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At least 703 records · Page 39Linked to original sources
PubMed1985

Central and peripheral causes of hyperreflexia in humans breathing 5% trimix at 650 m.

To clarify the mechanism of increased stretch reflex responsiveness in deep divers (hyperbaric hyperreflexia), comparative studies of stretch (T) and Hoffmann (H) reflexes were done on three men breathing 5% N2-0.5 bar O2-balance He at pressures up to 650 m of seawater (msw) (Atlantis IV simulated dive, F.G. Hall Laboratory, Duke Medical Center). Electromyography revealed increases at depth of up to 160% in the T reflex recruitment ratio (T reflex/Mmax) compared with surface controls. The H reflex recruitment ratio (Hmax/Mmax) did not change significantly. It is concluded that hyperbaric hyperreflexia is mainly due to increased muscle spindle sensitivity, presumably arising as a central effect on gamma-motoneuron activity. However, a purely peripheral effect of pressure on the spindle end-organ itself is not ruled out. Increases of 100-200% in muscle twitch peak force are reported and provide evidence that pressure can act directly on peripheral physiology. Postreflex clonic potentials (rebounds) during voluntary plantar flexion were significantly increased both in amplitude and number, leading to sustained clonus in one subject. In this respect, 5% N2 was less effective than 10% N2 of Atlantis III in controlling underdamping of the reflex loop. Conversely, the twitch contraction rate and clonic frequency in this study were only half as slowed compared with results from the earlier dive.

Central Nervous System↗
PubMed2005

Cormorants dive through the Polar night.

Most seabirds are visual hunters and are thus strongly affected by light levels. Dependence on vision should be problematic for species wintering at high latitudes, as they face very low light levels for extended periods during the Polar night. We examined the foraging rhythms of male great cormorants (Phalacrocorax carbo) wintering north of the Polar circle in West Greenland, conducting the first year-round recordings of the diving activity in a seabird wintering at high latitudes. Dive depth data revealed that birds dived every day during the Arctic winter and did not adjust their foraging rhythms to varying day length. Therefore, a significant proportion of the dive bouts were conducted in the dark (less than 1 lux) during the Polar night. Our study underlines the stunning adaptability of great cormorants and raises questions about the capacity of diving birds to use non-visual cues to target fish.

Adaptation, Physiological↗
PubMed2003

The comparative energetics and growth strategies of sympatric Antarctic and subantarctic fur seal pups at Iles Crozet.

The period of maternal dependence is a time during which mammalian infants must optimise both their growth and the development of behavioural skills in order to successfully meet the demands of independent living. The rate and duration of maternal provisioning, post-weaning food availability and climatic conditions are all factors likely to influence the growth strategies of infants. While numerous studies have documented differences in growth strategies at high taxonomic levels, few have investigated those of closely related species inhabiting similar environments. The present study examined the body composition, metabolism and indices of physiological development in pups of Antarctic fur seals (Arctocephalus gazella) and subantarctic fur seals (Arctocephalus tropicalis), congeneric species with different weaning ages (4 months and 10 months, respectively), during their overlap in lactation at a sympatric breeding site in the Iles Crozet. Body lipid reserves in pre-moult pups were significantly greater (t28=2.73, P<0.01) in subantarctic (26%) than Antarctic fur seals (22%). Antarctic fur seal pups, however, had significantly higher (t26=3.82, P<0.001) in-air resting metabolic rates (RMR; 17.1 +/- 0.6 ml O2 kg(-1) min(-1)) than subantarctic fur seal pups (14.1 +/- 0.5 ml O2 kg(-1) min(-1)). While in-water standard metabolic rate (SMR; 22.9 +/- 2.5 ml O2 kg(-1) min(-1)) was greater than in-air RMR for Antarctic fur seal pups (t9=2.59, P<0.03), there were no significant differences between in-air RMR and in-water SMR for subantarctic fur seal pups (t12=0.82, P>0.4), although this is unlikely to reflect a greater ability for pre-moult pups of the latter species to thermoregulate in water. Pup daily energy expenditure was also significantly greater (t27=2.36, P<0.03) in Antarctic fur seals (638 +/- 33 kJ kg(-1) day(-1)) than in subantarctic fur seals (533 +/- 33 kJ kg(-1) day(-1)), which corroborates observations that pups of the former species spend considerably more time actively learning to swim and dive. Consistent with this observation is the finding that blood oxygen storage capacity was significantly greater (t9=2.81, P<0.03) in Antarctic (11.5%) than subantarctic fur seal (8.9%) pups. These results suggest that, compared with subantarctic fur seals, Antarctic fur seal pups adopt a strategy of faster lean growth and physiological development, coupled with greater amounts of metabolically expensive behavioural activity, in order to acquire the necessary foraging skills in time for their younger weaning age.

Animals↗
PubMed1995

Respiratory and plumage gas volumes in unrestrained diving ducks (Aythya affinis).

Closed-circuit plethysmography and inert gas equilibration analysis were used to measure the volumes of gas in the respiratory system and plumage at the end of voluntary dives in unrestrained lesser scaup (Aythya affinis). Total (respiratory plus plumage) gas volumes were measured by helium dilution and estimated from body mass, body tissue density and buoyant force. These two techniques yielded results that differed by only 2.1 +/- 1.5%. Buoyancy decreased from a maximum of 3.46 +/- 0.16 N at immersion to a minimum of 2.65 +/- 0.16 N at 1.5 m depth at the end of the feeding phase of voluntary dives. At 0.193 +/- 0.013 L BTPS, the respiratory system contributed 52% of the initial buoyancy and 65% of the minimum value. The increasing relative influence of the respiratory system on buoyancy was due to the loss of 47 +/- 5% of the air in the plumage layer during the dive. These data differ significantly from estimates based on restrained ducks, and this has implications for modelling of mechanical costs of diving, oxygen storage capacity and thermal insulation in foraging ducks.

Air↗
PubMed1984

Morphological and physiological responses of the lungs of dogs to acute decompression.

The lung's response to decompression was studied in dogs anesthetized with pentobarbital sodium. Arterial pressure, hematocrit, right ventricular pressure, left ventricular end-diastolic pressure (LVEDP), dynamic compliance (CL), pulmonary resistance (RL), and arterial PO2, PCO2, and pH were measured prior to and for 3 h after a simulated air dive to 300 feet of seawater. Bronchoscopy was performed predive and at 3 h postdive. At 3 h animals were killed, and sections of lung were excised for histological examination. The decompression profile used regularly produced pulmonary hypertension, systemic hypotension, hemoconcentration, and arterial hypoxemia. CL fell in all but one dived animal. RL was more variable but remained unchanged postdive in most animals. The decompression stress did not alter the bronchoscopic and histological appearance of the airway mucosa. Pulmonary edema was regularly observed in histological sections and occurred without elevations of LVEDP. We concluded that noncardiac pulmonary edema is the principal response of the lung to decompression stress.

Animals↗
PubMed2001

Migratory movements, depth preferences, and thermal biology of Atlantic bluefin tuna.

The deployment of electronic data storage tags that are surgically implanted or satellite-linked provides marine researchers with new ways to examine the movements, environmental preferences, and physiology of pelagic vertebrates. We report the results obtained from tagging of Atlantic bluefin tuna with implantable archival and pop-up satellite archival tags. The electronic tagging data provide insights into the seasonal movements and environmental preferences of this species. Bluefin tuna dive to depths of >1000 meters and maintain a warm body temperature. Western-tagged bluefin tuna make trans-Atlantic migrations and they frequent spawning grounds in the Gulf of Mexico and eastern Mediterranean. These data are critical for the future management and conservation of bluefin tuna in the Atlantic.

Animal Identification Systems↗
PubMed1978

Thermal measurements on divers in hyperbaric helium-oxygen environments.

During a series of three saturation dives to simulated depths of 1000, 1200, and 1400 fsw at the Ocean Simulation Facility, measurements were made to establish the rate of heat loss of unclad divers in helium-oxygen gaseous environments. These measurements were part of a program to determine the dangers of cold stress and the temperature/time relationship tolerated by divers in cold diving bells or in hyperbaric chambers in which environmental conditions are uncontrolled. Three specific gaseous temperatures of 15, 20, and 25 degrees C were considered. In each experiment, as many as four subjects were monitored for body core and mean skin temperature over a 2-h testing period. One or two of the subjects were also monitored for mean body convective heat loss to determine physiological (shell) thermal insulation. Results of these experiments are expressed in depth-time-temperature three-dimensional graphs in whic, the temperature variable is one of the following: mean skin temperature change, mean body temperature change, or mean rectal (core) temperature change, each suitable for defining diver thermal limitations. It was also possible to rank body areas of the subjects in relation to heat loss and temperature decrease during exposure to the cold environment.

Adult↗
PubMed2000

Valsalva-induced syncope during apnea diving.

A young man had two dangerous episodes of transient loss of consciousness during apnea diving in a swimming pool. Medical and neurologic examination results were normal. Standard autonomic test results (including heart rate variability, baroreflex sensitivity, tilt-table test, and Valsalva ratio) were unremarkable, with the exception of an increased blood pressure decrease during early phase II of the Valsalva maneuver. Syncope with arrhythmic myoclonic jerks could be evoked by a strong straining maneuver. Simultaneous physiologic recordings showed extreme blood pressure and cerebral blood flow velocity decreases and electroencephalographic slowing during syncope. The electrocardiogram showed a continuous sinus rhythm with a progressive tachycardia. The authors' findings were not compatible with baroreflex failure or vasovagal mechanisms (Bezold-Jarisch reflex activation) as the underlying causes. The authors concluded that mechanical factors (strong reduction of blood reflux to the heart) in combination with a reduced threshold of the brain for developing ischemia-related arrhythmic myoclonic jerks were responsible for Valsalva-induced syncope in the patient.

Adult↗
PubMed1999

Assessment of oxygen levels in alternative designs of semiclosed underwater breathing apparatus.

A method for predicting the circuit oxygen levels in semiclosed underwater breathing apparatus (UBAs) is presented. Oxygen levels are assessed for traditional circuit designs using sonic metering valves to inject a constant mass flow of fresh makeup as well as two alternative respiration-rate-coupled gas dosage designs using demand injection valves. The impact of variations in diver depth, activity level, gas injection rate, circuit volume, and makeup gas composition on these circuit oxygen levels is demonstrated. Respiration-coupled, demand gas delivery systems are shown to have significantly reduced circuit oxygen variations over a wide range of diver activity levels when compared to constant mass flow injection systems. Additionally, the respiration-coupled designs are shown to have potential reduced gas usage at low diver activity levels, resulting in longer mission duration capability, when compared to constant mass injection systems.

Atmospheric Pressure↗
PubMed1987

Emotional and physiological effects of nitrous oxide and hyperbaric air narcosis.

Measurements of seven self-reported emotional states (happiness, activity, fear, anger, depression, fatigue, and anxiety) and three physiological variables (heart rate, systolic blood pressure, and diastolic blood pressure) were made among 16 subjects under four conditions: all subjects breathing normobaric air; several days later, immediately after half the subjects had breathed 30% nitrous oxide and the other half had breathed nomobaric air; the following day, subsequent to exposure of all subjects to a simulated depth of 57 m on air in a hyperbaric chamber; and several weeks after the hyperbaric chamber exposure, with all subjects breathing nomobaric air. The results showed that the physiological responses of the group that breathed nitrous oxide did not differ significantly from the control group following the hyperbaric chamber exposure, while self-reported happiness was lower among the nitrous oxide group than among the control group following hyperbaric chamber exposure. Nitrous oxide does not appear to benefit emotional or physiological adaptation to nitrogen narcosis associated with breathing hyperbaric air, and may even impair emotional adaptation, at least under these experimental conditions.

Adult↗
PubMed2004

The Bohr effect of haemoglobin in vertebrates: an example of molecular adaptation to different physiological requirements.

The Bohr effect, i.e. the pH dependence of the oxygen affinity of haemoglobins (Hbs) from a variety of vertebrates, and its modulation by temperature and other heterotropic effectors has been reviewed. Haemoglobins from vertebrates were not reviewed following the usual classification (i.e. mammals, birds, etc.); instead we have selected several key examples of animals, which are confronted with a similar environmental situation therefore displaying a similar life style. Hence, the paper starts from a description of the general concepts at the basis of the Bohr effect as exemplified by human HbA and goes towards the analysis of the modulation mechanisms which have been observed in different animals in response to the needs induced by: (i) life in cold environments; (ii) diving behaviour; (iii) flight; and (iv) aquatic life. The emerging picture indicates a complex organization of the information contained in the Hb molecule, the oxygen-binding properties of which depend both on the intrinsic characteristics of the protein and on its heterotropic interactions with ligands such as protons (Bohr effect), small anions like chloride and organic phosphates. In addition, each one of the functional effects induced by binding of a given effector appears to be under the strict control of temperature that enhances or decreases its relative weight with respect to all the others. It is just by this sophisticated network of interactions that the Hb molecule is able to satisfy the physiological requirements of a multitude of organisms without changing dramatically its quaternary structure.

Adaptation, Physiological↗
PubMed2003

Sensorineural hearing loss as the result of cliff jumping.

A case of unilateral, sudden sensorineural hearing loss and possible perilymphatic fistula as the result of cliff jumping into water is presented. The physiological mechanisms contributing to such a barotraumatic auditory injury are described. A conservative treatment protocol is reviewed as well as documented hearing recovery.

Adolescent↗
PubMedDate not supplied

Cardiac output and shunt during voluntary activity at different temperatures in the turtle, Trachemys scripta.

Red-eared slider turtles (Trachemys scripta) were chronically instrumented with blood flow probes for a long-term study of voluntary behavior in an enriched laboratory setting. Cardiovascular measures consisting of total cardiac output (Q(tot)), pulmonary blood flow (Q(pul)), systemic blood flow (Q(sys)), net cardiac shunt (Q(shunt)), heart rate (HR), and stroke volume (SV) were obtained during spontaneous activity at a constant body temperature (Tb=2 degrees C) and at unstable (variable) T(b)'s ranging from 19 degrees to 37 degrees C. The effects of temperature and activity differed between the pulmonary and systemic circuits, with increases in Q(sys) due to HR alone, while both HR and SV contributed to gains in Q(pul). At stable 20 degrees C, cardiovascular responses during diving, submerged swimming, and walking were qualitatively similar, and increases in Q(tot) during activity ( approximately 2 x resting levels) were due to greater gains in Q(pul) than Q(sys). At unstable T(b)'s and in general, net Q(shunt) while active depended on the integration of individual physiological influences such as heating, cooling, and initial behavioral state acting on the cardiovascular system. During activity, net left-to-right (L-R) shunts predominated at constant T(b) of 20 degrees C (mean shunt fraction approximately 30%-40%), while both net L-R and right-to-left (R-L) shunts of varying size were found at unstable T(b)'s (19 degrees - 37 degrees C).

Analysis of Variance↗
PubMed1996

Patent foramen ovale in underwater medicine.

The foramen ovale, between the right and left atria, exists in the foetal heart as a vital physiological communication. Haemodynamic closure occurs in the neonatal period with most people having permanent fusion of the foramen. In up to a third of adults the closure is functional only and a potential right to left atrial communication persists as a patent foramen ovale. Studies in patients with decompression illness after diving suggest a consistent increase in the prevalence of patent foramen ovale, as detected by transthoracic contrast echocardiography. The association is strongest for those patients with early onset of neurological decompression illness, particularly those cases occurring in the absence of other risk factors traditionally associated with decompression illness. However, patent foramen ovale is a common finding in the general population and the absolute risk of decompression illness, even in the presence of a patent foramen ovale, remains very low.

Decompression Sickness↗
PubMed1976

An ECG telemetry system for physiological studies on swimmers.

A low frequency telemetry system is described which has been designed to allow high quality ECG measurements to be made on active swimmers. The transmitting antenna is a small loop worn by the swimmer whilst the receiver is fed from a single wire loop around the swimming pool. Both ECG electrodes and the transmitter case are made in a waterproof form which allows the swimmer complete freedom of action to dive and swim normally. The transmitter can be constructed from normal miniature components although the present version has been assembled using thick film techniques which combine high reliability with a reduction in overall volume.

Coronary Care Units↗
PubMed1984

Physiological effects of ventilation with liquid fluorocarbon at controlled temperatures.

Body cooling, respiratory heat loss, and the physiological effects of liquid ventilation at various temperatures were studied in 10 adult cats with applications to the deep sea diver. The animals were stabilized on mechanical gas ventilation with 100% oxygen during a control period and then mechanically ventilated for 1 h with liquid fluorocarbon. Fluorocarbon (Rimar 101) temperatures of 10 degrees C, 20 degrees C, and 30 degrees C were used to ventilate the animals while rectal and subcutaneous body temperatures were being measured. For the 3 temperature conditions, respective cooling rates of 9.0 degrees C/h, 7.8 degrees C/h, and 3.6 degrees C/h, as well as respiratory heat losses of 65,637 J X kg-1 X h-1, 33,488 J X kg-1, X h-1, 18,036 J X kg-1 X h-1 were observed while maintaining effective physiological gas exchange [mean PaO2 = 353 +/- 28 (SEM) mmHg, mean PaCO2 = 30 +/- 2 (SEM) mmHg]. Changes in cardiovascular variables were noted as mild (35 degrees C-30 degrees C) and moderate (30 degrees C-25 degrees C) levels of hypothermia were reached. Cardiac output, oxygen consumption, heart rate, and mean blood pressure were significantly correlated with rectal temperature. The data presented herein quantitate the effects of liquid ventilation on body cooling and respiratory heat loss. Furthermore, the physiological alterations associated with the observed hypothermic condition could severely limit the effectiveness of a human diver if not carefully controlled.

Animals↗
PubMedDate not supplied

[Physiological and biochemical characteristics of the blood of the Greenland seal, Pagophilus groenlandicus].

High hemoglobin concentration, rich hemoglobin supply of the body and high specific weight of the blood were found in harp seal cubs. The erythrocyte number is relatively low which agrees with our previous studies on aquatic and semi-aquatic mammals. Serum proteins from both adult and young harp seals are separated into 5-8 fractions during agar-agar gel electrophoresis. Diving of seals for considerable periods is partly accounted for by high hemoglobin and myoglobin concentrations adn also by perfect supply of the organism by these pigments.

Age Factors↗