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  • Author: Tamara Stanciu x
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Abstract

The respiratory effort in hyperbaric conditions is of particular nature, leading to an increase of the respiratory flow of the diver and to the change of their pulmonary volumes. There are important criteria in the selection process of the most suitable divers. Some of these criteria are related to the respiratory function. In order to evaluate the divers respiratory function an examination of the pulmonary volumes is performed in regards to their variations measured by spirometry, of the increased oxygen consumption in hyperbaric conditions and of the production of carbon dioxide during the unitary dive at the depth of work using air as a respiratory mixture. The physical and physiological phenomena involved in the hyperbaric respiration have been studied in cooperation with “Ovidius” University of Constanta, Faculty of Medicine. A specific medical method of evaluation of the pulmonary ventilation, spirometry, the measurement of forced expiratory volume in the first second of a forced expiration, Tiffneau index, have been adapted to the under pressure breathing environment. The parameters have been studied as experimental determinations on diver groups, during simulated diving, using air as a respiratory mixture, at 50 [mH2O] in the Hyperbaric Complex of the Diving Centre

Abstract

In order to optimize the breathing apparatus in the open circuit for divers, theoretical calculus and numerical simulation of resistances specific to the potential flow of gas through the studied circuit were made. Respiratory gas flow simulation through three constructive versions of the second stage pressure reducer intake mechanism was done after modeling the respiratory air circuit through the two main restrictors: the first variable (between the seat and the piston) and the second fixed (the hole in the cylindrical piston). The results regarding the theoretical calculation and numerical simulation have been validated by experimental testing of two of the studied models. Experimental measurements were made on a tester at the Diving Center of Constanta's Hyperbaric Laboratory. The volume flow rate of supplied respiratory gas was recorded, together with the inspire depression that opens the mechanism, until the maximum flow rate for each constructive version. After validating the results of the theoretical calculation and numerical simulation on the two models, the conclusion is the same: the resistance decreases if the geometry of the cylindrical hole in the piston (the second fixed restrictor) changes in a conical hole