Aviat Space Envir Md
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Aviat Space Envir Md · Sep 1999
Short hypobaric hypoxia and breathing pattern: effect of positive end expiratory pressure.
The ventilatory effects of a 5-cm H2O positive end expiratory pressure (PEEP) and its influence on the breathing pattern during short hypoxic exposure both at rest and during physical exercise were studied. There were 22 healthy subjects who were submitted to normoxia and to 4-h of hypoxia in a hypobaric chamber (4500 m, PB = 589 hPa) both at rest and during an 8-min cycle ergometer exercise (100 W) without and with a 5 cm H2O PEEP. The results show that hypoxia compared with normoxia induces increases in tidal volume (VT) (+28.5%, p < 0.05 at rest; and +19.4%, p < 0.01 at 100 W) and in respiratory frequency (f) at 100 W (p < 0.05), and significant decreases in inspiratory (tI) (p < 0.05 at rest and at 100 W), and expiratory (tE) durations (p < 0.05 at 100 W). ⋯ However, PEEP does not alter the breathing pattern in hypoxia since VT/tI and tI/tt are unchanged. Heart rate and arterial O2 saturation are also unaffected by PEEP. In conclusion, this study shows that a 4-h hypoxia modifies ventilatory parameters and mean inspiratory flow (VT/tI) at rest and during exercise (100 W), whereas a 5-cm H2O PEEP does not alter the breathing pattern despite changes in ventilatory parameters are observed.
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Aviat Space Envir Md · Aug 1999
ReviewThe non-invasive assessment of stroke volume and cardiac output by impedance cardiography: a review.
Impedance cardiography (IC) is an inexpensive, reliable and noninvasive technique for determining stroke volume (SV) and cardiac output (CO). It relies on the measurement of phasic changes in transthoracic electrical resistivity, related to ejection of blood into the ascending aorta with each heart beat. Because of its non-invasive nature, IC is becoming increasingly used in clinical settings, as well as in many areas of physiological research. ⋯ The question of accuracy of IC in terms of absolute values of SV and CO remains to be determined. The methodological limitations, accuracy, reliability and reproducibility of IC are examined, as are some of the methods developed to improve these aspects of the technique. The application and utility of IC in aerospace medicine research is also addressed.
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Aviat Space Envir Md · Aug 1999
Comparative StudyPositive pressure generation by pneumatic and electronic O2 regulators: a bench experimental evaluation.
The introduction of advanced anti-G protection into agile fast fighter aircraft may result in the regular use of positive pressure breathing (PPB) for G protection by aircrew. Since PPB results in an external additional work of breathing (WoB), we compared the mechanical performance of the pneumatic and electronic O2 regulators designed for "Mirage 2000" and "Rafale" aircraft. ⋯ We concluded that the electronic control of mask pressure is relatively efficient but that the device would be improved by placing the site of the pressure measurement into the mask.
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Aviat Space Envir Md · Jul 1999
Comparative StudyReport of ejections in the Spanish Air Force, 1979-1995: an epidemiological and comparative study.
Ejection seats have saved many lives with more than 80% of pilots having survived an ejection. Nevertheless, ejection injuries are seen in all modern air forces. ⋯ The pilot position in the ejection seat, plane control, ejection inside the envelope, the pilot's training in how to assume the necessary body position at both egress and landing phases are determining factors for successful ejections.
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Aviat Space Envir Md · Jul 1999
Case ReportsLow-altitude overflights of fighters and the risk of hearing loss.
Much data are available on noise properties which cause hearing loss. There are not, however, reports on the effects of low-altitude overflight noise on the permanent threshold shift (PTS). ⋯ According to these results and the principles of noise evaluation, there should be no risk of permanent hearing loss when the distance to an overflying jet fighter is more than 200 m. However, we have received two claims, and the audiometric analyses of two subjects who had suffered hearing loss in one ear in Finland during the 1990s may indicate that there is very likely a connection between the incidents and the hearing losses.