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At least 775 records · Page 43Linked to original sources

PubMed1988

Physiological aspects of freezing behaviour in willow ptarmigan hens.

When threatened, wild willow ptarmigan (Lagopus lagopus lagopus) hens displayed freezing behaviour, i.e. motionless, crouched with head down and eyes open. But while non-incubating hens showed increased heart (HR) (from 229 +/- 18 to 254 +/- 33 beats min-1) and ventilation rates (VR) (from 25 +/- 2 to 31 +/- 4 breaths min-1), incubating hens showed bradycardia (from 208 +/- 40 to 102 +/- 13 beats min-1) and reduced VR (from 25 +/- 2 to 10 +/- 2 breaths min-1), which could be maintained for as long as 20 min. The bradycardia response became stronger as hatching approached. The bradycardia period was interspersed by short bursts of tachycardia and hyperventilation which presumably supplied oxygen to blood and muscles. The bradycardia period was typically followed by a period of increased HR (276 +/- 104 beats min-1) and VR (32 +/- 3 breaths min-1). Atropine abolished the bradycardia response, which was thus apparently due to parasympathetic stimulation. The bradycardia response observed in incubating ptarmigan hens, during forced diving of birds and mammals and during death feigning in other animals are all examples of how emotional stimuli trigger a basic bradycardia reflex.

Animals↗

PubMed1995

Videonystagmoscopy: its use in the clinical vestibular laboratory.

Vestibular function of a population including labyrinthine-defective patients and a control group of age-matched normal healthy volunteers was evaluated using videonystagmoscopy. This device is made of one or two CCD infra-red cameras mounted on diving glasses and allows observation of ocular movements on a video monitor and/or recording on a videotape. Eye movements are observed after rotations in a Bárány chair and during passive head tilts. With this simple and non-invasive test, a screening of vestibular function at bedside or during ENT clinical investigations can be performed. A further study with videonystagmography to quantify these results being prepared.

Humans↗

PubMed1980

Respiratory properties of the blood of Crocodylus porosus.

The blood of Crocodylus porosus has a high oxygen capacity (5.5 mmol . 1-1 at hematocrit = 28%). The shape of the oxygen equilibrium curve of the blood is described by 'n' = 2.7 in the physiological range of PCO2, and its oxygen affinity is described by the equation: log10P50 = 0.4163 + 0.0200 T degrees C + 0.3763 log10PCO2. Thus, the blood has a low oxygen affinity which is strongly sensitive to both temperature and PCO2. There is a high buffering capacity, 37 mmol . (1 . pH)-1, and a large Haldane effect, 0.93 mmol CO2 (mmol Hb)-1. The fixed-acid Bohr effect seems to be much reduced in comparison to the CO2-specific Bohr effect. We discuss the possibility that low levels of red cell organic phosphate may be an adaptive strategy to desensitise P50 to changes in plasma pH. The significance of the blood respiratory properties is discussed in terms of the life style of C. porosus, particularly in relation to ectothermy and diving.

Acid-Base Equilibrium↗

PubMed2000

Gas exchange and heart rate in the harbour porpoise, Phocoena phocoena.

The respiratory physiology, heart rates and metabolic rates of two captive juvenile male harbour porpoises (both 28 kg) were measured using a rapid-response respiratory gas analysis system in the laboratory. Breath-hold durations in the laboratory (12 +/- 0.3 s, mean +/- SEM) were shorter than field observations, although a few breath-holds of over 40 s were recorded. The mean percentage time spent submerged was 89 +/- 0.4%. Relative to similarly-sized terrestrial mammals, the respiratory frequency was low (4.9 +/- 0.19 breaths.min-1) but with high tidal volumes (1.1 +/- 0.011), enabling a comparatively high minute rate of gas exchange. Oxygen consumption under these experimental conditions (247 +/- 13.8 ml O2.min-1) was 1.9-fold higher than predicted by standard scaling relations. These data together with an estimate of the total oxygen stores predicted an aerobic dive limit of 5.4 min. The peak end-tidal O2 values were related to the length of the previous breath-hold, demonstrating the increased oxygen uptake from the lung for the longer dives. Blood oxygen capacity was 23.5 +/- 1.0 ml.100 ml-1, and the oxygen affinity was high, enabling rapid oxygen loading during ventilation.

Animals↗

PubMed1997

The effect of hyperbaric oxygen on irradiated oral tissues: transmucosal oxygen tension measurements.

PURPOSE: This study measured the effect of hyperbaric oxygen (HBO) treatment on transmucosal oxygen tension in irradiated human oral mucosa. PATIENTS AND METHODS: Ten patients received 30 dives of HBO as part of their treatment for mandibular osteoradionecrosis. A noninvasive, nonheated oxygen electrode was used to measure the tissue surface transmucosal oxygen tension directly on the attached gingiva. Measurements were done before, during, and after HBO treatment. The normal level of gingival surface transmucosal oxygen tension was measured in five healthy volunteers. RESULTS: During HBO treatment, the transmucosal oxygen tension increased significantly after five dives of HBO (P < .05). After 30 dives, the increases were from a mean of 50% to a mean of 86% of the transmucosal oxygen tension of normal healthy gingiva. CONCLUSION: An increase in the transmucosal oxygen tension is based on neo-angiogenesis. Patients with subischemic tissues, such as the study population with postirradiation mucosal and osseous necrosis, therefore may benefit from treatment with HBO.

Aged↗

PubMed1989

Effects of gas bubbling and other forms of convection on platelets in vitro.

Citrated platelet-rich human plasma was subjected to one of three experimental treatments at 37 degrees C for 15 min: stirring, bubbling (with stirring), and gentle agitation achieved by a rocking motion. The last two were "equiconvective" as judged by equilibration rates with CO2 and O2 but presumably differed in the shear stress they imposed on the cells. Stirring platelets in normal air or 5% CO2-air caused no significant aggregation. Bubbling air through platelet-rich plasma increased its pH and marked aggregation occurred. Bubbling CO2-air caused the platelet-rich plasma pH to attain its physiological level of 7.4 with less aggregation. In both cases, subsequent ADP-induced aggregation was diminished. Rocking (without stirring) in the presence of CO2-air caused negligible aggregation in platelets and an enhanced response to ADP. Because of the marked difference between the two equiconvective treatments, bubbling and rocking, the main factor in activating the human platelets is suggested to be shear stress (potentiated by high pH), with perhaps a lesser contribution from the air-plasma interface.

Adenosine Diphosphate↗

PubMed2005

Countercurrent compartmental models describe hind limb skeletal muscle helium kinetics at resting and low blood flows in sheep.

AIMS: This study evaluated the relative importance of perfusion and diffusion mechanisms in compartmental models of blood : tissue helium exchange in a predominantly skeletal muscle tissue bed in the sheep hind limb. Helium has different physiochemical properties from previously studied gases and is a common diluent gas in underwater diving where decompression schedules are based on theoretical models of inert gas kinetics. METHODS: Helium kinetics across skeletal muscle were determined during and after 20 min of helium inhalation, at separate resting and low steady-states of femoral vein blood flow in six sheep under isoflurane anaesthesia. Helium concentrations in arterial and femoral vein blood were determined using gas chromatographic analysis and femoral vein blood flow was monitored continuously. Parameters and model selection criteria of various perfusion-limited or perfusion-diffusion compartmental models of skeletal muscle were estimated by simultaneous fitting of the models to the femoral vein helium concentrations for both blood flow states. RESULTS: A model comprising two parallel perfusion-limited compartment models fitted the data well but required a 51-fold difference in relative compartment perfusion that did not seem physiologically plausible. Models that allowed a countercurrent diffusion exchange of helium between arterial and venous vessels outside of the tissue compartments provided better overall fit of the data and credible parameter estimates. CONCLUSIONS: These results suggest a role of arterial-venous diffusion in blood : tissue helium equilibration in skeletal muscle.

Administration, Inhalation↗

PubMed2002

Why did some ichthyosaurs have such large eyes?

Many species of extinct marine ichthyosaurs had much larger eyes for their body size than would be expected of extant marine mammals and reptiles. Sensitivity to low light at great depth for the deep-diving genus Ophthalmosaurus has recently been suggested as the reason for the large eyes of these animals. Here, we discuss the implications for vision at such depths and consider other optical factors determining eye size. We suggest that the large eyes of ichthyosaurs are more likely to be the result of simultaneous selection for both sensitivity to low light and visual acuity. The importance of the evolutionary history of extant marine mammals and extinct ichthyosaurs is discussed, as are ecological factors driving both acuity and sensitivity.

Adaptation, Physiological↗

PubMed1982

Creatine phosphokinase activities in rainbow trout, Salmo gairdneri, associated with rapid decompression.

Serum creatine phosphokinase (CPK) activity levels were monitored in rainbow trout following rapid decompression. Serum activity was elevated 8.5-fold at 24 h and 15-fold at 48 h after decompression from 100-feet sea water (fsw) dives of 1 1/2 h duration. Serum enzyme activity was unchanged in the 66-fsw group. Stress results indicated a proportional relationship exists between serum CPK activity and muscular activity. CPK activities were found to be 1,023 in skeletal (white) muscle and 255 mumol . min-1 . g-1 in heart ventricle. Elevated CPK activity was not associated with tissue necrosis and is considered a consequence of increased anaerobic respiration stimulated by muscular activity and pressure-induced peripheral hypoxia.

Animals↗

PubMed2001

Personality factors, stoicism and motivation in subjects under hypoxic stress in extreme environments.

Previous studies on the physiological and psychological adaptation of subjects to survival conditions involving high-altitude hypoxia (>6,500 m) have shown that personality factors are important in this adaptation. We, therefore, proposed personality traits assessments in two groups of subjects engaged in sporting activities under extreme hypoxic environmental conditions: a group of mountaineers at high altitudes (>5,500 m) and a group of free-lung divers at great depths (<30-60 m). These subjects were compared with two control groups: a group of subjects practicing no sport and another one practicing various competitive athletic activities involving speed constraints. The personality traits assessed concerned mainly the subjects' attitudes and their propensities to act out their feelings and fantasies; they were assessed using projective procedures, the Hand Test and Clark's Situational Pain Questionnaire based on the Sensory Decision Theory. Subjects trained in mountaineering and free-lung diving under extreme environmental conditions displayed a high degree of stoicism. These individuals shared some personality traits with other sportsmen, particularly aggressive tendencies and introversion although not to an extent which interfered with normal interpersonal relationships. However, at least when practicing these extreme sports, the subjects did retreat from society. One of our questions concerns the grounds for this social withdrawal, that is, whether it derives from a inner compulsion founded on personality factors or if it is merely an artifact of our perceptions of the subjects, created by the confluence of the individualistic nature of these sports and the extreme environments in which they are performed.

Acclimatization↗

PubMed2001

Bid, a widely expressed proapoptotic protein of the Bcl-2 family, displays lipid transfer activity.

Bid is an abundant proapoptotic protein of the Bcl-2 family that is crucial for the induction of death receptor-mediated apoptosis in primary tissues such as liver. Bid action has been proposed to involve the relocation of its truncated form, tBid, to mitochondria to facilitate the release of apoptogenic cytochrome c. The mechanism of Bid relocation to mitochondria was unclear. We report here novel biochemical evidence indicating that Bid has lipid transfer activity between mitochondria and other intracellular membranes, thereby explaining its dynamic relocation to mitochondria. First, physiological concentrations of phospholipids such as phosphatidic acid and phosphatidylglycerol induced an accumulation of full-length Bid in mitochondria when incubated with light membranes enriched in endoplasmic reticulum. Secondly, native and recombinant Bid, as well as tBid, displayed lipid transfer activity under the same conditions and at the same nanomolar concentrations leading to mitochondrial relocation and release of cytochrome c. Thus, Bid is likely to be involved in the transport and recycling of mitochondrial phospholipids. We discuss how this new role of Bid may relate to its proapoptotic action.

Animals↗

PubMed2001

Finding food in the open ocean: foraging strategies in Humboldt penguins.

Penguins are excellent "model" organisms allowing us to study the behaviour of marine homeotherms at sea. Penguins regularly return to their breeding colonies, enabling biologists to equip them with remote sensing devices such as physiological or behavioural data-loggers, radio- or satellite transmitters. Foraging trips at sea can last from days to weeks and after return of the birds to their breeding sites, the devices can easily be removed for analysis of on-board stored data, yielding a wealth of information. Investigation of penguin behaviour at sea becomes particularly revealing when other sources of information can be matched to the data set, such as satellite data on wind, temperature, ice cover, and chlorophyll-a concentrations. Penguins and other marine homeotherms are true inhabitants of the high seas. Depending on the season, the marine behaviour varies: during reproduction, penguins are central-place foragers, and must return regularly to their nest to feed their chicks. During the remainder of the year, there are no constraints and the birds travel large distances at sea. Breeding Humboldt penguins react to climatic change by varying their daily foraging range and dive duration. Similar to other representatives of the family Spheniscidae, Humboldt penguins avoid food shortages by migrating into more productive marine areas. Navigational clues such as daylength, sea surface temperature, local wind direction and olfaction might provide important aids in finding patchily distributed prey in the open ocean. DMS, a chemical compound produced by decaying algae, seems to be a further clue that indirectly points the way to feeding areas.

Journal Article↗

PubMed2005

Forecasting models to quantify three anthropogenic stresses on coral reefs from marine recreation: anchor damage, diver contact and copper emission from antifouling paint.

This research focuses on damage to coral reefs from three anthropogenic stresses: the dropping of anchors and their chains, human contact, and emission of copper from antifouling paints. Forecasting models are described that quantify degradation in terms of percentage of coral cover damaged/year or increasing levels of water toxicity/year. The models utilize a Monte Carlo simulation that applies a range of values or a probability distribution to each of the numerous uncertain variables. This model has the flexibility to adapt, and become more accurate, when users input assumptions specific to their diving sites. Given our specific assumptions for a frequently visited site, anchors and their chains forecast a distribution of coral reef cover damage with a mean of 7.11%+/-4.77%, diver contact forecast a distribution of coral reef cover damage with a mean of 0.67%+/-0.38%, and antifouling paint forecast a distribution of copper level increase in the water with a mean of 0.037+/-0.014ppb. The results support recommendations for the implementation and sustained use of several specific marine recreation practices.

Animals↗

PubMed2004

Effects of postnatal cocaine exposure and environmental enrichment on rat behavior in a forced swim test.

This study examined the effects of environmental enrichment on rats exposed to cocaine during the first month of life, in several categories of behavior observed in a forced swim test. Wistar rats were divided in four groups. The first included pups that were subjected to injections of cocaine hydrochloride (15 mg/kg body weight/day, subcutaneously, in two daily doses, from postnatal days 1 to 27) and reared in an enriched environment (CocEE); the second, pups that were subjected to injections of cocaine (as previously described) and reared in a standard environment (CocSE); the third, pups that were subjected to saline injections and reared in an enriched environment (SalEE); the fourth, pups that were subjected to saline injections and reared in a standard environment (SalSE). On postnatal days 26 and 27, rats were tested in a swimming pool in two 5-min sessions. The categories of behavior studied in this work were: fast swim, slow swim, struggling, diving, and immobility. Results showed that postnatal cocaine exposure decreased the time spent on fast swim during the two sessions and increased the immobility behavior during the second session in CocSE pups compared with SalSE pups. SalEE pups increased the time spent in fast swim, slow swim, and diving, and decreased the time spent in struggling and immobility during the two sessions compared with SalSE pups. CocEE animals spent more time in fast swim and struggling and less the time in immobility compared with CocSE pups. The present results suggest that postnatal cocaine exposure affects the ability of these animals to cope with stressful situations, and that environmental enrichment seems to enable the rats to adopt a more active strategy, one that allows them to better cope with this particular stress situation.

Animals↗

PubMed2004

Hypoxia-mediated down-regulation of Bid and Bax in tumors occurs via hypoxia-inducible factor 1-dependent and -independent mechanisms and contributes to drug resistance.

Solid tumors with disorganized, insufficient blood supply contain hypoxic cells that are resistant to radiotherapy and chemotherapy. Drug resistance, an obstacle to curative treatment of solid tumors, can occur via suppression of apoptosis, a process controlled by pro- and antiapoptotic members of the Bcl-2 protein family. Oxygen deprivation of human colon cancer cells in vitro provoked decreased mRNA and protein levels of proapoptotic Bid and Bad. Hypoxia-inducible factor 1 (HIF-1) was dispensable for the down-regulation of Bad but required for that of Bid, consistent with the binding of HIF-1alpha to a hypoxia-responsive element (positions -8484 to -8475) in the bid promoter. Oxygen deprivation resulted in proteosome-independent decreased expression of Bax in vitro, consistent with a reduction in global translation efficiency. The physiological relevance of Bid and Bax down-regulation was confirmed in tumors in vivo. Oxygen deprivation resulted in decreased drug-induced apoptosis and clonogenic resistance to agents with different mechanisms of action. The contribution of Bid and/or Bax down-regulation to drug responsiveness was demonstrated by the relative resistance of normoxic cells that had no or reduced expression of Bid and/or Bax and by the finding that forced expression of Bid in hypoxic cells resulted in increased sensitivity to the topoisomerase II inhibitor etoposide.

Animals↗

PubMed2004

Apnea-induced changes in time estimation and its relation to bradycardia.

INTRODUCTION: Both exercise and hypoxia affect human ability to estimate time, an alteration thought to be induced by changes in subjects' level of arousal. Apnea induces cardiovascular changes and a decrease in oxygen uptake that indicate changes in physiological arousal. We tested time estimation (TE) during brief periods of voluntary apnea. We hypothesized that there would be a relationship between TE and heart rate (HR), a physiological indicator of arousal. METHODS: Subjects were two different groups of seven triathletes. To measure TE, the target time interval (20 or 30 s) was demonstrated and the subject was then asked to reproduce it under various conditions. Experiment 1 required 1 min of breath-holding while immersed in a pool at 31 degrees C. Experiment 2 was performed seated on a cycle ergometer in a laboratory and involved short periods of apnea at rest and during exercise. RESULTS: TE during apnea was significantly greater than baseline during both immersion and at rest on the cycle (+27% and +17% compared with their respective baselines). A significant linear negative correlation was demonstrated between TE and HR. Training in apnea during exercise had no effect on TE. DISCUSSION: Although this study revealed a relationship between TE and HR, our results should be interpreted with caution. Further studies are needed to confirm the relationship between HR and TE. A misperception of elapsed time may be a contributing factor in diving accidents which involve inexperienced breath-hold divers.

Accidents↗

PubMed1980

Cerebral energy metabolism in mallard ducks during apneic asphyxia: the role of oxygen conservation.

Cerebral energy metabolism during apneic asphyxia was studied in ducks. Fluctuations in the reduced form of respiratory chain nicotinamide adenine dinucleotide (NADH) were monitored from the left cerebral hemisphere and used as an indicator of mitochondrial hypoxia. Electroencephalogram (EEG) and surface PO2 were recorded from the right hemisphere. Forced dives of 4- to 7-min duration on restrained ducks were characterized by bradycardia and an accumulation of NADH, which increased throughout the diving period. NADH returned to the preasphyxic level when breathing was resumed. In later experiments, asphyxia was produced by stopping artificial ventilation in paralyzed ducks. Asphyxia produced by this means caused similar changes in the measured variables (heart rate, blood pressure, and NADH fluorescence) to those obtained in forced submergence of nonparalyzed ducks. The inhibition of cardiovascular adjustments by atropine caused NADH to increase faster and tissue PO2 to decrease faster during apneic asphyxia than in nonatropinized ducks. We conclude that the oxygen-conserving cardiovascular adjustments play a key role in the increased cerebral tolerance to apneic asphyxia in ducks.

Animals↗

PubMed1999

CO2 excretion and postcapillary pH equilibration in blood-perfused turtle lungs

Turtles possess a significant postcapillary CO2 partial pressure (PCO2) disequilibrium between arterial blood and alveolar gas. There are several possible explanations for this blood disequilibrium including a slow rate of erythrocyte physiological anion shift (Cl-/HCO3- exchange) or inaccessibility of plasma HCO3- to red blood cell or pulmonary carbonic anhydrase. The present study characterized the contribution of erythrocyte anion exchange and pulmonary and erythrocyte carbonic anhydrase to CO2 excretion and, hence, to postcapillary CO2-HCO3--H+ equilibration in blood-perfused turtle (Pseudemys scripta) lungs. Turtle lungs perfused in situ with red cell suspensions containing inhibitors of erythrocyte anion exchange and/or pulmonary and red cell carbonic anhydrase produced significant postcapillary blood PCO2 and pH disequilibria, while no disequilibria were measured when lungs were perfused with control red cell suspensions. Erythrocyte anion exchange and pulmonary intravascular carbonic anhydrase contributed 11 % and 9 %, respectively, to CO2 excretion during single-pass perfusion, whereas red cell and pulmonary carbonic anhydrase contributed 32 % to the measured CO2 excretion. The lack of a measurable PCO2 disequilibrium during perfusion with control erythrocyte suspensions in this study suggests that alternative mechanisms may be responsible for the arterial-lung PCO2 disequilibrium measured during breathing or diving episodes in turtles.

Journal Article↗