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At least 757 records · Page 42Linked to original sources

PubMed1979

The square-root principle in the calculation of one-stage (no-stop) decompression tables.

A square-root formulation, square-root time x excursion depth = k, developed at the Royal Navy Physiologic Laboratory (RNPL) predicts the safe duration of air excursions at 1 ATA for periods up to 6 h (air) and up to 3 h (heliox atmosphere). At pressures above 1 ATA, the value of k was initially considered to be proportional to Haldanian multiples of ATA and not to the square-root ATA used in this paper. Excursions of infinite (infinity) duration can also be predicted from a square-root formula derived from the systematic heliox saturation excursions conducted at the Experimental Diving Unit in which net excursion depth = k square-root P abs. This paper presents a broad spectrum format that extends the square-root principle: 1) to values of k above 1 ATA in the RNPL formula and 2) to excursions for (infinity) time from habitat depths to 820 ft; and 3) which demonstrates a relationship between fractional time excursions and excursions for infinite periods of time. Application of the generalization that net excursion depths are proportional to square-root P abs would reduce to a minimum the number of programmed test dives and would, in addition, allow such dives to be conducted at relatively low pressures, with only occasional validating tests at deep depths.

Atmospheric Pressure↗

PubMed1992

The different types of general cold adaptation in man.

Different types of general cold adaptation have been described over the last 50 years. Metabolic adaptation (Alacaluf Indians, Arctic Indians Eskimos), insulative adaptation (coastal Aborigines of tropical northern Australia), hypothermic adaptation (bushmen of the Kalahari desert, Peruvian Indians) and insulative hypothermic adaptation (Central Australian Aborigines, nomadic Lapps, Korean and Japanese diving women). These different types of cold adaptation are related to the intensity of the cold stress and to individual factors such as diet, the level of physical fitness and body fat content. Thus, in natural environments, man develops a strategy of adaptation to cold, which takes into account environmental and individual factors. This strategy is susceptible to be modified when these conditions change. Caloric intake deficit could have been responsible for the hypothermic adaptation observed after J.-L. Etienne's journey to the North Pole. Physiological responses were adapted to maintain an acceptable level of energetic reserves with a moderate hypothermia, which was not life threatening for the climatic conditions encountered by the polar explorer.

Acclimatization↗

PubMed2003

Exercise during pregnancy and the postpartum period.

The physiologic and morphologic changes of pregnancy may interfere with the ability to engage safely in some forms of physical activity. A woman's overall health, including obstetric and medical risks, should be evaluated before prescribing an exercise program. Generally, participation in a wide range of recreational activities appears to be safe during pregnancy; however, each sport should be reviewed individually for its potential risk, and activities with a high risk of falling or those with a high risk of abdominal trauma should be avoided during pregnancy. Scuba diving also should be avoided throughout pregnancy because the fetus is at an increased risk for decompression sickness during this activity. In the absence of either medical or obstetric complications, 30 minutes or more of moderate exercise a day on most, if not all, days of the week is recommended for pregnant women.

Exercise↗

PubMed2005

Molecular phylogenetics of the siphonophora (Cnidaria), with implications for the evolution of functional specialization.

Siphonophores are a group of pelagic colonial hydrozoans (Cnidaria) that have long been of general interest because of the division of labor between the polyps and medusae that make up these "superorganisms." These polyps and medusae are each homologous to free living animals but are generated by an incomplete asexual budding process that leaves them physiologically integrated. They are functionally specialized for different tasks and are precisely organized within each colony. The number of functional types of polyps and medusae varies across taxa, and different authors have used this character to construct phylogenies polarized in opposite directions, depending on whether they thought siphonophore evolution proceeded by a reduction or an increase in functional specialization. We have collected taxa across all major groups of siphonophores, many of which are found exclusively in the deep sea, using remotely operated underwater vehicles (ROVs) and by SCUBA diving from ships in the open ocean. We have used 52 siphonophores and four outgroup taxa to estimate the siphonophore phylogeny with molecular data from the nuclear small subunit ribosomal RNA gene (18S) and the mitochondrial large subunit ribosomal RNA gene (16S). Parsimony reconstructions indicate that functionally specialized polyps and medusae have been gained and lost across the phylogeny. Maximum likelihood and Bayesian analyses of morphological data suggest that the transition rate for decreased functional specialization is greater than the transition rate for increased functional specialization for three out of the four investigated categories of polyps and medusae. The present analysis also bears on several long-standing questions about siphonophore systematics. It indicates that the cystonects are sister to all other siphonophores, a group that we call the Codonophora. We also find that the Calycophorae are nested within the Physonectae, and that the Brachystelia, a historically recognized grouping of short-stemmed taxa, are polyphyletic. [Cnidaria; colonial animals; deep sea; division of labor; functional specialization; Hydrozoa; phylogenetics; Siphonophores.].

Animals↗

PubMed2001

Mechanisms of cell survival in hypoxia and hypothermia.

Most animals experience some degree of hypoxia and hypothermia during the course of their natural life history either as a consequence of ambient 'exposure' per se or through metabolic, respiratory and/or circulatory insufficiency. A prevailing experimental approach has been to probe tissues from natural models of hypoxia-tolerant and cold-tolerant vertebrates to look for common mechanisms of defence against O(2) lack and hypothermia. The ability to sustain vital cellular functions in severe cases of either condition varies widely amongst the vertebrates. Like humans, the vast majority of mammals are unable to survive prolonged periods of hypothermia or O(2) deprivation owing to irreversible membrane damage and loss of cellular ion homeostasis in vital organs such as the brain and heart. However, numerous hibernating endotherms, neonatal and diving mammals as well as many ectotherms can tolerate prolonged periods that would, in clinical terms, be called asphyxia or deep hypothermia. The key to their survival under such conditions lies in an inherent ability to downregulate their cellular metabolic rate to new hypometabolic steady states in a way that balances the ATP demand and ATP supply pathways.

Adaptation, Physiological↗

PubMed1989

[The physiology of gas exchange in divers].

After a short reminder of Boyle's law and the physiology of oxygen and nitrogen, a mathematical model will be discussed (without formulas). Its limitations are shown in relation to the calculation of partial gas pressures in different human organs. Such models are already used in closed circuit anesthesia delivery systems and valuable insights can be obtained by this way, which enable us to calculate better nitrogen decompression tables.

Diving↗

PubMed1979

Bubble production in agarose gels subjected to different decompression schedules.

The relative effectiveness of seven different (military, commercial, and experimental) decompression schedules in reducing bubble formation within aqueous gels has been evaluated quantitatively under rigorously controlled conditions. Specifically, visual counts have been conducted of the bubbles formed in highly purified agarose gels subjected to the different decompression schedules. The order of effectiveness among these schedules in reducing bubble formation in the agarose gel samples was as follows: Model 1 greater than Royal Naval Physiological Laboratory approximately French Ministry of Labor greater than Yount et al. greater than Japanese Department of Labor greater than United States Navy greater than French Navy. It was concluded that the depth at which slow decompression commences is a major factor, along with the total decompression time, in determining the extent of bubble formation.

Decompression↗

PubMedDate not supplied

Biomechanics and energetics in aquatic and semiaquatic mammals: platypus to whale.

A variety of mammalian lineages have secondarily invaded the water. To locomote and thermoregulate in the aqueous medium, mammals developed a range of morphological, physiological, and behavioral adaptations. A distinct difference in the suite of adaptations, which affects energetics, is apparent between semiaquatic and fully aquatic mammals. Semiaquatic mammals swim by paddling, which is inefficient compared to the use of oscillating hydrofoils of aquatic mammals. Semiaquatic mammals swim at the water surface and experience a greater resistive force augmented by wave drag than submerged aquatic mammals. A dense, nonwettable fur insulates semiaquatic mammals, whereas aquatic mammals use a layer of blubber. The fur, while providing insulation and positive buoyancy, incurs a high energy demand for maintenance and limits diving depth. Blubber contours the body to reduce drag, is an energy reserve, and suffers no loss in buoyancy with depth. Despite the high energetic costs of a semiaquatic existence, these animals represent modern analogs of evolutionary intermediates between ancestral terrestrial mammals and their fully aquatic descendants. It is these intermediate animals that indicate which potential selection factors and mechanical constraints may have directed the evolution of more derived aquatic forms.

Animals↗

PubMed2006

Dehydration effects on the risk of severe decompression sickness in a swine model.

BACKGROUND: Several physiological factors have been suspected of affecting the risk of decompression sickness (DCS), but few have been thoroughly studied during controlled conditions. Dehydration is a potential factor that could increase the risk of DCS. It has been suggested that hydration may enhance inert gas removal or increase surface tension of the blood. HYPOTHESIS: Dehydration increases DCS risk. METHODS: Littermate pairs of male Yorkshire swine (n=57, mean +/- 1 SD 20.6 +/- 1.7 kg) were randomized into two groups. The hydrated group received no medication and was allowed ad lib access to water during a simulated saturation dive. The dehydrated group received intravenous 2 mg x kg(-1) Lasix (a diuretic medication) without access to water throughout the dive. Animals were then compressed on air to 110 ft of seawater (fsw, 4.33 ATA) for 22 h and brought directly to the surface at a rate of 30 fsw x min(-1) (0.91 ATA x min(-1)). Outcomes of death and non-fatal central nervous system (CNS) or cardiopulmonary DCS were recorded. RESULTS: In the hydrated group (n=31): DCS=10, cardiopulmonary DCS=9, CNS DCS=2, Death=4. In the dehydrated group (n=26): DCS=19, cardiopulmonary DCS=19, CNS DCS=6, Death=9. Dehydration significantly increased the overall risk of severe DCS and death. Specifically, it increased the risk of cardiopulmonary DCS, and showed a trend toward increased CNS DCS. In addition, dehydrated subjects manifested cardiopulmonary DCS sooner and showed a trend toward more rapid death (p < 0.1). CONCLUSION: Hydration status at the time of decompression significantly influences the incidence and time to onset of DCS in this model.

Analysis of Variance↗

PubMed2002

Interactions between locomotion and ventilation in tetrapods.

Interactions between locomotion and ventilation have now been studied in several species of reptiles, birds and mammals, from a variety of perspectives. Among these perspectives are neural interactions of separate but linked central controllers; mechanical impacts of locomotion upon ventilatory pressures and flows; and the extent to which the latter may affect gas exchange and the energetics of exercise. A synchrony, i.e. 1:1 pattern of coordination, is observed in many running mammals once they achieve galloping speeds, as well as in flying bats, some flying birds and hopping marsupials. Other, non-1:1, patterns of coordination are seen in trotting and walking quadrupeds, as well as running bipedal humans and running and flying birds. There is evidence for an energetic advantage to coordination of locomotor and respiratory cycles for flying birds and running mammals. There is evidence for a mechanical constraint upon ventilation by locomotion for some reptiles (e.g. iguana), but not for others (e.g. varanids and crocodilians). In diving birds the impact of wing flapping or foot paddling on differential air sac pressures enhances gas exchange during the breath hold by improving diffusive and convective movement of air sac oxygen to parabronchi. This paper will review the current state of our knowledge of such influences of locomotion upon respiratory system function.

Animals↗

PubMed1986

Three descending interneurons reporting deviation from course in the locust. II. Physiology.

The DNI, DNM and DNC descending interneurons all have very similar properties and are each at the convergence of visual, ocellar, wind-hair and other mechanoreceptor inputs. The 3 neurons respond almost exclusively to movement of the animal in space about its three axes of rotation. All are spatially and directionally selective. Movements in the preferred sense produce increasingly strong responses with amplitude and absolute position, while movements in the antipreferred sense usually elicit no response at all. Movements in the preferred sense, but towards, rather than away from, the normal flying position start to produce responses only as the animal approaches the normal flight position. The neurons function as feature detectors, responding only to specific sorts of deviation from course. DNI, DNM and DNC differ from one another principally in their directionality. DNI responds optimally to a diving banked turn to the ipsilateral side, DNM to downwards pitch, and the DNC to a diving banked turn to the contralateral side. The DN neurons contribute to the production of steering manoeuvres. They appear to be representatives of a larger class of descending interneurons bringing exteroceptive sensory input to the thoracic locomotory neuropil. The occurrence of this class of units in locusts and other insects is discussed.

Animals↗

PubMed2003

Environmental and infectious conditions in sports.

The hearts and lungs of athletes are subject to damage from a wide array of infections and environmental factors. Mild to moderate exercise has been shown to be beneficial to overall health, and strenuous exercise simply requires proper rest and rehabilitation to ensure its beneficial effects as well. Simple colds and URTIs are very common in athletes and do not usually require significant intervention. Any suspected cardiac infection mandates a thorough evaluation and proper management to prevent catastrophic consequences. High altitudes can be helpful in enhancing performance, but caution must be exercised at even modest altitude to prevent serious complications. With diving, participants should know their time limits and ascend properly to avoid serious complications. Keeping the heart and lungs in a good state of health is a major priority for the weekend warrior and world-class athletes alike. A thorough knowledge of infections and environmental issues in the cardiopulmonary health of athletes should always be of highest priority.

Air Pollutants↗

PubMedDate not supplied

Evidence for endothermic ancestors of crocodiles at the stem of archosaur evolution.

Physiological, anatomical, and developmental features of the crocodilian heart support the paleontological evidence that the ancestors of living crocodilians were active and endothermic, but the lineage reverted to ectothermy when it invaded the aquatic, ambush predator niche. In endotherms, there is a functional nexus between high metabolic rates, high blood flow rates, and complete separation of high systemic blood pressure from low pulmonary blood pressure in a four-chambered heart. Ectotherms generally lack all of these characteristics, but crocodilians retain a four-chambered heart. However, crocodilians have a neurally controlled, pulmonary bypass shunt that is functional in diving. Shunting occurs outside of the heart and involves the left aortic arch that originates from the right ventricle, the foramen of Panizza between the left and right aortic arches, and the cog-tooth valve at the base of the pulmonary artery. Developmental studies show that all of these uniquely crocodilian features are secondarily derived, indicating a shift from the complete separation of blood flow of endotherms to the controlled shunting of ectotherms. We present other evidence for endothermy in stem archosaurs and suggest that some dinosaurs may have inherited the trait.

Alligators and Crocodiles↗

PubMed1981

Effects of CO2 insensitivity and respiratory pattern on respiration in divers.

In a study of respiratory function under hyperbaric conditions one diver (TM) was found to have an extremely low ventilatory response to exercise with a postinspiratory pause typical of certain "carbon dioxide retaining divers." The respiratory function of diver TM is compared with that of four other divers having a normal ventilatory response. In exercise at 4 ATA hypoventilation and hypercapnia were potentiated to a greater extent in TM than in the other divers. Diver TM maintained a ventilation 25%-50% lower than that of the other divers and whereas their end-tidal Pco2 remained within reasonable limits (Pco2 less than or equal to 55 mmHg), that of TM rose to levels considered hazardous (Pco2 less than or equal to 76 mmHg). Results suggest that when a diver exhibits a postinspiratory pause in the breathing cycle, mixing of alveolar and dead space gas takes place. As a result, physiological dead space calculated according to the Bohr formula is unusually small. As alveolar Pco2 will rise during postinspiratory pause, mean arterial Pco2 may be lower than end-tidal Pco2. Such a respiratory pattern has a greater ventilatory efficiency than normal and may afford the diver some protection, albeit incomplete, from hypercapnia.

Atmospheric Pressure↗

PubMed1986

Use of EEG digital filtering and display for HPNS diagnosis.

Divers show symptoms of a condition known as the high pressure nervous syndrome (HPNS) at depths greater than about 180 m. A symptom that possibly lends itself to an objective diagnosis is a change in the frequency content of the EEG signal with increased slow wave (theta, 4-8 Hz) and decreased fast wave (alpha, 8-13 Hz) activity. Therefore, a method was developed, first, to obtain the power in the EEG frequency bands by digital filtering and, second, to display band-indices and ratios during a dive, in a format suitable for rapid appraisal. The formulas for the cascaded 2nd order Butterworth bandpass filters are given together with the corresponding FORTRAN program. EEG signals from 3 subjects taped during the Duke University Atlantis IV dive to a depth of 650 m were analyzed and displayed by the above method as well as by a Fast Fourier Transfer signal analyzer. The results suggest the theta: alpha ratio, which is a one-parameter EEG evaluation in the frequency domain, is a valuable descriptor for the objective HPNS diagnosis.

Computers↗

PubMed1982

Equations for predicting diver regional skin temperatures as a function of mean skin temperature.

A series of linear algebraic equations have been derived from those of Kerslake (Flying Personnel Research Committee Memo 213, R.A.F. Institute of Aviation Medicine, 1964) for predicting the regional skin temperatures of a quasi-euthermic diver having pronounced vasoconstriction. The equations were developed by numerically analyzing twelve regional skin temperatures recorded from five resting subjects exposed to a hyperbaric chamber environment of 20 degrees C, 95% helium, and 5% oxygen pressurized to the equivalent of 200 msw (650 fsw). The independent variable of the basic correlation is an arbitrarily defined mean skin temperature; the empirical equations were developed for the purpose of assisting a designer in estimating regional supplementary heating requirements for a diver wearing a thermal protection garment of known composition. The developed equations were authenticated by comparing the predicted normalized regional temperature with the respective experimental normalized temperature obtained from several set of physiological data collected during the evaluation of the Naval Coastal System Center's diver thermal protecting garment (DTP). The results of these comparisons of nondimensionalized temperatures indicated that the derived correlations should accurately predict the skin temperature of the principal regions as a function of mean skin temperature with a normal error of no more than 15%.

Atmospheric Pressure↗

PubMed2002

[Regelsberger's intravenous oxygen therapy--an interpretation of results in practice from a biochemical and physiological point of view].

Results of intravenous (i.v.) application of medical oxygen described by users are interpreted by means of biochemical and physiological knowledge. It is shown that i.v. oxygen therapy produces changes in metabolism which can also occur independently of the course of illness. Apart from the general improvement in oxygen availability, i.v. oxygen therapy causes eosinophilia, which can be valued as an increase in undetermined cellular immunological resistance. Furthermore, rheological qualities of the blood as well as diuresis are improved, the release of oxygen into the tissue is increased, and the blood pH is normalized. Compared with hyperbaric oxygen therapy, i.v. oxygen therapy seems to have less side effects. Application is less complicated, less expensive but probably of higher efficacy. This statement does not apply to issues related to diving medicine.

Blood Chemical Analysis↗

PubMed1995

Development of highly potent and selective phosphinic peptide inhibitors of zinc endopeptidase 24-15 using combinatorial chemistry.

Several hundred phosphinic peptides having the general formula Z-(L,D)Phe psi (PO2CH2)(L,D)Xaa'-Yaa'-Zaa', where Xaa' = Gly or Ala and Yaa' and Zaa' represent 20 different amino acids, have been synthesized by the combinatorial chemistry approach. Peptide mixtures or individual peptides were evaluated for their ability to inhibit the rat brain zinc endopeptidases 24-15 and 24-16. Numerous phosphinic peptides of this series act as potent (Ki in the nanomolar range) mixed inhibitors of these two peptidases. However, our systematic and comparative strategy led us to delineate the residues located in P2' and P3' positions of the inhibitors that are preferred by these two peptidases. Thus, endopeptidase 24-15 exhibits a marked preference for inhibitors containing a basic residue (Arg or Lys) in the P2' position, while 24-16 prefers a proline in this position. The P3' position has less influence on the inhibitory potency and selectivity, both peptidases preferring a hydrophobic residue at this position. On the basis of these observations, we have prepared highly potent and selective inhibitors of endopeptidase 24-15. The Z-(L,D)Phe psi-(PO2CH2)(L,D)Ala-Arg-Met compound (mixture of the four diastereoisomers) displays a Ki value of 70 pM for endopeptidase 24-15. The most selective inhibitor of endopeptidase 24-15 in this series, Z-(L,D)Phe psi (PO2-CH2)(L,D)Ala-Arg-Phe, exhibits a Ki value of 0.160 nM and is more than 3 orders of magnitude less potent toward endopeptidase 24-16 (Ki = 530 nM). Furthermore, at 1 microM this selective inhibitor is unable to affect the activity of several other zinc peptidases, namely endopeptidase 24-11, angiotensin-converting enzyme, aminopeptidase M, leucine aminopeptidase, and carboxypeptidases A and B. Therefore, Z-(L,D)Phe psi (PO2CH2)(L,D)Ala-Arg-Phe can be considered as the most potent and specific inhibitor of endopeptidase 24-15 developed to date. This new inhibitor should be useful in assessing the contribution of this proteolytic activity in the physiological inactivation of neuropeptides known to be hydrolyzed, at least in vitro, by endopeptidase 24-15. Our study also demonstrates that the combinatorial chemistry approach leading to the development of phosphinic peptide libraries is a powerful strategy for discovering highly potent and selective inhibitors of zinc metalloproteases and should find a broader application in studies of this important class of enzymes.

Amino Acid Sequence↗