PubMed · 9784458
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R M Leach, P J Rees, P Wilmshurst. 1998-10-24. Hyperbaric oxygen therapy.. https://doi.org/10.1136/bmj.317.7166.1140
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The International Standard ISO 7933 (1989) Hot environments--Analytical determination and interpretation of thermal stress using calculation of required sweat rate has been proposed for the evaluation of climatic stress within the European system of CEN standards. Comparison of results of studies performed in climatic chambers and those in the field with the predictions of ISO 7933 show that there are considerable problems in using this index in practice. In its present state of development, ISO 7933 seems to be rather a step towards a useable index for evaluating climatic conditions rather than an established climatic index which is applicable in practice. Within the CEN standards, the deficiencies of ISO 7933 are reflected mainly by a restriction of the limits of application within EN 12 515 (1997) which is based on ISO 7933.
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Investigations were performed during 24 simulated air dives under pressure 0.74 MPa in which 16 divers took part. Before, during and after dives intrathoracic pressure, mean arterial pressure, ECG, rheoplethysmogram and intervalocardiogram were recorded continuously with the Valsalva maneuvers. Variables of heart pumping function, peripheral vascular system, phasic heart cycle structure were calculated. For evaluation of autonomic homeostasis variational and spectral analysis of cardiac rhythm were used. In hyperbaria a part of hemodynamic response peculiarities to intrathoracic pressure increase were common to all divers and caused by hyperoxia and increased density of breathing medium, which lead to the appearance of bradycardia, decrease of cardiac output, peripheral vasoconstriction enhancement. Other observed features were determined by alterations in sympathetic and parasympathetic nervous system tonus. These changes were rather complex and highly individual. Our data may benefit evaluation of hyperbaric factor stressful action on blood flow and autonomic nervous system.