Plasma sodium-osmotic dissociation and hormonal interaction with drinking-induced hypervolemia at 2800 m altitude.

PURPOSE: To study hormonal factors that may account for the dissociation between beverage-induced plasma sodium p[Na+] and osmotic p[Osm] concentrations that appear to refute the high theoretical correlation between p[Na+] and p[Osm]. METHODS: Ten men (24 +/- SD 3 yr of age) sat reclining (head up) for 12 h in a chamber (21-23 degrees C dry bulb, 25-33% relative humidity) at 2800 m (9184 ft, 539 mm Hg) altitude (ALT), and at 321 m (1053 ft, 732 mm Hg) on the ground (GND). During 1000-1030 hours they consumed 3 fluids (12 ml x kg(-1),X = 948 ml x d(-1)) with large differences in sodium and osmotic contents: AstroAde (AA) with 185 mEq x L(-1) Na+ and 283 mOsm x kg(-1), Performance 1 (Shaklee) (P1) with 22 mEq x L(-1) Na+ and 365 mOsm kg(-1), or H2O at ALT; and only H2O on the GND. RESULTS: After drinking: plasma volume (PV) increased at 1200 hours by 8.3% (p < 0.05) with AA but was not significantly (NS) changed in the other sessions (Xdelta = +0.9%, range -0.9 to 2.8%); p[Na+] and p[Osm] were unchanged. Urinary rates and free-water clearances were attenuated with AA and P1 vs. those with H2O. Correlations between and among p[Na+] and p[Osm] suggest that the pNa+ ion is more tightly controlled than pOsm; and that there was no clear hormonal response that could account for this dissociation from theoretical considerations. CONCLUSIONS: There is significant dissociation between plasma sodium and osmotic concentrations after fluid intake. Induction and maintenance of hypervolemia requires increased (near isotonic) drink Na+ osmols rather than increased non-ionic osmols.

Exercise- and methylcholine-induced sweating responses in older and younger men: effect of heat acclimation and aerobic fitness.

The purpose of this investigation was to examine the effects of aging and aerobic fitness on exercise- and methylcholine-induced sweating responses during heat acclimation. Five younger [Y group-age: 23 +/- 1 (SEM) years; maximal oxygen consumption (VO2max): 47 +/- 3 ml.kg-1.min-1], four highly fit older (HO group- 63 +/- 3 years; 48 +/- 4 ml.kg-1.min-1) and five normally fit older men (NO group -67 +/- 3 years; 30 +/- 1 ml.kg-1.min-1) who were matched for height, body mass and percentage fat, were heat acclimated by daily cycle exercise (approximately 35% VO2max for 90 min) in a hot (43 degrees C, 30% RH) environment for 8 days. The heat acclimation regimen increased performance time, lowered final rectal temperature (Tre) and percentage maximal heart rate (%HRmax), improved thermal comfort and decreased sweat sodium concentration similarly in all groups. Although total body sweating rates (Msw) during acclimation were significantly greater in the Y and HO groups than in the NO group (P < 0.01) (because of the lower absolute workload in the NO group), the Msw did not change in all groups with the acclimation sessions. Neither were local sweating rates (msw) on chest, back, forearm and thigh changed in all groups by the acclimation. The HO group presented greater forearm msw (30-90 min) values and the Y group had greater back and thigh msw (early in exercise) values, compared to the other groups (P < 0.001). In a methylcholine injection test on days immediately before and after the acclimation, the order of sweat output per gland (SGO) on chest, back and thigh was Y > HO > NO, and on the forearm Y = HO > NO. No group differences were observed for activated sweat gland density at any site. The SGO at the respective sites increased in the post-acclimation test regardless of group (P < 0.01), but on the thigh the magnitude of the increase was lower in the NO (P < 0.02) and HO (P = 0.07) groups than in the Y group. These findings suggest that heat tolerance and the improvement with acclimation are little impaired not only in highly fit older but also normally fit older men, when the subjects exercised at the same relative exercise intensity. Furthermore, the changes induced by acclimation appear associated with an age-related decrease in VO2max. However methylcholine-activated SGO and the magnitude of improvement of SGO with acclimation are related not only to VO2max but also to aging, suggesting that sensitivity to cholinergic stimulation decreases with aging.

Sodium chloride-citrate beverages attenuate hypovolemia in men resting 12 h at 2800 m altitude.

BACKGROUND: The mechanism for reduction and restoration of total body water and plasma volume (PV) during initial exposure to acute altitude (ALT) is not clear but may involve involuntary dehydration; i.e., delayed voluntary fluid intake. METHOD: Ten men (24 +/- SD 3 yr, 180.8 +/- 8.1 cm height, 78.8 +/- 12.8 kg weight, 1.99 +/- 0.19 m2 surface area, and 12.2 +/- 4.0% body fat) were in a semi-reclining position for 12 h in a chamber at 2800 m (539 mmHg) ALT or at 321 m (732 mmHg; ground). They ate a controlled breakfast (450 kcal + 3 ml x kg(-1) H2O) on the ground, and lunch and dinner at ALT (or on the ground) for a total daily intake of 2850 kcal (14% PRO, 67% CHO, 16% fat, 2.6g NaCl). At hour 10 they consumed fluid-electrolyte beverages or water (12 ml x kg(-1), 948 ml x d(-1)) in 4 sessions at weekly intervals. Beverage compositions were: a) 185 mEq x L(-1) Na+, 283 mOsm x kg(-1); b) 21.6 mEq x L(-1) Na+, 365 mOsm x kg(-1); c) water at ALT; and d) water on the ground. RESULTS: After 10 h at ALT % deltaPV (Hb-Hct) decreased (p < 0.05) by: a) 9.0 +/- SE 1.5%; b) 6.2 +/- 1.7%; c) 7.4 +/- 2.2%; and d) by 9.0 +/- 2.4%, respectively. After drinking from 1000-1030 h, PV at 1200 h changed by: a) +8.3 +/- SE 2.0% (p < 0.05); b) +2.8 +/- 2.7% (NS); c) -0.9 +/- 1.5% (NS); and d) by +0.8 +/- 3.5% (NS), respectively. The similar ground-induced hypovolemia suggests a response to confinement rather than an ALT effect and involuntary dehydration does not appear to be implicated. CONCLUSION: The significant increase in PV after consuming the (a) NaCl-NaCitrate beverage indicates that drink ionic composition appears to be more important than its osmolality for restoring PV in these conditions. Practical considerations: Because this hypovolemia was probably due to the confinement rather that reduced ambient pressure, appropriate countermeasures could be consumption of isotonic beverages, elastic stockings, leg exercise, and leg elevation.

Maximal skin vascular conductance in subjects aged 5-85 yr.

This study examined maximal forearm skin vascular conductance (FVCmax) as a function of age in 74 healthy male and female subjects ranging in age from 5 to 85 yr. The skin temperature of the left forearm was uniformly clamped at 42 degrees C by spraying a fine mist of water over the surface. Forearm blood flow (FBF) was measured by venous occlusion plethysmography (Hg-in-Silastic strain gauge). After 60 min of heating, a reactive hyperemia maneuver was performed to verify that forearm skin blood flow was maximal by using laser Doppler flowmetry to isolate the skin component of FBF. The maximal FBF of each subject was then divided by mean arterial pressure to yield FVCmax (in ml.100 ml-1.min-1.100 mmHg-1), i.e., minimal resistance. The model that best fits the data was curvilinear, as described by FVCmax = 13.1 + 86.9 (age-0.75) (r2 = 0.52, P < 0.001). The exclusion of subjects younger than 18 yr of age simplified the model to a linear fit with a slope of -0.16 conductance units/yr for adults. Interindividual variability remained constant across the entire age span. Once the age effect was considered, there were no significant effects of gender, adiposity, resting blood pressure, physical activity level, or body surface area on FVCmax.

Influence of opioids in hypothalamic nuclei on cold thermogenesis of lean and obese LA/N-cp rats.

An overactive endogenous opioid peptide system (EOP) in the hypothalamus of the obese rats could contribute to a subnormal metabolic response to cold stress. Specific mu, delta, kappa opioid receptor antagonists and naloxone were infused into cannulaes aimed at the paraventricular nucleus (PVN) of awake freely moving obese (LA/N-cp corpulent) and lean littermate rats. Metabolic responses were measured by indirect calorimetry during thermoneutrality (30 degrees C) and at 10 degrees C for 60 minutes each. When expressed relative to metabolic body size (kg(-.75)) obese rats had lower values (obese = 21.1 +/- 1.9 vs. lean = 27.9 +/- 2.7 ml x kg(-.75) x min, mean +/- s.d., p < 0.05) at 10 degrees C during saline infusion. EOP antagonist infusions at 30 degrees C had no effect on metabolic rate for either lean or obese animals. Mu (23.5 +/- 3.4 ml x kg x (-75) x min) and delta (23.0 +/- 2.0) antagonism and naloxone (25.0 +/- 2.3) significantly increased the metabolic response to cold in obese but not lean rats. These data suggest that certain subtypes of EOP receptors in or near PVN are overactive in obese rats. This overactive state may inappropriately inhibit the thermogenic response to cold stress in obesity.

Preservation of endothelial cells in excised rat carotid arteries. Effects of transmural pressure and segment length.

When arteries are excised, they collapse and shorten spontaneously, which can result in damage to the endothelium. To determine if an intact endothelial cell layer could be preserved in excised vessels, we isolated and cannulated rat carotid artery segments (in situ length, Lis, 10-20 mm) at both ends while maintaining both transmural pressure (70 mm Hg) and Lis, while either transmural pressure or Lis, or after allowing vessel collapse and shortening (n = 4 vessels per treatment). After each treatment, vessel segments were perfused with fixative and stained with AgNO3 to visualize endothelial cells. The amount of endothelial cell loss was quantified using stereological analysis of video microscopic images of the luminal surface. Results demonstrated that maintenance of both Lis and transmural pressure minimized endothelial cell denudation (1.6 +/- 0.9%); permitting the vessel to collapse and shorten resulted in the greatest loss of endothelial cells (59.4 +/- 13.2%); and maintenance of either pressure or Lis resulted in intermediate endothelial cell loss (13-30%). We conclude that the spontaneous collapse and shortening that normally accompany the excision of arterial segments result in substantial endothelial cell loss, which can be virtually eliminated with the maintenance of transmural pressure and vessel segment length. These findings have implications for surgical and experimental procedures requiring intact endothelium.

Energy turnover and heat exchange in mature lean and obese Zucker rats acutely exposed to three environmental temperatures for 24 hours.

Differences between lean (FA/?, n = 6) and obese (fa/fa, n = 6) mature male Zucker rats' energy turnover and heat storage were compared during a 24-h period when the animals were exposed to ambient temperatures of 30, 15 or 5 degrees C. Energy turnover was examined through measurements of heat production rates via indirect calorimetry and heat loss rates via direct calorimetry. Heat storage rates were calculated as the difference between heat production and heat loss rates. Predicted heat storage rates were also calculated as the product of the change in core temperature and the calculated specific heat of the animal based on body composition (carcass) analysis. A minimal heat loss rate was determined for each animal representing a period of least activity. Various comparisons were made: between groups (lean/obese), temperature (30, 15, 5 degrees C), calorimetry method (indirect/direct), period (light/dark), heat storage (experimental/predicted), and minimal heat loss. Immediately before a test, pretest weight and colonic temperature were obtained. Then, the animal was placed into the calorimeter chamber and remained there unrestrained for 24 h. Normal light/dark periods were maintained. On removal from the calorimeter, core temperature and body weight measurements were again obtained. Upon completion of all tests, body composition was analyzed and surface area determined. Energy turnover, i.e. both heat production and heat loss in the lean and obese animals differed among the 30, 15 and 5 degrees C exposures. The obese animals had relatively greater heat production rate and heat loss rate (kcal/day or kcal/kg (FFM)/day than the lean animals at 30, 15 and 5 degrees C. But, on a relative basis, the increments in heat production in the cold environments were greater for the lean animals. Both the lean and obese animals tended to be more active during the dark period when at 30 degrees C, but the difference was less at 15 degrees C and even less at 5 degrees C. Experimental heat storage rates did not differ significantly from predicted values at any of the temperatures with the possible exception of the animals at 5 degrees C. It was concluded that the mature obese Zucker rats had no major discernible defect in thermoregulation as revealed by rates of heat production and loss, although three of the obese rats did elicit a drop in colonic temperature during exposure to 5 degrees C, i.e. their excessive subcutaneous adiposity and thermal insulation did not prevent a fall in colonic temperature.(ABSTRACT TRUNCATED AT 400 WORDS)

Breath-by-breath monitoring of respiratory gas concentrations during compression and decompression.

We compared six systems for sampling respiratory gases from within a hyperbaric chamber to provide online gas concentrations by a mass spectrometer (MS) outside the chamber. Gas at hyperbaric pressure was sampled through either a capillary and mass flow controller (system 1), a capillary and micrometering manual valve (system 2), or a capillary alone (system 3) by a vacuum pump outside the chamber. In each system, a small amount of decompressed gas was drawn into the MS for analysis while the balance vented into the room. Systems 4-6 were constructed from systems 1-3, respectively, by eliminating the vacuum pump. Using a square wave respiratory simulator, which generated known gas concentration profiles within the chamber, MS analyses were recorded from each sampling system at compression and decompression rates of 20 meters of sea water.min(-1) and chamber pressures from 1.0 to 6.0 atm abs. Inspiratory and end-expiratory concentrations of nitrogen (0.0 and 1.0%, respectively) and carbon dioxide (0.0 and 4.2%, respectively) were accurately determined at respiratory rates of up to 70 breaths.min(-1) with a sensitivity of 0.05% and without pressure artifact.

Detection of venous air embolism by continuous mixed venous oximetry in dogs.

Continuous mixed venous oxygen saturation (SvO 2) was evaluated as a monitor of venous air embolism in a canine model. Nineteen dogs were anesthetized, paralyzed, and mechanically ventilated. Invasive monitoring included SvO 2, systemic and pulmonary artery blood pressures, and thermodilution cardiac outputs. Air boluses of 0.25 and 0.5 ml/kg were injected in six dogs and 1 ml/kg in all. All 1 ml/kg emboli were detected by greater than or equal to 5% decreases in the SvO 2. The SvO 2 decreased from 82 +/- 8% to 72 +/- 11% (mean +/- SD), an average decrease of 9 +/- 5% (p = 0.004). Time to the SvO 2 nadir was 2.6 +/- 2.5 min. Of the 0.5 and 0.25 ml/kg emboli, 50% and 17% were detected, respectively. Cardiac output decreased from 2.9 +/- 0.8 to 2.1 +/- 0.8 L/min after the 1 ml/kg emboli (p = 0.02). The 1 ml/kg emboli increased pulmonary artery pressures and decreased systemic blood pressure in 100% and 75% of animals, respectively. Peak changes in pulmonary artery pressure occurred at 1.2 +/- 0.8 min. In the present study, time to maximum change was greater for SvO 2 than for pulmonary artery pressure changes. Use of fiberoptic pulmonary artery catheters for continuous measurement of SvO 2 can add a new diagnostic modality to venous air embolism detection in patients who require a pulmonary artery catheter for other medical indications.

Venous air emboli with 15N2: pulmonary excretion and physiologic responses in dogs.

Venous air embolism occurs with decompression sickness as well as during a wide variety of surgical procedures in hospitalized patients. We developed a canine model to allow documentation and quantitation of pulmonary excretion of intravascular air emboli both in a control air breathing state and during treatment. We utilized 15N2 (a stable, nonradioactive isotope of room air nitrogen, 14N2) as the nitrogen component of venous air emboli (1 ml.kg-1) given to 27 anesthetized mongrel dogs ventilated with room air (tidal volume = 15 ml.kg-1). End-tidal 15N2 was measured and the embolism diagnosed by increased levels in exhaled gases. Exhaled gases were also collected in Douglas bags and the 15N2 recovered was quantitated by a helium dilution technique. Systemic and pulmonary artery pressure changes and quantitation of excreted 15N2 were documented after embolism during a control state with continued room air (21% oxygen) ventilation, and after treatments with either a) 100% oxygen ventilation; b) compression to 2128 mmHg, or 2.8 atm abs, and room air ventilation; or c) a combination of 100% oxygen ventilation and 2.8 atm abs compression. Increased end-tidal 15N2 was characteristic of all emboli, and use of 15N2 allowed accurate measurement of excreted gas during both room air and 100% oxygen ventilation. Embolic gas recoveries were not increased significantly by any of the treatments.

Hyperbaric nitrous oxide as a sole anesthetic agent in humans.

Nitrous oxide (N2O) has been used to produce analgesia and anesthesia for more than 100 yr. However, because of its high MAC value (1.04), general anesthesia with N2O can usually be attained only in a hyperbaric environment. Because of the sparsity of documentation for human physiologic responses to hyperbaric N2O, we studied eight male volunteers at 2 ATA (1520 mm Hg) anesthetized with N2O only for periods of 2-4 h. N2O partial pressures ranged from 836 to 1368 mm Hg. The anesthetic state was associated with tachypnea, tachycardia, increases in systemic blood pressure, mydriasis, diaphoresis, and at times, clonus and opisthotonus. A stable level of physiologic activity was difficult to maintain.

Effects of exercise in cool water on body weight loss.

Seven obese women (greater than 30 per cent body fat, mean = 43 per cent) performed moderate exercise (30 to 40 per cent of maximal oxygen consumption) for 90 min during head-out immersion in cool water (17 to 22 degrees C) five times per week for eight weeks to determine if cold exposure and the attendant caloric deficit in body heat stores would lead to body weight loss. Exercise was on a cycle ergometer that was modified for underwater use. Body weight, body fat, fat-free body weight, and caloric intake did not change significantly as a result of the exercise program in cool water. The significant heat debts incurred were presumably repaid without an increase in energy expenditure. The caloric balance and the thermal data obtained suggest that body heat stores were slowly repaid during recovery by resting metabolic heat production associated with a reduced rate of body heat loss. Maximal oxygen uptake did not increase significantly. No metabolic or thermal evidence was found to support cold adaptation in the obese women. Ergometer exercise in water as well-tolerated, as evidenced by no exercise-related injuries and an adherence rate of 93 per cent. It was concluded that, while cold exposure does not increase caloric expenditure significantly in obese individuals, exercising regularly in cool water may be beneficial as it may motivate obese people to exercise at higher intensity for thermal comfort and the water environment may help prevent injuries.

Equipment Update: Penn State's Foldable Rigid Stretcher.

Because moving a player improperly can compound a head or neck injury, the authors designed and built a foldable rigid stretcher with an adjustable traction bar.

Validity of the ultrasonic technique as a method of measuring subcutaneous adipose tissue.

Subcutaneous adipose tissue measurements, at abdomen, suprailiac, subscapular, and mid-triceps sites, made with the ultrasonic and skinfold caliper techniques were compared using data from 20 women and 17 men from a pool of subjects of 22 women and 20 men. In addition, comparisons were made between ultrasonic, soft-tissue roentgenographic and skinfold caliper techniques at the suprailiac and mid-triceps sites on 6 women and 12 men. Repeat measurements with the ultrasonic technique produced correlation coefficients of 0-87 and above. Correlations between skinfold caliper and ultrasonic measurements were generally higher among women than men over each of the four sites. A highly significant relationship, r = 0-88, was observed between the ultrasonic measurements and soft-tissue roentgenograms over the mid-triceps site. The correlation between the fat-muscle interface measured on the roentgenogram and ultrasonic measurements at the suprailiac site was 0-78. Multiple echoes and interfaces were observed at the suprailiac site on some subjects.