During mixed gas saturation diving (to 3-49.5 ATA) daily urine flow increases by about 500 ml/day, with no changes in fluid intake and glomerular filtration rate. The diuresis is accompanied by a significant decrease in urine osmolality and increase in excretion of such solutes as urea, K+, Na+, Ca2+ and inorganic phosphate (Pi). The fall in urine osmolality is mainly due to a reduction of free water reabsorption which is associated with a suppression of insensible water loss and the attendant inhibition of antidiuretic hormone (ADH) system. The increase in urea excretion may be associated with a reduction of urea reabsorption at the collecting duct as a consequence of ADH suppression. The rise in K+ excretion is due to a facilitated K+ secretion at the distal tubule as a result of increased aldosterone, urine flow and excretion of impermeable anions such as Pi. The activation of aldosterone system is partly attributed to a transient dehydration induced by early hyperbaric diuresis. The increase in Na+ excretion in the face of enhanced aldosterone secretion indicates that the Na+ transport in the proximal tubule is markedly inhibited (by unknown mechanism). The Pi excretion increases with no changes in plasma level of parathyroid hormone (PTH), thus it may be due to an inhibition of Na+-Pi cotransport in the proximal tubule. The increase in Ca2+ excretion may be secondary to the inhibition of Na+ transport at the proximal tubule. Precise information on the proximal tubular Na+ transport is important to understand the mechanisms of impaired solute transport under hyperbaric conditions.
A measurement system was employed to detect gustatory evoked potentials from human scalp by stimulus of a taste solution with the use of a laser beam device. The evoked potentials for four taste qualities (i.e., sweet-sucrose, salty-sodium chloride, sour-tartaric acid, and bitter-quinine-HCl) were measured before and after treatment with a sweet suppressing agent (i.e., gymnema sylvestre extract) to the tongue of a human. The solution was given to the chorda tympani nerve located 20 mm from the apex of the tongue and 15 mm from the left side of the center line. The maximum potential level and its latency were evaluated. Artificial saliva was used as a control solution. The evoked potentials obtained were averaged by eight evoked potentials to detect the peak of the evoked potential more clearly. The latencies for taste stimuli were found on two kinds of peaks at approximately 50 ms and 180 ms. These peaks are P1 and P2. The purpose of this study is to investigate the influence of sweet suppressing agent on P1 and P2. The influence of the sweet suppressing agent to evoked potential by salty, sour, and bitter taste stimuli was not recognized, but the responses to sweet (sucrose) were abolished after treatment with a sweet suppressing agent. It was recognized that the peak P2 originated from the taste stimulus. The peak P1 did not suffer the influence of the sweet suppression, so it was considered that the response to P1 was due to sensations other than the gustatory response, such as somatosense.
In order to understand the role of clothing covering and uncovering the hands, feet, legs, thighs, buttocks and hypogastric region for human thermoregulation at an ambient temperature of 10°C, two series of experiments were conducted on six healthy male subjects wearing three different kinds of clothing in Expt. 1 and four different kinds of clothing in Expt. 2. The three kinds of clothing used in Expt. 1 were, clothing A covering the whole body surface area except the head, clothing B covering the whole body surface area except the head and feet, and clothing C covering the whole body surface area except the head, hands and feet. The four kinds of clothing used in Expt. 2 were clothing C used in Expt. 1, clothing D covering the whole body surface area except the head, hands, feet and legs, clothing E covering the whole body surface area except the head, hands, feet, legs and thighs, and clothing F covering the whole body surface area except the head, hands, feet, legs, thighs, buttocks and hypogastric regions. The starting time of the experiment, the subject measurement variables and the garments used were all kept constant throughout the experiment. The subjects were instructed to enter a chamber at room-temperature and various sensors were attached. The subjects were then instructed to relax until a quasi-steady temperature state was reached. The subjects were then moved into a chamber at 10 ± 0.2°C, 50 ± 5% RH. for two hours. The main results can be summarized as follows: 1) The level of rectal temperatures of subjects wearing clothing C were maintained significantly better than the temperatures of subjects wearing clothing A and B who experienced a significant drop in temperature in the 10°C chamber in Experiment 1. 2) In Experiment 2, the rectal temperatures of subjects wearing clothing E were maintained significantly better than subjects wearing clothing C, D and F, who also experienced significant drops in temperature in the 10°C chamber. These different behavior patterns of rectal temperatures were discussed in terms of the counter-current heat exchange system.
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