[abstract] APPARENT CEREBRAL HYPOXIA DURING EXERCISE IN HYPEROXIC ATMOSPHERES

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[abstract] APPARENT CEREBRAL HYPOXIA DURING EXERCISE IN HYPEROXIC ATMOSPHERES

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Title: [abstract] APPARENT CEREBRAL HYPOXIA DURING EXERCISE IN HYPEROXIC ATMOSPHERES
Author: Clarke, JR; Fothergill, DM
Abstract: Visual effects such as scintillating scotomata and concentric visual field contraction (tunnel vision) are usually associated with retinal or cerebral hypoxia. We have observed 8 incidents of such visual disturbances when divers were engaged in heavy cycling exercise in the dry under hyperoxic hyperbaric conditions. Two of the incidents have been previously summarized (Proc. Internat. Conf. on Environ. Ergonomics-IV, 120-121, 1990). All incidents occurred on saturation dives with inspired PO2 ranging from 0.4 to 1.2 atm abs, with depths from 30 to 305 msw. End-tidal CO2 was at or below 66 mmHg while divers breathed from fixed resistors or SCUBA regulators. The maximum peak-to-peak mouth pressures ranged from 30 to 72 cmH2O, and were divided equally between inspiration and expiration, or had larger inspiratory pressures than expiratory. Peak-to-peak esophageal pressures, when available, ranged between 60 and 104 cmH2O. The visual events were not associated with disturbances of heart rhythm, but were often associated with headache. Nitrogen narcosis was not consistently associated with the symptoms. While the cerebrum may not have been hyperoxic (Eur. J. Appl. Physiol., 71:475-484, 1995) we have no reason to believe that the retinal blood was hypoxemic. Therefore, the divers may have been experiencing retinal hypoxia as a presyncopal symptom heralded by reduced retinal (and perhaps cerebral) blood flow, acting through an unknown mechanism. In these conditions, we suggest that end-tidal CO2 may not accurately reflect cerebral tissue CO2 levels. Thus, both tissue hypoxia and hypercarbia might have been present. Transcranial blood flow measurements may help resolve some of the questions raised by these observations. (Supported in part by NMRDC Work Unit No. 63713NM0099.01B-1428).
Description: Undersea and Hyperbaric Medical Society, Inc. (http://www.uhms.org )
URI: http://archive.rubicon-foundation.org/471
Date: 1996

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  • UHMS Meeting Abstracts
    This is a collection of the published abstracts from the Undersea and Hyperbaric Medical Society (UHMS) annual meetings.

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