The optimum intrapulmonary pressure in underwater respiration / by W.D.M. Paton and A. Sand.

  • Paton, William D. M.
Date:
[1947?]
Catalogue details

Licence: In copyright

Credit: The optimum intrapulmonary pressure in underwater respiration / by W.D.M. Paton and A. Sand. Source: Wellcome Collection.

    1/20 (page 119)
    [Reprinted from the Journal of Physiology, 1947, Vol. 106, No. 2, p. 119.] PRINTED IN GREAT BRITAIN J. Physiol. (1947) 106, 119-138 612.217 THE OPTIMUM INTRAPULMONARY PRESSURE IN UNDERWATER RESPIRATION , By W. D. M. PA TON and the late A. SAND From the National Institute for Medical Research, London (Received 2 August 1946) In self-contained breathing sets, oxygen, or a mixture of oxygen and nitrogen, is rebreathed from a counter-lung (a flexible breathing bag), connected to the subject’s mouth or face-mask by flexible tubing. The bag is inflated from gas cylinders carried by the subject. When these sets are worn underwater, the pressure of the water upon the chest wall is counteracted by the pressure exerted by the water on the counter-lung and thence transmitted to the gas space within the lungs. The equalization of pressure within and without the lungs can, however, only be approximate, since the chest of~a diver in the erect position is exposed not to a single hydrostatic pressure, but to a pressure which increases from above downwards. It is well known that helmet divers are sensitive to small variations in the pressure of gas respired. J. S. Haldane (1907) described in detail the sensation resulting from too low a pressure of air in the helmet, and ascribed what he observed to the rigidity of the helmet. Provision is, in fact, made for the helmet diver to adjust pressure within the helmet by means of the helmet exhaust valve. In the counter-lung breathing set, however, the diver has no delicate control of the pressure of gas in his breathing bag, apart from being able to vary the degree of filling of the bag with gas. The pressure of gas delivered to the lungs is thus fixed by the position of the bag in the water with respect to the lungs. It is evident that a breathing bag carried by an erect diver at waist level (high intrapulmonary pressure) imposes a considerable resistance to expiration, and conversely, a bag carried at head level (low intrapulmonary pressure) makes inspiration very difficult. In the breathing sets normally in use, the counter-lung is carried either on the chest, or on the back or as a ring around the neck, and there are considerable subjective differences in comfort according to the type of bag used. The present investigation was undertaken to discover the optimum position of the breathing bag by defining the permissible limits of pressure variation for respiratory function. It soon became clear that the pressure of respired gas is discriminated