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At least 1,171 records · Page 65Linked to original sources
PubMed1992

Neurology of microgravity and space travel.

Exposure to microgravity and space travel produce several neurologic changes, including SAS, ataxia, postural disturbances, perceptual illusions, neuromuscular weakness, and fatigue. Inflight SAS, perceptual illusions, and ocular changes are of more importance. After landing, however, ataxia, perceptual illusions, neuromuscular weakness, and fatigue play greater roles in astronaut health and readaptation to a terrestrial environment. Cardiovascular adjustments to microgravity, bone demineralization, and possible decompression sickness and excessive radiation exposure contribute further to medical problems of astronauts in space. A better understanding of the mechanisms by which microgravity adversely affects the nervous system and more effective treatments will provide healthier, happier, and longer stays in space on the space station Freedom and during the mission to Mars.

Adaptation, Physiological↗
PubMed1992

Paradoxical air embolism in pigs with a patent foramen ovale.

Recent studies have indicated that divers with a patent foramen ovale (PFO) are at risk of developing some forms of decompression sickness. Thus, the objective of the present study was to investigate if the occurrence of paradoxical air embolism (PAE) was enhanced in pigs with a PFO compared to the occurrence in pigs without such a defect. Out of 54 pigs, 18 had a PFO (group PFO), and the other 36 composed the controls (group C). The pigs were anesthetized, mechanically ventilated, and received venous air infusion at four different rates (0.050, 0.075, 0.100, and 0.200 ml.kg-1.min-1). PAE was monitored by use of a transesophageal echocardiographic probe to detect if any arterial air bubbles were present in the left atrium or the aorta. We found that PAE appeared at a lower infusion rate in group PFO than in group C. When PAE occurred, the mean pulmonary arterial pressure and the mean arterial pressure were significantly higher in pigs with a PFO than in the control pigs. Finally, the infused air volume per kilogram of body weight in group PFO was significantly lower than that observed in group C. The results demonstrated that the risk of PAE occurring in mechanically ventilated pigs with a PFO was greater compared to the risk observed in pigs without a PFO.

Animals↗
PubMedDate not supplied

Tissue nitrogen elimination in oxygen-breathing pigs is enhanced by fluorocarbon-derived intravascular micro-bubbles.

UNLABELLED: The present study tested the hypothesis that intravascular micro bubbles generated by i.v. infusion of a 2 % dodecafluoropentane (DDFP) emulsion will enhance tissue denitrogenation during oxygen breathing. Eleven spontaneously breathing pentobarbital anesthetized pigs were studied. Six pigs were treated with 0.08 ml/kg of DDFP-emulsion infused over 30 min and five (control) pigs received a matching dose of emulsion vehicle. Circulatory parameters were recorded. The pigs were connected via a tracheal tube to a closed circuit oxygen-primed breathing loop allowing volume measurements and nitrogen analysis by gas chromatography every 7 min. The nitrogen washout was recorded for up to four hrs in each group. The cumulative nitrogen yield during oxygen breathing was considerably larger in treated animals than in controls. Thus, the amount of nitrogen eliminated in the controls in 120 min was achieved already after 65 min in animals treated with the DDFP-emulsion. Blood pressure and cardiac output remained stable and were not different between the two groups during the four hrs of nitrogen washout. The central venous oxygen tension was significantly higher in the treated animals during oxygen breathing than in the controls. This difference was, in all probability due to enhanced oxygen transport by the micro-bubbles. CONCLUSION: Intravascular micro-bubbles generated by i.v. infusion of a small dose of 2 % DDFP-emulsion very effectively enhanced denitrogenation by oxygen breathing and deserve study as a means to improve prevention and treatment of decompression sickness.

Algorithms↗
PubMed2005

Cardiovascular neuroregulation during acute exposure to 40, 70, and 100% oxygen at sea level.

BACKGROUND: Humans encounter increased partial pressures of inspired oxygen in some kinds of diving as well as during use of hyperoxic mixtures to shorten decompression times and hyperbaric oxygen therapy for decompression sickness or other clinical conditions. Although it is known that hyperoxia may affect cardiovascular regulation, such effects are generally obscured by stress and the diving reflex. In this study, we evaluated cardiovascular neuroregulation for various levels of hyperoxia in a laboratory setting. METHODS: There were 10 healthy adults who were exposed to 21, 40, 70, and 100% oxygen administered via mask as a series of stepwise increases. Subjects breathed at a fixed respiratory rate of 15 breaths x min(-1) while their heart rate (HR) and blood pressure (BP) were measured continuously over 5-min intervals. RESULTS: HR decreased with increasing fraction of inspired oxygen (FIO2) (21%: 65 +/- 9, 40%: 63 +/- 9, 70%: 61 +/- 8, 100%: 60 +/- 8 bpm) and the high-frequency power of HR variability (an index of cardiac parasympathetic activity) increased as FIO2 rose (21%: 773 +/- 565, 40%: 880 +/- 590, 70%: 966 +/- 681, 100%: 1114 +/- 715 ms2); both changes were significant at the 70% and 100% oxygen levels. The low-frequency power of systolic BP variability (an index of vasomotor sympathetic activity) did not change. Low- and high-frequency transfer function gains (indices of arterial-cardiac baroreflex function) increased with FIO2. CONCLUSION: Parasympathetic activity and arterial-cardiac baroreflex function increased with hyperoxia in a dose-dependent manner. This increase may help reduce the likelihood of arrhythmias during diving.

Administration, Inhalation↗
PubMed2006

Robert Hooke, inventor of the vacuum pump and the first altitude chamber (1671).

Robert Hooke (1635-1703), an assistant researcher to Robert Boyle (1627-1691), invented the first functional British air pump. Applying it to scientific research, Hooke operated the world's first hypobaric chamber in 1671, using it for self-experimentation. He recorded the first physiological observations in an artificial altitude-equivalent environment up to 2400 m. Though Hooke's experiment showed some methodological insufficiencies, his imaginative experimental techniques were remarkable for their time and were indicative of the lively intellectual atmosphere of the Royal Society and the significant contributions of Hooke, who was a member. Two centuries passed before the French physiologist Paul Bert (1830-1886) conducted his famous laboratory-supported investigations of high altitude physiology. Bert played a decisive role in the discovery of the causes of decompression sickness; a contribution Hooke could not make due to the technical deficiencies of the 17th century.

Altitude↗
PubMedDate not supplied

NIHSS applied to cerebral neurological dive injuries as a tool for dive injury severity stratification.

BACKGROUND: Evaluation via National Institutes of Health Stroke Scale (NIHSS) upon presentation in hospital triage following ischemic stroke is predictive of recovery or progression to neurological deficits. Cerebral injuries sustained while diving have symptoms similar to stroke. Applying the NIHSS to dive injuries may successfully summarize neurological dive injuries, providing a standardized tool for study of dive injury data. METHODS: We retrospectively determined NIHSS scores for a diverse population of 192 divers presenting to the University of Hawaii recompression chamber from 1983-2002, both prior to initial treatment and after all treatment. Spinal and vestibular decompression sickness cases were excluded. RESULTS: The performance of the NIHSS among this diving population was similar to its performance as an accepted tool in evaluation of ischemic stroke, although results are influenced by the abundance of mild injury cases in the data set. The estimated C-statistic with NIHSS predicting no observable deficit was 0.88, and predicting post NIHSS of 0-1 was 0.85 (vs. 0.86 when applied to stroke). Sensitivity for predicting recovery (NIHSS 0-1) at discharge was 0.99 (vs. 0.97 for stroke). CONCLUSIONS: The NIHSS applied to cerebral dive injuries has adequate predictive ability and correlates with other measures of dive injuries, while providing a standardized, more graduated scale. The NIHSS may be useful as a standardized measurement for evaluation of treatment regimens and adjunctive therapy for diving injuries.

Adolescent↗
PubMed2006

[Patent foramen ovale, stroke, and echocardiography: diagnostic methodology and appropriateness of indications].

A patent foramen ovale is a frequent remnant of embryological development with clinical importance in stroke, decompression sickness, and migraine headache. The proposed mechanisms of stroke include paradoxical embolization, in situ thrombosis within the canal of the foramen, associated atrial arrhythmias. Cardiac right-to-left shunts can be identified by echocardiography and by transcranial Doppler ultrasound with the use of contrast agents and a Valsalva maneuver as provocation procedure. Relative value of different diagnostic tests, appropriate timing of the Valsalva maneuver, use of a diagnostic time window, and threshold in contrast agent microbubbles detection are thoroughly discussed. The value of echocardiography or of other diagnostic tests does not elucidate the effect of test results on patient management. The appropriate use of imaging requires an understanding of both the capabilities of the imaging technique and the value of therapy used to treat the identified condition. New information that does not improve outcome has no value. In patients with a cryptogenic stroke and an atrial septal abnormality the evidence is insufficient to determine whether warfarin or aspirin is superior in preventing recurrent stroke or death, but minor bleeding is more frequent with warfarin. There is insufficient evidence to evaluate the efficacy of surgical or endovascular closure.

Echocardiography, Transesophageal↗