Biomedical subjects

Mirit Eynan

Publications and source records attributed to Mirit Eynan.

6 recordsLinked to original sources

PubMed2006

CO2 detection in closed-circuit oxygen divers with and without a distracting task.

INTRODUCTION: Elevated arterial PCO2 (hypercapnia) increases the risk of CNS oxygen toxicity when diving with enriched oxygen gas mixtures. A CO2 detection and retention test is conducted as a matter of routine at the Israel Naval Medical Institute for physiological training, and as a screening tool for divers who may be prone to suffer from CNS oxygen toxicity. This test does not include an "attention distracter", which would provide a better simulation of the true situation during actual diving. The purpose of the present study was to examine the hypothesis that the addition of cognitive tasks to the CO2 detection and retention test might alter divers' detection ability. METHODS: We assessed ventilatory and perceptual responses to variations in inspired CO2 (range 0-5.6 kPa, 0-42 mmHg) during moderate exercise, with and without the addition of cognitive tasks, in 15 Israel Navy combat divers on active duty. The first stage was the CO2 detection training session, followed by the CO2 detection test session (TEST) and the CO2 detection test session while doing cognitive tasks (COGN). The latter two sessions were performed by some of the subjects in reverse order. RESULTS: We found that the mean (+/- SD) PICO2 at the detection threshold was significantly lower in the COGN (1.7 +/- 0.8 kPa, 12.7 +/- 6.0 mmHg) than in the TEST (2.4 +/- 0.6 kPa, 18.1 +/- 4.5 mmHg). The mean PETCO2 while inspiring 5.6 kPa (42 mmHg) CO2 was not significantly different in the two tests. CONCLUSION: We suggest that the ability to detect CO2 during a dive is not impaired, but rather improves when the diver's attention is focused on other tasks.

Carbon Dioxide↗

PubMed2004

Response to CO2 in novice closed-circuit apparatus divers and after 1 year of active oxygen diving at shallow depths.

Elevated arterial Pco(2) (hypercapnia) has a major effect on central nervous system oxygen toxicity in diving with a closed-circuit breathing apparatus. The purpose of the present study was to follow up the ability of divers to detect CO(2) and to determine the CO(2) retention trait after 1 year of active oxygen diving with closed-circuit apparatus. Ventilatory and perceptual responses to variations in inspired CO(2) (range: 0-5.6 kPa, 0-42 Torr) during moderate exercise were assessed in Israeli Navy combat divers on active duty. Tests were carried out on 40 divers during the novice oxygen diving phase (ND) and the experienced oxygen diving phase. No significant changes were found between the two phases for the minimal mean inspired Pco(2) that could be detected. The mean (with SD in parentheses) end-tidal Pco(2) during exposure to an inspired Pco(2) of 5.6 kPa (42 Torr) was significantly higher in the novice diving phase than in the experienced diving phase [8.1 kPa (SD 0.7), 62 Torr (SD 5) and 7.8 kPa (SD 0.6), 59 Torr (SD 4), respectively; P < or = 0.001]. One year of shallow oxygen diving activity with a closed-circuit apparatus does not affect the ability to detect CO(2) nor does it lead to increased CO(2) retention; rather, it may even bring about a decrease in this trait. This finding suggests that acquiring experience in oxygen diving with a closed-circuit apparatus at shallow depths does not place the diver at a greater risk of central nervous system oxygen toxicity due to CO(2) retention.

Adult↗

PubMed2003

Heat acclimation prolongs the time to central nervous system oxygen toxicity in the rat. Possible involvement of HSP72.

Oxygen toxicity of the central nervous system (CNS-OT) can occur during diving with oxygen-enriched gas mixtures, or during hyperbaric medical treatment. CNS-OT is characterised by convulsions and sudden loss of consciousness, which may be fatal in diving. Heat acclimation is known to provide cross-tolerance to various forms of stress in different organs, including the brain. We hypothesised that heat acclimation may delay the onset of CNS-OT in the rat. Male Sprague-Dawley rats were acclimated to an ambient temperature of 32 degrees C for 4 weeks. Rats in the control group were kept at 24 degrees C. Both groups were exposed to oxygen at 608 kPa. EEG was recorded continuously until the appearance of the first electrical discharge preceding clinical convulsions. CO(2) production was measured simultaneously with the EEG. Latency to CNS-OT was measured and brain samples were taken for evaluation of heat shock protein 72 (HSP72) levels by Western blot analysis at the end of the acclimation period and during 4 weeks of deacclimation. Latency to CNS-OT was twice as long in the heat-acclimated rat, with insignificant changes in CO(2) production. This prolongation continued for 2 weeks during deacclimation. There was a significant increase in the level of HSP72 following heat acclimation, with a subsequent decrease during deacclimation. We conclude that heat acclimation prolongs latency to CNS-OT in a way that does not involve changes in metabolic rate. During deacclimation there was a linear relationship between latency to CNS oxygen toxicity and the level of HSP72. A possible beneficial effect of HSP72 is discussed.

Acclimatization↗

PubMed2003

Training improves divers' ability to detect increased CO2.

BACKGROUND: Elevated arterial PCO2 (hypercapnia) is a known risk in diving with closed circuit breathing apparatus. In a retrospective study, we determined CO2 retention and the ability to detect CO2 in novice divers who were either CO2-recognition-trained subjects (TS) or untrained subjects (UTS). METHODS: Ventilatory and perceptual responses to variations in inspired CO2 (range 0-5.6 kPa, 0-42 mm Hg) during moderate exercise were assessed in novice Israeli Navy divers on active duty. Tests were carried out on 231 TS and 213 UTS. RESULTS: The minimal mean inspired PCO2 that could be detected was 4.8 +/- 1.6 kPa (36 +/- 12 mm Hg) in UTS and 2.9 +/- 0.7 kPa (22 +/- 5 mm Hg) in TS (p < 0.0001). No significant changes were found in PETCO2 between the two groups during exposure to a PICO2 of 5.6 kPa (42 mm Hg). There were 46 TS who were found to be CO2 retainers (more than +1 SD above the mean) and 19 were classified as poor detectors (more than +1 SD above the mean). Seven subjects exhibited both traits. During actual oxygen diving performed later by this group, the only four cases of CNS-oxygen toxicity were among those seven subjects (p < 0.01). CONCLUSIONS: We conclude that CO2 recognition training improves the diver's capability to detect CO2. We suggest that a diver who is both a poor CO2 detector and a CO2 retainer will be prone to CNS-oxygen toxicity.

Adult↗

PubMed2003

Hyperoxia may reduce energetic efficiency in the trained rat.

BACKGROUND: Several studies have been conducted in recent years in the attempt to improve running performance by the use of hyperbaric oxygen, but there is disagreement as to whether this has any beneficial effect. The purpose of this study was to measure the effect of 24 h breathing 100% O2 in normobaric conditions on energetic efficiency in the trained rat. METHODS: Experiments were carried out on trained rats whose oxygen consumption was evaluated during the training period and on its completion. At the end of the training period, the rats were divided into two groups: 1) rats exposed to air (21% O2) in normobaric conditions; and 2) rats exposed to 100% O2 in normobaric conditions. In addition, two groups of sedentary rats were used: 3) sedentary rats exposed to air (21% O2) in normobaric conditions; and 4) sedentary rats exposed to 100% O2 in normobaric conditions. Energetic efficiency was estimated by measuring O2 consumption at submaximal exercise (45 m.min-1, 10 degrees incline). RESULTS: Training alone reduced O2 consumption by 18% during submaximal exercise. Exposure to 100% oxygen for 24 h in normobaric conditions reversed the effect of complete training by elevating the O2 consumption by 17%, which was close to the oxygen consumption of the rats during the incomplete training period. CONCLUSIONS: Our results suggest that prolonged exposure to hyperoxia induces a reduction in the energetic efficiency of the trained rat. The relevance of these findings to sports and diving is discussed.

Animals↗

PubMed2002

Heat acclimation-induced elevated glycogen, glycolysis, and low thyroxine improve heart ischemic tolerance.

Based on our observations of energy sparing in heat-acclimated (AC) rat hearts, we investigated whether changes in preischemic glycogen level, glycolytic rate, and plasma thyroxine level mediate cardioprotection induced in these hearts during ischemia-reperfusion insults. Control (C) (24 degrees C), AC (34 degrees C, 30 days), acclimated-euthyroid (34 degrees C + 3 ng/ml l-thyroxine), and control hypothyroid (24 degrees C + 0.02% 6-n-propyl-2-thiouracil) groups were studied. Preischemic glycogen was higher in AC than in C hearts [39.0 +/- 8.5 vs. 19.2 +/- 4.2 (SE) micromol glucose/g wet wt; P < 0.0006], and the lactate produced vs. glycogen level during total ischemia ((13)C-NMR spectroscopy) was markedly slower (AC: -0.82x, r = 0.98 vs. C: -4.7x, r = 0.9). Time to onset of ischemic contracture was lengthened, and the fraction of hearts experiencing ischemic contracture was lowered. Pulse pressure recovery was improved in AC compared with C animals before, but not after, absolute sodium iodoacetate-induced glycolysis inhibition. Acclimated-euthyroid hearts exhibited decreased ischemic tolerance, whereas induced hypothyroidism in C improved cardiotolerance. Thus higher preischemic glycogen and slowed glycolysis are associated with hypothyroidism and are likely important mediators of the improved ischemic tolerance exhibited by AC hearts.

Acclimatization↗