Large inter-individual differences exist in the degree of bradycardia induced by breath-hold facial immersion. The purpose of this study was to examine baroreceptor sensitivity in subjects who exhibit a strong response and in those who exhibit a minimal response. Thirty-nine healthy volunteers. were screened with three trials of breath-hold facial immersion during mild steady-state cycling. The six subjects displaying the greatest bradycardia were selected as responders and the six showing the least as non-responders. Baroreceptor sensitivity was estimated in each subject by examination of the heart rate and blood pressure responses to a controlled Valsalva manoeuvre and to isometric handgrip exercise. Regression lines for changes in systolic blood pressure over time showed a flatter response in the responders both during isometric handgrip exercise (p<.05) and over the 25 s immediately following release (p<.01). One interpretation of these findings is that the non-responders are less able to maintain a resting level of arterial blood pressure. As well, regression lines for the change in diastolic blood pressure over the period 25 to 55 s post-release of isometric handgrip exercise had different slopes in the two groups (p<.05). A positive mean slope calculated for the responders and a negative mean slope calculated for the non-responders, when plotted with the average intercepts, suggested an undershoot in diastolic blood pressure upon release in the responders. This may represent an attempt to regain resting levels of arterial blood pressure through peripheral vasodilitation. Direct measures by arterial catheter, in a sub-sample of four subjects, suggested that the blood pressure overshoot during the recovery phase of the Valsalva manoeuvre may not have been large enough to demonstrate group differences in baroreceptor sensitivity. / Thesis / Master of Science (MS)

The scope of extreme-environment diving defined within this work encompasses diving modes outside of the generally accepted no-decompression, open-circuit, compressed-air diving limits on selfcontained underwater breathing apparatus (scuba) in temperate or warmer waters. Extreme-environment diving is scientifically and politically interesting. The scientific diving operational safety and medical framework is the cornerstone from which diving takes place in the scientific community. From this effective baseline, as evidenced by decades of very low DCS incidence rates, the question of whether compressed air is the best breathing medium under pressure was addressed with findings indicating that in certain depth ranges a higher fraction of oxygen (while not exceeding a PC 2 of 1.6 ATA) and a lower fraction of nitrogen result in extended bottom times and a more efficient decompression. Extremeenvironment diving under ice presents a set of physiological. equipment, training and operational challenges beyond regular diving that have also been met through almost 50 years of experience as an underwater research tool. Diving modes such as mixed-gas, surface-supplied diving with helmets may mitigate risk factors that the diver incurs as a result of depth, inert gas narcosis or gas consumption. A close approximation of inert gas loading and decompression status monitoring is a function met by dive computers, a necessity in particular when the diver ventures outside of the single-dive profile into the realm of multi-level, multi-day repetitive diving or decompression diving. The monitoring of decompression status in extreme environments is now done exclusively through the use of dive computers and evaluations of the performance of regulators under ice have determined the characteristics of the next generation of life-support equipment for extreme-environment diving for science. These polar, deep and contaminated water environments require risk assessment that analyzes hazards such as cold stress, hydration, overheating, narcosis, equipment performance and decompression sickness. Scientific diving is a valuable research tool that has become an integral methodology in the pursuit of scientific questions in extreme environments of polar regions, in contaminated waters, and at depth.

Dissertation (Ph.D.) - Simon Fraser University, 2006. / Theses (School of Kinesiology) / Simon Fraser University. Includes bibliographical references. Also issued in digital format and available on the World Wide Web.

Thesis (M.S.)--University of Wisconsin--Madison, 1980. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 201-205).

Thesis (Ph.D.) - University of Queensland, 2006. / Includes bibliography.

Elite springboard divers typically make very precise and reproducible movements when they perform the same dive many times. However, variability is always present in both technique and outcome. While it is desirable to have low outcome variability this may necessitate real-time adjustments which result in increased technique variability from trial to trial. The aim of the present research was to determine whether feedback control adjustment is used during (a) the hurdle takeoff, (b) the dive takeoff, and (c) the dive flight phase. 15 forward pike dives and 15 forward 21⁄2 somersault pike dives, performed by an international diver, were video recorded at 250 Hz and manually digitised followed by DLT reconstruction of joint centre locations. Orientation angle and joint angles were calculated and fitted with quintic splines to give angular velocities. Foot placements, mass centre location and velocity were determined along with angular momentum about the mass centre. In the hurdle takeoff no adjustment was made to reduce the variability in the foot location at hurdle landing. In the dive takeoff phase an angle-driven simulation model was used to determine the expected variation in mass centre velocity and angular momentum at the instant of takeoff arising from the variation in velocity and angular momentum at touchdown. The simulated variation at the instant of takeoff was greater than the variation in the recorded performances indicating that some adjustment had been made during the takeoff phase. In the flight phase an angle-driven simulation model was used to determine the expected variation in orientation angle at water entry arising from the variation in velocity and angular momentum at takeoff. The variation in the orientation angle at entry obtained from the simulations was greater than the variability in the actual performances, indicating that the diver had used feedback control adjustments in the flight phase to reduce his performance outcome variability. The variation in the angular momentum at takeoff was reflected in the average hip angle in flight, indicating that the hip angle was adjusted to be larger to compensate when the initial angular momentum was greater. The use of feedback control adjustments found in this study demonstrated that variability has a functional role in human movement.

The enzymatic organization of muscle tissue usually is examined in only a select few muscles of any one animal species. However, because the functional demands placed on individual muscles can vary so widely from muscle to muscle, it is inappropriate to generalize findings from one or two muscles to muscle tissue in general. The differences or similarities in metabolic machinery between skeletal muscles of a wide functional range provides crucial information with respect to a particular animals' whole body metabolism. Nowhere is this understanding more important than in the diving marine mammal which must operate as a closed system (with respect to oxygen supply) while submerged. The goals of this thesis are: 1) to provide a broad body of information on the metabolic organization of a large cross-section of marine mammal muscles, both functionally and with regard to location, 2) to assess the implications of the enzyme differences between muscles to the diving habit, and 3) to compare the metabolic organization of skeletal muscle among several species of marine mammal with different diving abilities and habits. A series of 13 enzymes were measured in 21 skeletal muscles of the harbor seal, Phoca vitulina. In addition, 23 enzyme activity ratios were calculated and analyzed for these muscles. A similar analysis of 22 muscles from fin whales, Balaenoptera physalis. was conducted --including 7 key enzymes and 15 activity ratios. Overall, both the maximum activities and the enzyme activity ratios are consistent with the idea that marine mammal muscle is typical mammalian muscle, exhibiting few significant differences from terrestrial species with respect to catabolic enzymes. The only obvious exception to this in the species examined is observed with fin whale locomotory muscle which has extremely high activities of lactate dehydrogenase (over 2000 units/gm wet wt at 25°C) due to an apparent scaling phenomenon. Tight control of this high potential glycolytic flux is indicated by pyruvate kinase activities that scale downward. Comparisons of enzyme relationships between muscles of harbor seals seem to indicate a very aerobically poised metabolic make-up. This is especially true with respiratory and locomotory muscles, which also show a high tendency to utilize fat. This pattern of enzyme activities and activity ratios in the locomotory muscles of harbor seal is evidence that muscle contractile activity while diving is powered primarily through oxidative pathways and largely based on fat as fuel. The majority of non-locomotory muscles appear to be more able to function anaerobically utilizing carbohydrate. This pattern may correlate with circulatory redistributions while diving that preferentially fuel the locomotory muscles with oxygen, leaving the inactive muscles significantly more hypoperfused and, therefore, candidates for energy saving O₂ sparing (metabolic depression). Fin whales exhibit an opposite pattern, with enzyme profiles more typical of "white" muscle. Unlike harbor seals, the locomotory muscles of fin whales are consistently the least oxidatively poised of the muscles examined. This apparently more anaerobic nature of fin whale muscle is possibly complicated by scaling adaptations, but appears to be a real phenomenon. The examination of three to four skeletal muscles from each of three additional phocid seal species from Antarctica, leopard seals (Hydrurga leptonyx). crab-eater seals (Lobodon carcinophagus). and Weddell seals (Leptonychotes weddelli) confirm that the harbor seal pattern of enzyme profiles is fairly consistent among phocid seals. By these criteria skeletal muscles of phocid seals (particularly the locomotory and respiratory muscles) appear to be designed for sustained aerobic metabolism during diving regardless of the habits or diving capabilities of the seal. / Science, Faculty of / Zoology, Department of / Graduate

The extreme elevation in plasma levels of norepinephrine (NE) and epinephrine (EP) which occurs during forced diving of ducks (Anas platyrhynchos) was studied before and after denervation of the adrenal glands. Elevated PaCO₂, decreased arterial pH, decreased blood glucose as well as low PaO₂ have been described as causal factors in this response. These variables, as well as blood pressure, heart rate and breathing frequency were measured in ducks dived after breathing air or pure 0₂ to clarify and quantify the mechanism involved and its physiological function. Both NE and EP concentration increased by up to 2 orders of magnitude in the 4 minute dive period, but by a significantly lesser amount if the duck breathed 0₂, before the dive. While pH and PaCO₂ were well correlated with the changes in plasma NE and EP levels during both air and 0₂ dives, both pH and PaCO₂ changed more in the 0₂ trials, indicating that they are not the primary cause of the response. Plasma glucose levels were variable. PaO₂ values less than normal correlated well with increasing NE and EP concentrations, but at high PaO₂s, there was no correlation, suggesting that hypoxia is the permissive state for the full response. Compared with breathing air, breathing O₂ before the dive attenuated the diving bradycardia, eliminated the decrease in blood pressure normally observed during dives, and caused more extreme changes in pH, PaC0₂, and of course, PaO₂. Denervating the adrenals decreased the amounts of both catecholamines released during dives after breathing air and 0₂, EP significantly more than NE. Adrenal denervation per se did not cause a significant change in heart rate, blood pressure, arterial gas tensions, pH, or plasma glucose changes during dives although the operation caused increased variation in some of the parameters. In ducks, the cause for the catecholamine release is decreasing PaO₂ and full expression of the response is dependent on intact innervation of the adrenal gland, although there is a component that is unaffected by denervation. While possible roles for this response are discussed, the true physiological function of this response remains cast in shadows. / Science, Faculty of / Zoology, Department of / Graduate

Cardiovascular responses evoked during forced submersion enable the Pekin duck (Anas platyrhynchos) to survive protracted periods of asphyxia. The responses include an extraordinary bradycardia and intense peripheral vasoconstriction with the result that blood flow is favoured to those organs most susceptible to lack of oxygen. These adjustments appear to be mediated via the caudal brainstem following stimulation of peripheral and central arterial chemoreceptors. The minor role that baroreceptors play in the generation of these responses was demonstrated by the persistence of the cardiovascular changes following peripheral arterial baroreceptor denervation. Isolation of the cephalic circulation from the systemic circulation enabled a series of experiments to assess the relative contributions from peripheral chemoreceptors, located in the carotid bodies, and from unidentified central chemoreceptors within the cranial circulation. A declining arterial P0₂ in the systemic circulation appeared especially potent in evoking bradycardia during submersion. Increased arterial PC0₂, likewise, resulted in a reduced heart rate. Similar changes in the blood gas levels of the cephalic circulation did not elicit significant bradycardia. However, both receptor groups responded to arterial hypoxic hypercapnia by activating substantial reduction in peripheral blood flow, as reflected by the rise in hind limb vascular resistance. Although baroreceptors may continue to mitigate changes in arterial blood pressure and cause some change in heart rate and vascular resistance, chemoreceptors appear to be predominantly responsible for the changes during submersion. The cardiac response to chemoreceptor stimulation during submersion was discovered to habituate following repetitive diving. Habituation was so pronounced in some ducks that after several training sessions the bradycardia during 40-second forced dives was abolished. Habituation of the cardiac response appeared dependent on the intensity of chemoreceptor stimulation. With severe arterial hypoxia, produced by either prolonging dive times or by reducing the pre-dive inspired oxygen content, little or no cardiac habituation was observed. Tests were conducted to demonstrate efficacy of the cardioinhibitory efferent discharge. Maintained sensitivity of chemoreceptors was suggested by the lack of change in oxygen breathing tests before and after training. Furthermore, the persistence of stimulus intensity was established and these observations led to the suggestion that the locus of habituation is within the CNS. The demonstration that the level of bradycardia was dependent on arterial P0₂ in both naive and habituated animals argues against the contention that the diving response is a fear response. Further evidence against this view was provided by the demonstration that the diving response remains essentially intact following transection in the rostral mesencephalon below the level of the hypothalamus. It is concluded that chemoreceptor-driven cardiovascular changes evoked as part of the diving response are mediated by regions of the CNS below the rostral brainstem. Modification of these responses can be produced in the intact animal by simple forms of learning. However, it remains uncertain at what level this influence arises. / Science, Faculty of / Zoology, Department of / Graduate

Title: Historical development of freediving. Objectives: The goal of this thesis is to describe the historical development of freediving. Methods: To achieve the goal, it has been analysed all available information including literature, internet software, materials about diving, descriptions, comparisons and an interview. Results: This thesis shall provide, to those interested in the sport and to general public, a comprehensive and clear description of historical development of freediving from the early beginnings to the present. Keywords: history, sport, diving, swimming, freediving