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Adaptive Changes of Ventilation in SCUBA (Self Contained Underwater Breathing Apparatus) Diving Hiromichi Ohiwa 1,2 1Department of Hygiene, Tokyo Medical and Dental University, School of Medicine 2JMSDF, Underwater Medical Laboratory, Yokosuka pp.905-912
Published Date 1969/10/15
DOI https://doi.org/10.11477/mf.1404202081
  • Abstract
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In an open circuit SCUBA diving, the flow resistance of the equipment increases more than ten times of the resistance without equipment, and accordingly the breathing work increases in proportion to the increase of the viscous resistance. At the same time, the hypoventilation is observed.

To study this hypoventilation in diving as a phenomenon of the adaptive changes from the standpoint of the ventilatory mechanics, the author carried out the following experi-mental work.

The subjects, three well trained profes-sional SCUBA divers, having nearly the same predicted pulmonary functions, were exposed to the simulated depths of 0 m (sea level), 30 m (the air way resistance is two times larger than that at 0 m) and 50 m in a hy-perbaric chamber. There, at each depth, they were subjected by a light exercise (60 kg.m by a bicycle ergometer-RMR=1. 5-equivalent to an underwater swimming speed only by kicking with fins of 25 m/min) in 5 minutes.

In SCUBA diving, the significant decrease of the minute respiratory volume was observ-ed because of the decrease of the respiratory rate. In this case, it might be considered that the decrease of the alveolar ventilation (VA) is also due to that of the respiratory rate, as the alveolar volume (VA) is almost constant.

It was clearly recognized that the high alv. Pco2 was accompanied with the decrease of the oxygen equivalent. This tendency was also more manifest at the SCUBA diving compared with the cases of the other diving systems. In this case, a decrease of the ventilatory response to CO2 was observed in these three subjects.

Also the CO2 output decreased by the dec-rease of VA with the increase of the depth. Accordingly it might be assumed that there is a tendency of the CO2 accumulation in the body under hyperbaric environment.

The most characteristic phenomenon in this experiment was the slight increase or rather the decrease of the CO2 uptake during the SCUBA diving with a large ventilatory resistance by this equipment compared with the cases of the other diving systems.

It might be due to an adaptive change in the well trained divers, as they can restrict the breathing work in a lower level against the estimated increase of the breathing work under a pressure in question.

To acquire the minimum alveolar ventila-tion, the respiraory rate decreased instead of the tidal volume, as the decrease of the ventilatory rate minimizes the breathing work. The resulted decrease of the flow rate is not so influenced by the high atmos-pheric pressure, and the elastic resistance becomes more dominant than the nonelastic ones such as the viscous resistance.

This decrease of the respiratory rate shows the most optimum rate from the standpoint of the breathing work.


Copyright © 1969, Igaku-Shoin Ltd. All rights reserved.

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電子版ISSN 1882-1200 印刷版ISSN 0452-3458 医学書院

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