The aim of these experiments was to investigate the influence that dietary manipulation has upon acid-base balance and substrate availability at rest and during high intensity exercise. It was hoped to identify some of the mechanisms that may control the utilisation of energy substrate and influence the onset of fatigue during high intensity exercise. A pattern of dietary and exercise manipulation intended to alter carbohydrate (CHO) and fat availability was undertaken during the first two experiments. In addition to influencing energy substrate availability, the diet and exercise regimen also significantly influenced resting acid-base balance and high intensity exercise capacity. The reduction in exercise performance afer administration of a low CHO, high fat, high protein diet may have been due to the diet-induced acidosis produced by this diet. However, it is also probable that glycogen availability was influencing exercise performance in this situation. A fixed period of exercise under the same experimental conditions indicates that a higher than normal muscle glycogen content may dictate the pattern of substrate utilisation during high intensity exercise. In a second series of experiments it was demonstrated that dietary manipulation alone will influence acid-base balance and exercise capacity. A high fat, high protein diet will produce a metabolic acidosis but will not influence total muscle glycogen content. In this situation, it is unlikely that a reduction in high intensity exercise performance can be attributed to the availability of muscle glycogen. It is possible that a change in fat availability, rather than muscle glycogen content, will influence the pattern of substrate utilisation during high intensity exercise. However, it is unlikely that a change in fat availability will be responsible for the reduction in exercise capacity recorded after a high fat, high protein diet. The reduction in exercise capacity may be the result of a diet-induced acidosis. Although it is unlikely that dietary acidosis will influence H+ efflux from muscle it may influence pre-exercise muscle buffering capacity. The resulting greater decline in muscle pH during exercise after a high fat, high protein diet may influence muscle function: firstly, by inhibiting the activation of muscle contraction which is due possibly to a reduction in the release of Ca2+ from the sarcoplasmic reticulum and a reduction in the affinity of the myofilaments to Ca2+. Secondly, by inhibiting muscle relaxation which is thought to result from a disruption in actin-myosin corss-bridge separation and a reduction in the rate of Ca2+ removal from the myofibril cytoplasm. Thirdly, by inhibiting muscle glycolysis at the point of PFK. Finally, there is some evidence to suggest that the rate of muscle lactate efflux and/or the metabolic fate of lactate produced during high intensity exercise are different from normal after a period of dietary manipulation.

Changes in heart rate; oral temperature; mean skin temperature; urinary pH, volume, sodium, potassium, chloride, urea and creatinine; salivary pH, sodium, potassium and urea; expired air and oxygen consumption have been monitored in young men doing ( 1) exercise on an ergometer for 4 min at 10C, 20C, 30C and 40C dry bulb 50% rh at 120-320 W; (2) 20 min at 30C dry bulb at 50% rh, 60% rh, and 85% rh at 120W, 145W and 170W; and (3) 60 min at 20C, 30C and 40C dry bulb and 50% rh at 170w. Changes in work rate, environmental temperature, relative humidity and exposure time were found to correlate well with the urinary and salivary changes and in most cases changes in both work rate and ambient temperature produced simple summation effects. The increase in salivary components correlated well with the decrease in urinary components. Salivary sodium, potassium and Na+/K+ ratio increased significantly when work intensity, exposure time and environmental temperature were increased. Salivary urea correlates significantly with increased exposure time. The elevated values for salivary components may be explained on the basis of volatilization caused by forced ventilation during exercise; increased penetration of plasma components into saliva; increased water reabsorption, decreased sodium reabsorption, and increased potassium secretion in the ductile system of the salivary glands due to increased sympathetic activity. The results show that changes in saliva give a valid indication of the body's response to work and environmental stress and suggest that saliva could be used to study the combined effects of work and heat in places where it is impracticable to obtain samples of blood or urine.

No description available.

No description available.

Platelets of divers undergo changes following exposure to high pressures and decompression. Since the latter is associated with formation of intravascular bubbles, platelet-rich plasma (PRP) was treated to reproducible doses of bubbles of air, with and without enrichment by 5% Co2 (to maintain physiological pH). PRP was also subjected to stirring and a 'rocking' procedure. Bubbles caused significant aggregation, measured turbidimetrically, of human (but not bovine) platelets, particularly without pH control, whereas little occurred with stirring and rocking. Bubbling inhibited subsequent ADP-induced aggregation of human platelets, more markedly without pH control. Bovine cells were unaffected, thus apparently less sensitive to bubbles. Since rocking was shown to be equiconvective to bubbling, aggregation associated with bubbling is not due simply to exposure of the gas/liquid interface, shear stress exerted by bubbles possibly being culpable. The importance of pH control in in vitro work was also demonstrated. PRP was next separately equilibrated (by rocking) with 5 atmospheres absolute (ata) pN2O, with 101 ata pN2 (these being approximately narcotically equipotent) and with 100 ata pHe (extremely weakly narcotic). 5 ata pN2O caused least inhibition of ADP-induced aggregation, and hydrostatic pressure (applied independently, using He and a floating plastic barrier which reduced dissolving of gas) was shown to swamp narcotic effects. It was suggested that inhibition by high pressure was due to blocking of prostaglandin synthesis. Finally, the effect of hydrostatic pressures of up to 51 ata on platelet ATP release was examined using a luciferin-luciferase assay. ADP-induced secretion was either completely blocked or partially reduced by high pressure. These effects could be important to divers suffering haemorrhages at great depths. Furthermore, in vitro hyperbaric studies are of potential value in elucidating activation pathways in platelets and other excitatory cells.

No description available.

Physiological and psychological indicators of stress were measured in a cohort of 20 female nurses working 12 hour, 7.5 hour and 'nine to five' shift patterns in intensive care units conducted over a period of four years. Saliva samples were collected by each subject at four specified times during each shift over a period for one week and repeated every few months. Two consecutive days were used to compare days on duty, days off duty and the first day at work following days off. Salivary cortisol levels were measured by RIA. Secretory immunoglobulin A (SIgA), also a physiological indicator of stress, was determined with an indirect sandwich ELISA using a monoclonal antibody. Salivary cortisol levels of nurses were higher and SIgA levels lower prior to starting 12 hour shift following a day off compared with nurses working other shifts. Simultaneous psychological measures obtained by selfreports of perceived demands, coping and moods showed these nurses did not perceive themselves to be stressed. The findings of the study suggest that nurses working 12 hour shifts prepare for work differently perhaps in anticipation of long hours of work. Furthermore, salivary cortisol levels were considerably higher compared with those cited in studies of acute stress under laboratory conditions. In contrast, 20 nurses undertaking an academic examination, considered an acute stressful event, reported increased anxiety and mental and emotional demands and had higher salivary cortisol concentrations prior to the event, albeit lower than the longitudinal study. SIgA levels were lower prior to the examination but not significantly so. A positive correlation between cortisol and SIgA levels was apparent, however, only 6 months later when the subjects no longer perceived themselves to be stressed.

No description available.

Results of the first investigation into possible acclimatisation to cold and thermal status of Antarctic divers are presented. Over a year, on average one subject dived on alternate days and the other four subjects once a week. Divers wore 7mm or 10mm wet suits in water ca-1^oC. Mean dive duration was 30min, and mean depth of immersion 9m. Surface mean wind speed was 10 knots and mean ambient temperature -2^oC. Over the year subjects rectal and skin temperatures, and thermal comfort were monitored before, during and after immersion on 26 dives. Severe body cooling (Hall 1972) occurred on 75%, rectal temperature decreased to below normal (although never to clinically hypothermic levels) and there was a marked, exponential drop in skin temperature. End-of-dive finger temperatures were always at a level at which impairment of function would be expected. Divers were usually uncomfortably cold at the end of dives. During the year repeated monthly measurements were made of: skinfold thickness, body weight, body fat weight and fat-free mass: basal metabolic rate: rectal and skin temperatures, metabolic rate, shivering, thermal comfort, adrenaline, noradrenaline and cortisol excretion during immersion to the neck in water at 20^oC for one hour: time of onset of cold-induced vasodilatation, temperature and pain responses of left index finger immersed at 0^oC for half an hour. Differences between the responses of divers at different months of the year and between divers and nondivers were tested by analysis of variance. It was found that divers shivered less and had less thermal discomfort (by verbal rating scales) than nondivers (as they had similar metabolic rates this suggests greater nonshivering thermogenesis). It was also found that divers extracted more oxygen from inspired air while immersed to the neck than nondivers. In both divers and nondivers there was a winter increase of skinfold thickness and body fat weight and a winter decrease of fat-free mass, and while these may be an adaptation to cold, it is possible that other stimuli were responsible. No significant differences were found between any of the other parameters tested. Monthly measurements of physical fitness, and time spent outside and in various activities indicated that these were not important complicating factors in the acclimatisation studies. A comparison of Antarctic dives and laboratory cold water immersions showed that while dives led to a greater fall of peripheral temperature and lower peripheral thermal comfort the laboratory immersions led to a greater fall in rectal temperature and trunk skin temperature. In this thesis, it is proposed that while Antarctic divers were subject to considerable thermal stress there was little evidence of cold acclimatisation.

A study was made on seventeen young men at a Polar scientific research station over a period of one year. Serial observations were made of body composition, energy expenditure and performance. Weather recordings were carried out in order to determine the influence of seasons on the various parameters described and an attempt made to ascertain any groupings of the individuals. Body composition was recorded weekly by weighing and by skinfold thickness measurements that were subsequently converted into total body fat estimations. Both these parameters increased predominantly during the first six months. Activity patterns derived by personal diary recall showed that on average ten per cent of time was spent outside, with a variation between summer and winter. Mean energy expenditure derived from these figures was at a level of 3600 kcal/day. This compares favourably with results from previous polar expeditions and distinction is made between a static and a travelling scientific station. Discussion is centred on a proposed stress triad that includes isolation, darkness and severe weather. Various combinations of these environmental stresses are considered and an evaluation is made of their effects on performance that was measured using a cycle ergometer. It is shown that the group became significantly more fit over the year and that the correlation between fitness change and energy expenditure is poor. The influence of body composition on fitness is considered and a re-appraisal is made of cold acclimatization. It is confirmed that Man on a static scientific research station spends only a small proportion of time outside and the conclusion is drawn that Antarctica now, with the facilities of modern building insulation techniques and specialised clothing, together with an adequate diet, is a desirable habitat for Man who may soon colonize the region to exploit natural resources.