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The pressure-flow characteristics of inspiration have been studied, with particular reference to breathing dense gas at raised environmental pressure. The inspiratory pressure-flow relationship was determined from maximal and submaximal breaths performed by divers at pressures equivalent to 18, 39 and 56 msw, and compared with the relationship measured at sea level. Inspiratory flow limitation was found at every depth, becoming more severe as environmental pressure was increased. Similar studies performed at sea level in subjects breathing dense gas mixtures or breathing against a fixed resistance also showed some evidence for inspiratory flow limitation. Evidence was also found for sudden, transient flow interruptions breathing dense gas at raised environmental pressure and at sea level. An additional effect of high pressure on inspiration was observed, which leads to a distinctive pattern of oscillatory flow and which may be related to the High Pressure Neurological Syndrome. Flow oscillations developed in divers suffering from HPNS. These were of the same frequency range as muscle tremors associated with the syndrome. A mechanism of dynamic inspiratory airway compression has been proposed to explain these results.

There is no abstract available for this thesis. / School of Physical Education

Thesis (Ph. D.)--Sommerville College, Oxford, 1988. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 426-437).

Thesis (Ph. D.)--UCLA, 2008. / Vita. Description based on print version record. Includes bibliographical references (leaves 198-209).

During the late 1970s, when oil exploration and extraction from the North Sea were at a peak, there was increasing concern about the number of episodes of unexplained confusion, loss of consciousness and deaths during dives. Previous field measurements on divers had demonstrated that divers became hypothermic with little or no sensation of cold, despite suit heating using tepid water pumped from the surface. This thesis describes laboratory experiments designed to document and to determine the cause of 'insidious' hypothermia. Initially, it was shown that uniform skin cooling in tepid water could produce subnormal body temperatures in all subjects tested, whether or not they had been acclimatised to cold. This symptomless fall in deep body temperature could be reversed by further chilling the hands and feet using a separate water circulation system, while the rest of the body remained in tepid water. The rise in deep body temperature was shown to be due to an increase in metabolic rate caused by shivering, with cold-acclimatised subjects shivering less. The main cause of 'insidious' hypothermia is therefore inadequate skin stimulation of thermoregulatory reflexes by lukewarm water, with previous cold water exposure further reducing responses. The next series of experiments was designed, to assess the impairment of memory and reasoning processes by oold, since most previous evidence find been inadequate or anecdotal. Psychological tests were administered during the unusual physiological circumstances on rewarming after oold immersion, where subjects felt warm and comfortable, but had a low or falling deep body temperature. The results clearly showed that the ability to form new memories was seriously impaired, even by mild falls in temperature, and that reasoning processes were greatly prolonged, although remaining accurate. The current work has therefore successfully determined the cause of the hypothermia which occurs in lukewarm water, and has shown that mental abilities are seriously affected early in the development of hypothermia.

No description available.