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At least 649 records · Page 36Linked to original sources
PubMed1996

Parasympathetic control of heart period during early postnatal development in the rat.

Basal autonomic control of the heart period (HP) changes considerably during the early postnatal period in the rat. Although studies in the developing animal have examined the ability of the sympathetic branch to decrease HP during physiological challenge, few studies have examined the emerging capabilities of the parasympathetic branch to alter HP during early development. To determine the extent of parasympathetic control of HP in the young rat, we used a modified dive reflex procedure and electrical stimulation of the vagal nerve to examine the range of parasympathetic effects on HP in postnatal day 3-24 rats. Modified dive reflex manipulations produced maximal parasympathetically-mediated HPs that were longer just after birth and at weaning than at intervening ages. Direct vagal nerve stimulation studies revealed significant decreases with age in the HP at maximal vagal activation and in the intrinsic HP. The dynamic range, or difference between minimal and maximal parasympathetic effects on HP was similar across ages when assessed from the results of vagal stimulation. Nerve stimulations also revealed age-independent and relatively linear transfer functions relating parasympathetic stimulation frequency and HP during early life. Therefore, several parameters characterizing parasympathetic control of HP, including the dynamic range and transfer function, remain reasonably stable throughout the early postnatal period in the rat. These data provide a framework delineating the autonomic limits within which cardiac responses operate in the young rat. Knowledge of changes in these limits across time affords a firmer physiological basis for cross-age comparisons of autonomically-mediated cardiac changes.

Animals↗
PubMed1993

Nonmagnetic hyperbaric chamber for in vivo NMR spectroscopy studies of small animals.

A description is given of the design, construction, and initial use of a polycarbonate resin hyperbaric chamber for in vivo NMR spectroscopy studies of anesthetized, ventilated rats in a horizontal bore 4.7 Tesla magnet. The chamber and its associated equipment, initially used for hyperbaric studies of rats in states of extreme hypercapnia, are also well suited for conventional hyperbaric studies, such as those related to hyperbaric oxygen therapy, oxygen toxicity, and diving. Basic technical challenges that required innovations involved: a) preservation of magnetic field homogeneity; b) avoidance of a metallic chamber body that would overload gradient and RF coils; c) physiological monitoring; and, d) remote control and stabilization of electromagnetic and physiologic factors (especially ventilatory stability) during pressure changes. A small paramagnetic bulk magnetic susceptibility shift from chamber-associated hyperbaric oxygen was observed when chamber oxygen tensions were only one atmosphere. High-quality NMR imaging and spectroscopy were demonstrated during hyperbaric conditions.

Animals↗
PubMed1982

Evaluation of different decompression schedules by an agarose gel bubble technique.

It is well known that diving decompression schedules vary according to country and that Navy schedules are often different from civilian ones. Furthermore, it is difficult to compare them effectively, because the bends incidence for each schedule is rarely known accurately. We have evaluated various decompression schedules by an agarose gel bubble technique in which the appearance of bubbles in a dry chamber at a controlled temperature was used, and we report this as a useful method of evaluating decompression tables. It is generally accepted that decompression sickness symptoms are due to bubble formation and the body's subsequent physiological reaction. Individual differences and physical conditions are also influential factors. However, bubble formation appears to be the most important factor in initiating symptoms. As the number of bubbles is influenced by the physical decompression ratio, it can be estimated which decompression schedule is more likely to minimize the number of bubbles. Nine decompression schedules were studied in this experiment: U.S. Navy Table, French Navy Table, Japanese Standard Decompression Schedule Numbers 1 and 2, Royal Naval Physiological Laboratory Table, French Ministry of Labor Table, Model 1 Table by Mano et al., Washington State Table, and Blackpool Table.

Decompression↗
PubMed1985

A review of the pathophysiology and potential application of experimental therapies for cerebral ischemia to the treatment of cerebral arterial gas embolism.

This review considers the pathophysiology of air embolism that occurs as a result of diving and iatrogenic accidents. Various experimental therapies are classified according to their potential mechanism of action. The effectiveness and prospects for application to the clinical situation are assessed for each therapy. Hyperbaric oxygen remains the most effective therapy, and it is one that is simple to apply. The physiologic changes that occur after gas embolism are complex, however, and future improvements in therapy will demand close clinical supervision and multiple individually tailored therapeutic decisions rather than a simple protocol.

Animals↗
PubMed2000

Computed chest tomography in an animal model for decompression sickness: radiologic, physiologic, and pathologic findings.

This study was conducted to investigate the early pulmonary effects of acute decompression in an animal model for human decompression sickness by CT and light microscopy. Ten test pigs were exposed to severe decompression stress in a chamber dive. Three pigs were kept at ambient pressure to serve as controls. Decompression stress was monitored by measurement of pulmonary artery pressure and arterial and venous Doppler recording of bubbles of inert gas. Chest CT was performed pre- and postdive and in addition the inflated lungs were examined after resection. Each lung was investigated by light microscopy. Hemodynamic data and bubble recordings reflected severe decompression stress in the ten test pigs. Computed tomography revealed large quantities of ectopic gas, predominantly intravascular, in three of ten pigs. These findings corresponded to maximum bubble counts in the Doppler study. The remaining test pigs showed lower bubble grades and no ectopic gas by CT. Sporadic interstitial edema was demonstrated in all animals--both test and control pigs--by CT of resected lungs and on histologic examination. A severe compression-decompression schedule can liberate large volumes of inert gas which are detectable by CT. Despite this severe decompression stress, which led to venous microembolism, CT and light microscopy did not demonstrate changes in lung structure related to the experimental dive. Increased extravascular lung water found in all animals may be due to infusion therapy.

Acute Disease↗
PubMed1989

Respiratory mechanics of the loggerhead sea turtle, Caretta caretta.

Respiratory mechanics were evaluated in excised lungs and in spontaneously breathing loggerhead sea turtles (Caretta caretta). Respiratory compliance curves reflect the pressure volume characteristics of the body wall. Compliance values are comparable to those of reptiles having simpler lung structure. Maximum flow rates in excised lungs (18-25 ml.sec-1.kg-1) were only slightly below the range reported for marine mammals. During spontaneous tidal breathing expiratory flow rates (11.8 ml.sec-1.kg-1) were lower than maximum values. In the sea turtle, respiratory adaptations including reduced airway resistance and muscular contribution to breathing are similar to marine mammals. These mechanical specializations shorten breathing time, which contributes to diving performance.

Animals↗
PubMed1997

Contribution of endopeptidase 3.4.24.15 to central neurotensin inactivation.

The tridecapeptide, neurotensin elicits naloxone-insensitive analgesia after its intracebroventricular administration in mice. We used this central pharmacological effect to assess the putative contribution of the endopeptidase 3.4.24.15 to central inactivation of the peptide. By means of combinatorial chemistry, we previously designed the first potent endopeptidase 3.4.24.15 inhibitor. This agent, Z-(L,D)Phe psi(PO2CH2)(L,D)Ala-Lys-Met (phosphodiepryl 21), is shown here to behave as a fully specific endopeptidase 3.4.24.15 inhibitor, as demonstrated by the absence of effect on a series of other exo- and endopeptidases belonging to various classes of proteolytic activities present in murine brain membranes. Furthermore, central administration of phosphodiepryl 21 drastically prolongs the forepaw licking latency of mice tested on the hot plate and injected with sub-maximally active doses of neurotensin. Altogether, our results demonstrated that, in addition to endopeptidase 3.4.24.16, endopeptidase 3.4.24.15 likely contributes to the physiological termination of the neurotensinergic message in murine brain.

Analgesia↗
PubMed1988

Effect of training on maximal oxygen uptake and aerobic capacity of locomotory muscles in tufted ducks, Aythya fuligula.

1. The effects of artificial swim training on maximal oxygen consumption and heart rate, as well as on the capillarity and oxidative capacity of locomotory muscles, have been studied in the tufted duck, Aythya fuligula. 2. The artificial training programme resulted in a 27% increase in maximal oxygen consumption, mainly as a result of an increase in muscle capillarity (20% increase in capillary/fibre ratio). In addition, activity of an oxidative enzyme, citrate synthase, increased (by 42%) and there was a significant transformation of fibre types in the lateral gastrocnemius muscle. 3. Altering the duration and nature of the training stimulus, for example flying and diving, can bring about different degrees of muscular adaptation, particularly in oxidative capacity.

Adaptation, Physiological↗
PubMed2003

Development, survival and fitness performance of Helicoverpa zea (Lepidoptera: Noctuidae) in MON810 Bt field corn.

Helicoverpa zea (Boddie) development, survival, and feeding injury in MON810 transgenic ears of field corn (Zea mays L.) expressing Bacillus thuringiensis variety kurstaki (Bt) Cry1Ab endotoxins were compared with non-Bt ears at four geographic locations over two growing seasons. Expression of Cry1Ab endotoxin resulted in overall reductions in the percentage of damaged ears by 33% and in the amount of kernels consumed by 60%. Bt-induced effects varied significantly among locations, partly because of the overall level and timing of H. zea infestations, condition of silk tissue at the time of egg hatch, and the possible effects of plant stress. Larvae feeding on Bt ears produced scattered, discontinuous patches of partially consumed kernels, which were arranged more linearly than the compact feeding patterns in non-Bt ears. The feeding patterns suggest that larvae in Bt ears are moving about sampling kernels more frequently than larvae in non-Bt ears. Because not all kernels express the same level of endotoxin, the spatial heterogeneity of toxin distribution within Bt ears may provide an opportunity for development of behavioral responses in H. zea to avoid toxin. MON810 corn suppressed the establishment and development of H. zea to late instars by at least 75%. This level of control is considered a moderate dose, which may increase the risk of resistance development in areas where MON810 corn is widely adopted and H. zea overwinters successfully. Sublethal effects of MON810 corn resulted in prolonged larval and prepupal development, smaller pupae, and reduced fecundity of H. zea. The moderate dose effects and the spatial heterogeneity of toxin distribution among kernels could increase the additive genetic variance for both physiological and behavioral resistance in H. zea populations. Implications of localized population suppression are discussed.

Animals↗
PubMed2001

The reduced oxygen breathing paradigm for hypoxia training: physiological, cognitive, and subjective effects.

UNLABELLED: The current training program for hypoxia familiarization requires a low-pressure chamber that places aviator trainees at risk for decompression sickness. A cost-effective reduced oxygen-breathing (ROB) paradigm that decreases oxygen (O2) concentration leading to normobaric hypoxia was assessed as an alternative to the hypobaric chamber. PURPOSE: To help establish the validity of the ROB paradigm, this report documents cognitive performance, cardiopulmonary and subjective changes during ROB exposure. METHODS: Performance on a two-dimensional tracking task, as well as BP, heart rate, end-tidal carbon dioxide (ETCO2), O2 saturation, and subjective reports of hypoxia symptoms were observed in 12 U.S. Navy divers during exposure to normoxic air followed by one of four experimental gas mixtures per session. All participants received all gas conditions that differed in their relative concentrations of O2 and nitrogen (6.20/93.80, 7.00/93.00, 7.85/92.15, and 20.85/79.15% O2/N2). RESULTS: ROB caused increases in tracking task error (p < 0.0001). ROB also increased heart rate (p < 0.001) and systolic BP (p = 0.004), and decreased ETCO2 and O2 saturation (p < 0.0001). Finally, subjects responded to ROB-induced hypoxia with higher subjective symptom ratings (p < 0.0001). CONCLUSIONS: These data are consistent with those expected from hypoxic states and support the validity of the ROB paradigm for hypoxia training. Future validation studies comparing a ROB device with hypobaric chambers are needed.

Adaptation, Physiological↗
PubMed1984

The interactions between pressure and anaesthetics.

Compression of animals causes excitation, which has recently posed a barrier to deeper diving. The broad question addressed here is how far the inert gas breathed modifies the excitatory effects of hydrostatic pressure. By using aquatic animals we first show that helium postpones the onset of pressure-induced paralysis by some 35 atm. Next we show that in mammals compressed with helium, five anaesthetic gases (nitrogen, argon, nitrous oxide, carbon tetrafluoride, sulphur hexafluoride) all elevated dose-dependently the median pressure of four distinct phases of the high pressure neurological syndrome (h.p.n.s.) (complete spasms, clonic convulsions, tonic convulsions and non-tonic death). All the gases were equally efficacious relative to their anaesthetic potency. However, the sensitivity of each phase of the h.p.n.s. to anaesthetic gases differed. Most notably, the median pressure for tonic convulsions was elevated about three times more by a given partial pressure of anaesthetic gas than were the median pressures for complete spasms or non-tonic death. These observations can be fitted remarkably well by the hypothesis that a given phase of the h.p.n.s. is activated when some hydrophobic region is compressed beyond a certain critical amount by the application of pressure. Absorption of an inert gas in this region will cause it to expand, tending to elevate the median pressure for that phase of the h.p.n.s. Our data and analysis allow the following conclusions relevant to diving practice. All gases protect against the h.p.n.s. but some phases of this complex syndrome are more effectively controlled than others. Although addition of a second inert gas to helium allows substantial increases in the pressure at which h.p.n.s. occurs, the onset of anaesthesia (or inert gas narcosis) will limit the ultimate gain. The composition of therapeutic gas mixtures becomes more narrowly defined as the pressure increases. The optimum mixture may be different for each phase of the h.p.n.s., and the order of presentation of the h.p.n.s. symptoms may be changed by the second inert gas. We may also predict that physiological sites may exist where helium acts like an anaesthetic. If such sites resulted in physiological dysfunction, addition of a second gas would exacerbate the situation.

Anesthetics↗
PubMed1997

Improved probabilistic decompression model risk predictions using linear-exponential kinetics.

Using a data base of 2,383 air and nitrogen-oxygen dives resulting in 131 cases of decompression sickness (DCS), risk functions were developed for a set of probabilistic decompression models according to survival analysis techniques. Parameters were optimized using the method of maximum likelihood Gas kinetics were either traditional exponential uptake and elimination, or an exponential uptake followed by linear elimination (LE kinetics) when calculated supersaturation was excessive. Risk functions either used the calculated relative gas supersaturation directly, or a delayed risk using a time integral of prior supersaturation. The most successful model (considering both incidence and time of onset of DCS) used supersaturation risk, and LE kinetics (in only 1 of 3 parallel compartments). Several methods of explicitly incorporating metabolic gases in physiologically plausible functions were usually found in lumped threshold terms and did not explicitly affect the overall data fit. The role of physiologic fidelity vs. empirical data fitting ability in accounting for model success is discussed.

Decompression Sickness↗
PubMed2001

Common themes of adaptation to hypoxia. Insights from comparative physiology.

Many vertebrate animals have superior tolerance to environmental hypoxia compared to humans. For example, turtles tolerate an environment of 100% N2 for several hours, without apparent ill effect. This hypoxia tolerance is not limited to heterotherms, as some species of marine mammals, such as the northern elephant seal, may voluntarily dive for periods of up to 2 hours. Torpid bats exhibit prolonged periods of apnea and passive diffusion of oxygen down their trachea through an open glottis supplies a significant amount of the oxygen uptake. The Ruppell's griffon holds the known avian record of flight at 11,278 m, and other birds regularly migrate at altitudes over 8000m. These animals exhibit diverse adaptations for tolerating their hypoxic environment, many of which are poorly understood. Some of theses strategies include 1) the ability to lower metabolic rate when exposed to hypoxia 2) the ability to recruit alternate biochemical pathways for energy production 3) a left shifted oxy-hemoglobin dissociation curve 4) more efficient pulmonary gas exchange 5) the ability to alter blood flow distribution under hypoxic stress. Although there are common themes of animal adaptation to hypoxic stress, many animal solutions are unique.

Acclimatization↗
PubMed1991

The effect of submergence on heart rate and oxygen consumption of swimming seals and sea lions.

Respiratory, metabolic, and cardiovascular responses to swimming were examined in two species of pinniped, the harbor seal (Phoca vitulina) and the California sea lion (Zalophus californianus). 1. Harbor seals remained submerged for 82-92% of the time at swimming speeds below 1.2 m.s-1. At higher speeds, including simulated speeds above 1.4 m.s-1, the percentage of time spent submerged decreased, and was inversely related to body weight. In contrast, the percentage of time spent submerged did not change with speed for sea lions swimming from 0.5 m.s-1 to 4.0 m.s-1. 2. During swimming, harbor seals showed a distinct breathhold bradycardia and ventilatory tachycardia that were independent of swimming speed. Average heart rate was 137 beats.min-1 when swimming on the water surface and 50 beats.min-1 when submerged. A bimodal pattern of heart rate also occurred in sea lions, but was not as pronounced as in the seals. 3. The weighted average heart rate (WAHR), calculated from measured heart rate and the percentage time spent on the water surface or submerged, increased linearly with swimming speed for both species. The graded increase in heart rate with exercise load is similar to the response observed for terrestrial mammals. 4. The rate of oxygen consumption increased exponentially with swimming speed in both seals and sea lions. The minimum cost of transport calculated from these rates ranged from 2.3 to 3.6 J.m-1.kg-1, and was 2.5-4.0 times the level predicted for similarly-sized salmonids. Despite different modes of propulsion and physiological responses to swimming, these pinnipeds demonstrate similar transport costs.

Aerobiosis↗
PubMed2001

Effects of temperature and aquatic P(O2) on the physiology and behaviour of Apalone ferox and Chrysemys picta.

Softshell turtles overwinter in the same bodies of water as some emydids, but their reduced shell and increased non-pulmonary gas exchange may contribute to a different mechanism of overwintering. The dynamics of bimodal respiration, diving behaviour and blood acid-base status in Apalone ferox and Chrysemys picta were investigated under two different temperatures combined with three different aquatic P(O2) levels. Both species obtained oxygen through pulmonary and non-pulmonary routes. Apalone ferox obtained more oxygen through non-pulmonary routes and increased its non-pulmonary V(O2) in response to both higher aquatic P(O2) and lower temperatures. Both species increased pulmonary V(O2) in response to higher temperatures. As a consequence of the greater reliance of A. ferox on pulmonary V(O2), warmer temperatures caused plasma P(CO2) and [HCO(3)(-1)] values to increase significantly compared with C. picta. Apalone ferox, which is efficient at bimodal respiration, displayed a high degree of plasticity with respect to both its respiratory and acid-base profiles, behaving more like an aquatic air-breathing fish in bimodal respiration at low temperature and more like a terrestrial air-breather at high temperature. Chrysemys picta, which is poor at bimodal respiration, was highly dependent on aerial gas exchange at both temperatures. Aquatic P(O2) did not change any of the behavioural variables measured. At warm temperatures, A. ferox met O(2) demands by increasing the rate of lung ventilation, which resulted in a significantly greater number of breathing bouts per hour and breaths per emersion period. However, the number of breaths per bout was not affected by temperature. As temperatures decreased, A. ferox utilized its non-pulmonary respiration ability and significantly increased its dive duration. Apalone ferox became less active at colder temperatures by significantly increasing the duration of inactive periods (from 4 to 18 min) and by significantly decreasing the frequency of activity bursts. Chrysemys picta also met the higher gas-exchange demands associated with increased temperature by increasing the rate of lung ventilation; however, this increase was not as large as that measured in A. ferox. Chrysemys picta displayed multiple rhythmic breaths per bout. These results indicate that, unlike aquatic P(O2), temperature is an important factor in the regulation of diving and ventilatory behaviour in turtles. The species responded to temperature in dissimilar ways because of differences in their bimodal respiration ability.

Acid-Base Equilibrium↗
PubMed1992

T wave changes in humans and dogs during experimental dives.

Electrocardiogram (ECG) analysis was performed in three human divers studied at 21 and 23.5 ATA while they breathed various gas mixtures containing H2 and/or He (COMEX HYDRA IX experiment) and in five dogs exposed to 91 ATA of He-O2 or He-N2-O2. In all cases, the O2 partial pressure was slightly higher than its physiological value. These human and animal studies reveal that elevated pressure of different inert gases did not change the resting heart rate or its respiratory fluctuation. However, the T wave amplitude increased in proportion to the gas density in the three divers; this was also found in four of the five dogs studied. Changes in peak T wave configurations were also observed in the dog experiments. Positional changes in QRS or T vectors cannot explain these T wave changes.

Animals↗