it did not dilute the concentrated blood, suppress the rise of body temperature, or result in a rise of low blood pressure.     

Human vascular fluid responses to cold stress are not altered by cold acclimation

Repeated cold water immersion can induce the development of an insulative type of cold acclimation in man. This investigation determined if repeated cold water immersion produced changes in vascular fluid responses to cold stress in addition to the previously reported changes in thermoregulation. Seven male subjects performed a standardized cold air and cold water exposure before and again after a cold acclimation program. The cold acclimation program consisted of daily immersion (90 min) in cold water (18 degrees C, stirred) repeated 5 times/wk for 5 consecutive wk. Cold acclimation did not alter the responses of plasma volume or electrolyte concentrations, nor urinary flow or electrolyte excretion during either cold air or cold water exposure. The percent reduction in plasma volume was larger (P less than 0.01) in cold water (-17%) than in cold air (-12%). Cold water immersion resulted in greater (P less than 0.01) diuresis than cold air exposure. Plasma K+ concentration increased (P less than 0.01) during cold (both air and water) exposure, whereas plasma Na+ concentration was unchanged. Calculated renal clearance and urinary excretion rate of both Na+ and K+ increased during cold (both air and water) exposure. The magnitude of plasma volume reduction during cold exposure was not correlated with either the degree of body cooling or diuresis. It is concluded that a) insulative cold acclimation does not influence vascular fluid responses to cold stress, and b) although vascular fluid shifts, body cooling and diuresis are all greater in cold water than in air, a consistent relationship among these parameters could not be established for an individual's response.