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At least 595 records · Page 33Linked to original sources
PubMed1977

Transient visually evoked potential.

A light delivered to the human eye will instigate changes in electrical potentials recorded over the visual cortex that last for some finite time, at least several hundred milliseconds. If the rate of stimulation is sufficiently low, the response is completed before the next visual stimulus arrives; the cortical potential is then called a transient evoked response. This review of the transient evoked potential describes the techniques by which the response is obtained, the problems inherent in its use, and procedures by which these difficulties can be overcome or minimized. A summary of the research results from the field enumerates those findings which have been well established and replicated by many investigators, those that are more controversial or as yet inconclusive, and the many practical applications of the technique for science and medicine. Finally, the needs for an underlying physiological theory and for future research are discussed.

Color Vision Defects↗
PubMed1999

Effects of repeated apneas on apneic time and diving response in non-divers.

Human breath-hold divers usually perform a series of dives with short intervals. Repeated apneas prolong apneic time, and an accentuated diving response has been suggested to be the cause. The aim of this study was to investigate the effect of repeated apneas on apneic time and diving response in humans. Forty-one subjects performed a series of five apneas with face immersion in water of 10 degrees C, separated by 2-min intervals. Apneas were performed at rest and to individual maximal duration. Heart rate, mean arterial pressure, skin capillary blood flow, and respiratory movements were recorded. Thirty-eight of the subjects were used for analysis of cardiovascular parameters, and in 23 subjects the physiologic breaking point could be detected by the involuntary breathing movements. Heart rate reduction and blood pressure increase were most prominent during the first apneic face immersion, whereas skin capillary blood flow reduction was most intense in the second apneic face immersion. Blood pressure and skin capillary blood flow during recovery from apneic episodes also changed throughout the series. Repetition increased apneic time by 55% and postponed the occurrence of involuntary breathing movements by 27% in subjects passing the physiologic breaking point. We conclude that both physiologic factors, associated with the accumulation of CO2, and psychologic factors, related to the capacity to withstand the respiratory drive, contribute to the prolongation of apneic time whereas an increased diving response does not contribute.

Adult↗
PubMedDate not supplied

An experimental psychophysiological approach to human bradycardiac reflexes.

Bradycardic reflexes in man are both of scientific and clinical interest. Using the methods of experimental psychophysiology, control over relevant independent variables permits the study of fine-grained temporal physiologic response topographies, and of psychological factors that may modify the reflex. In addition, information can also be sought through interdisciplinary collaborations with experimental physiologists in order to shed light on the mechanism of the reflexes. These general features of the approach are illustrated by presenting data on two bradycardic reflex preparations: the laboratory dive analog, and the 90-degree negative tilt. The dive-analog studies have shown that a) the dive-reflex proper is a late-occurring bradycardia accompanied by a late-occurring vasoconstriction; and b) for the elicitation of this reflex, both breath-holding and face immersion are necessary. In addition, the physiologic manipulation of temperature affects the reflex in an inverse way over the range of 10 degrees to 40 degrees C, while the sense of control (a psychological variable) attenuates the reflex. The negative-tilt preparation produces a bradycardic response that is ideal as a Pavlovian unconditional response. Some Pavlovian conditioning arrangements, especially an "imaginational" form, do produce significant conditional bradycardic responding, and this has both potential clinical (e.g., biofeedback-related) and theoretical (e.g., S-R vs. S-S accounts of Pavlovian conditioning) applications. The paper ends with a comment on the cognitive paradigm shift in psychology. Although this shift is of importance, it is suggested that it is also important to "remember the response."

Biofeedback, Psychology↗
PubMed1998

Maintaining safe oxygen levels in semiclosed underwater breathing apparatus.

Semiclosed circuit underwater breathing apparatus (UBAs) are far more conserving of limited gas supplies than either steady-flow, open circuit or demand, open circuit systems. Semiclosed systems recirculate most of the diver's breathing gases, while injecting only a small percentage of the total circuit flow with a fresh makeup supply. The fresh, injected gas supply delivers the necessary makeup to compensate for the oxygen that the diver consumes during each pass through the lungs. This gas-conserving feature makes the utility for semiclosed UBAs for long-duration, deep diving applications more practical than either of the open circuit designs. However, although more gas conservative, these systems maintain variable oxygen levels during a dive that can fluctuate widely with changes in the diver's activity level, depth of the dive, makeup gas composition, or variations in the total circuit volume. It is essential that the oxygen levels in the circuit always remain within physiologically safe limits; neither too low to avoid the onset of hypoxia, nor too high to risk oxygen toxicity. This article presents an analytical assessment of the oxygen levels in semiclosed UBAs. This model allows the designers of semiclosed circuits to predict the effects of UBA circuit volumes, makeup gas compositions, injection rates for the makeup gas, diver depths, and initial circuit oxygen levels on the time-dependent levels of oxygen in these circuits. By using this analytical tool, judicious selection of these design variables can result in the most efficient utilization of the fresh gas supply carried by the diver, and ensure the safe operation of these UBA designs.

Air Conditioning↗
PubMed1999

Analysis of cerebral bioelectrical activity during the compression phase of a saturation dive.

Considering previous studies on EEG brain mapping in the course of saturation dives, the authors studied the same standards of EEG performance during the compression phase of a saturation dive reaching -250 m. An increase of theta and beta rhythms was observed, especially in the midline anterior regions of the brain, during the entire compression period, while an increase of delta activity was noted only at -100 m. These results confirm our hypothesis that the compression profile is physiologically correct, because the EEG modifications decreased during the stay at maximum depth.

Air Pressure↗
PubMed1997

[Incidence of vertigo in diving].

Vertigo is relatively common after diving. Although it may be the result of the changes in pressure, it can also be a feature of decompression accidents, of clinical toxicity, simply be a manifestation of altered physiology resulting from immersion in a weightless environment in which all the organs involved in maintaining equilibrium (vestibular system, proprioception and vision) are affected. It seemed to us to be of interest to study the incidence of vertigo in naval divers by means of an anonymous questionnaire. The responses were elicited over a 3 month period from 333 divers. 45 divers reported clinical sensations of vertigo, an incidence of 13.5%. If this figure is related to the number of dives, the incidence falls to 0.06%. No decompression accidents were reported. The main aetiology was barotrauma, 42% being of alternobaric and 36% of pressure type. The remaining aetiologies were sensory illusions in 6% of cases, and other non-ENT causes in 16%. After a review of the physiopatholgy and study of the case hisotries, there is a discussion of the features which allow the aetiology to be determined and treatment planned.

Adult↗
PubMed1996

Diving behaviour and haemoglobin function: the primary structure of the alpha- and beta-chains of the sea turtle (Caretta caretta) and its functional implications.

The amino acid sequence of the alpha- and beta-chains of haemoglobin (Hb) from the loggerhead sea turtle (Caretta caretta) has been determined. Comparison with that of human Hb shows differences in several residues involved in both alpha 1 beta 1 and alpha 1 beta 2 packing contacts. On the whole, in spite of the mutations, the essential characteristics of both interfaces seem to be maintained. The functional properties of the sea turtle Hb have been investigated at different temperatures and as a function of proton, chloride and organic phosphate concentrations. In addition to overall similarities shared with most of the vertebrate Hbs previously described, this molecule shows significant differences which could be related to the life behaviour of the turtle. In fact, while the shape of the Bohr-effect curve is well adapted for gas exchange during prolonged dives, the very small enthalpy change for O2 binding ensures that O2 delivery becomes essentially insensitive to the temperature changes of the environment. Moreover, and similarly to the case of emperor penguin Hb, the small alkaline Bohr effect appears to be only choride-linked, since the pH dependence of the O2 affinity is abolished in the absence of this ion. These functional characteristics are discussed on the basis of the primary structure of alpha- and beta-chains.

Adaptation, Physiological↗
PubMed1993

Effects of elevated pressures of inert gases on cytosolic free Ca2+ of human platelets stimulated with ADP.

Platelets were exposed to elevated pressures of helium (He), nitrogen (N2), and He/xenon (He/Xe, 85/15), and stimulated with ADP (5 microM). He to 36 atmospheres absolute (ATA) inhibited the ADP-stimulated increase in [Ca2+]i, measured by Fura-2/AM, with most of the effect occurring by 9 ATA. N2 caused a similar but initially greater effect and it was bimodal, with inhibition being less at 36 ATA than at 18 ATA. N2 also significantly depressed basal levels at 18 and 36 ATA. In the He/Xe mixture, the effect on ADP-stimulated [Ca2+]i was no different from He alone at the same pressures, but basal levels were significantly depressed. In a calcium-free medium both He and N2 moderately depressed the already-reduced response to ADP stimulation but only N2 significantly depressed basal levels at all pressures. These results indicate that raised pressures of inert narcotic gases, as well as pressure per se (represented by He), can affect cell [Ca2+]i sufficiently to have physiological consequences. This, together with previous findings in this laboratory, may have implications for some of the neurological problems associated with deep diving.

Adenosine Diphosphate↗
PubMed2006

Alternobaric vertigo--really a hazard?

OBJECTIVE: To determine the prevalence of alternobaric vertigo (AV) in sport divers and to find out whether AV led to dangerous situations underwater. Furthermore, to examine whether objective neurootologic tests are associated with the manifestation of AV. DESIGN: Retrospective cohort study. PARTICIPANTS: Sixty-three sport divers with an average diving experience of 10 years and 650 dives were questioned regarding their medical and diving history and the manifestation of vertigo during diving. METHODS: Microscopic otoscopy, tympanometry, stapedius reflexes, hearing threshold for air and bone conduction, caloric video-oculography including analysis of the slow-phase velocity of the nystagmus, acoustic brain stem responses, and magnetic resonance imaging were performed to find possible differences between divers with and without AV. RESULTS: We found 17 divers with AV (27%). There was no significant difference in all measured parameters apart from sex and history of middle ear equalization difficulty in divers with AV. Ten (59%) of 17 female divers and 7 (15%) of 46 male divers experienced AV, representing a significant sex difference (p < 0.001). Correlation with our divers' outpatient clinic revealed that female divers had a significantly higher incidence of middle ear equalization disorders which could be an explanation for the predominance of female divers with symptoms of AV. None of the divers reported any dangerous or life-threatening situations following AV. Whether AV leads to dangerous situations underwater remains unclear, but this hypothesis is not supported by our data. CONCLUSION: Alternobaric vertigo is a common finding in divers. In our study group, female divers had a four-time higher risk to suffer AV. Our data do not support the thesis that AV is a life-threatening condition.

Acoustic Impedance Tests↗
PubMed2002

Traumatic tetraplegia: noninvasive respiratory management in the acute setting.

A 15-yr-old patient with high-level spinal cord injury developed ventilatory failure 24 hr after hospital admission and required continuous ventilatory support. Although he lost all ventilator-free breathing tolerance, he was managed by receiving noninvasive intermittent positive-pressure ventilation rather than intermittent positive-pressure ventilation via an endotracheal intubation. Cooperative, uncomplicated, acutely injured patients with spinal cord injury who develop ventilatory failure are candidates to use noninvasive intermittent positive-pressure ventilation to avoid intubation.

Acute Disease↗
PubMed2006

Changes in body temperature in king penguins at sea: the result of fine adjustments in peripheral heat loss?

To investigate thermoregulatory adjustments at sea, body temperatures (the pectoral muscle and the brood patch) and diving behavior were monitored during a foraging trip of several days at sea in six breeding king penguins Aptenodytes patagonicus. During inactive phases at sea (water temperature: 4-7 degrees C), all tissues measured were maintained at normothermic temperatures. The brood patch temperature was maintained at the same values as those measured when brooding on shore (38 degrees C). This high temperature difference causes a significant loss of heat. We hypothesize that high-energy expenditure associated with elevated peripheral temperature when resting at sea is the thermoregulatory cost that a postabsorptive penguin has to face for the restoration of its subcutaneous body fat. During diving, mean pectoral temperature was 37.6 +/- 1.6 degrees C. While being almost normothermic on average, the temperature of the pectoral muscle was still significantly lower than during inactivity in five out of the six birds and underwent temperature drops of up to 5.5 degrees C. Mean brood patch temperature was 29.6 +/- 2.5 degrees C during diving, and temperature decreases of up to 21.6 degrees C were recorded. Interestingly, we observed episodes of brood patch warming during the descent to depth, suggesting that, in some cases, king penguins may perform active thermolysis using the brood patch. It is hypothesized that functional pectoral temperature may be regulated through peripheral adjustments in blood perfusion. These two paradoxical features, i.e., lower temperature of deep tissues during activity and normothermic peripheral tissues while inactive, may highlight the key to the energetics of this diving endotherm while foraging at sea.

Animals↗
PubMed1995

3-D eye movement measurements on four Comex's divers using video CCD cameras, during high pressure diving.

Previous studies have shown the vulnerability of the vestibular system regarding barotraumatism (1) and deep diving may induce immediate neurological changes (2). These extreme conditions (high pressure, limited examination time, restricted space, hydrogen-oxygen mixture, communication difficulties etc.) require adapted technology and associated fast experimental procedure. We were able to solve these problems by developing a new system of 3-D ocular movements on line analysis by means of a video camera. This analyser uses image processing and forms recognition software which allows non-invasive video frequency calculation of eye movements including torsional component. As this system is immediately ready for use, we were able to realize the subsequent examinations in a maximum time of 8 min for each diver: oculomotor tests including saccadic, slow and optokinetic traditional automatic measurements; vestibular tests regarding spontaneous and positional nystagmus, and reactional nystagmus to the pendular test. For pendular induced nystagmus we used appropriate head positions to stimulate separately the lateral and the posterior semicircular canal, and we measured the gain by operating successively in visible light and complete darkness. Recordings were done during a simulated onshore dive to an ambient pressure corresponding to a depth of 350 m. The above examinations were completed on the first and last days by caloric tests with the same video system analyser. The results of the investigations demonstrated perfect tolerance of the oculomotor and vestibular systems of these 4 divers thus fulfilling the preventive conditions defined by Comex Co. We were able to overcome the limitations due to low cost PC computer operation and cameras (necessity of adaptation to pressure, focus difficulties and direct light exposure eye reflexions). We still have on line accurate measurements even on the torsional component of the eye movement. Due to this technological efficiency we also present some mathematical aspects of the software.

Adult↗