Breathing under high ambient pressure.

LORD, GEORGE P., GEORGE F. BOND, AND KARL E. SCHAEFER. Breathing under high ambient pressure. J. Appl. Physiol. 21 (6): 1833-1838. 1966.—The acute effect of high ambient pressure on expiratory airflow was studied in healthy adult males in the ambient pressure range from 1.0 to 7.0 atmospheres absolute pressure (Ata) using a hyperbaric chamber. Changes in flow were assessed with the maximum expiratory flow-volume curve. The decrease in flow was compared to that occurring in dense high molecular weight gas mixtures. In addition, expiratory gas flow was studied in three men during 12 days at 7.0 Ata in 90% helium. The findings demonstrate that: 1) high ambient pressure and high molecular weight gas of equal density produce similar changes in expiratory flow; 2) in the pressure range from 1.0 to 4.0 Ata in air the greatest decrease in maximum expiratory flow occurs at high lung volumes, while from 4.0 to 7.0 Ata the greatest flow change occurs at low lung volumes; 3) the long-term changes in expiratory flow in high-pressure helium can be explained by the change in physical properties of the breathing mixture; and 4) there are no clinically apparent untoward effects from prolonged high-pressure helium breathing.